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THE 20TH ANNUAL CONGRESS OF THE INTERNATIONAL

SOCIETY FOR TECHNOLOGY IN ARTHROPLASTY

ISTA 2007 ISTA 2007 O OCTOBERCTOBER 4 4--6, 20076, 2007 PPARISARIS M MARRIOTTARRIOTT R RIVEIVE G GAUCHEAUCHE H HOTELOTEL ANDAND C CONFERENCEONFERENCE C CENTERENTER P PARISARIS, F, FRANCERANCE

Symposium Objectives:

• Evaluate new technologies for joint replacement, implant design and materials or biological solutions.

• Interact with and learn from world-renowned orthopaedic surgeons and orthopaedic researchers.

Program Chair: Yves Catonne, M.D. (Paris)

PROCEEDINGS BOOK

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ISTA 2007 The 20th Annual Congress of The International Society for Technology in Arthroplasty

PROCEEDINGS BOOK

Contents

Welcome Message 3 ISTA Board of Directors 4 ISTA 2007 Organizing Committee 4 Layout of Exhibitors 5 Acknowledgement of Exhibitor Support 6 Program/Social Events 7 Program at a Glance 8-10 Agenda 11-32 - Thursday, October 4 - Friday, October 5 - Saturday, October 6 Invited Lectures / Oral Presentations 33-215 Poster Presentations 216-254

October 4-6, 2007 The Paris Rive Gauche Hotel and Conference Center

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WELCOME MESSAGE

Dear Colleagues: It is a privilege for me to Welcome you to Paris for the 20th Congress of the International Society for Technology in Arthroplasty (ISTA). ISTA is the only scientific orthopaedic society dedicated to the idea of providing a constructive environment for engineers and surgeons in the field of orthopaedics to come together to share their work and ideas. After two previous Congresses in France (Nice in 1990 chaired by Jean Manuel Aubaniac and Marseille in 1998 chaired by Jean-Noel Argenson), it is good to have the annual ISTA meeting back in France. The ISTA approach is different from that of conventional medical societies. Rather than presenting long-term results of recognized techniques, ISTA provides an opportunity for companies, engineers, R&D departments and surgeons to present new ideas, research and new technologies. Presentations range from fundamental (laboratory studies, biotechnology, design, etc.) to clinical (preliminary trial results, surgical techniques, CAOS, etc.) with any combination thereof. We hope every participant will enjoy their stay in Paris. We commend all of the ISTA 2007 participants and exhibitors who have come together to exchange their recent research in artificial joint technology and I thank profusely all of those organizations who have contributed in many different ways to the creation of this Congress. I am looking forward to hearing the many stimulating papers and hope that this Congress will be the most exciting and enjoyable. I also welcome the opportunity to promote international friendship and cultural exchanges in the old and historic city of Paris. Thank you for your participation. Yves Catonne Program Chair

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INTERNATIONAL SOCIETY FOR TECHNOLOGY IN ARTHROPLASTY OCTOBER 4-6, 2007

The Marriott Paris Rive Gauche Hotel and Conference Center ISTA BOARD OF DIRECTORS, 2006-2007 President Yves Catonné (Paris) First Vice President Won Yong Shon (Seoul) Second Vice President Richard D. Komistek (Knoxville) First Past President Peter Walker (New York) Second Past President Takashi Nakamura (Kyoto) Secretary General Nico Verdonschot (Nijmegen) Executive Director Richard D. Komistek (Knoxville) Treasurer Raj Sinha (Rancho Mirage) Members Hani Haider (Omaha), John Hollingdale (Bucks), Sam Nasser (Sterling Heights) Claude Rieker (Winterthur), Jeffrey K Taylor (Sacramento) ISTA 20th ANNUAL CONGRESS, PARIS, FRANCE, OCTOBER 4-6, 2007 Chairman Yves Catonné (Paris) Co chairmen Thierry Judet (Garches), Jean Manuel Aubaniac (Marseille) Organizing Committee Levon Doursounian (Paris), Christian Dumontier (Paris),

Denis Huten (Paris), P Landreau (Paris), Jean Yves Lazennec (Paris), Remy Nizard (Paris), Philippe Piriou (Garches), Laurent Sedel (Paris)

Invited speakers Jean Noel Argenson (Marseille), Gérard Deschamps (Dracy le Fort), Andreas Halder (Berlin), Marcel Kerboull (Paris), Jacques Yves Nordin (Paris) Dominique Saragaglia (Grenoble), Laurent Sedel (Paris), Thomas Schmalzried (Los Angeles), Marc Siguier (Paris)

PREVIOUS MEETINGS 1990 Nice, France chairman: Jean-Manuel Aubaniac 1991 San Francisco, USA chairman: William Bargar 1992 Windsor, United Kingdom chairman : Peter S. Walker

1993 Amelia Island USA chairman : Bernard Stulberg 1994 Amsterdam, Netherlands chairman : Riek Huiskes 1995 Porto Ricco chairman : Riyaz Jinnah 1996 Rome, Italy chairman : Giani Randelli 1997 San Diego, USA chairman : Jeffrey Taylor 1998 Marseille, France chairman : Jean-Noël Argenson 1999 Chicago, USA chairman : Rick Sumner 2000 Berlin, Germany chairman : Peter Thümler 2001 Hawaii, USA chairman : Hironobu Oonishi 2002 Oxford, United Kingdom chairman : Peter Mac Lardy Smith 2003 San Francisco, USA chairman : Ian Clarke 2004 Rome, Italy chairman : Giorgio Gasparini 2005 Kyoto, Japan chairman : Takashi Nakamura 2006 New-York, USA chairmen : Chit Ranawat and Peter S. Walker

Internet Web www.ista.to

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Exhibitor Layout

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Titanium Sponsor

Exhibitors Finsbury Orthopaedics Japan Medical Materials Kinamed Tornier Zimmer

A Special Thanks to: Depuy Orthopaedics for their support of the “Hap” Paul Award.

Douglas Dennis, M.D. and Smith and Nephew for their support of the Student Biomechanics Award. .

Finsbury Orthopaedics

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Program at a Glance …………… 8-10 Agenda ………………………….. 11-32 Abstracts …………………………. 33-215 Posters …………………………….. 216-254

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Social Events Presidential Reception Wednesday, October 3 - 6:30 pm—7:30 pm Luxembourg Room Paris Marriott Rive Gauche Hotel & Conference Center Complimentary Spouses are welcome to attend.

Gala Awards Dinner Friday, October 5 7:00 pm-10:00 pm Automobile Club de France (Meet at the Club) Tickets required. Tickets can be obtained from the ISTA Registration desk.

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ISTA 2007 PROGRAM AT A GLANCE Wednesday, October 3, 2007 Thursday, October 4, 2007

La Seine C Room La Seine B Room

ISTA Registration (La Seine Ballroom Foyer)

Speaker Ready Room

(Le Pont des Arts Room)

Presidential Reception 6:30 pm—7:30 pm

(Luxembourg Room- Level 3)

Exhibitor & Poster Set-Up (La Seine Ballroom Foyer)

8pm - 10pm

ISTA Registration (La Seine Ballroom Foyer) 6:30am - 5pm

Exhibitors & Poster Display (La Seine Ballroom Foyer) 7am - 5pm

Luncheon Buffet —12:15pm - 1:15pm Restaurant Le Patio (Level 3)

The Challenging Primary THA: Roundtable Discussion Moderator: JN Argenson

4 Speakers

A3– Hip– Polyethylene Bearing in THR

Chair: Hironobu Oonishi Philippe Massin 10 Presentations– 7 min each

B1– Knee– TKR Kinematics 1 Chair: Richard Komistek Darryl D’Lima 6 Presentations– 7 min each

Coffee Break/Exhibitors/Posters B3– Knee– TKR Computerized-

Assisted Surgery 1 Chair: William L. Bargar Invited: Dominique Saragaglia 4 Presentations– 7 min each

Coffee Break/Exhibitors/Posters B5 Unicompartimental Knee

Chair: Jean Manuel Aubaniac Jean Yves Jenny Invited: Gerard Deschamps Jean Noel Argenson 6 Presentations– 7 min each

Coffee Break/Exhibitors/Posters

A1– Hip– THR Femoral Stem

Chair: Joseph Fetto Herni Migaud 10 Presentations– 7 min each

B4– Knee– TKR Computerized- Assisted Surgery 2

Chair: S. David Stulberg Remy Nizard 9 Presentations– 7 min each

A2– Hip– Bearing Surfaces Chair: Ian C Clarke Aldo Toni 9 Presentations– 7 min each

Speaker Ready Room (Le Pont de Arts Room) 6:30am - 5pm

B2– Knee– TKR Kinematics 2 Chair: Peter S. Walker Michel Bercovy 6 Presentations– 7 min each

Welcome - Yves Catonne, M.D., Program Chair 7:45am

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ISTA 2007 PROGRAM AT A GLANCE

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Friday, October 5, 2007






A5– Hip– THR Alumina on Alumina

Chair: Laurent Sedel Jeffrey Taylor Invited: Laurent Sedel 5 Presentations– 7 min each

Luncheon Buffet - 12pm - 1pm Restaurant Le Patio (Level 3)


A6– Hip– MIS THR Chair: Raj Sinha Thierry Judet Invited: Marc Siguier 4 Presentations– 7 min each

A7– Hip– CAS THR Chair: Herni Judet Hani Haider 8 Presentations—7 min each “HAP” Paul Award Paper Presentation: Nico Verdonschot Yves Catonne

Launch of New ISTA Web Site - Hani Haider

Gala Awards Dinner - Automobile Club de France 7pm - 10pm—meet at the Club


B6– Knee– TKR Design, Mobile Bearing

Chair: Louis Lootvoet Jean-Louis Briard 8 Presentations– 7 min each

B7– Knee– TKR Technique: Approach, Ligament Balancing

Chair: Richard Cohen Peter S. Waler Invited: Dominique Saragaglia 10 Presentations– 7 min each

Luncheon Buffet—12:25pm - 1:15pm Restaurant Le Patio (Level 3)

B8– Knee– TKR Deep Flexion

Chair: Samih Tarabichi Bruno Tillie

7 Presentations– 7 min each

A4– Hip– THR Metal-On-Metal

Chair: Claude Rieker Christian Delaunay Invited: Thomas Schmalzried 9 Presentations– 7 min each

B9– Knee– TKR Various Chair: Nobuo Takai Jacques Tabutin Invited: Giorgio Gasparini 8 Presentations– 7 min each

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ISTA 2007 PROGRAM AT A GLANCE

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Saturday, October 6, 2007





Coffee Break/Exhibitors/Posters A9– Hip– Planning THR

Chair: John Hollingdale Moussa Hamadouche 9 Presentations– 7 min each

Luncheon Buffet — 12pm - 1pm Restaurant Le Patio (Level 3)

A10– Hip– THR Revision

Chair: Jacques Tabutin Denis Huten Invited: Marcel Kerboull


A11– Hip Resurfacing

Chair: Koen DeSmet William Macaulay Invited: Philippe Piriou 12 Presentations– 7 min each

B10– Hip and Knee: THR and TKR Coating Chair: Sam Nasser Jean Alain Epinette 5 Presentations– 7 min each

Luncheon Buffet - 12:25pm - 1:25pm Restaurant Le Patio (Level 3)

B13– Hip and Knee– THR and TKR

Chair: David Markel Vincenzo Denaro Invited: Jacques Yves Nordin


A8– Hip– THR

Chair: Young Yong Kim Marcel Kerboull 9 Presentations– 7 min each

B14– Ankle

Chair: Thierry Judet Nobuo Takai 4 Presentations– 7 min each


B11– Upper Limb

Chair: Levon Doursounian Taco Gosens 5 Presentations– 7 min each

B12– Spine Chair: Jean-Yves Lazennec Fabien Bitan 7 Presentations– 7 min each

4:15 Adjournment

5:05 Adjournment

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The Paris Rive Gauche Hotel and Conference Center

AGENDA Wednesday, October 3, 2007 3:00 pm – 6:00 pm ISTA Registration La Seine Ballroom Foyer 3:00 pm - 6:00 pm Speaker Ready Room Le Pont des Arts Room 6:30 pm – 7:30 pm Presidential Reception Luxembourg Room—Level 3 Spouses invited to attend 8:00 pm – 10:00 pm Exhibitor Set-Up La Seine Ballroom Foyer 8:00 pm – 10:00 pm Poster Set-Up La Seine Ballroom Foyer Thursday, October 4, 2007 6:30 am – 5:00 pm ISTA Registration La Seine Ballroom Foyer 6:30 am—5:00 pm Speaker Ready Room Le Pont des Arts Room 7:00 am – 5:00 pm Exhibitors La Seine Ballroom Foyer 7:00 am – 5:00 pm Poster Display La Seine Ballroom Foyer 7:45 am Welcome Yves Catonne, M.D., Program Chair La Seine Ballroom C All Attendees 8:00 am – 10:05 am A1– HIP—THR FEMORAL STEM La Seine Ballroom C

Chairmen: Joseph Fetto (New York) Henri Migaud (Lille)

8:00 am – 8:05 am Session overview and objectives 8:05 am – 8:15 am A1-1—Mid to Long Term Results of a Lateral Flare Customized Uncemented Stems in Patients Younger Than 55 Years of Age Alejandro Leali, Joseph Fetto 8:15 am – 8:25 am A1-2—Investigation of New Concept of Buffered Implant Fixation in Rat Model: Measurement of BV/TV Using Micro-CT in Comparison with Cemented Implant Fixation Choi, Donok, Park, Sukhoon, Hwang, Deuk Soo, Yoon, Yong-San 8:25 am – 8:35 am A1-3—Two Year Results of a Short, Metaphyseal Length Femoral Stem in Prmary Total Hip Arthroplasty Mark Dolan, S David Stulberg 8:35 am – 8:45 am A1-4—Evaluation of Tensile Strain Distribution in Loaded Proximal Femur in Relation to Lengths of Cementless Stems Nakamura, Takuya, Sumihiko, Maeno 8:45 am—8:55 am A1-5 —Alloclassic SL Offset Stem Conception Christian Delaunay, Falah Bachour, Henri Migaud 8:55 am—9:05 am A1-6—Non-Destructive Evaluation of Damage Accumulation in Carbon Nanotube Reinforced and Unreinforced Acrylic Bone Cement Martin Browne, Polly Sinnett-Jones, Ian Sinclair

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9:05 am—9:15 am A1-7—Mid-Term Results of a Novel Lateral Flare Non-Cemented Hip Stem. A Clinical, Radiographic and Densitometry Study Alejandro Leali, Joseph Fetto 9:15 am—9:25 am A1-8—Stem Fit and Thigh Pain in Uncemented Total Hip Replacement Amar Ranawat 9:25 am—9:35 am A1-9—Rotational Stability Based on Displacements Obtained by Three-Dimensional Finite Element Analysis When Torsion Loading is Applied to Hip Prostheses Sakai R, Sato K, Sato Y, Itoman M, Mabuchi K 9:35 am—9:45 am A1-10—Excellent Long-Term Survival (15-20 years) of Uncemented Gritblasted Straight Tapered Titanium Stems in Young and Active Patients (<55 years) Peter R. Aldinger, Alexander W Jung, Marc Thomsen, Volder Ewerbeck, Dominik Parsch 9:45 am—10:00 am Panel discussion/Q&A 10:00 am – 10:20 am Coffee Break/Exhibitors/Poster Display 10:20 am –12:15 pm A2– HIP—Bearing Surfaces La Seine Ballroom C Chairmen: Ian C Clarke (Los Angeles) Aldo Toni (Bologna) 10:20 am – 10:25 am Session overview and objectives 10:25 am – 10:35 am A2-1—In Vivo Correlation of Sound and Separation for Different Bearing Surfaces Diana Glaser, Hal Cates, Richard Komistek, MR Mahfouz, D Dennis 10:35 am – 10:45 am A2-2—Effect of Bearing Diameter and Radial Clearance on Wear of Ceramic- On-Metal Total Hip Replacements Hani Haider, Joel Weisenburger, Malcolm Naylor, David Schroeder, Richard Croson, Benjamin O’Brien, Kevin Garvin 10:45 am – 10:55 am A2-3—Virtual Hip Simulator: New Method for Implementing In Vivo Kinematics During the Design of THA Components John Mueller, Filip Leszko, Richard Komistek, Mohamed Mahfouz 10:55 am – 11:05 am A2-4—19 To 21 Year Clinical Results of Total Hip Prosthesis With Ceramic Head Combined with UHMWPE Socket Oonishi Hiroyuki, Kim Sok Chol, Kyomoto Masayuki, Iwamoto Mikio, Masuda Shingo, Ueno Masaru, Oonishi Hironobu 11:05 am – 11:15 am A2-5—A Novel Way to Measure Friction of Total Hip Replacement Systems During a Walking Cycle on a Multi-Station Hip Simulator Joel Weisenburger, Malcolm Naylor, David Schroeder, Bruce White, Anthony Unsworth, Kevin Garvin, Hani Haider 11:15 am – 11:25 am A2-6—Novel Ceramic-On-Metal Hip Replacements Sophie Williams, Claire Brockett, Graham Isaac, Anton Schepers, Dick van der Jagt, Anke Brekon, Cath Hardaker, John Fisher 11:25 am – 11:35 am A2-7—Aging of Retrieved Zirconia Femoral Heads Margarita Montero, A Murcia, M. Fernandez-Fairen 11:35 am—11:45 am A2-8—Wear, Ion Release and Mechanical Properties of Diamond-On-Diamond Total Hip Bearings Jeffrey Taylor, A. Stan Despres, Malcolm Naylor, David Schroeder, German Loesener, Vaneet Singh, David Harding, Richard Dixon, Troy Medford 11:45 am—11:55 am A2-9—The Emergence of a New Type of Ceramics in Total Arthroplasty: The Alumina Matrix Composite (AMc) - A 6 Year Follow-up Bernard Masson

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11:55 am – 12:15 pm Panel discussion/Q&A 12:15 pm – 1:15 pm Group Luncheon restaurant Le Patio (Level 3)

1:15 pm – 2:40 pm The Challenging Primary THA: La Seine Ballroom C A Roundtable Discussion with the Experts

Moderator: JN Argenson (Marseille)

1:15 pm – 1:20 pm Session overview and objectives (JN Argenson) 1:20 pm – 1:35 pm S-1—My Experience with Resurfacing in the Young Patient Thomas Schmalzried (Los Angeles) 1:35 pm—1:50 pm S-2—Modular Neck is My Option Aldo Toni (Bologna) 1:50 pm—2:05 pm S-3—The Use of Cementless Fixation in Dysplastic Hips Andreas Halder (Berlin) 2:05 pm—2:20 pm S-4—Cement Will Solve the Problem Moussa Hamadouche (Paris) 2:20 pm—2:40 pm Panel Discussion/Q&A 2:40 pm—4:40 pm A3 HIP—Polyethylene Bearings in THR La Seine Ballroom C Chairmen: Hironobu Oonishi (Osaka) Philippe Massin (Angers) 2:40 pm – 2:45 pm Session overview and objectives 2:45 pm—2:55 pm A3-1—The Influence of Acetabular Shell Rim Support on the Polyethylene Liner Rim Stress Pattern Nick Dong, W Schmidt, MA Kester, A Wang, NM Nogler, M. Krismer 2:55 pm—3:05 pm A3-2 — Deformation of Metal-Backed Acetbular Components and the Impact of Liner Thickness in a Cadaveric Model David Markel, Judd Day, Ryan Siskey, Steven Kurtz, Kevin Ong, Imants Liepins 3:05 pm—3:15 pm A3-3 —Monitoring Degradation of the Implanted Hip Construct Integrity Using Acoustic

Emission Mark Mavrogordato, Andrew Taylor, Mark Taylor, Martin Browne 3:15 pm—3:25 pm A3-4 — Simulator Wear of Polyethylene Using Large Diameter XLPE Hip Cups T. Sorimachi, A Gustafson, I Clarke, PA Williams, K Yamamoto 3:25 pm—3:35 pm A3-5—Comparison of Retrieved Ceramic TKP to Metallic TKP After Long-Term Clinical Use Oonishi Hiroyuki, Kim Sok Chol, Kyomoto Masayuki, Iwamoto Mikio, Masuda Shingo, Ueno Masaru, Ooinishi Hironobu 3:35 pm—3:45 pm A3-6—Migration of Wear Debris of Polyethylene Depends of the Bone Micro–architecture Philippe Massin, H Libouban, C Gaudin, P Mercier, MF Basle, D Chappard 3:45 pm—3:55 pm A3-7—Comparisons of In Vivo Oxidation and Wear Between Retrieved Polyethylene Inserts with Gamma and EOG Sterilization in Total Knee Prostheses Kim Sok Chol, Oonishi Hiroyuki, Kyomoto Masayuki, Iwamoto Mikio, Masuda Shingo,

Ueno Massaru, Oonishi Hironobu 3:55 pm —4:05 pm A3-8—Effect of Zirconia Femoral Head on Polyethylene Wear Rates Maruyama Masaaki

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4:05 pm—4:15 pm A3-9—Inhibitory Effects of Erythromycin on Weear Debris Induced VEgf/flt-1 Gene Activation and Osteolysis in a Mouse Model Weiping Ren, Renwen Zhang, Bin Wu, Yuhong Ding, Paul H Wooley, Monica Hawkins, Ralph Blasier, David C Markel 4:15 pm—4:25 pm A3-10—Second Generation Highly Crossed Linked UHMWPE. Sequential Irradiation and Annealing J Nevelos, A Essner, A Wang, S Yau, J Dumbleton 4:25 pm—4:40 pm Panel discussion/Q&A 4:40 pm Adjournment

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Thursday, October 4, 2007 6:30 am – 5:00 pm ISTA Registration La Seine Ballroom Foyer 6:30 am—5:00 pm Speaker Ready Room Le Pont des Arts Room 7:00 am – 5:00 pm Exhibitors La Seine Ballroom Foyer 7:00 am – 5:00 pm Poster Display La Seine Ballroom Foyer 7:45 am Welcome Yves Catonne, M.D., Program Chair La Seine Ballroom C All Attendees 8:00 am – 9:25 am B1—KNEE—TKR Kinematics (1) La Seine Ballroom B Chairmen: Richard Komistek (Knoxville) Darryl D’Lima (La Jolla) 8:00 am – 8:05 am Session overview and objectives 8:05 am – 8:15 am B1-1 —Evolution of Knee Kinematics Concepts: From History to Modern Data Michel Bercovy 8:15 am – 8:25 am B1-2—Total Knee Arthroplasty Outcome: A New Tool for Objective Analysis of Gait Coordination Brigitte Jolles, Hooman Dejnabadi, Estelle Martin, Pierre-Francois Leyvraz, Kamiar Aminian 8:25 am – 8:35 am B1-3—Effect of Meniscal Attachment Technique on Knee Contact Mechanics Darryl D’Lima, Oliver Kessler, Clifford Colwell, Jr. 8:35 am – 8:45 am B1-4—In Vivo Comparison of TKA Kinematics With Ultra Congruent and Congruent Polyethylene Inserts in Natural Knee II CR TKA John Mueller, Stanton Longenecker, Mathew Anderle, Richard Komistek, MR Mahfouz 8:45 am – 8:55 am B1-5—Stable Tibiofemoral Kinematics Without Post/Cam Substitution Pradeep Moonot, GT Railton, S Mu, SA Banks, R Field 8:55 am – 9:05 am B1-6—Experimental and Numerical Analyses of the Contact Pressure and Kinematics at the Tibial/Femoral Interface in a Bi-Cruciate StabilizedTKA During Gait Labey Luc, Innocenti Bernardo, Wong Pius, Bellemans Johan, Victor Jan 9:05 am—9:25 am Panel discussion/Q&A 9.25 am –10:40 am B2—Knee—TKR Kinematics 2 La Seine Ballroom B Chairmen: Peter S. Walker (New York) Michel Bercovy (Paris) 9:25 am—9:30 am Session overview and objectives 9:30 am—9:40 am B2-1—Knee Moments and Shear Measured In Vivo During Activities of Daily Living After Total Knee Arthroplasty Darryl D’Lima, Shantanu Patil, Nikolai Steklov, Shu Chien, Clifford Colwell, Jr. 9:40 am—9:50 am B2-2—An Analysis of In Vivo Knee Forces While Rising From a Chair After Knee Arthroplasty Darryl D’Lima, Shantanu Patil, Nikolai Steklov, Clifford Colwell, Jr.

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9:50 am—10:00 am B2-3—Pattern of Muscle Activity and Tibiofemoral Contact Forces Assessed by Integration of Imaging and Motion Analysis Techniques Before and After Total Knee Replacement Valter Santilli, Romildo Don 10:00 am—10:10 am B2-4—In Vivo Measurements of Loads and Moments Three Months Post- Operatively Using an Instrumented Tibial Tray Bernd Heinlein, Ines Kutzner, Andreas Halder, Alexander Beier, Alwina Bender, Antonius Rohlmann, Friedmar Graichen ,Georg Bergmann 10:10 am—10:20 am B2-5—Kinematic Analysis of Total Knee Arthroplasty of Which the Design Concept is Medial Pivot Motion Yamamoto Keitaro, Suguro Toru, Banks Scott, Nozaki Hiroyuki, Nakamura Takashi, Miyazaki Yoshiyasu, Kogame Katsunori 10:20 am—10:30 am B2-6—In Vivo Contact Areas and Stresses for Multiple TKA Types A Sharma, R Komistek, GR Scuderi, HE Cates, SL Longenecker, F Liu 10:30 am—10:40 am Panel discussion/Q&A 10:40 am—11:00 am Coffee Break/Exhibitors/Poster Display 11:00 am—12:15 pm B3—Knee—TKR Computerized-Assisted Surgery (1) Chairmen: William L. Bargar (Sacramento) La Seine Ballroom B Invited: Dominique Saragaglia 11:00 am – 11:05 am Session overview and objectives 11:05 am—11:20 am S-5—Invited Speaker: Dominique Saragaglia Navigation in TKR: My Experience 11:20 am—11:30 am B3-1—Navigation Improves Accuracy and Reproducibility of Soft Tissue Balance in TKA S. David Stulberg, Mark Yaffe, Samuel Koo 11:30 am—11:40 am B3-2—Introduction of a Novel Navigation System for Assessment of Passive Knee Kinematics and Ligamentous Stability Measured Pre–and Post Total Knee Arthroplasty Mark Nadzadi, Timo Ecker, Stephen Murphy 11:40 am—11:50 am B3-3—Learning Curve of a Navigation System for Total Knee Replacement: A Multicentric Study Jean-Yves Jenny, Rolf Miehlke, Alexander Giurea 11:50 am—12:00 noon B3-4—Navigation-Assisted Total Knee Arthroplasty in Patients with Extra- Articular Deformity Maeda Toru, Kabata Tamon, Naito Mitsuhiro, Taga Tadashi, Ando Tomonari, Kitaoka Katsuhiko, Tsuchiya Hiroyuki, Tomita Katsuro 12:00 noon-12:15 pm Panel discussion/Q&A 12:15 pm – 1:15 pm Group Luncheon restaurant Le Patio (Level 3) 1:15 pm—3:00 pm B4—Knee—TKR Computerized-Assisted Surgery (2) Chairmen: S. David Stulberg (Chicago) La Seine Ballroom B Remy Nizard (Paris) 1:15 pm – 1:20 pm Session overview and objectives 1:20 pm—1:30 pm B4-1—Accuracy and Reliability of Limb Alignment Control Using Surgical Navigation During Total Knee Arthroplasty Stephen Murphy, Timo Ecker

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1:30 pm—1:40 pm B4-2—How About Deformation of Japanese OA Knee? Measurement with OrthoPilot in TKA Katsuya Kanesaki 1:40 pm—1:50 pm B4-3—Alignment of Total Knee Arthroplasty: A Comparison of Mechanical And Computer Assisted TKA Surgery Nicholas Wegner, Alfred Cook, Joe Feinglass, S. David Stulberg 1:50 pm—2:00 pm B4-4—Comparison of Mechanical Axis Measurements: Intra-Operative Navigation Versus Postoperative Standing Films Jennifer Smail, Michael Swank 2:00 pm—2:10 pm B4-5—Computer Knee Arthroplasty with MNS (Medacta Navigation System): Comparative Study Between Standard and Minimally Invasive Cutting Guides Emanuele Rinciari, Valeria Di Caro, Fabio Licata 2:10 pm—2:20 pm B4-6—Reliability of Computer Assisted Gap and Ligament Balancing in Total Knee Replacement Chin Pak Lin, Pang Hee Nee 2:20 pm—2:30 pm B4-7—Navigated Freehand Bone Cutting for Total Knee Replacement Surgery: Experiments with Seven Independent Surgeons Hani Haider, O. Andres Barrera, Craig Mahoney, Amar Ranawat, Chitranjan Ranawat, Kevin L. Garvin 2:30 pm—2:40 pm B4-8—Computer-Assisted, Minimally Invasive Versus Conventional Knee Arthroplasty: A Prospective, Randomized Study Sean Ng, AQ Dutton, SJ Yeo, KY Yang, NN Lo, HC Chong 2:40 pm—2:50 pm B4-9—How Accurate Are Three Different Reference Axes in Total Knee Arthroplasty? Tadashi Taga, Tamon Kabata, Toru Maeda, Daigo Sakagoshi, Mitsuhiro Naito, Tomonari Ando, Katsuro Tomita 2:50 pm—3:00 pm Panel discussion/Q&A 3:00 pm—3:20 pm Coffee break/Exhibitors/Poster Display 3:20 pm—5:10 pm B5—Unicompartimental Knee La Seine Ballroom B Chairmen: Jean Manuel Aubaniac (Marseille) Jean Yves Jenny (Strasbourg) Invited: Gerard Deschamps (Dracy le Fort) Jean Noel Argenson (Marseille) 3:20 pm – 3:25 pm Session overview and objectives 3:25 pm—3:40 pm S-6 Invited Speaker: Gerard Deschamps Radiological Target in Unicompartimental Knee Prosthesis 3:40 pm—3:50 pm B5-1—In Vivo Comparison of Knee Kinematics for Subjects Implanted with a Zimmer Uni-Compartmental High-Flex Knee System During Weight Bearing and Non-Weight Bearing Activities Mueller John Kyle, Akizuki, Shaw, Zingde, Sumesh, Komistek, Richard, Mahfouz, Mohammed, Anderle, Mathew 3:50 pm—4:00 pm B5-2—The Lateral Compartment in Knees with Isolated Medial and Patellofemoral Compartment Arthritis: A Histologic Analysis of Articular Cartilage Lalit Puri, Todd Moen, William Laskin, Ronald Hendrix 4:00 pm—4:10 pm B5-3—What You Plan is What You Get: Precise, Accurate Placement of Unicondylar Knee Implants Using Haptically Guided System Martin Roche

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4:10 pm—4:20 pm B5-4—In Vivo Kinematic Comparison for Subjects Having Both Cruciate Ligaments Versus Those Using a PS TKA A Sharma, R Komistek, P Hernigou, MR Mahfouz, MR Anderle, X Wang 4:20 pm—4:30 pm B5-5—Precision of the Positioning of an Unicompartmental Knee Prosthesis by a Mini-Invasive Navigated Technique Jean-Yves Jenny, Eugene Ciobanu, Cyril Boeri 4:30 pm—4:40 pm B5-6—Can Rules Proposed for Fracture Healing Explain the Formation of Radiolucency Under the Tibial Components of Knee Replacement Hans A Gray, Amy B Zavatsky, David W. Murray, Harinderjit S Gill 4:40 pm—4:55 pm S-7 Invited Speaker: Jean Noel Argenson UKA: A Solution for the Young Arthritic Knee? 4:55 pm—5:10 pm Panel discussion/Q&A 5:10 pm Adjournment

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FRIDAY, October 5, 2007 6:30 am – 5:00 pm ISTA Registration La Seine Ballroom Foyer 6:30 am—5:00 pm Speaker Ready Room Le Pont des Arts Room 7:00 am – 5:00 pm Exhibitors La Seine Ballroom Foyer 7:00 am – 5:00 pm Poster Display La Seine Ballroom Foyer 8:00 am – 10:00 am A4—HIP—THR Metal-On-Metal La Seine Ballroom C Chairmen: Claude Rieker (Winterthur) Christian Delaunay (Longjumeau) Invited: Thomas Schmalzried (Los Angeles) 8:00 am – 8:05 am Session overview and objectives 8:05 am—8:20 am S-8 Invited Speaker: Thomas Schmalzried Metal on Metal THR: Long Term Experience 8:20 am – 8:30 am A4-1—Acetabular Cup Angle and Early Loosening in Metal on Metal Articulation at the Hip Joint Jonathan Jeffers, A Roques, A Taylor, MA Tuke 8:30 am – 8:40 am A4-2—Serum Metal Ion Levels After Metal-on-Metal Hip Resurfacing Arthroplasty for Asian Patients Kabata Tamon, Maeda Toru, Sakagoshi Daigo, Naito Mitsuhiro, Taga Tadashi, Ando Tomonari, Tomita Katsuro 8:40 am – 8:50 am A4-3—Ten Years Follow-Up in Cobalt Serum Determination After Metal-On-Metal Hip

Prosthesis Jean-Yves Lazennec, Patrick Boyer, Joel Poupon, Marc-Antoine Rousseau, Phillipe

Ravaud, Yves Catonne 8:50 am – 9:00 am A4-4—Metal-On-Metal Hip Replacement Using Metasul Cups Cemented Into Muller Reinforcement Rings After a Mean 5-Year (3-8) Follow-Up: Improvement Of Acetabular Fixation by Comparing With Direct Cementation to Bone J Girard, S Herent, A Combes, Y Pinoit, D Bocquet, H Migaud 9:00 am – 9:10 am A4-5—Surface Analysis of Retrieved Metal To Metal Implants T Sorimachi, TK Donaldson, IC Clarke, K Yamamoto 9:10 am – 9:20 am A4-6—Histopathology of Revised Hip Resurfacing For Suspected Metal Sensitivity Pat Campbell, Scott Nelson, Christina Esposito, Andres Shimmin, Koen De Smet 9:20 am—9:30 am A4-7—The Fate of Sleeved Heads on Metal-On-Metal Bearing Outcome Christian Delaunay, Henri Migaud, Philippe Laffargue 9:30 am—9:40 am A4-8—Second Generation of Metal-On-Metal Cemented Total Hip Replacements: 10 Years of Clinical and Biological Follow-up JY Lazennec, P Boyer, J Poupon, MA Rousseau, F Laude, Y Catonne, G Saillant 9:40 am—9:50 am A4-9—Wear and Ions in Retrieved Metal-Metal Total Hip Replacements: A Hip Simulator Comparison of 28mm MOM Ian Clarke, T Sorimachi, Y Lazennec, T Ishida, H Shirasu

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9:50 am – 10:00 am Panel discussion/Q&A 10:00 am – 10:20 am Coffee Break/Exhibitors/Posters 10:20 am—12:00 noon A5—HIP—THR Alumina on Alumina Chairmen: Laurent Sedel (Paris) La Seine Ballroom C

Jeffrey Taylor (Sacramento) 10:20 am—10:35 am Lifetime Achievement Award Professor Laurent Sedel 10:35 am —10:45 am LA-1 Hydrxyapatite Granules in Femoral Stem Revision Surgery Laurent Sedel, Didier Hannouche, Christophe Nich, Remy Nizard 10:45 am – 10:50 am Session overview and objectives 10:50 am – 11:00 am A5-1—The Potentialities of Electroconductive Si3N4-TiN Ceramic Composite for Complex Shaped Implantable Devices, Machined Through Electrical Discharge Machining( EDM) F Bucciotti, MN Mazzocchi, A Bellosi 11:00 am – 11:10 am A5-2—The Occurrence of the Squeaking Phenomenon in Total Hip Arthroplasty Using Alumina Ceramic-On-Ceramic Bearings Stephen Murphy, Timo Ecker, Moritz Tannast 11:10 am – 11:20 am A5-3—Revision Total Hip Replacement for Ceramic Head Fracture: A Long Term Follow-up Vineet Sharma, Amar Ranawat, Vijay Rasquinha, Chitranjan Ranawat 11:20 am – 11:30 am A5-4—A Standardization Proposal of Test Method for Impact Resistance of Ceramic Femoral Head for Hip Joint Prostheses Tsutsumi Sadami, Mizuno Mineo, Todo Mitsugu, Nishida Masaru, Hattori Masaaki 11:30 am – 11:40 am A5-5—Wear of Large Ceramic Bearings Thomas Pandorf 11:40 am – 12:00 noon Panel discussion/Q&A 12:00 noon – 1:00 pm Group Luncheon restaurant Le Patio (Level 3)

1:00 pm – 2:10 pm A6—HIP—MIS THR La Seine Ballroom C Chairmen: Raj Sinha (Rancho Mirage)

Thierry Judet (Garches) Invited: Marc Siguier (Paris)

1:00 pm – 1:15 pm S-9 Invited Speaker: Marc Siguier, Thierry Siguier Mini Invasive THR Using an Anterior Approach: A 20 Year Experience 1:15 pm – 1:25 pm A6-1—In Vivo Comparison of Hip Mechanics for Subjects Implanted With a MIS or Traditional Surgical Technique - Extended Study Diana Glaser, TM Miner, Richard Komistek, MR Mahfouz, D Dennis, F Liu 1:25 pm – 1:35 pm A6-2—Modified “Mini-Posterior” Approach for Total Hip Replacement Michael Moran Holly Zhang 1:35 pm – 1:45 pm A6-3—Percutaneously Assisted Total Hip Arthroplasty (PATH): A Less Invasive Technique W. Seth Bolling, Michelle Riley, Jason Snibbe

1:45 pm – 1:55 pm A6-4—Learning Curve in Minimally Invasive Approaches in THA: Comparison Between

Lateral Mini Incision, Minimally Invasive Anterior Approach and Minimally Invasive Antero Lateral Approach Speranza Attilio, Iorio Raffaele, In gallina Antonello, D’Arrigo Carmelo, Ferretti Andrea

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1:55 pm—2:10 pm Panel discussion/Q&A 2:10 pm—2:30 pm Coffee Break/Exhibitors/Posters 2:30 pm – 4:30 pm A7—HIP-CAS THR La Seine Ballroom C Chairmen: Henri Judet (Paris) Hani Haider (Omaha) 2:30 pm – 2:35 pm Session overview and objectives 2:35 pm – 2:45 pm A7-1—Validation of an Imageless Computer Navigation System for Acetabular Cup Placement in THA William Bargar 2:45 pm – 2:55 pm A7-2—Validation With Robotics of Documentation and Analysis of Surgical Skills Through Real-Time Motion Recording of Navigated Arthroplasty Instruments Andres Barrera, Kevin Garvin, Alisa Gilmore, Hani Haider 2:55 pm – 3:05 pm A7-3—Estimation of Soft Tissue Thickness in Imageless Navigation of Cup Orientation in THA Ko, Byung-Hoon, Park, Suk-Hoon, Hwang, Deuk Soo, Yoon, Yong-San 3:05 pm—3:15 pm A7-4—Navigation in Hip Resurfacing: Report of Initial Results Michael Swank, Leslie Korbee 3:15 pm – 3:25 pm A7-5—Is Lewinnek’s Plane a Reliable Reference for Hip Navigation? Jacques Tabutin, Yannick Pinoit, Henri Migaud, Philippe Laffargue, Jean Puget 3:25 pm—3:35 pm A7-6—Reduction of Robot Milling Time Exploiting Inhomogeneos Bone Property in THA Park, Suk-Hoon, Kim, Nam-Jung, Shin, Hyun-Joon, Yoon, Yong-San 3:35 pm—3:45 pm A7-7—Navigated Control of the Cup Orientation During Total Hip Replacement Jean-Yves Jenny, Jean-Claude Dosch, Cyril Boeri, Marius Uscatu 3:45 pm—3:55 pm A7-8—Computer-Assisted “Fine Tuning” Survivorship Analysis with the Orthowave Software in Hip Arthroplasty Jean-Alain Epinette 3:55 pm—4:15 pm Panel discussion/Q&A 4:15 pm—4:30 pm A7-9 “HAP” PAUL AWARD PAPER Presentation: Nico Verdonschot (Nijmegen) Yves Catonne (Paris) In Vitro Performance of Silicon Nitride Ceramic in Total Hip Bearings B Sonny Bal, R Lakshminarayanan, Ashok Khandkar, Aaron A Hoffman, Mohamed N Rahaman 4:30 pm Launch of the new ISTA Web Site– Hani Haider 4:45 pm Adjournment 7:00 pm Gala Awards Dinner Automobile Club de France Presentation of Lifetime Achievement Award (Meet at the Club) Ryder Golf Trophy (Europe vs America) Europe: Gerard Saillant and Jacques Yves Nordin America: Richard Komistek

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FRIDAY, October 5, 2007 6:30 am – 5:00 pm ISTA Registration La Seine Ballroom Foyer 6:30 am—5:00 pm Speaker Ready Room Le Pont des Arts Room 7:00 am – 5:00 pm Exhibitors La Seine Ballroom Foyer 7:00 am – 5:00 pm Poster Display La Seine Ballroom Foyer 8:00 am—9:45 am B6— Knee—TKR Design, Mobile Bearing Chairmen: Louis Lootvoet (Namur) La Seine Ballroom B Jean-Louis Briard (Bois Guillaume) 8:00 am—8:05 am Session overview and objectives 8:05 am—8:15 am B6-1—In Vivo Comparison of Knee Kinematics for Subjects Implanted with a LCS RP PCS or a LPS Flex Mobile Bearing TKA Kazuo Hirakawa, Sumesh Zingde, Richard Komistek, MR Mahfouz, Mathew Anderle 8:15 am—8:25 am B6-2—Is Lower Wear the Main Benefit of Rotating Platform Mobile Bearing Total Knees? Kevin Garvin, Benjamin O’Brien, Richard Croson, Hani Haider 8:25 am—8:35 am B6-3—In Vivo Assessment of Axial Rotation in Mobile Bearing TKA Sumesh Zingde, Ray Wasielewski, Richard Komistek, Mohamed Mahfouz 8:35 am—8:45 am B6-4— Mobile Verses Fixed Bearing in Deep Flexion After Total Knee Replacement Samih Tarabichi 8:45 am—8:55 am B6-5—Gender Comparison of In Vivo Kinematics for Normal and TKA Subjects Richard Komistek, MR Mahfouz, Diana Glaser, R Booth, GR Scuderi, JN Argenson, S Zingde, M Anderle 8:55 am—9:05 am B6-6—Clinical Results of Ceramic Total Knee Prosthesis Used for 26 Years Oonishi Hironobu, Kim Sok Chol, Oonishi Hiroyuki, Kyomoto Masayuki, Iwamoto Mikio, Masuda Shingo, Ueno Masaru 9:05 am—9:15 am B6-7—Wear Response Sequentially Enhanced Polyethylene in Knee Joint Tsukamoto Riichiro, Shoji Hiromu, Hirakawa Kazuo, Yamamoto Kengo, Clarke Ian 9:15 am—9:25 am B6-8—Mobile Bearing Knee 30 Years of Experience. What has been proven? Report of 450 LCS RP with 10-15 Years Follow-up Jean-Louis Briard 9:25 am—9:45 am Panel discussion/Q&A 9:45 am—10:05 am Coffee Break/Exhibitors/Posters

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10:05 am –12:25 pm B7—KNEE– TKR Technique: Approach, Ligament Balancing Chairmen: Richard Cohen (Atlanta) La Seine Ballroom B Peter S Walker (New York) Invited: Dominique Saragaglia (Grenoble) 10:05 am—10:10 am Session overview and objectives 10:10 am—10:20 am B7-1—Evaluation of Intra Articular ‘Pinless’ Navigation in the Setting of Limited Incision Total Knee Arthroplasty Richard Walker, Kenny Mai, Rajeev Jain, Adam Rosen 10:20 am—10:30 am B7-2—Does the Size of Incision in TKA Matter? MIS TKA, Facts and Fictions Samih Tarabichi 10:30 am—10:40 am B7-3—Total Knee Arthroplasty by Transverse Incision Tomohiro Ojima 10:40 am—10:50 am B7-4—Possibilities of an Instrumented Linkage for TKR Surgery RE Forman, Peter Walker, CS Wei, G Scuderi, G Klein 10:50 am—11:00 am B7-5—Hip Position for Measuring Flexion Gap in Total Knee Arthroplasty Shinro Takai, Noriki Nakachi, Nobuyuki Yoshino, Yoshinobe Watanabe, Takashi Matsushita 11:00 am—11:10 am B7-6—Varus Balance Becomes Predominant at Flexion After Posterior Cruciate-Retaining Total Knee Arthroplasty Nobuyoshi Watanabe, NobuyukiYoshino, Yukihisa Fukuda, Nobuhiko Fujita, Shinro Takai 11:10 am—11:20 am B7-7—Dynamic Soft Tissue Balancing Senseor for Total Knee Arthroplasty Masahiko Suzuki, Jin Miyagi, Itsuo Sakuramoto, Kunio Fujiwara, Ryoichi Michihiro, Kouichi Kuramoto 11:20 am—11:30 am B7-8 —Fixed Genu Valgum: The Sliding Lateral Condylar Osteotomy as a Means to Balance Safely the Lateral Soft Tissues: Report of 74 Cases with at Least 5 Years Follow-up Jean-Louis Briard, Jens Boldt, PolawatWitoolkollachit, Guo Lin, Jean Zahlaoui 11:30 am—11:40 am B7-9—Severe Genu Valgum: How We Deal With? Louis Lootvoet, O Himmer, B Leyn, G Allard 11:40 am—11:50 am B7-10—The Need for Demand Matching Total Knee Replacement and the Obese Patient Richard Cohen 11:50 am—12:05 noon S-10 Invited Speaker: Jean Manuel Aubaniac Staged Approaches in Surgical Treatment of Knee O.A. Modular Compartmental Knee Arthroplasty 12:05 pm—12:15 pm Panel discussion/Q&A 12:15 pm —1:15 pm Group Luncheon 1:15 pm — 2:45 pm B8 —KNEE—TKR Deep Flexion La Seine Ballroom B Chairmen: Samih Tarabichi (Dubai) Bruno Tillie (Arras) 1:15 pm—1:20 pm Session overview and objectives 1:20 pm—1:30 pm B8-1—Deep Flexion Kinematics in Patients with a Medial Rotation Knee Arthroplasty P Moonot, GT Railton, S Mu, SA Banks, RE Field

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1:30 pm—1:40 pm B8-2—Kinematic Difference Between Subjects Having Low and High Flexion at the Same Flexion Angles: A Multicenter Study DA Dennis, A Sharma, RD Komistek, MR Mahfouz, MR Anderle, CR Little, F Liu 1:40 pm—1:50 pm B8-3—In Vivo Kinematics of High-Flexion Total Knee Arthroplasty Masashi Tamaki, Tetsuya Tomita, Tetsu Watanabe, Takaharu Yamazaki, Hideki Yoshikawa, Kazuomi Sugamoto 1:50 pm—2:00 pm B8-4—Achieving Normal Knee Motion in a TKR Design G Yildirim, Peter Walker, Jason Boyer 2:00 pm—2:10 pm B8-5—Thigh Calf Contact: Does It Affect the Loading of the Knee in the High Flexion Range? J Zelle, M Barink, Malefijt De Waal, N Verdonschot 2:10 pm—2:20 pm B8-6—Deep Flexion After Total Knee Arthroplasty Nakamura Shinichiro,Takagi Haruki, Asano Taiyo, Nakamura Takashi 2:20 pm—2:30 pm B8-7—Activities of Daily Living for Muslims in the Middle East: A Kinematic Comparison Between Normal Knees and High Flexion Total Knee Arthroplasty Sam Tarabichi, Urs Wyss, Stacey Smith 2:30 pm—2:45 pm Panel discussion/Q&A 2:45 pm—3:00 pm Coffee Break/Exhibitors/Posters 3:00 pm—4:55 pm B9—KNEE—TKR VARIOUS La Seine Ballroom B

Chairmen: Nobuo Takai (Tokyo) Giorgio Gasparini (Rome) Invited: Giorgio Gasparini (Rome) 3:00 pm—3:05 pm Session overview and objectives 3:05 pm —3:20 pm S16—Invited Speaker: Giorgio Gasparini Trabecular Metal in Knee Prosthesis 3:20 pm—3:30 pm B9-1—Three Dimensional Bone Creation and Landmarking Using Two Still X-Rays Mohamed Mahfouz, Emam Fatah, Hatem Dakhakhni, Rimon Tadross, Richard Komistek 3:30 pm—3:40 pm B9-2—Combination View: A New Roentgenographic Technique to Assess the Rotation of the Femoral Component Noriki Nakachi, Nobuyoshi Watanabe, Yukihisa Fukuda, Naoya Shimazaki, Nobuyuki Yoshino, Takashi Matsushita, Shinro Takai 3:40 pm—3:50 pm B9-3—Anterior Cruciate Ligament Retaining Total Knee Arthroplasty: The Cases Survived 20 Years or More Kiyohiro Nagase, Atsushi Kusaba, Saiji Kondo, Hiroyuki Okumo, Yujiro Mori, Yoshikatsu Kuroki 3:50 pm—4:00 pm B9-4—Morbidity and Mortality After Simultaneous Bilateral TKA as Compared To Single TKA S Tarabichi, AR Tarabichi 4:00 pm—4:10 pm B9-5—Gender Differences in Osteoarthritic Knee Joint Geometry Noaya Shimazaki, Noriki Nakachi, Nobuyuki Yoshino, Nobuyoshi Watanabe, Takashi Matsushita, Shinro Takai 4:10 pm—4:20 pm B9-6—Three Dimensional Patellar Tracking During Total Knee Replacement With and Without Patellar Resurfacing: An In-Vitro Study Claudio Belvedere, Alberto Leardini, Andrea Ensini, Fabio Catani, Sandro Giannini

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4:20 pm—4:30 pm B9-7—Resurfacing Versus Not Resurfacing the Patella in Total Knee Arthroplasty: 4 Year Results N Bonin, J Mercado, G Deschamps, D Dejour 4:30 pm—4:40 pm B9-8—Allograft-Prosthetic Composite for Proximal Femur Reconstruction After Limb Salvage Surgery for Bone Tumors: Surgical Technique and Results Nicola Fabbri, Costantino Errani, Davide Donati, Marco Manfrini, Mario Mercuri 4:40 pm -4:55 pm Panel discussion/Q&A 4:55 pm Adjournment 7:00 pm Gala Awards Dinner Automobile Club de France Presentation of Lifetime Achievement Award (Meet at the Club) Ryder Golf Trophy (Europe vs America) Europe: Gerard Saillant and Jacques Yves Nordin America: Richard Komistek

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SATURDAY, October 6, 2007 6:30 am – 5:00 pm ISTA Registration La Seine Ballroom Foyer 6:30 am—5:00 pm Speaker Ready Room Le Pont des Arts Room 7:00 am – 5:00 pm Exhibitors La Seine Ballroom Foyer 7:00 am – 5:00 pm Poster Display La Seine Ballroom Foyer 8:00 am – 9:50 am A8—HIP– THR La Seine Ballroom C Chairmen: Young Yong Kim (Seoul) Marcel Kerboull (Paris) 8:00 am – 8:05 am Session overview and objectives 8:05 am—8:15 am A8-1—The Exeter Total Hip Prosthesis in Patients Under 40 Years at 2 to 12 Years After Surgery Berend Schreurs, DJC de Kam, R Klarenbeek, JWM Gardeniers 8:15 am – 8:25 am A8-2—Assessing Agreement Between Clinical and Software-Assessed Hip Range of Motion Evan Baird, Jonathan Zelken, Joseph Lipman, Luis Moya, Robert Buly 8:25 am – 8:35 am A8-3—An Algorithm for the Surgical Treatment of Congential Hip Dysplasia In Adults Roberto Binazzi, A Bondi, A Manca 8:35 am – 8:45 am A8-4—Prearthrotic Pathomorphologic Alterations of the Hip Joint Predicting Subsequent Osteoarthritis Ecker, Timo, Tannast, Moritz, Puls, Marc, Siebenrock, Klaus, Murphy, Stephen 8:45 am – 8:55 am A8-5—Use of Complimentary Non-destructive Evaluation Methods to Evaluate The Integrity of the Bone-Cement Interface SY Leung, A New, Martin Browne 8:55 am – 9:05 am A8--6—The Influence of Cup Anteversion, Abduction Angle and Head Diameter on the Jumping Distance Eddy Sariali, Bernard Masson, Jean-Yves Lazennec, Yves Catonne 9:05 am – 9:15 am A8-7—One-Stage Bilateral Uncemented Hip Arthroplasty a Simultaneous Procedure for Dysplastic Osteoarthritis Kusaba Atsushi, Kondo Saiji, Kuroki Yoshikatsu 9:15 am—9:25 am A8-8 —Unexpected Anatomic Relationships in the Proximal Femur: Implications For Implant Design Carl Deirmengian 9:25 am – 9:35 am A8-9—THR in Congential Hip Dysplasia Luc Kerboull, M Hamadouche, Marcel Kerboull 9:35 am—9:50 am Panel discussion/Q&A 9:50 am—10:10 am Coffee Break/Exhibitors/Posters

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10:10 am – 12:00 noon A9—HIP– Planning THR La Seine Ballroom C Chairmen: John Hollingdale (Bucks) Moussa Hamadouche (Paris) 10:10 am—10:15 am Session overview and objectives 10:15 am—10:25 am A9-1—Precision of a Three-Dimensional Planning of Primary Total Hip Prosthesis Using a Cementless Stem Eddy Sariali, G Pasquier, A Mouttet, Yves Catonne 10:25 am—10:35 am A9-2—Computer Planned Two-Stage Hip Arthroplasty for High-Ridin Hips—THA After Leg

Elongation Hirotaka Iguchi, Takanobu Otsuka, Nobuhiko Tanaka, Masaaki Kobayashi, Yuko Nagaya,

Hideyuki Goto, Shinji Hisazaki, Yoichi Taneda, Nobuyuki Watanabe, Yukio Yoshida, Yoshihiro Shibata, Toshiyukiu Kawanishi, Takayuki Hirade, Kowase, Peter Walker, Joseph Fetto

10:35 am—10:45 am A9-3—The Use of TeraRecon for Preoperative Planning of Complex Hip Reconstructions CL Emory, LX Webb, RH Jinnah, J Tan 10:45 am—10:55 am A9-4—A New Method for the Evaluation of Total Hip Arthroplasty Based on Bi-Planar Low Dose X-Rays A Baudoin, JY Lazennec, Y Catonne, M Gorin, J Dubousset, D Mitton, W Skalli 10:55 am—11:05 am A9-5—An Intraoperative Leg Length Caliper and Digital Preoperative Templating is More Accurate in Restoring Femoral Length and Offset in Total Hip Arthroplasty Than Digital Templating Alone Ivan Tomek, Ryan Stehr, Stephen Kantor 11:05 am —11:15 am A9-6—Orientation the Acetabular Cup: Lying Position Correlates with Standing But Not Sitting Position Jean-Yves Lazennec, Marc-Antoine Rousseau, Patrick Boyer, Michel Gorin, Yves Catonne 11:15 am—11:25 am A9-7—Geometry of the Femur in DDH with High Anteversion and its Lateral Flare Custom and Off-The-Shelf Stems Strategy Hirotaka Iguchi, Takanobu Otsuka, Nobuhiko Tanaka, Masaaki Kobayashi, Yuko Nagaya,

Hideyuki Goto, Shinji Hisazaki, Yoichi Taneda, Nobuyuki Watanabe, Yukio Yoshida, Yoshihiro Shibata, Toshiyukiu Kawanishi, Takayuki Hirade, Kowase, Peter Walker, Joseph Fetto

11:25 am—11:35 am A9-8—Gender Specific Femoral Anteversion Variation in Patients Undergoing Total Hip Arthroplasty Nirav Shah, Raju Ghate, S. David Stulberg 11:35 am—11:45 am A9-9—Modular Neck Prosthesis Antonio Croce, Marco Ometti 11:45 am—12:00 noon Panel discussion/Q&A 12:00 noon—1:00 pm Group Luncheon 1:00 pm —2:45 pm A10-HIP-THR Revision La Seine Ballroom C Chairmen: Jacques Tabutin (Cannes) Denis Huten (Paris) Invited: Marcel Kerboull (Paris) 1:00 pm—1:05 pm Session overview and objectives 1:05 pm—1:20 pm S11 Invited Speaker: Marcel Kerboull The Kerboull Acetabular Reinforcement Device in Major Acetabular Reconstructions

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1:20 pm—1:30 pm A10-1—The Use of Structural Periacetabular Allografts in Acetabular Revision Surgery: 2.5 to 5 Years Follow-Up Stefan Schelfaut, Steve Cool, Michiel Mulier 1:30 pm—1:40 pm A10-2—Pelvic Osteolysis: The Value of Radiographs in its Assessment and its Relationship with Wear Shon Won Yong, Han Sang Wan, Gupta Siddhartha 1:40 pm—1:50 pm A10-3—The Use of Cemented Unconstrained Tripolar Cup to Treat Recurrent Dislocation: A Multicenter Study Moussa Hamadouche, David Biau, Nocolas Barba, David Ropars, Thierry Musset, Francois Gaucher, Jean Pierre Courpied, Franz Langlais 1:50 pm—2:00 pm A10-4—Advantages of the Bipolar Acetabular Component in Total Hip Revision JL Rouvillain, E Garron, W Daoud, Th Navarre 2:00 pm—2:10 pm A10-5—Distally Locked Stems for Revision Hip Arthroplasties with Severe Femoral Bone Loss: Results of 101 Cases After a Mean Follow-Up of 6 Years (5-12) Olivier May, Marc Soenen, Philippe Laffargue, Yannick Pinoit, Henri Migaud 2:10 pm—2:20 pm A10-6—The Use of Diaphyseal or Trochanteric Diaphyseal External Reinforcement Plates in Femoral Revisions Jean-Pierre Roux 2:20 pm—2:35 pm Panel discussion/Q&A 2:35 pm—5:05 pm A11-HIP RESURFACING 1 Chairmen: Koen DeSmet (Gent) La Seine Ballroom C William Macaulay (New York) Invited: Philippe Piriou (Garches) 2:35 pm—2:40 pm Session overview and objectives 2:40 pm—2:50 pm S12 Invited Speaker: Philippe Piriou Anterior Approach for Hip Resurfacing: Advantages and Disadvantages 2:50 pm—3:00 pm A11-1—Malpositioned Cups as Reason for Revision in Metal-On-Metal Hip Resurfacing Arthroplasty Roel De Haan, Edwin Su, Pat Campbell, Koen DeSmet 3:00 pm—3:10 pm A11-2—An Independent Review of Results after Birmingham Hip Resurfacing Arthroplasty at Seven Years Robert Steffen, Hemant Pandit, Peter McLardy-Smith, Roger Gundle, David Beard, Barbara Marks, Harinderjit Singh Gill, David Murray 3:10 pm—3:20 pm A11-3—Femoral Head Resurfacing Using Imageless Navigation– Accuracy of Navigation Rehan Gul, M Falworth, R Oakshott, S Zadowe 3:20 pm—3:30 pm A11-4—Resurfacing of the Hip: An OnBench Biomechanical Study Pier Francesco Indelli, David Dominguez, Kenichi Kitaoka, Thomas Vail 3:30 pm—3:40 pm A11-5—Cement Distribution and Thermal Necrosis in Failed Hip Resurfacing William Lundergan, E Ebramzadeh, Pat Campbell, Brook Wager, Christina Esposito, Koen De Smet, Harlan Amstutz 3:40 pm—3:50 pm A11-6—Total Hip Resurfacing in the USA: A Prospective, Single Surgeon Report on 1 Year Minimum Follow-Up William Macaulay, G Clerici-Bagozzi 3:50 pm—4:00 pm A11-7—The Choice of Surgical Approach for Hip Resurfacing Affects Femoral Head Blood Supply: An Analysis of Four Different Approaches Robert Steffen, Kieran O’Rourke, Koen De Smet, Darren Fern, Mark Norton, Peter McLardy-Smith, Harinderjit Gill, David Murray

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4:00 pm—4:10 pm A11-8—Cement Pressure During Hip Resurfacing Head Implantation Mike Tuke, Adam Brooks, Michael Rigby, John Ivory, Xiao Hu, Andy Taylor 4:10 pm—4:20 pm A11-9—Metal Ion Levels and X-Ray Follow-Up as Predictors for Problems and Outcome in Hip Resurfacing Arthroplasty Koen De Smet, Roel De Haan, Harinderjit Gill, Edward Ebramzadeh, Pat Campbell 4:20 pm—4:30 pm A11-10—Is Metal-on-Metal Resurfacing Hip Arthroplasty Conservative for Acetabular Bone? A Comparison of Acetabular Bone Conservation Between Conservative THA and Metal-on-Metal Resurfacing Hip Arthroplasty Using Computed Tomography Naitoh Mitsuhiro, Kabata Tamon, Maeda Toru, Taga Tadashi, Ando Tomonari, Tomita Katsuro 4:30 pm—4:40 pm A11-11—Implant Retrieval Analysis of Failed Hip Resurfacings Pat Campbell, Christina Esposito, Scott Nelson, Zhen Lu, Koen DeSmet, Harlan Amstutz 4:40 pm—4:50 pm A11-12—A Mechanical Analysis of Femoral Resurfacing Implant for Osteonecrosis of the Femoral Head Daigo Sakagoshi 4:50 pm—5:05 pm Panel discussion/Q&A 5:05 pm Adjournment

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SATURDAY, October 6, 2007 6:30 am – 5:00 pm ISTA Registration La Seine Ballroom Foyer 6:30 am—5:00 pm Speaker Ready Room Le Pont des Arts Room 7:00 am – 5:00 pm Exhibitors La Seine Ballroom Foyer 7:00 am – 5:00 pm Poster Display La Seine Ballroom Foyer 8:00 am – 9:15 am B10-HIP AND KNEE: THR and TKR COATING Chairmen: Sam Nasser (Sterling Heights) La Seine Ballroom B Jean Alain Epinette (Bruay Labussiere) 8:00 am – 8:05 am Session overview and objectives 8:05 am—8:15 am B10-1—A 10-17 Years Experience with HA in Knee Arthroplasty Based Upon a Prospective Orthowave Study Jean-Alain Epinette 8:15 am—8:25 am B10-2—Wear of Titanium Niobium Nitride Coated Total Knee Replacements Joel Weisenburger, Richard Croson, Fereydoon Namavar, Kevin Garvin, Hani Haider 8:25 am—8:35 am B10-3—Porous Titanium Particles for Application in Impaction Grafting: Basic Mechanical Characteristics and In-Vivo Testing of Osteoconductive Potential Luc HB Walschot, Rene Aquarius, Nico Verdonschot, Wim Schreurs, Pieter Buma 8:35 am—8:45 am B10-4—Total Knee Replacement for Rheumatoid Arthritis by Using Improved Cement Technique by Interposing Hydroxyapatite Granules Kim Sok Chol, Oonishi Hironobu, Oonishi Hiroyukiu, Hirotsugu Ohashi 8:45 am—8:55 am B10-5—On The Development of Smart Durable Coatings to Promote Biointegration While Preventing Biofilm Formation Fereydoon Namavar, Kevin Garvin, John Jackson, J. Graham Sharp, Ethan Mann, Kenneth Bayles, Hani Haider 8:55 am—9:15 am Panel discussion/Q&A 9:15 am – 10:45 am B11-UPPER LIMB La Seine Ballroom B Chairmen: Levon Doursounian (Paris)

Taco Gosens (Tilburg) 9:15 am—9:20 am Session overview and objectives 9:20 am—9:35 am S-13 Invited Speaker: Thierry Judet (Garches) Prosthesis of the Radial Head: Technique ad Indications 9:35 am—9:45 am B11-1—Clinical Results of Total Elbow Arthroplasty with Fine Total Elbow Joint System Masayuki Sekiguchi, Kazuaki Tsuchiya, Yoshiyasu Miyazaki, Yurika Kanai, Yoshiyuki Ohikata, Ayako Kubota, Hirofumi Kawakami, Muneki Saito, Keitaro Yamamoto, Toru Suguro 9:45 am—9:55 am Communication: Christian Dumontier 9:55 am—10:05 am B11-2—Metal ad Polyethylene Prosthesis for CMC 1 Joint Arthritis T Gosens, MGFG Schreibers, J Janssens 10:05 am—10:15 am B11-3—Total Finger Arthroplasty with Fine Total Finger Joint System in

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Rheumatoid Arthritis Patients Masayuki Sekiguchi, Toru Suguro, Yoshiyasu Miyazaki, Yoshijuki Ohikata, Hirofumi Kawakami, Muneki Saito, Keitaro Yamamoto, Junichi Nakamura, Kazuaki Tsuchiya 10:15 am—10:25 am B11-4—Total Evolutive Shoulder System: Preliminary Experience of a Non-Designer with a New Concept of Shoulder Prosthesis T Gosens 10:25 am —10:35 am B11-5—Computer-Aided Navigation for Shoulder Arthroplasty: Implications as a Research Tool Vineet Sarin, Matthew Williams, Hussein Elkousy, Rodney Stanley, Gary Gartsman, T. Bradley Edwards 10:35 am—10:45 am Panel discussion/Q&A 10:45 am—11:00 am Coffee Break/Exhibitors/Posters 11:00 am—12:25 pm B12-Spine La Seine Ballroom B Chairmen: Jean-Yves Lazennec (Paris) Fabien Bitan (New York) 11:00 am—11:05 am Session overview and objectives 11:05 am—11:15 am B12-1—3D In Vivo Contact Force Determination of Normal, Fused and Degenerative Cervical Spines F Liu, RD Komistek, JS Cheng, MR Mahfouz, A Sharma, D Glaser 11:15 am—11:25 am B12-2—Use of Charite, Artificial Disc in Combination with Spinal Fusion in Double-Level Degenerative Disc Disease of the Lumbar Spine (Hybrid Construct): A Prospective Study of Twenty-Four Patients with a 1Year Follow-Up Fabien Bitan, S Hanan, J Shearer 11:25 am—11:35 am B12-3—ESP Lumbar Spine Prosthesis: About a Clinical Series of 50 Patients Hugues Pascal-Moussellard, Jean-Yves Lazennec, Olivier Ricard, Marc Antoine Rousseau, Yves Catonne 11:35 am — 11:45 am B12-4—Mobidisc Lumbar Spine Prosthesis Evaluation Jerome Allain 11:45 am—11:55 am B12-5—In Vivo Kinematics of Two Types of Ball-and-Socket Cervical Disc Replacements in the Sagittal Plane: Cranial Versus Caudal Geometric Center MA Rousseau, PH Cottin, A Nogier, JY Lazennec, W Skalli 11:55 am—12:05 pm B12-6—Determination of In Vivo, Three Dimensional Motion of the Cervical Spine Under Variable Conditions JS Cheng, F Liu, RD Komistek, MR Mahfouz, A Sharma, D Glaser 12:05 pm—12:15 pm B12-7—In Vivo 3D Intervertebral Kinematics After Cervical Disc Replacement Using the EOS Stereoradiography System Marc Antoine Rousseau, S Laporte, L Devun, Jean Yves Lazennec, T Dufour, W. Skalli 12:15 pm—12:25 pm Panel discussion/Q&A 12:25 pm—1:25 pm Group Luncheon restaurant Le Patio (Level 3) 1:25 pm —3:00 pm B13-HIP AND KNEE: THR and TKR La Seine Ballroom B

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Chairmen: David Markel (Southfield) Vincenzo Denaro (Rome) Invited: Jacques Yves Nordin (Paris) 1:25 pm—1:40 pm S-14 Invited speaker: Jacques Yves Nordin (Paris) The Guepar Group Prosthesis: History and Evolution 1:40 pm—1:45 pm Session overview and objectives 1:45 pm—1:55 pm B13-1—The Results of a One Stage Joint Revision for Infected Joints Using Radical Debridement and Antibiotic Impregnated Cemented Total Joint Revision Gerhard Maale, Jorge Casas-Gamen, Allen Rueben 1:55 pm—2:05 pm B13-2—The Value of a Subjective Score for the Patello-Femoral Assessment in Total Knee Arthroplasty Nicolas Bonin, Gerard Deschamps, David Dejour 2:05 pm—2:15 pm B13-3—Characterization of the Inflammatory Response to Bone Graft Substitutes Using the Murine Air Pouch Model S. Trent Guthrie, Bin Wu, Zheng Song, Paul Wooley, David Markel 2:15 pm—2:25 pm B13-4—Single Use Surgical Instruments to Reduce the Incidence of Bone Necrosis and Eliminate Cross Contamination Alex Dickinson, A Taylor, T Bird, J Latham, R Wadey, M Browne 2:25 pm—2:35 pm B13-5—Laser Melting Technologies for Improved Flexibility During Implant Manufacture Anne Roques, Andy Taylor 2:35 pm—2:45 pm B13-6—Complications Encountered with the Use of Constrained Acetabular Prostheses Versus Large Diameter Metal on Metal Modular Heads in Total Hip Arthroplasty. A Restrospective Comparative Study Christophe Pattyn, Roel De Haan, Georges Van Maele, Koen DeSmet 2:45 pm—3:00 pm Panel discussion/Q&A 3:00 pm—4:15 pm B14-ANKLE La Seine Ballroom B Chairmen: Thierry Judet (Garches) Nobuo Takai (Tokyo) 3:05 pm—3:15 pm S-15 Invited Speaker: Thierry Judet 3:15 pm—3:20 pm Session overview and objectives 3:20 pm—3:30 pm B14-1—A New Design of Ankle Prosthesis targeting Ligament Isometry: Intra– and Post-Operative Validation Measurements Alberto Leardini, Fabio Catani, Matteo Romagnoli, Loris Bianchi, Maria Teresa Miscione, Sandro Giannini 3:30 pm—3:40 pm B14-2—In Vivo Determination of the Mobile Bearing Total Ankle Prosthesis Kinematics Filip Leszko, Richard Komistek, Mohamed Mahfouz, Thierry Judet, Michel Bonnin, Jean-Alain Colombier, Sheldon Lin 3:40 pm—3:50 pm B14-3—Design Rationale and Mechanical Test of 3-Component Mobile-Bearing Total Ankle Arthroplasty Yamamoto Keitaro, Suguro Toru, Nakamura Takashi, Miyazaki Yoshiyasu, Kogame Katsunori, Kubota Ayako, Kuramoto Koichi 3:50 pm—4:00 pm B14-4—Fixed or Mobile Bearing Total Ankle Replacement Designs: What Really Matters? Hani Haider, Lori K Reed, Ben O’Brien, Kevin L Garvin 4:00 pm—4:15 pm Panel Discussion/Q&A 4:15 pm Adjournment

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MID TO LONG TERM RESULTS OF A LATERAL FLARE CUSTOMIZED UNCEMENTED STEMS IN PATIENTS YOUNGER THAN 55 YEARS OF AGE. AUTHORS: Alejandro Leali, MD (*) Joseph F. Fetto, MD (**) AFFILIATION: (*) Hospital for Special Surgery, Department of Orthopedic Surgery, New York, NY (**) New York University/ Hospital for Joint Diseases, Department of Orthopedic Surgery New York, NY 530 First Ave. #5B, New York, NY 10016 Phone: 212-263-7296 E-Mail” [email protected] Background: First generation uncemented stems for THA were associated with high rates of thigh pain, aseptic loosening and stress shielding. To minimize these problems a high metaphyseal loading femoral stem that incorporates a lateral flare in the proximal body was designed and initially available as a custom implant. Materials and Methods: 35 consecutive patients (40 hips) younger than 55 years of age (average 45.2 years, range: 30 to 55 years) were prospectively followed for an average of 10.2 years (range 6.7 to 13.2 years). All patients received a customized lateral flare cementless femoral stem designed to provide a high metaphyseal fit in the proximal femur. The preop-erative diagnoses included primary osteoarthritis in nine patients, avascular necrosis in sixteen patients, congenital hip dysplasia in seven patients and secondary osteoarthritis due to slipped capital femoral epiphysis in three pa-tients. Clinical evaluations were performed before the operation, three, six and twelve months after the surgery; and yearly thereafter utilizing the Harris Hip Score (HHS)24. Anteroposterior and lateral films of the involved hip as well as anteroposterior view of the pelvis were assessed along with clinical follow-ups. Immediate postopera-tive and last follow-up x-rays were evaluated and rated by a qualified orthopedic surgeon from another academic institution who was blinded to the clinical results. The stems were rated for stability, and the presence of osteoly-sis, progressive radiolucent lines, stress shielding, bone resorption, cancellous or cortical thickening and visible periprosthetic bone density changes was recorded. The distance from the tip of the greater trochanter to a repro-ducible reference point on the stem was used to measure axial migration of the stem. Results: There was one patient with aseptic loosening of the stem and one patient with late deep infection necessitating sub-sequent revisions. The mean preoperative Harris hip score was 47 and 97 at the latest follow-up. The mean axial migration was 0.51 mm, femoral osteolysis was found to be circumscribed to the proximal femur in Gruen zones 1 (15%) and 7 (7.5%) in patients with accelerated polyethylene wear. Radiographic changes consistent with new bone apposition underneath the lateral flare of the stem in zone 2 as well as in zones 6 and 7 were found in 72.5% of the cases. Conclusions: This study demonstrated that a custom lateral flare stem for primary arthroplasty in the young patient population achieves excellent clinical results with low rates of aseptic loosening.

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INVESTIGATION OF NEW CONCEPT OF BUFFERED IMPLANT FIXATION IN RAT MODEL: MEASUREMENT OF BV/TV USING MICRO-CT IN COMPARISON WITH CE-MENTED IMPALANT FIXATION Choi, Donok, Park, Sukhoon, Hwang, Deuk Soo, Yoon, Yong-San. Department of Mechanical Engineering, KAIST, Daejeon, 305-701, South Korea TEL : +82-42-869-3022, FAX : +82-42-869-3210, E-mail : [email protected]

Presently, two kinds of orthopaedic implant fixation methods are popular: cemented and cementless. In the cemented fixation, there are two kinds of concept according to surface finish: taper-lock and composite-beam the-ory. However, any methods of implant fixation have not enough longevity because of interface failure due to ce-ment layer fracture, stress shielding, wear debris, micromotion and so on. In this study, we are suggesting a new concept of implant fixation. It uses a strong plastic buffer instead of the cement to reduce the medium failure and promote bone ingrowth. The buffer should transfer.

We manufactured implant with 3° taper angle and 15mm length using stainless Kirschner-wire with a diame-

ter of 1.6mm and used PEEK for the buffer. The PEEK buffer had a porous surface and several diameters ranged 1.8mm ~ 2.6mm to fit the rat femur size. Sprague-Dawley rats (average weight: 608.3g) received implantations in bilateral femurs under anesthesia. For the load-bearing, femurs were cut at the middle and implants were inserted. The distal region of the implant was fixed using cement, while the proximal region of the implant was fixed using cement and buffer respectively and randomly. Rats were sacrificed at 2 and 4 weeks after the operation and im-planted femurs were harvested. Soft tissue was removed and the femurs were frozen.

The femurs were scanned by micro-CT (Harmony 90M-3p-4, DRGEM, Korea, 85 kV, 80µA, 1000ms).

Bone volume per total volume (BV/TV) was measured. After 2 weeks, BV/TV is 0.60 ± 0.09(average ± standard deviation) for buffer and 0.66 ± 0.05 for cement; after 4 weeks, 0.61±0.03 and 0.59±0.05, respectively. There are no difference between buffer fixation and cement fixation (P = 0.175 at 2 weeks, P = 0.497 at 4 weeks). However, change with time was different between buffer fixation and cement fixation. Change of BV/TV was not significant between at 2 weeks and at 4 weeks in buffer fixation (P=0.351), but BV/TV decreased over time at the cement fixation in cement fixation (P =0.026).

This results show the potential of buffered fixation compared to cement fixation although bone volume frac-

tion does not represent the status of implant-bone interface directly. We are going to compare the strengths of in-terfaces for these two fixations.

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TWO YEAR RESULTS OF A SHORT, METAPHYSEAL LENGTH FEMORAL STEM IN PRIMARY TOTAL HIP ARTHROPLASTY Author: Mark Dolan, M.D. 1527 N. Hudson Ave Unit 1N, Chicago, IL 60610 Phone: 312-343-0587 Fax: 312-482-8177 E-Mail: [email protected] Introduction: The purpose of this study is to evaluate the two year results of a short, metaphyseal length femoral stem design in primary THA. Methods: Sixty-eight patients underwent 70 consecutive primary THA with a cementless femoral stem and were prospec-tively followed clinically and radiographically. The anatomic, titanium alloy femoral stems with a hydroxyapetite coated plasma spray porous coating in the proximal one half of the component were 70-105 mm long. Clinical results were evaluated using Harris Hip Scores and inquiring about thigh pain. Radiographic results were evalu-ated using anteroposterior and lateral views of the hip as well as anteroposterior views of the pelvis. The initial post-operative films and most recent follow-up radiographs were evaluated for evidence of subsidence, osteolysis, radiolucent lines, and bone ingrowth. Results: At a minimum of two year follow-up, the average Harris Hip Score was 91. No patient had thigh pain. Radio-graphic evaluation revealed bone ingrowth in all cases. There have been no instances of fractures or subsidence. One patient underwent revision of the acetabular component for recurrent dislocations. There were no revisions associated with the femoral stem. Discussion and Conclusions: The short femoral prosthesis presented here is a next step in the progression of femoral implant design. Benefits of the new stem design include increased ease and reproducibility of insertion, especially when used with a MIS ante-rior approach. The ultra-short stem design avoids the issues of proximal to distal mismatch and variations in the femoral bow. In addition, the short stem design is more preserving of native femoral bone which may prove bene-ficial in revision surgery. As demonstrated in this study, a short femoral prosthesis can be used to achieve excellent clinical results with a low rate of early aseptic loosening.

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EVALUATION OF TENSILE STRAIN DISTRIBUTION IN LOADED PROXIMAL FEMUR IN RELATION TO LENGTHS OF CEMENTLESS STEMS Nakamura Takuya1), Sumihiko Maeno2)

1)Department of Orthopaedic Surgery, Toyama Prefectural Central Hospital 2-2-78 Nishinagae, Toyama, 930-8550 Japan Phone:+81-76-424-1531, Fax:+81-76-422-0667, e-mail:[email protected] 2)Hip Joint Development & Technology Department, Japan Medical Materials Corporation Background: The short stem has an advantage in bone preservation in total hip arthroplasty. To evaluate the influence of the length of cementless stems on loaded proximal femur, the tensile strain was measured by the experimental strain analysis and the FEM analysis. Methods: Cementless stems in several lengths (130mm [standard length], 100mm, 70mm and 50mm, ABC Hip System[K-Max series], JMM, Osaka, Japan) were evaluated. The strain distribution was measured with three-element strain rosettes after implantation of the stem into the Sawbone Composite Femora #3306 (Pacific Research Laboratories, Vashon Island, WA, USA). FEM analysis of the stem in the same length was also conducted. The changes of strain distribution in relation to differences of setting angle of the stem in the femora and the thickness of the cortical bone were also evaluated by the FEM analysis. Results: The tensile strain showed its peak in the lateral area 50-70 mm from the bone cutting line regardless of the stem length, with anterior transition distally. In the experimental analysis, the strain was lower when the stem length was short, whereas the FEM analysis showed higher strain in the proximal area when the stem length was short. On the other hand, the strain was bigger with the decreased valgus angle and the increased flexion angle of the femur. The tensile strain was also higher when the cortical bone is thinner. Discussion: It was found that the tensile strength is more susceptible to the fixation angle of the stem and the thickness of corti-cal bone than the stem length. Therefore it is important that the stem length stays within the range of the solid cor-tical bone to reduce the risk of femoral fracture.

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ALLOCLASSIC SL OFFSET STEM CONCEPTION DESIGN BASED ON CLINICAL EVIDENCE Christian P. Delaunay*, Falah Bachour, Henri Migaud Clinique de l'Yvette, 67-71, route de Corbeil, 91160 Longjumeau, France Tel : 00 (331) 69 10 30 30 / Fax : 00 (331) 69 10 31 33 / [email protected] INTRODUCTION: Anatomic hip references indicated average femoral offset of 47.2 mm (+/- 6.1) and natural CCD angle of 125° (+/-4.8°). Ninety different commercialized THA restored only 33% of anatomic offset in 50 hips and a 131° neck angle stem restores only 68% of offset. There are concerns regarding leg-length inequality: when (+) it can be associated with pain and paresthesia, or (-) with instability that both may indicate revision and lead to litigation. Lack of offset restauration reduces lever arm and induces abductor muscle weakness, increases prevalence of limp and the need for walking aids. Lateralization has either negative effects, increases bending strain and strain in the medial cement mantle (compensated by decrease in joint force) and can create trochanteric bursitis (Iliotibial-band) and buttock pain, and positive effects : decreasing hip joint reactive force (-6% when offset + 5.4mm), that reduces PE wear. There are 4 methods to increase implant offset : 1/ increasing neck length ; 2/ decreasing CCD angle ; 3/ increasing neck length and medialisation ; and 4/ combination of increasing neck-length and decreasing CCD angle.

METHOD: A radiographic study templating 223 pre-operative hips comparing the Alloclassic-SL standard stem with 4 commercialized lateralized stems. The distance measured between natural head center of rotation and center of ball head defined the “Norm” (X horizontal offset, Y vertical length) : the closer the norm to 0, the better the case scenario.

RESULTS:

Median offset value (600 digitalised measures) was 44.8mm, with 50% between 40.5mm (lower quartile) and 50.4mm (upper quartile). The Alloclassic SL standard stem indicated a median norm of 6mm. The difference in norm for the Alloclassic SL Standard stem versus the control lateralized stems was mainly affected by the offset lag X, and not by the Y. But, Alloclassic SL standard me-dialised only hips with medium + and larger offsets. Thus, an Offset SL stem version was a real need for the 2 superior offset value quartiles.

DISCUSSION:

Choice of the basic lateralization concept was based on the fact that the Alloclassic SLO (SL Offset) stem might no be a “new” implant (no change below the resection line). As there was no need to modify the height of the ball head center, between the 4 methods to increase implant offset, the 4th was chosen. As the needed addition to restore “at best” the lever arm was constant or decreasing with size, a constant neck lengthening of 6.25mm and CCD reduction of 10° was applied. To check this option, a second radiographic study compared Alloclassic SL Standard and SL Offset stem tem-plates. Results confirmed the change in offset gap X that was reduced by 6mm. Finally, Alloclassic SL and SL Offset stems with medium necks covered anatomic hip offsets range from 32.7mm to 56.5mm.

CONCLUSION: After 11,800 Alloclassic SL Offset stems sold worldwide, no deleterious effect (ie, implant fracture) was reported to the manufacturer. Adjunction of the “Offset” option allows the Alloclassic-system to “cover” > 90% of natural hip offsets. Confirmation “in vivo” of the validity of the theoretical conception protocol was observed.

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NON-DESTRUCTIVE EVALUATION OF DAMAGE ACCUMULATION IN CARBON NANOTUBE REINFORCED AND UNREINFORCED ACRYLIC BONE CEMENT Browne, Martin, Sinnett-Jones, Polly E. and Sinclair, Ian. Bioengineering Sciences Research Group, University of Southampton, Southampton, SO17 1BJ, UK Telephone +44 2380 593279, Fax +44 2380 593016, [email protected] As the benefits of hip arthroplasty are extended to the younger patient population, the implanted construct will be subjected to ever increasing demands as patients seek to continue the active lifestyle to which they were accus-tomed. In particular, the implant fixation media, usually acrylic bone cement, and its interfaces, will be expected to cope with increased loading for longer lifetimes. The development of carbon nanotube (CNT) reinforced bone ce-ment has shown some promise, with an order of magnitude improved fatigue lifetime as well as reduced exotherm during cure (Sinnett-Jones et al 2007). The present study has focussed on assessing the mechanical performance of this material using acoustic emission (AE). AE monitoring allows distinct failure ‘patterns’ or ‘signatures’ to be established in real time (Browne et al. 2005). AE parameter based analysis is an established method for characterising failure modes in composite materi-als (e.g. Bar et al. 2005) and a similar approach was adopted in the present study. Samples of (i) CMW1 acrylic bone cement and (ii) Polymethylmethacrylate (PMMA) reinforced with 2wt% CNTs, were subjected to tensile fatigue testing. In situ AE monitoring was employed to identify the location and evolution of damage along the gauge length of the sample. Scanning electron microscopy and micro-focus com-puted tomography were employed to verify the AE findings. AE was able to identify distinct differences in failure mechanisms between samples, most notably the spread of damage across the gauge length with time was greater for the CNT reinforced PMMA. For CMW-1 the presence of internal defects and pores dominated the failure process; acoustic activity was prevalent in these regions, although not necessarily in all regions with defects. Damage accumulation and subsequent failure tended to focus at a single point along the gauge length. For the CNT reinforced PMMA, evidence of crack bridging was observed in the form of long fibrous projections of CNT from the cement surface, together with fibre pullout and fibre fracture, the latter particularly implying reasonable levels of load transfer to the CNTs. In terms of the micromechanics of failure, the presence of nanotubes resulted in a greater apparent incidence of damage initiation (more active sites) with a more diffuse damage accumulation process with increased potential for crack coalescence. Improved fatigue behaviour in the CNT-containing material may then be seen as consistent with cracks being formed but growing relatively slowly (or indeed arresting) via mechanisms such as crack bridging.

References Sinnett-Jones, P. et al., (2007) "Carbon nanotube reinforcement of bone cement." Engineers and Surgeons: Joined at the Hip. 19th–21st April. Westminster, London Browne, M., et al., (2005). "The acoustic emission technique in orthopaedics - a review." Journal of Strain Analy-sis for Engineering Design, 40(1): 59-79. Bar, H. N., et al., (2005). "Parametric analysis of acoustic emission signals for evaluating damage in composites using a PVDF film sensor." Journal of Nondestructive Evaluation, 24(4): 121-34.

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MID-TERM RESULTS OF A NOVEL LATERAL FLARE NON-CEMENTED HIP STEM. A CLINICAL, RADIOGRAPHIC AND DENSITOMETRY STUDY AUTHORS: Alejandro Leali, MD (*) Joseph F. Fetto, MD (**) AFFILIATION: (*) Hospital for Special Surgery, Department of Orthopedic Surgery, New York, NY (**) New York University/ Hospital for Joint Diseases, Department of Orthopedic Surgery 530 1st Ave. #5B, New York, NY 10016 Phone: 212-263-7296 E-Mail: [email protected] Background: Over the past decade, several design modifications have been introduced for uncemented femoral stems intended to increase initial stability by virtue of a tighter “press fit”. These designs may be classified into two general catego-ries: anatomic and straight. The purpose of this paper is to report the clinical, radiographic and periprosthetic den-sitometry results of a novel cementless stem design that incorporates a proximal lateral extension (“lateral flare”) ensuring a high metaphyseal fit. Methods: Fifty-eight consecutive patients who received a non-cemented, proximally porous coated ‘lateral flare’ hip stem were followed for an average of 4.3 years (range 36-70 months). Patients were clinically and radiographically fol-lowed at 3 weeks, 3 months, 6 months, 1 year and yearly thereafter. In addition, a subset of 18 consecutive patients (20 hips) was studied with dual X-Ray Absorptiometry Scans (DEXA) at the same intervals during the first year and at 24 months after surgery. Results: The average pre-operative Harris Hip Score was 47 (range 36-58). This increased to an average of 97 (range 87-100) at the latest follow-up. There were no cases of aseptic or septic loosening. Two patients were excluded from further subsidence evaluation after each sustained a periprosthetic fracture due to a significant trauma that occurred at 26 and 48 months after the index operation respectively. The average subsidence of all patients at the 3 year fol-low-up was 0.51 mm (SD 0.31 mm). Radiographically, there were signs of osseointegration in all cases with densi-fication of the cancellous bone underneath the lateral flare of the hip stem in Gruen Zones 1 and 2, as well as medi-ally in Zones 6 and 7. The periprosthetic bone densitometry data showed more than 95% of bone stock preserva-tion proximally 24 months after surgery with greater gains underneath the lateral flare of the stem, confirming the radiographic and clinical observations. Discussion: The extended lateral proximal geometry of this stem design appears to afford both initial and long term component stability as reflected by the low subsidence values over time. The maintenance of periprosthetic bone stock over time and the absence of stress shielding can be explained by the predominantly proximal loading pattern intended by this stem.

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STEM FIT AND THIGH PAIN IN UNCEMENTED TOTAL HIP REPLACEMENT Author: Amar Ranawat, M.D. 130 East 77th Street, New York, NY 10021 Phone: 212-434-4700 E-Mail: [email protected] Introduction: Thigh pain has is a common occurrence after uncemented THR. Stem design is a known factor in causation of thigh pain after THR. The aim of his study was to find any correlation between stem sizes and fit in the diaphysis and thigh pain. Methods: Radiographs of 400 patients, who had uncemented THR with accolade stem, were reviewed. Radiographic data was divided into those with stem size less than and more than 3. AP radiographs were analyzed for stem fitting in Gruen zones 5 and 6. All patients were specifically asked for symptoms of thigh pain. Results: Out of 400 patients, only 12 had significant thigh pain. All these patients had stem size 4 and above. All of these patients had osteointegerated stems. There was no thigh pain in patients with stem size 3 and below. Pain resolved in 8 patients and none of the 12 needed a revision. Radiological analysis showed that all the patients with thigh pain had a tighter stem fit in Zone 5 compared to Zone 6, implying a more diaphyseal than metaphyseal fit. Pa-tients with no thigh pain had a proximal metaphyseal fit. Patients with thigh pain had a higher cortical index than the rest of the group. Conclusion: This study shows that thigh pain is more common in patients who achieve a diaphyseal fit with a tapered stem. It is not seen in patients with more proximal fit. The study calls for a change in design of tapered design so that diaphy-seal fit doesn’t occur before the metaphyseal fill.

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ROTATIONAL STABILITY BASED ON DISPLACEMENTS OBTAINED BY THREE- DIMENSIONAL FINITE ELEMENT ANALYSIS WHEN TORSION LOADING IS APPLIED TO HIP PROSTHESES Sakai Rina, Sato K, Sato Y, Itoman M, and Mabuchi K (Address: 1-15-1 Kitasato, Sagamihara City, Kanagawa 228-8555, Japan) (Phone & Fax: +81-42-778-9647, E-mail: [email protected]) INTRODUCTION: The rotational stability of cementless hip prostheses corresponds to their design of fixation parts. The appropriate design of a femoral stem is important for secure primary fixation. The relative displacement of the bone and stems in the rotational direc-tion should be used for the evaluation of the initial fixability and stability of stems. This paper addresses the issue of the fixation method of hip stems and their rotational stability. MATERIAL AND METHODS: Specimens comprised four kinds of hip prostheses. Different kinds of finite element models of the four femoral stems were constructed for computer simulation. Common conditions of analyses were: (i) a torsion load of 18.9 Nm was applied to the proximal femur as the intra-rotation; (ii) a stepping load of 1800 N was applied to the proximal tip of the stem; and (iii) rigid contact existed between the distal end of the model femur and the rigid base. Rotational displacement that reproduced a torsion moment was analyzed. The rotational displacement of the stem with respect to the bone tissue on the proximal part was deter-mined in each axial direction by three-dimensional finite element analysis. RESULTS: It was found that the relative rotational displacement obtained by finite element analysis was 0.21 mm for the Intra-Medullary Cruciate stem, 0.10 mm for the VerSys stem, 0.67 mm for the PerFix SV stem, and 0.33 mm for the Duetto SI stem. All stems were markedly displaced in the proximal region. The displacement of the distal end was found to be larger in the PerFix SV stem than in the remaining stems. DISCUSSION AND CONCLUSIONS: The largest rotational displacement by analysis was observed in the PerFix SV stem. The characteristic fixation device of this stem is a flange, which was designed for the prevention of sinking. It was found that this fixation device could not prevent stem rotation. The smallest relative displacement in the rotational direction was observed in the Duetto SI stem. The designing prin-ciple of this stem is that the proximolateral projection fits the medullary space in Japanese patients. It was suggested that the displacement of the Duetto SI stem in the rotational direction was reduced by the projection in the medullary space because the shape of this stem is not a general cylinder but flat. After the Duetto SI stem, the VerSys stem showed the second smallest dis-placement in a rotational direction on both analysis and measurement. In this stem, the fin structure for fixation is designed to enhance rotational stability by wedging the fins into the bone. The characteristic fixation parts will resist displacement in a rota-tional direction. The Intra-Medullary Cruciate stem showed the third smallest relative displacement in a rotational direction after the VerSys stem on both analysis and measurement. In this stem, it was considered that the pin-locking structure could mechanically fix the bone and stem, and prevent displacement. Judging from rotational displacement obtained by two ap-proaches, three types of stem (Intra-Medullary Cruciate stem, VerSys stem, Duetto SI stem) provided rotational stability.

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EXCELLENT LONG-TERM SURVIVAL (15-20 YEARS) OF UNCEMENTED GRITBLASTED STRAIGHT TAPERED TITANIUM STEMS IN YOUNG AND ACTIVE PATIENTS (< 55 years) Peter R. Aldinger, Alexander W. Jung, Marc Thomsen, Volker Ewerbeck, Dominik Parsch

Stiftung Orthopädische Universitätsklinik, Heidelberg, Germany

Priv. Doz. Dr. med. Peter R. Aldinger Stiftung Orthopädische Universitätsklinik Heidelberg Schlierbacher Landstrasse 200a 69118 Heidelberg, Germany Tel: +49-6221-965 Fax: +49-6221-969270 [email protected] Background:

There are only few documented and published series of long term results (> 15 years) for uncemented hip arthro-plasty components. However these implants are frequently used in young and active patients.

Methods:

We evaluated the clinical and radiographic results of the first consecutive 154 implantations of an uncemented, grit blasted, double tapered straight femoral stem (CementLess Spotorno (CLS), Zimmer, Warsaw, IN) in 141 patients under the age of 55 (mean 47, range 13 - 55) years with a mean follow-up of 17 (range 15 - 20) years.

Results:

During follow-up 20 patients (20 hips, 13 %) had died and 7 (7 hips, 5 %) were lost to follow-up. 12 patients (12 hips, 8 %) underwent femoral revision - One for infection, 5 for periprosthetic fracture and 6 for aseptic loosening of the stem. Overall survival of the stem was 92 % at 17 years (95 %-confidence limits, 87 - 97 %), survival with femoral revision for aseptic loosening as an end point was 95 % (91 - 99 %). Aseptic loosening only occurred after an intraoperative fracture or if the femoral component was undersized at the time of surgery (canal fill index, CFI < 80 %). The survival of the acetabular components was inacceptably low with 38 % (95 %-confidence limits, 26 - 50 %) survival at 17 years for Mecron threaded cups and 68 % (95 %-confidence limits, 54 - 82 %) for Weill threaded cups. The median Harris-Hip-Score at follow-up was 83 points (range 28 - 100) and highly dependent on the Charnley class. No case of thigh pain was found. Osteolysis smaller than 1 cm was found in the proximal Gruen zones (1 and 7) in 5 % of the cases (7 hips). Osteolysis and radiolucent lines in regions 2 to 6 on anteriopos-terior (AP) radiographs were not seen.

Conclusions:

The long-term results with this type of femoral component are excellent even in the second decade and compare favorably with cemented stems in this young and active age group. Aseptic loosening did only occur in the pres-ence of an undersized femoral implant. There was no case of aseptic loosening in the group of correctly sized femoral implants. However the high rate of cup loosening are concerning in this subgroup of young patients.


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IN VIVO CORRELATION OF SOUND AND SEPARATION FOR DIFFERENT BEARING SURFACES Glaser Diana, a, Cates Hb, Komistek RD a, Mahfouz MRa, Dennis Dc a University of Tennessee, Knoxville, TN, USA b Tennessee Orthopaedics Clinic, Knoxville, USA c Colorado Joint Replacement, Denver, CO, USA Diana Glaser, 301 Perkins Hall, University of Tennessee, Knoxville, TN 37917 Email: [email protected], Phone: 865-974-1936, Fax: 865-946-1787 Audible squeaking of hip replacements is a commonly observed phenomenon reported as far back as 1950. Squeaking is often associated with hard-on-hard bearing surfaces though some noise of polyethylene bearings has also been previously reported. The causes and the conditions of audible hips are not truly understood yet and no known studies have been able to correctly analyse the measured audible effects. Therefore, a need for objective research on hip replacements regarding noise sources has become essential. The current study objective was to correlate 3D hip kinematics and subsequent audible effects using a sensor device for subjects having a THA under in vivo conditions and to evaluate if separation might be a reason for undesired sound. Post-operative gait kinematics and related sound of twenty subjects were analyzed under in vivo, weight-bearing conditions using video fluoroscopy and sound measurement while performing gait on a treadmill. The subjects included in the study had metal-on-metal, metal-on-polyethylene, ceramic-on-ceramic, ceramic-on-polyethylene or metal-on-metal polyethylene-sandwich THA. The surgical procedure was performed by the same, fellowship-trained surgeon. All patients with excellent clinical results, without pain or functional deficits were invited to par-ticipate in the study (HHS > 90). The sound senor was externally attached to the pelvic and femoral bony promi-nences and detected frequencies that were propagated through the hip interaction. A data acquisition system was used to amplify the signal and filter out noise generated by undesired frequencies. The signal was converted to sound and then correlated with the fluoroscopic images that were converted to three-dimensions using a model fitting software package. In vivo translational and rotational kinematics were used to determine the distance be-tween the femoral head and the acetabular component and diagnose if separation had occurred. Subjects with metal-on-polyethylene and ceramic-on-polyethylene THA experienced femoral head sliding (separation) within the acetabular component. A “clicking” sound was detected when the femoral head impacted the polyethylene liner. Subjects with metal-on-metal or ceramic-on-ceramic THA also experienced femoral head sliding, but very different sounds were generated. Ceramic-on-ceramic THA subjects experienced a “squeaking” sound that varied in magnitude, while subjects having a metal-on-metal THA exhibited a sound similar to a “rusty door hinge”. Squeaking and screeching sounds are possibly an outcome of a forced vibration which is induced by a driving force and results in dynamic response. The driving force can be associated with the impact following hip separation and the dynamic response may lie for some implants in the range of audible frequencies of the human ear. This study correlated three-dimensional THA kinematic data with sound under in vivo weight-bearing conditions. Variable audible signals were detected for the different bearing surfaces, leading to the assumption that the type of material could affect the attenuation of frequencies. Also, implant design and the pattern of sliding of the femoral head within the acetabular cup could lead to frequency and sound variations. Sound and frequency identification under in vivo conditions for THA generates new possibilities for better understanding of wear and failure modes in THA.

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EFFECT OF BEARING DIAMETER AND RADIAL CLEARANCE ON WEAR OF CERAMIC-ON-METAL TOTAL HIP REPLACEMENTS Haider, Hani; Weisenburger, Joel N; Naylor, Malcolm G*; Schroeder, David W*; Croson, Richard E, and Garvin, Kevin L Department of Orthopaedic Surgery and Rehabilitation, University of Nebraska Medical Center, 985360 Nebraska Medical Center - Scott Technology Center, Omaha, NE 68198-5360, USA Phone : (402) 559 5607, Fax : (402) 559 2575, E-mail : [email protected] * Biomet Inc., Warsaw IN, USA. To eliminate UHMWPE debris, hard-on-hard bearing surfaces are regaining favour. Besides metal-on-metal and ceramic-on-ceramic combinations, the most novel are ceramic-on-metal hips, which combine the high hardness of bulk ceramic heads with the toughness of metallic shells. This combination is intended to eliminate the risk of fracture for a thin brittle ceramic shell, provide reduced metal-ion release compared with a totally metal-on-metal system, and target lower adhesive-wear from articu-lation of identical materials. However, the differential hardness and bulk properties of ceramic-on-metal may be associated with a different sensitivity to the radial clearance between head and liner. This study investigates the wear rates of two sizes of ce-ramic-on-metal THRs, with two different radial clearances. Twelve THRs comprising transformation toughened, platelet reinforced alumina femoral heads (Biolox-Delta, CeramTec, Germany) and CoCr acetabulum shells were simultaneously tested on a hip simulator (AMTI, Boston). Six 28mm and six 36mm diameter THRs were tested. Three from each group had a higher clearance (HC) of 81.7±3.7µm, and three had a lower clearance (LC) of 29.5±4.3µm. The specimens were mounted anatomically and were lubricated with bovine serum diluted with deionized water to have 20g/l protein concentration. The lubricant was continually circulated and kept at 37°C. The THR specimens were subjected to the loading and rotations of the walking cycle as specified in ISO-14242-1 at 1Hz for 5 million cycles (Mc), without distraction. The loading and rotations were continually observed to ensure consistency with the desired waveforms. The femoral heads and acetabular liners were carefully cleansed, gravimetrically weighed and the lubricant was changed at 0, 0.25, 0.5, and every 0.5Mc afterwards. The weight change of the HC and LC 36mm liners was <1.0mg at 5Mc (0.051±0.072mg/MC, 0.061±0.044mg/MC, respec-tively), and most actually gained weight. All three 28mm HC liners exhibited “break-away” wear in that they relatively quickly lost several milligrams (5.99mg, 6.37mg, 8.50mg) after showing nearly no measurable wear. One 28mm LC liner also showed break-away wear (10.22mg). All alumina femoral heads gained net weight by 5Mc. Our simulator results confirmed extremely small wear overall for ceramic-on-metal THRs. As in one other study, we did find “run-in” wear on all combinations and we conclude that ceramic-on-metal is not free of this phenomenon. The low-clearance and large diameter showed the lowest wearing combination. Small clearance and large diameters increase the contact area between bearing surfaces, reduce contact stress and increase the lubricant film thickness, resulting in lower wear. Al-though doubling or tripling the clearance had no measurable effect on the very modest wear for the larger hip size, it increased the presence of break-away wear in the smaller size, which is worthy of note. It is likely that the observed weight gain of all alumina femoral heads was due to material transfer from the softer CoCr acetabular liners. This was evidenced by dark regions/stripes on the femoral heads that could not be removed in the cleaning process.

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VIRTUAL HIP SIMULATOR: NEW METHOD FOR IMPLEMENTING IN VIVO KINEMATICS DURING THE DESIGN OF THA COMPONENTS Mueller John Kyle P., Leszko Filip, Komistek Richard D., Mahfouz Mohamed R. Correspondence: Richard D. Komistek 301 Perkins Hall University of Tennessee Knoxville, TN 37996 Email: [email protected] Presenting author: Phone: (262) 352 5208, Fax: (865) 671-2157, [email protected] One of the crucial steps in designing a new total hip arthroplasty (THA) system is predicting its future range of motion. The spatial motion of the human hip joint is complicated and depends on the activity performed. A simple in-plane rotation test (most often maximum flexion/extension or abduction/adduction) used during the designing process may mislead the engineer and direct him to optimize the future implant for non-physiologic range of mo-tion. Therefore, the objective of this study was to develop a virtual hip simulator as a design tool that could imple-ment in vivo kinematics of daily activities obtained from fluoroscopy to any hypothetical THA design and predict its performance. To enable comparison and analyses of artificial and normal hip joint a consistent coordinate system was proposed and implemented with CAD software. Any THA design may be loaded into the simulator. The femur and pelvis (resected according to the surgical procedure used) models may be included in the analysis to enable the implant-bone and bone-bone impingement detection. The in-vivo kinematics data were obtained from fluoroscopy based on previously reported methods [1,2,3] and imported into the simulator. The software then uses these data to mimic the motion of the normal hip joint using the THA components. The global minimum distance between relevant components is measured, and hence the impingement risks (both implant and bony), as well as the error of implant orientation allowed in the surgical procedure are monitored throughout the range of motion. User defined motion may be imported if desired. The simulator was tested on one existing THA design (VerSys, Zimmer Inc.), one non-existent, hypothetical de-sign and normal hip anatomy obtained from computed tomography. The highest impingement risk for VerSys THA was 72.7% and 72.3% during gait and step up, respectively. The smallest anteversion error allowed in placing the acetabular cup, before impingement would occur during gait and step up, was 49.8° and 30.8°, respectively. The higher risk was generally observed for stem-cup impingement rather than femur-pelvis, but it may conceivably be different for other THA designs. The range of motion test using the 3D, in-vivo kinematics data provides the engineer with much more comprehen-sive information of the implant performance and its vulnerable areas. More activities, including those which pose a high risk of THA failure, will be implemented in this virtual hip simulator. Using in vivo kinematics of day to day activities to predict the risk of impingement and the acceptable error when surgically placing a newly designed component, as is acoomplished in this study, is valuable when determining whether a design is viable. [1] Dennis DA, et al.: Clin Orthop, 1996. [2] Dennis DA, et al.: Clin Orthop Rel Res, 1998 [3] Hoff W, et al.: Clin Biomech, 1998

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19- TO 21-YEAR CLINICAL RESULTS OF TOTAL HIP PROSTHESES WITH CERAMIC HEAD COMBINED WITH UHMWPE SOCKET Oonishi Hiroyuki*, Kim Sok Chol*, Kyomoto Masayuki**, Iwamoto Mikio**, Masuda Shingo**, Ueno Masaru**, Oonishi Hironobu* * H. Oonishi Memorial Joint Replacement Institute, Tominaga Hospital, 4-48, 1-chome, Minato-machi, Naniwa-ku ,Osaka, 556-0017 Japan Phone: 81-6-6568-1601 Fax: 81-6-6568-1608 E-mail: [email protected] ** Japan Medical Materials Corporation, Osaka, Japan INTRODUCTION: Cemented total hip arthroplasty has been one of the most successful orthopedic procedures since Charnley. The commonly used bearing couple of total hip prostheses (THPs) consists of a metal head with an ultrahigh-molecular-weight polyethylene (UHMWPE) socket. We have been using alumina ceramic heads to reduce polyethylene wear debris, as well as a modified ce-menting technique named the “Interface Bioactive Bone Cement (IBBC)” method to improve the fixation of implants [1,2]. In this study, we studied the long-term clinical results of THPs with an alumina ceramic head using the IBBC method. MATERIALS AND METHODS: THPs (Type 6; Kyocera Corp., Kyoto, Japan) consisting of an alumina ceramic head (28mm in diameter) with an UHMWPE socket were used. Hydroxy apatite (HA) granules (Boneceram-P; Sumitomo-Osaka Cement Co. LTD., Chiba, Japan) for the IBBC method were manufactured by sintering at 1150 C. HA granules of 0.3 - 0.5 mm diameter were smeared on the bone sur-face just before cement fixation of the implant. 285 joints (212 patients) were implanted by one senior surgeon from January 1986 to December 1988, and, 265 joints (192 patients) could be followed. Patient age at surgery was 29 to 81 years old (mean : 64), and the diagnoses were osteoarthrisis in 227 hips (168 patients), rheumatoid arthritis in 30 hips (19 patients), and necrosis of femoral head in 8 hips (5 patients). A radiolucent line, loosening, osteolysis, and wear of the UHMWPE socket were ob-served using radiographs. RESULTS: In IBBC, a radiolucent line appeared as a “space” between the HA layer and the cement, and loosening appeared as a “separation” between the HA layer and the cement. A space appeared in three joints (1.4%) on the acetabulum and in four joints (1.8%) on the femur, and a separation appeared in three joints (1.4%) on the acetabulum. Osteolyses were noted in one joint (0.5%) on the acetabulum and in two joints (0.9%) on the femur. There was no revision surgery. DISCUSSION: In our previous study, we reported that socket thickness affected clinical wear rate of the socket and the wear rate of sockets with an alumina ceramic head was 20 % lower than that of sockets with a metal head [3]. With reduction of wear debris by ceramic heads, osteolysis could be reduced. Fixation of THPs to bone has been maintained long-term by using IBBC. As a re-sult, the long-term clinical results of THP with alumina head using IBBC were excellent. REFERENCES 1. Oonishi H, Wakitani S, Murata N, et al. Clinical Orthopaedic and Related Research, 379 (2000), 77-84 2. Oonishi H, Kadoya Y, Iwaki H, et al. J of Arthroplasty, 16(200), 784-789 3. Oonishi H, Tsuji E and Kim YY, J Mat. Sci Mat in Med (1998) 393- 401

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A NOVEL WAY TO MEASURE FRICTION OF TOTAL HIP REPLACEMENT SYSTEMS DURING A WALKING CYCLE ON A MULTI-STATION HIP SIMULATOR Weisenburger, Joel N; Naylor, Malcolm G*; Schroeder, David W*; White, Bruce F**; Unsworth, Anthony***; Garvin, Kevin L; and Haider, Hani Department of Orthopaedic Surgery and Rehabilitation, University of Nebraska Medical Center, 985360 Nebraska Medical Center - Scott Technology Center, Omaha, NE 68198-5360, USA Phone : (402) 559 5607, Fax : (402) 559 2575, E-mail : [email protected] *Biomet Inc., Warsaw IN, USA. **AMTI Inc, Watertown MA, USA *** University of Durham, UK With the boom in metal-on-metal hip resurfacing and novel ceramic-on-metal total hip replacements (THRs) with extremely low wear, accurate tribological measurements become difficult. Characterizing THR friction can help in this, especially if the progress of such friction can be tracked during wear tests. Friction measurement can also be used as a tool to study the effects of acetabular-liner deformation during insertion, and possible femoral head “clamping”. Previously, friction-factors were estimated for THRs undergoing flexion motion in dedicated friction simulators or in pendulum systems. This study estimates THR friction during wear testing. A twelve-station hip simulator (AMTI, Boston) was used. The 6-degree-of-freedom (DOF) load-cell underneath each femoral-head was utilized to measure the frictional torque. Three separate friction-factors for the flexion/extension, abduction/adduction and internal/external rotations were computed using force and moment equilibria in three dimensions, transformed to account for the offset in load-cell position from the hip-center. The friction fac-tors were measured 200 times (@100Hz) over two 1Hz cycles of walking (ISO14242-1), at several intervals of 5-million-cycle (Mc) hip wear-tests. Metal-on-UHMWPE (MOP), metal-on-metal (MOM) and ceramic-on-metal (COM) hip combinations were tested. Six were standard 36mm MOP and six were MOP with coated CoCr heads. One 32mm MOM THR was tested, for 1.0Mc. Six specimens were 28mm COM, three with high radial-clearance (HC) and three with low (LC). Six were 36mm COM, in two clearance groups also. All were lubricated with di-luted bovine serum with 20g/l protein concentration at 37ºC. Both the coated and standard MOP THRs had friction-factors of 0.032 at the start (±0.004 as standard-deviation among the three samples), which dropped within 0.5-1.0Mc to a minimum of 0.028±0.005. The friction-factor of coated CoCr-MOP then increased to 0.041±0.009 @5Mc, while uncoated MOP increased only to the initial value (0.032±0.004). The 32mm MOM sample gave 0.052 friction-factor initially (±0.0004 sd. within five walking-cycles), which was the highest factor of all tested. It dropped to 0.024±0.0001 at 1.0Mc. COM THRs with LC showed higher friction than the HC of the same size (28mm LC 0.024±0.001, HC 0.019±0.002; 36mm LC 0.022±0.001, HC 0.018±0.0007, with all standard-deviations being among hip specimens). The results confirmed the well-established running-in effect where THRs start with a rapidly dropping wear-rate; here manifested as an initially decreasing friction factor. For MOP, the articulating surfaces became polished and wore to optimum conformity , before scratches reversed this trend. The coated MOP samples rose in friction due to wear of the coating which produced deeper and more numerous scratches than for standard MOP. All COM THRs had lower initial friction-factors than MOP or MOM. The MOM friction-factor dropped to the COM range by 1.0Mc. We speculate that reducing the clearance for COM THRs results in marginally higher friction-factor due to viscous losses from an increased lubricant film thickness, indicative of hydrodynamic rather than mixed lubrication. The friction factors found in this study were close to factors published in other studies. The method presented here however facilitates on-line sampling throughout the progress of a prolonged wear test.

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NOVEL CERAMIC-ON-METAL HIP REPLACEMENTS Williams, Sophie; Brockett, Claire L, Isaac, Graham H; Schepers, Anton; van der Jagt, Dick; Brekon, Anke; Hardaker, Cath; Fisher, John Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Leeds LS2 9JT, UK Tele +44 113 343 2214 Fax +44 113 242 4611 Email [email protected] Ceramic-on-metal (ceramic head and metal liner, COM) hip replacements have shown reduced wear in comparison to metal-on-metal (MOM) bearings (Firkins et al., 1999). Lower wear has been attributed to a reduction in corro-sive wear, smoother surfaces and improved lubrication, differential hardness and reduction in adhesive wear. The aim of this study was to further assess the performance of novel differential hardness COM THRs by; • A wear simulator study under standard conditions to compare MOM, COM and ceramic-on-ceramic (COC)

bearings and measurement of the Co, Cr and Mo ion release into the serum lubricant • “Edge loading” hip simulator testing to compare COM and MOC (metal head on ceramic liner) bearings • Clinical study, assessing cobalt and chromium ion blood levels for patients with COP (ceramic-on-

polyethylene), COC, COM and MOM THRs

Components used were made of zirconia-platelet toughened alumina (Biolox Delta) heads, high carbon (0.2wt%) CoCrMo alloy and GUR1020 polyethylene (DePuy International Ltd, UK). Hip simulator testing applied a twin-peak loading cycle and walking motions with the prosthesis in the anatomical position. The lubricant (25% calf-serum) was changed approximately every 0.33Mc, wear was measured gravimetrically. Standard condition hip simulator testing was carried out for 5 million cycles. Hip simulator testing with edge loading was conducted for 2 million cycles, a standard simulator cycle was adapted so the head sub-luxed in the swing phase forcing the head onto the edge of the cup at heel strike (Williams et al., 2006). In the clinical study, patients were selected to have either a COC, COM, COP or MOM 28mm-diameter bearing (supplied by DePuy International Ltd). Blood sam-ples were collected at regular follow-ups, frozen and analysed using high resolution Inductively Coupled Plasma Mass Spectrometry. The total overall mean wear rate of the MOM THR (1.01±0.38mm3/Mc) was significantly higher in comparison to the COM and COC (<0.015mm3/Mc). The ion levels measured for MOM serum lubricant were siginificantly greater than COM and COC. The total overall mean wear rate under edge loading conditions for the MOC bearings (0.71±0.30mm3/Mc) was significantly higher than the wear rate for the COM bearings (0.09±0.025mm3/Mc). The contact of the head against the rim of the cup at heel strike caused deep stripe wear on the metallic heads of the MOC bearings. In the clinical study, 31 hips had metal-ion measurement (with >6 months follow-up, average age of <50). Results, expressed as mean difference in metal ion levels from the pre-operative levels to the latest follow-up were 0.12, -0.14, 0.01, and 0.58ug/l for the COC, COP, COM, and MOM groups respectively for cobalt and similarly –0.16, -0.20, 0.11, and 0.48 ug/l for chromium. COM reduced wear compared to MOM. Reduced wear and ion levels from COM bearings will address some of the concerns associated with MOM THRs regarding reports of elevated ion levels clinically. This data is reflected in the clinical study, although numbers are relatively small and follow-up short, there is a trend towards lower metal ion levels with the COM than with the MOM bearing. These studies have provided valuable data demon-strating reduced wear and ion level release with COM bearings.

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AGING OF RETRIEVED ZIRCONIA FEMORAL HEADS Montero M

AGING OF RETRIEVED ZIRCONIA FEMORAL HEADS Montero M. Murcia A. Fernández -Fairén M. Avda. Rufo García Rendueles 6, 11D 33203 Gijón .Asturias. Spain Tel: +34630199143 Fax: +34985131743 E-mail: [email protected] This research was done in the Instituto de Cirugia Ortopédica y Traumatologia de Barcelona. Spain, and it was designed to study zhip replacement heads. Yttria-stabilized tetragonal zirconia may undergo extensive transformation to the monoclinic phase under and/or hydrothermal stress with degradation of mechanical and tribologic properties. The hypothesis of this study is progressive phase transformation of zirconia in service in vivo is directly correlated to the time of imand to patient-related factors. The subsequent decrease in fracture toughness and increase in surface roughness and wear is relatecreased monoclinic content. We carried out a study on 47 yttria-stabilized tetragonal zirconia femoral heads retrieved from failed total hip arthroplasties after 2 of implantation. Age, weight, and activity of the patients were retrieved from clinical records. Monoclinic content, fracture toughnroughness, and wear were measured. Our findings included: very high correlation was found between monoclinic content in the weight bearing surface and time of impla0.97), and between increase in monoclinic content and decrease in toughness (r = -0.92), increased surface roughness (r = 0.88), an0.89). No correlation was observed between the raise in monoclinic content and age, weight, or activity of the patients. Aging of

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WEAR, ION RELEASE AND MECHANICAL PROPERTIES OF DIAMOND-ON-DIAMOND TOTAL HIP BEARINGS Taylor, Jeffery K; Despres, A. Stan; Naylor, Malcolm G*; Schroeder, David W*; Loesener, German; Singh, Vaneet; Harding, David; Dixon, Richard; and Medford, Troy Dimicron Inc, 1186 South 1680 West, Orem, UT 84058 Phone (801) 221-4591, Fax (801) 426-4846, Email [email protected] * Biomet Inc., Warsaw IN, USA. Polycrystalline Diamond Compact (PDC) offers potential advantages over other hard-on-hard hip bearings, includ-ing low friction, ultimate hardness, reduced metal ion release compared to metal articulations, and increased strength/toughness compared to ceramic-on-ceramic articulations. This study investigates in-vitro wear rates, metal ion release and burst strength for a 28mm diamond-on-diamond system. Six sets of 28mm PDC femoral heads and 28/41mm PDC acetabular liners (Dimicron, Utah) were tested on a hip simulator (AMTI, Boston). Radial clearances were 18-42 microns. Two active load soak combinations were in-cluded to correct for material transfer from mating Ti6Al4V trunnions/shells. Specimens were mounted anatomi-cally and lubricated with bovine serum diluted to 17g/l protein concentration. Components were subjected to a 3kN walking cycle (ISO14242-1) for 5 million cycles (Mc), without distraction. The lubricant was changed and the components cleaned, dried and weighed at 0, 0.25, 0.5, and every 0.5Mc thereafter.

All heads and liners gained weight during the test. Potential mechanisms include protein adsorption and hydration of metallic phases. Contributions from free water absorption appear to be small. Weight changes were corrected by subtracting weight gains for the active load soak components. Corrected wear curves were bi-phasic, with a 2Mc run-in period followed by steady-state wear. Corrected overall wear rates were 0.23±0.05mm3/Mc (heads) and 0.00±0.03mm3/Mc (liners). Head wear rates were 0.63±0.12mm3/Mc (run-in) and 0.11±0.10mm3/Mc (steady-state). Following the test, samples were subjected to a more rigorous cleaning/drying procedure, giving final over-all wear rates of 0.32±0.17mm3/Mc (heads) and -0.15±0.12mm3/Mc (liners). Thus, diamond-on-diamond wear rates were comparable to steady-state values reported for metal-on-metal.

Serum samples were removed at daily intervals for the first 1Mc, digested and analyzed by Inductively Coupled Plasma. Cobalt and chromium concentrations were below the detection limit (0.050ppm). Metal-on-metal hip simulator tests have been reported to give 110-150ppm Co (run-in) and 15-38ppm Co (steady-state) at 0.5Mc drain intervals.

Ion release was also studied by 21-day elution tests in Hanks’ balanced salts acidified at pH of 6, simulating a post-operative hematoma condition. Maximum average cobalt elution rates were 0.62 ppm/day(pH6). An ASTM F75 CoCrMo control sample gave maximum cobalt elution rates of 0.04 ppm/day (pH7.4) and 0.51 ppm/day (pH6). Minimal essential media (MEM) cytotoxicity studies demonstrated no detectable toxic response to implant eluates. PDC and wrought CoCrMo heads were subjected to cyclic polarization electro corrosion testing in de-aerated Hanks’ solution at pH7.6 and pH4 (n=3). Heads were tested on Ti6Al4V trunnions to include galvanic corrosion/crevice corrosion effects. PDC samples showed no evidence of localized corrosion, although one of the CoCrMo controls showed a temporary breakdown with light pitting. Burst tests were performed on PDC heads and liners. 28mm standard neck-length heads gave a mean strength of 55.1±8.0kN (minimum 41.8kN) when tested on 4o taper Ti6Al4V trunnions (n=6). Liners were tested in 52/41mm Ti6Al4V shells using CoCr heads. Tests were terminated at 200kN without fracture. This preliminary evaluation of a 28mm diamond-on-diamond hip system showed similar wear rates to metal-on-metal but with greatly reduced metal ion release, and increased strength/toughness compared to ceramic-on-ceramic articulations. Further testing continues including micro-separation wear testing and biocompatibility studies.

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THE EMERGENCE OF A NEW TYPE OF CERAMICS IN TOTAL HIP ARTHROPLASTY; THE ALUMINA MATRIX COMPOSITE (AMc) - 6 YEARS FOLLOW-UP Bernard Masson, Scientific Consultant MSc.Ph. 6 Rue Eric Tabarly, Toulouse, France 31320 Phone: 00336 87 60 99 47 Fax: 00335 34 66 45 48 Demand for ceramic bearings is increasing rapidly because of excellent clinical results. Alumina offers advantages such as chemical resistance, excellent bioinertness and tribology. However, alumina has limited strength, therefore the applications are restricted to certain designs. Zirconia materials have been used clinically but reveal problems due to poor hydrothermal stability. Thus, there is a strong need for new bearing material that combines strength and stability. The ceramic named Alumina Matrix Composite (AMC) uses the following principle of transformation toughening: Firstly, the dispersing of small particles of Y-TZP Zirconia in the alumina matrix and secondly the reinforcement by introduction of an anisotropic crystal-like whiskers. This process dissipates the crack energy that is associated with an increase of strength. The examination of the tribological situation of AMC, especially under challenging conditions of hydrothermal ageing and under severe micro separation, shows the aptitude of this material in wear applications. Alumina Matrix Composite offers a better mechanical resistance than alumina while maintaining the structural stability and equivalent tribological qualities. This ceramic composite will enable new application possibilities to be offered in orthopaedics. This is a material that has been very thoroughly evaluated and tested as a permanent implant material for the last 9 years. The results of this evaluation and testing process have been included in the manufacturer’s Master File at the Food and Drug Administration and approved. Its first clinical use in the United States was in June of 2001. Since its introduction, the Alumina Matrix Composite has been implanted in more than 65,000 patients around the world.

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THE INFLUENCE OF ACETABULAR SHELL RIM SUPPORT ON THE POLYETHYLENE LINER RIM STRESS PATTERN *Dong, Nick G.; * Schmidt, W.; Kester, M.A.; Wang, A.; **Nogler, M.M.;** Krismer, M.

*Stryker Orthopaedics, 325 Corporate Drive, Mahwah, NJ 07430 USA

** Department of Orthopaedics, University of Innsbruck, Austria

E-Mail: [email protected] Introduction:

High tensile stress in the acetabular cup liner rim has been considered as a contributing factor of the UHMWPE liner failure. It has been reported that increased tensile stress in polyethylene liner rim are present in vertically placed acetabular cups. To date however, there has been no data of the stress in the liner when it is assembled in different shells. The objective of this study was to investigate the effect of back side metal support on the stress level at the rim of polyethylene liner in vertical loading angle.

Material and method:

Twelve 3-D CAD model assemblies consisted of: A) CoCr femoral heads in 22, 28, 32, 36, 40 and 44mm diame-ters. B) Corresponding 22, 28, 32, 36, 40 and 44mm ID with generic 45.7mm OD N2VAC UHMWPE acetabular liners and C) Generic Ti-6Al-4V 52mm OD / 45.7mm ID hemispherical acetabular shell with and without 2mm high integrated rim. One-half of the assembly models were imported from Pro/Engineer Wildfire v2.0 to ANSYS Workbench v10.0. in symmetry boundary condition. The material properties were determined experimentally for UHMWPE and obtained from published data for CoCr and Ti alloy.

Each component was meshed with 10-noded, tetrahedral elements (type SOLID92). The finite element mesh of the UHMWPE liner and acetabular shell was refined in the vicinity of the edge load application.

Bonded contact (surface contact element type CONTA174 and target contact element type TARGE170) were as-sumed at the acetabular liner to shell interface, while frictionless sliding contact was considered at the femoral head to acetabular liner interface.

The backside of the acetabular shell was constrained in all translational degrees of freedom. A load of 2,450N was applied through the femoral head center to the edge of the UHMWPE insert to simulate the rim loading condition for vertically placed acetabular cup without head subluxation. Maximum principal stresses at the UHMWPE liner rim of the articulating surface were evaluated with and without the supporting rim for different femoral head sizes and liner thicknesses.

Results:

The maximum principal stresses at rim of UHMWPE liners were tensile stress patterns for rim unsupported condi-tions when poly thickness was below 9mm. Stress patterns were compressive in all rim supported conditions and the rim unsupported conditions with poly thickness above 9mm. All stress levels were below the yield strength of UHMWPE (19MPa) in this model.

Conclusion:

The rim back support changed the stress pattern to compressive, a preferred stress pattern to avoid fracture, for all poly thicknesses. In the no rim support condition, the stress pattern was tensile when poly thickness was under 9mm and increased quickly if poly thickness is below 5mm. For both scenarios, the stress levels increased quickly when poly thickness is below 2.8 mm. The actual stress level in the poly could be much higher considering the locking mechanism detail but should follow the same trend discovered in this study. These stress pattern trends could become of increasing concern with the shrinking unsupported poly thicknesses associated with the use of larger femoral heads.

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DEFORMATION OF METAL-BACKED ACETABULAR COMPONENTS AND THE IMPACT OF LINER THICKNESS IN A CADAVERIC MODEL Markel, David; Day, Judd; Siskey, Ryan; Kurtz, Steven; Ong, Kevin; Liepins, Imants 22250 Providence Drive, Suite 401 Southfield, MI. 48075 Tel: 248-569-0306 [email protected] Introduction: Acetabular component deformation during press-fit implantation has been reported. This study compared deforma-tion of cups with standard and thin polyethylene inserts during impaction and subsequent loading. Methods:

Six young pelvii were implanted with Trident PSL cups (Stryker). In each pelvis, a thin (3.8-5.4 mm) polyethylene insert was randomly implanted on one side. On the contralateral side (paired control), a standard thickness liner (7.9-11.4 mm) was implanted. The thickness difference was 4.1-6.1 mm. The cups were tested under maximum static load of 2.2 kN followed by 10 cyclic loads between 0.1 and 1.2 kN. Shell and liner diameters were measured pre and post implantation and after mechanical testing. Differences between the measured and nominal diameters (“pinch”) were determined.

Results: All shells experienced pinching deformation on implantation. Deformation decreased significantly following liner insertion and loading. No significant differences were noted in liner and shell deformations between thin and thick liner groups. Step-wise linear regression indicated that initial shell deformation and donor BMD were significant predictors of liner deformation. Discussion: The reduction in shell deformation after liner insertion and loading may be due to a settling-in effect, visco-elastic bone creep, and/or plastic bone deformation under loading. Although liner deformation was somewhat affected by thickness, differences in patient BMD and surgical preparation may be more important factors for pinching in both standard and thin liners.

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MONITORING DEGRADATION OF THE IMPLANTED HIP CONSTRUCT INTEGRITY USING ACOUSTIC EMISSION Mavrogordato Mark N. Taylor Andrew, Taylor Mark, Browne Martin. Bioengineering Sciences Research Group, School of Engineering Science, University of Southampton, Highfield, Southampton, SO17 1BJ, UK Tel: ++44 (0)2380 597665 Fax: ++ 44 (0)2380 593016 E-mail: [email protected] One of the limiting factors affecting the longevity of cemented hip replacement is the failure/fracture of the cement mantle. Pre-clinical testing methods of cemented hip prostheses aim to identify prospective failure mechanisms and hence influence prosthetic design such that the incidence of revision surgery may be reduced. Unfortunately, it is still difficult to identify early signs of failure during testing without interruption, or even destruction of the test specimen. There is therefore a demand for a cost effective, simple, non-destructive system to identify early signs of failure during pre-clinical testing. The Acoustic Emission (AE) technique has the potential to detect the earliest stages of damage initiation and pre-dict and locate propagation and eventual failure within the bone cement. It can also distinguish between different types of failure mechanism such as cement cracking or interfacial de-bonding. AE is well suited to such investiga-tions as it is passive, and provides results in real time, allowing the test to be stopped before failure if necessary. An experimental study has been conducted that correlates the onset and location of AE activity with observations of crack formation using a micro-computed tomography (CT) scanner. Simplified stem constructs consisting of a square section, tapered, stainless steel 316L femoral stem mounted in a cylindrical tufnol tube to simulate bone, and Technovit® to represent bone cement were CT-scanned prior to testing and then subjected to a Felicity loading regime (Duesing 1989). CT scans were taken of the construct before testing, and then monitored continuously us-ing the AE technique during the loading regime. Three AE sensors mounted directly onto the Technovit® surface were used to detect and analyse the acoustic activity in real time. The onset of permanent damage was identifiable from the detection of events below the stress limit of the previous load cycle. The constructs were then re-scanned to visually assess the extent of damage accumulation. Using the CT scans, located acoustic events were related to structural changes within the construct. Acoustic activ-ity indicative of failure was detected prior to any observed changes in the CT image. Crack formation within the cement layer was shown to correlate well with bursts of acoustic activity. The results have demonstrated that the AE technique can be used to detect, locate, and anticipate failure of the bone cement layer. The technique provides a powerful tool to further understand the behaviour of cemented hip arthroplasty. References: Duesing, L. (1989). Acoustic Emission Testing of Composite Materials. Annual Reliability and Maintainability Symposium, IEEE.

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Introduction: Increased crosslinking and processing of polyethylene (XPE) is reputed to produce the lowest wear. In total hip replacements (THR) this has been paralleled by a trend to larger femoral-head diameters. In contrast the Charnley paradigm has always been to use the smallest diameter THR. However, from recent data it is known that that crosslinking from 30 to 75kGy on average will produce 70-75% wear decrease. Thus there is a trade off with the increased diameters contributing more wear but can be offset by additional crosslinking to minimize wear. The objective of our study was to evaluate the wear performance of highly-crosslinked polyethylene (HXPE) in con-temporary large diameters. Methods: The historical control (32mm XPE: 30kGy) and 44mm liners (HXPE: 75kGy) were immersed 11 weeks to assess fluid absorption. The hip simulator used a standard physiological walking (0.2-3.0kN load). The liners were mounted anatomically (inclined 50°). The lubricant was alpha-calf serum (diluted to 20mg/ml protein). During wear study, 12 ‘soak-control’ liners were loaded synchronously (‘load’) and six liners were immersed in a water bath (‘free’). Wear measurements were carried out to million cycles (3Mc) duration and wear assessed by gravim-etric technique. Each 24-hours, we collected serum samples and stored them frozen (-25°C).

Result: In the pre-wear study, all free-soak liners showed uniform weight gains (1.56mg and 0.83mg for 32 and 44mm diameter liners, respectively). During the wear study, the fluid-absorption gain for 44mm free-soak liners averaged 1.31mg. With load-soak liners, gains averaged 0.43 and 2.22mg for 32 and 44mm diameters, respectively. Overall, the 44mm weight gain was approximately 5-fold higher than the 32mm liners.

The 32mm wear-liners demonstrated weight-loss range 300-425mg with mean 352mg. The 44mm wear-liners demonstrated range 42.4-72.7 mg with mean 59.6mg. Thus the gross weight loss for 32mm liners averaged 5.9-fold greater than 44mm liners. Note the linear regression coefficients (r) were greater than 0.994 and the experi-mental variance was better than ± 10%. Converting to net volumetric wear, 32mm liners demonstrated wear-rate of 119.6mm3/Mc that contrasted with the 19.5mm3/Mc with 44mm liners. The 6-fold wear reduction was in favor of the 44mm liners. Discussion and Conclusions: From simulator wear literature, it is known that increased crosslinking from 30 to 75 kGy resulted in a 70-75% wear decrease (considering same ball diameter: Williams et al, 2007). However each 1mm increase in ball diame-ter was reputed to add 10% more wear debris (Clarke et al, 1996). In our study with 32mm and 44mm diameters this could have more than doubled the wear volume (12mm x 10% = 120% added debris). However the 44mm diameter HXPE liners exhibited a 6-fold reduction in volumetric wear compared to our 32mm XPE controls. This wear trending appeared very stable (regression coefficients r > 0.99 and variance within +10%) and appeared as a significant finding, even at 3Mc duration. Therefore under laboratory conditions, the superior crosslinking and processing of the 44mm HXPE liners adequately compensated for THR ball diameter increased from 32mm to 44mm.

SIMULATOR WEAR OF POLYETHYLENE USING LARGE DIAMETER XLPE HIP CUPS Sorimachi T.1, Gustafson A.2, Clarke IC.1, Williams PA.1, Yamamoto K.3 1. Loma Linda University Medical Center, Department of Orthopaedics, CA, USA 2. GUSTAFSON ORTHOPEDIC CORPORATION, Loma Linda CA, USA 3. Department of Orthopaedic Surgery, Tokyo Medical University, Tokyo, Japan Address) 11406 Loma Linda Drive, Suite 606 Loma Linda CA 92354, USA Phone) 1-909-558-6490, Fax) 1-909-558-6018, E-mail) [email protected]

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COMPARISON OF RETRIEVED CERAMIC TKP TO METALLIC TKP AFTER LONG-TERM CLINICAL USE

Oonishi, Hiroyuki1, Kim, Sok Chol1, Kyomoto, Masayuki2, Iwamoto, Mikio2, Masuda, Shingo2, Ueno, Masaru2, Oonishi, Hironobu1 1 H. Oonishi Memorial Joint Replacement Institute, Tominaga Hospital 4-48, 1-chome, Minato-machi, Naniwa-ku ,Osaka, 556-0017 Japan Phone: 81-6-6568-1601 Fax: 81-6-6568-1608 E-mail: [email protected] 2 Japan Medical Materials Corporation, Osaka, Japan INTRODUCTION: We started to use a total knee prosthesis (TKP) consisting of a femoral component (F-comp) made of alumina ceramic and a UHMWPE counterpart in late 1970s. In earlier studies, we addressed on the wear pattern and vol-ume of a ceramic TKP retrieved after 23 years of clinical use. In the present study, the wear pattern of Co-Cr F-comps retrieved after long-term service was investigated in comparison with the result of ceramic F-comp in order to evaluate the efficacy of ceramic bearing surface in TKP. MATERIALS AND METHODS: The ceramic TKP was implanted in 1979 and retrieved in January 2002. In the Co-Cr TKP cohort, one was im-planted in April 1993 and retrieved in June 2004 (case 1, Zimmer, Warsaw, IN, USA). The other was implanted in October 1987 and retrieved in July 2004 (case 2, PCA type, Howmedica, Rutherford, NJ, USA). The wear pattern and the linear wear of Co-Cr TKPs were investigated. The worn surfaces of the Co-Cr F-comp and the UHMWPE tibial insert were observed with an optical microscope and a scanning electron microscope (SEM). The surface roughness was measured by a surface roughness analyzer. The shapes of the medial and the lateral areas of the UHMWPE insert were measured by a shape tracer. The linear wear was calculated by compar-ing the shape of the retrieved component with the unused one. RESULTS AND DISCUSSIONS: In the microscopic observation, a part looking frosted was observed in the articulating area of the Co-Cr F-comps. The SEM observation revealed a lot of scratches in anterior-posterior direction in such worn area. The roughness of the worn surface of Co-Cr F-comps was significantly higher compared to the unworn surface. The linear wear rate of the UHMWPE insert in case 1 was calculated as 0.08 mm/year from the maximum wear distance of 1.680 mm. In case 2, extreme wear was found through the entire thickness of the UHMWPE insert at the medial area, and the linear wear was determined to be more than 6 mm/year. The surface damage and the wear of the UHMWPE insert are closely related to the clinical performance of TKP. From this viewpoint, the material of the F-comp is important because the scratching damage on the UHMWPE insert surface is produced by micro asperities on the counter surface of F-comp. Protrusive scratches were fre-quently observed on the Co-Cr F-comp retrieved after clinical use, whereas the ceramic F-comp substantially maintained the virginal surface aspect. From this observation, we consider that UHMWPE component is less sus-ceptible to wear with ceramic F-comp. This is because ceramics is harder and less plastic than Co-Cr, changes in surface roughness hardly occur, especially in a way to cause protrusive deformation. In addition its surface mor-phology, only with hollow shape by nature, works to prevent wear even under a third body condition. Therefore, ceramic F-comp has a large advantage on the wear of UHMWPE insert.

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Migration of Wear Debris of Polyethylene Depends of the Bone Microarchitecture

P. Massin 1,3, H. Libouban 3, C. Gaudin 3, P. Mercier 2,3, MF Baslé 3, D Chappard 3* 1 Service d’Orthopédie, CHU d'Angers, 49933 ANGERS Cedex - FRANCE. 2 Laboratoire d’Anatomie, Faculté de Médecine, 49045 ANGERS Cedex - FRANCE. 3 INSERM, EMI 0335, LHEA, Faculté de Médecine, 49045 ANGERS Cedex - FRANCE. please send all correspondence to:

Short running title: Migration of PE particles Title length: ; abstract: 214; total manuscript length: words. The mechanism of hip arthroplasties loosening is related to the migration of wear debris throughout the implant environment. In vivo, polyethylene particles were shown to infiltrate the bone implant interface, and the medullary spaces of the cancellous bone, in which their migration appears related to the bone porosity. This hypothesis was tested in vitro. Bone Samples, with a high or low trabecular volume, were harvested in 20 calves and 20 human cadavers. They were extensively washed to remove marrow cells. Bone cylinders were filled with a light-curing monomer having the same viscosity than bone marrow. Polyethylene (PE) particles were deposited at the surface of the polymer. The bone cylinders were agitated during 7 days on an orbital shaker and the gel was left to polymerize under UV light. X-ray microtomography was performed to characterized 3D bone volume and architecture. Cylinders were sectioned and observed under polarized light. Migration of PE particles strongly depended on trabecular bone volume and architecture. We found a linear relationship between speed migration and bone volume and an exponential relationship between speed migration and bone architecture. The present in vitro model highlighted the key role of bone architecture in the migration of wear particles. This would be an explanation for the development of inflammatory raction at distance from a prosthesis.

* Daniel CHAPPARD, M.D., Ph.D. Tel: (33) 241 73 58 65

INSERM, EMI 0335, LHEA Fax: (33) 241 73 58 86

Faculté de Médecine, e-mail: [email protected]

49045 ANGERS Cédex - FRANCE

* Daniel CHAPPARD, M.D., Ph.D. Tel: (33) 241 73 58 65

INSERM, EMI 0335, LHEA Fax: (33) 241 73 58 86

Faculté de Médecine, e-mail: [email protected]

49045 ANGERS Cédex - FRANCE

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COMPARISONS OF IN VIVO OXIDATION AND WEAR BETWEEN RETRIEVED POLYETHYLENE INSERTS WITH GAMMA AND EOG STERILIZATION IN TOTAL KNEE PROSTHESES Kim Sok Chol1, Oonishi Hiroyuki1, Kyomoto Masayuki2, Iwamoto Mikio2, Masuda Shingo2, Ueno Masaru2, Ooni-shi Hironobu1 1 H. Oonishi Memorial Joint Replacement Institute, Tominaga Hospital, 4-48, 1-chome, Minato-machi, Naniwa-ku ,Osaka, 556-0017 Japan Phone: 81-6-6568-1601 Fax: 81-6-6568-1608 E-mail: [email protected] 2 Japan Medical Materials Corporation, Osaka, Japan INTRODUCTION: Gamma-ray irradiation at a dose of 25–45 kGy in air is the typical sterilization method for the UHMWPE compo-nent of an artificial joint. However, many previous studies reported that the gamma-sterilized UHMWPE contain-ing free radicals degraded with substantial oxidation in vivo. It was a matter of concern that oxidatively degraded UHMWPE might decrease the wear resistance or fracture toughness. On the other hand, some previous studies reported that the oxidation index of the degraded UHMWPE in total hip prosthesis (THP) was lower in vivo than in vitro. It has also been reported that the oxygen content might be almost zero in the body and that the oxidation index was lower in the worn area than in the unworn area in THP. In this study, we evaluated the influence of gamma-ray and ethylene oxide gas (EOG) sterilizations on in vivo oxidation and wear of retrieved total knee pros-thesis (TKP). METHODS: Retrieved UHMWPE inserts with gamma-ray (PCA; Howmedica and IB; Zimmer) and EOG (KOM, N-KOM and KU; Kyocera) sterilization of clinical use for 6–23 years were studied. The oxidation index of the retrieved UHMWPE inserts was measured by a microscopic Fourier transform infrared spectrophotometer. Thin slices of the cross-section of worn and unworn (intercondylar) area were prepared from each insert. The oxidation index was calculated as the ratio of the area of the carbonyl absorption peak to the area of the methylene absorption peak, according to ASTM F2102. The shapes of the medial and lateral areas of the UHMWPE inserts were determined by a shape measurement instrument. By comparison of the shape of the retrieved component with that of the origi-nal one, the linear wear was calculated. RESULTS AND DISCUSSION: In the worn area, the oxidation index of the gamma-ray sterilized insert was slightly higher compared with that of EOG sterilized one. In the unworn area, especially for subsurface, the oxidation index of insert was substantially higher in gamma-ray sterilized insert than in EOG sterilized one. The linear wear of gamma-ray sterilized inserts was not so different from that of EOG sterilized one. But, the values of gamma-ray sterilized inserts varied for each insert. For example in PCA, extreme damage to the medial area of the insert was caused by the penetration of the insert. When the damage (in vivo oxidation and wear) in UHMWPE insert is discussed, the resin fabrication and sterilization method have to be considered. The fabrication method of PCA, specifically heat-press after ma-chining is probably a primary factor. The oxidative degradation of worn area proceeded more rapidly compared with unworn area, because the TKP insert was fully exposed to the body fluid. The contact of insert with the oxy-genated body fluid is assumed to be a mechanism of in vivo degradation with the above results. Free radicals pro-duced by gamma-ray sterilization are also responsible for oxidative degradation. In conclusion, the sterilization methods affect in vivo oxidation, and gamma-ray sterilization has an undesirable influence (e.g. delamination and fracture) upon wear resistance of UHMWPE TKP inserts.

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EFFECT OF ZIRCONIA FEMORAL HEAD ON POLYETHYLENE WEAR RATES Author: Maruyama Masaaki 666-1, Shinonoi Ai, Nagano, Japan 388-8004 Phone: 81 26 292-2261 Fax: 81 26 293 0025 E-Mail: [email protected]

Use of Zirconia ceramics as a surface modification to the bearing component of orthopedic implants may be an effective means of reducing wear debris at the bearing interface. <Materials and Methods> Of primary and revision total hip arthroplasties (THAs) performed between January 1997 and October 1999 at our hospital, seventy-six THAs (72 patients: female 73 THAs in 69 patients, male three THAs in three patients) with Zirconia femoral head followed up a minimum of 6 years (mean 8.0 +/- 0.9 years). Diagnoses of the patients were osteoarthritis for 70 hips, osteonecrosis of the femoral head for three hips, rheumatoid arthritis for two hips, and revision for one hip. Mean age at surgery was 60.2 +/- 10.0 years old (range, 26 to 78), and mean body weight was 53.6 +/- 8.1 kg (range, 41.3 to 75.5). All patients had implantation of a cemented straight collarless Ti-6Al-4V femoral component with a cemented all polyethylene socket. Polyethylene was not cross-linked and sterilized using ethylene oxyside gas. All prosthetic heads were Zirconia and were attached to the stem with a taper lock. Socket wear were meas-ured directly on the AP radiographs using anastigmatic objective. <Results> The mean linear wear rate of polyeth-ylene was 0.15 +/- 0.07 mm per year. Eight patients were ranked as heavy wear rate (0.25 mm per year or more). Focal osteolysis was recognized in ten hips (acetabulum: 4, femur: 10). The direction of wear was lateral in 26 cases, vertical in 48 cases, and medial in one case. Of the 76 arthroplasties, no femoral component and one acetabular component was judged to be radiographically loose. Discussion: A lot of factors related to polyethylene wear in THA reported in the literature, including factors related to the pa-tients (age, gender, and activity level) and to the components (head diameter and quality; thickness, quality, and fixation method of polyethylene). The aim of the current study was to examine the influence of Zirconia ceramics of femoral heads on polyethylene wear in THA. In a study of socket wear in the Charnley low friction arthroplasty (LFA), the mean linear wear rate of polyethylene was 0.11 mm per year. In the current study, Zirconia of the femo-ral was might not result in decrease in polyethylene wear. In vitro, the wear rate was significantly decreased by using Zirconia on polyethylene. One of the causes of the discrepancy may be quality of the socket. Gamma ray irradiation has been shown to decrease the degeneration and wear resistance of polyethylene. All of the sockets used in the current study were not irradiated at sterilization. Polyethylene socket was sterilized using gamma air irradiation in the Charnley LFA. The other cause may be quality of Zirconia, such as degeneration in vivo or ad-verse effect of heat conductivity. Further examination must be inevitable for evaluation of effect of Zirconia femo-ral head on polyethylene wear rates.

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INHIBITORY EFFECTS OF ERTHROMYCIN ON WEAR DEBRIS-INDUCED VEgf/flt-1GENE ACTIVATION AND OSTEOLYSIS IN A MOUSE MODEL Weiping Ren1,2*, Renwen Zhang3, Bin Wu2, Yunhong Ding2, Paul H.Wooley2, Monica Hawkins3, Ralph Blaiser2, and David C. Markel2 1Department of Biomedical Engineering, 2Orthopaedic Surgery, Wayne State University, Detroit, Michigan 48201; 3 Stryker Company, Rutherford, New Jersey 07070 Address correspondence to: Weiping Ren, MD, Ph.D. Department of Biomedical Engineering Wayne State University 818 W. Hancock Detroit, MI 48201 Tel: (313)577-8118 Fax:(313)577-8333 Email: [email protected]

A highly vascularized and inflammatory periprosthetic tissue augments the progress of aseptic loosening, a major clinical problem after total joint replacement. The purpose of this study is to investigate the therapeutic effect of EM on ultra high molecular weight polyethylene (UHMWPE) particle- induced VEGF/VEGF receptor 1 (Flt-1) gene activation and inflammatory osteolysis in a mouse osteolysis model. UHMWPE particles were introduced into established air pouches on BALB/c mice, followed by implantation of calvaria bone from syngeneic littermates. Erythromycin (EM) treatment started 2 weeks after bone implantation (2 mg/kg/d, i.p. injection). Mice without drug treatment, as well as mice injected with saline alone were included. Each group contained 10 mice. Pouch tissues were harvested two weeks after bone implantation for histological analysis. Expression of VEGF, Flt-1, RANKL, IL-1, TNF and CD68 was measured by immuno-histological stain. Osteoclast formation was determined by tartrate-resistant acid phosphatase (TRAP) staining, and implanted bone resorption was analyzed by micro CT (�CT).

Statistical analysis was performed using ANOVA method. Exposure to UHMWPE induced pouch tissue inflammation, increase of VEGF/Flt-1 proteins, and increased bone resorption. EM treatment significantly improved UHMWPE particle- induced tissue inflammation, reduced VEGF/Flt-1 protein expression, and diminished the number of TRAP+ cells, as well as the implanted bone resorption. This study demonstrated that EM, newly identified as an osteoclast inhibitor, targeted not only to RANK/NF�B signaling, but also down regulated VEGF and Flt-1 gene expression. The molecular mechanism of EM action on VEGF/Flt-1 signaling- mediated osteoclastogenesis warrants further investigation. These data provide a biological rationale for the VEGF/Flt-1-targeted treatment strategy, especially at the early stage of wear debris-induced inflammatory response.

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Second Generation Highly Crossed Linked UHMWPE. Sequential Irradiation and Annealing J. Nevelos, A Essner, A Wang, S Yau, J Dumbleton

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ACETABULAR CUP ANGLE AND EARLY LOOSENING IN METAL ON METAL ARTICULATION AT THE HIP JOINT Jeffers, Jonathan RT; Roques, A; Taylor A; Tuke, MA, Suave, P Finsbury Development, Leatherhead, Surrey, UK. Tel.: +44 (0)1372 360 830. E-mail: [email protected] Metal-on-metal hip replacements/resurfacings depend on fluid film lubrication to minimise friction at the interface and keep the wear rates low. If the fluid film lubrication regime is prevented from occurring, high wear rates can be expected and the associated debris may cause osteolysis and loosening of the components. With respect to fluid film lubrication in metal-on-metal articulations, the placement of the acetabular component is crucial. If the component is placed in too steep an angle, the area for load transfer at the bearing surface is re-duced, and with it the ability to generate a fluid film. In this study we selected metal-on-metal patients with excellent follow-up (still functional at 30-36 years), and compared them to patients with poor follow-up (components retrieved at 1-4 years) to investigate the relationship between acetabular cup angle and high levels of wear associated with the loss of fluid film lubrication. Wear measurements were made of the retrieved components to identify any distinctive patterns. The patients with excellent survivorship (n=6) had a mean acetabular cup angle of 25º (sd 8º), while the patients with poor survivorship (n=8) had a mean acetabular cup angle of 62º (sd 11º) in the frontal plane. Wear measure-ments of the retrieved components from the latter group showed extremely high levels of wear on the superior edge of the component (~200μm). These results may have an implication for revision of hip resurfacing as the femoral component can easily be re-vised to a stemmed modular component, but a well fixed acetabular component is difficult and time consuming to revise. Failure to revise an acetabular component with a steep angle may therefore compromise the survival of the revised hip. Navigation can reduce the outliers in the acetabular cup angle data, but brings with it increased cost and the risk of over-reliance whereby the surgeon may follow the computer rather than his/her own judgement. There may there-fore still be scope for innovative mechanical alignment instruments to assist the surgeon without the cost and com-plication of computer navigation.

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SERUM METAL ION LEVELS AFTER METAL-ON-METAL HIP RESURFACING ARTHROPLASTY FOR ASIAN PATIENTS Kabata Tamon, Maeda Toru, Sakagoshi Daigo, Naito Mitsuhiro, Taga Tadashi, Ando Tomonari, Tomita Katsuro, Department of Orthopaedic Surgery, Kanazawa University School of Medicine, Kanazawa, Japan

Objective: Metal-on-Metal hip resurfacing arthroplasty is being used in young active patients. It is well recognized that metal-on-metal bearings lead to a significant increase in serum cobalt and chromium, which may have potential chronic adverse biological effects. We prospectively monitored changes in serum cobalt and chromium levels after Metal-on-Metal hip resurfacing arthroplasty. Materials and Methods: 14 patients (5 male, 9 female) implanted unilaterally with a Birmingham hip resurfasing (BHR) prosthesis were included into the investigation after obtaining informed consent. The average age of the patient groups was 47 years (34-57). Two hips were diagnosed with osteonecrosis and twelve were with OA. The average femoral head diameter was 46mm (42-50). Venous blood samples were taken at 3, 6, 12, 18, 24 and 36 months after surgery. Serum cobalt and chromium levels were measured using inductively coupled plasma mass spectrometry and atomic absorption spectrometry. Patients were asked if any other illnesses had occurred at each follow up stage, and renal function was checked by measurement of serum BUN and creatinine concentration levels. Implant sta-bility was checked by plain radiography. Results: Both serum cobalt and chromium levels increased for six months and gradually declined thereafter. The mean serum cobalt and chromium levels at six months were 2.99μg/l and 0.24μg/dl respectively, which was almost 20 to 50% greater than at 36 months. There was no adverse affect on renal function during the study period. All im-plants were stable and functioning well, with no radiographic evidence of loosening. Discussion: Several hip simulator studies have shown that metal-on-metal bearings exhibit a higher running-in wear in the first one million cycles, followed by a very low steady-state wear rate. Our results that the levels of metal ion increased up to 6 months postoperatively, followed by a gradual decline during the next 30 months are compatible with the results of hip simulator studies. Large-diameter metal-on-metal articulations are thought to benefit from fluid film lubrication. Thus, a further reduction of wear particle generation and metal ions may be expected after the first 3 years in situ. We do not know how much the metal ion levels decrease. Further monitoring will be needed.

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TEN YEARS FOLLOW-UP IN COBALT SERUM DETERMINATION AFTER METAL- ON-METAL HIP PROSTHESIS Jean-Yves Lazennec PhD, Patrick Boyer MD, Joel Poupon MD, Marc-Antoine Rousseau MD, Phillipe Ravaud PhD, Yves Catonne MD. Département de chirurgie orthopédique Hopital La Pitié-Salpétrière, 47-83 Boulevard de l’hôpital, 75013 Paris Introduction: Systemic cobalt and chromium release has been demonstrated from metal-on-metal hip prostheses. Concerns exist about this release as the results of allergic or carcinogenic toxicities. Purpose of this study was to determine pro-spectively the serum cobalt concentration at long term. In addition, we investigated whether bilateral joint replace-ment could significantly affect the serum cobalt concentration compared to unilateral replacement. Methods: We included in this study 73 patients who underwent a cemented metal-on-metal hip prosthesis using the Me-tasul® bearing surface. There were 50 unilateral and 23 bilateral hip replacements. At multiple time-points until 10 years after the operation, blood samples were taken in order to dose Serum cobalt concentrations collected into free-metal vacutainers. Serum samples were analyzed using atomic absorption spectrometry. Results: In the unilateral joint replacement group, the median serum cobalt concentration was 23.5 mmol/l at one year after surgery, 21.7 mmol/l at five years and 26.1 at ten years. Regarding the bilateral group, the median serum cobalt concentration was 64.7 mmol/l at one year after surgery, 59.2 mom/l at five years and 103.9 mmol/l at ten years. Discussion and Conclusion: This study brings out new informations about systemic cobalt release from Metasul® metal-on-metal hip prosthe-sis at long term. Values are significantly below detection limit and remain in a constant range after the run-in-phase. Bilateral replacement increase by 3 to 5-fold systemic cobalt release and raises questions about elimination. Metal ions long term effects are still undetermined.

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METAL-ON-METAL HIP REPLACEMENT USING METASUL CUPS CEMENTED INTO MULLER REINFORCEMENT RINGS AFTER A MEAN 5-YEAR (3-8) FOLLOW-UP: IMPROVEMENT OF ACETABULAR FIXATION BY COMPARING WITH DIRECT CEMENTATION TO BONE Girard J, Herent S, Combes A, Pinoit Y, Bocquet D, Migaud H CHRU Lille, Orthopédie C, 59037 Lille cedex. E-Mail: [email protected] Introduction: High rates of early acetabular loosening and osteolysis were reported using cemented Metasul™ cups (Weber and Muller with Metasul inlay). The use of metal-on-metal was pointed out to explain these loosening that mainly oc-curred for small diameters of cups (under 50 mm) directly cemented to bone. It was argued that using metal-on-metal increased the stiffness by comparing with conventional polyethylene cemented cups. But others incriminated the Metasul™ bearing and advocated to stop its clinical use. This retrospective study was undertaken to know if the same components cemented into a reinforcement ring (instead of direct cementation to bone) had the same rate of failure. Material and Methods: Twenty-three hip replacements using a Muller Metasul™ cup cemented into a Muller reinforcement ring were in-serted between 1998 and 2004. During the same period 628 cementless Metasul™ cups (Allofit™) were used in the same department. A cemented fixation was indicated when the press fit was not adequate because a massive acetabular graft was requested (20 hips) or because of a severe acetabular deformity (2 hips). These 23 replace-ments were performed in 22 patients (16 females, 6 males), mean aged 44 (24-56). Six were primary procedures (3 dysplastic hips, 2 protrusions, 1 late sequelae of hip infection), and 17 were revision arthroplasty. The Metasul™ bearing was used in 28 millimeters in diameter and all the cups were cemented (low viscosity cement) into a Mul-ler reinforcement ring fixed with at least 5 screws to pelvic bone (13 cups had an external diameter less than 50 millimeter). The stems were fixed with cement in 2 hips and cementless in 21. All the patients were assessed yearly by means of Merle d’Aubigne hip score and AP and lateral radiographs. Cup fixation was evaluated. Results: No patient was lost at a mean follow-up of 5 years (3-8). No hip was revised because of cup loosening. The Merle d’Aubigne hip score increased from 12.9 (7-17) before surgery to 17.5 (16-18) at follow-up. No migration or oste-olysis was observed on the acetabular side. There was no radiolucency identified around Metasul™ cups, nor be-tween bone and reinforcement ring. No femoral osteolysis was observed but a repeated femoral revision was per-formed because of post-operative shaft fracture that occurred at 6 weeks. Discussion and Conclusion: The results of Muller Metasul™ cups cemented into a reinforcement ring are quite different from those observed when the cup is cemented directly to pelvic bone. Half of the cups had a diameter under 50 millimeters that were pointed out as producing the higher rate of early loosening (occurring usually between 24 and 36 months). The majority of patients were young and active. Using a cemented Metasul™ cup was the only way to use bearings with improved wear-resistance as we were unable to obtain primary fixation of press fit sockets. These results are promising as they allowed the use of improved wear resistance bearings when press-fit cementless fixation is not adequate, however a longer follow-up is required to confirm this encouraging data.

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SURFACE ANALYSIS OF RETRIEVED METAL TO METAL IMPLANTS Sorimachi Takeshi1, Donaldson T.K.1, Clarke I.C. 1, Yamamoto K.2 1. Loma Linda University Medical Center, Department of Orthopaedics, California USA 2. Department of Orthopaedic Surgery, Tokyo Medical University, Tokyo, Japan Address) 11406 Loma Linda Drive, Suite 606 Loma Linda CA 92354, USA Phone) 1-909-558-6490 Fax) 1-909-558-6018 E-mail) [email protected] Introduction: Metal-on-metal (MOM) bearings have revolutionized total hip replacements (THR) by providing thin but strong cups, permitting use of large diameter femoral heads. However there have been some problems. We present an interesting case revised at 39 months. The patient was a 55-year old woman weighing 145lbs who had a primary THR in August 2003 for a painful, arthritic left hip. Patients’ complaint post-operatively was a sensation of “snapping” accompanied by some pain in her left hip and her symptoms were slowly getting worse. Prior to revi-sion, she described this hip sensation as a “deep popping” and also noted pain in her lower back. Pre-operative radiographs showed no signs of cup or stem loosening. Her leg length was symmetrical, range of motion was good but she walked with a mild limp on the left side. CT scans showed the anterior inferior aspect of her metal cup was uncovered 1cm. She was revised to a 36mm femoral head (0-neck) and polyethylene liner in a 54mm socket with added 30mm screw (Biomet Inc, Warsaw IN). Material and Method: On retrieval, visible implant damage was visually assessed under directional lighting. Reflected Light (RLM) and Scanning Electron Microscopy (SEM) techniques were combined with laser interferometer for surface analyses. Microscopic observations were carried out before and after implant cleaning. Wear types were compared to our 6-grade scale and wear maps prepared (Shirasu et al, 2006). Results: Both stem and cup were well fixed at surgery and no evidence of infection was found. It was noted that the ante-rior gluteal attachments were partially pulled off the trochanter and the tissues were colored somewhat gray. After revision the patient’s cup coverage and hip stability appeared excellent. The RLM and SEM studies found many overlapping areas of severe 3rd-body, multidirectional scratches on the load-bearing areas of both ball and cup. Metal transfer layers were also noted on the CoCr bearing surfaces. The backside of the porous-coated cup surface also showed a burnishing that was likely caused by soft tissue abrasion against the protruding anterior flange of the shell. Discussion: With only 3-years follow-up, the multi-directional scratches on both CoCr bearing surfaces was a surprising find-ing as was the anterior porous-coated shell abraded by the tendon. It was therefore likely that titanium debris from the shell triggered a severe 3rd body wear of the CoCr surfaces and resulted in gray staining of the periarticular tissues by metal debris. The smeared surfaces were likely a coating of titanium and this is being studied further. It has been anticipated that the benefit of MOM bearings will be very low wear, of the order 0.2 to 5mm3 per year (Clarke et al, 2005OCNA). However in some cases, adverse MOM wear may be triggered by serendipitous events contributing unanticipated 3rd body wear. It is currently unknown whether some MOM bearings will be more sen-sitive to 3rd body wear events than metal-polyethylene THR.

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HISTOPATHOLOGY OF REVISED HIP RESURFACINGS FOR SUSPECTED METAL SENSITIVITY Campbell Pat A, Nelson Scott, Esposito Christina, Shimmin Andrew 1, De Smet Koen 2. JVL Research Cntr, Orthopaedic Hospital /UCLA 2400 S. Flower St, Los Angeles CA 90007. 1213 742 1134, fax 213 744 1175, [email protected] Failures attributed to metal sensitivity have been described in association with older generation hips using stainless steel, or metal-on-metal designs with high wear. Osteolysis in a small number of hips with modern generation, low-wearing metal-on-metal bearings has been attributed to metal sensitivity[1]. The histopathological description of tissues from hips with failed metal-on-metal implants varies from low levels of histiocytic infiltration to unusual lympho-plasmacytic accumulations not previously seen in tissues from metal-polyethylene implants [2]. These descriptions typically are based on small numbers of samples. With the accumulation of over 200 specimens in our laboratories, the aim of this study was to review the histopathology of tissues from a wide range of failed metal-on-metal implants, with particular focus on those cases that were revised for suspected metal sensitivity. Materials and Methods: Only cases in which infection had been excluded were studied. Periprosthetic tissues accompanying failed im-plants were routinely processed into paraffin, sectioned and stained with hematoxylin and eosin. A subset of cases with unusual lymphocytic infiltrations were stained with markers for lymphocytes, macrophages and plasma cells. The results of these analyses were reviewed with clinical variables, radiographs and implant wear measurements by coordinate measuring machine. Results: Approximately one third of the tissues from failed hips had perivascular or diffuse lymphocyte aggregates, usually rated mild to moderate. Tissue histiocytes filled with haematin and often with visible metal particles were com-mon, and were particularly abundant in enlarged bursae from hips with high wear (>100 microns maximum femo-ral wear depth). There was a trend for more lymphocytic and macrophagic infiltration with higher wear. Immu-nological staining showed a mix of B and T lymphocytes. Tissues from patients whose implants were removed for suspected metal sensitivity were extensively infiltrated with diffuse and perivascular lymphocytes, often in combi-nation with plasma cells. There was commonly abundant fibrin attached to the tissue surface which was usually eroded and necrotic. The wear of implants in these cases was generally low. Discussion: The pattern of inflammation in tissues from metal-on-metal hips has been described as lymphocytic vasculitis and the term ALVAL (aseptic lymphocytic vasculitis associated lesions) has been coined to describe these particular histopathological features [1]. Clinically, as well as histologically, patients with metal sensitivity differ from pa-tients with failed metal-on-metal total hip replacements with wear debris. When tissue biopsies from patients with otherwise unexplained pain show abundant lymphocytes, plasma cells, extensive necrosis and fibrin deposition, and all other causes for their pain has been eliminated, a diagnosis of metal sensitivity should be considered. Timely revision should then be performed to avoid progressive local tissue damage. 1.Willert et al. J Bone Joint Surg 87:28, 2005 2.Davies et al. J Bone Joint Surg 87:18, 2005 1Melbourne Orthop Gp, Australia 2ANCA Clinic Gent Belgium

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THE FATE OF SLEEVED HEADS ON METAL-ON-METAL BEARING OUTCOME Christian P. Delaunay, Henri Migaud, Philippe Laffargue Clinique de l'Yvette, 67-71, route de Corbeil, 91160 Longjumeau, France Tel : 00 (331) 69 10 30 30 / Fax : 00 (331) 69 10 31 33 / [email protected] INTRODUCTION: In a previous comparative study [1], 10-year survivorship of MoM 28mm bearings from revision for any reason was 81.5% (95% CI, 57–93.5%) for the original Weber design with sleeved heads and 98.7% (81–99.9%) for the sleeveless current design. In addition, dislocation rate (5%) was partly explained by early impingement favored by head sleeve with unfavorable head-neck ratio (<2). Aim of the current study was to assess the effect of head sleeve on the outcome of 2 series of primary total hip arthroplasties (THA) with 28mm MoM (Metasul™) articulations.

MATERIAL and METHODS:

From January 1995 to December 2004, 642 primary THAs with 28mm Metasul bearings were used in 2 institutions (Lille University, 396 THAs and Clinique de l’Yvette, 246 THAs). On the femoral side, cementless Alloclassic-SL taper was used in all hips except in 3 (3 Müller cemented straight stems). On the acetabular side, 3 cup designs were used: 25 Weber cemented PE cups and 375 cementless press-fit titanium cups in Lille; and 246 cementless titanium threaded cups (Alloclassic-CSF) in Longjumeau. Thirty-one heads (4.8%) had a sleeve (group S+) with an extra long (XL) neck in 9 occasions, while 611 heads were without sleeve (group S-).

RESULTS:

Overall, 15 reoperations (2.3%) were necessary: 7 revisions were in the S+ group (22.6%) and 8 in the S- group (1.3%). This difference was highly significant (Chi2, P = 0.0001). Eleven of these 15 reoperations were due to dis-location and/or impingement: the 7 revisions in the group S+ and 4 of the 8 revisions in the group S- (P = 0.11). Conversely, the 11 revisions for dislocation and/or impingement were associated with 7 of the 31 sleeved heads (22.6%) and 4 of the 611 non-sleeved heads (0.6%); this difference was highly significant (P = 0.0001).

DISCUSSION:

Head-neck ratio is defined as favorable if > 2. Using the 28mm size on a 12-14mm Morse cone without sleeve, the ratio ranged from 1.83 at the cone level to 1.75 at the prosthetic neck base level; with head sleeve of the original design (+ 2.2mm), the ratio decreased to 1.6 at any neck level. All metallic impingement between any head sleeve (CoCr alloy) and acetabular metallic bearing (CoCr) or titanium shell generated Co and Cr particles that are detect-able in urine and blood. This test was useful for detection of mechanical MoM articulation dysfunction according to Archibeck mode 2 in the previous study [1,2]. In opposition, with the same 28mm size and 12-14 Morse cone configuration, but on a slimmer neck, head neck ratio became even more favorable (2.43 at the cone level). In any patient, no general toxic effect could have been detected thus far.

CONCLUSIONS:

Main cause of MoM failure was due to impingement favored by head sleeve and excessive cup anteversion. Co level survey showed to be a good indicator of MoM bearing behavior. According to the current knowledge, head sleeves must be avoided and head-cone compatibility is of paramount importance.

REFERENCES: 1) Delaunay C. Metal-on-metal bearings in cementless primary total hip arthroplasty. J Arthroplasty, 2004, 19, 35-40. 2) Archibeck MJ, Jacobs JJ, Roebuck KA, et al. The basic science of peri-prosthetic osteolysis. J Bone Joint Surg

Am 2000;82:1478-1489.

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SECOND GENERATION OF METAL ON METAL CEMENTED TOTAL HIP REPLACE-MENTS: 10 YEARS OF CLINICAL AND BIOLOGICAL FOLLOW-UP JY LAZENNEC *, P BOYER*, J POUPON**, MA ROUSSEAU, F LAUDE* , Y CATONNE*, G SAILLANT * Département de chirurgie orthopédique Hopital La Pitié-Salpétrière, 47-83 Boulevard de l’hôpital, 75013 Paris* Département de toxicologie, Hopital Lariboisière, 2 rue Ambroise Paré, 75010 Paris** E-Mail: [email protected] Introduction : The second generation of metal on metal prosthesis appeared at the end of the 1980s as a serious alternative to metal on polyethylene bearing couples. Short term clinical results were promising ; however certain questions per-sist concerning clinical, radiological and biological aspects. Release of chromium and cobalt from the bearing couple is one of these aspects.

Material and Methods: The aim of this study is to analyse the results of a series of 97 cemented total hip prosthesis comprising a titanium femoral stem and the Metasul® metal-metal bearing couple.Mean follow-up is 9 years ( 7-12 ) Results: Complications were marked by 12 revisions out of which 2 were for recurrent early dislocations, 8 for clinical and radiological failure, 2 for worrying radiological alterations. During these revisions we observed a serious infiltra-tion of metal debris 4 times, leading to an alternative strategy using an alumina-alumina bearing couple. Three more revisions are planned for rapidly evolving radiological alterations. 30 implants show radiological signs of preoccupying deterioration on the acetabular side. 8 segmentary femoral osteolysis have been observed. 12 patients suffer from recurrent subluxation. Concerning the global evolution of metal serum levels, cobalt remain stable after 5 years. The values are 3 to 4 times above those of a non exposed subject but largely below ratios considered toxic. The evolution of serum chro-mium levels is similar to cobalt. Implantation of two prosthesis in one same patient leads to significant increase in serum metal ratios. Discussion and Conclusion: This series raises questions concerning the reliability of the metal on metal bearing couple. Osteolysis is an un-solved problem. Today cemented fixation is debatable although this series doesn’t allow this parameter to be held directly responsible. Nothing points to any shortcomings concerning the taper fixation or the metallurgy of the femoral stem. The study of the serum metal levels seems a good indicator of the impingement situations and the functioning of the bearing couple .

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WEAR AND IONS IN RETRIEVED METAL-METAL TOTAL HIP REPLACEMENTS— A HIP SIMULATOR COMPARISON OF 28 MM MOM , Ian C. Clarke1, T. Sorimachi, Y. Lazennec, T. Ishida1, and H. Shirasu 1 Peterson Tribology Lab, Department Joint Research Center, Loma Linda University California, USA and 2Department of Orthopaedic Surgery, Tokyo Medical University, Tokyo, Japan Corresponding author Ian Clarke, Ph.D. Director, Peterson Tribology Lab Department Joint Research Center Loma Linda University, School of Medicine 11406 Loma Linda Drive, Suite 606 Loma Linda, CA 92354 Phone: (909) 558-6490 Fax: (909) 558-6018 E-mail: [email protected]

The objective of this study was to correlate in-vivo, retrieval and laboratory wear studies of metal-on-metal (MOM) bearings. Twelve MOM bearings (28mm Metasul, Zimmer) with follow-ups to 10 years were retrieved for various reasons including pain, osteolysis and cup loosening. Patients averaged 55 years of age. All had the Weber Low profile cup cup design of UHMWPE ‘sandwich’ design (SULENETM). The bearings were both CoCr (PROTASULTM ; ISO 5832-12). The Alize femoral stem in Ti64 alloy was cemented in all cases. The MOM bearings were analyzed by light microscope, laser in-terferometry, scanning electron microscopy SEM) and contour measurements (CMM).

Worn areas were described by grading system (0-6) depending on the severity of burnishing and 3rd body scratching. On the femoral heads the main central wear zone and peripheral stripe wear zones were conspicuous under the SEM and generally grades 5-6. The MOM liners featured central wear zones and in some cases rim stripes and impingement damage. Stripe inclination varied specifically from 10-30o relative to the base of the ball. Generally the liner wear ranking was one grade less severe than with femoral heads, i.e. there was more wear damage on the heads. Worn areas were also larger on the femo-ral heads achieving 600mm2 to the liners with 300mm2 maximum. Typical studies from our standard simulator wear studies of 32mm MOM demonstrated peak run-in wear-rates up to 15 mm3 per million cycles with an overall wear rate of 1.6 mm3/Mc and comparable to previous studies. Serum lubricants became noticeably gray with MOM wear rates > 3 mm3/Mc and dark-ened significantly with wear > 7mm3/Mc. Ion studiesshowed Co:Cr ratios at 2.26 as in the alloy with concentrations averaging 40ppm during run-in phase and 10ppm during steady-state phase.

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THE POTENTIALITIES OF ELCTROCONDUCTIVE Si3N4-TiN CERAMIC COMPOSITE FOR COMPLEX-SHAPED IMPLANTABLE DEVICES, MACHINED THROUGH ELECTRI-CAL DISCHARGE MACHINING (EDM) Bucciotti F., Mazzocchi M., Bellosi A. ISTEC-CNR, Via Granarolo 64, 48018 Faenza (Ra) Phone: +39 0546 699723/Fax: +39 0546 46381/E-mail: [email protected] Silicon nitride-based ceramics have been ascertained to be suitable materials for permanent biomedical devices, as articular prosthesis, reconstructive surgery, fixture systems, due to their high mechanical and tribological proper-ties, as well as for their biocompatibility. Owing to the high hardness, the production of complex shapes from sim-ple pieces of silicon nitride trough conventional mechanical machining, using diamond tools, is difficult and ex-pansive. In this work we investigated the properties of electroconductive silicon nitride/titanium nitride ceramic composite and a possible processing route, that allows the net-shaping of complex components by electrical discharge ma-chining (EDM). Fully dense pieces were obtained by hot pressing, using alumina and yttria as sintering aids. The tests on the final dense electroconductive composites evidence that the EDM can be applied as a low-cost and highly efficient route to obtain complex shapes. Bulk and surface characteristics and properties of the composite Si3N4-TiN were investigated, among which: hard-ness, strength, Young’s modulus, wettability against liquid including SBF, surface modification due to exposure to liquids for long term, the biochemical issues from cells in cytotoxicity tests. Microstructure and the machined surface were examined by scanning electron microscopy (SEM) and energy dis-persion spectroscopy (EDS); phase composition before and after EDM was checked by XRD analyses. The thick-ness of the electro-machined layer and the roughness of the carved surfaces were measured by SEM and pro-filometer respectively. The most relevant results are the following: the composite is constituted by β-Si3N4 and TiN grains, these ones connected each other to form a through electrical conductive network. The grain boundary phases consist of silicates and oxinitrides of the cations contained in the sintering aids, located in the triple points and the interfaces in between the Si3N4 grains. As for the mechanical properties, the hardness approaches 15 GPa, the Young’s Modulus is 354 GPa, the room temperature flexural strength is about 850 MPa. The in-vitro test results stress the nontoxicity of the materials both of the dense hot pressed composite and of the β-Si3N4-sintering aids powder mixtures and of the TiN powders. Melting and evaporation are the mechanism to be invoked for the ablation of Si3N4-TiN at a microscale of the EDM machining. The thickness of the altered microstructure layer and the surface roughness of the Si3N4-TiN ce-ramic composite is strictly correlated with EDM parameters: selected working parameters, such as low voltage (about 50-60 V) and current (about 0.5-1.5 A), yielded the best results in this sense. The microstructure of the composite EDM treated surface showed the formation of a surface layer of 10-20μm in thickness, that evidences the superpositioning of cavities and craters with a range of diameters and shapes. Results will be presented concerning either the comparison of the surface characteristics and roughness of surfaced deriving from EDM and form surfaced mechanically polished. The results of in-vitro tests depend on the surface characteristic parts. Examples of the potentialities of the experimented processing procedures in term of complexity of the final shapes for specific mini-fixtures and prostheses are presented.

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THE OCCURRENCE OF THE SQUEAKING PHENOMENON IN TOTAL HIP ARTHROPLASTY USING ALUMINA CERAMIC-ON-CERAMIC BEARINGS Murphy, Stephen B.; Ecker, Timo M., Tannast, Moritz Center For Computer Assisted and Reconstructive Surgery New England Baptist Bone and Joint Institute 125 Parker Hill Avenue Suite 545 Boston, MA 02120 Phone: 617-232-3040 Fax: 617-754-6436 e-mail: [email protected] While providing superior hardness and improved wear characteristics, hard bearings such as metal-on-metal, or ceramic-on-ceramics bearings have different lubrication properties than cocr-on-poly bearing couples. Recently, a high incidence of squeaking had been reported with the use of the Stryker Trident total hip arthroplasty. In their report, the authors recommended that all patients complete a questionnaire that specifically asks about squeaking, in order to gain a proper assessment of the incidence of the problem. The purpose of this study was to assess the incidence of squeaking following alumina ceramic-ceramic total hip arthroplasty in our patient population. Since September of 2006, when the first squeaking incidences were reported, all patients returning in routine clini-cal followup who had undergone alumina ceramic-ceramic THA (Transcend, Wright Medical Technology, Mem-phis; Ceramtec, Plochingen, Germany) at any time since June of 1997 answered a questionnaire concerning squeaking. Specifically, patients have been asked the question, “Has your hip ever squeaked?” If the answer was yes, then additional questions concerning the frequency were then completed. The implant design uses an 18 de-gree taper between the titanium shell and the ceramic liner with the ceramic liner mounted flush with the metal rim. Questionnaires concerning 245 hips were obtained after a mean followup of 30.7 ± 29.7 months (range 0.4 – 114.2). Of 245 hips, patients stated that their hip had never squeaked in 241 (98.4 %) of these. Four patients (1.6 %) stated that the hip had squeaked at least once at some point since surgery. Squeaking had occurred once or more a year in two hips, but since disappeared. One hip squeaked once or more a month and one hip squeaked once or more a day with squatting exercises. None of these patients was able to reproduce the squeak voluntarily nor could it be elic-ited on examination. Further, when asked, non of the patients were limited in any given activity by the squeaking. Radiographically, there were no cases of osteolysis or loosening in any of the 245 hips. Squeaking following alumina ceramic-ceramic total hip arthroplasty using the implants described above may occur in approximately 1.6 % of patients without causing pain or dysfunction and without radiographic evidence of loos-ening or osteolysis.The difference in occurrence and frequency between the current study and prior reports of metal-backed, recessed ceramic liner designs suggests that the incidence of squeaking in hard bearings is affected by design considerations, surgical technique or both.

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REVISION TOTAL HIP REPLACEMENT FOR CERAMIC HEAD FRACTURE:

A LONG TERM FOLLOW-UP

Vineet Sharma, MD, Amar S. Ranawat,MD, Vijay J. Rasquinha, MD, Chitranjan S. Ranawat, MD 130 East 77th St. 11th Floor, New York, NY 11355 Phone: 212-434-4700 E-Mail: [email protected] Fracture of the ceramics has and will continue to be a dreaded complication after THA with ceramic articulation. Ceramic fracture is a difficult situation as the results of revision reported in literature with various bearing surfaces are disappointing. The purpose of this study was to look at long term results of revision THA for ceramic head fractures. Methods: Out of 87 THA with ceramic on polyethylene bearing surface done by the senior author between 1990 and 1992, there were 8 cases of ceramic head fracture. All the fractures occurred while doing routine daily activities. All hips were treated with complete anterior and posterior synovectomy and exchange of bearing surface to cobalt-chromium on polyethylene. All patients were followed on a regular basis after revision for wear, osteolysis and implant loosening. One patient was lost to follow up and another refused to particiapte in the study. The mean follow up after revision was 10.5 years. These patients were matched with 6 patients who had primary THA dur-ing the same period with a cobalt-chromium on polyethylene articulation. Wear rate was measured in both group of patients to see if ceramic particles lead to increased third body wear after revision. Results: There was no revision for osteolysis or aseptic loosening at a mean follow up of 10.5 years. One hip was revised for infection which occurred 12 months after the revision. The mean Harris hip score was XX at the last follow up. The linear and volumetric wear rate was the same after revision as in the control group. Conclusion: We conclude that revision THA done for ceramic head fracture has a favorable outcome provided a complete and thorough synovectomy is performed. The clinical and radiological results are the same and third body wear is not more compared to the control. Keywords: ceramic fracture, revision total hip, wear rate

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A STANDARDIZATION PROPOSAL OF TEST METHOD FOR IMPACT RESISTANCE OF CERAMIC FEMORAL HEAD FOR HIP JOINT PROSTHESES TSUTSUMI, Sadami, MIZUNO, Mineo, TODO, Mitsugu, NISHIDA, Masaru, HATTORI, Masaaki, ASAOKA Nobuyuki Institute for Frontier Medical Sciences, Kyoto University, Shogoin, Sakyo-ku, Kyoto 606-8507 Japan Tel: +81-75-751-4130 Fax: +81-75-751-4126 E-Mail: [email protected] This research was commissioned by the Ministry of Economy, Trade and Industry, Japan, and is intended to pro-pose an International Standard evaluating impact resistance of ceramic femoral head for hip joint prostheses. This test method should be used for material development, material comparison, quality assurance, characterization, reliability analysis and design data generation. This test method is to determine the impact resistance by observing the fracture existence or non existence after applying the impact with free falling weight to a test specimen, based on the Cone Cavity Contact Method using for measurement of compression fracture strength in guide line for ceramic femoral head for partial and total hip joint in United States FDA. An impact loading was applied with increasing a falling weight mass (M) or a falling height (H) so as increasing a suitable impact energy gradually from a low impact energy without impact fracture. In the first and second test, the same condition of impact energy shall be applied in order to ensure the fitness of a trunnion and a femoral head. The initial impact energy shall be not greater than 20J. The increment of impact energy per one impact shall be not greater than 10J. An impact energy is calculated from the following equation; E = H･M･g where E is the impact energy (J), H is the falling height (m), M is the mass of the falling weight (kg), and g is the gravity acceleration 9.8 (m/s2). A test shall be done repeatedly with increasing gradually impact energy until a fracture occurs in a test specimen. The impact energy at the test condition just before leading to a failure shall be the maximum impact resistance. Several round robin tests were conducted by three institutions for the specimens of alumina and zirconia heads. The results measured for the same specimens were not much difference among the all institutions, and it indicates the reproducible and effectiveness of this test method.

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WEAR OF LARGE CERAMIC BEARINGS Thomas Pandorf Ceramtec, Fabrikstr. 23-29, Plochingen, Germany 73207 Phone: 49 71536 11844 Fax: 49 71536 1116844 E-Mail: [email protected] Large diameter ceramic bearings are of increasing interest due the enlarged range of motion, enhanced stability of the artificial joints, and reduced risk of dislocations. Larger diameter hard on hard bearings may as well change the wear characteristics due to larger wear areas, different lubrication behaviour from changed diameter tolerances as known from Me-Me large bearings. But not only hard-on-hard bearings are of interest. With new low wear highly crosslinked polyethylenes, wear behavior of ceramic against XPE is of new interest. Three different wear studies were conducted: 1. Ce-Ce: Alumina matrix bearings of 36 mm, 40 mm and 44 mm with different diameter tolerances were tested according to DIN EN 14242. Roundness of ball head and insert as well as clearance of the bearing partners have been varied. 2. Ce-XPE: 36 mm bearings were compared to Me-XPE. Biological activity of the produced particles was inves-tigated. Ce-Ce: 36 mm diameter bearings in microseparation mode with two different ceramic materials were tested, one a pure alumina, the other an alumina matrix composite. The different wear studies show: 1. Large ceramic bearings have a very low wear rate. The influenced of the clearance on wear rate is negligible. 2. Using a ceramic ball head against highly crosslinked polyethylene reduces the wear rate by 50% compared to metal ball heads. Even in microseparation mode the wear volume is very low compared to other bearing materials. The wear volume is similar to previously performed microseparation wear studies of 28 mm bearings. The wear volume depends on the used combination of the two different bearing materials. The superior wear characteristics of large ceramic bearings was proven in all tribological test setups. The use of ceramics in a hip replacement will significally reduce the risk of osteolysis leading to an increase in the durability in the human body.

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IN-VIVO COMPARISON OF HIP MECHANICS FOR SUBJECTS IMPLANTED WITH A MIS OR TRADITIONAL SURGICAL TECHNIQUE- EXTENDED STUDY Glaser Diana a, Miner TMb, Komistek RD a, Mahfouz MRa, Dennis DAb, Lui Fa a University of Tennessee, Knoxville, TN, USA a Rocky Mountain Musculoskeletal Research Laboratory, Denver, Colorado Diana Glaser, 301 Perkins Hall, University of Tennessee, Knoxville, TN 37917 Email: [email protected], Phone: 865-974-1936, Fax: 865-946-1787 The minimally invasive surgery (MIS) becomes popular because of the potentially reduced soft tissue damage and the complimentary benefits, but its superiority over the traditional technique is a subject of continuing controversy. Most often reported advantages of MIS include shorter hospitalization and rehabilitation, improved cosmetic ap-pearance, less pain and risk of complications, decreased surgical time and blood loss. However, a comparison of separation as well as contact and muscle forces among different surgical approaches has not been examined yet but is useful in understanding THA performance. The present study is an extension to previously reported comparison of 3D in vivo kinetics of traditional and MIS THAs.1 This extended study includes additional subjects, subdivides MIS into different categories, controls for various parameters to reduce influence of marginal factors, and evalu-ates hip separation besides the kinetics. Fifteen subjects were evaluated under in vivo conditions using fluoroscopy while performing gait on a treadmill. Five subjects were implanted using a MIS anterolateral (AL), five using a MIS posterolateral (PL), and five with a traditional approach. All subjects received a cemented THA with similar femoral head diameter. Surgery was per-formed by a single incision, and subjects were matched for age, body mass index, and diagnosis to control for vari-ables possibly influencing performance and gait characteristics. The average post-operative follow-up duration at the time of analysis was 6.4 months (3-12), 4.7 months (3.5-4.5) and 3.7 months (2.3-6.5) for patients implanted using a standard, AL MIS and PL MIS approach, respectively and was not significant different (p>0.05). The pro-cedure for obtaining the kinematics and kinetics is identical to the previous report1. In vivo translational and rota-tional kinematics, derived from 3D-to-2D image registration technique, were input as temporal functions in a 3D inverse dynamics mathematical model to determine contact mechanics. The traditional subjects experienced significantly higher magnitude and incidence of hip separation than any of the MIS groups (p<0.05). The maximum peak force (MPF) of 4.1 times body weight (BW) was achieved by a tradi-tional study group patient, while the MPF for PL MIS and AL MIS study group patients were 3.3 and 3.6 BW, respectively. The average MPF for the traditional THA patients was 3.5 BW, while AL (p=0.03) and PL MIS (p=0.02) group achieved only 2.9 and 3.2 BW, respectively. There was also a significantly higher variance within the traditional THA subjects indicating more inconsistent results and a significantly longer hospitalization. No sig-nificant difference was observed between both MIS procedures. This is the first study to compare in-vivo weight-bearing kinematics, separation and kinetics for traditional, AL MIS and PL MIS subject groups. Our data indicated in all analyzed parameters differences between the MIS group and the traditional, with favorable results for the MIS subjects. This may be related, at least in part, to a reduction in disruption of supporting soft tissue structures. The force patterns were similar to those derived using telemetry.2 Randomized controlled testing with more patients as well as long-term follow-up studies will be required to defini-tively prove the MIS advance over the standard approach. [1] Glaser et al., 2006, ISTA Proceedings, New York City, p. 68. [2] Bergmann G. Hip98, 2001. J. Biomechanics, Vol. 34, No. 7, cd-rom attachment.

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MODIFIED “MINI-POSTERIOR” APPROACH FOR TOTAL HIP REPLACEMENT Moran, Michael C., Zhang, Holly Midland Orthopedic Associates, S.C., 2850 S. Wabash Ave., Suite 100, Chicago, Illinois, 60616, USA Phone: 312.842.4600 Fax 312.842.8690 Email: [email protected] This study was undertaken to assess the safety and efficacy of the Modified “Mini-Posterior” (MMP) approach, which includes preservation upper part of the posterior capsule, the piriformis tendon, and other structures that are released with the traditional “mini-posterior” approach. The MMP approach is performed with removal of a femo-ral neck segment without hip dislocation, followed by a step-wise exposure of the inferior acetabulum. Translation of the femur is minimized by systematic positioning of the femur during acetabular and femoral preparation. Newly designed instruments are used to facilitate the approach. Eighty-seven minimally invasive THRs were studied. Thirty-six hips underwent a traditional "mini-posterior" ap-proach. Fifty-one hips then underwent an MMP approach. Pain management protocols and physical therapy regi-mens were the same for each group. Clinical and radiographic evaluations were performed preoperatively and at six weeks, three months, and one year postoperatively. The mean surgical time was 62 minutes (range, 44-85 minutes) in the mini-posterior group and 65 minutes (range, 49-81 minutes) in the MMP group. No patients in either group donated autologous blood preoperatively and no patients in either group required perioperative blood transfusion. The mean time to ambulation without a cane in the “mini-posterior” group was 28 days (range, 14-88 days) and in the MMP group, 12 days (range, 4-42 days). Harris Hip Scores and SF-12 scores were higher in the MMP group at six weeks and at three months but not at the one-year evaluation. There were two complications in the mini-posterior group. These included one case of intraoperative fracture dur-ing broach impaction and one case of postoperative dislocation. There were two complications in the MMP group, including one case of sciatic nerve palsy possibly related to the difficulty of exposure with the MMP approach. The other complication in the MMP group was an intraoperative greater trochanteric fracture which was related to tension on the “tethered” greater trochanter by preserved soft tissue structures.. Radiographic assessment showed no statistically significant difference between the two groups in accuracy of acetabular or femoral component orientation. However, the MMP group showed better equalization of leg length, a finding attributed to greater preservation of soft tissue attachments in the MMP group. The speed of functional recovery in the MMP group was clearly faster and occasionally startling. However, the MMP approach may be associated with an increased potential for sciatic nerve palsy and greater trochanteric frac-ture. The MMP approach is technically demanding and requires adherence to specific steps to be performed safely. NOTE: The podium presentation of this paper will include 3D computer animation of the surgical procedure in addition to intraoperative video.

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PERCUTANEOUSLY ASSISTED TOTAL HIP ARTHROPLASTY (PATH): A LESS INVASIVE TECHNIQUE Author: W. Seth Bolling, Michele Riley, Jason Snibbe 120 South Spalding Drive #400, Beverly Hills, CA 90212 Phone: 310-860-3470 Fax: 310-659-2724 E-Mail: [email protected] Introduction: We have developed and evaluated a new posterior approach for less invasive total hip arthroplasty. Tendon attach-ments are preserved, while maintaining excellent visualization and access. This paper will describe the technique and present clinical results. Methods: The first 250 patients were followed prospectively for a minimum of 2 years. The new technique requires release of only piriformis or conjoined tendon. Specially designed retractors, cup holder/alignment guide, and reamer driver are used. Acetabular reaming and impaction are carried out through a distally placed 1cm “portal.” Acetabular reamers are powered by the very low profile 8mm drive shaft to preserve visualization and control. Careful, selective reaming is then accomplished by “steering” the femur. Results: Mean incision length was 8.3 cm. Harris Hip scores improved from 48.9 preoperatively to 95.5 postoperatively. EBL averaged 227 cc per hip with an 8% transfusion rate. Component positioning was within recommended pa-rameters in 96% of patients. There were no dislocations, nerve injuries, or wound problems. Hospital stay aver-aged three days. Discussion: Compared to reported MIS THA results, the new tissue-preserving PATH technique provided better results with a shorter hospital stay, less bleeding, and fewer transfusions. Our clinical and radiographic results are comparable to those reported for traditional THA techniques, but with fewer complications. We have found no increased risk of component malposition, dislocation, or other adverse effects. Also, we believe this technique has a shorter learn-ing curve than previously described techniques for less invasive THA.

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LEARNING CURVE IN MINIMALLY INVASIVE APPROACHES IN THA: COMPARISON BETWEEN LATERAL MINI INCISION, MINIMALLY INVASIVE ANTERIOR APPROACH AND MINIMALLY INVASIVE ANTERO LATERAL APPROACH Speranza Attilio, Iorio Raffaele, In gallina Antonello, D’Arrigo Carmelo, Ferretti Andrea Via F. Marchetti 19, 00199 Roma (RM) Italy; +393391980755 E-Mail: [email protected] Orthopaedic Unit, S. Andrea Hospital University “La Sapienza” Rome, Italy E-Mail: a.speranza753virgilio.it Introduction: In the last few years minimally invasive surgery in hip replacement is becoming more popular among orthopaedic surgeons because of less morbidity and faster rehabilitation. However several complications have been reported especially in the so called “learning curve” (first twenty cases). The purpose of this study is to evaluate the learning curve of three different minimally invasive approaches. Methods and Materials: In this study three different surgical approaches of THA were evaluated: lateral mini incision (Group A), mini-mally invasive anterior approach (Group B) and minimally invasive antero lateral approach (Group C). The first twenty cases of each surgical approach were elected and compared with a control group (Group D) of 149 total hip replacement operated using a lateral standard approach (> 12 cm) in the same period by the same experienced surgeon. In all cases a specialized dedicated surgical instrumentation was used. Inclusion criteria to enter the study group ( A-B-C Groups) were: BMI< 30, diagnosis of primary osteoarthritis, age< 75 years. The following parameters were evaluated: intra and post operative complications, total blood loss ( calculated ac-cording to Rosencher method ), time of surgery, component placement, length of hospital stay and functional out-comes (HHS, WOMAC) at six weeks. Results: No dislocations, infections and early aseptic loosening were detected in groups A, B and C. No significant differ-ences were detected regarding the length of hospital stay in all groups . In group B the time of surgery was signifi-cantly higher than in group D. The total blood loss of group A, B and C was statistically lower than group D. Clini-cal outcomes at six weeks in groups B and C were significantly better that in group A and D. The following complications were detected: Group A: two sciatic nerve palsy (one transient and one permanent), one greater trochanter fracture, one femoral stem malposition. Group B: one greater trochanter fracture, one proximal femoral fracture (crack) , one rupture of tensor fasciae latae , two haematomas. Group C: no complications were detected. In control group D (149 patients) the following complications were observed: one proximal femoral fracture, one case of cup malposition ( in a severe case of dysplasia) and one infection. Conclusions: The main advantages of all MIS approaches seem to be the reduced total blood loss, even in the learning curve. However during learning curve the minimally invasive approaches seem to have a higher rate of complications than the standard procedures even in selected patients. In muscle sparing approaches (anterior and antero lateral ) the early functional outcomes are better than other approaches ( standard and mini incision). Among the evaluated minimally invasive procedures, the antero lateral approach seems to be safer and less demanding than others.

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VALIDATION OF AN IMAGELESS COMPUTER NAVIGATION SYSTEM FOR ACETABU-LAR CUP PLACEMENT IN THA Author: William L. Bargar, M.D. Sutter Institute for Medical Research 1020 29th St. #450, Sacramento, CA 95816 Phone: 916-453-5844 Fax: 916-733-8259 E-Mail: [email protected] Imageless computer-assisted navigation systems have emerged in an effort to more accurately position the acetabu-lar component in total hip arthoplasty. These systems, with real-time adjustments for pelvic position changes, have been speculated to improve cup position and reduce positional outliers. The accuracy of these systems has not fully been validated. Purpose: The current study compares values of operative inclination and operative anteversion of acetabular cup position acquired by an imageless navigation system to post-operative pelvic CT scan measurements of inclination and anteversion in an attempt to identify the error of an imageless navigation system and validate its accuracy. Methods: Twenty-five patients (26 hips) with a mean BMI of 26.1 underwent total hip arthroplasty with the use of an image-less computer navigation system for the placement of the acetabular cup. Post-operative CT scans were obtained for all patients. 3D models of each patient’s pelvis and acetabular component were created and operative inclina-tion and anteversion determined. Results: Intra-operative computer navigation values for operative inclination and operative anteversion were 38.8º±3.5º and 32.2º±6.8º, respectively. CT scan values for operative inclination and operative anteversion were 39.4º±4.0º and 32.6º±7.0º, respectively. The mean absolute value difference between the intra-operative computer navigation values and CT scan values for each patient for operative inclination and operative anteversion were 1.8º±1.2º and 2.0º±2.0º, respectively. Bland-Altman and standard deviation analysis indicate comparable values given by each measurement technique. With 95% confidence, the CT scan values are no greater than 2.3º and 2.7º of the ob-served CAS values of inclination and anteversion, respectively. Conclusions: An imageless computer navigation system can provide real-time determination of the acetabular cup position with good accuracy in a non-obese patient population undergoing primary total hip arthroplasty.

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VALIDATION WITH ROBOTICS OF DOCUMENTATION AND ANALYSIS OF SURGICAL SKILLS THROUGH REAL-TIME MOTION RECORDING OF NAVIGATED ARTHRO-PLASTY INSTRUMENTS Barrera O. Andres; Garvin, Kevin. L.; Gilmore, Alisa N and Haider, Hani Department of Orthopaedic Surgery and Rehabilitation, University of Nebraska Medical Center, 985360 Nebraska Medical Center - Scott Technology Center, Omaha, NE 68198-5360, USA Phone : (402) 559 5607 – Fax : (402) 559 2575 – E-mail : [email protected] Formal assessment of surgical skills and analysis of critical-paths are not widely used in orthopaedics partly due to the lack of objective quantification, reliability, and sensitivity of existing methods. Current surgical skill assess-ment methods also require additional instrumentation, cost and time. Such problems can be overcome by a novel method recently introduced to record the motion of arthroplasty surgical instrumentation for documentation, surgi-cal-skill assessment, and safety analysis. This method uses an existing computer-aided-orthopedic-surgery (CAOS) navigation system without compromising its functions of real-time tracking, rendering, or simulations. The stored data allow playback to view realistic 3D simulations of the complete bone cutting/refining process. This study aimed at validating the system/methodology and its sensitivity using an articulated robotic arm as a reli-able actuator of a surgical instrument with controlled paths, to see how well its motion characteristics are captured and analysed. Software was incorporated into a customized CAOS-navigation system to log dynamic position/orientation of in-struments and bones. An oscillating saw (equipped with reference-frames for infrared-tracking) was fixed at the end-effector of a Kuka-KR-15 robot. Well-defined sequences of movements were programmed for the robot, simu-lating the starting of a TKR femoral distal cut. Known errors were deliberately programmed-in; the saw was placed +/-100mm away from the intended plane to be cut, and tilted +/-30º in roll and pitch. The sequence was repeated at different speeds while the CAOS system logged data. Simultaneously the robot recorded the coordi-nates from its encoders. The data was used to compute errors in distance from the cutting instrument to the plane to be cut D(mm), and to compute pitch P(º) and roll R(º). Linear/angular speeds and accelerations of the saw, and length (L) of the whole path were also computed. Different sampling rates for the robot (T=48.0ms) and CAOS (T=66.7ms) necessitated data synchronization before cross-correlation and statistical analysis were carried out (using MatLab). Signal correlation (robot vs. CAOS) for linear positional offset (D), Pitch (P), and Roll (R) was >0.96 for all cases. Average offset (c) and gain (m) values for D were m=1.01, c=0.35mm, for Pitch m=0.99, c=0.01º and for Roll m=0.99, c=0.08º. Trajectory (L) was 5% longer for CAOS with average L=491mm. Noisier signals resulted from CAOS than the robot, and its fluctuations caused the extra length. Low-pass filtering of the CAOS signal did not significantly improve the D correlation, but those of speed and acceleration increased by one and two orders of magnitude respectively, while the L difference dropped to 0.07%. The very high correlations (≈1), very low offsets (≈0), and almost unitary gain throughout validated the acquisition and analysis system as a measurement device. The 0.35mm offset for D signals pointed to registration errors in either the CAOS or the robot, and indeed these were later traced to the former. Beyond documentation and analysis of surgical skills, such data can be used for training and optimization of surgical plans, bone-cutting approaches, and as teaching input for robotics in orthopaedics. Experimental trials on different surgeons are the next step to characterize bone-cutting skills for arthroplasty.

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ESTIMATION OF SOFT TISSUE THICKNESS IN IMAGELESS NAVIGATION OF CUP ORIENTATION IN THA Ko, Byung-Hoon., Park, Suk-Hoon., *Hwang, Deuk Soo., Yoon, Yong-San Department of Mechanical Engineering, KAIST, South Korea Daejeon, 305-701 * Medical School Orthopedic Department, Chungnam National University, South Korea. Daejeon, 301-721 TEL :+82-42-869-3022, FAX :+82-42-869-3210, E-mail:[email protected]

When using an imageless navigation system for THA, it is difficult to accurately measure the anatomical land-marks of the pelvis for determining the anterior pelvic plane (APP). The measured APP is commonly used to de-fine the acetabular cup orientation. However, there is difference between the measured and actual APP due to the measurement error by the unknown thickness of soft tissue at the anatomical landmarks, especially at the pubic symphysis. The misinterpretation in cup angles when using wrong pelvic reference plane can be substantial, par-ticularly for anteversion. The object of this work is to establish the estimation formula for the unknown soft tissue from the statistical analysis of the patients’ B.M.I. and indentation depth.

In our study, the linear relation between the soft tissue thickness and patient’s physical parameters (BMI, indenta-tion displacement) was found. The proposed method was applied to the shape of probe tip for measuring anatomi-cal landmarks using imageless navigation systems. The actual thickness of soft tissue was measured using a port-able ultrasound imaging system (SONOACE PICO®, Medison) and linear probe (HL5-9ED®, MEDISON) for 25 volunteers in supine positions. In order to obtain the indentation depth of the soft tissue on the pubic bone, 3D po-sition measurement device (MicroScribe, IMMERSION Inc.) was used. The diameter of the flat ended tip was 6mm. Simultaneously, the compressive force was measured with a S-beam load cell (BONGSHIN LOAD-CELL®) during sounding. In addition, the positions of both ASIS and the center of the pubic bone were measured to obtain the distances between both ASIS points and the pubic bone. A multiple regression analysis was used to estimate the thickness the soft tissue (p< 0.05).

The estimation Equation for the unknown soft tissue thickness can be expressed in terms of BMI and displacement:

Y= Y(mm): soft tissue thickness under minimum force (0 ~ 0.5N)

: body mass index (mm): displacement under maximal force (20 ~ 25N) The mean error between the thickness, as estimated by the linear equation, and by the ultrasound image was less than 0.2 ± 4 mm. When the cup inclination is 40° and anteversion is 15°, before correcting the soft tissue thickness, the rotational error of APP results in -7.85° ± 3.2° in the cup anteversion. By using the estimation formula, the cup orientation error was significantly decreased to -0.09° ± 1.96° in anteversion and -0.05° ± 0.49° in abduction (p < 0.05). The misinterpretation of acetabular cup angles increases with the rotational error of the pelvic reference frame. The difference between the ideal and measured plane affect the rotational error of the reference frame. With the pro-posed estimation equation, it is possible to reduce the error in the anteversion that occurs as a result of the differ-ence between the actual and measured pelvic plane.

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NAVIGATION IN HIP RESURFACING: REPORT OF INITIAL RESULTS

Author: Michael L. Swank, Leslie L. Korbee Cincinnati Orthopaedic Research Institute E-Mail: [email protected] Introduction: Use of the Birmingham Hip Resurfacing implant system was approved in the United States by the FDA in May of 2006. A com-puter assisted surgery (CAS) software program has been developed to enable navigation of the hip resurfacing procedure, primarily the placement of the pin which secures the hip resurfacing implant into the femoral head. That software is the BrainLAB Vector Vision Hip SR package. The goal of navigation in hip resurfacing is to overcome some of the challenges associated with conven-tional hip resurfacing and improve patient outcomes by preventing femoral neck notching. With the BrainLAB Vector Vision Hip SR software package, the surgeon uses a pre-calibrated CAS drill guide to navigate the cen-tral pin directly to the planned position with millimeter precision. The software provides the surgeon with real-time risk information, warning the surgeon if the implant position does not correspond to the treatment plan. The optimal position of the head implant can be easily defined by controlling in varus/valgus position and depth of the femur component in real-time. The purpose of this study is to use the BrainLAB Vector Vision Hip SR software in conjunction with the Birmingham Hip Resurfac-ing implant and to then evaluate the final position of the implant post operatively along with patient outcomes. Method: All patients undergoing hip resurfacing procedure with the Birmingham Hip Resurfacing implant system were enrolled prospec-tively. To date twenty one resurfacing patients have been evaluated. Data has been collected on preoperative planning of the stem shaft angles, and the intro-operative report of these angles along with the post operative data from navigation and from post opera-tive imaging. The preliminary outcome of the patients enrolled in the trial has been recorded and analyzed including skin to skin time, anesthesia time, blood loss, post operative complications, length of stay and mortality and morbidity. These measures were compared to thirty-seven age matched controls undergoing navigated total hip replacement surgery. Subjects were excluded from the study if they failed to meet any of these criteria: poor quality of bone stock to support the implant; age greater than 60; anatmic abnormalities of the femoral head that would inhibit placement of the femoral resurfacing component; any routine contraindication to total hip replacement surgery, including but not limited to active infection, heart failure, lung failure, or severe untreated bleeding abnormalities, untreated anemia, or pregnancy. Data was collected from the subject’s hospital medical record concerning blood loss, operative time, operative mortality, length of stay and morbidity. Results: The results revealed that the resurfacing group and the primary total hip replacement groups had identical lengths of stay with 2.0 days. Both groups also had 100% discharge to home, had no transfusions, and no major complications. Analysis of the stem shaft angles comparing the data from computer screenshot to the post operative film revealed that there was a mean difference of 6 de-grees from final computer screenshot to post operative x-rays. The variability of measurement error on film images is approximately 5 degrees. A summary of the other clinical results are: mean skin to skin time for resurfacing cases = 110 minutes vs. 77 minutes for primary total hips in this initial series; mean anesthesia time for resurfacing cases = 155 minutes vs. 115 minutes for primary total hips; mean surgical blood loss for resurfacing cases was 438 cc’s vs. 284 cc’s for primary total hips. Discussion: The comparison of the neck shaft angles from the intra-operative measurements vs the post-operative films confirmed that the final verification from the navigation software corresponded well to the radiographic data. The variance between the planned neck shaft angle and the final date from x-ray was only 1-2 degrees with all components in valgus placement with no femoral notching. With these results, it appears that there is a tendency to increase the post operative valgus of the stem component which could reflect a deficiency on post operative femoral rotation capture on radiographs compared to intra-operative nevigation data from computer screenshots. Of note is that there was no increased varus observed in the component placement. Component placements for all cases are within safe parameters and variances from plan are within the error inherent with radiographic measurements. Preliminary clinical outcomes were comparable to those for age-matched primary total hip patients. However, there was increased skin to skin and anesthesia time of 30-40 minutes, which may be due to the learning curve for this initial series of cases. From this preliminary data, it appears that navigation in hip resurfacing offers the surgeon necessary information for optimizing placement of the resurfacing stem. In this initial series the early clinical outcomes were compared to those observed with primary total hip replacement. References: 1. Barrett AR, Davies BL, Gomes MP, Harris SJ, Henckel J, Jakopec M, Rodriquez v Baena FM, Cobb JP. Preoperative planning

and intraoperative guidance for accurate computer-assisted minimally invasive hip resurfacing surgery. Proc Inst Mech Eng{H} 2006; 220 (7): 759-73.

2. Hess T, Gampe T, Kottgen C, Szawlowski B, Intraoperative navigation for hip resurfacing. Methods and first results. Or-thopade. 2004 Oct;33(10):1183-93.

3. Allison C. Minimally invasive hip resurfacing. Issues Emerg Health Technol.2005 Mar;(65):1-4.

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IS LEWINNEK’S PLANE A RELIABLE REFERENCE FOR HIP NAVIGATION?

TABUTIN Jacques, PINOIT Yannick, MIGAUD Henri, LAFFARGUE Philippe, PUGET Jean CH Cannes – 15 avenue des Broussailles – 06401 CANNES Cedex 01 0033 4 93 69 71 30 / 0033 4 92 18 67 30 / [email protected] The anterior pelvic plane (APP : defined by the antero superior iliac spines and the pubic symphysis) is generally considered as the vertical plane. Is this true? Does its orientation vary between upright and recumbent position ? Does it vary after THA? Is there a relation with pelvic version? Materiel and Methods: Strict lateral X-Rays views were done in 106 standing patients : 82 THA without hip or knee flexion contracture (40 having sustained a dislocation), 24 without any joint pathology : these last patients have had there radiographs done first standing then lying flat. Moreover 19 stable prostheses had X-Rays before and after the THA. Were measured: the angle between vertical and anterior pelvic planes (positive if cranially open), the angle between the vertical axis and the pelvic axis (from center of S1 to center of femoral heads) : pelvic version.

Results:

Neither sex (1.7° +/- 6 for men 1.5° +/- 5.9 for women) nor age had any influence on the orientation of Lewinnek’s plane or on the pelvic version. The anterior pelvic plane was not vertical in 38% of cases (+/- 5°). There was no significant difference between the groups of patients as for the orientation of the APP : 2.9 +/- 5.7° for the THA, 1.2 +/- 5.2° for healthy patients and the same was observed in the total hip groups : 3.5 +/- 5.8° in the dislocation group 2.3 +/- 5.5° in the stable group. In standing patients pelvic version varied more widely (14 +/- 9.2 ; -9 to + 31) than orientation of APP (2.3 +/- 5.8° ; - 18 to + 18) refering to vertical. In the 24 healthy subjects the change from standing to lying significantly (p = 0,0002) influenced APP orientation : from 1.2 to 2.25°, with wide varia-tions (-10 to + 12). In the 19 patients with pre and post X- Rays the THA did not significantly influence APP orien-tation (-1° +/- 7) but it varied by more than 5° for 7 patients.

Discussion: Orientation of the APP is not dependent on sex or age. APP orientation varies less than pelvic version but it does not reflect well modifications induced by pelvic morphology. Navigation systems seem to improve the control of cup inclination but the same is not true for anteversion, especially when guidance relies on the APP. In 38% of cases this reference is not reliable, and even transcutaneous palpation of the bony landmarks is an added source of error. Considering the APP as vertical in upright position may induce an error of about 10° (half the anatomical anteversion). Moreover the APP orientation varies from orthostatism to clinostatism. This is generally not taken into account and may lead to impingement or dislocation. Conclusion: The APP does not seem quite reliable as a reference plan in the upright position. Lateral decubitus and draping for the operation alter considerably the precision. A more functional, kinematics based navigation might be a solution.

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REDUCTION OF ROBOT MILLING TIME EXPLOITING INHOMOGENEOS BONE PROPERTY IN THA Park, Suk-Hoon., Kim, Nam-Jung., Shin, Hyun-Joon., Yoon, Yong-San. Department of Mechanical Engineering, KAIST, Daejeon, 305-701, South Korea TEL : +82-42-869-3022, FAX : +82-42-869-3210, E-mail : [email protected]

Total hip arthroplasty is one of the most successful operations in orthopedic surgery. However, post-surgical re-sults depend largely on the surgeon’s skill. For the more accurate shaping of the femur as well as the alignment of the inserted stem, many surgical robots for THA have been developed and commercialized. The most popular ro-bot system for THA is ROBODOC. This surgery robot showed improved results in terms of the error in the orien-tation and in the fit of the implant. However, additional surgical procedures are required with the systems, as it uses a CT image for the registration. Moreover, the surgical system needs a large exposure to fix the femur. To alleviate this problem, we developed a compact robot system known as ARTHROBOT. This system uses a block-gage-based registration; therefore, CT/MRI images are not needed. However, this robot is fixed to the femur with specially designed bone clamp and needs a large incision for the bone clamp. Thus we developed a second version to reduce the incision size; a robot system that is fixed into the femoral cavity was designed. The performance was acceptable with the plastic model bones. However, the time required for the milling with this system is a little bit too long. In this study, an adaptive control method is suggested to reduce the time that is needed for shaping the femur with the milling robot. The femur is composed of different property bone, cortical bone and cancellous bone. If the ro-bot cut hard part of the bone with high speed, the shaped canal became inaccurate because of the tool vibration. However, when the robot cut relatively soft bone with high velocity, accurate cut is possible. In the suggested adaptive control method, the force at the milling tool tip is measured to monitor the bone hardness and the tool transfer rate is changed accordingly, a single axis force sensor was attached between the milling tool and the robot. The suggested method was incorporated into our robot and validated. The machining time were compared between the constant tool feed rate and actively controlled tool feed rate using plastic model bones(SAWBONES®, USA) and fresh bovine bones. Average shaping time was decreased from 760±20 seconds to 250±20 seconds with the

plastic bones and from 450±20 seconds to 170±40 seconds with the bovine femurs. It was possible to reduce the machining time to one third using the robot in THA by the adaptive control using the force measurement at the tool. We are further studying on the more efficient control algorithm considering the heat damage by the high speed milling tool.

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NAVIGATED CONTROL OF THE CUP ORIENTATION DURING TOTAL HIP REPLACEMENT JENNY Jean-Yves, DOSCH Jean-Claude, BOERI Cyril, USCATU Marius Hôpitaux Universitaires de Strasbourg, Centre de Chirurgie Orthopédique et de la Main, 10 avenue Baumann, F-67400 Illkirch-Graffenstaden (France) Tel +33388552145, Fax +33388552146, E-mail [email protected] INTRODUCTION: Positioning of the cup of a total hip replacement (THR) is considered critical for the short and long term results of the procedure. The precise recording of the position of the pelvis is a prerequisite during this procedure to get a confident reference for cup orientation. It has been demonstrated that the conventional, non navigated measure-ments are less than optimal. CT based navigation systems have been demonstrated to improve the accuracy of the recording of the pelvic position. Non image based navigation system might allow the same accuracy at lower costs.

The anterior pelvic plane (Lewinnek) is an accepted reference to determine the 3D pelvic orientation. We designed this study to validate the accuracy of a non image based navigation system for cup orientation during total hip re-placement according to the Lewinnek plane, with post-operative 3D CT-scan analysis. MATERIAL AND METHODS: 50 cases of navigated total hip replacement have been analysed. Navigation was performed with the OrthoPilot ® system (Aesculap, Tuttlingen, FRG), a non image based system. A localizer was implanted on a screw on the ante-rior iliac crest. Three relevant landmarks (both antero-superior iliac spines and pubis) were palpated with a navi-gated stylus, defining the anterior pelvic plane (Lewinnek plane). Acetabular preparation and cup implantation were performed under navigation control. Safe zone for acetabular implantation was defined pre-operatively : 40 to 50° of abduction, 10 to 20° of flexion in comparision to the anterior pelvic plane. The final orientation of the cup was registered intra-operatively by the navigation system, and compared to the 3D CT-scan measurement of the cup positioning with the same reference frame. RESULTS: 2 CT-scan were considered unreliable for cup orientation, and consequently 48 cases were analyzed. There was no significant difference between the intra-operative (42° ± 4°, range: 35 to 49°) and post-operative (44° ± 5°, range: 30 to 57°) measurements of the cup abduction. The mean paired difference was 2°: this difference was significant (p<0.05), but of little clinical significance. 41 cases /48 (85%) showed a difference less than 5°. 42 cases /48 (87%) were considered within the safe zone of abduction.

There was no significant difference between the intra-operative (15° ± 3°, range: 6 to 22°) and post-operative (19° ± 7°, range: 2 to 32°) measurements of the cup flexion. The mean paired difference was 4°: this difference was significant (p<0.05), but of little clinical significance. 28 cases /48 (58%) showed a difference less than 5°. 38 cases /48 (79%) were considered within the safe zone of abduction.

When considering both criteria together, 35 cases /48 (73%) were considered in the safe zone for both cup abduc-tion and flexion. DISCUSSION: The navigation system used allowed an accurate positioning of the cup in abduction. The flexion positioning was less accurate, but the differences observed (mainly less than 5°) are probably clinically irrelevant. Furthermore, the accuracy was higher than that observed with conventional, manual implantation. CONCLUSION: The navigation system used allows improving the accuracy of cup placement in comparison to conventional, man-ual techniques.

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COMPUTER-ASSISTED "FINE TUNING" SURVIVORSHIP ANALYSIS WITH THE ORTHOWAVE SOFTWARE IN HIP ARTHROPLASTY EPINETTE Jean-Alain, CRDA, 21 résidence Voltaire, 62700 Bruay LaBuissière,France Tel: 33321531949, Fax: 33321531961; e-mail: [email protected]

Evaluation of clinical performance in Joint Arthroplasty is essential in the long run. The use of Kaplan-Meier based cumulative survival rates can be seen as the most convenient tool for assessing long term results. Un-fortunately, this survivorship analysis is too often used as a rough method while displaying figures that concern only retrieval as endpoint, including as potential bias either non implant-related causes or not revised obvious fail-ures. The OrthoWave™ outcome study software (ARIA, France), beside usual clinical and radiologic assessments, has been designed to "fine tune" the cumulative survival curves with various selections of end points, providing survival rates that can differ tremendously depending on what needs to be specifically analysed.

Naturally OrthoWave™ allows for "classical" survival analyses, with either retrieval due to any cause, or

implant-related failures as end points, for the two components as a whole or separately for each of them, in the entire population or selected groups or subgroups, with confidence intervals and available comparisons between two cohorts including statistical tests.

However, any "retrieval" rate or even "failure" rate cannot sum up all questions related to a given clinical

series. (1) A patient would like to anticipate the outcome of his surgery, and would be interested in the expected "reoperation" rate that means for him the need for undergoing another potential surgery. (2) Governments or third party payers would take care of the "revision" rate that illustrates the global success or not of any primary hip re-placement, whatever the cause of revision, be it implant-related or not. (3) Conversely, surgeons are mostly inter-ested while fitting any implant in the "implant-related" failure rate of this particular implant. (4) Finally, whilst trying to compare as an example the fixation provided by HA-coated implants versus cemented ones, surgeons will take into account only mechanical loosening. OrthoWave™ allows on real time to get all these various analyses, through a specific "chain" of serial questions answered during the collection of data, i.e. reoperation with or with-out revision, due to an implant failure or not, this implant failure being or not related to a mechanical loosening. Additionally, the program allows for customizing any other specific endpoint, such as a pain that becomes "severe" or any osteolysis occurring post-operatively.

Based upon a series of 2,972 primary HA-coated hip implants at 20-year of maximal follow-up, prospec-

tively analyzed with the OrthoWave™ software, various cumulative survival curves have been displayed and al-lowed for a complete and deepened study, with final rates widely extended from 81,67% up to 98,46%, yet upon the same group of patients. Obviously, survivorship analysis looks like Aesop's tongue, and surely can afford the best and the worst about reliability in report of clinical results. It is critical to ask the right question to get the ap-propriate answer in any case. Modern computerized tools must give the availability to "fine tune" these various survival curves with appropriate selection of endpoints, and selection of criteria, so as to obtain powerful, versatile and reliable means for assessing long term clinical outcomes in Arthroplasty.


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“HAP” PAUL AWARD PAPER

In Vitro Performance of Silicon Nitride Ceramic in Total Hip Bearings

B. Sonny Bal, MD1, R. Lakshminarayanan, PhD,2 Ashok Khandkar, PhD,2 Aaron A. Hoffman, MD,3 and Mo-hamed N. Rahaman4

1Department of Orthopaedic Surgery, University of Missouri-Columbia

2Amedica Corporation, Salt Lake City, Utah

3School of Medicine, University of Utah, Salt Lake City, Utah

4Department of Materials Science and Engineering, University of Missouri-Rolla

Acknowledgement: This work was supported by a Phase 1 NIH-SBIR Program grant titled: Composite Metal –Ceramic Bearings for THA Implants, Grant # R44-AR45517-01 Address correspondence to: B. Sonny Bal, MD, MBA Department of Orthopaedic Surgery University of Missouri MC213, DC053.00 One Hospital Drive Columbia, Missouri 65212 Tel: 573-882-6762 Fax: 573-882-1760 Email: [email protected]

Abstract

Silicon nitride is a ceramic material used in industrial applications. We hypothesized that this ceramic

material would be suitable for THA bearings; prototype femoral heads and acetabular inserts were fabricated by

sintering, followed by hot isostatic pressing of the raw ceramic particles. The resulting ceramic composite had a

flexural strength of 950 ± X MPa, Weibull modulus of 19, and fracture toughness of 9.6 ± X MPa.m1/2. Aging of

this material for 100 hours at 122°C (250°F) had no measurable impact on the flexural strength. When tested in a

hip simulator against Si3N4 or cobalt–chromium femoral heads, Si3N4 cups produced low wear rates that were com-

parable to alumina-alumina couplings. We conclude that Si3N4 ceramic may offer novel articulations in total hip

arthroplasty, such as those between CoCr femoral heads and ceramic acetabular inserts.


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THE EXETER TOTAL HIP PROSTHESIS IN PATIENTS UNDER 40 YEARS AT 2 TO 12 YEARS AFTER SURGERY Authors: Schreurs BW, DJC de Kam, R Klarenbeek, JWM Gardeniers Department of Orthopedics Radboud University Nijmegen Medical Centre P.O. Box 9101 6500 HB Nijmegen The Netherlands mail adress [email protected] tel 31-24-3613918 fax 31 24 3540230 Introduction: Total hip arthroplasties (THA) in younger patients are associated with high failure rates. Since 1994 we implant the Exeter cemented prosthesis, in case of acetabular bone loss reconstructions with bone impaction grafting (BIG) and cemented cup are done. The purpose of this study was to evaluate the outcome the primary cemented Exeter prosthesis in patients younger than 40 years. Methods: Between 1994 and 2005 we performed consecutive 104 THA in 78 patients with a mean follow-up of 6.2 years (2-12 years), none was lost to follow-up. The mean age at surgery was 31 years (16-40 years). Acetabular BIG was used in 54 cases (52%). HHS, medical files and radiographs were analyzed. Results: 3 patients died during FU (4 THAs). 11 revisions were performed: 5 aseptic cup loosenings, 3 septic loosenings and 3 because of recurrent luxations (revision of 2 heads and 1 cup). Only 1 case of the 54 acetabular BIG had aseptic cup loosening. The mean HHS was 89 (46-100). Using Kaplan-Meier analysis, cumulative survival with endpoint revision for any reason was 87,2% (95%C.I. 77,7-92,9%) at 7 years. Survival with endpoint aseptic loosening of the cup was 94,0% (95%C.I. 85,9â€“97,5%) at 7 years; there were no revisions for aseptic stem loosenings. Conclusions: Primary THA with the Exeter prosthesis in younger patients show promising mid-term results. The use of BIG in reconstruction of acetabular defects appears to be an excellent treatment.

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ASSESSING AGREEMENT BETWEEN CLINICAL AND SOFTWARE-ASSESSED HIP RANGE OF MOTION Authors: Evan Baird BS; Jonathan Zelken BA; Joseph Lipman MPH; Luis Moya MD; Robert Buly MD

Hospital for Special Surgery 535 East 70th Street New York, NY 10021 Femoroacetabular impingement is a major contributor to osteoarthritis and surgical techniques to man-age it are forthcoming. Despite advances, no objective means of quantifying the degree of impingement has been reported. Eleven patients with FAI who had preoperative pelvic CT scans were evaluated clinically via visual as-sessment and electronically via 3D-modeling software using a novel technique that is inexpensive, read-ily available to the public, and noninvasive. Clinical estimations of hip motion were compared to elec-tronic predictions using this technique. There was not a difference between clinical estimations and electronic predictions of hip flexion (p=0.67). There was a difference in the other components of the hip impingement test, including adduction (p<0.05), internal rotation (p<0.05) and external rotation (p<0.05). These differences may have been attributable to the effect of outliers on a small sample size.

While obstacles exist, there is promise for this technique as a non-invasive adjunct to physical examination.

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AN ALGORITM FOR THE SURGICAL TREATMENT OF CONGENITAL HIP DYSPLASIA IN ADULTS Binazzi R., Bondi A ., Manca A. ISTITUTO ORTOPEDICO GALEAZZI 20161 MILAN - ITALY +39-02.6621.4839 (fax –4770) [email protected] Congenital Hip Dysplasia in Northern Italy is a fairly common condition (4.5%). In these cases, Total Hip Re-placement for degenerative arthritis can be technically difficult. In fact, the Hip anatomy can be severely altered and components placement (especially the cup) is always complicated.

In the last 20 years, in dysplastic cases we have used the following protocol: 1) in CROWE Grade I and II we per-form a single-stage THR in a routine manner; the cup has to be medialised reaming the posterior acetabular wall 2) in CROWE Grade III we perform a single-stage operation, sometimes with intra-operative “wake-up” test to control Sciatic Nerve function; 3) in CROWE Grade IV we use an original two-stage procedure with progressive lowering of femoral epiphysis followed by THR. The first stage consists in a fascio-mio-arthrolysis (Adductor’s tenotomy, gluteal fasciotomy, Psoas’ Z-lengthening, capsulectomy, femoral head resection) and application of an External Fixator (3 pins in the Ileus and 3 in the Femur). Then we start a progressive lowering of the femoral epiphysis (about 1.5-2 mm/day) until the femoral neck is in the right position to allow a THR (usually after 2-3 weeks). We have used this technique in 15 cases (9 females and 4 males, 1 bilateral). The average limb lengthening was 6.1 cm. In all cases the cup was placed in the paleo-acetabulum and we have always used a straight, cement-less, conical stem (in order to be able to correct neck anteversion) with metal-on-metal articulation. Average FU was 7.1 years. Lateral grafting was required in 3 cases (20%). Overall primary type components were utilized in all cases but one (93%).

Satisfactory results were obtained in 11 cases (73%).

No nerve palsies and no pin site infection were seen. One dislocation occurred treated conservatively. One cup needed revision for loosening. No femoral component was revised.

THA in CDH arthritis is more difficult and requires particular experience of the Surgeon in order to get good re-sults. Crowe IV requires placing the cup in the anatomic position, which creates significant technical issues with respect to the femur. Femoral shortening osteotomy is the current standard, but this approach is complicated and requires revision type femoral components. The two-stage technique described here minimizes the technical chal-lenges of this surgery and facilitates the use of primary hip components.

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PREARTHROTIC PATHOMORPHOLOGIC ALTERATIONS OF THE HIP JOINT PREDICT-ING SUBSEQUENT OSTEOARTHRITIS Ecker, Timo M.; Tannast, Moritz; Puls, Marc; Siebenrock, Klaus-A. and Murphy, Stephen B. Center for Computer Assisted and Reconstructive Surgery New England Baptist Bone and Joint Institute 125 Parker Hill Avenue Suite 545 Boston, MA 02120 Phone: 617-232-3040 Fax: 617-754-6436 e-mail: [email protected] Osteoarthrosis of the hip frequently occurs in the absence of osteoarthrosis of other large joints suggesting there are morphologic factors specific to the hip leading to its destruction. While developmental dysplasia, Perthes dis-ease or slipped capital femoral epiphysis are recognized causes of secondary osteoarthrosis, a large number of ar-thritic hips cannot be categorized and are diagnosed with osteoarthritis of unknown etiology. Recently, femoro-acetabular impingement ahs been accepted to cause hip arthrosis. Many authors subsequently have proposed that relief of FAI may delay or prevent the progression of secondary osteoarthrosis. The purpose of the current study is to quantify morphologic parameters of FAI that are predictive of subsequent osteoarthrosis of the hip and their occurrence among hips with osteoarthritis of unknown etiology. Hip joints contralateral to 365 consecutive hips treated by total hip arthroplasty were evaluated. All hips with dis-ease patterns other than primary idiopathic osteoarthrosis were excluded. Further, hips with endstage arthrosis were excluded to eliminate the effect of secondary osteophytes on the morphologic measurements. Of the remain-ing hips, 20 hips that were in patients aged 60 or more without arthrosis (Tonnis grade 0 or 1) were compared to 78 hips that had developed Tonnis grade 2 osteoarthrosis. Conventional x-rays and CT-studies were available for all hips. These were analyzed for the presence or absence of deformities. In addition we calculated the predicted range of motion of each hip using three-dimensional models derived from the CT images and using a software algorithm that had previously been introduced and validated. The non-arthritic hips showed significantly fewer pathomorphologic findings and had greater hip flexion and greater internal rotation in flexion. Specifically, all of the hips that did not become arthritic over a 60 year period had alpha angles of less than 65 degrees, hip flexion of at least 100 degrees, internal rotation in flexion of at least 21 degrees, and femoral anteversion of more than 0 degrees. This study shows that 94.9 % of hips that developed osteoarthrosis have at least one abnormal morphologic pa-rameter. The differences among both groups were statistically significant. Malformations that cause early impinge-ment in flexion and flexion/internal rotation, especially pistol grip lesions and high alpha angles, are clearly associ-ated with the development of osteoarthrosis. No hip survived without arthrosis with anteversion less than 0 de-grees, an alpha angle of greater than 65.6 degrees, flexion of less than 100 degrees, or internal rotation in 90 de-grees of flexion of less than 21 degrees. With endstage arthritic hips excluded, this study furthermore demonstrates that these malformations predate endstage arthrosis and are not secondary to the osteoarthritic process and the ex-clusion of cases with systemic arthritis suggests that the etiology of arthrosis in the hip that was replaced was due to specific hip pathomorphology. Concluding, hips that are predestined to develop arthrosis due to pathomorphol-ogy may potentially be identified at an early stage, long before the development of osteoarthrosis. Thus, efforts to prevent destruction of these joints with early joint preserving surgery might represent an adequate therapeutic ap-proach.

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USE OF COMPLIMENTARY NON-DESTRUCTIVE EVALUATION METHODS TO EVALUATE THE INTEGRITY OF THE BONE-CEMENT INTERFACE Leung SY, New A, Browne, M Bioengineering Sciences Research Group, University of Southampton, Southampton, SO17 1BJ, UK Telephone +44 2380 59765, Fax +44 2380593016, [email protected] The integrity of the bone-cement interface is vital to the long term performance of a cemented hip prosthesis[1]. If interfacial failure occurs, the prosthesis may migrate and become macroscopically loose. Although many studies have examined the strength of the interface, few have studied the initiation of failure at a microstructural level. Finite element (FE) models of the bone-cement interface provide a relatively rapid and convenient means for studying its behaviour. However, these models require experimental validation, for example, to confirm failure paths. In the present study, a test has been developed to study the initiation and progression of failure at an ana-logue bone-cement interface under static loading. To enable confirmation of damage development and the associ-ated failure paths, non destructive techniques were employed; acoustic emission (AE) was used to predict the onset of damage and failure loci, and these findings were confirmed using high resolution computed tomographic imag-ing. Cement-cancellous bone analogue specimens were manufactured and tested in four-point bending. Duocel alumin-ium foam (ERG, Ca) was used as a cancellous bone analogue to eliminate problems with specimen variability. Cement was mixed and pressurised into the foam to produce cement/cement-foam (composite)/foam tri-layer specimens with cement penetration depths of approximately 3mm and cement mantle thickness of 2mm, similar to values reported in the literature[2]. The specimens were machined into four point bend specimens with dimensions of 10 x 12 x 50mm following guidelines suggested by BS ISO 12108:2002[3]. The samples were subjected to in-crementally increased loading. During the test, AE was used to detect the onset of permanent damage in the sam-ple. Testing was suspended when the Felicity effect was observed, indicative of critical damage[4]. This corre-sponded to acoustic emission events with high amplitude (>70dB), high energy (>102eu) and high durations ac-companied by medium rise times. Damage was evaluated using CT with a maximum resolution of 20µm before and after testing.

Using AE, the damage loci could be located before complete failure of the specimen. Located events corresponded well with cracks in the test-pieces subsequently observed in the tomographic images. The specimens in this study contain two interfacial regions at the cement-composite interface and the composite-foam interface. The tomo-graphic images showed that damage in the form of cracks initiated in the cement at the composite-foam interface. Cement pedicles at the composite-foam interface played a role in the failure process; cracks initiated in the region where the pedicles met the composite region. The pedicles formed a notch in the cement causing localised stress concentrations which led to damage initiation within the cement. In contrast, there was no fracture of the alumin-ium foam, but bending and deformation was identified, characterised by low amplitude AE events. References 1. Jasty, M, et al, J. Bone Jt Surg, 72A, pp1220-1229, 1990 2. Maher SA, McCormack BAO, Proc IMechE Part H, 213, pp347-354, 1999 3. British Standard/International Standard BS ISO12108:2002. British Standards Institute, London Duesing, L, Proc Ann Reliablity and Maintainability Symposium, pp128-134, 1989

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THE INFLUENCE OF CUP ANTEVERSION, ABDUCTION ANGLE AND HEAD DIAMETER ON THE JUMPING DISTANCE E. Sariali, B. Masson, JY. Lazennec, Y. Catonné Introduction: The jumping distance is the lateral translation of the femoral head centre required before dislocation occurs. The smaller the distance, the higher the theoretical dislocation risk. The aim of our study was to evaluate this jumping distance and its variation according to the implant characteristics. Method: The jumping distance was calculated as a function of the cup anteversion and abduction angles, the head diameter and the head offset defined as the distance between the centers of the cup and the head. Head diameters 28, 32, 36, 40, 44 and 48 were analysed. The abduction angle has been increased from 0 to 80° with a 10° increment. The anteversion angle has been increased from 0 to 40° with a 5° increment. Results: The jumping distance was found to decrease strongly as the cup abduction angle increased (2.5 mm each 10°). It increased by 0.5 mm for a 10° increase in the anteversion. The jumping distance increased as the head diameter increased except between 36 and 40 mm where a decrease of 1.25 mm was found. The net gain obtained by in-creasing the diameter, decreased when abduction angle increased : for 60° abduction angle, there was no signifi-cant difference between a 32 and a 48mm diameter. The jumping distance decreased by 0.92mm for each 1mm increase in head offset. Conclusion: The gain in stability obtained by using a large femoral head is negligible in the case of a high cup abduction angle. The anteversion has a slight influence on the jumping distance.

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ONE-STAGE BILATERAL UNCEMENTED HIP ARTHROPLASTY A SIMULTANEOUS PROCEDURE FOR DYSPLASTIC OSTEOARTHRITIS Kusaba Atsushi, Kondo Saiji, and Kuroki Yoshikatsu Institute of Joint Replacement and Rheumatology, Ebina General Hospital Phone: +81-462-33-1311 Fax: +81-462-32-8934 e-mail: [email protected]

In Japan, the most patients require hip arthroplasty have the acetabular dysplasia. Since February 2002, for very severe bilateral hip lesions we adapt the simultaneous bilateral hip arthroplasty. Some authors have reported simul-taneous bilateral hip arthroplasty, however, there have been few report concerning simultaneous surgery for dys-plastic hips.

Materials: We evaluated 43 (3 male and 40 female) dysplastic patients with the minimum of three-year follow-up. We used anterolateral approach in all hips. The average of follow-up was 4.1 (3.0-5.0) years. The average age at the surgery was 56 (43-73). The diagnosis at the surgery was dysplastic osteoarthritis for all hips, including 20 hips of subluxa-tion, one hip of unreduced congenital dislocation, six hips of failed osteotomy, and seven hips of avascular head necrosis after congenital dislocation (Perthes like head deformity: coxa plana and vara with relative overgrowth of the greater trochanter). Spongiosa Metal cup (GHE: ESKA implants, Lübeck, Germany) was used for 34 patients and Zweymüller type cup (Alloclassic cup: Sulzer Medical Co. Ltd., Winterthur, Switherland, recently Zimmer Co. Ltd. deals the implants / Bicon cup: Plus Orthopedics AG, Aarau, Switzerland) for nine patients. Spongiosa Metal stem (GHE: ESKA implants, Lübeck, Germany) was used for 18 patients and Zweymüller type stem (Alloclassic stem: Sulzer Medical Co. Ltd., Winterthur, Switherland, recently Zimmer Co. Ltd. deals the implants / SL stem: Plus Orthopedics AG, Aarau, Switzerland) for nine patients for 25 patients. For 13 patients, Zweymüller type stem was combined with Spongiosa Metal cup because of the excessively narrow canal. Acetabuloplasty was adapted for three hips. Against the severe contracture, thirty-eight hips required adductor ten-don release and three hips extensive tendon release. Results: The average duration of surgery for a patient was 156 (106-242) minutes. The average blood loss for a patient was 917 (183-1893) milliliters. In all patients the autotransfusion compensated the blood loss. We had no severe pe-rioperative complications such as DVT or PE, dislocation, and infection. All implants were stable. The average hip score was 46 (21-83) before the surgery and was 86 (68-98) at the final follow-up. The score was improved in all patients.

Discussion: In comparison with two-staged surgery, the advantage of the simultaneous surgery was easier after treatment, bet-ter improvement in hip score, better range of motion, and the saving cost and time. On the other hand, the one-stage surgery is systematic-invasive and the after treatment in very early stage was a little bit difficult for the pa-tients. It is concluded, that in selected patients with bilateral dysplastic hip necessitating bilateral hip replacement, the simultaneous bilateral surgery is advantageously carried out in one session.

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UNEXPECTED ANATOMIC RELATIONSHIPS IN THE PROXIMAL FEMUR: IMPLICATIONS FOR IMPLANT DESIGN Author: Carl Deirmengian E-Mail: [email protected] Introduction: The reproduction of normal anatomic relationships is an implicit goal of THA. Control over femoral offset and head height is limited to finite values by the native canal and metaphyseal widths. The purpose of this study is to define implant-relevant relationships in the proximal femur. Methods: 300 AP hip radiographs, using an internal rotation jig, were prospectively evaluated digitally with strict quality control measures. 13 distinct anatomic values, defined to be implant relevant, were measured in the proximal fe-mur. Additionally, implant data was analyzed for 1127 consecutive THA. Results: The average height of the femoral head from the lesser trochanter does not significantly increase with increasing metaphyseal width or canal diameter. More narrow metaphyses were related to valgus necks and higher femoral heads. Wider metaphyseal widths were related to the medial calcar anatomy of varus femoral necks and resulted in lower femoral heads. In fact, larger metaphyseal widths and canal diameters are associated with a shorter head height from the lesser trochanter in females. Average offset increased progressively with both canal width and metaphyseal width. Analysis of implant data from 1127 consecutive THA provided clinical validation of the data, exhibiting unexpected trends. Conclusions: Although most implant geometries increase the base head height with progressive stem sizes, an inverse trend was found in this study. The combination of a wide metaphysis with a varus neck and low head height is challenging to reproduce during THA, and found more often in female patients. Case examples are provided, with identifying anatomic characteristics and clinical implications.

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THR IN CONGENITAL HIP DYSPLASIA Luc Kerboull, M Hamadouche, Marcel Kerboull

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PRECISION OF A THREE-DIMENSIONAL PLANNING OF PRIMARY TOTAL HIP PROS-THESIS USING A CEMENTLESS STEM E. Sariali*, G. Pasquier**, A. Mouttet***, Y. Catonné Introduction: The goal of the study was to determine the precision of a three-dimensional pre-operative planning tool using a specific software (HIP-PLAN®) and an anatomic cementless neck-modular stem. Method: 223 patients who underwent a primary total hip replacement had a CT Scan before and after surgery. A pre-operative three-dimensional planning based on the CT-scan was performed. A cementless cup and a neck-modular stem were used. A computational matching of the pre-operative and the post-operative CT-scans was performed in order to compare the values of the planned anteversions and the planned displacement of the hip rotation center to the post-operative values. Results: The implanted component was the same as the one planned in 89% for the cup and 94% for the stem. For the mean femoral anteversion, there was no significant difference between the planned value (26.1° +/- 11.8) and the post-operative value (26.9° +/- 14.1). There was a poor correlation between the planned values and the actual ones for the acetabular cup anteversion (coefficient 0.17). The hip rotation center was restored with a precision of 0.73 mm +/ 3.5 horizontally and 1.2 mm +/- 2 laterally. Limb length was restored with a precision of 0.3 mm +/- 3.3 and the femoral off-set with a precision of 0.8 mm +/- 3.1. There was no significant modification of the femoral off-set (0.07 p=0.7) which was restored or slightly increased in 93% of cases. Almost all the surgical difficulties were predicted. Conclusion: HIP-PLAN® software is a reliable three-dimensional pre-operative planning tool which allows acurate prediction of components and hip anatomy.

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COMPUTER PLANNED TWO-STAGE HIP ARTHROPLASTY FOR HIGH-RIDING HIPS -THA AFTER LEG ELONGATION Hirotaka Iguchi, Takanobu Otsuka, Nobuhiko Tanaka, Masaaki Kobayashi, Yuko Nagaya, Hideyuki Goto, Shinji Hisazaki, Yoichi Taneda, Nobuyuki Watanabe, Yukio Yoshida, Yoshihiro Shibata, Toshiyuki Kawanishi, Takayuki Hirade, Kowase, Peter S. Walker, Joseph Fetto Nagoya City University, Graduate School of Medical Sciences, Department of Arthroplastic Medicin 1 Kawasumi Mizuho Nagoya City Japan +81-52-842-0266(Fax), [email protected](email) When a patient with high-riding hip has coxalgia and requires total hip arthroplasty, there are so many problems. One of the problems is the deformity of the femur and pelvis. The femur has never properly loaded so it doesn’t have normal femoral ge-ometry. The original acetabulum is not well differentiated and will have new acetabulum. So finding proper prosthesis is very difficult. Another problem is the leg length difference. Many muscles have been abnormally located for long term. The other is the sciatic nerve problem. It has been said that 3cm elongation in a surgery is the safe limit. As a solution of these problems we have performing a two stage surgery supported by computer 3D preoperative planning and modeling system. Method: First, the 3D geometry form pelvis to bilateral ankles was obtained by multi slice CAT scan. The images were translated into CAD data and the planning was done. The recommend elongation and cup position were considered on the system. The surgical procedures were almost the same with the way Binazzi et al. have presented at 18th annual congress of ISTA using eternal fixa-tion and elongation device. The safe pin insertions, depths and directions for each pin were planned. Then chemical wood mod-els were manufactured by personal CNC machine. The pins insertion was examined on the model. Result: Since 2005, 6 cases were operated by this method. Three cases were replaced with custom lateral flare stems. The lateral flare custom stems can transfer the load to the cortical bone at very high proximal part of the femur to reduce stress shielding. They also have very definite end point of the insertion, so the planned leg length can be achieved. The anteversion can also be ad-justed by the stems. One case was replaced with off-the-shelf lateral flare stem. This case did not require the adjustment of the anteversion, the same specific stem with less cost could be used. The other 2 cases were replaced with modular conical stems. These stems can adjust the anteversion and the length intra operatively. One case required as much as 7cm elongation but it was not sure that 7cm elongation could be surely obtained. So the length adjustability was regarded more important than the physio-logical load transfer. Another case had had shaft deformity; correcting osteotomy was planned at the same time. The conical stem was expected to have intra medullar nail function. In all 6 cases, no sciatic palsy, no fracture or no infection was observed. Conclusions: Computer 3D preoperative planning and modeling system played a good role in the 2 stage arthroplasy for high riding hips.

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THE USE OF TeraRecon FOR PREOPERATIVE PLANNING OF COMPLEX HIP RECONSTRUCTION Emory CL, Webb LX, Jinnah RH, Tan J Department of Orthopaedic Surgery, Wake Forest University Baptist Medical Center Medical Center Blvd. Winston-Salem, NC 27157 E-Mail: [email protected] Reconstruction technology has improved significantly in the last few years. Trauma surgeons have made extensive use of the TeraRecon® system to accurately assess fracture patterns in the pelvis. Considerable numbers of these patients will eventually require total hip reconstruction. The use of this technology contributes greatly to preoperative planning and facilitates the coordination of subspe-cialty services in the operative management of complex reconstructions. Virtual surgery confers numerous poten-tial advantages in the perioperative period, most notably in terms of operative time and implant availability during surgery. A case report and the mechanics of this new technology will be presented.

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A NEW METHOD FOR THE EVALUATION OF TOTAL HIP ARTHROPLASTY BASED ON BI-PLANAR LOW DOSE X-RAYS A BAUDOIN1, JY LAZENNEC2, Y CATONNE2, M GORIN, J. DUBOUSSET3, D MITTON1, W SKALLI1. 1 Laboratoire de Biomécanique, 151 Boulevard de l’Hôpital, 75013 Paris Tel : 03.44.24.63.64, mail : [email protected] 2 Service Chirurgie Orthopédie – Hôpital pitié Salpêtrière - Paris 3 Hôpital St Vincent de Paul INTRODUCTION: The analysis of complications after total hip arthroplasty (THA), such as prosthesis luxation or lower limb length inequality, is limited to standard frontal X-rays. In some cases, Computed Tomography Scanner (CT-scan) is made but the patient is in supine position which is not the functional configuration. The EOS® low radiation 2D-3D X-ray scanner (Biospace Med, Paris, France) allows simultaneously head to feet frontal and lateral X-rays with the patient in a standing position. Methods to obtain a three dimensionnal (3D) pa-tient specific bone recontruction were already proposed [1,3]. Thanks to these 3D models, a quantification of mor-phological and positionnal parameters is avalaible. Therefore, the aim of this study was the use of the EOS® device as a new diagnosis system for patient undergoing troubles after THA. MATERIALS & METHODS: Ten patients with THA problems had CT-scan exam as well as standard X-rays evaluation [2]. In complement, X-rays with the EOS® scanner were performed in standing, sitting and squatted position. The bones of each patient (lower limbs, pelvis and spine) were reconstructed using the standing X-rays. . Morphological parameters (pelvic incidence, femoral torsion) were evaluated and compared between 3D models issued respectively from EOS® and from CT Scans. Positionnal parameters (sacral slope, acetabular functional anteversion) were calculated in the standing, sitting and squatted positions. . The prosthesis position was also evaluated. RESULTS & DISCUSSION: The mean error between the EOS 3D models and the CT-scan was 3.5° and 5° for respectively the acetabular ante-version and the femoral torsion. The quantification of positionnal and morphological parameters in different positions is avalaible for the native osseous structure and also the prosthetic elements. Lower limbs torsion and pelvis anteversion and rotation could also be calculated thanks to the EOS 3D reconstructions, which made it an alternative of the CT-scan. CONCLUSION: The biplanar X-Ray device with 3D reconstruction provided an accurate 3D reconstruction which could be of ma-jor interest to evaluate the position of the prosthesis elements after THA. It also provides the ability to evaluate the influence of the 3D pelvis position and lower limb torsions on the hip arthroplasty. REFERENCES: [1] Laporte S et al., A Biplanar Reconstruction Method Based on 2D and 3D Contours: Application to the Distal Femur. Computer Methods in Biomechanics and Biomedical Engineering 2003; 6(1):1-6. [2] Lazennec et al. Hip spine relationship : application to total ip arthroplasty. Hip International 2007; 17: 91 – 104. [3] Mitton D, Deschenes S, Laporte S, Godbout B, Bertrand S, De Guise JA, Skalli W. 3D Reconstruction of the pelvis from bi-planar radiography. Computer Methods in Biomechanics and Biomedical Engineering 2006; 9(1):1 - 5.

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AN INTEROPERATIVE LEG LENGTH CALIPER AND DIGITAL PREOPERATIVE TEMPLATING IS MORE ACCURATE IN RESTORING FEMORAL LENGTH AND OFFSET IN TOTAL HIP ARTHROPLASTY THAN DIGITAL TEMPLATING ALONE Authors: Ivan Tomek, MD and Ryan Stehr, BSc, Stephen Kantor, MD One Medical Center Drive Lebanon, NH 03753 Phone: 603-650-8949 Fax: 603-650-2097 E-Mail: [email protected] Introduction: Along with implant orientation, the proper restoration of abduction muscle tension at the hip joint one of the most important factors influencing the stability of total hip arthroplasty (THA). While acetabular implant position also influences abductor muscle tension, it is the inaccurate restoration of femoral length and offset that often leads to a limb that is too short or too long after surgery. The purpose of the current study was to compare the post-operative femoral length and offset after primary total hip arthroplasty in patients whose surgery was performed with and without an intraoperative leg length caliper. Methods and Materials: Fifty consecutive patients underwent primary THA with a mini-posterior approach. All had their pre-operative radiographs digitally templated using a magnification-calibrated software package (TraumaCad, Orthocrat Limited, Israel). Post-operative restoration of leg length and offset in the first 25 consecutive patients (Group 1) was accom-plished by templating for femoral component size and offset, by taking pre-operative radiographic measurements from landmarks (center-of-head to lesser trochanter) and then attempting to restore them in the operating room. The same templating process was undertaken in the next 25 consecutive patients, except that a leg length caliper designed to intraoperatively record pre- and post-operative femoral offset and length was used in addition (Group 2). Results: In Group 1, the femoral component size was correctly predicted by digital templating in 71 percent of cases, and within 1 size in an 82 percent of cases. In Group 2, digital templating the femoral component size correctly pre-dicted the size in 67 percent of cases, and within one size in 84 percent of cases (p = 0.64). Proximal femoral leg length was restored to within a mean of 6.1±3.8 mm in Group 1 and within 3.6±2.7 mm in Group 2 (p < .05). Pa-tients femoral offset was restored to within 4.7±2.9 mm in Group 1 versus 3.8±2.6 mm in Group 2 (p=0.55). There were 8 patients in Group 1 with a leg length difference of > 5 mm, compared to only 2 patients in Group 2. Conclusion: An intra-operative leg length caliper combined with magnification-calibrated digital templating resulted in better accuracy of femoral length restoration compared to templating alone in patients undergoing total hip arthroplasty. In addition, the proportion of patients with post-operative length differences exceeding 5 mm was greater in the group where a leg length caliper was not used. Our results suggest that while all templated patients had a clinically satisfactory restoration of leg length and offset, an intra-operative caliper improved accuracy and reduced the pro-portion of patients whose post-operative leg length difference was more than 5 mm.

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ORIENTATION THE ACETABULAR CUP: LYING POSITION CORRELATES WITH STANDING BUT NOT SITTING POSITION Jean-Yves Lazennec, Marc-Antoine Rousseau, Patrick Boyer, Michel Gorin, Yves Catonne Département de chirurgie orthopédique Hopital La Pitié-Salpétrière, 47-83 Boulevard de l’hôpital, 75013 Paris Introduction: Hip dislocation remains a relevant complication of total hip arthroplasty .The implants position plays a major role , especially cup anteversion . It has been demonstrated that anteversion measured on CTscan depends on the pelvic position in a lying patient. This prospective study evaluates the influence of pelvic tilt according to standing and sitting positions. Methods: Sacral slope and inclination of the cups (frontal and sagittal) were measured on standing and sitting radiographs in 328 THA patients. Anteversion was calculated according to usual CTscan procedure (axial sections in lying posi-tion). The results were compared to a previously described protocol replicating standing and sitting positions : CTscan sections were oriented according to sacral slope. Results: The difference between the lying, standing, sitting positions was significant regarding the parameters of ther cup position. The acetabular parameters in lying position highly correlated to the one in standing position, while poorly correlated with sitting position. Lying anteversion angle was 24.2° (SD6,9°) Posterior pelvic tilt in sitting position, (sacral slope decrease) was linked to anteversion increase 38,8° (SD5,4°) . Anterior pelvic tilt in standing position (sacral slope increase) was linked to lower anteversion (31,7° SD5,6°). Anteversion values are correlated to sacral slope variations. Discussion and Conclusion: Our study confirms the interest CTscan sections oriented according to sacral slope . The strong correlation between lying and standing measurements suggests that classical CTscan protocol is relevant for standing anteversion. Ac-cording to the poor correlation between lying and sitting positions, it is less contributive for the investigation of dislocations in sitting position.

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GEOMETRY OF THE FEMUR IN DDH WITH HIGH ANTEVERSION, AND ITS LATERAL FLARE CUSTOM AND OFF-THE-SHELF STEMS STRATEGY Hirotaka Iguchi, Takanobu Otsuka, Nobuhiko Tanaka, Masaaki Kobayashi, Yuko Nagaya, Hideyuki Goto, Aiharu Furuya, Shinji Hisazaki, Yoichi Taneda, Nobuyuki Watanabe, Yukio Yoshida, Yoshihiro Shibata, Toshiyuki Ka-wanishi, Takayuki Hirade, Kowase, Peter S. Walker, Joseph Fetto Nagoya City University, Graduate School of Medical Sciences, Department of Arthroplastic Medicin 1 Kawasumi Mizuho Nagoya City Japan +81-52-842-0266(Fax), [email protected](email) DDH or Developmental Dysplastic Hips are known to have high anteversion and high neck-shaft angle. When total hip arthroplasty is planned for a DDH patient, it is always the question what shall be done with the anteversion. Some surgeons answer that high anteversion should be normalized, some surgeons answer that the anteversion should be left as it has been. Since 1989 we have been developing very high proximal load transfer cementless custom stem system with lateral flare. It can be designed for any anteversion angle. To reduce the manufacturing cost and manufacturing duration, an off-the-shelf stem system was also developed with the same designing policy. Then we have obtained many options. One is leave the anteversion as it has been, using the off-the-shelf stem; an-other is to reduce the anteversion down to normal angle such as 15 degrees. We also have another option to reduce the angel between the normal and the angle as it has been. To solve the question, we have analyzed the 3D geometry of the 195 DDH femurs and 225 THA cases. Materials and Methods: The whole length femoral geometries were assembled by CAT scan data. The anteversion and the neck-shaft an-gles were measured using the conventional way. The 3D relation among head, lesser trochanter and posterior condylar line were also assessed. Results: The most part of the anteversion was not located around the neck but it is located at mid diaphysis. It can be trans-lated that normal proximal femur and normal distal femur are connected with large twist. The careful observation has revealed that there are some cases huge osteophytes at posterior side of the hip have reduced the functional anteversion angle.

Conclusion: In most of the DDH cases, higher anteversion is accepted, but in some cases the abnormal kinetics caused to make posterior osteophytes and it reduced the functional anteversion. From this result, in all cases we analyze the femo-ral geometries by our 3D planning system. From this result, our policy is founding osteophyte reaction to reduce the anteversion, we make a custom stem to adjust the functional anteversion, and for the other cases we use the off-the-shelf stems.

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GENDER SPECIFIC FEMORAL ANTEVERSION VARIATION IN PATIENTS UNDERGO-ING TOTAL HIP ARTHROPLASTY Nirav A Shah MD, Raju Ghate MD, S. David Stulberg MD Correspondence: Nirav A. Shah, MD, 701 S. Wells Street, #1603, Chicago, IL 60607 Phone: 312.203.4664 Fax 630.460.2255 E-Mail: [email protected] There is wide variance in femoral anteversion in patients undergoing THA, and there is no evidence to customize implants for femoral anteversion based on gender.

There is a current interest in customizing features of THA implants based on gender. The purpose of this study was to determine if there was an identifiable and consistent gender characteristic of femoral anteversion in patients undergoing primary THA. Consecutive 100 males and 100 females undergoing primary THA had computed tomography scans of the proxi-mal and distal femur to determine preoperative femoral anteversion. All patients had a diagnosis of primary os-teoarthritis. Patients were grouped based on gender and femoral anteversion data was collected and compared. Other than gender, the two groups had similar demographics.

The mean femoral anteversion was +10.6 degrees (SD +/- 10.4) for males and +12.9 degrees (SD +/-14.2) for fe-males. The difference was not statistically different (p < .05). Female range of anteversion was from –14 to +35 degrees. Male range of anteversion was from –28 to +35 degrees. Standard error of measurement for males was 1.04 and for females 1.42. P=.185, Power .8 and Confidence Intervels of 95%.

The data show that there is a wide range of femoral anteversion in patients undergoing primary THA for OA. Ad-ditionally, there is no gender specific statistically significant difference in femoral anteversion. The study supports that femoral implant anteversion should not be gender specific.

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MODULAR NECK PROSTHESIS Croce, Antonio, Ometti, Marco (Istituto Ortopedico G.Pini, Piazza A. Ferrari,1 - 20122 Milano) (3354666648/[email protected]) To obtain the best results is essential setting the prosthesis in the more correct anatomic position, to reduce the stress that cause components’wear. The neck orientation is one of the responsables of the mechanic load of the implant; in fact, to this are correlated the relation with the cup (centre of rotation), the position on the frontal plan (varus/valgus middle/lateral) and the position on the traslateral plan (ante/retroversion). The modular necks act on three spatial variables (length-offset-version) indipendently and sequentialy, allowing to reach 27 points in the space; furthermore, disposing of heads with 3 lenghts, the real disponibility become of 81 points in the 3 dimen-sions. When we have a minimum error about cup’s position, the use of modular necks allow to correct this and so we can use the tribology ceramic-ceramic. The stem’s preoperatory planning maintains a great importance, but, in any case, the surgeon also must have the possibility to intra-operationally correct malpositioning. Usual, we estimate the implant’s orientation and length both manually and through a radiographic intra-operationally control, so we can choose the best tribology neck/head. The sandglass double cone form was projected to assure the anchorage in these zones that offer the greater force resistance. Fretting’s prove have shown that the modular tribology produces negligible debris. Metallic debris are decidedly lower than the debris produced by a normal stable prosthesis, esteemed in 10mg/year. In conclusion, the modula neck allows to correct the length and the vesion indipendently and sequentialy, to use the ceramic-ceramic tribology also with light cup’s malpositioning, to intra-operationally correct the implant’s orientation; modular components produce negligible debris; there is a riduction of the mechanic stress through the sandglass form.

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THE USE OF STRUCTURAL PERIACETABULAR ALLOGRAFTS IN ACETABULAR REVI-SION SURGERY: 2.5 TO 5 YEARS FOLLOW-UP Schelfaut Stefaan, Cool Steve, Mulier Michiel. Weligerveld 1, 3212 Pellenberg, BELGIUM Phone: + 32 474/580685 Fax: + 32 16 33 88 24 e-mail: [email protected] Introduction: ‘Acetabular bone loss’ presents a major reconstructive challenge in total hip arthroplasty (THA). The increasing incidence in Belgium of primary total hip arthroplasty over a 10 years, especially in younger patients, results in an increase in the number of acetabular revisions. Loss of acetabular bone loss is a consequence of removal of bone during the original procedure, subsequent prosthetic failure and osteolysis resulting from wear particles of cement and polyethylene. The use of bone-grafting may restore bone stock, besides restoration of normal anatomy and leg length, and facilitate further revision surgery. Although the use of structural massive allografts to achieve the above goals continues to be controversial. Materials and methods: From January 2002 to June 2004, fourteen acetabular revisions with a cemented cup, entirely supported by a deep frozen structural periacetabular allograft without use of reinforcement ring were performed at our institution. The acetabular defect were all non-contained and classified as Paprosky type III. The clinical assessment was done us-ing a modified, anamnestic Harris Hip Score. Radiographic analysis involved a general qualitative evaluation. The amount of graft resorption was quantitatively analyzed using a digital measurement system (Imagika ®). Results: Kaplan-Meier survivorship of these reconstructions was 67.1 % at 42 months. Four patients (mean age 59 years and mean 3.5 procedures) were re-revised after a mean period of 32.5 months: 3 because of allograft fragmentation with collapse of the total construction and 1 showed recurrent dislocation after the patient had been hospitalized and bedridden for unrelated pathology during three months. Ten patients were available for analysis with an aver-age age of 70 years, a mean follow up of 43.5 months (3.6 years) and a mean of 2.1 previous hip revision proce-dures at time of operation. In this group anamnestic HHS was 72.9 %, three times higher then the preoperative score. All patients had a remarkable pain reduction. Radiographically, a mean resorption of 17.1 % in six out of ten patients was observed. No sound evidence for union was found in nine out of ten patients. In the four re-revised patients no bone stock restoration was found. Conclusions: This study discourages the use of periacetabular structural allografts that support the cup entirely in ambulatory demanding patients. In contrast to the current literature, no proof was found of bone stock restoration. The bicorti-cal allograft seems to function as a passive, bio-compatible dead scaffold with less intrinsic strength compared to the more promising synthetic materials. Therefore we recently introduced the use of custom made porous coated trifangle acetabular prosthesis to overcome such extensive acetabular bone losses. Using a three dimensional model of the hemipelvis, the prosthesis is designed to fit as much as possible the defect and allowing appropriate initial fixation by screws in pubis, ischium and ilium. The bio-compatible coating materials may promote long term rigid fixation and stability of the implant.

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PELVIC OSTEOLYSIS – THE VALUE OF RADIOGRAPHS IN ITS ASSESSMENT AND ITS RELATIONSHIP WITH WEAR

Shon Won Yong, Han Sang Wan, Gupta Siddhartha Orthopedic Department, Guro Hospital, Korea University Guro-Dong 80#, Guro-Ku, Seoul, Korea Phone No: 82-2-2626-3805, 1150 Fax No : 82-2-863-4605 E-mail : [email protected]

Periacetabular osteolysis, which often remains asymptomatic, is a major source of complication following total hip arthroplasty. We evaluated the sensitivity and specificity of radiographs in detecting osteolysis and its accuracy in predicting the lysis volume, in 118 THA with cementless cups, by comparing with the computed tomography val-ues (CT) taken as the gold-standard. Correlation between total wear, 2D lysis area and 3D lysis volume was as-sessed. Though the AP radiograph was only 57.6% sensitive it was 92.9% specific and very sensitive (92.9%) for lesions >1mL. 3D CT volumes showed good correlation with total wear (r=.594) and 2D lysis area (r=.74) but the estimates of volume from radiographs were highly inaccurate making radiographs useful only as a screening tool.

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THE USE OF CEMENTED UNCONSTRAINED TRIPOLAR CUP TO TREAT RECURRENT DISLOCATION: A MULTICENTER STUDY Hamadouche Moussa, Biau David, Barba Nicolas, Ropars David, Musset Thierry, Gaucher François,Courpied Jean Pierre, Langlais Franz 27 rue du Faubourg St Jacques, 75014, Paris, France E-Mail: [email protected] Introduction: Although a number of methods have been described to treat recurrent dislocation following total hip arthroplasty (THA), this complication remains a challenging problem. The unconstrained tripolar cup principle (so called dual mobility) was introduced in France in 1974. The purpose of this study was to evaluate the minimum 2-year results of a cemented unconstrained tripolar cup to treat recurrent dislocation. Methods: A prospective multicenter series included 51 patients (51 hips) treated for recurrent dislocation (mean: 3.3 ± 1.4). There were 39 females and 12 males with a mean age of 71.3 ± 11.5 years. The mean number of previous THAs was 1.8 ± 1.1. A single cup design was used (Medial cup, Aston Medical, France) consisting of a stainless steel outer shell with grooves for cement fixation with a highly polished inner surface. This shell articulates with a mo-bile intermediate component with an opening diameter smaller than the 22.2 mm femoral head. The centre of rota-tion of the polyethylene component is medialized compared with the outer shell. No locking ring or other mean of constraint is used. The shell was cemented in an acetabular reinforcement device in 24 hips, and graft was used in 15 hips. Results: At the latest review, one patient had died, one was lost to follow-up, and one had acetabular revision 32 months after the index procedure for recurrent dislocation. The mean follow-up was 31 months (24 to 50 months). The mean Merle d’Aubigné hip score was 15.9 ± 2.0 at the latest follow-up. Radiographic analysis revealed radiolucent lines around the cup in 11 hips (21%), and one cup showed evidence of progressive radiolucent lines associated with cup migration. The survival rate of the cup at 36 months, using dislocation and/or mechanical failure as the end-point, was 94.1 ± 4.2%. Discussion and Conclusion: An unconstrained tripolar cup is effective in the treatment of recurrent dislocation, and the results compare favora-bly with other devices. However, because of the rate of radiolucent lines around the cup and related concerns about long-term fixation, the use of such a device should be reserved to specific situations.

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ADVANTAGES OF THE BIPOLAR ACETABULAR COMPONENT IN TOTAL HIP REVISION JL Rouvillain, E Garron, W Daoud, Th Navarre Orthopaedic Department, La Meynard University Hospital, BP 632 Fort de France 97261 Martinique Tel/ fax 596 596 55 22 28. Email : [email protected] Introduction: The bipolar acetabular component allows a important range of motion and avoids hip dislocation. This component gives good results in primary hip replacement and this component seems to be very usefull in revision THA Material and Methods: The bipolar acetabular component in the revision THA was used since december 2004 . 31 patients were fol-lowed up with the functional scores of Postel-Merle d’Aubigné and Harris, and radiographic analysis preoperative, postoperative and at the last follow-up. Two different acetabular cups were used. When the host bone was good enough a cimentless acetabular cup was implanted with peripherical screws. In 12 cases, when the bone loss was too important , the acetaular cup was cimented in a ring fixed to the host bone and packed morcellised allographs. Results: The surgical approach was anterolateral. All cases were revised for aseptic loosening of the acetabular component. The average delay between the THA and the revision was 11 years. The acetabular bone loss according to the SOFCOT score was in 10 cases stade 1 , 11 cases stade 2, 8 cases stade 3 and 2 cases stade 4. The PMA score increased from 5 to 12,8 and the of Harris score from 34 to 68 points Complications were a fibular palsy in a Marfan desease and a dislocation at 21 day post operative reduced by external reduction and stable after 16 months. Discussion: The rate of the THA dislocation in revision in the literature is reported from 5 to 30 %. In important acetabular deficiencies, this components allows to replace the head center in a physiologic situation, and gives a very good function . Conclusion: The bipolar acetabular component gives good results and allows to decrease the important dislocation rate in acetabular reconstruction.

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DISTALLY LOCKED STEMS FOR REVISION HIP ARTHROPLASTIES WITH SEVERE FEMORAL BONE LOSS. RESULTS OF 101 CASES AFTER A MEAN FOLLOW-UP OF 6 YEARS (5-12) MAY Olivier, SOENEN Marc, LAFFARGUE Philippe, PINOIT Yannick, MIGAUD Henri Orthopedic Department, Salengro Hospital, University Hospital of Lille Place de Verdun, 59000 Lille, FRANCE Phone +33320446828 Mail [email protected] INTRODUCTION: Cementless revision hip arthroplasties require a stable initial fixation that does not compromise a subsequent bone reconstruction. These two principles appear not compatible particularly in case of severe femoral bone loss that usually requires distal fixation that may induce stress shielding and finally adverse bone reconstruction. To treat that type of complex femoral loosening we introduced the use of distally locked revision stems in 1994. The goal of the current study was to assess if these components fulfill the two objectives: strong fixation and bone recon-struction. MATERIALS AND METHOD: One hundred and one cementless femoral revision stems with distal locking by screws (Ultime(tm) Wright-Cremascoli) were inserted from 1994 to 2001. These stems were smooth distally and porous coated to the proximal third. The indication of these components was severe bone loss (Paprosky grade IIC and III in 51%) when press fit distal fixation could not be obtained. The use of bone graft was limited to segmental defects or to treat trochanteric non-union. An extended trochanteric osteotomy was performed in 89%. The revision was performed because of aseptic loosening in 43,4%, peri-prosthetic fracture in 24,2% and infected loosening in 25,2%. The results were assessed after a mean follow-up of 6 years (5-12). RESULTS: Thirteen patients deceased and 2 were lost for follow-up. All the extended trochanteric osteotomies healed. Merle d'Aubigné hip score increased from 8.3 to 13.4, but thigh pain was observed in 44%. Bone reconstruction was sig-nificant according to Hoffman index at the 3 levels of assessment (lesser trochanter, 5 cm below and 10 cm below). The 5-year survivorship was 87% considering aseptic revision for any reason. Seventeen repeated femoral proce-dures were performed: 9 related to thigh pain (because there was no proximal osteointegration) which were changed for short primary stems (as bone reconstruction was observed in all cases), 8 because of stem fractures (all occurred at the level of the proximal hole with the same stem size (12mm in diameter and 250mm in length) be-cause there was no proximal fixation as long as the stems had limited proximal coating). DISCUSSION: This series has the longest follow-up using locked revision stems. Despite severe pre-operative bone loss, primary fixation and significant bone reconstruction were obtained for all the cases without extensive bone grafting. The major weakness, thigh pain and stem rupture, were related to inadequate femoral coating for these cementless stems which did not achieved osteointegration. Conversely, the reoperations were simple, allowing the use of short primary designs as bone reconstruction was achieved in all cases without extensive bone grafting. These locked stems allow a strong primary distal fixation that does not compromise bone regeneration. An improvement of femoral coating (extension to 2/3 and use of hydroxyapatite) may reduce the rate of thigh pain and reoperation.

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THE USE OF DIAPHYSEAL OR TROCHANTERIC-DIAPHYSEAL EXTERNAL REINFORCEMENT PLATES IN FEMORAL REVISIONS Dr Jean-Pierre Roux E-mail: jean pierre roux <[email protected]> 1) This technique is used to reinforce as a principal revision of femurs and to avoid numerous post-operative com-plications - Wrong ways - Secondary fractures - Bad cancellous fill in - Non-trochanterian union 2) Since January 2005, it has been performed in 11 cases : - Simple reconstruction (5) - Reconstruction as the Exeter technique (6) - Trochanterian pseudarthrosis union (4) - Flap union (2) - Massive homograft synthesis (1) - Cortical-cancellous homograft synthesis (4) - Cemented stem (9) - Cementless stem (2) 3) More often the plates has been put at the beginning of the surgery (7) acting as a main anatomical reference in the reconstruction and the femoral shaft alignment. Sometimes it has been put only as a final reinforcement (4). 4) From January 2005 to June 2007 it has been put : - 2 simple diaphyseal plates - 7 trochantero-diaphyseal plates from BIOMET 254 mm - 2 Integra plates from LEPINE 250 mm In all the cases the immediate relieved support has been authorized. 5) In parallel, the major revision techniques with Wagner approach or distal locking has been used only in extreme cases which are fewer (2).

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MALPOSITIONED CUPS AS REASON FOR REVISION IN METAL-ON-METAL HIP RE-SURFACING ARTHROPLASTY De Haan Roel, Su Edwin, Campbell Pat, De Smet Koen. ANCA Medical Centre, Krijgslaan 181, 9000 Ghent, Belgium +3292525903, +3292526457, [email protected] Revisions of metal-on-metal hip resurfacings have usually involved femoral problems such as neck fracture or col-lapse of the femoral head. In our series, acetabular problems were the predominant cause of revision. The aim of this study was to describe the revision options and results in patients who have had failed hip resurfacing, espe-cially of the acetabular component. Methods: We performed 37 revisions of failed hip resurfacing arthroplasties. Revisions were performed after an average of 26.2 months. The average age at revision was 49.2 and 27 patients were females. Results: The predominant mode of failure was a malpositioned acetabular component (65%). Other reasons for revision were a malpositioned femoral component (19%), loosening of the femoral component ( 14%), osteolysis, loosening of the acetabular component and femoral neck fractures. Most of the malpositioned acetabular components were revised because of excessive abduction (average 71.6°) or insufficient anteversion (average 3.4°). In 7 cases only a revision of the cup was necessary. In 8 patients only the head was replaced for a stem with modu-lar head. In the other 22 cases the resurfacing arthroplasty was replaced by a ceramic-on-ceramic total hip arthro-plasty. In 29 patients the cup was changed. The average increase in cup-diameter was 1.2 mm. Four patients had dislocations after the revision-surgery and 1 required re-revision for recurrent dislocation. Three other patients had also a re-revision (average 25 months). Discussion: Malpositioned components accounts for more than 60% of the failures. Because in hip resurfacing there is a greater chance of bone-prosthetic impingement, implant positioning is of paramount importance. One advantage of hip resurfacing is an easier conversion to a secondary procedure. In our series however, 7 pa-tients (19%) had a complication and 4 patients (11%) needed a second revision. Four dislocations occur because the stability of the prostheses after revision is reduced for two reasons. First because of the decrease in head diame-ter after revision and second because metallosis affected large amounts of capsular tissues which had to be re-moved and normally provides stability for the hip. We demonstrate that revision of hip resurfacing can be performed with a minimal increase in bone loss. This study shows that the average increase in cup diameter after revision is only 1.2 mm in those hips exposed with a postero-lateral approach. Correct placement of the components is critical for optimal functioning of the bearings. The resurfacing procedure is more technically demanding than routine total hip replacement. Optimal acetabular component positioning may be more difficult to achieve because of difficulty in exposing the socket and an inability to visualize cup seating due to the solid nature of the component and instruments. While malpositioned acetabular components may seem to be a preventable cause of failure, this may only be achieved through better training, better instruments, increased experience with the technique and a better understanding of the problem.

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AN INDEPENDENT REVIEW OF RESULTS AFTER BIRMINGHAM HIP RESURFACING ARTHROPLASTY AT SEVEN YEARS Author 1/ Presenter: Robert T Steffen, MD, MRCS Author 2: Hemant G Pandit, FRCS Author 3: Peter McLardy-Smith, FRCS Author 4: Roger Gundle Author 5: David J Beard, DPhil Author 6: Barbara Marks Author 7: Harinderjit Singh Gill, PHD Author 8: David Murray, MD NOC, Botnar 2, Windmill Road Oxford, Oxfordshire, UK Phone: 44 7887 715977 Fax: 44 1865 227671 E-Mail: [email protected] Introduction: Resurfacing hip replacements are widely used but there is a paucity of independent outcome data to support this popularity. The aim of this study was to report the five year clinical outcome and seven year survival of an inde-pendent series. Methods: 610 Birmingham hip resurfacings were implanted in 532 patients (median age 52 years, range 16-82 years) and were followed for between two to eight years. Outcome was evaluated using the Oxford and Harris Hip Scores. Activity level was assessed by the UCLA score and any implant related complications or revisions were recorded. Radiographs were assessed for each patient. Results: Only two patients were lost to follow up. There were 23 revisions out of 608, giving an overall survival of 95% (95% CI 85-99%) at seven years. Fractured neck of femur (n=13) was the most common reason for revision, fol-lowed by aseptic loosening (n=4). Three patients had failures that were possibly related to metal debris. Full clini-cal follow up data at five years were available on 120 patients. At a minimum of 5 year follow-up 93% had excel-lent or good outcome according to the Harris Hip Score. The mean Oxford Hip Score was 16.1 points (SD 7.7) and the mean UCLA activity score was 6.6 points (SD 1.9). There were no patients with definite evidence of radio-graphic loosening or greater than 10% of neck narrowing. Discussion and Conclusion: The results demonstrate that with the Birmingham Hip Resurfacing, implanted using the extended posterior ap-proach, the seven year survival is similar to the reported survival rates for cemented and hybrid THRs in young active patients. However, further study is needed to address the early failures; particularly those related to fracture and metal debris.

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FEMORAL HEAD RESURFACING USING IMAGELESS NAVIGATION - ACCURACY OF NAVIGATION GUL, REHAN* , Falworth M, Oakshott R, Zadowe S SPORTSMED SA, 32 Payneham Road Stepney, Adelaide South Australia Email. [email protected] Introduction: Femoral head resurfacing is a surgical option for younger patients; however the technique is more complex and demanding for a surgeon. Instrumentation for femoral head resurfacing is based on the placement of guide pin through the head and neck. Incorrect positioning of guide pin may result in femoral neck notching or varus place-ment of the implant that can increase the risk of post operative femoral neck fracture.1

Navigation for Hip resurfacing has been proposed to reduce implant variability2 and also help to recreate the opti-mal neck shaft angle especially in the presence of previous deformities like SUFE or Perthes. Aim: The aim of the study is to assess the accuracy of the Ci ASR imageless navigation software in placement of im-plant. We also compared the variation between the pre operative surgical plan and the final placement of implant. Methods: In an ongoing prospective study, neck shaft angle of each patient was measured using preoperative CT scan to es-tablish a base line. A pre op. neck shaft WISH angle was decided by the senior author (RO). All patients under-went surgery using posterior approach and femoral heads were resurfaced using Ci ASR Hip navigation software (Depuy/Brain). Neck shaft angles were calculate intra operatively using computer, and were adjusted according to the wish angle. Angles were measured after final placement of implant. CT scan was performed to confirm the final neck shaft angle. Results: 25 hips in 23 patients with mean pre op. neck shaft angles of 127.42 (115 – 139). Mean post op. angle was 135.10 (125 – 147) When we compared means – no statistically significant difference was found between pre op angle vs calculated angle (p=>0.05), no statistically significant difference was found between the final intra operative vs. post operative angle (p=>0.05). No statistically significant difference was found between adjusted vs. final angles (p=>0.05).There was a statistically significant difference when pre op angles were compared with post op angles (p= <0.05). Conclusion: The early results confirm the Ci ASR imageless navigation software not only allow accurate restoration of neck shaft angle but it also allow the surgeon to adjust the neck shaft angle and helps in accurate placement of implant in both AP and Lateral planes References 1. Daniel J, Pynsent P, McMinn DJ. Metal on metal resurfacing of the hip in patients under the age of 55 years with osteoarthritis. J Bone Joint Surg Br 2004; 86(2): 177-184 Hodgson AJ, Inkpen KB, Shekhman M, et al. Computer assisted femoral head resurfacing. Computer Aided Sur-gery, Sept/Nov 2005; 10 (5/6): 337 - 343

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RESURFACING OF THE HIP: AN ON-BENCH BIOMECHANICAL STUDY

Pier Francesco Indelli, David Dominguez, Kenichi Kitaoka, and Thomas Parker Vail Casa di Cura Santa Chiara Firenze, Florence, Italy and Department of Orthopaedic Surgery, Duke University Medical Center, Durham, North Carolina, U.S.A. E-Mail: [email protected] INTRODUCTION: The objective of this study was to evaluate the biomechanical proprieties of a hip resurfacing system in terms of failure of the implant with different positioning of the prosthesis in cadaveric femurs. MATERIAL and METHOD: The study has been divided in 3 phases. First phase: Six-teen cadaveric femurs were tested to failure using a stan-dard MTS device once the Conserve Plus (Wright Medical) system was implanted: 8 femurs after a 4mm notching of the neck and 8 contralateral without notching. Second phase: Six-teen cadaveric femurs were tested using a 210 Kg axial load: 8 with the Conserve Plus system implanted at 140º and 8 contralateral with 10º of varus. Third phase: Eight femurs were tested with the implant having 10 º of excessive antiversion of the component and 8 with the implant having 10 º of excessive retroversion. The control group was represented by 16 femurs having the sys-tem implanted following the natural version of the femoral neck. RESULTS: An average of 4865 Newtons (N) was necessary for the failure of the implant after notching, compared to 7043 N without notching. The varus alignment of the implant showed a statistical different increase of the stress on the femoral neck: 15% postero-superiorly and 21% antero-superiorly. The neutral alignment at 140º showed a decrease of the overall stress on the femoral neck. Adding 10 º of excessive anteversion or retroversion did not show any statistical difference in terms of failure of the implant when compared to the anatomical alignment. CONCLUSIONS: This biomechanical study showed that the correct positioning of the implant represents a fundamental requirement for the success of the hip resurfacing procedure. The notching of the neck decreases significantly the biomechani-cal proprieties of the implant, while the varus alignment increases the stress on the superior neck cortex.

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CEMENT DISTRIBUTION AND THERMAL NECROSIS IN FAILED HIP RESURFACINGS Lundergan William, Ebramzadeh E, Campbell Pat, Wager Brook, Esposito Christina, De Smet Koen 1, *Amstutz, Harlan C.2 JVL Res Center, Orthopaedic Hospital/UCLA 2400 S. Flower St, Los Angeles CA 90007 1213742 1134, Fax 213 744 1175, [email protected] Hip resurfacings differ in the choice of cement type, volume, degree of penetration and the clearance between the implant and bone (mantle). One of the concerns with excessive cement penetration is thermal necrosis, which may contribute to a fibrous interface and instability. The primary aim of this study was to measure the amount and dis-tribution of cement in retrieved specimens from designs that differed in amount of desired cement and to look for correlations with failure mode. Secondly, we histologically examined short term failures for evidence of thermal necrosis around the cement interface. Materials and Methods: Fifty femoral specimens that failed for fracture, acetabular problems and femoral loosening from 1 week to 10 years were studied. Nineteen had a “tight fit” design and 31 had a cement mantle design. Coronal, 3mm sections were used for the measurement of cement mantle, depth of cement penetration and area of the head that was ce-mented. Histological samples were examined for bone viability and membrane formation. Logistic regression analysis was used to assess the relative effects of the cement measurement variables on the risk of failure. Results There was considerable variation in mantle thickness and cement penetration within and between the groups. Typically there was more cement in the proximal region and least at the edge of the components regardless of de-sign because implants were often not fully seated. The total percentage of the femoral head sections occupied by cement (mantle, cement–filled fixation pegs or cysts, and penetration combined) ranged from 11% to 90% and was significantly greater in loosening failures (52%) compared with other failure modes (p = 0.001). There was more cement in female cases (47% compared with 37%) and more penetration in the tight fit design. The bone within the cement-penetrated areas was necrotic, as was the bone up to 3mm below the cement zone in short-term failures. Loosening was associated with fibrous membrane formation between the cement and bone, and adjacent bone was often undergoing active osteoclastic erosion. The bone-cement interfaces in several of the longer-term specimens with deep cement showed evidence that early thermal necrosis had healed without mem-brane formation. Discussion: Cementing technique and bone quality are important factors that will determine cement penetration, fixation and femoral survivorship. The variability noted in these failed hip resurfacings shows that the control of the cement mantle thickness and penetration may be difficult. In particular, not fully seating the component and overfilling the head were noted. Femoral loosening was most affected by cement amount. Despite large amounts of cement in some cases, healed necrotic interfacial bone showed that membranes were not an inevitable feature of cement fixa-tion but the often extensive necrosis in short term cases shows that steps to reduce thermal necrosis, such as gener-ous pulsatile lavage and early reduction should be performed. Further studies to optimize the amount and distribution of cement to provide sufficient cement for fixation without compromising femoral head bone integrity, are recommended. 1ANCA Medical Clinic, Gent Belgium 2St Vincent’s Hospital, Los Angeles.

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TOTAL HIP RESURFACING IN THE USA: A PROSPECTIVE, SINGLE SURGEON REPORT ON 1-YEAR MINIMUM FOLLOW-UP Macaulay, William; Clerici-Bagozzi, Giuseppe Center for Hip & Knee Replacement Department of Orthopaedic Surgery New York Presbyterian Hospital at Columbia University Medical Center 622 W 168th Street, PH 1146 New York, NY 10032 Phone: (212)-305-6959, Fax: (212)-305-4024, Email: [email protected] Introduction: Total Hip Resurfacing (THRe) has seen a resurgence of interest in last decade in the form of a modern metal-on-metal articulation. FDA approved in the U.S. for only one year, perpetuation of this technique can only be sup-ported through the prospective demonstration of efficacy with validated pain and function outcome measures and survivorship comparable to conventional total hip arthroplasty. Materials & Methods: Seven consecutive Conserve Plus THRe’s (CP’s, Wright Medical Technology Inc., Arlington, TN, USA) immedi-ately followed by 14 consecutive Birmingham THRe’s (BHR’s; Smith & Nephew Inc., Memphis, TN, USA) were performed in 21 patients (15 males/ 6 females; mean age of 50 ± 12 years). Average body mass index (BMI) of the patient population was 29 ± 6 BMI (range, 22-47), respectively. Outcomes were prospectively assessed via the SF-12, WOMAC, and Harris Hip Score (HHS). No patients were lost to follow-up. Student’s t-test was performed using Microsoft Excel 2003 (Microsoft Corp., Redmond, WA, USA). Results: Minimum follow-up was one year with a mean follow up period of 17 months (range, 12-30). Of the 21 hips, mean preoperative HHS and WOMAC pain scores improved significantly from 56 ± 17 (range, 34-100) to 92 ± 8 (range, 65-100) (p<0.0001) and from 51 ± 9 (range, 20-100) to 97 ± 88 (range, 70-100) (p<0.0001), respectively. Addi-tionally, average SF-12 Physical Component scores significantly increased from 33 ± 9 (range, 17-49) at baseline to 51 ± 8 (range, 28-60) at time of follow-up (p<0.0001). Overall stiffness and physical function assessed via the WOMAC index also exhibited statistically significant improvement, bettering from mean baseline scores of 40 ± 20 (range, 0-75) and 53 ± 17 (range, 10-79) to 75 ± 24 (range, 13-100, p<0.0001) and 90 ± 9 (range, 65-100, p<0.0001), respectively. No significant prosthesis/bone interface radiolucencies were found upon thorough radio-graphic review at 1 years post THRe. No femoral neck fractures, dislocations, infections or re-operations were observed. Discussion & Conclusion: The significant improvements observed in hip function & stiffness, and decreases in pain at 3 months and one year after this initial series of THRe, are excellent. Coinciding results from the physical and mental components of the SF-12 assessment indicate reassurance of physical improvements regarding patient lifestyle. These were observed in the absence of complications which is particularly important because other authors’ series have demonstrated rates of early femoral neck fractures as high as 20%. Clinical and radiographic follow up will continue on a yearly basis to assess the mid and long-term efficacy of THRe. Only longer-term outcomes can provide an accurate com-parison to today’s gold standard, the total hip replacement.

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THE CHOICE OF SURGICAL APPROACH FOR HIP RESURFACING AFFECTS FEMORAL HEAD BLOOD SUPPLY-AN ANALYSIS OF FOUR DIFFERENT APPROACHES Author 1/ Presenter: Robert- T Steffen, MD, MRCS Author 2: Kieran S O'Rourke, MD Author 3: Koen Aime DeSmet, MD Author 4: Darren Fern, MD,FRCSC Author 5: Mark Norton, MD Author 6: Peter McLardy-Smith, FRCS Author 7: Harinderjit S Gill, PHD Author 8: David W Murray, MD NOC, Botnar 2, Windmill Road Oxford, Oxfordshire, UK Phone: 44 7887 715977 Fax: 44 1865 227671 E-Mail: [email protected] Introduction: Avascular necrosis of the femoral head after resurfacing hip replacement is an important complication which may lead to fracture or failure. The surgical approach may affect the blood supply to the femoral head. We compared the changes in femoral head oxygenation resulting from the extended posterior approach to those resulting from the anterolateral approach, the trochanteric flip approach and a modified, soft tissue preserving posterior approach. Methods: We recruited 48 patients who underwent hip resurfacing arthroplasty (HRA) to measure bone oxygen levels. A calibrated gas-sensitive electrode was inserted in the femoral head following division of the fascia lata. Intra-operative X-ray confirmed correct electrode placement. Baseline oxygen concentration levels were recorded imme-diately after electrode insertion and continuous measurements were then performed throughout surgery. All results were expressed relative to the baseline, which was considered as 100% relative oxygen concentration and changes during surgery through the posterior approach (n=10), the antero-lateral approach (n=12), the trochanteric flip ap-proach (n=15) and the modified posterior approach (n=11) were compared. Results: The relative oxygen concentration at the end of the procedure was significantly reduced when hip resurfacing was performed through the posterior (22%, SD 31%, p<0.005) or a modified posterior (35%, SD 31%, p<0.005) ap-proach, but recovered in the anterolateral (123%, SD 99%, p=0.6) and trochanteric flip group (89%, SD 62%, p=0.5). Sub-group analysis of these two relatively blood preserving approaches showed that intra-operative oxygen concentration was significantly more consistent during surgery through the trochanteric flip approach (p<0.02). Discussion and Conclusion: This study has demonstrated that disruption of blood flow to the femoral head during HRA is dependent on the surgical approach. We, therefore, believe that blood supply preserving approaches (i.e. anterolateral, trochanteric flip) may be associated with a lower risk of avascular necrosis and femoral neck fracture.

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CEMENT PRESSURE DURING HIP RESURFACING HEAD IMPLANTATION Tuke, Mike*; Brooks, Adam**; Rigby, Michael**; Ivory, John**; Hu, Xiao, Q*; Taylor, Andy* * Finsbury Orthopaedics, Leatherhead, Surrey KT22 7BA, UK, Tel: +44 (0) 1372 360830, Fax: +44 (0) 1372 360779, Email: [email protected] ** Great Western Hospital, Swindon, Wiltshire SN3 6BB, UK During a hip resurfacing, cement pressure inside the cemented head is required to achieve a dense mantle and to facilitate cement penetration into the cancellous bone. However, excess pressure should also be avoided to reduce the risk of potential damage to the femur and vascular system. In this paper, the cement pressure inside the resur-facing head was measured under different conditions and a slot technique to achieve an optimal pressure was de-veloped. A pressure strain gauge transducer was mounted through an ADEPT resurfacing head with the pressure measure-ment surface at the same level as the internal surface of the head. The position of the transducer was 45° from the polar axis. The data from the transducer were taken by a data logger at a frequency of 160 Hz under hammering and 1 Hz under pressing. Polyurethane foam blocks were machined into the shape of prepared femurs with a cylin-der diameter ranging from 41.00 to 42.30 mm to fit the internal central diameter of 41.94 mm of the resurfacing head. Two Ø4 mm slots were cut along the cylindrical length of the foam cylinders to relieve the pressure at the beginning of implantation and to regain the pressure after the closure of the slots when the head was fully seated. Palacos LV bone cement was hand mixed at 21°C and the insertion was carried out between 2-3 minutes. The measurement was carried out under two different conditions: pressing and hammering. During hammering, the prepared femur was placed on a polystyrene block to simulate the soft body of patient. With the increase of femur size and insertion time, the insertion resistance increased significantly and finally some heads could not be fully seated due to small clearance and high viscosity. The cement pressure inside the resurfac-ing head can be affected by various factors including loading rate (pressing or hammering), femur cut size, slot size, and insertion time. In this study, the peak pressures of all fully seated components were compared. The mean peak pressure during the hammering procedure was 0.35 ±0.15 MPa, which was at least three times higher than that from the hand pressing method (0.10 ±0.02 MPa). It was concluded that the hammering method should be avoided as much as practically possible to reduce the risk of trauma to the femoral bone and to the vascular system. With the hand pressing method, the pressure increased slightly from 0.08 to 0.12 MPa with the increase of the cut femur diameter. During an operation, surgeons can run the cylinder reamers too quickly down the head and back so they may cut a spiral due to the offset teeth and get a bigger size. The variation of bone density will vary the amount of cement that can penetrate the head, and may also change the cut size even with a right reaming tech-nique. In this case, the slot technique can provide pressure relief at beginning of insertion whilst regaining the pres-sure at the end of the insertion.

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METAL ION LEVELS AND X-RAY FOLLOW-UP AS PREDICTORS FOR PROBLEMS AND OUTCOME IN HIP RESURFACING ARTHROPLASTY De Smet Koen A., De Haan Roel, Gill Harinderjit1, Ebramzadeh Edward 2, Campbell Pat 2. Anca Medical Center, Krijgslaan 181 9000 Gent, Belgium.+3292525903, +3292526457, [email protected] While the limitations of radiographs to detect wear in metal-on-metal implants are well known, using metal ion measurements to monitor wear is not generally performed. The clinical experience in this large volume resurfacing center was reviewed to determine if the ion measurement was justified. Almost 300 patients provided blood sam-ples which were tested by AAS for cobalt and chromium levels in the serum. Initially, ions were taken mainly in cases with suspected high wear, but later, samples were taken more routinely as part of the clinical assessment. The optimum intervals for assessment were reviewed based on the study of 3300 radiographs from over 2000 patients. This included 45 revisions (pre-revision HHS was 73/100, range 40-96), where there were 65% malpositioned cups, 8 cases of severe metallosis, 6 with neck narrowing, and 7 with osteolysis. The routine radiographic assess-ment was based on the standing pelvis and AP, lateral profile views of the hip, in order to fully examine the com-ponent interface features such as lucent lines, component position, (particularly cup angle and anteversion) and bone features such as osteolysis and neck narrowing. Recommendations and Discussion: Well functioning unilateral resurfacings typically had ion levels < 5 µg/l at 2 years. Much higher ion levels (up to 94 µg/l ) were associated with malpositioned components (steep cup angles with a mean of 64.38 degrees, range 55-98). Revisions of such cases were often noted to have metallosis, and bursa formation which required extensive soft tissue removal. Prior to revision the serum chromium levels averaged 19.9µg/l (range 0.4-93.0), and serum cobalt levels averaged 15.9µg/l (range 13.0-94.0). The intra-operative joint fluid chromium levels had a mean of 3190 µg/l (range 19.0-29080) and fluid cobalt levels were 808.0 µg/l (range 13.0-5120). There was a high positive correlation between both the hip fluid levels and serum levels (p < 0.001). These cases were revised up to 70 months post-operatively and had not been followed routinely by the referring surgeons. To avoid the risks from high wear, cases with malpositioned cups and high metal ions should receive an early revision to THR, preferably with ceramic-ceramic bearings. The higher the metal ions, the sooner and the bigger the lucent lines around the stem, and osteolysis will be seen. If the patient is seen earlier than 2 years, the negative findings on x-ray may not be seen and only the metal ion serum levels can be used as a diagnostic tool to help the decision making process for revision of malpositioned implants. These observations suggest the following:

1) metal ion levels can be used as a diagnostic and follow-up tool in hip resurfacing ion levels with radiology findings and can predict resurfacing outcome and an estimation of the expected problems at revision

2) the use of these 2 exams is important because follow-up tools such as the Harris Hip Score are sometimes not useful

3) in the absence of high ions, lucent lines around the stem and high abduction angles (>50 degrees), a good long term outcome can be predicted

1Nuffield Orthopaedics, University of Oxford. 2UCLA/Orthopaedic Hospital, Los Angeles

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IS METAL-ON-METAL RESURFACING HIP ARTHROPLASTY CONSERVATIVE FOR ACETABULAR BONE? A comparison of acetabular bone conservation between conservative THA and Metal-on-Metal Resurfacing Hip Arthroplasty using Computed Tomography

Naitoh Mitsuhiro, Kabata Tamon, Maeda Toru, Taga Tadashi, Ando Tomonari, Tomita Katsuro Department of Orthopaedic Surgery, Kanazawa University School of Medicine, 13-1 Takaramachi Kanazawa Ishikawa, 920-8641, Japan Phone: +81-76-265-2374, Fax:+81-76-234-4261, E-mail: [email protected] Purpose: Recently, Metal-on-Metal Resurfacing Hip Arthroplasty (MOMRHA) has attention again and is being performed especially for young active patients. Compared with conventional Total Hip Arthroplasty (THA), MOMRHA can preserve more bone stock for the femoral side. However, the preservation of bone stock after MOMRHA has not been assessed on the acetabular side. The purpose of this study is to compare conservation of acetabular bone after MOMRHA and conventional THA. Patients and Methods: Two series of patients, one of 32 consecutive patients who had a conventional THA with a HA coated pressfit acetabular component (Trident, Stryker), and a second series of 18 consecutive patients who had a MOMRHA (Birmingham hip resurfacing, Smith & Nephew) were included in this study. DICOM formatted CT data was taken preoperatively and posteoperatively for all cases. We measured the maximum bony acetabular diameter using a 3D-templating system (Hip-OP) preoperatively, and calculated the ratio of the maximum acetabular diameter to the implanted acetabular component size postoperatively. We compared the maximum acetabular diameter / the im-planted acetabular component size ratio (Acetabulum-Component ratio) in both groups. From the post operative CT, we also evaluated the position of the implanted acetabular components. Results: The Acetabulum-Component ratio was 1.03±0.02 with MOMRHA, and 1.02±0.01 with conventional THA. No significant difference was found between the two groups. In both groups, no acetabular components perforated the medial wall of the acetabulum indicating that correct medial positioning was achieved. Conclusion: Our results indicate that removal of bone on the acetabular side in MOMRHA is comparable with that of conven-tional THA.

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IMPLANT RETRIEVAL ANALYSIS OF FAILED HIP RESURFACINGS Campbell Pat, Esposito Christina, Nelson Scott, Lu Zhen, De Smet Koen 1, Amstutz Harlan C 2. JVL Research Cntr, Orthopaedic Hospital 2400 S. Flower St, Los Angeles CA 90007 USA 213 742 1134 fax 213 744 1175, [email protected] Introduction: Metal-on-metal bearings have eliminated wear-induced osteolysis as the major cause of failure but current compli-cations include femoral neck fractures and femoral component loosening. This lab has performed retrieval analysis on over 180 failures to understand which failures may be preventable through optimized patient selection and sur-gical techniques.

Materials and Methods: Five different designs from 25 surgeons at different levels of experience and using different implant types were studied. The main reason for failure was femoral neck fracture; other reasons included component loosening, acetabular malposition, sepsis and unexplained pain, including suspected metal sensitivity. Component wear was measured with a coordinate measuring machine. The implants were sectioned, the slices were radiographed then decalcified for routine histology. Results: Wear was generally a few microns per year with the exception of cases revised for poor acetabular position, where focal edge loading caused higher wear rates resulting in tissue metallosis and often enlarged, fluid-filled bursas or local muscle necrosis. Osteolysis within the femoral head was also found with high wear and delayed revision. Cement penetration was highly variable ranging from almost zero to almost complete filling. Incomplete seating and layers of cement exceeding manufacturer recommendations were common. There was significantly more ce-ment in femoral loosening cases (p < 0.001) although in some, the lack of cement penetrations was considered the cause of complete dissociation of bone from the implant. The bone surrounded by cement was dead but nearby, the bone was mostly viable and remodelling, except in a small number of cases with total ischemia which fractured after more than a year through the interface between dead and living bone. Short-term fractures occurred through areas of new woven bone at the component neck junc-tion, consistent with repair of surgical damage. Lymphocytic infiltrates were present in variable amounts in ap-proximately one third of cases, but were only considered as possibly indicating an immune reaction in 3 of the cases revised for unexplained pain. These cases had low component wear suggesting that these patients were aller-gic to metal wear products. Discussion: Many of these failures appear to be the result of technical errors such as incomplete seating, possibly resulting in additional force to place the implant. Many short-term fractures occurred through healing areas of the neck includ-ing uncovered reamed bone, and microfracture repair. While some components loosened completely because of inadequate cementation, we found more cement in the loosened femoral heads. One finding of concern was the metallosis, bursa swelling and necrosis in cases with socket malposition. The correct placement of both the acetabular and femoral components is critical to avoid focal high wear and metallosis. The timely revision of mal-functioning implants or those in patients with metal hypersensitivity is recommended to avoid local tissue prob-lems and osteolysis. 1ANCA Clinic, Krigslaan 181, 9000 Gent, Belgium 2St Vincent’s Hospital, Los Angeles, CA

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A MECHANICAL ANALYSIS OF FEMORAL RESURFACING IMPLANT FOR OSTEONECROSIS OF THE FEMORAL HEAD Presenting Author: Daigo Sakagoshi Takaramachi 13-1 Kanazawa Ishikawa Japan 920-8641 E-Mail: [email protected] Background: Femoral head resurfacing became a popular procedure for avascular necrosis of femoral head. However, it is not clear about changes in femoral mechanics after femoral resurfacing arthroplasty associated with individual extent of necrosis. We evaluated changes in resurfaced femoral mechanics for the various extent of ne-crosis with finite element analysis method.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" Materials and Method: This study uses computer tomography based finite element analysis to determine the stress distribution and distortion of implant, bone and cement in the resurfaced femoral head. We set three patterns of necrosis by depth from the surface of femoral head. Extension of necrosis from 0 to a quarter of femoral head diameter is type A, from a quarter to a half is type B, from a half to three-fourths is type C. And we set five types of different stem angle from 125 to 145 degrees for the axis of femoral shaft. For these models we evaluated biomechanical changes associated with extent of osteonecrosis and stem angles. Results: Stress distribution at the bone-cement interface increased with expansion of necrosis at each stem angles. The maximum stress of the prosthesis was observed around stem shaft at each models, and which de-creased with stem angle ranged from 130 to140 degrees. Discussion and Conclusion: This study indicated that resurfacing for large extent of osteonecrosis and excessive varus or valgus implantation of prosthesis would have a potential adverse biolomechanical effects.

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EVOLUTION OF KNEE KINEMATICS CONCEPTS. FROM HISTORY TO MODERN DATA Michel Bercovy Clinique les Fontaines & University Paris XII 54 Bd ARISTIDE BRIAND - 77008 MELUN FRANCE Phone +33614707008 Fax +33140430430 [email protected] The classic concept of knee kinematics is based on "rollback" which describes a posterior displacement of the femoral condyles on the tibial articular surface during knee flexion. This concept gave birth to the postero stabi-lised design by John Insall, and is since 1980 at the origin of the majority of TKA designs. This paper aims to describe the bases of this concept and how modern kinematics data has fine tuned our under-standing of knee kinematics and opened new possibilities in TKA design. In 1836, the Weber brothers, through anatomical observations on cadaver, described for the first time the posterior displacement of the femoral condyles during flexion. In 1891 Braune and Fisher demonstrated a progressive and asymmetric variation of the condyles radius in the sagital plane. In 1911 Fick reanalyzed the condyles shapes by using 3 rather than 2 dimensions and concluded that the flexion extension axis of the knee was not in the sagital plane, but was offset at the top of conus, with a fixed radius, this radius being different for each condyle. These concepts prevailed until the seventies when Kapandji summarized these theories and was at the origin of Insall's came on post said posterostabilised design were the condyles are constrained to a constant posterior displacement on the tibia. During the nineties, modern 3D in-vivo technology demonstrated different knee kinematic patterns. Fluoroscopic gait analysis by Dennis and Komistek emphasized that the displacement of the lateral condyle is in general in a posterior direction, but could also occur in an anterior direction. These translations were combined with a lift-off of the lateral condyle. The data obtained on MRI studies by Pinskerova and Freeman on one side and by TODO on the other side showed clearly that the movements were not that of the femoral facet centre (or rigid body), but that they resulted in the displacement of the contact point between femoral condyles and tibia as a consequence of the difference of the shapes of both articular surfaces during flexion. Furthermore Smith suggested that these movements were more constrained by the dynamic forces resulting from soft tissue balance than from bone geometry. Finally it was shown by Kanekasu on in-vivo studies that knee kinematics consisted in general in an external rota-tion with posterior displacement of the lateral condyle, but that this movement could occur in an anterior and inter-nally rotated direction during deep flexion above 120° and is associated with an upward elevation of the lateral condyle. Conclusion: Modern studies demonstrate that knee kinematics is not limited it to a simple posterior constrained displacement of the femur on the tibia but that the natural movement occurs in 3D. The volume has the shape of a cone with a me-dial summit and a lateral base. In this conic volume, the displacement of the lateral condyle is in general posterior and externally rotated, but it may be anterior, internally rotated and with an upward elevation. These concepts on knee kinematics open new possibilities in TKA design.

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TOTAL KNEE ARTHROPLASTY OUTCOME: A NEW TOOL FOR OBJECTIVE ANALYSIS OF GAIT COORDINATION Jolles Brigitte M, Dejnabadi Hooman, Martin Estelle, Leyvraz Pierre-Francois, Aminian Kamiar. Hôpital Orthopé-dique de la Suisse Romande (HOSR), Centre Hospitalier Universitaire Vaudois, University of Lausanne, 1005, Lausanne, Switzerland. Tel : +41 21 545 06 29 ; Fax : +41 21 545 04 16, [email protected]

Introduction: Coordination is a strategy chosen by the central nervous system to control the movements and maintain stability during gait. Coordinated multi-joint movements require a complex interaction between nervous outputs, biome-chanical constraints, and proprioception. Quantitatively understanding and modeling gait coordination still remain a challenge. Surgeons lack a way to model and appreciate the coordination of patients before and after surgery of the lower limbs. Patients alter their gait patterns and their kinematic synergies when they walk faster or slower than normal speed to maintain their stability and minimize the energy cost of locomotion. The goal of this study was to provide a dynamical system approach to quantitatively describe human gait coordination and apply it to patients before and after total knee arthroplasty. Methods: A new method of quantitative analysis of interjoint coordination during gait was designed, providing a general model to capture the whole dynamics and showing the kinematic synergies at various walking speeds. The pro-posed model imposed a relationship among lower limb joint angles (hips and knees) to parameterize the dynamics of locomotion of each individual. An integration of different analysis tools such as Harmonic analysis, Principal Component Analysis, and Artificial Neural Network helped overcome high-dimensionality, temporal dependence, and non-linear relationships of the gait patterns. Ten patients were studied using an ambulatory gait device (Physilog®). Each participant was asked to perform two walking trials of 30m long at 3 different speeds and to complete an EQ-5D questionnaire, a WOMAC and Knee Society Score. Lower limbs rotations were measured by four miniature angular rate sensors mounted respec-tively, on each shank and thigh. The outcomes of the eight patients undergoing total knee arthroplasty, recorded pre-operatively and post-operatively at 6 weeks, 3 months, 6 months and 1 year were compared to 2 age-matched healthy subjects. Results: The new method provided coordination scores at various walking speeds, ranged between 0 and 10. It determined the overall coordination of the lower limbs as well as the contribution of each joint to the total coordination. The difference between the pre-operative and post-operative coordination values were correlated with the improve-ments of the subjective outcome scores. Although the study group was small, the results showed a new way to objectively quantify gait coordination of patients undergoing total knee arthroplasty, using only portable body-fixed sensors. Conclusion: A new method for objective gait coordination analysis has been developed with very encouraging results regarding the objective outcome of lower limb surgery.

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EFFECT OF MENISCAL ATTACHMENT TECHNIQUE ON KNEE CONTACT MECHANICS D’Lima, Darryl D, Kessler, Oliver, Colwell Jr, Clifford W. (11025 N. Torrey Pines Road, Suite 140, La Jolla, Ca 92037) (858-332-0166/858-332-0140/[email protected]) This research was done at the Shiley Center for Orthopaedic Research and Education at Scripps Clinic and was designed to study meniscal attachment technique.

INTRODUCTION: The meniscus is a load sharing structure and acts as a cushion to distribute knee stresses. Loss of the meniscus sub-stantially reduces contact area and is associated with increased contact stresses, resulting in cell death and matrix degeneration. Meniscal tears and partial or total meniscectomy have been associated with early onset OA. Thera-peutic replacement could restore load bearing and contact conditions. Both allograft and artificial replacements may suffer from attachment technique issues such as site of attachment and biomechanics of attachment technique. We developed a computation model of the knee to study the effect of meniscal attachment technique on knee-contact biomechanics. METHODS: Surface geometry of femoral and tibial cartilage and the menisci was segmented and reconstructed from an MRI of a normal knee using a commercially available program (MIMCS, Materialise, Belgium). A solid mesh was gener-ated from the surface geometry in Hypermesh (Altair Inc, Santa Ana, CA). Subchondral bone was treated as rigid surfaces. Femoral and tibial cartilage was meshed with linear elastic isotropic (stiffness = 15 MPa) hexahedral elements. The medial meniscus was meshed as an orthotopic elastic material: 20 MPa stiffness (radial/vertical directions), 150 MPa stiffness (circumferential direction), and 58 MPa shear modulus to simulate increased stiff-ness and strength due to the circumferential collagen fiber organization. Meniscal horns attachments were simu-lated using springs The stiffness of the springs was modulated to simulate no attachment, suture constructs (mean stiffness, 1–50 N/mm), and bone plug anchorage. Axial load representing bodyweight (600N) acting on the entire knee was applied on the femur with the knee in full extension. Contact area, contact stresses, and meniscal horn displacement were computed during the applied load using a commercial finite element analysis package (MSC.MARC, MSC.Software, Santa Ana, CA). RESULTS: In the intact condition, femoral contact area was 289mm2 and peak stresses reached 2.93 MPa, (average, 1.04 MPa). With total meniscectomy, femoral contact area decreased by 26% with a concomitant increase in mean con-tact stresses (36%) and peak contact stresses (17%). Replacing the meniscus without suturing the horns did little to restore femoral contact area because the horns separated easily under load (>4mm displacement) and circumferen-tial stiffness was insufficient to maintain meniscofemoral contact. Suturing the horns increased contact area and reduced peak/mean contact stresses. Low stiffness sutures (1 N/mm) allowed the horns to displace up to 2.5mm. Sutures of the highest stiffness (50N/mm) reduced displacement to sub-millimeter levels. Increasing suture stiff-ness correlated with increased contact stresses as greater tibiofemoral load was transferred to the meniscus. A small incremental benefit was seen of simulated bone plug fixation over the highest stiffness suture construct. DISCUSSION & CONCLUSION: The specific values of these contact outcomes may not apply to all knees, however, trends may be broadly applica-ble. Our results indicate that the method of horn fixation is critical to restoring normal conditions. Suturing the horns with high tensile stiffness sutures approximated the contact conditions generated while using bone plugs for fixation. Suturing the rim was also tested but did not appear to substantially affect contact conditions. This model may also be useful in predicting the effect of biomaterial mechanical properties and meniscal replacement shape on knee contact conditions.

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IN VIVO COMPARISON OF TKA KINEMATICS WITH ULTRA CONGRUENT AND CONGRUENT POLYETHYLENE INSERTS IN NATURAL KNEE II CR TKA Mueller, John Kyle P., Longenecker, Stanton L., Anderle, Mathew R., Komistek, Richard D., Mahfouz, Mohamed R. Correspondence: Richard D. Komistek 301 Perkins Hall University of Tennessee Knoxville, TN 37996 Email: [email protected] Presenting author: Phone: (262) 352-5208, Fax: (865) 946-1787, [email protected] The objective of this study was to determine the in vivo kinematics for subjects implanted with a Natural Knee II cruciate retaining (CR) total knee arthroplasty (TKA) implanted with either an ultra congruent polyethylene (UCPE) insert or a congruent polyethylene (CPE) insert. Forty subjects implanted by a single surgeon were asked to perform maximum weight-bearing flexion while under fluoroscopic surveillance. Four patients with an average age of 73.5 years (60 to 83 years, Standard Devia-tion=11.4) and 36 subjects with average age of 69.9 years (48 to 85 years, Standard Deviation=8.4) were im-planted with a Natural Knee II TKA with UCPE and CPE inserts, respectively. The in vivo 3-D kinematics of the TKA, including the femorotibial contact positions, axial rotation and occurrences of condylar lift off greater than 1 mm along with maximum flexion angle were determined by analyzing fluoroscopic images throughout flexion at 30 degree increments. The average weight-bearing flexion was 106 and 112 degrees with 75.0% and 80.6% of the TKA reaching a maxi-mum flexion greater than 100 degrees for subjects having UCPE and CPE inserts, respectively. The average amount of posterior femoral rollback (PFR) of the lateral condyle was -3.1 mm (-8.0 to -0.4 mm, Standard Devia-tion=3.5) and -6.7 mm (-14.1 to 0.3 mm, Standard Deviation=3.7) with 100% and 97% of the TKA experiencing PFR for the UCPE and CPE groups, respectively. The medial condyle experienced, on average, 1.4 (-1.2 to 2.5 mm, Standard Deviation=1.8) and 1.5 mm (-4.3 to 8.0, Standard Deviation=2.6) anterior movement with 25% and 16.7% of the TKA experiencing PFR in the UCPE and CPE groups, respectively. The average amount of axial rotation was 5.3 and 9.6 degrees, for subjects implanted with UCPE and CPE inserts, respectively. One of the 36 (3%) TKA from the CPE group had opposite axial rotation. None (0%) of the subjects with UCPE inserts experi-enced condylar lift-off and 9 of the 36 (25%) with CPE inserts experienced condylar lift-off greater than 1 mm. Although only 4 were analyzed, the TKA with UCPE inserts averaged less posterior translation of the lateral condyle and less positive axial rotation than TKA with the CPE inserts, suggesting that polyethylene geometry may have an affect on Natural Knee II CR TKA kinematics. The Natural Knee II CR TKA, designed to perform similar to the normal knee, experiences minimal medial translation in the anterior direction and consistent posterior femoral rollback of the lateral condyle. This results in consistent normal axial rotation. In fact, the only TKA to experience opposite axial rotation was also the only TKA which experienced anterior movement of the lateral condyle. Previous investigations into CR TKA have shown they experience inconsistent and variable kinematics from TKA to TKA, however the Natural Knee II CR TKA experiences fairly consistent kinematics as is evidenced by only 1 CPE TKA experiencing opposite axial rotation and anterior movement of the lateral condyle.

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STABLE TIBIOFEMORAL KINEMATICS WITHOUT POST/CAM SUBSTITUTION Authors: Moonot P, Railton GT, Mu S, Banks SA, Field R Correspondence: 1A, Cotswold Road, Sutton, Surrey, SM2 5NG, UK Tel: 0044 7916120887 Fax: 0044 2082963475 Email: [email protected] Introduction and Aims: Many authors suggest that PCL sacrifice and substitution with a post/cam type mechanism are required to achieve repeatable and stable tibiofemoral motion with total knee arthroplasty. The goal of this study was to evaluate the performance of an asymmetric, medial rotation knee arthroplasty design during a dynamic stair climbing activity. Method: Fifteen knees in thirteen subjects with primary medial rotation total knee arthroplasty were observed performing a step-up/down activity on a 25cm riser. Knee motions were recorded using lateral fluoroscopy. Subjects averaged 74 years of age and nine were female. Subjects were an average of 17 months post-operative, and scored 94 points on the International Knee Score and 99 on the Functional Score. Digitized fluoroscopic images were corrected for geometric distortion and 3D models of the implant components were registered to determine the 3D position and orientation of the implants in each image. Results: Tibiofemoral translations during the stair activity were quite small throughout the flexion range. From full exten-sion to 20° flexion, the medial and lateral condyles moved an average of 1mm posterior, and from 20° to 60° flex-ion the condyles moved an average of 1mm anterior. No ‘paradoxical’ translation of the medial condyle was ob-served. Conclusion: Patients with medial rotation knee arthroplasty exhibited stable tibiofemoral motion during a stair climbing activ-ity. Contrary to numerous previous reports on non-PS fixed-bearing total knee arthroplasty, no anterior sliding of the femur with flexion was observed. An asymmetric tibiofemoral surface with one compartment providing AP stability and the opposite compartment allowing rotational freedom appears to provide sufficient intrinsic con-straint to control tibiofemoral motions during dynamic weight-bearing activities. The absence of post-cam system may be beneficial as this may reduce the wear debris in the joint and may increase the longevity of the knee arthro-plasty.

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B1-6 EXPERIMENTAL AND NUMERICAL ANALYSES OF THE CONTACT PRESSURE AND KINEMATICS AT THE TIBIAL/ FEMORAL INTERFACE IN A BI-CRUCIATE STABILISED TKA DURING GAIT Labey Luc, Innocenti Bernardo, Wong Pius, Bellemans Johan, Victor Jan European Centre for Knee Research, Technologielaan 11bis, 3001 Heverlee, Belgium Tel + 32 16 301418, Introduction A bi-cruciate stabilized total knee replacement, featuring a post-cam mechanism to replace the function of the cruciate ligaments, is designed to reproduce the kinematics of the native human knee. In this work, the results are presented of an analysis of the contact pressures and the kinematics of such an implant during normal gait using both numerical and experimental techniques. Materials and methods A Journey Bi-Cruciate Stabilized Knee System (Smith&Nephew, Inc., Memphis, TN) was placed in the Prosim Knee Joint Simulator (Simulation Solutions, Stockport, UK) using bone cement. K-scan 4000 pressure sensitive film (Tekscan, South Boston, USA) was fixed to the insert. The wear simulator was programmed to simulate a full gait cycle using the load data from the ISO14243-1 standard. These measurements were recorded during 10 gait cycles. A three-dimensional explicit finite element model of this knee system was developed in order to simulate a gait cycle for verification and comparison with the experimental results. Joint kinematics analysis was performed using gait cycles identical to those in the experimental study. Results and discussion The Teskscan measurements showed that the contact areas were generally larger on the medial side than on the lateral side (85 vs. 73 mm² at the point of maximum load). The maximum average contact pressure (during stance) reached values up to 6 MPa. This is an underestimate, though, since the sensor saturated at stresses above 12 MPa. Combining the real load (as measured with the load cell of the wear simulator) with the contact area given by the pressure sensitive film, gives a maximum average contact pressure of 8 MPa. Peak pressures were always larger than 12 MPa during stance. In the FEA analysis, the average contact pressures were slightly higher on the lateral condyle than on the medial condyle (6 MPa vs. 5 MPa), since the contact area was smaller laterally (235 mm² vs. 300 mm²). The peak contact pressure reached a maximum on the medial condyle, which was only slightly higher than 15 MPa. Contact areas calculated by the FEA were greater than those determined experimentally, because the sensor has a lower threshold at which it detects pressure (0.1 MPa). In FEA, the center of pressure (cop) of the lateral femoral condyle moved posteriorly in the first third of stance phase (0-0.2 sec) over a distance of 8 mm, came back to almost its original position during the second third of the stance phase (0.2-0.4 sec) and moved posteriorly again during the last third of stance. During the initial swing phase, the lateral contact point moved posteriorly over 2 cm. The medial contact point exhibited similar behavior to the lateral contact point during the stance phase, although with a smaller amplitude. During the entire swing phase, the medial contact point moved only slightly. The experiments showed similar kinematics of both cop’s during the stance phase, though less pronounced. The large displacement of the lateral cop during swing phase could not be verified experimentally. The Tekscan re-cordings showed almost no displacement of this point during swing phase. Conclusion In this work, analyses of the contact pressure and the kinematics between the femoral and tibial components were conducted. The results from the numerical contact model were verified with the experimental technique. Overall, the experiments and computer simulations showed quite satisfying agreement, concerning contact ar-eas, contact pressures as well as kinematics. The discrepancies that were observed can usually be attributed to un-avoidable differences between experiments and computer simulations. The obtained stresses are significantly below the yield strength of conventional UHMWPE. Both experiments and computer simulations show kinematics of the implant which is comparable to kinematics observed from native human knees.

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KNEE MOMENTS AND SHEAR MEASURED IN VIVO DURING ACTIVITIES OF DAILY LIVING AFTER TOTAL KNEE ARTHROPLASTY D'Lima, MD, Darryl D, Patil, Shantanu, Steklov, Nikolai, Chien, Shu, Colwell Jr, Clifford W. (11025 N. Torrey Pines Road, Suite 140, La Jolla, Ca 92037) (858-332-0166/858-332-0140/[email protected])

This research was done at the Shiley Center for Orthopaedic Research and Education at Scripps Clinic and was designed to study all six components of tibial forces after TKA.

INTRODUCTION: Component survivorship, implant wear, and integrity of the bone–implant interface have been shown to be depend-ent on tibiofemoral forces in total knee arthroplasty. We have previously reported the axial knee forces in vivo. In this study, a second-generation, force-sensing device that measured all six components of tibial forces was tested.

METHODS: A custom tibial component was manufactured by Zimmer, Inc., based on the Natural Knee II (NK-II) tibial tray design. The tray and locking mechanism were identical to the standard design for implantation with a standard insert. The stem was instrumented with strain gauges to measure three orthogonal forces and three moments and a microtransmitter for telemetry through a tantalum antenna. Details of the implant design and accuracy have been previously reported. The instrumented tibial component was implanted in a 74-Kg, 83-year-old male. Three months after surgery, knee kinematics, ground reaction forces, and knee forces were measured during activities of daily living. RESULTS: Peak total force was 2.1 xBW (times body weight) during walking, 2.5 xBW during chair rise, 3.1 xBW during stair climbing, and 2.2 xBW during squatting. Overall, the axial component of force averaged 86% of the total knee force and greater than 98% of the forces during stance phase of gait. Peak anteroposterior (AP) and me-diolateral (ML) shear forces were substantially lower than the axial component for all the activities studied. Peak anterior shear force was 0.30 xBW during walking, 0.17 xBW during chair rise, 0.26 xBW during stair climbing, and 0.15 xBW during squatting. Overall, AP shear was mainly directed anteriorly for all activities. During walk-ing and stair climbing, ML shear was medially directed during the swing phase and during heel strike, changing to a lateral direction early in the stance phase. External knee flexion moments increased with knee flexion angle and peaked at 5.7% BWxHt (flexion = 90°) dur-ing chair rise and 4.3% BWxHt (flexion = 82°) during squatting. The flexion moment generated by the joint reac-tion force on the tibial tray peaked at a much lower levels: 1.9% BWxHt for chair-rise activity and 1.7% BWxHt for squat activity. However, a strong linear correlation was noted between the external knee flexion moment and the flexion moment measured at the tibial tray (r2 = 0.81 for chair rise and r2 = 0.87 for squat activity). Peak adduction moment generated by the joint reaction force was 0.53 %BWxH (percent body weight x height) during walking, 0.35 %BWxH during chair rise, 0.53 %BWxH during stair climbing, and 0.26 %BWxH during squatting. External adduction moment correlated poorly with and was typically 10 times greater than adduction moment generated by the joint reaction force. DISCUSSION: The axial component of forces predominated during all activities studied. Shear forces were very modest com-pared to total knee forces. One reason could be that the soft tissues around the knee absorbed most of the external shear forces. External knee moments did not correlate well with moments generated at the tibial tray. These results highlight the importance of direct measurements of knee forces.

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AN ANALYSIS OF IN VIVO KNEE FORCES WHILE RISING FROM A CHAIR AFTER KNEE ARTHROPLASTY D’Lima, Darryl D., Patil, Shantanu, Steklov, Nikolai, Colwell Jr, Clifford W. (11025 N. Torrey Pines Road, Suite 140, La Jolla, Ca 92037) (858-332-0166/858-332-0140/[email protected])

This research was done at the Shiley Center for Orthopaedic Research and Education at Scripps Clinic and was designed to analyze in vivo knee forces while rising from a chair after TKA. INTRODUCTION: Rising from a chair generates substantially higher flexion moments than walking. Pain or reduction in knee func-tion affects the ability to rise from a chair, particularly in the older population. The height of the chair seat is a major factor affecting the ability to rise from a chair. Elderly patients with chair-rise difficulties typically require a seat height at 120% of the knee joint to floor distance (Weiner DK, J Am Geriatr Soc, 1993 ). Even in young, nor-mal subjects, knee moments during chair rise were significantly affected by the height of the chair (Rodosky, J Orthop Res, 1989). Another important factor is implant design. Femoral components with longer extension mo-ment arms can reduce quadriceps forces during a deep knee bend (D’Lima, Clin Orthop, 2001). We directly meas-ured in vivo knee forces during chair rise in two knee arthroplasty patients implanted with force-sensing tibial trays.

METHODS: One patient (JW: male, 147 lbs, 80-years old) was implanted with a tibial tray that measured axial forces (D'Lima et al., Clin Orthop 2005). The other patient (PS: male 163 lbs, 82-years old) was implanted with a tibial tray that measured the three orthogonal forces and three moments (Kirking et al., J Biomech, 2005). The height of the chair seat was varied between 85% and 120% of the patients’ knee joint to floor distance. The effect of seat height on knee kinematics and tibial forces were analyzed.

RESULTS: The vertical component of force predominated during chair rise, averaging 98 ± 3% of the magnitude of the total force. The relative height of the chair seat did not significantly affect peak total tibial force. Peak anterior shear components were small (range, 0.1 – 0.3 xBW) but did change with seat height: peak anterior shear at seat height levels of 85% and 90% were twice as high as those at seat height levels of 100% and 120% (p = 0.002).

As expected peak knee flexion angle increased with decreasing seat height (r2 = 0.95, p = 0.02). Peak flexion mo-ments increased with decreasing seat height (r2 = 0.88). Flexion moments generated at the tibial tray (measured directly by the instrumented tibial prosthesis) correlated strongly with peak flexion angle during chair rise (r2 = 0.79). Note that the flexion moment on the tibial tray is generated by the net joint reaction force. Therefore, a net joint reaction force acting posterior to the center of the tray exerts a positive flexion moment and would be consis-tent with femoral rollback. DISCUSSION: The ability to rise without support from a chair with a seat height as low as 85% of knee joint to floor distance in-dicates a reasonable postoperative recovery by 6 months. Despite the reports of increased external knee flexion moments with lower seat heights, our data indicate that net joint reaction force magnitudes were not substantially increased. Anterior shear on the tibial tray did increase, although the magnitude was relatively low. The increas-ing flexion moment on the tray may be of importance to the bone–implant interface.

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PATTERN OF MUSCLE ACTIVITY AND TIBIOFEMORAL CONTACT FORCES ASSESSED BY INTEGRATION OF IMAGING AND MOTION ANALYSIS TECHNIQUES BEFORE AND AFTER TOTAL KNEE REPLACEMENT Santilli, Valter, Don, Romildo Address fo correspondence: Dipartimento di Scienze dell’Apparato Locomotore - Università degli Studi di Roma La Sapienza - Piazzale Aldo Moro, 5 - 00185 Roma (Italia) Author’s phone number: +39 06 49 91 41 92 Fax: +39 06 49 91 41 92 E-mail address: [email protected] The development of abnormal tibiofemoral contact forces during repetitive activities of daily life is crucial for both the progression of knee osteoarthrosis and the wear of polyethylene insert. Static evaluation of joint contact areas during weight-bearing standing posture, as achieved by imaging techiniques, provides useful information for iden-tifying biomechanical factors involved in both processes, but it does not allow to measure the load applied at the joint during movement, which includes not only body weight, but also muscle forces. Similarly, motion analyses provides information concerning knee kinematics and kinetics and the pattern of muscle activity around the joint, but it fails in providing quantitative data about the actual loads supported by the tibial insert and, more important, its distribution on the insert surface. In this research, that was done in the University of La Sapienza in Rome, we developed an integrated imaging - motion analysis technique aimed at studying the load actually applied at the tibiofemoral interface and its distribu-tion on contact areas, and at testing the hypothesis that a relationship may exist between the load pattern and the characteristics of muscle activity during activities of daily living. The digitized data from imaging techniques were used to obtain the position of anatomical structures around the knee joint during execution of walking, stair ascent and descent and squatting motion which were recorded by means of a motion analysis system including an 8-cameras optoelectronic system, 2 force platforms and a 16-channels electromyography. We tested a sample of nor-mal subjects and a sample of patients affected by knee osteoarhrosis, both before and after total knee arthroplasty. The main results of our study are: i) the degree of knee flexion is the main factor affecting the size of contact areas; ii) co-activity index of quadriceps muscle and hamstrings, which is greater in osteoarthritic patients than in normal subjects, is positively correlated to the contact forces and to the contact areas, with no significant effect on the con-tact pressures; iii) the position of contact areas significantly varies among subjects, but not within subject among the different motor activity; iv) stair descent is the motor activity showing the higher values of contact pressures in patients with knee osteoarthrosis, whereas squatting motion is the most striking activity in normal subjects; v) the load and muscle pattern do not significantly change after knee replacement. This newel technique can be used as a pre-operative assessment to provide the surgeon information concerning the knee load pattern, to establish appropriate pre- and post-operative rehabilitation management aimed at preventing abnormal loads, to provide the patient information concerning what motor activities may affect the duration of the prostheses and to project knee prostheses design that may take into account the need for differential mechanical properties of different regions of the polyethylene insert according to the patient’s peculiar load pattern.

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IN VIVO MEASUREMENTS OF LOADS AND MOMENTS THREE MONTHS POST-OPERATIVELY USING AN INSTRUMENTED TIBIAL TRAY

Heinlein, Bernd; Kutzner, Ines; Halder, Andreas; Beier, Alexander; Bender, Alwina; Rohlmann, Antonius; Graichen, Friedmar; Bergmann, Georg Charite, Universitaetsmedizin Berlin, Campus Benjamin Franklin, Biomechanics Lab, Hindenburgdamm 30, Berlin, Germany Phone: +49-30-8445-4730, Fax: +49-30-8445-4729, Email: [email protected]

Introduction: An instrumented tibial tray was developed to enable six-component load measurements in a primary total knee replacement [1]. Two metallic plates are separated by a small gap allowing load-dependent deformation of the prosthesis. Six semiconductor strain gages were placed inside the hollow stem measuring the corresponding strains. The prosthesis was calibrated pre-operatively. Combinations of 6 known load components [2] were applied on 21 points on top of the tibial tray. For each loading point the six strain gages produce six signals which are de-pendent on these six load components. In vivo load measurement data are extremely valuable for improving knee arthroplasty, better understandiung of the knee biomechanics and advising patients. Methods: The prosthesis was implanted using conventional surgical technique in a 63 year old male patient suffering from gonarthrosis of the left knee. First measurements were taken immediately post-operatively. Subsequent measure-ments were taken 1, 2, 4, and 10 weeks post-operatively. All activities were captured on a digital video tape simul-taneously with the strain gage signals [3]. The activities performed included standard physiotherapy, level walking and stair climbing with and without crutches, stationary cylcling, treadmill walking with different walking speeds, squatting and getting out of a chair with and without support. Results: The calibration resulted in an accuracy of the prosthesis better than 5 % for all load components including crosstalk. Only the medio-lateral force component had a slightly lower accuracy. Stable signals were obtained im-mediately after mounting the external coil and antenna to the patients leg. Specialized software displays the forces and moments in combination with a video clip of the performed activity. The direction and magnitude of the resul-tant force is displayed in three orthogonal planes. The resultant force increased from approx. 1.5* BW one week postoperatively to 2*BW after 4 weeks while walk-ing with crutches. The rotation moment along the long axis of the tibia increased in the same period from 3.5 to 9.5 Nm. The varus-valgus moment peaked at approx. 20 Nm throughout the first 4 weeks postoperatively. The antero-posterior and medio-lateral shear forces increased from approx. 0.12*BW to 0.2*BW. After 10 weeks the patient was able to walk without crutches. However, the increase in loading was relatively low. The resultant force showed maximum values up to 2.5*BW, depending on the walking speed. Stationary cycling showed values in the range of 1*BW for the resultant force. Discussion: The values for the moment along the long axis of the tibia were suprisingly high. According to the ISO standard for wear testing of tibial inserts, the expected and recommended value is only 6 Nm compared to nearly 10 Nm measured in this first patient. The amount of UHMWPE wear using such an enhanced value is supposed to in-crease dramatically. Further implantations and measurements in up to 10 patients will give statistical power to these values. References: [1] Heinlein et al., J Biomech 2007. [2] Bergmann et al., J. Biomech. 1985. [3] Graichen et al. Med Eng Phys 1996. Acknowledgements This project was supported by Zimmer GmbH, Winterthur, Switzerland.

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KINEMATIC ANALYSIS OF TOTAL KNEE ARTHROPLASTY OF WHICH THE DESIGN CONCEPT IS MEDIAL PIVOT MOTION Yamamoto, Keitaro., Suguro, Toru., Banks, Scott A., Nozaki, Hiroyuki., Nakamura, Takashi., Miyazaki, Yoshiyasu., Kogame, Katsunori. (Address) Department of Orthopaedic Surgery, School of Medicine, Toho University,

6-11-1 Omorinishi, Ota-ku, Tokyo, 143-8541 JAPAN (Phone/FAX/e-mail) +81-3-3762-4151/+81-3-3763-7539/[email protected] Purpose: Recently, total knee arthroplasty (TKA) has been generalized as an operation to which an excellent clinical result can be acquired. However, younger and more demanding patients require even greater implant longevity and func-tional performance, and there are many variations in the prosthesis design. We did the analysis of postoperative functional assessment in vivo in the two type of TKA of which the design concept was medial pivot motion. It was examined whether medial pivot motion was actually reproduced.

Materials and Methods: Objects are 16 OA cases 16 joints. Single-radius medial pivot TKA (Single-TKA) was performed at 8 joints, and anatomical geometry TKA (Anatomical-TKA) was performed at 8 joints. All samples PCL were retained. Postop-erative functional assessment was performed in 16 patients using ‘shape-matching’ technique. Single-plane fluoro-scopic imaging was used to record and quantify the motions of knees during a stair-step activity. With a 3D model of TKA prosthesis, 3D-to-2D model-to-image registration can be used to estimate spatial tibiofemoral motions. Result: Single-TKA showed external rotation in early stages of flexion, internal rotation was shown after mid flexion, tibial internal rotation was revealed an average 8.2° with flexion to 90°. Anatomical-TKA showed internal rotation between extension and flexion, tibial internal rotation was revealed an average 16.9° with flexion to 90°. Condylar translations exhibited a medial pivot pattern from 0° to 90° flexion in Anatomical-TKA, with an average of 0 mm medial condyle translation and 9.0 mm posterior translation of the lateral condyle. As a result, medial pivot motion was accepted in these TKA models. However, the contact point on tibiofemoral surface and the rotation angle showed some difference in these TKA models.

Conclusion: Postoperative functional assessment of kinematics with in vivo was performed by the difference of the prosthesis design after the operation. Internal rotation by medial pivot motion was observed in all cases. These results are due to difference of design between two types of the prosthesis.

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IN VIVO CONTACT AREAS AND STRESSES FOR MULTIPLE TKA TYPES Sharma A1, Komistek RD1, Scuderi GR2, Cates HE3, Longenecker SL4, Liu F1 1University of Tennessee, Knoxville, TN, USA 2Insall Scott Kelly Institute, New York, NY, USA 3Park West Hospital, Knoxville, TN, USA 4St. Vincent’s Medical Center, Jacksonville, FL, USA Correspondence: Adrija Sharma 301 Perkins Hall University of Tennessee Knoxville, TN 37996 Email: [email protected] Phone: 865) 974-0198 Fax: (865) 946-1787 Recently, a new technique was developed to determine the in vivo contact stresses in TKA. This methodology first determines the in vivo kinematics, then the in vivo mechanics of the knees, which included bearing surface forces and contact areas for both condyles. The process has been validated and has proven to be highly accurate. Then, the algorithm determines the in vivo contact stresses of both condyles throughout flexion. The objective of this study was to assess the in vivo contact stresses for six different TKAs.

In vivo contact stresses were assessed for 44 subjects having a TKA. Ten subjects were implanted with a high flexion-type posterior stabilized (PS) TKA, 10 with a high flexion-type posterior cruciate retaining (PCR) TKA, seven with a mobile bearing PS TKA, seven with a fixed bearing PS TKA, six with a non high flexion-type PCR TKA, and four with a PCR TKA with an ultra congruent polyethylene insert. Each subject was asked to perform a deep knee bend to maximum knee flexion and the contact stresses were assessed from full extension to maximum knee flexion.

The medial contact forces for all the implants were found to be similar ranging from about 0.5 BW at full exten-sion to about 2.7BW at full flexion. The high flexion TKA however experienced slightly higher values of lateral contact forces reaching a maximum value of 1.2BW at full flexion compared to the traditional TKAs, which ex-perienced a maximum force value near 1.0 BW at full flexion. Interestingly, the subjects having either a high flex-ion TKA or a PCR TKA with an ultra congruent insert were able to maintain higher contact areas, especially for the medial condyle, throughout the flexion cycle compared to those subjects having a more traditional-type TKA. These higher contact areas, leading to lower contact stresses were statistically greater from mid-flexion to maxi-mum knee flexion for those subjects having a high flexion-type TKA. In deeper flexion ranges, subjects having a traditional-type TKA experienced lesser contact areas, again most noticeably for the medial condyle. Contact stress values for all TKA were less than the yield strength of polyethylene for all TKA, expect for those subjects having a traditional type fixed bearing PS TKA in deep flexion ranges.

The results from this study revealed that the in vivo contact stresses vary for the different TKA analyzed for sub-ject-to-subject comparisons within each group. Subjects having a TKA that was designed to accommodate high flexion ranges experienced higher contact areas and lower contact stresses. Therefore, there may be a clinical ad-vantage for those subjects having either a high flexion-type TKA or subjects implanted with an ultra congruent insert due to the lower contact stresses exerted at the bearing surface interface.

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NAVIGATION IMPROVES ACCURACY AND REPRODUCIBILITY OF SOFT TISSUE BALANCE IN TKA Stulberg, S. David, Yaffe, Mark A., Koo, Samuel S. S. David Stulberg, MD Northwestern Orthopaedic Institute 680 N. Lake Shore Dr. Ste 1028, Chicago, IL 60611 P: 312.664.6848 F: 312.475.5624 [email protected]

INTRODUCTION: Proper soft tissue balance and ligament stability is essential to the performance of a total knee arthroplasty (TKA). To date there is no widely accepted concept of the optimal amount of medial-lateral laxity following TKA. There have been several previous studies examining the relationship between medial-lateral laxity and clinical outcome measures such as the Hospital for Special Surgery score (HSS) and the Knee Society score (KSS). These studies have found improved clinical outcome meas-ures with increased varus-valgus laxity1, improved outcomes with reduced laxity2, or no correlation at all between outcomes and laxity 3. It is clear that despite the variation in surgeon preference regarding the target degree of total knee laxity, there is widespread agreement that a proper balance between medial and lateral laxity is essential in order to prevent instability, in-creased contact stresses, and premature failure of the TKA. The purpose of this study was to: Determine the amount of medial-lateral laxity at the completion of TKAs performed using navigation Determine the extent to which medial-lateral balance was achieved using navigation Determine the relationship between clinical outcome measurements and amount of laxity METHODS: Forty-eight consecutive computer-assisted TKAs were performed by a single surgeon who had extensive prior experience in computer-assisted TKA. The Aesculap Orthopilot™ navigation system was used to evaluate pre and post-operative unstressed and stressed mechanical axis and medial-lateral laxity. Laxity was defined as the total medial-lateral excursion in degrees with the knee extended and slightly flexed. The intra-operative goal was to achieve a balanced knee with optimal limb and implant alignment. Balance was defined as the difference in maximum varus and valgus excursion in degrees from a mechanical axis of zero degrees. No soft tissue releases were performed in this study. Clinical examinations were performed at four weeks, six months, and one year. The Knee Society scoring system was used to assess clinical and patient-perceived functional outcomes. Full-length weight-bearing and lateral radiographs were obtained to evaluate limb and implant alignment. RESULTS: Average unstressed pre and post-operative mechanical axis was 5.6˚ (range: -12˚ - 16˚) and 0.52˚ (range: -2˚ - 3˚) respectively. Average pre-operative medial-lateral laxity was 8.6˚ (range: 3˚-16˚) and post-operative laxity was 2.8˚ (range: 0˚-6˚). 42% had greater varus laxity, 31% of TKAs had greater valgus laxity, and 27% had equal varus and valgus laxity. 71% of TKAs were balanced within 1˚ of equal varus and valgus laxity. DISCUSSION: This is the first study to assess the effectiveness of a navigation system on soft tissue and ligament balance in TKA. The use of a navigation system produced accurate and reproducible outcomes in terms of both knee balance and stability. Compared to previous studies that found an average post-operative medial-lateral laxity of 10.6˚, 8.3˚, and 8.0˚ respectively when manual instruments were utilized,3-5 the use of a navigation system produced a significantly tighter knee. There was no correlation between laxity, range of motion, and Knee Society Score in this study.

CAS makes it possible to define both an appropriate medial-lateral laxity as well as a desirable balance. CAS allows the status of ligaments and knee balance at the conclusion of a TKA to be correlated with immediate and long-term clinical results. Navi-gation offers the potential to significantly reduce variability in post-operative laxity and produce reproducible, balanced knees. This study provides a baseline to further assess and develop the concept of optimal soft tissue balance and knee laxity in com-puter-assisted TKA. REFERENCES: 1. Edwards E, Miller J, Chan KH. The effect of postoperative collateral ligament laxity in total knee arthroplasty. Clin

Orthop Relat Res. Nov 1988(236):44-51. 2. Mitts K, Muldoon MP, Gladden M, Jr., Padgett DE. Instability after total knee arthroplasty with the Miller-Gallante II

total knee: 5- to 7-year follow-up. J Arthroplasty. Jun 2001;16(4):422-427. 3. Yamakado K, Kitaoka K, Yamada H, Hashiba K, Nakamura R, Tomita K. Influence of stability on range of motion

after cruciate-retaining TKA. Arch Orthop Trauma Surg. Feb 2003;123(1):1-4. 4. Matsuda Y, Ishii Y, Noguchi H, Ishii R. Varus-valgus balance and range of movement after total knee arthroplasty. J

Bone Joint Surg Br. Jun 2005;87(6):804-808. 5. Kuster MS, Bitschnau B, Votruba T. Influence of collateral ligament laxity on patient satisfaction after total knee

arthroplasty: a comparative bilateral study. Arch Orthop Trauma Surg. Jul 2004;124(6):415-417.

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INTRODUCTION OF A NOVEL NAVIGATION SYSTEM FOR ASSESSMENT OF PASSIVE KNEE KINEMATICS AND LIGAMENTOUS STABILITY MEASURED PRE- AND POST TO-TAL KNEE ARTHROPLASTY Nadzadi, Mark E. ; Ecker, Timo M. ; Murphy, Stephen B. Center for Computer Assisted and Reconstructive Surgery New England Baptist Bone and Joint Institute 125 Parker Hill Avenue Suite 545 Boston, MA 02120 Phone: 617-232-3040 Fax: 617-754-6436 e-mail: [email protected] Computer Assistance during total knee replacement helps the orthopedic surgeon to control for proper overall limb alignment, component sizing and positioning and ligament balancing. Yet, the passive kinematic behavior of the normal, arthritic, and replaced knee is still undefined and the assumption that reproducing normal passive kinemat-ics will optimize function following total knee arthroplasty has not yet been proven. The purpose of the current study is to assess passive knee joint laxity and kinematics of anesthetized patients before and after undergoing total knee replacement using a novel navigation system. Ten consecutive patients undergoing CAS – TKA were evaluated. Reference frames were routinely affixed to the femur and tibia and registration with the navigation system (‘Achieve CAS’, Smith & Nephew / Orthosoft) was performed. A second infrared navigation system (Polaris, NDI) controlled by a novel analysis software was initial-ized for the laxity and kinematic measurements. Laxity assessment included varus / valgus thrusts at predefined flexion angles. Internal and external rotation of the tibia, and anterior/posterior drawer tests were performed after the same pattern. Kinematic assessment was made by flexing the knee to a maximum and returning the knee to full extension. Tibial rotation was captured by repeating the kinematic measurements with a significant internal and external rotation force. All measurements were repeated several times to ensure complete data capture. The TKA operation then proceeded normally, with routine landmark digitization and guidance from the Achieve CAS sys-tem. Once the final components were installed, the laxity and kinematic protocol was repeated. The raw data was processed through the novel software and clinical rotations of the knee were reported in concurrence with Grood and Suntay [2]. Joint translation scenarios were assessed by tracking the relative motion of various femoral land-marks to the tibial plateau. Each patient exhibited unique results, but certain trends emerged. Neutral alignment was achieved in all cases. Maximum flexion was comparable pre and post-intervention. Laxity as described above, tightened post-operatively. Although the overall rotational laxity became tighter post-intervention, the repeatability of the kine-matic path was more apparent in the intact knee data. The femur posteriorly translates both pre and post interven-tion, but the post-intervention kinematics exhibit marked paradoxical motion known to exist in contemporary CR-style TKA. Additionally, the intact knee clearly exhibited medial pivoting with almost pure posterior translation of both femoral condyles on the tibia after about 80 degrees of flexion. The TKA data shows a more sporadic behavior in the kinematics, however, the overall laxity of the joint is tighter post-operatively. The ACL was initially intact, but sacrificed during the TKA operation in which a CR-style device was implanted, this might have some influence on the kinematic paths observed In conclusion, data is presented on a novel software system using contemporary navigation hardware that permits data capture and subsequent comparison of the knee laxity and kinematics of TKA patients, pre- and post- surgical intervention. This capability holds the potential for evaluation of different component designs and different surgical intervention plans and for qualitatively and quantitatively comparing laxity and kinematic characteristics.

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LEARNING CURVE OF A NAVIGATION SYSTEM FOR TOTAL KNEE REPLACEMENT. A MULTICENTRIC STUDY JENNY Jean-Yves, MIEHLKE Rolf K, GIUREA Alexander Hôpitaux Universitaires de Strasbourg, Centre de Chirurgie Orthopédique et de la Main, 10 avenue Baumann, F-67400 Illkirch-Graffenstaden (France) Tel +33388552145, Fax +33388552146, E-mail [email protected] INTRODUCTION:

Accuracy of implantation is an accepted prognostic factor for the long term survival of total knee replacement (TKR). The use of navigation demonstrated a significant higher accuracy of implant orientation in comparison to conventional methods. However, these systems are often thought to be technically demanding, to increase operat-ing time and to involve a long learning curve. We performed a prospective, multicenter study to compare the accu-racy of implantation of a TKR measured on post-operative X-rays in experienced and less experienced centers.

MATERIAL AND METHODS:

All centers used the same navigation system (OrthoPilot ®, Asculap, Tuttlingen, FRG): 4 had already a significant experience with it (group A – 182 cases), 9 centers were considered as beginners with less than 10 cases performed prior to the study (group B – 221 cases). Accuracy of implantation was measured on post-operative antero-posterior and lateral long leg X-rays with five items: mechanical femoro-tibial angle, coronal orientation of the femoral component, sagittal orientation of the femoral component, coronal orientation of the tibial component, sagittal orientation of the tibial component.

When the measured angle was in the expected range, one point was given. The accuracy note was defined as the sum of all points given for each patient, with a maximum of 5 points (all items fulfilled) and a minimum of 0 point (no item fulfilled). The mean accuracy note was compared in the two groups by a Student t-test at a 0.05 level of significance. Power of the study was 0.80.

RESULTS:

There were no significant differences in pre-operative parameters between the two groups, except for the clinical KSS. The mean operative time was significantly longer in group B than in group A (110 minutes vs 90 minutes, p=0.01). However this difference occurred mainly during the first twenty cases in the beginner centers where we observed a clear tendency to achieve the same operative time as the experienced centers at the end of the study. The mean accuracy note was 4.3 ± 0.8 (range, 1 to 5) in the control group and 4.3 ± 0.9 (range, 1 to 5) in the study group (p > 0.05). The power of the study to detect a 0.25 point difference in the post-operative accuracy note was retrospectively calculated to be 0.80. There was no significant differences between the two groups for all individ-ual radiographic items.

DISCUSSION:

This study is, to our knowledge, the first one which investigates the learning curve of navigated TKR The used navigation system allowed a very accurate implantation of a TKR in both experienced and less experienced cen-ters. The learning curve of the used navigation system can be regarded as very short in high volume TKR centers (about 30 cases).

CONCLUSION: There was no detectable learning curve with respect to accuracy of TKR implantation, clinical outcome and com-plication rate. The duration of the learning curve when considering the operating time was 30 cases.

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NAVIGATION-ASSISTED TOTAL KNEE ARTHROPLASTY IN PATIENTS WITH EXTRA-ARTICULAR DEFORMITY Maeda Toru, Kabata Tamon, Naito Mitsuhiro, Taga Tadashi, Ando Tomonari, Kitaoka Katsuhiko, Tsuchiya Hiro-yuki, Tomita Katsuro Department of Orthopaedics Surgery, Kanazawa University, School of Medicine 13-1 Takaramachi Kanazawa Ishikawa, 920-8641, Japan Phone: ＋81-76-265-2374, Fax:＋81-76-234-4261, E-mail: [email protected] Background: Long term studies have shown that reliable pain relief and functional improvement can be obtained in over 90% of patients for 10 to 15 years after total knee arthroplasty（TKA）. Basic principles can be followed for most cases, but patients with extra-articular deformity or posttraumatic arthrosis are outliers. TKA for these patients continue to provide challenges because they require modification of the technique or prosthesis to correctly perform total knee arthroplasty and optimize results... This study reports on the results we obtained using navigation-assisted TKA for patients with extra-articular deformity. Materials & Methods: Four patients with an average age of fifty-nine years (range fifty-four to sixty-three) with arthritis of the knee and extra-articular femoral and/or tibial deformity(s) underwent TKA using an image-free navigation system (Stryker Navigation, Kalamazoo, MI). Deformities were caused by fracture malunion, periarticular osteotomy, rickets, and skeletal dysplasia. Three patients had a history of a previous operation on the affected side. Two patients needed a corrective osteotomy before TKA, because the mechanical axis of the lower extremity deviated from the knee center. A standard medial parapatellar approach was used in all patients. The navigation system was used to assist the surgeon in accu-rate bony resection, and to orient the implants (ScorpioⓇ, Stryker, Mahwah, NJ). A standard postoperative rehabilitation proto-col was done in all patients, including immediate full weight bearing. Results: We could obtain good mechanical alignment of the leg and a good balanced knee in all cases. There were no complications. Illustrative Case: Deformity after fracture malunion. At the age of 59, a male patient suffered from multiple injuries, including a right femoral condylar fracture from an accident while at work. His orthopedic surgeon performed the first round of treatment. But the femur developed a malunion and the right knee pain and contracture occurred. As the pain continued to increase, he was referred to our hospital when he was 61 years old. At the initial physical examination, the right knee showed a valgus deformity and the range of motion in the right knee was markedly limited. A hip-to-ankle radiograph demonstrated a severe valgus deformity, and computer tomography showed 20°of external rotation compared with the left side. In light of the patient’s symptoms and age, TKA was indicated. Initially, to obtain normal alignment of the femur, a correctional osteotomy was performed using a Taylor spatial frame. One year later, TKA was performed using Navigation to guide bone cuts and implant position. At his most recent physical examination, he had no pain and his quality of daily life was improved. He was very satisfied with the operation. Discussion: Extra-articular deformity may make TKA difficult, because of an altered mechanical axis and distorted anatomical landmarks. In addition, significant deformity of the canal makes traditional intramedullary instrumentation impractical. Using the naviga-tion system, approximate best alignment of the prosthesis in relation to the mechanical axis of the limb can be obtained.

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ACCURACY AND RELIABILITY OF LIMB ALIGNMENT CONTROL USING SURGICAL NAVIGATION DURING TOTAL KNEE ARTHROPLASTY Murphy, Stephen B.; Ecker, Timo M. Center For Computer Assisted and Reconstructive Surgery New England Baptist Bone and Joint Institute 125 Parker Hill Avenue Suite 545 Boston, MA 02120 Phone: 617-232-3040 Fax: 617-754-6436 e-mail: [email protected] Malpositioned components and limb malalignment after total knee arthroplasty can be associated with poor func-tion, accelerated prosthesis wear and associated problems. In order to control for these parameters, surgeons utilize various methods ranging from simple visual estimation to extramedullary and intramedullary mechanical instru-ments. All these methods are highly susceptible to measurement errors. The application of surgical navigation to total knee arthroplasty can improve these errors by enabling the surgeon to plan component size and position, to perform and check bone cuts sequentially to prevent cumulative errors, and to predict and measure limb alignment and ligament balance. This study summarizes our experience with navigated total knee arthroplasty with emphasis on limb alignment and navigation-related complications. 235 consecutive TKA were performed by the same surgeon using the same implants. 204 procedures were per-formed using image free navigation and 31 procedures were performed with fluoroscopic navigation. During the procedure, reference frames were percutaneously affixed to the femur and tibia using 2-pin fixation. Subsequently, alignment and ligament balance were assessed and all bone cuts were tracked using navigation. Postoperatively, full-limb standing films were obtained for all patients. Femoral alignment was measured by drawing a parallel line through the distal femoral condyles. Then, a perpendicular line was drawn from the hip center to the knee center and the angle was measured. The tibial alignment was measured by drawing a parallel line to the tibial plateau. Then, a perpendicular line was drawn from the center of the talus to the center of the tibial plateau and the angle was measured. Varus angles were considered negative values and valgus angles positive. The total of the femoral and tibial angles resulted in the overall alignment. All patients were assessed clinically for the occurrence of com-plications. Alignment as measured on full leg films showed femoral alignment of 0.44° ± 1.1 varus (range, -4 to 3), tibial alignment of 0.66° ± 1.3 valgus (range, -4 to 4) and overall alignment of 0.24° ± 1.2 valgus (range, -4 to 4). There were no statistically significant differences between limb alignment using image-free or fluoroscopic naviga-tion.There was one tibial stress fracture (0.4 %) which healed uneventfully. One of the 940 (0.1%) pin-sites was treated with antibiotics for infection. There were no vascular or nerve injuries. Correct limb alignment is achieved with a mean accuracy of less than 0.5 degrees and a standard deviation of about 1 degree. Only 3 (1.3 %) limbs have limb alignment of 4 degrees of varus or valgus and no limbs had limb align-ment of 5 or more degrees from a neutral mechanical axis. The use of 2-pin, percutaneous fixation of reference frames has the advantages that the reference frames have excellent stability and that they can be placed away from the primary incision, allowing the primary incision to be smaller than it would be otherwise. Application of surgi-cal navigation to total knee arthroplasty using 2 pin, percutaneous reference frame fixation results in a safe and reliable procedure and provides good accuracy with very few complications.

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HOW ABOUT DEFORMATION OF JAPANESE OA KNEE? - Measurement with OrthoPilot in TKA Author: Katsuya Kanesaki 1-1 Harayamamachi Omuta Fukuoka Japan E-Mail: [email protected] INTRODUCTION: Osteo-arthrosis is the very popular disease in the world. In Japan, the OA knee is the primary in almost all cases. And the over 90 percentage cases of the OA knee have the varus deformity. Generally say that the OA of medial type is shaved off distal medial condyle and the lateral type is off posterior lateral condyle. So we examined the typical role of tendency of the angle between the femoral mechanical axis and femoral distal joint line using the cases of our navigated TKA. This angle is shown that the valgus or varus deformity is the origin from the femoral side or from the tibial side. The result will lead us to the correct osteotomy of the distal femoral side. ( METH-ODS) We have 56 navigated TKA cases. All cases are osteo-arthrosis of the knee. In the navigated TKA with Or-thoPilot, at the time just after arthrotomy and making the rigid body for both femur and tibia, the measurement is done. The measurement point is before menisectomy and release of the around ligamentus tissues. RESULTS: There were 39 knees with the varus deformity and 17 knees with the valgus deformity. The average of the varus deformity was 6.7±4.3 degrees and of the valgus deformity was 2.3±2.8 degrees. Next the angle between the femoral mechanical axis and the joint line of distal femur was 1.9±2.8 degrees in the group of the varus deformity, and 5.8±2.6 degrees in the group of the valgus deformity. Only 5 knees revealed the femoral varus in the group of varus deformity. DISCUSSION: In the situation of the manual TKA with the rod of intra-medullary, the decision for the cutting angle of distal fe-mur is only on the long leg sagittal X-ray of standing position. When the medial oblique view is got, the femoral shape reveals more lateral bowing rather than the normal one. If the angle of the distal femoral cutting line is de-cided with this external rotated X-ray, the angle between the femoral shaft axis and the joint line of the distal femur will be bigger valgus rather than normal one. And it is also difficult to get the good ligament balance with the con-tractured medial collateral ligament and the structures of medial side of the knee. Our results suggest that in the group of the varus deformity, the angle between the femoral mechanical axis and the joint line of distal femur is almost perpendicular. And in the group of the valgus deformity, it is about 6 degrees “femoral valgus”. In other words, the knee of the varus deformity is origin from the tibial deformity and the knee of the valgus deformity is from the femoral deformity. CONCLUSION: In TKA, especially the varus deformity cases, the cutting thickness of the distal femur is almost the same between both medial and lateral condyle. In the other for the valgus deformity, the thickness of medial condyle is bigger than lateral condyle. Our results suggest that the thickness of lateral femoral distal cutting is not so small rather than medial one. And if there is a lot of discrepancy between them, it is not correct osteotomy according to the mechanical axis.

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ALIGNMENT OF TOTAL KNEE ARTHROPLASTY: A Comparison of Mechanical and Computer Assisted TKA Surgery Nicholas Wegner, BS; Alfred Cook, MD; Joe Feinglass PhD; S. David Stulberg, MD 680 N. Lake Shore Drive #1028 Chicago, IL 50511 Phone: 312-664-6848 Fax: 312-664-9274 E-Mail: [email protected] Background: Computer assisted surgery (CAS) is beginning to emerge as one of the most important technologies in orthopedic surgery, and many of the initial applications have focused on reconstructive surgery of the knee. However because CAS technologies are still in the early phases of development and implementation, the appropriate roles for these technologies are not yet clear. In a previous study using a standard mechanical, intramedullary alignment total knee arthroplasty (TKA) system, we found the variation between the mechanical axis of the leg and the anatomical axis of the femur had a standard deviation of less than 1.02 degrees in the coronal plane and 1.09 degrees in the sagittal plane.

The purpose of this study is to compare the mechanical alignment of the leg in both the coronal and sagittal planes following a TKA employing a currently used CT-free navigation TKA system with the alignment of the leg fol-lowing a TKA using a preset distal femoral cutting jig attached to a IM rod placed manually in the center of the femoral shaft. Methods: Sixty-two computer assisted TKAs were performed on 53 patients using the Aesculap OrthopilotTM navigation system. During each procedure, the angle between the planned mechanical alignment of the leg (0 degrees) and the angle of the actual distal femoral cut was measured. This data was then compared to an estimate of the variability of the distal femoral cut using a preset standard intramedually alignment system, which was calculated by mathe-matically combining the anatomic variability of the femur (which included the placement of the IM rod) from our previous study with the variability introduced in making the distal femoral cut resulting from movement of the cutting jig. Results: Using the CT-free navigation system, the standard deviation between the planned and actual alignment of the leg was 0.71 degrees in the coronal plane and 1.06 degrees in the sagittal plane. The standard deviation using the pre-set mechanical, intramedullary alignment system was estimated to be 1.23 degrees in the coronal plane and 1.54 degrees in the sagittal plane. Conclusions: Using current CT-free navigation systems, surgeons can expect 95 percent of postoperative alignments to fall within 1.42 degrees (2 x 0.71 degrees) of the mechanical axis in the coronal plane and 2.12 degrees -(2 x 1.06 de-grees) in the sagittal plane. With current mechanical techniques, 95 percent of postoperative alignments should fall within 2.46 degrees (2 x 1.23 degrees) of the mechanical axis in the coronal plane and 3.08 degrees -in the sagittal plane (2 x 1.54 degrees). Thus, computer assisted TKA systems result in only slightly better mechanical alignment in both the coronal and sagittal planes (difference in 95 percent confidence intervals: coronal: 2.46 degrees -1.42 degrees = 1.04 degrees; sagittal: 3.08 degrees - 2.12 degrees = 0.96 degrees).

The greatest difference in alignment between the mechanical and navigated system will result in the sagittal plane in femurs with large anterior femoral bows. Any femurs with anatomic abnormalities introducing greater than nor-mal variation will also increase the variation between the mechanical and navigated systems. This information needs to be taken into consideration when choosing which systems will be most appropriate when performing a TKA.

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COMPARISON OF MECHANICAL AXIS MEASUREMENTS: INTRA-OPERATIVE

NAVIGATION VERSUS POSTOPERATIVE STANDING FILMS Jennifer M. Smail1, Michael L. Swank2 1Cincinnati Orthopaedic Research Institute, & University of Cincinnati Department of Orthopaedic Surgery 2Cincinnati Orthopaedic Research Institute INTRODUCTION: Mechanical axis alignment of limbs following total knee arthroplasty is well established as a critical factor in the function and long term success of implants. The use of computer navigation systems to provide additional information intra-operatively has been espoused as a valuable tool for improving component placement and thus outcomes. Recognition of navigation as a tool designed to augment rather than replace the surgeon’s decision making capacity is key to its successful implementation. A basic understanding of how the data received by the navigation software is used to generate information such as alignment is important so that data can be used with judgment rather than taken as absolute truth. Final alignment data generated when implants are in place is a final checkpoint for the surgeon to assess whether pre-operative planning alignment goals have been achieved. The amount of reliance which can be placed on this data, however, is not necessarily clear. Visual inspection of the limb provides a very rough estimate of alignment which may or may not match the number on the navigation screen. The importance of recognizing this value in the context of what the initial navigated pre-component limb alignment values were cannot be overemphasized. Comparison of this navigation data to actual radiographic mechanical axis data provides an excellent basis for judging the precision of intra-op data. To date, however, the authors are unaware of any studies which offer this comparison. METHODS: Since August 2005 all total knee arthroplasty patients for a single high-volume total joint surgeon have routinely had long standing films taken approximately one year post-op. All films are digital and mechanical axis is measured by the same surgeon using femoral head to talar dome centers. These measurements are made during the clinic visit, functionally blinding the measurer from intra-op data which is stored in raw form separately from patient charts. This database was searched for patients whose implants (all DePuy PFC or LCS) were placed using the BrainLAB VectorVision navigation system. This system is imageless and is based upon anatomic points selected by the surgeon with references mounted on two tibial pins and two femoral pins. Raw intra-operative navigation data available from October 2003 through October 2006 was searched for patients also appearing in the long standing film database. Eighty five patients were identified with both long standing film data and navigation data. This data was compared to evaluate the correlation between the pairs of measurements as well as the variability within each data set. RESULTS: The mean alignment obtained from the navigation system was 1.0 degrees, while the mean long standing film alignment was 0.8 degrees, difference of 0.2 degrees. The mean difference between pairs was 1.8 degrees, with a standard deviation of 1.97 and a correlation coefficient of 0.32. The range of differences between the pairs from navigation system final alignment ranged from 0 degrees to 10 degrees, with 85% of the differences falling within 0 to 3 degrees. The data are presented in Graph 1 below. DISCUSSION: This study is very focused in its purpose which is to evaluate the intra-operative mechanical axis data provided by one image-free navigation system and compare it to post-operative long standing films. Usage of navigation systems in total knee arthroplasty continues to increase and the available literature addressing navigated knees is still limited in some areas. Long term outcome data has not yet been generated given the relatively recent arrival of navigation. It has been suggested that the available data on conventional non-navigated knees show such good results that current navigation systems may not be able to offer a significant improvement. Time will have to pass before this debate can be addressed. What can be addressed, however, are the multitude of other factors which can be studied over a short time period such as blood loss, operative time, complications, short –term function, and alignment. Alignment in navigated knees is a good surrogate for long term outcome data due to the well-documented correlation betlongevity. One of the anticipated benefits of navigation is a reduction in the number of coronal alignment outliers. The results of mechanical axis determination observed on long standing X-ray correlate reasonably well with the mechanical axis values recorded intra-operatively during navigated total knee replacement. The difference between pairs of 1.8 degrees is influenced by many factors including measurement error inherent to the digital X-ray system, possible learning curve error, possible increased error with large pre-operative deformity, error from comparing alignment while anesthetized prone to alignment while standing, and error in the navigation system which could have many sources such as data point entry or c alculation of hip center. Further analysis of the data will be able to identify learning curve error and any correlation with pre-operative deformity. Knowledge of this degree of correlation and its contributing factors is valuable information for judging the validity of navigational tools.

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COMPUTER KNEE ARTHROPLASTY WITH MNS (MEDACTA NAVIGATION SYS-TEM): COMPARATIVE STUDY BETWEEN STANDARD AND MINIMALLY INVASIVE CUTTING GUIDES

Emanuele Rinciari, Valeria Di Caro, Fabio Licata Casa di Cura Villa Salus Viale R. Margherita 15/b, 98121 Messina (Italy) phone number: + 39 339 2704868, fax number: + 39 090 45558, e-mail address: [email protected]

In this study we compare the early results in terms of accuracy, blood loss, post-op pain, and AROM, ob-tained using navigation system for primary total knee arthroplasty with Evolis (Medacta) prosthesis either us-ing the standard cut guides adapted to navigation, either using minimally invasive dedicate cut guides. From january 2001 until june 2007 we have performed 360 TKA primary implants assisted by navigation con-trol using regular instruments; from march 2006, until today, 155 minimally invasive TKA. The minimally invasive technique, assisted by MNS (Medacta Navigation System) is quite simple and fast. It is an open system, CT and RX free, based on geometric and morphologic data acquired during the operation. It provides useful informations for the ligament balancing. The minimally invasive TKA means a smaller skin incision, around 8 cm long, and limited midvastus ap-proach that minimally invade extensor mechanism without eversion of the patella. The morfing needs about 7 minutes. The femoral cutting guide is a “five in one” guide. The method is efficient for every patient with a submillimetric accuracy. 95 % of the patients are within the 177º-183º intraoperative target. The method provide very helpful data to correctly plan and balance the surgical procedure. The global accuracy has been improved by these new mechanical devices compared with the previous. The minimally invasive technique permits a short and easier recovery.

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RELIABILITY OF COMPUTER ASSISTED GAP AND LIGAMENT BALANCING IN TOTAL KNEE REPLACEMENT Author: Pak Lin Chin, Pang Hee Nee Outram Road Singapore Phone: 65 8123 1062 E-Mail: [email protected] It is unknown whether ligament and gap balancing with CAS is as reliable as it has been shown to be in restoring mechanical axis in TKR 140 patients were randomized into 2 groups in a prospective trial. All patients had the same CR prosthesis. Group 1 - TKR performed with conventional instrumentation. Group 2 - After tibial cut, ligamentous balancing was per-formed after inserton of a soft tissue tensioner. Femoral component sizing, AP placement, rotation and insert thick-ness to achieve balanced gaps were then determined virtually using CAS. After femoral cuts, the definitive pros-thesis and insert were then implanted without use of provisional trials. Post-operative results including range of motion, Knee Society, Oxford Knee and SF-36 scores, weight bearing lateral X-rays and KT-1000 testing at 30 and 70 degrees were not significant between the 2 groups (p>0.05). There was no difference in complications. CAS gap and ligament balancing in TKR is reliable and safe technique and offers the possibility of surgery without the use of provisional trials which is useful in minimally invasive approaches.

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NAVIGATED FREEHAND BONE CUTTING FOR TOTAL KNEE REPLACEMENT SUR-GERY: EXPERIMENTS WITH SEVEN INDEPENDENT SURGEONS Haider, Hani; Barrera O. Andres; Mahoney, Craig R; Ranawat, Amar S; Ranawat, Chitranjan S; and Garvin, Kevin. L Department of Orthopaedic Surgery and Rehabilitation, University of Nebraska Medical Center, 985360 Nebraska Medical Center - Scott Technology Center, Omaha, NE 68198-5360, USA Phone : (402) 559 5607 – Fax : (402) 559 2575 – E-mail : [email protected] Previously introduced novel navigated-freehand bone cutting technology for TKR developed at our laboratory was tested by only two surgeons within our hospital institution. This study reports a more formal experimental evalua-tion in the hands of many external surgeons with widely-varying TKR expertise. Seven orthopaedic surgeons at different stages of their career were invited to participate in testing. A distal femur was simulated on a surgical table by identical replicas molded from synthetic material of similar cutting-feel as real bone. An early version of the laboratory-built Nebraska Orthopaedics Minimally Invasive Surgery System (NoMiss) was used to navigate the bone-specimen and an oscillating-bone-saw fitted with passive reference frames. It was programmed with the ideal locations of the five distal-femur plateau-cuts for a widely-used TKR. Preparation also included registration of each bone prior to cutting. The graphical interface provided real-time graphical guidance during cutting. Each surgeon performed five timed experiments in a one-day session. Each experiment required the completion of all five cuts of one bone-specimen. The level of comfort and satisfaction felt by the surgeon were documented, and the quality of each cut was assessed quantitatively. Implant “fit” and “alignment” were physically measured with a navigated implant trial and produced numeric fit and alignment indi-ces. All cut bones were also digitized to compute smoothness and alignment indices representing how rotated (in 3D) and offset the implant was relative to ideal. The surgeons varied in speed but showed a steep learning-curve, with 10.2±4.3min average cutting-time. This was even faster than measured in our previous studies, which were in-turn faster than with conventional instruments, promising savings in surgeon and OR tourniquet times. From the thousands of digitized surface-points on each cut-surface, the average-roughness Ra was 0.19mm, and the difference between the highest-50-peaks and lowest-50-valleys was <1.2mm. These also confirmed previous measures, that smoothness was reproducible and adequate, especially for cemented cases. Although tightness was not targeted for this cemented implant, 21 out of 35 bones were tight on the implant-trial, and others slightly loose (without cementation). Worst looseness was in the “flexional” sense with average range <1.6°, and <1mm in translation. Average implant alignment error was 1.2°, and always <4.7° sagittally, <3.6° frontally and <2° axially. Linear-translation errors averaged 1.4mm, and <4.2mm everywhere, with some systematic undercutting evident of the distal plateau. Digitization and 3D analysis of all cut-surfaces echoed the above results, showing the extreme-outliers to be the chamfers which were treated as less important by most surgeons. This study showed high reproducibility of cuts and a narrow envelope of alignment error. Alignment with NoMiss in previous studies was much superior to cutting with conventional TKR cutting blocks, and this was echoed here with a wide range of independent surgeons. Qualitative feedback from the surgeons surpassed our expectations, even with the bare-minimum level of technology used. We anticipate significant further improvements with the inclusion of novel smart software/hardware techniques. We now more confidently believe that this technique can revolutionize future arthoplasty to free it from bone-cutting jigs.

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COMPUTER-ASSISTED, MINIMALLY INVASIVE VERSUS CONVENTIONAL KNEE ARTHROPLASTY: A PROSPECTIVE, RANDOMIZED STUDY Ng Y C, Dutton A Q, Yeo S J, Yang K Y, Lo N N, Chong H C Department of Orthopaedic Surgery, Singapore General Hospital, Outram Road Singapore 169608 Phone: +5-63214047; Fax: +65-62262684 [email protected] Background: There is little information on the feasibility of computer navigation through a minimally invasive approach for total knee arthroplasty where the anatomic landmarks for registration may be obscured. Aim: To determine the radiographic accuracy and rate of functional recovery of patients who underwent computer-assisted, minimally invasive versus patients undergoing conventional total knee arthroplasty. Methods: 108 consecutive patients were randomized to undergo computer-assisted, minimally invasive or conventional total knee arthroplasty. Peri-operative pain management was standardized. The clinical parameters, long leg radiographs and functional assessment scores were evaluated up to 2 years post-operatively. Result: Patients who underwent computer-assisted, minimally invasive total knee arthroplasty had a significant longer op-erative time by a mean of twenty minutes (p<0.001) and a significantly shorter inpatient stay of 3.3 days versus 4.5 days (p=0.001) for the conventional arthroplasty group. Significantly more computer-assisted, minimally invasive total knee arthroplasty patients were able to independently walk for more than 30 minutes at one month (p=0.04). The ideal coronal tibio-femoral angle within 3 degrees was achieved in significantly more computer-assisted, mini-mally invasive patients (92%) versus 67% for conventional total knee arthroplasty patients (p=0.003). At 2-year follow up, there was overall improvement in both groups with no difference in Knee Society, Oxford Knee and SF-36 outcomes between the two techniques of arthroplasty. Conclusion: Specific clinical parameters reflected an early increased rate of functional recovery with computer-assisted, mini-mally invasive total knee arthroplasty within the first post-operative month. Its main advantage is an improved post-operative radiographic alignment compared to conventional total knee arthroplasty without any increase in short-term complications.

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HOW ACCURATE ARE THREE DIFFERENT REFERENCE AXES IN TOTAL KNEE ARTHROPLASTY? Tadashi Taga, Tamon Kabata, Toru Maeda, Daigo Sakagoshi, Mitsuhiro Naito, Tomonari Ando, Katsuro Tomita Department of Orthopaedic Surgery, Kanazawa Univercity 13-1 Takaramachi Kanazawa City, Ishikawa Prefecture

For total knee arthroplasty (TKA), correct rotational alignment of the femoral prosthesis is important for correct patella tracking, patellofemoral joint contact forces, valus-valgus positioning in flexion, correct rotational align-ment of the tibia in extention and the avoidance of anterior femoral notching. This study evaluated the most reli-able anatomic axis that could be used to determine the rotational orientation of the femoral component when those axes commonly when those axes commonly used in total knee arthroplasty. Materials and Methods: Computed tomography images of the femur from 22 male and 65 female without any evidence of degenerative arthritis and bone pathology of the knee were included in this study. The average age of the patients was 55.4 years(range,25-82 years).Four distinct angular parameters, the trochlear line (Won Y Y The Journal of Arthroplasty 2007), the surgical epicondylar axis, the Whiteside’s line, and the posterior condylar axis were measured using reconstructed CT images vertical to mechanical axis from the 3D template (Japan Medical Material Corporation). Finally the angles of these axes relative to the surgical epicondylar axis were measured on the slice, and are ex-pressed as the “trochleoepicondylar angle,” “Whiteside-epicondylar angle,”and “posterior condylar an-gle,”respectively. Results: The mean value of the trochleoepicondylar angle was 9.5°±3.6 (2.3-19.8) of internal rotation in all subjects. The average Whiteside-epicondylar angle was 86.8°±4.4（72.8-98.2）for all subjects.

The posterior condylar angle had a mean value of 3.2°±2.2（0.1-10.7）. Discussion: Optimal rotational alignment of the femoral components is an important factor to reduce patellofemoral problems after TKA. To assess the rotational alignment of the distal end of the femur radiologically, CT or MRI have been used. Some studies have used cadavers or patients receiving TKAs. No studies have examined the rotational align-ment measured by 3D reconstructed computer tomography. Our results showed that the posterior condylar axis had a mean value of 3.2°relative to the surgical epicondylar axis ,with a smaller deviation (2.2°) than that of the Whiteside’s axis. The variation of Whiteside’s axis about the mean degree suggests that this axis should not be used alone as a rotational assessment guide. Rotation should ide-ally be checked against several axes to avoid errors in rotation positioning of the femoral prosthesis.

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IN VIVO COMPARISON OF KNEE KINEMATICS FOR SUBJECTS IMPLANTED WITH A ZIMMER UNI-COMPARTMENTAL HIGH-FLEX KNEE SYSTEM DURING WEIGHT BEAR-ING AND NON-WEIGHT BEARING ACTIVITIES Mueller, John Kyle P., Akizuki, Shaw, Zingde, Sumesh1, Komistek, Richard D., Mahfouz, Mohammed R., Anderle, Mathew R. Correspondence: Richard D. Komistek 301 Perkins Hall University of Tennessee Knoxville, TN 37996 Email: [email protected] Presenting author: Phone: (262) 352 5208, Fax: (865) 671-2157, [email protected] The advancements in surgical technique and instrumentation have encouraged a minimally invasive surgical (MIS) approach for Uni-compartmental Knee Arthroplasty (UKA). However, research has yet to prove whether MIS ap-proaches lead to a beneficial outcome for the patient. Also, clinical experience has shown an increased demand for high flexion, greater than 120 degrees, for post-implanted patients especially in certain ethnic populations. The objective of this study was to determine in vivo kinematics for subjects implanted with the Zimmer Uni-compartmental High-Flex Knee System (ZUK) with MIS during weight-bearing and non-weight bearing activities. 3D femorotibial contact positions for 30 medial implants from 18 subjects (12 bi-lateral) implanted by a single surgeon with average age of 76 years (68 to 83 years, Standard Deviation=5) and average post-operative time of 9.7 months (3.9 to 19.0 months, Standard Deviation=4.1) were evaluated for 3 activities. Each subject was asked to perform a Deep Knee Bend (DKB) from full extension to maximum knee flexion, one full Gait cycle and Passive flexion (PF) while under fluoroscopic surveillance. The average ROM for patients having a medial ZUK was 106 degrees (70 to 130 degrees, Standard Devia-tion=15.0) and 121 degrees (106 to 138 degrees, Standard Deviation=7.2) for DKB and PF respectively. Posterior Femoral Rollback (PFR) was seen during DKB and the stance phase of Gait with the subjects demonstrating on average -5.3 mm (-15.7 to 3.3 mm, Standard Deviation=5.3) and -1.0 mm (-6.1 to 4.3 mm, Standard Devia-tion=2.4) of medial PFR for DKB and Gait, respectively. The average contact position for PF was -10.1 mm (-16.3 to -2.8 mm, Standard Deviation=3.2). On average, normal axial rotation was seen during the DKB activity while a negative axial rotation was seen during the gait and PF activities. The ZUK saw 8.0 degrees (-1.3 to 22.0 degrees, Standard Deviation=5.7), -0.1 degrees (-14.5 to 9.9 degrees, Standard Deviation = 5.6) and -3.0 degrees (-10.8 to 4.8 degrees; Standard Deviation=4.1) of axial rotation for DKB, gait and PF, respectively. A comparison based on post-op time consisting of patients with less than 6 months post-op time, between 6 months and 1 year post-op time and greater than 1 year post-op time revealed similar results for all categories during DKB, Gait and PF. However, it was found that, PF ROM was significantly (p<0.05) higher than DKB ROM. Also, significant differences (p<0.05) were found in the contact position of the femur on the tibia for PF when compared at the maximum flex-ion of DKB. This study revealed that ROM in a ZUK implanted with MIS is dependant on whether an activity is weight bearing or non-weight bearing. A significant drop in ROM was seen between the DKB (weight bearing) and PF (non-weight bearing) activities. Also, since there was no statistical difference between subjects based on post-op time, it can be suggested that MIS may enable subjects to have normal function of their affected knees in a shorter amount of time.

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THE LATERAL COMPARTMENT IN KNEES WITH ISOLATED MEDIAL AND PATELLOFEMORAL COMPARTMENT ARTHRITIS: A HISTOLOGIC ANALYSIS OF ARTICULAR CARTILAGE Puri, Lalit; Moen, Todd C.; Laskin, William; Hendrix, Ronald Northwestern University Department of Orthopaedic Surgery 645 North Michigan Avenue, Suite 910 Chicago, IL 60611 Phone: (312) 908 7937; Fax: (312) 908 8479; E-mail: [email protected] Background: The decision to perform a tissue-sparing arthroplasty, such as a unicompartmental or bicompartmental knee arthro-plasty, is based on the assumption that the tissue to remain in the knee is healthy and free of osteoarthritis. The determination of the extent, or lack thereof, of osteoarthritis in the knee is based primarily on radiographic find-ings. To our knowledge, there has never been a study directly examining the articular cartilage of a radiographi-cally normal-appearing compartment in a knee with osteoarthritis in other compartments. The purpose of this study was to examine, at a histologic level, in patients with radiographic evidence of isolated medial and patel-lofemoral osteoarthritis and a radiographically normal lateral compartment, the extent of osteoarthritis in the lateral compartment. Methods: 10 patients with radiographic evidence of medial and patellofemoral osteoarthritis and a radiographically disease-free lateral compartment were identified. This was done with Kellgren-Lawrence scoring of the individual com-partments. These patients then underwent a tricompartmental total knee arthroplasty. The resected lateral femoral condyle and lateral tibial plateau were evaluated histologically to evaluate the extent of osteoarthritis at a micro-scopic level. This was done by histologic grading using the Histologic/Histochemical Grading System of Mankin. Results: The average Kellgren-Lawrence score for the lateral compartments was 1.2 +/- 0.4, consistent with “doubtful” for the presence of osteoarthritis. The average Mankin Scores for the lateral compartment tissue was 2.5 +/- 0.8, which is consistent with “mild” osteoarthritic changes. Discussion: This study suggests that in patients with radiographic evidence of isolated knee medial and patellofemoral com-partment osteoarthritis, and a radiographically unaffected lateral compartment, that there is mild osteoarthritis pre-sent at a microscopic level. The clinical significance of this finding is unknown, and further investigation is war-ranted.

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WHAT YOU PLAN IS WHAT YOU GET: PRECISE, ACCURATE PLACEMENT OF UNI-CONDYLAR KNEE IMPLANTS USING HAPTICALLY GUIDED SYSTEM Author: Roche, Martin W. Holy Cross Hospital, 4725 N. Federal Highway, Orthopedic Ctr, Ft. Lauderdale, FL, 33308, USA (tel.) +1.954.958.4800; (fax) +1.954.958.4899; (email) [email protected] INTRODUCTION: Today, standard orthopaedic technique for joint arthroplasty when conducted in a MIS manner results in certain difficulties primarily due to limited visibility from a smaller incision. A minimally invasive approach certainly has the potential to further improve a patient’s functional outcome, however the approach reduces the ability to iden-tify a number of surgical landmarks and therefore makes intra-operative orientation and proper positioning of the implant components even more difficult. Recent innovations within the medical community such as image-guided surgery (IGS) are designed to enable minimally invasive surgical technique. However, this visual feedback from current IGS systems is not enough. Combining the vision of IGS and the precision of intelligent physician-assisted instrumentation can enable the surgeon to perform MIS surgery in the most reliable, reproducible, and accurate manner. MATERIAL AND METHODS: The author is utilizing the Haptic Guidance System™ (MAKO Surgical Inc., Fort Lauderdale, Florida, USA) on a routine basis for inlay unicondylar knee arthroplasty (UKA). The Haptic Guidance System (HGS) integrates an IGS device with a robotic arm. It is designed to aid an orthopaedic surgeon’s use of standard surgical tools, such as high speed drill systems, during the preparation of a patient’s anatomy for UKA. It uses patient anatomical landmarks as reference points to precisely positioning standard surgical instrumentation or other devices within the anatomy. Due to the tactile feedback from the HGS, this system helps a surgeon perform minimally invasive tech-nique with more precise resurfacing cuts, which could not be achieved using standard surgical technique. Presently, 32 patients have been operated on for an isolated medial osteoarthritis. The patient population consists of 14 women and 18 men, with a mean age of 73 years. Radiographs have been evaluated by an independent re-viewer for component alignment, prosthesis subsidence, radiolucencies, and osteolytic lesions in the various Gruen zones on AP, lateral and patella view radiographs of the knee. RESULTS AND DISCUSSION: Initial results have shown a consistently accurate placement of the implant to the planned placement (± 1mm, ±1°). In the post-op review, as well as subsequent 6 week and 3 month follow-up, no patient has presented with prosthe-sis subsidence, radiolucency or osteolytic lesions. 32% of the patients were discharged within 1 hospital day. The author did observe a learning curve using the system, with additional operative time required during the first implantations. Operative time, however, was quickly reduced to a time neutral position comparable with tradi-tional UKA procedures. Patient quality of life and well-being scores measured via the WOMAC questionnaire, SF-12 questionnaire and the Knee Society Score have provided positive feedback from patients already evaluated at 6 weeks (N=22) and 3 months (N=14). WOMAC total scores improved 44.5% (41.5 to 23) at 6 weeks and 54.2% (41.5 to 19) at 3 months. SF-12 physical component scores improved 24.6% (31.55 to 39.30) at 6 weeks and 31.2% (31.55 to 41.40) at 3 months. Total Knee Society Scores showed improvement of 55.9% (93 to 145) and 62.4% (93 to 151) at 6 weeks and 3 months, respectively. Patient satisfaction with the procedure has been positively influenced by the minimal incision size, minimal need for pain-killers post-operatively, and quick return to normal active daily life. In conclusion, this system offers the potential to orthopaedic surgeons of various experience levels to perform highly accurate MIS procedures in a reliable and reproducible manner.

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IN VIVO KINEMATIC COMPARISON FOR SUBJECTS HAVING BOTH CRUCIATE LIGAMENTS VERSUS THOSE USING A PS TKA Sharma A1, Komistek RD1, Hernigou P2 Mahfouz MR1, Anderle MR1, Wang X1

1University of Tennessee, Knoxville, TN, USA 2Chu Henri Mondor Hospital, Creteil, France Correspondence: Adrija Sharma 301 Perkins Hall University of Tennessee Knoxville, TN 37996 Email: [email protected] Phone: 865) 974-0198 Fax: (865) 946-1787 Previous in vivo fluoroscopic studies have not assessed the effectiveness of the cam/post mechanism in posterior stabilized (PS) TKA compared to the cruciate ligaments in unicondylar knee arthroplasty (UKA). Therefore, the objective of this study was to compare the in vivo kinematics for subjects implanted with a Ceragyr Mobile Plateau PS (MB) and a Hermes fixed bearing PS (FB) TKA with the Hermes UKA (Ceraver Osteal, France).

Forty four implanted knees (17 with MB PS TKA, 16 with FB PS TKA and 11 with a UKA) were analyzed under in vivo conditions while subjects performed a deep knee bend. All the UKA in this study were medial condyle re-placements. The kinematics were captured using fluoroscopy, evaluated using a 3D to 2D registration technique and analyzed from full extension to maximum knee flexion.

On average, the UKA group experienced significantly greater weight-bearing (96.0°) compared to subjects having a MB PS TKA (79.8°) and a FB PS TKA (76.9°). Subjects having a MB PS TKA experienced only -3.0 mm of posterior femoral rollback, with subjects having a FB PS TKA experienced -11.7 mm. The medial condyle motion patterns were even more variable as the MB PS TKA exhibited a 1.6 mm anterior slide, while the FB PS TKA demonstrated an average motion of -10.9 mm in the posterior direction. Subjects having a medial UKA experi-enced - 4.2 mm of posterior motion. The subjects having a FB PS TKA experienced on 0.8o of axial rotation, while the subjects having a MB PS TKA experienced 6.6° of normal rotation. Subjects having a UKA experienced -0.8° of reverse rotation. Condylar lift-off was not detected for subjects having a MB PS TKA, while 4/16 subjects hav-ing a FB PS TKA experienced at least 1.0 mm of lift-off.

Interestingly, in this study, subjects having either a FB or MB PS TKA experienced significantly less weight-bearing range-of-motion than subjects who retained their cruciate ligaments with a UKA. Subjects having a FB PS TKA experienced greater posterior motion of both condyles, but exhibited minimal axial rotation, while subjects having a MB PS TKA achieved greater axial rotation, but minimal posterior motion of both condyles.

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PRECISION OF THE POSITIONING OF AN UNICOMPARTMENTAL KNEE PROSTHESIS BY A MINI-INVASIVE NAVIGATED TECHNIQUE JENNY Jean-Yves, CIOBANU Eugène, BOERI Cyril Hôpitaux Universitaires de Strasbourg, Centre de Chirurgie Orthopédique et de la Main, 10 avenue Baumann, F-67400 Illkirch-Graffenstaden (France) Tel +33388552145, Fax +33388552146, E-mail [email protected] INTRODUCTION:

Unicompartmental knee replacement (UKR) is accepted as a valuable treatment for isolated medial knee os-teoarthritis. Minimal invasive implantation might be associated with an earlier hospital discharge and a faster reha-bilitation. However these techniques might decrease the accuracy of implantation, and it seems logical to combine minimal invasive techniques with navigation systems to address this issue.

MATERIAL AND METHODS:

The authors are using a non image based navigation system (ORTHOPILOT TM, AESCULAP, FRG) on a routine basis for UKR. We prospectively studied 60 patients who underwent navigated minimally invasive UKR for pri-mary medial osteoarthritis at our hospital between October 2005 and October 2006. We established a nonnavigated control group of 60 patients who underwent conventional implantation of a UKA at our hospital between April 2004 and September 2005. There were 42 male and 78 female patients with a mean age of 65 years (range, 44-87 years). There were no differences in all preoperative parameters between the two groups.

The accuracy of implant positioning was determined using predischarge standard anteroposterior and lateral radio-graphs. The following angles were measured: femorotibial angle, coronal and sagittal orientation of the femoral component, coronal and sagittal orientation of the tibial component. When the measured angle was in the expected range, one point was given. The accuracy was defined as the sum of the points given for each angle, with a maxi-mum of five points (all items fulfilled) and a minimum of 0 point (no item fulfilled). Our primary criterion was the radiographic accuracy index on the postoperative radiograph evaluation. All other items were studied as secondary criteria.

RESULTS: The mean accuracy index was similar in the two groups: 4.1 ± 0.8 in the study group and 4.2 ± 1.2 in the control group. 36 patients (60%) in the control group and 37 patients (62%) in the study group had the maximum accuracy index of five points. All measured angles were similar in the two groups. There were no differences between the percentages of patients in the two groups achieving the desired implant positions. Mean operating time was similar in the two groups. There were no intraoperative complications in either group. The groups had similar major posto-perative complication rates during hospital stay (3% for both).

DISCUSSION:

The used navigation system is based on an anatomic and kinematic analysis of the knee joint during the implanta-tion. The modification of the existing software for minimal invasive approach has been successful. It enhances the quality of implantation of the prosthetic components and avoids the inconvenients of a smaller incision with poten-tiel less optimal visuliazation of the intra-articular reference points. However, all centers observed a significant learning curve of the procedure, with a significant additional operative time during the first implantations. The postoperative rehabilitation was actually easier and faster, despite the additional percutaneous fixation of the navi-gation device.

CONCLUSION:

This system has the potential to allow the combination of the high accuracy of a navigation system and the low invasiveness of a small skin incision and joint opening.

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CAN RULES PROPOSED FOR FRACTURE HEALING EXPLAIN THE FORMATION OF RADIOLU-CENCY UNDER THE TIBIAL COMPONENTS OF KNEE REPLACEMENTS? Hans A Gray1 Amy B Zavatsky1 David W Murray2 Harinderjit S Gill2

1 Department of Engineering Science University of Oxford Oxford, UK 2 Oxford Orthopaedic Engineering Centre Nuffield Department of Orthopaedic Surgery (NDOS) University of Oxford Nuffield Orthopaedic Centre NHS Trust Oxford, UK Please address all correspondence to: Harinderjit S Gill Oxford Orthopaedic Engineering Centre Nuffield Department of Orthopaedic Surgery (NDOS) University of Oxford Nuffield Orthopaedic Centre NHS Trust Windmill Road, Headington Oxford OX3 7LD, UK Tel: +44 (0)1865 227457 Fax: +44 (0)1865 227966 Email: [email protected] The poor understanding of radiolucency commonly seen under the tibial component of the Oxford Unicompartmental Knee Replacement (OUKR) has led to unnecessary revision surgeries. It is widely accepted that radiolucency is a result of soft tissue formation similar to that formed in a fracture callus. We aimed to investigate whether tissue differentiation rules proposed for fracture healing can explain formation of radiolucencies under OUKRs. A 2D finite element (FE) model based on a validated FE model of a cadaveric tibia was run over 365 iterations. After each iteration, new material properties were calculated based on a remodelling rule. Density plots analogous to patient radiographs were generated and compared with patient radiographs. The model was able to simulate the formation of radiolucency in a realistic manner.

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IN VIVO COMPARISON OF KNEE KINEMATICS FOR SUBJECTS IMPLANTED WITH A LCS RP PCS OR A LPS FLEX MOBILE BEARING TKA Hirakawa Kazuo, Zingde Sumesh M, Komistek Richard D, Mahfouz Mohammed R, Anderle Mathew R Corresponding Author: Richard D. Komistek, Ph.D. Professor, Biomedical Engineering Center Director University of Tennessee 301 Perkins Hall Knoxville, TN 37996-2030 Phone: 865-974-4159 Fax: 865-671-2157 Email: [email protected] Previous studies have documented that surgeon variability and surgical technique are important factors influencing knee kinematics for subjects implanted with a TKA. Hence, when comparing knee kinematics for two different TKA designs it becomes important to keep these factors constant. Therefore, the objective of this study was to de-termine and compare the in vivo kinematics for subjects implanted with either a LCS RP PCS or a LPS Flex TKA from full extension to maximum knee flexion implanted by the same surgeon. Three-dimensional femorotibial contact positions for thirty-three subjects (12 LCS RP PCS and 21 LPS Flex), im-planted by a single surgeon, were evaluated using fluoroscopy. All subjects had post-op HSS scores of at least 90. On average, the subjects demonstrated 92.3 and 102.0 degrees of weight bearing range of motion for the LCS RP PCS and LPS Flex TKAs, respectively. Posterior femoral rollback (PFR) of the medial condyle was -0.1 and -2.0 mm for the LCS RP PCS and LPS Flex groups respectively, while the corresponding values for the lateral condyle were -3.1 and -5.4 mm for the LCS RP PCS and LPS Flex groups respectively. On average both groups exhibited normal axial rotation patterns from full extension to maximum knee flexion, with an average of 3.5 and 4.6 degrees for the LCS RP PCS and LPS Flex groups respectively. Condylar lift-off greater than 1.0 mm was experienced by none of the subjects in the LCS RP PCS group and 3/21 subjects in the LPS Flex group. In spite of the variability in the results from the two groups, no statistical difference was found (p>0.05) in any category of comparison. However, subjects implanted with the LPS Flex implants were, on average, 6.7 years older and 4.1 months earlier post-op than the subjects in the LCS RP PCS group. This might suggest an advantage of one TKA design over the other. Also, condylar lift-off was not equally distributed among the two groups, which may suggest that the implantation procedure itself could be responsible in determining the occurrence of lift-off.

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IS LOWER WEAR THE MAIN BENEFIT OF ROTATING PLATFORM MOBILE BEARING TOTAL KNEES? Garvin, Kevin L; O’Brien, Benjamin W; Croson, Richard E and Haider, Hani Department of Orthopaedic Surgery and Rehabilitation, University of Nebraska Medical Center, 985360 Nebraska Medical Center - Scott Technology Center, Omaha, NE 68198-5360, USA. Phone: +1-402-559 5607, Fax: +1-402-559 2575, Email: [email protected]

Besides reducing contact stress, the rolling-sliding curvilinear motion in rotating platform bearings is separated from the axial rotation motion onto two separate articulating surfaces. This reduces cross-paths which accelerate UHMWPE wear. Various studies have compared mobile bearings with fixed bearing TKRs, but the mobility of the bearing had not been the only difference. Either the femoral component or other design details were different and/or the testing had been performed under the displacement-control regime, where the two types of bearings had been given different pre-selected kinematics as test inputs. As the kinematics affect wear, prescribing different motions as inputs indirectly dictates the wear results. This study compared the resulting kinematics and wear of mobile to fixed bearings, with the same identical femoral components, and with exactly the same force-control inputs, including identical soft-tissue simulation. Four Fixed Bearing (FB) and four Rotating Platform (RP) PFC Sigma PCL retaining TKR specimens were in-stalled in a fully staggered order on two 4-station force-control knee simulators. They were tested for 6 million walking cycles at 1Hz with diluted serum lubricant with 20g/l protein concentration at 37°C. They were given identical ISO standard force inputs and spring-based soft-tissue restraint simulating a resected ACL and retained PCL. The AP displacement and axial rotation and many other variables were logged to prove their consistency, and to compare to the ideal (desired) waveforms. The wear was measured gravimetrically and surfaces of all the ar-ticulating surfaces were photographed at different stages to record the features of the articulation/wearing regions. The kinematics of the RP revealed a more anterior position of the tibia relative to the femur during stance com-pared to the FB. The AP displacement was similar for the two in stance, but the RP showed marginally less AP range in the swing phase. Both showed similar trends of internal-external (IE) rotation during stance, but the RP intermittently rotated around a rotationally offset range, shifted by up to ± 2°. The IE rotations of the FB were gen-erally smaller (peaking at 4°-5° internally just before toe off) than the RP (peaking at 8°-10° internally). Two of the RP specimens showed very infrequent, transient and mostly temporary dislocations of the UHMWPE insert. The wear rate for the FB averaged 8.14±2.63 mg/million cycles and the RP averaged 6.78±1.74 mg/million cycles (p > 0.05). Both were very low wear rates compared to other implants tested similarly in the same laboratory. The slightly lesser wear was accompanied by increased rotational laxity for the RP compared to the FB. The DePuy PFC Σ polyethylene wear was not significantly lower in the rotating platform design. Our in vitro study did not address other benefits of the rotating platform design such as rotating laxity, less stress transmitted to the prosthetic bone interface and tibial self-aligning. The benefits of rotating platforms should be considered multi-factorial, involving higher rotational laxity especially at higher flexion, less torques on the bone reducing the risk of loosening and self-aligning for more central patellar tracking.

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IN VIVO ASSESSMENT OF AXIAL ROTATION IN MOBILE BEARING TKA Wasielewski Ray, Komistek Richard D, Mahfouz Mohamed R, Zingde Sumesh M Corresponding Author: Richard D Komistek, PhD Professor, Biomedical Engineering Center Director University of Tennessee 301 Perkins Hall Knoxville, TN 37996-2030 Phone: 865-974-2093 Fax: 865-671-2157 Email: [email protected]

Discussions continue to revolve around mobile vs. fixed bearing TKA and whether either TKA type offers an ad-vantage to the patient. Over the past 12 years, over 2500 knees have been analyzed in our laboratory using fluoros-copy. The objective of this study was to analyze previously collected data for mobile bearing TKA to assess possi-ble advantages for patients with respect to axial rotation of the implanted components. Patients were each asked to perform a deep knee bend to maximum flexion, while under fluoroscopic surveillance. Using an accurate model-fitting analysis, in vivo data was recovered in three dimensions and analyzed to deter-mine patient’s axial rotation patterns, specifically the magnitude and pattern of rotation. Seven different mobile bearing TKA groups were analyzed and compared to both fixed bearing TKA and the normal knee. Three significant findings were recovered from the data: (1) On average, the mobile bearing TKA groups experi-enced minimal axial rotation of the femoral component relative to the tibial component (Range = -1.1o to 6.3o), significantly less than the normal knee averaging 27.7o (p<0.001); (2) a high incidence of subjects having a mobile bearing TKA experienced an opposite axial rotation pattern compared to the normal knee (Range = 10 to 75%); and (3) the mobile bearing insert often rotates less than 2.0o with respect to the tibial component and, at times ro-tates in the wrong direction. Although, conceptually it would appear that a mobile bearing TKA would offer the patient a greater advantage to achieve a more normal axial rotation pattern, under in vivo conditions these seven TKA types did not afford statis-tically greater amounts of axial rotation when compared to a fixed bearing TKA (p>0.05).

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MOBILE VERSUS FIXED BEARING IN DEEP FLEXION AFTER TOTAL KNEE REPLACEMENT Samih Tarabichi, M.D. P. O. Box 32238, Dubai, UAE 32238 E-Mail: [email protected] Introduction: Literature fails clearly to indicate an advantage of a mobile bearing over the fixed bearing implant. The purpose of this study is to compare result of mobile bearing verses fixed bearing Total Knee replacement done by single sur-geon and to see if there is any advantage for the mobile bearing. Material and Methods: Eight hundred sixty two cases of a mobile bearing LPS Flex implant was compared to four hundred twenty six cases of fix bearing LPS implant done from January of 2001 to January 2006, both group was performed by the same surgeon and the same postoperative cause was done in both group. Documentation for complication and knee score were done in both groups and statistics and analyses were curried out for this result. Also three kinematics evaluation was curried on for ten patients of each group to asset the tibia femoral movement in both groups in deep flexions. Results: We had three Knee dislocations in the mobile bearing group none in the fixed bearing group the rest of the compli-cation were similar in both group. Average range of motion was the same in both groups. Knee score was similar in both groups. Canamathic assessment confirmed in both group excessive exteneraltation of the femur over the tibia and in fixed bearing group it confirms the spelling of the lateral femoral condoral from the tibial Plato which wrist concern about the safety Fix bearing in deep flexion. Discussion and Conclusion: There was no clear advantage of Mobil bearing over fixed bearing implant, mobile bearing requires a better sophis-tical balance to reduce rate of Knee dislocation postoperatively. The mobile bearing knee seems to be more accom-modating to deep flexion over Hundred & Fifty degrees and concern should be raised about the fixed bearing in deep flexion activity.

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GENDER COMPARISON OF IN VIVO KINEMATICS FOR NORMAL AND TKA SUBJECTS Komistek RDa, Mahfouz MRa, Glaser Da, Booth Rb, Scuderi GRc, Argenson JNd, Zingde Sa, Anderle Ma a University of Tennessee, Knoxville, TN, USA b Tennessee Orthopaedics Clinic, Knoxville, USA c Rocky Mountain Musculoskeletal Research Laboratory, Denver, Colorado Diana Glaser, 301 Perkins Hall, University of Tennessee, Knoxville, TN 37917 Email: [email protected], Phone: 865-974-1936, Fax: 865-946-1787 Sexual dimorphism, better known as gender difference, is a well recognized phenomenon. The gender differences between the human species are found not only in size, but are obviously present in shape and behaviour. Neverthe-less, a debate has recently begun about the importance and the supposed advantages of Gender Specific total knee arthroplasty. Therefore, the objective of this study was to evaluate in vivo kinematics for any relevant differences between male and female knees, investigate if the variance is significant for movement and articulation of the knee and determine if these kinematic differences justify gender specific knee implants. Twenty normal knees and 321 implanted knees were included in the study and categorized in four groups: Normal Male (n=10), Normal Female (n=10), Implanted Male (n=111) and Implanted Female (n=210). The breakdown for the implanted knees was 35% male and 65% female, similar to the reported percentages of males vs. females re-ceiving TKA in the USA. Ten different TKA designs were included in this study and none of the implants were reported to be gender specific at the time of analysis. All subjects were analyzed using video fluoroscopy while performing deep knee bend activity. Both the femoro-tibial and patello-femoral joints were analyzed. A previously published 3D-to-2D registration technique [1,2] was used to determine 3D rotational and translational kinematics. The main parameters included for comparison were range of motion, medial and lateral anterior/posterior (A/P) translations, axial rotation and lift off. Non-implanted female knees achieved greater weight-bearing range-of-motion (p<0.01), a more posterior lateral condyle contact position (p<0.01; 0 to 60o), and greater internal tibial rotation (p<0.01; 0-60o) than their male counterparts. After TKA, the males achieved greater weight-bearing range-of-motion (p<0.01) and the females achieved similar femoral contact positions and axial rotation patterns, losing their pre-TKA differences. Implanted females lost on average 7.5 degrees of flexion, 1.8mm lateral condylar position and 4 degrees of axial rotation more than the implanted males. There are greater differences between implanted and normal patello-femoral joint kinematics in female knees than in male knees. In this analysis, the data has revealed that females experienced greater kinematic changes after TKA relative to males. Sexual differences which influence the motion of the females and males and are relevant not only from morphological but also from mechanical point of view have been found. Those differences seem to be critical in terms of range of motion and patello-femoral articulation. The compromise of normal axial rotation for the females following TKA may be the reason for the greater loss of weight-bearing range of motion. The greater loss of poste-rior position on the lateral side in the implanted females may lead to increased patellar complications among the females following TKA. These results provide support for the design of a femoral knee prosthesis better suited to the anatomies more typically observed in females. However, at this time it is unclear if a Gender Specific TKA would achieve the implant design goals and recover normal female kinematic patterns. Further research is now being conducted to bring more insight. [1] Dennis DA, et al.: Clin Orthop Rel Res, 1998 [2] Hoff W, et al.: Clin Biomech, 1998

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CLINICAL RESULTS OF CERAMIC TOTAL KNEE PROSTHESIS USED FOR 26 YEARS Oonishi Hironobu*, Kim Sok Chol*, Oonishi Hiroyuki*, Kyomoto Masayuki**, Iwamoto Mikio**, Masuda Shingo**, Ueno Masaru** * H. Oonishi Memorial Joint Replacement Institute, Tominaga Hospital, 4-48, 1-chome, Minato-machi, Naniwa-ku ,Osaka, 556-0017 Japan Phone: 81-6-6568-1601 Fax: 81-6-6568-1608 E-mail: [email protected] ** Japan Medical Materials Corporation, Osaka, Japan INTRODUCTION: We started clinical use of a total knee prosthesis (TKP) made of alumina ceramics in late 1970s, based on the good clinical results we already had with ceramic femoral heads in THA and favourable results of knee simulation tests of a ceramic component. The knee simulation test showed 0.3mm linear wear of the UHMWPE insert in case of metal femoral component combination, whereas virtually no wear observed with ceramic femoral component with less than one-tenth of metal TKP. In this study, we investigated the long-term clinical performance of the ceramic TKPs. MATERIALS AND METHODS: The first generation of the ceramic TKP was used between 1981 and 1985. It consisted of a femoral component (F-comp) and a tibial component (T-comp), both made of polycrystalline alumina ceramics, and a UHMWPE insert. The raw material of alumina ceramics has a purity of 99.5%<. Both cemented and cementless fixation were at-tempted for the femoral and the tibial components. The second generation used from 1990 to 1996 consisted of an alumina ceramic F-comp, a T-comp of titanium alloy, and a UHMWPE insert. In the third generation used from 1993 to 1998, the F-comp had a porous coating of ceramic beads to improve fixation between the bone cement and the F-comp. We compared the wear of metal TKPs and ceramic TKPs which were retrieved after a long term service. We also examined findings of clinical radiographic observation. RESULTS AND DISCUSSION: A total of 137 ceramic TKPs of first generation were followed up for 20 to 23 years after implantation. All the rate of loosening, sinking and revision were higher with cementless fixation than cemented. In the second and third generations, all components were implanted using the bone cement. In a total of 249 joints with 6 to 14 years fol-low-up, neither loosening nor sinking was observed. Radiolucent line was observed in the medial and lateral areas of the tibia at rates of 4.3% and 2.1% respectively. No osteolysis was observed in any case. A close observation of wear in retrieved implants is important for examination of the clinical performance of artifi-cial joints. The findings with metal F-comp/UHMWPE bearing surface in retrieved TKPs were compared with those we had in the previous clinical investigations with ceramic F-comp/UHMWPE combination. Metal TKPs exhibited a higher wear rate than ceramic TKPs, with scratched surface damages. The lower wear rate with much less surface damage found in the previous study suggests the possibility of a long term durability and performance of the ceramic TKP. REFERENCES 1. Oonishi H, Tsuji E, Mizukoshi T, et al., Bioceramics 1991;3:137-145.

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WEAR RESPONSE SEQUENTIALLY ENHANCED POLYETHYLENE IN KNEE JOINT Tsukamoto. Riichiro1, Shoji. Hiromu1, Hirakawa. Kazuo2, Yamamoto. Kengo3, Clarke. Ian C1, 11406 Loma Linda Drive, Suite606, Loma Linda, CA, 92354, USA 1-909-558-6490, Fax: 1-909-558-6018, E-mail; [email protected]

In total replacements, Crosslinked polyethylene (XLPE) has been shown to be effective in reducing wear in experi-mentally. However, XLPE has not found widespread in clinical use in TKR, primarily because the crosslinking processes inevitably leads to reductions in critical mechanical properties such as toughness and fatigue strength. Thus improvements have been suggested with improved wear resistance XLPE for tibial inserts and improved me-chanical properties. Therefore the aim of this study was to compare the wear of conventional versus a new sequen-tially enhanced UHMWPE run against CoCr femoral implants. Our hypothesis was that the sequentially enhanced tibial inserts would offer superior wear performance.

Compression molded GUR1020 UHMWPE was processed by irradiating to 30 kGy followed by annealing at 130°C for 8 hours. This cycle was repeated twice sequentially resulting in a cumulative dose of 90 kGy (SXPE). CR tibial inserts were machined from SXPE and 3-Mrad DurationTM stock (Stryker Inc: controls). SXPE inserts were gas-plasma sterilized. Knee simulation was conducted on a 6 station simulator. Lubricant was serums (20mg/ml protein) with additive EDTA. Serum was changed every 0.5million cycles until 5 Mc and every 1 million cycles until 10 Mc. Wear trends assessed by linear regression techniques.

The weight-loss patterns showed uniform linear trending (regression coefficient > 0.95). Wear of the control im-plants (CoCr / UHMWPE) averaged 4 mm3/Mc with the good control of experimental variance. Wear of the SXPE implants (CoCr / SXPE) averaged 0.64 mm3/Mc, also with good control of experimental variance.

The most significant finding was that the SXPE tibial inserts reduced wear by 7-fold compared to control. There was a clearly a beneficial effect of sequentially enhanced UHMWPE for knees. Our long term study now to 10 Mc duration was comparable to a prior study that showed a 5-fold wear reduction for SXPE with 5 Mc duration of study. Thus SXPE implants may prove excellent for active patients who may otherwise risk high wear rates over many years of use.

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MOBILE BEARING KNEE 30 YEARS OF EXPERIENCE. WHAT HAS BEEN PROVEN? REPORT OF 450 LCS RP WITH 10-15 YEARS FOLLOW-UP Jean-Louis Briard, Polawat Witoolkollachit, Guo Lin Clinique du Cèdre, Bois-Guillaume cedex 76235 France E-Mail: [email protected] 1n 1977, the LCS mobile bearing knee was designed to address polyethylene wear, tibial fixation and patellar com-plications. Reports by the designers has shown excellent survivorship at 20 years. The meniscal bearings carry a higher risk of bearing wear or fracture but the rotating platform has shown remarkable survivorship. Most of the complications occur early in these series with rotating platform. Analysis of our experience with the LCS RP with a 10-15 years follow-up is important and should parallel these long term studies. Instability is a very exceptional complication in our experience where we sticked with the classic method using the tibial cut first method, balance of the soft tissues when necessary and flexion gap first with the horse shoe distrac-tor. There were no case of polyethylene wear despite some significant undercorrection. The fixation of the tibial im-plant failed in few cases with cementless technique as observed with any cementless implant experience. Loosening with cemented implants was quite exceptional. Patellar replacement with mobile bearing patella has shown few cases of polyethylene wear after 5-10 years neces-sitating revision. Most of the time the patella was not resurfaced and only one case required a subsequent replace-ment. Today post-operative range of motion is an important issue. This was studied with reference to the the preoperative motion, the patient’s weight and age. A study was made to correlate this flexion motion with the position of the prosthetic condyles in reference to the epicondyles.

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EVALUATION OF INTRAARTICULAR ‘PINLESS’ NAVIGATION IN THE SETTING OF LIMITED INCISION TOTAL KNEE ARTHROPLASTY Walker, Richard H; Mai, Kenny; Jain, Rajeev K; Rosen, Adam S Division of Orthopaedic Surgery, Scripps Clinic, 10666 North Torrey Pines Road, La Jolla, CA 92037, USA Tele 858-554-9882; Fac 858-554-6210; Email [email protected] PURPOSE: The goal of the study was to evaluate the potential for replacing total knee arthroplasty (TKA) intramedullary (IM) instrumentation with less invasive intraarticular, so called pinless navigation, thereby eliminating violation of the IM canal by either IM guide rods or metaphyseal / diaphyseal extraarticular navigation pins. METHODS: Thirty consecutive unilateral TKA procedures were evaluated during September 2006 to February 2007. An in-traarticular navigation system was incorporated into a limited incision TKA protocol (incision length 2.5 times patellar height; e.g. 12.5 cm). Percutaneous metaphyseal / diaphyseal pins were not necessary. Use of navigation was incorporated in a transitional, stepwise manner, as follows. For Group I, the initial ten TKA, distal femoral (FEM) and tibial (TIB) osteotomies were dictated by IM instru-mentation and were then assessed regarding mechanical alignment (MA) by intraarticular navigation trackers (NAV). For Group II, the subsequent ten TKA, distal FEM and TIB osteotomies were dictated by NAV and were then assessed regarding MA by IM instrumentation. For Group III, the last ten TKA, distal FEM and TIB osteotomies were dictated solely by NAV, and IM instru-mentation was not used. Anterior-posterior FEM osteotomies were dictated by mechanical instrumentation. FEM and TIB TKA component MA on standing digital hip-to-ankle radiographs were measured independently by four orthopedists (varus desig-nated as [+]; valgus as [-]; outliers as > +3°). RESULTS: Demographic differences among the three groups were unremarkable. Group I (osteotomies dictated by IM, assessed by NAV): NAV assessment showed mean FEM and TIB osteot-omy MA of -0.5° and +0.6°, with no outliers. Radiographic assessment showed mean FEM and TIB component MA of 0.0° and -0.7°, with one outlier (-4°). Group II (dictated by NAV, assessed by IM): NAV assessment showed mean FEM and TIB osteotomy MA of -0.3° and +0.7°, with no outliers. Radiographic assessment showed mean FEM and TIB component MA of +0.7° and 0.0°, with no outliers. Group III (dictated by NAV, no IM): NAV assessment showed mean FEM and TIB osteotomy MA of 0.0° and -0.1°, with no outliers. Radiographic assessment showed mean FEM and TIB component MA of +0.3° and +0.8°, with no outliers. CONCLUSION: This intraarticular, ‘pinless’ TKA NAV system:

1) demonstrated a neglibible intraoperative variance in MA when compared to IM instrumentation; 2) afforded component position to meet the conventional MA goals of postoperative radiographic assess-

ment; 3) eliminated violation of the IM canal that occurs with either IM guide rods or navigation systems utilizing

extraarticular metaphyseal / diaphyseal tracker pins; 4) eliminated percutaneous pin placement in conjunction with a limited incision TKA exposure; and 5) is now under evaluation regarding tibiofemoral gap balance assessment.

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DOES THE SIZE OF INCISION IN TKA MATTER? MIS TKA, FACTS AND FICTIONS Author: Samih Tarabichi, M.D. P.O. Box 32238, Dubai, UAE 32238 E-Mail: [email protected] INTRODUCTION: The majority of papers covering MIS total knee describe a surgical approach where the quads tendon is violated. This presentation describes a modified subvastus approach using MIS technique. The results are compared to the regular subvastus approach. MATERIAL AND METHODS: 742 total knee replacements were performed through MIS subvastus approach from November 2002 to February 2005. All cases were performed by the same surgeon. The subvastus approach was modified to allow more quads excursion so the surgery can be performed without dislocating the patella. The data was processed at University of Dundee. The results were compared to the results of 361 cases of standard subvastus approach performed by the same surgeon. RESULTS: The average skin incision for the MIS group was 10.2 CM. as compared to 18.4 to the standard subvastus. There was no significant difference in the blood loss between the two groups. The progress with rehabilitation was the same in both groups as well. Hospital stay was also the same .the average range of motion was also the same. DISCUSSION: Kanasaki et al. (ISTA 2002) has shown that patients who had subvastus approach were able to regain the ability to do a straight leg raising faster than the standard parapateller incision. The results in this paper confirm the same showing that the ability of patients to rehabilitate is not related only to the size of the incision. Having relatively small incisions help in shorten hospital stay but did not make any difference in blood loss and post op movement. CONCLUSION: The subvastus approach is a true quad sparing approach and it can be performed through 10 cm. incision safely even in heavy patients with severe knee deformity. However it should be stressed that MIS surgery does not neces-sarily leads to better outcome.

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TOTAL KNEE ARTHROPLASTY BY TRANSVERSE INCISION Author: Tomohiro Ojima Fukushima 7-42 Yatsuo Japan—939-2376 E-Mail: [email protected] Objective: The longitudinal wounds associated with TKA are generally conspicuous for several months, and a few patients have been un-satisfied with hypertrophic scars during the several-year period following surgery. In general the wound horizontal to the skin crease heals better than the wound vertical to it. In the present study, it was hypothesized that if the transverse incision can be safely utilized for TKA, wounds will heal better and feature less scar formation than with longitudinal incision. Patients and Methods: A consecutive series of 36 patients (41 knees) who underwent primary TKA with the Scorpio NRG Posterior Stabilizer system were examined. The first 21 knees were performed by the longitudinal-incision procedure and the last 20 knees were by the transverse-incision procedure. Skin incisions were performed at the level of the inferior pole of the patella in the transverse-incision group, and performed at the anterior straight midline in the longitudinal-incision group. The incision was extended, if necessary, to perform the operation safely in both incision group. Other than the incisions, the procedures used were the same in both groups. The operative time, blood loss, and any complications were noted in order to evaluate the safety of the new inci-sion. KSS scores and X-rays in all knees were evaluated at 12 months after operation. Scar assessment included the following objective and subjective categories: length, width, color, and undulation. Each patient was asked whether they had problems with the healing of their wound. Results: There were no significant differences in operative time or blood loss between the groups. There were no significant differences in KSS score and radiologically between the groups. Wound problems were noted once in each group: a subcutaneous hema-toma in the transverse-incision group and delayed healing was noted in the longitudinal-incision group. There was no wound infection, necrosis required scar revision, hypesthesia, or limited ROM in either group. The mean length of transverse-incision scars was almost the same (about 15 cm) as that of longitudinal-incision scars in flexion position. The maximum width of trans-verse-incision scars was significantly smaller than that of longitudinal-incision scars. The color of most wounds in the trans-verse-incision group was already matched with surrounding skin at 12 months after operation. On the other hand two wounds in the longitudinal-incision group were raised over 1 mm compared to the surrounding skin. A higher proportion of patients who had a transverse incision than patients who had a longitudinal incision thought that their scar was excellent, rather than average, in appearance. Two patients felt their operation scar was unacceptable in appearance. Conclusions: It is as easy in transverse incision as in longitudinal incision in the eversion of patella and subluxation of the knee joint. Postop-erative clinical and radiological results were the same in both incisions. As there was no major skin trouble postoperatively, transverse incision is thought to be safely utilized for TKA. Considering the advantages of better wound healing and less scar formation, this new approach may be an alternative option in TKA.

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POSSIBILITIES OF AN INSTRUMENTED LINKAGE FOR TKR SURGERY RE Forman, Peter S Walker, CS Wei, G Scuderi, G Klein New York University-Hospital for Joint Diseases, NEW YORK, USA Standard mechanical instruments have been successful and are widely used. Optical and EM navigations systems offer advantages but so far their use is not widespread. Another approach to computer-assisted TKR surgery is an Instrumented Linkage which is potentially compact and low cost. We designed and evaluated such a system, and compared it with a mechanical system using ergonomic criteria. A lightweight 6 DOF instrumented linkage using angular encoders was developed, where one end is fixed to the bone, and the other end is used to digitize bony landmarks or measure orientations of jigs or cut surfaces. Bearing grade PEEK material was used for its low friction and wear properties. The lengths of the links were designed to reach all of the points at the ankle and around the kne itself. The center of the femoral head is determined using the kinematic method. The linkage is used to place and adjust a special slotted cutting guide using computer screen visuals. Ligament balancing is achieved by connecting between tibia and femur. Accuracy was determined by measuring multiple points on a special set-up which simulated the surgical situation. The mean accuracies of points were less than 1mm and the mean angular errors less than 1 deg. Comparisons were made on a full-leg sawbone set-up for each step of the procedure regarding time, convenience, accuracy and cost, between the linkage system and a standard mechanical system. In the comparison tests on the saw-bone knees, at each step, the times taken between Standard Instruments and the Linkage were comparable, yet convenience was enhanced with the Linkage due to the lighter weight and decreased bulk. The ease of checking the cuts and correcting if necessary was improved. The cost of manufacturing the in-strumented linkage system was similar to that of the mechanical instruments it would replace. Optical or EM navigation systems are expensive and possibly best suited to high volume situations. An instru-mented linkage system may have a broad application due to surgeon preference for its ergonomic characteristics compared with mechanical instrumentation, coupled with no increase in cost.

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HIP POSITION FOR MEASURING FLEXION GAP IN TOTAL KNEE ARTHROPLASTY Shinro Takai, MD1, Noriki Nakachi, MD1, Nobuyuki Yoshino, MD2 Yoshinobe Watanabe, MD1, Takashi Matsushita, MD1 1) Department of Orthopaedic Surgery, Teikyo University School of Medicine, Tokyo, Japan 2) Department of Orthopaedic Surgery, Kyoto Kujo Hospital, Kyoto, Japan Introduction: Soft tissue balancing remains the most subjective and artistic part of current techniques in total knee arthroplasty. The flexion gap is traditionally measured at approximately 45 degree of hip flexion and 90 degree of knee flexion on the operation table. Despite of aiming equal joint gaps or tensions in flexion and extension, the influence of the thigh weight on the flexion gap has not been documented. Therefore, the purpose of this study was to examine the flexion gaps at the 90-90 degree flexed position and the traditional 45-90 degree flexed position of hip-knee joints. Materials and Methods: Thirty patients with osteoarthritic knee underwent total knee arthroplasty. After the sacrifice of PCL, soft tissue releases, and bone cuts, the specially designed tenser which has two load cells was employed. 160N was applied to open the joint gaps at the traditional 45-90 degree flexed position as well as the 90-90 degree flexed position of hip-knee joints. Results: The flexion gap at the 90-90 degree flexed position of hip-knee joints was 2.1±1.2mm wider than that of the tradi-tional 45-90 degree flexed position of hip-knee joints. It showed the significant difference of flex gap in between the two different hip flexion angles (p<0.001). Discussions: At the traditional 45-90 degree flexed position of hip-knee joints on the operation table, the flexion gap is approxi-mately 45 degree to the gravitation and influenced by the thigh weight. To avoid the influence of the thigh weight, the flexion gap should be checked at the 90-90 degree flexed position of hip-knee joints, to obtain equal joint gaps or tensions in flexion and extension.

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VARUS BALANCE BEOMES PREDOMINANT AT FLEXION AFTER POSTERIOR CRUCIATE-RETAINING TOTAL KNEE ARTHROPLASTY Nobuyoshi Watanabe1, Nobuyuki Yoshino1, Yukihisa Fukuda1, Nobuhiko Fujita1, Shinro Takai2 Department of Orthopaedic Surgery, Kyoto Kujo Hospital Department of Orthopaedic Surgery, Teikyo University Correspondence to: Nobuyoshi Watanabe, MD Department of Orthopaedic Surgery, Kyoto Kujo Hospital Karahashi Rajomon-cho10, Minami-ku, Kyoto 601-8453, Japan Tel: +81-75-691-7121 Fax: +81-75-691-5311 [email protected] Proper soft tissue balance is an important factor for a successful outcome of total knee arthroplasty (TKA). Soft tissue has the viscoelastic property and thus it was hypothesized that the corrected varus-valgus balance at TKA, which is the difference between varus and valgus laxities, would return to the preoperative balance. We evaluated preoperative and postoperative varus-valgus laxities and balances at full extension and 80º flexion of 20 posterior cruciate-retaining (CR) TKA by measuring stress roentgenograms before, and one and 12 months after surgery. Roentgenograms at 80º flexion were taken by kneeling view. Data was expressed as positive value when the me-dial compartment was open. Varus laxities at extension were 7.5º, 3.1º, and 3.2º whereas valgus laxities were 2.0º, -2.1º, and -2.8º before and 1 and 12 months after surgery. Varus laxities at 80º flexion were 6.4º, 3.8º, and 5.3º whereas valgus laxities were 3.2º, -1.7º, and -0.6º, respectively. There was no significant difference between values of one and 12 months at both knee angles. The balances were 9.5º, 0.9º, and 0.4º at extension and 9.6º, 2.1º, and 4.8º at 80º flexion before, and one and 12 months after surgery. There was no significant difference between the values of one and 12 months at extension. However, interestingly, a significant difference was found between the values of one and 12months at 80º flexion. Furthermore, varus balances increased in 14 of 20 knees at 80º flexion. However, only 3 knees showed increase at extension. It was concluded that varus-valgus balance returns to the preoperative one and varus balance becomes predominant at 80º flexion one year after CR-TKA.

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DYNAMIC SOFT TISSUE BALANCING SENSEOR FOR TOTAL KNEE ARTHROPLASTY Masahiko Suzuki, Jin Miyagi, Itsuo Sakuramoto, Kunio Fujiwara, Ryoichi Michihiro, Kouichi Kuramoto Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, 1-8-1 Inohana Chuo-ku Chiba city Japan 2608677 Fax +81-432262116, Tel +81-432262117, E-mail; [email protected] Preference; poster presentation Topics; 5 computer-assisted surgery Introduction: Poor soft tissue balance in total knee arthroplasty often causes instability, subluxation, excessive polyethylene wear, and loosening after surgery. Mechanically designed instruments for soft tissue balance have been used only in static conditions such as full extension and 90º flexion. On the other hand, recent navigation and robotic surger-ies require more precise assessment of soft-tissue balance. Therefore, we developed a dynamic soft-tissue balanc-ing sensor with six force transducers. Methods: A tibial tray for the trial procedure was constructed with six force transducers. Miniature force transducers (12 mm in diameter) were symmetrically fixed in the anterior, middle, and posterior areas of a tibial tray. Each of the six transducers measured the local axial compressive force. Data were sent to a PC through an amplifier. Thus, the measures determined were the total compressive force, the force distribution in the mediolateral direction, the force distribution in the anteroposterior direction, and the center of gravity. The prototype tibial tray was implanted in three cadaver knees along with flat surface cruciate-retaining component and tibia insert (Hi-tech knee, Nakashima Propeller Co. Ltd., Okayama, Japan). The quadriceps was loaded with 50N and the hamstrings with 50N (25N each for the medial and lateral groups). Forces on the tibial tray were recorded during 90º flexion and extension. A Shape sensor was attached to the cadaver to record the knee flexion angle simultaneously. In the same condition, a computerized contact area and pressure measurement system, K-Scan (Tekscan, South Boston, USA) was used to detect forces under the tibial insert. Results: The soft tissue balancing sensor with six force transducers showed the laterally predominant load (lateral pivot motion) during 90º flexion and extension of the knee in three cadavers. The laterally predominant loads in the study were similar to those recorded by K-Scan. Discussion: Soft-tissue balancing is a critical factor in total knee arthroplasty. Standard mechanically designed instruments for assessing soft tissue balance are effective in reducing the difference in loads measured at 90º flexion and at exten-sion. However, those instruments provide neither continuous data during flexion and extension, nor digital data which helpful to robotic surgery. K-Scan can provide continuous and digital data, but the sensor films are fragile. The soft-tissue balancing sensor with six force transducers is more durable in intraoperative use and has the same function as K-Scan.

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FIXED GENU VALGUM: THE SLIDING LATERAL CONDYLAR OSTEOTOMY AS A MEAN TO BALANCE SAFELY THE LATERAL SOFT TISSUES. REPORT OF 74 CASES WITH AT LEAST 5 YEARS FOLLOW-UP Jean-Louis Briard, Jens Boldt, Polawat Witoolkollachit, Guo Lin, Jean Zahlaoui. Clinique du Cèdre, Bois-Guillaume cedex 76235 France E-Mail: [email protected] Fixed genu valgum are still very challenging. The release of the lateral soft tissues carry a higher risk of flexion instabilities as frequently reported. All the studies have shown that the lateral collateral ligament is the primary lateral soft stabilizer. There is no purely soft tissue technique which permits to release, lengthen this structure and still maintains immediate stability in flexion. Even the pie crusting technique injured most of the time this structure even if it seems to make healing safer. The study of the deformity has shown that in genu valgum, the femur is usually a femur valgum with an oblique joint line. At the time of the surgery, we will try to build an horizontal prosthetic joint line. Ligament balance is usually fine in flexion and doesn’t require any release as the Trans epicondylar line is parallel to the tibial cut. On the contrary, in extension the extension gap is trapezoidal and requires lengthening of the pos-terior and lateral structures in order to be rectangular with the knee in neutral. A sagittal osteotomy of the lateral condyle allows all the lateral structures (lateral collateral ligament, Popliteus tendon and some posterior capsule) to slide only distally. This allows enough space for the extension gap with excellent stability without changing the flexion gap which remains totally stable. This reports concerns a serie of 74 cases with the use of the LCS rotating platform with minimum follow-up of 5 years. All the details of the operations are reported. The post operative stability has been studied with varus/ valgus stress xrays at 20 & 70° under 5 dN stress at 3à cmm from the joint line. There was only one case of non-union non symptomatic discovered on these xrays. All the results were reported according to the knee society score. Careful study of the xray was carried out as well as the correlation with the excellent post operative flexion. This technique is advised for the treatment of fixed genu valgum as it allows safe soft tissue balance without risk of post operative instability.

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B7-9 SEVERE GENU VALGUM: HOW WE DEAL WITH? Louis Lootvoet, O Himmer, B Leyn, G Allard

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B7-10 THE NEED FOIR DEMAND MATCHING TOTAL KNEE REPLACEMENT AND THE OBESE PATIENT Richard Cohen, M.D., Atlanta, GA PURPOSE: The purpose of this study was to find a goal/solution using demand matching for total knee replacement in the growing obese patient population while protecting the soft tissue envelope. INTRODUCTION: The current definition of obesity defines a patient with a BMI of >30 as obese, a BMI of >40 as morbidly obese and a BMI of >50 as massively obese. Most implants recommend a BMI of 35 or less for safe usage. Yet 30.5% of the American population as of 2000 is considered obese, and of those patients in need of a TKR, more than 50% have a BMI of greater than 30. Obese patients also have different needs from their TKR surgery, including: a decrease in the need for flexion, a lower level of activity and a longer need for survivability. In terms of the prostheses being used surgically, there is a greater structural demand on the prostheses as well as the soft tissue “envelope.” MATERIALS AND METHODS: Prostheses options are currently limited for use in obese patients. The primary use would be an unconstrained versus constrained LCCK prostheses. The constrained LCCK may be the best alternative implant available today. Unicompartmental and Rotating Hinge Knee (RHK) are also implant options but have known soft tissue problems in the past. RESULTS: For the past 25 months, 122 LCCK total knee replacements have been performs in patients with a BMI of greater than 35. The population breakdown is 74 female and 48 male. These patients will be followed for the next 5 years with great attention paid to instability due to soft tissue failure. DISCUSSION AND CONCLUSION: More research is needed on this patient population, specifically gait analysis studies that measure preoperatively and postoperatively patient groups with a BMI of less than 25 or higher than 35. Stress x-rays should be done for these groups as well. The issue is currently being addressed in the media saying that surgeons are wary of the extra risk and work of obese patients and many won’t replace their hips or knees (Wall St. Journal 2.28.06). While TKR in obese patients is not for every joint surgeon, steps can be taken to provide the care needed for this population. Specifically, holistic and bariatric care for patients provided by joint centers that have significant ex-perience with obese patient care.

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DEEP FLEXION KINEMATICS IN PATIENTS WITH A MEDIAL ROTATION KNEE ARTHROPLASTY Authors: Moonot Pradeep, Railton GT, Mu S, Banks SA, Field RE Correspondence: 1A, Cotswold Road, Sutton, Surrey, SM2 5NG, UK Tel: 0044 7916120887 Fax: 0044 2082963475 Email: [email protected] The performance of total knee arthroplasty in deeply flexed postures is of increasing concern as the procedure is performed on younger, more physically active and more culturally diverse populations. Several implant design factors, including tibiofemoral conformity, tibial slope and posterior condylar geometry have been shown directly to affect deep flexion performance. The goal of this study was to evaluate the performance of a fixed-bearing, asymmetric, medial rotation arthroplasty design during lunge and kneeling activities. We hypothesized that medial tibiofemoral conformity would prevent femoral anterior translation, permit near-normal femoral external rotation and permit a high range of kneeling flexion.

Thirteen study participants (15 knees) with primary total knee arthroplasty (Medial Rotation Knee, Finsbury, Sur-rey, UK) were observed performing a weight-bearing lunge activity to maximum comfortable flexion and kneeling on a padded bench from 90° to maximum comfortable flexion using lateral fluoroscopy. Subjects averaged 74 years of age and nine were female. Subjects were an average of 17 months post-operative, and scored 94 points on the International Knee Score and 99 on the Functional Score. Digitized fluoroscopic images were corrected for geometric distortion and 3D models of the implant components were registered to determine the 3D position and orientation of the implants in each image.

At maximum weight-bearing flexion, the knees exhibited 115° of implant flexion (102°-125°), 3° (-3° to 14°) tibial internal rotation, and the medial and lateral condyles were located 9mm (5mm to 16mm ) and 11mm (6mm to 23mm) posterior to the AP midline of the tibial plateau. The tibial sulcus, or lowest point on the tibial insert, is located approximately 5mm posterior to the AP midpoint, thus the medial and lateral condylar locations corre-spond to 4mm and 6mm of posterior translation from a standing position. Significant condylar separation from the articular surfaces was not observed in this weight-bearing activity. At maximum kneeling flexion, the knees exhibited 119° of implant flexion (101°-139°), 2° (-7° to 17°) tibial inter-nal rotation, and the medial and lateral condyles were located 9mm (3mm to 14mm) and 11mm (5mm to 25mm) posterior to the AP midline of the tibial plateau. There was no paradoxical movement of the femoral condyles during the whole range of flexion in both the activi-ties.

The medial rotation knee exhibited kinematics of the normal knee with a medial pivot. The patients exhibited ex-cellent kneeling flexion and posterior translation of the femur with respect to the tibia. Axial rotation averaged only 5°, but varied considerably according to the patients’ posture and foot positioning during the activity. The medially conforming articulation beneficially controls femoral AP position to permit deep flexion in patients who require such motion as part of their lifestyle. Also because of the absence of the cam-post system the third degree wear generated from the wear of the post is not seen, which may increase the survivorship of these knees.

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KINEMATIC DIFFERENCE BETWEEN SUBJECTS HAVING LOW AND HIGH FLEXION AT THE SAME FLEXION ANGLES: A MULTICENTER STUDY Dennis DA1, Sharma A2, Komistek RD2, Mahfouz MR2, Anderle MR2, Little CR2, Liu F2

1Colorado Joint Replacement, Denver, CO, USA 2University of Tennessee, Knoxville, TN, USA Correspondence: Adrija Sharma 301 Perkins Hall University of Tennessee Knoxville, TN 37996 Email: [email protected] Phone: 865) 974-0198 Fax: (865) 946-1787 In vivo fluoroscopic studies have determined that the kinematic patterns for TKA are often quite variable. Previous kinematic studies have concentrated on reporting the overall performance for a design and have not explored the possibility that the kinematics exhibited by subjects having low flexion and high flexion for the same design for the same flexion angles might be different. Therefore, the objective of this study was to compare the in vivo kinemat-ics for subjects having a TKA who were not able to achieve high flexion versus those subjects who routinely ex-perience greater weight-bearing flexion to determine which variables are statistically different between these two groups.

Two hundred subjects having a TKA were evaluated using fluoroscopy during a deep knee bend to determine their in vivo kinematics. Eighty-two of these subjects experienced less than or equal to 95° of weight-bearing flexion (Group 1), while 118 subjects achieved greater than or equal to 110° (Group 2). All the implants were manufac-tured by Depuy (Warsaw, IN, USA) and included PCL retaining (PCR), PCL sacrificing (PCS) and posterior stabi-lized (PS) designs and also rotating platform (RP), fixed (FIX) and AP glide (APG) designs. The study included traditional designs like the Sigma and the LCS as also high flexion designs like the Sigma RP-F. Statistical analy-sis at 95% confidence level was conducted in order to determine which variables are different for a subject, having a TKA, who experienced greater weight-bearing flexion.

Both the lateral and the medial condylar contact positions for subjects in Group 2 were significantly more posterior (p<0.05) than the subjects in Group 1 at 0°, 30°, 60°, 90° and maximum flexion. Interestingly, although the contact positions were statistically different, the amount of posterior femoral rollback was not different between these groups from full extension to 90° flexion (p>0.05). However, this trend changed when assessing overall motion form full extension to maximum knee flexion as subjects in Group 2 achieved statistically greater posterior femoral rollback of both condyles (P<0.05). The overall amount of axial rotation and the incidence of lift off for the two groups were statistically similar. Since subjects in Group 2 achieved greater weight-bearing flexion, it could be expected that these subjects would experience greater posterior femoral rollback at maximum flexion. However, it is interesting that these subjects achieved statistically more posterior contact positions of both condyles at each increment of knee flexion. It was also interesting that axial rotation did not play a role in the subjects in Group 2 achieving greater weight-bearing knee flexion.

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IN VIVO KINEMATICS OF HIGH-FLEXION TOTAL KNEE ARTHROPLASTY Masashi Tamaki,MD1, Tetsuya Tomita,MD,PhD2, Tetsu Watanabe,MD,PhD2, Takaharu Yamazaki,PhD2, Hideki Yoshi-kawa,MD,PhD2, Kazuomi Sugamoto,MD,PhD1 From 1. Dept. of Orthpaedic biomaterial science, Osaka University Graduate School of Medicine, Osaka, Japan 2. Dept. of Orthopaedics, Osaka University Graduate School of Medicine, Osaka, Japan Introduction: Recently knee implants designed for high flexion have been introduced, and these design concepts propagated the safe performance of deep knee bending with a normal knee kinematics. The objective of this study was to evaluate in vivo kinematics of the high flexion posterior stabilized fixed bearing total knee arthroplasty (TKA) in weight-bearing deep knee bending motion. Patients and Methods: Fifteen patients implanted with Scorpio NRG PS TKA (Stryker Orthopedics) were assessed in this study. The Scorpio NRG is a recent product that design modifications from the previous Scorpio Knee System were reduction of the radius curvature of femoral component and more relaxed geometry of the posterior aspect of tibal insert to allow an axial rotation. Patients were examined during a deep knee bending motion using the sagittal plane fluoro-scopic images. Femorotibial motion was determined using 2D/3D registration technique, which used computer -assisted design models to reproduce the position of femoral and tibial components from single-view fluoroscopic images. We evaluated flexion angles and axial rotation angles of femoral component relative to tibial component; and anteroposterior (AP) translation of the lowest point for medial and lateral of femoral condyle on the tibial in-serts. Results: The average range of motion between femoral and tibial component was 124.1º (110 ~ 148). The average rotation of femoral component was 13.5º (5.2 ~ 20.5) external rotation. In terms of AP translation, the medial lowest point moved anteriorly by 1.0mm from extension to 60º flexion, and posteriorly by 5.5 mm from 60º to maximum flex-ion. The lateral lowest point moved posteriorly by 15.3mm from extension to maximum flexion. The kinematic pathway was a medial pivot from extension to 60º flexion, and a bicondylar rollback from 60º to maximum flexion. Conclusion: The external rotation of femoral component reached 13.5 degree and increased up to maximum flexion. The pivot pattern of the Scorpio NRG TKA was a medial pivot pattern that was observed in normal knee kinematics.

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ACHIEVING NORMAL KNEE MOTION IN A TKR DESIGN G Yildirim, Peter S Walker, Jason Boyer New York University-Hospital for Joint Diseases, NEW YORK, USA Current total knee replacements are successful in treating the arthritic knee, but the evidence is that normal patterns of knee motion are not restored. In addition, paradoxical anterior sliding of the femur on the tibia can occur in the first half of the flexion range. Our paper examines new knee replacement designs which incorporate geometrical features to regain anatomical knee motion. Four types of total knee replacements were examined. 1) TCP: Standard total condylar replacement with partially conforming double-dished surfaces 2) PS: Standard posterior stabilized with a central post-cam for femoral rollback after 750 flexion. 3) PSR: A modified total condylar with a central ramp and with more dished medial tibial surfaces. This combina-tion was intended to promote internal tibial rotation with flexion. 4) ASR: Surfaces as in PSR above, an extended post/recess in the intercondylar region, and an anterior medial femoral recess/tibial ramp feature to prevent paradoxical motion. A custom made dynamic machine capable was constructed to simulate a full flexion-extension activity such as crouching and squatting, under the action of quadriceps and hamstrings muscle forces. Data on three-dimensional knee kinematics was gathered using an optical motion tracking system. The intact knee was tested, then after ACL resection, then with the four TKR’s. Subsequent computer modeling showed the 3-D motion paths. Six fresh knee specimens were tested. A resected ACL caused the loss of internal tibial rotation. Both PS and CR designs behaved similar to this. How-ever the two medial pivot designs followed the path of the intact anatomical knee. Paradoxical motion was also prevented by the recess-ramp feature of the ASR design. The PSR design allowed some anterior slide up to 30 de-grees followed by the medial pivoted roll back of the femur. The ASR design prevented the paradoxical anterior shift of the femur at all degrees of flexion and provided a clear medial pivot point with a correlated comparison to the anatomical knee motion. The clinical advantages of the anatomic knee motion designs are expected to be improved AP stability, evident as ‘clinical stability’ in function, improved patella tracking, normal lever arms for the quadriceps, anatomic ligament length patterns, and increased range of flexion.

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THIGH-CALF CONTACT: DOES IT AFFECT THE LOADING OF THE KNEE IN THE HIGH-FLEXION RANGE?

Zelle, J., Barink M., De Waal Malefijt, M., Verdonschot, N.

Orthopaedic Research Lab, UMC St. Radboud, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands

E-Mail: [email protected]

Introduction:

Recently, high-flexion knee implants have been developed to provide for large range of motion (ROM) after total knee arthroplasty (TKA). Based on the fact that knee forces increase with larger flexion angles, it is commonly assumed that high-flexion implants are subjected to larger loads than conventional implants. However, high-flexion studies often do not consider thigh-calf contact which occurs during deep knee flexion. Thigh-calf contact is expected to reduce knee forces in the high-flexion range.

The purpose of this study was to analyze the effect of thigh-calf contact on the loading of the knee joint. In a previ-ous study it was shown that thigh-calf contact is substantial: ±70% bodyweight (BW) transfers through the contact between thigh and calf during activities such as squatting and kneeling. In this study, we hypothesized that thigh-calf contact reduces the internal knee forces and thereby the loading of the implant during high-flexion. Addition-ally, we evaluated the influence of body mass index (BMI) variations on the thigh-calf contact characteristics and the subsequent joint forces.

Materials & Methods:

A two-dimensional sagittal mathematical model of the knee was generated to evaluate the effect of thigh-calf con-tact on the internal joint forces. The mathematical model was primarily utilized to demonstrate the possible effect of BMI changes on the knee forces. Subject specific thigh-calf contact characteristics were included in the model.

The effect of thigh-calf contact on the prosthetic stresses and deformations was evaluated using a three-dimensional dynamic finite element (FE) knee model. The FE model consisted of a distal femur, a proximal tibia and fibula, high-flexion components of the PFC Sigma RP-F (DePuy, J&J), a quadriceps and patella tendon and a non-resurfaced patella. Both tibio-femoral and patello-femoral contact were defined in the model. Non-linear elas-tic-plastic material properties were used to model the polyethylene. A squatting movement was simulated including typical thigh-calf contact characteristics.

Results:

Thigh-calf contact considerably reduced both the internal joint forces and the polyethylene stresses during deep knee flexion. During maximal flexion (155°), the compressive and shear knee force computed by the mathematical model decreased from 4.37 to 3.07 x BW and 1.31 to 0.72 x BW, respectively. Simultaneously, the maximal joint force shifted from occurring at maximal flexion to the flexion angle at which thigh-calf contact initiated (±130° of flexion). During maximal flexion, the Von Mises stress and contact stress at the tibial post decreased from 24.83 MPa to 15.86 MPa and from 49.32 MPa to 28.06 MPa, respectively. Subject specific joint forces computed by the mathematical model demonstrated that an increased BMI enhanced the effect of thigh-calf contact through an early initiation of soft-tissue contact.

Discussion:

The current study confirms that thigh-calf contact reduces the knee forces in the high-flexion range. Both the joint forces and the polyethylene stresses reduced significantly when thigh-calf contact was included. Moreover, West-ern knee patients who typically have a high BMI and fairly obese leg segments benefit relatively more from the joint force reducing effect of thigh-calf contact.

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DEEP FLEXION AFTER TOTAL KNEE ARTHROPLASTY

Nakamura, Shinichiro1.2 Takagi, Haruki 2 Asano, Taiyo2 Nakamura, Takashi1 Shogoin-kawaharacho54, Kyoto city, Japan Institution: 1 Kyoto University 2 Fukui Red Cross Hospital +81-75-751-3652/ +81-75-751-8409/ [email protected]

In Japan and the Middle East, daily life on the floor is so common that deep flexion of the knee is critical. The Japanese word, ‘Seiza’ means sitting down with the buttocks in full contact with the heels. There were few reports about the status of the components in the Seiza position. In this study the status in deep flexion was investigated and a comparison between the two different types of tibial inserts was made.

In our institution, to achieve the Seiza position was set up preoperatively as a goal for the patients who had a strong desire. From 1999 to 2005, 22 patients (33 knees) tried to achieve the Seiza position and 17 patients (25 knees) could achieved. 10 patients (16 knees) were agreed with this investigation. X-ray and fluoroscopic examination were made in all patients and computed tomography (CT) was made in 8 patients (12 knees). All patients under-went TKA with Bisurface knee prosthesis (Japan medical material, Kyoto, Japan). Two different inserts (flat type: 9knees, dish type: 7knees) were used. Subjects' knees were imaged using X-ray and fluoloscopy. Rotation angle and subluxation rate were determined in CT.

The X-ray observations of the patients in the Seiza position were classified into 3 groups. Group I was the case in which the components kept in contact. Group II was the case in which the components got out of contact com-pletely. Group III was the case in which the components came in contact in the medial site but the components got out of contact in the lateral site. In flat type cases, 6 knees were in Group I, 2 knees in Group II, and 1knee in Group III. In dish type cases, no knee was in Group I, 2 knees in Group II, and 5 knees in Group III. Dish type tibial inserts showed a tendency to cause lift-off in the medial site. From the CT in the Seiza position, the mean tibial internal rotation angle was 17.2 degrees in flat type cases and 11.7 degrees in dish type cases. The mean sub-luxation rate was 20.2% in flat type cases, and 9.7% in dish type cases. Bisurface knee prosthesis has a unique ball-and-socket joint in the mid-posterior portion, which causes smooth femoral roll back in deep flexion and allows 30 degrees rotation in the flat type and 15 degrees rotation in the dish type. When rotation force is applied to the component in the Seiza position, posterior subluxation is restricted be-cause the dish type insert has a high wall in the posterior portion. Therefore lateral contact point becomes a ful-crum and the ball joint of the femoral component transfers anteriorly. The ball joint moves onto the socket and medial lift-off occurs. In the medial lift-off patients, high pressure can be applied on the lateral side and the ante-rior socket joint. On the other hand, the flat type allows larger rotation and subluxation than the dish type and the motion is very similar to the healthy knee motion.

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mailto:81-75-751-8409/%[email protected]�

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ACTIVITIES OF DAILY LIVING FOR MUSLIMS IN THE MIDDLE EAST: A KINEMATIC COMPARISON BETWEEN NORMAL KNEES AND HIGH FLEXION TOTAL KNEE ARTHROPLASTY Authors: Sam Tarabichi,M.D., Urs Wyss,PHD. Stacey M. Smith P. O. Box 32238, Dubai, UAE 32238 E-Mail: [email protected]

Background: Achieving full flexion is critical for total knee arthroplasty patients in the Middle East and Asia, where activities of daily living require a full range of motion. Published kinematic data for these populations is limited. The objec-tive of this study was to compare the normal knee kinematics of Muslim subjects with those of Muslim total knee arthroplasty (TKA) patients with high flexion arthroplasties. Methods: An electromagnetic tracking system was used to record the motion of the lower limb segments of 14 normal Mus-lim subjects and 10 Muslim TKA patients. Subjects performed high flexion activities of daily living such as kneel-ing, Muslim prayer, sitting cross-legged and squatting. Results: For most activities, the range of motion and maximum angles in three dimensions did not significantly differ be-tween the normal and TKA groups. A statistically significant difference in the mean range of flexion/extension (but not the mean maximum flexion or mean maximum extension values) was found for the prayer activity only. The majority of normal subjects exhibited an internal rotation pattern with two distinct inflection points and a para-bolic abduction pattern over the range of flexion. Fewer TKA patients exhibited these patterns. Conclusions: Overall, the range of motion and ability to perform activities of daily living did not differ between normal Muslim subjects and Muslim TKA patients with a high flexion mobile bearing total knee arthroplasty. However, patterns of internal rotation and abduction that were exhibited by the majority of normal subjects were evident in fewer TKA patients. Therefore, although the range of motion was not significantly affected by the prosthesis, the pat-terns of motion for some subjects may have changed. Comparing the normal knee kinematics of Muslim subjects with those who had TKA during activities of deep flex-ion.

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THREE-DIMENSIONAL BONE CREATION AND LANDMARKING USING TWO STILL X-RAYS Mahfouz Mohamed R, Fatah Emam E A, Dakhakhni Hatem E, Tadross Rimon, Komistek Richard D

Corresponding Author: Mohamed R Mahfouz, Ph.D. Professor, Biomedical Engineering University of Tennessee 301 Perkins Hall Knoxville, TN 37996-2030 Phone: 865-974-2093 Fax: 865-671-2157 Email: [email protected] The objective of this study was to accurately re-create three-dimensional bone models from two still two-dimensional x-rays and to define pertinent landmarks and axes throughout the lower extremity. Initially, a statistical atlas was cre-ated for both the femoral and tibial bones. A calibration target is attached to the subject’s femur and tibia. The cali-bration target allows the algorithm to calculate the camera parameters and to perform scene calibration. Then, the user scans the two still x-rays (in any two planes, not necessarily perpendicular) into the system. As these images are acquired, the system estimates the pose and shape of each bone using the statistical bone atlas. The average shape of the bone and various modes of variation are captured by principle component analysis (PCA) of an atlas of bones. The optimization steps allow the reconstruction algorithm to find the change shape parameters and orienta-tion of the bone in order to find the best parameters that can reconstruct the bone with high accuracy. Pertinent landmarks are then located by the algorithm and rigidly defined on each bone. Then the automated analysis used these defined landmarks to accurately reconstruct the posterior condylar line, transe-picondylar axis, mechanical axis, varus/valgus alignment and cutting planes. An error analysis was conducted using fresh cadavers. Initially, these cadavers were CT scanned to recover the ground-truth three-dimensional bone models. Then, two still x-rays were taken in arbitrary planes and these x-rays were entered into the system for three-dimensional bone recovery. Matching the CT scanned bones with the bones recovered using our system revealed an accuracy of 98%. This is the first system developed that can accurately recover three-dimensional bones and associated, pertinent landmarks for live subjects using two still x-ray images. The system has proven to be highly accurate and can be used during a clinic visit preoperatively or intra-operatively during the surgery. This new system may be beneficial to surgeons for pre-operative planning, intra-operatively as a component of computer assisted surgery and/or for post-operative assessment.

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COMBINATION VIEW: A NEW ROENTGENOGRAPHIC TECHNIQUE TO ASSESS THE ROTATION OF THE FEMORAL COMPONENT Noriki Nakachi1, Nobuyoshi Watanabe2, Yukihisa Fukuda2, Naoya Shimazaki1, Nobuyuki Yoshino2, Takashi Ma-tsushita1, Shinro Takai1 1)Department of Orthopaedic Surgery Teikyo University School of Medicine Tokyo, Japan 2) Department of Orthopaedic Surgery Kyoto Kujo Hospital, Kyoto, Japan Radiographic assessment of component rotation has been not always possible without using computed tomography or magnetic resonance imaging. Therefore, the purpose of the present study was to assess the rotational alignment of the femoral component using plane radiography. Eighty three patients from 89 knees who underwent primary total knee arthroplasty (TKA) were evaluated radiographically before and after surgery using kneeling view, The kneeling view is a postero-anterior projection vertical to the tibia at 70 to 80° flexion of the knee. Using this view, the posterior 2/3 of the femoral condyle can be visualized and the clinical transepicondylar axis and posterior condylar line can be described. The angle between the clinical TEA and PCL was defined as the condylar twist angle. Therefore, kneeling view plane radiography can be a simple and convenient substitute for CT in measuring the rotational alignment of posterior femoral condyle. Axial images of patellofemoral articulation were also ob-tained after TKA, and then superimposed to the kneeling view images along the outline of the femoral component. That is, this technique is combination of kneeling view and axial view can demonstrate the relationship between the rotational alignment of the femoral component and the patellofemoral joint after TKA. We named this tech-nique “Combination view”, In this view, the transepicondylar axis and posterior condylar line can be seen. In re-sults, the condylar twist angle was 5.7±1.6° preoperatively and 2.6±0.9° postoperatively. The external rotation of the femoral component was 3.2±1.1°. After TKA, The patellar tilt angle and lateralization of the patella was highly correlated to the the condylar twist angle. We concluded that “Combination view”, which is a simple radio-graphic technique, can easily provide data regarding rotation of the femoral component onto the femoral condyle.

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ANTERIOR CRUCIATE LIGAMENT-RETAINING TOTAL KNEE ARTHROPLASTY - THE CASES SURVIVED 20 YEARS OR MORE Kiyohiro Nagase, MD., Atsushi Kusaba, MD., Saiji Kondo, MD., Hiroyuki Okumo, MD., Yujiro Mori, MD., and Yoshikatsu Kuroki, MD. Institute of Joint Replacement and Rheumatology,, Ebina General Hospital Introduction: Twenty more years ago, we regarded the prosthesis that had an anatomical structure and the physiological knee motion as the ideal prosthesis. Based on this idea, we preserved both the anterior and posterior cruciate ligaments at the surgery and employed Glundei-Thomas Implant (ESKA Implants, Lubeck, Germany) since 1980. As the implant had an anatomical-shaped weight-bearing portion in the tibial plates (cemented, without the metal back) and the medial-lateral separated tibial plates, it was very similar to the non-constrained implants. According to O`Conner, the separated tibial plates provide strong endurance against the uneven distribution of the load and thus the prevalence of aseptic loosening in the tibial plates was low. We evaluated five knees in four patients with the periodic follow-up. All patients were female. Case Report Case 1. Both sides knee were replaced when she was twenty years old for juvenile rheumatoid arthritis. Before the replace-ments, the joint destruction was so severe that the range of motion was limited to 40 degrees. She could not walk without dou-ble crutches. The alignment of the lower extremities relatively remained. During the surgery, we preserved the anterior cruciate ligaments, which had enough volume. Twenty-six years after the surgery, the knee alignment was excellent and no sinking of the tibial plates was found. She could walk without canes at the final follow-up. Case 2. The right knee was replaced preserving the anterior cruciate ligament for stage III Rheumatoid arthritis when she was 50 years old. Before the surgery, the knee alignment was fair. Fifteen years after the surgery, a slight sinking and polyethylene wear occurred in both medial and lateral tibial plate. However, after that these changes did not progress. The control of the arthritis was good, the patient had no compliment and the good knee alignment was kept at the final follow-up. Case 3. 50 year-old-female. The right knee was replaced because of the traumatic osteoarthritis after the femoral fracture. At the surgery, the varus osteotomy was necessary for the valgus deformity (the femoral-tibial angle: 156 degrees). Twenty-two years after the surgery, the motion range was 100 degrees, the femoral-tibial angle was 179 degrees, and no sinking of the tibial plate occurred. Case 4. 62 year-old female. The right knee was replaced because of the osteoarthritis. The varus deformity still remained after the surgery. Fifteen years after the surgery, a slight sinking of the tibial plate occurred, however, after then the sinking did not progressed at 21 year after the surgery. Discussion Most knees with this type of implants have been revised around 15 years after the surgery because of aseptic loosening in the tibial plate. The revision rate was 11%. The all revised knees had the insufficiency of the anterior cruciate ligamant function at the surgery while all survived knees had the good function of the anterior cruciate ligamant. From this fact we recognize the indication of this type implant is almost same as that of the hemiarthroplasty. In all knees, the alignment was still good or excel-lent at the final follow-up. Observing these knees survived for more than twenty years, this old type implant can be spotlighted again, as the bone resection is minimum and the physical knee motion is obtained.

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MORBIDITY AND MORTALITY AFTER SIMULTANEOUS BILATERAL TKA AS COMPARED TO SINGLE TKA Authors: S.Tarabichi,M.D. and A.R.Tarabichi E-Mail: [email protected] Introduction: Simultaneous bilateral TKA is a good option in certain group of patients such as those who have gross knee de-formity, however morbidity and mortality are major concerns .the majority of previous papers covering this topic used data from multiple surgeons in deferent setting. This paper reviews the results of patients who had simultane-ous bilateral TKA and compares it to the results of single TKA carried out by the same surgeon in the same insti-tution using same intra operative and post operative protocols. Material and Methods: 558 patients underwent simultaneous bilateral TKA while 485 underwent single TKA carried out by the same sur-geon. The pre-op medical evaluation was carried out by a special multidisciplinary medical team. The decision to proceed with simultaneous TKA was made based on the clinical findings before surgery. There were no additional special cares for the simultaneous group. Post op protocols were the same for both groups Results: Blood transfusion was higher in the simultaneous group (71%) as compared to (34 %) in a single knee group. We had 8 unscheduled ICU admission in the simultaneous group compared to 2 in the individual. Surprisingly DVT was less common in the simultaneous group. We had one death in the simultaneous group. The average knee score and average range of motion were the same in both groups. Discussion and conclusion: Simultaneous bilateral TKA is safe and convenient. A special multidisciplinary team is needed to ensure proper care. Simultaneous bilateral TKA is convenient and economical for some patients. This paper shows this procedure to be safe if certain precautions were taken.

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GENDER DIFFERENCES IN OSTEOARTHRITIC KNEE JOINT GEOMETRY

Noaya Shimazaki1, Noriki Nakachi1, Nobuyuki Yoshino2, Nobuyoshi Watanabe2, Takashi Matsushita1, Shinro Takai1

1) Department of Orthopaedic Surgery, Teikyo University School of Medicine Tokyo, Japan

2) Department of Orthopaedic Surgery, Kyoto Kujo Hospital, Kyoto Japan 2-11-1 Kaga, Itabashiku, Tokyo Japan 173-8605 Phone: 81-3-3964-1211 Fax: 81-3-3964-4097 E-Mail: [email protected] 562 osteoarthritic knees rated as stage 1or more according to Kellgren's osteoarthritic knee classification were se-lected randomly and analyzed radiologically. Eighty cases with the height of 155-160 cm, for which a large num-ber of male and female cases are available (34 male cases, 46 female cases), were extracted for analysis. The val-ues measured were significantly larger in male than in female in any region. In order to clarify differences in mor-phology between the sexes, the ratio between the values measured of various regions was computed. As a result, the value obtained by dividing the length of medial femoral condyle in anterior-posterior direction and the depth of medial femoral condyle in proximal-distal direction by the width of femur at articular level was 0.87±0.03, 0.56±0.03 in female against 0.81±0.04, 0.52±0.03 in male, respectively. The value obtained by dividing the length of medial tibial condyle in anterior-posterior direction by the width of tibia at articular level was 0.61±0.05 in fe-male against 0.59±0.04 in male. When the differences between the sexes were studied, the values measured of various regions were significantly larger in males than in females even in the group of the same height. Morpho-logically, the knee of males tended to have a larger width than that of females.

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THREE-DIMENSIONAL PATELLAR TRACKING DURING TOTAL KNEE REPLACEMENT WITH AND WITHOUT PATELLAR RESURFACING: AN IN-VITRO STUDY Belvedere Claudio, Leardini Alberto, Ensini Andrea, Catani Fabio, Giannini Sandro Corresponding Author: Alberto Leardini Istituti Ortopedici Rizzoli, Movement Analysis Lab, Bologna , 40136, Italy Ph: ++39 051 6366522 Fax: ++39 051 6366561 Email: [email protected]

Clinical literature for total knee arthroplasty (TKA) reports contrasting evidence on the efficacy of patellar resur-facing. Patellar mal-tracking after TKA, generally associated to prosthetic component misalignment in both tibio-femoral (TF) and patello-femoral (PF) joints, introduces anterior knee pain and patellar subluxation. Femoral and tibial components are implanted with no care of patellar tracking. It is still unclear whether the resurfaced patella adapt better to the prosthetic femoral trochlea. The aim of this study was to identify whether resurfacing can re-store better the natural patellar tracking. For this aim, a three-dimensional system able to track femur and tibia was specially adapted for this purpose by including technical and anatomical references for the patella. The technique was tested in-vitro, to be potentially included in the future in surgical navigation systems.

Eight amputated legs with the knee free from anatomical defects, intact capsules and quadriceps tendons were ana-lyzed using the Stryker® Knee Navigation System (Kalamazoo, MI-USA). In addition to standards, a prototypal new tracker was manufactured for the patella. TF flex/extension, intra/extra rotation, ad/abduction were calculated according to standard mathematical conventions. PF flex/extension, medial/lateral tilt, rotation and shift were cal-culated according to a recent proposal by these authors. Five trials of passive knee flexions were performed with a 100N pulling-force on the quadriceps, before and after TKA (cruciate-retaining Scorpio®, Allendale, NJ-USA), both with and without patellar resurfacing.

The mean difference over the 0°-120° TF flexion arc between the intact and replaced knee, both before and after resurfacing, was calculated for each of these kinematics variables. For all three TF rotations, these differences were smaller than 4°, regardless of resurfacing. Before resurfacing, PF flexion, rotation and tilt had mean differences equal respectively to 4.1°, 3.2°, and 7.6° averaged over the eight knees. These become respectively 3.5°, 6.6°, 10.9° after resurfacing. The ranged of PF shift dropped down from -8.0 / 6.8 mm to -3.2 / 5.8 by resurfacing.

This in-vitro study is among the very few reporting quantitative comparisons between resurfacing and not resurfacing TKA by using three-dimensional kinematics and anatomical reference frame definitions. Resurfacing changed knee kinematics only a little, apart for PF shift which was then more physiological. Unfortunately large shift is in fact cause of high stress to the retinacula and can result in anterior knee pain, important reason for TKA failure. Intra-operative measurements of patellar tracking can support considerably the surgeons about the suitability and the precise loca-tion of resurfacing.

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RESURFACING VERSUS NOT RESURFACING THE PATELLA IN TOTAL KNEE ARTHROPLASTY: 4 YEAR RESULTS

Authors: N.Bonin, J.Mercado, G.Deschamps, D.Dejour 8 Avenue Ben Gourion 69009 Lyon France E-Mail: [email protected] Introduction:

Patellar resurfacing in total knee arthroplasty is a topic debated in the literature. Concerns include fracture, disloca-tion, loosening, and extensor mechanism injury. Residual anterior knee pain has been reported when the patella is not resurfaced.

Material:

2 homogenous groups of 94 patients were treated with a single prosthesis that featured an anatomically designed patellofemoral articulation and a third condyle postero-stabilization system with a rotating tibial plateform (HLS Noetos®, Tornier). In Group 1, all patellas were left not resurfaced whereas in group 2, all patellas were resur-faced.

Method:

At 3 to 5 years follow-up, 80 patients in group 1 (85%) and 77 patients in group 2 (80%) were clinically and radio-graphically reviewed by an independent observer. International Knee Society (IKS) score and subjective score were used. Femoropatellar pain was assessed with a specific patellar score based on Visual Analog Scale (VAS). The lower the score the better the result. Results:

Four patients in the unresurfaced group and two in the resurfaced group required repeat surgery for patellofemoral complications. 91 percent of patients with a non resurfaced patella were satisfied or very satisfied with their total knee arthroplasty versus 96% with patellar resurfacing. 3 patients were considering further surgery for anterior knee pain in group 1 whereas 1 patient in group 2. IKS score was not different between the 2 groups. Specific pa-tellar score was 2.19/10 in group 1 versus 1.81/10 in group 2. The difference was not significant.

Discussion:

As a number of comparative studies in the literature, no significant difference could be found between patellar re-surfacing or not resurfacing in total knee arthroplasty. Nevertheless, a higher incidence of anterior knee pain could be seen in the non resurfacing group. The occurrence of anterior knee pain could only be predicted in patella baja where resurfacing gives better results.

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188

ALLOGRAFT-PROSTHETIC COMPOSITE FOR PROXIMAL FEMUR

RECONSTRUCTION AFTER LIMB SALVAGE SURGERY FOR BONE

TUMORS: SURGICAL TECHNIQUE AND RESULTS

Authors: Nicola Fabbri, Costantino Errani, Davide Donati, Marco Manfrini, and Mario Mercuri

Department of Musculoskeletal Oncology, Istituto Ortopedico Rizzoli, Bologna, Italy

E-Mail: [email protected]

Purpose: Allograft-Prosthetic Composite represents a reliable option for proximal femur replacement. Ad-vantages over megaprostheses are soft tissue repair, abduction strength, hip stability, quality of gait, and load transfer by bone rather than prosthetic stem, possibly affecting implant survival. Purpose of this paper was to review surgical technique and results. Methods: 60 patients who received an APC after proximal femur resection were reviewed. Basic implant consisted of an uncemented tapered long stem prosthesis cemented in the allograft and press-fitted in the host bone. Details of surgical technique included: 1) accurate preoperative planning; 2) host femur preparation, selection of appropriate implant, and under-reaming of the host me-dullary canal in order to get adequate distal fixation; 3) prosthesis cementation in the allograft; 4) introduction of the composite implant, press-fitted in host medullary canal; 5) careful abductors and iliopsoas repair to allograft tendons. Key points for successful fixation are absolute rotational stability and satisfactory bone-bone contact at the time of surgery. Results:

There were 2 septic failures and no dislocations. Most common complication was fracture of allograft greater trochanter (30%), requiring surgery only in 1 case and never substantially affect-ing function. Incidence of trochanteric fracture decreased from 77% to 35% by switching implant design from 145° to 135° neck angle, improving offset and abductors function. Bone grafting of allograft-host union was required in 10% of cases.

Conclusions: According to MSTS, results were satisfactory in 90% of the patients, with average score 91% (75%-96%). Allograft-Prosthesis Composite is a successful procedure for reconstruction of the proximal femur. Careful surgical technique is the key to excellent function and low complication rate. No money or other forms of benefit were received for this paper.

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A 10-17 YEARS EXPERIENCE WITH HA IN KNEE ARTHROPLASTY BASED UPON A PROSPECTIVE ORTHOWAVE STUDY EPINETTE Jean-Alain CRDA, 21 résidence Voltaire, 62700 Bruay LaBuissière,France Tel: 33321531949, Fax: 33321531961; e-mail: [email protected]

A bioactive bond between the implant and the host bone that provides lasting, stable implant fixation without the use of acrylic cement is a goal as important in the knee as it is in the hip. Our experience with Hydroxyapatite coated total knee arthroplasty began in 1990 with the HA-coated Omnifit™ Knee (Stryker, Mahwah, NJ, USA). The whole study has been carried out with the OrthoWave™ outcome study software suite (ARIA, France), which allows for collection of all kinds of data and related images, and complete analysis of clinical scores, radiographic patterns and cumulative survival curves.

The series is a 10-17 years consecutive, prospective and non-selective study of 197 primary cases with 10-year of minimum follow-up, and 11.6-year as average follow-up. The average age was 70.1 years, including 13.2% of pa-tients over 80 years. Aetiology was mainly Osteoarthritis in 89.9%. The choice of HA-coated knees at the time of surgery has been in all cases dictated by the need of primary mechanical stability, whatever the age or aetiology. Post operative cares were strictly similar to cemented implants, including allowed immediate full weight bearing. At review, 1.5% of patients were lost to follow-up, 47.2% of not implant-related deaths could be recorded, 4.6% of knees have been retrieved for accidental fractures of secondary septic lesions, and mechanical failure occurred in 1.5% of knees.

Some concerns about long term follow-up series have been stressed during this study, with 78,03-year as the aver-age age at last review, including 44% of patients over 80 years, which explains difficulties while assessing clinical scores with only 25% of patients belonging to the Charnley Class A, i.e. with no other significant impairment. For the 104 knees which could be consistently enrolled in the clinical scoring at review, pain was none in 97%, with total lack of patellar pain in 98%. Average flexion was 111° with 50% of knees over 120°. The mean International Knee Score (IKS) values were 94.87 points and 88.94 points for "Knee Score" and "Function Score" respectively. We thus recorded 97.7 % (knee score) and 78.9% (function score) of excellent and good results (>=80 points), with interestingly no significant difference at 0.05 between the youngest and oldest patients. Radiographic assessment indicated very good HA-bone fixation interfaces for both the femoral and tibial components. Furthermore, the HA coating appeared over time to aid in filling post-operative gaps, which should be viewed as a very desirable attrib-ute for a fixation surface. At follow-up, the revision rate was 1.52 %, including two loose knees and one case of severe lysis at respectively 5, 8 and 12 years post-operatively. The cumulative survival rate at 13 years, taking into account all failures, was 96.33%. These results compare very favorably with previously published cemented and porous series.

Hydroxyapatite is not a “magic powder”, and technical skills and appropriate design are certainly more important than the interface. However, the very encouraging results reported in the current study make us very confident in the ultimate outcome of bioconductive coatings in knee arthroplasty

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WEAR OF TITANIUM NIOBIUM NITRIDE COATED TOTAL KNEE REPLACEMENTS Weisenburger, Joel N; Croson, Richard E, Namavar, Fereydoon; Garvin, Kevin L, Haider, Hani Department of Orthopaedic Surgery and Rehabilitation, University of Nebraska Medical Center, 985360 Nebraska Medical Center - Scott Technology Center, Omaha, NE 68198-5360, USA Phone : (402) 559 5607, Fax : (402) 559 2575, E-mail : [email protected] Certain metallic ions released from total knee replacement (TKR) can trigger immune response and allergic reactions. Nickel is one such ion. Currently the only options for sensitive patients are nitrogen-ion-implanted or oxidized-zirconium (Oxinium) coated femoral components. Patients would benefit from more options. A novel coating, PVD Titanium-niobium-nitride (TiNbN), is intended as a diffusion barrier to prevent migration of Ni to the surface and help bind nickel within the substrate. This coating also has sufficient hardness and therefore may resist abrasion and reduce overall wear, or at least not prohibitively compromise them. This study investigates the wear of UHMWPE tibial inserts paired with TiNbN coated femoral components. Testing was performed on a four-station Instron-Stanmore force-control knee simulator which applies flexion, and induces anatomically realistic joint reaction forces and torques between tibia and femur (ISO 14243-1), and includes a spring-based system to simulate soft-tissue restraining forces and torques. Four 65mm Vanguard-PS CoCrMo femoral components were tested. Three of them were coated in PVD-TiNbN and one was uncoated for control. They articulated on the same 10mm direct-compression-molded Vanguard-PS (ARCOM) UHMWPE fixed bearing inserts interlocked into Maxim Ti-6Al-4V alloy Tibial base-plates. The specimens were lubricated with bovine serum diluted with de-ionized water to have 20g/l protein concentration, at 37°C. Deionized-water was added to substitute for evaporation. The TKR specimens were subjected to the force-control waveforms of the walking cycle as specified in ISO-14243-1 for 8.0 million cycles (Mc) at 1Hz. The loading, rotations, and torques were continually observed to ensure consistency with the desired waveforms. The tibial bearing inserts were weighed at 0, 0.1, 0.5, and every 0.5Mc afterwards for 8.0Mc. The lubricant was changed at each wear measure-ment interval. Liquid absorption was corrected by the use of two passive-soak-control bearing inserts maintained in similar temperature-controlled serum during the test. Both the coated and uncoated TKRs showed almost linear wear. After correction for liquid absorption, the three coated-CoCr TKRs showed an average wear rate of 11.17±0.83mg/Mc and an average overall net-weight loss at 8Mc of 92.40±7.57mg. The single uncoated control displayed an average wear rate of 9.04mg/Mc and a net-weight loss of 68.28mg. A 5-million cycle test had previously been completed using two specimens identical to the uncoated TKRs. They displayed average wear rates of 9.20 and 9.02mg/Mc in the previous test, which were not significantly different from the wear rate of the single uncoated control here. At 5Mc, it was noted that the TiNbN coating had worn off from a small area of the medial condyles. These bare regions continued to increase in size as the test progressed to 8Mc. The PVD-TiNbN-coated TKR’s moderately higher wear rate may be due to the morphology of the surface of the femoral component introduced by the coating process. The benefits that TiNbN coated implants can offer to patients sensitive to nickel ions may outweigh any negatives due to the slightly higher wear rate, however, the coating process must be altered to create a more durable coating, at least on this TKR design.

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POROUS TITANIUM PARTICLES FOR APPLICATION IN IMPACTION GRAFTING: BASIC MECHANICAL CHARACTERISTICS AND IN-VIVO TESTING OF OSTEOCONDUCTIVE POTENTIAL Walschot Luc HB; Aquarius Rene; Verdonschot Nico; Schreurs Wim; Buma Pieter. Radboud University Nijmegen Medical Centre, Orthopaedic Research Laboaratory, P.O. Box 9101,Nijmegen, The Netherlands E-Mail: [email protected] Introduction: Bone impaction grafting (BIG) is a surgical technique to restore the bone stock loss in revision hip arthroplasty by impaction of allograft bone particles (BoP) in the bony defects. There are many alternative materials for allograft bone developed of which most of them are ceramic based materials (HA/TCP). In this study we assessed the feasi-bility to use porous titanium particles (TiP) as an alternative bone grafting material. The goal of this study was to compare impactability, graft layer stability and elasticity of TiP, bioceramic particles (CeP; BoneSave®, Stryker) and BoP. In addition, an in–vivo model was used to study the osteoconductive potential of impacted TiP. Materials and Methods: In-vitro testing: TiP, CeP and BoP were subjected to impaction to measure impactability (impaction strain) fol-lowed by an confined compression test to measure deformation (loading strain) and stiffness of the material. In-vivo testing: Twelve goats were operated on both knees condyles. Six different graft materials were impacted in each goat in cylindrical defects (Ø 8 mm, depth 10 mm): BoP, CeP and four groups of TiP. The four groups of TiP consisted of uncoated TiP (TiP), uncoated TiP mixed with BoP (TiP/BoP), and TiP with two different ceramic coatings (TiPc1, TiPc2). Goats were killed twelve weeks after operation. Fluorochrome labeling were used to measure time-dependence of bone ingrowth. Bone ingrowth distance (mm) from the periphery to the center of the defect was quantified. Results: Impactability TiP were more impactable than BoP (impaction strain 0.78 ± 0.03, 0.47 ± 0.01, respectively; p < 0.001). The firm entanglement of impacted TiP led to very cohesive samples. Impacted specimens of BoP were less cohesive. CeP fragmented during impaction and did not lead to cohesive samples. Graft layer stability and stiffness TiP and CeP showed almost no deformation with a loading strain of 0.009 ± 0.001 and 0.017 ± 0.002, respectively, which was only a small fraction of the loading strain of BoP (0.29 ± 0.05, p < 0.001). TiP (209 ± 20 MPa) were about 2.5 times as stiff as BoP (80 ± 18 MPa, p < 0.001). CeP (334 ± 47 MPa) were about 4 times as stiff as BoP and therefore stiffer than TiP (p < 0.001). Osteoconductive properties Bone ingrowth distance was time dependent. After twelve weeks, CeP showed the largest bone ingrowth distance (3.8 ± 0.1) and uncoated TiP showed a significantly smaller bone ingrowth distance then all other groups (2.0 ± 1.0, p < 0.001). There was no significant difference in bone ingrowth distance of BoP compared to coated TiP (BoP vs TiPc1: p = 0.2; BoP vs TiPc2: p = 0.7). Discussion and Conclusion: TiP are at least as impactable as BoP. After impaction, TiP create a very coherent and stable graft layer that has about the same elasticity as a graft layer of a mixture of BoP and CeP. Uncoated TiP have a lower osteo-conductive potential than BoP and biphasic CeP but this was improved by the application of a coating. Hence, although more research is warranted, TiP with a bioceramic coating is a promising bone substitute material for impaction grafting.

Acknowledgement: This study was financed by Fondel Finance BV, Rotterdam, The Netherlands.

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TOTAL KNEE REPLACEMENT FOR RHEUMATOID ARTHRITIS BY USING IMPROVED CEMENT TECHNIQUE BY INTERPOSING HYDROXYAPATITE GRANULES Kim, Sok Chol 1, Oonishi, Hironobu 1, Oonishi, Hiroyuki 1, Hirotsugu, Ohashi 2

1 Department of Orthopaedic Surgery, Tominaga Hospital 1-4-48, Minatomachi, Naniwa-ku, Osaka-shi, 556-0017, Japan Phone:+81-6-6568-1601 Fax:+81-6-6568-1608 E-mail: [email protected] 2 Department of Orthopaedic Surgery, Saiseikai-Nakatsu Hospital, Osaka In order to make the fixation at bone/bone cement interface improve, we are using a modified cementing technique using hydroxyapatite (HA) granules in all cases of total joint replacements. We call this technique Interface Bioac-tive Bone Cement (IBBC) and clinically applied for more than twenty years. Components were cemented after HA granules were smeared onto the bone surface. We have also used this method for the cases of rheumatoid arthritis (RA). Results of total knee replacements (TKRs) for RA patients with this method for 14 years from 7 years were evaluated. TKRs for RA using IBBC technique were performed in 60 knees from 1990 to 1993. 54 knees were clinically and radiologically evaluated at a mean follow-up period of 10.2 years (7 to 14 years). Follow-up rate was 90.0%. As a control, results of TKA (for RA) with conventional cementing technique (Non-IBBC) which in 27 knees were used. The appearance part of radiolucent line (RLL) around tibial components and loosening of tibial components were investigated according to progress. Radiography was evaluated using Knee Society's Evaluation System. At the time of the final follow-up, the prevalence of RLL was significantly higher in all parts. Furthermore, RLL which appeared more than three years after the operation was only one (1.9%). In IBBC group periprosthetic oste-olysis of the tibial components were observed in two knees (3.7%). Aseptic loosening of the tibial component was only one case (1.9%) because of breakage of the polyethylene tibial insert. Histologically, the majority of HA gran-ules were incorporated into remodeled trabeculae and highly convoluted bone-cement interface was maintained. There was no significant inflammatory or foreign body reactions against interposed HA granules. In IBBC, bone cement bound to HA mechanically immediately after surgery and HA granules bound to the bone physicochemically after bone ingrowth into the spaces around the HA granules. Thus, we believe that IBBC is a method combining the advantage of cementless HA coating and bone cement. In the absence of HA granules, spaces will appear between bone and bone cement due to osteoporosis and/or atrophy after long years. However, in IBBC, bone and bone cement will remain in close contact due to osteoconductive effect of HA. Thus, we believe that the reduced incidence of RLL is attributable to the continued bone formation and remodeling adjacent to HA granules. In conclusion, the cementing technique with HA granules was associated with very low incidence of loosening, osteolysis and RLL in TKR for RA. There were no untoward clinical complications attributable to the use of HA granules.

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ON THE DEVELOPMENT OF SMART DURABLE COATINGS TO PROMOTE BIOINTEGRATION WHILE PREVENTING BIOFILM FORMATION Namavar, Fereydoon; Garvin, Kevin L; Jackson1, John D.; Sharp2, J. Graham; Mann1, Ethan; Bayles1, Kenneth W., and Haider, Hani. Department of Orthopaedics and Rehabilitation, Univ. of Nebraska Medical Center, Omaha, NE 68198, USA. 1Department of Pathology and Microbiology Univ. of Nebraska Medical Center 2Department of Genetics, Cell Biology and Anatomy, Univ. of Nebraska Medical Center, Phone (402) 559-8558; fax (402) 559-2575; [email protected] Orthopaedic artificial implants are generally remarkably successful devices, with premature failure rates of only a few percent. To extend longevity, optimal component materials should be wear resistant, bactericidal, and encour-age biointegration. We have initiated programs to devise and develop implants that will combine osseointegrative properties, in areas where bone is in contact with the implant, while preventing bacterial biofilm formation on the implant surface. Ideally, the bone contacting surface should interact positively with mesenchymal stromal cells and their pre-osteoblast progeny to promote and maintain osseointegration. Increased osseointegration of the surface will lead to faster tissue integration and vascularization, which will prevent bacterial adhesion and biofilm formation on the implant surface [Gristina AG, I. Clin. Orthop., 298:106. 1994]. In addition, the surface should be anti-infective through surface morphology and chemistry. If possible, the surface also should be designed to be “smart” and boost its anti-infective properties in response to the presence of infectious agents. Hydroxyapatite (HA) coating on implant surfaces has been studied for decades because of its bioactive properties. However, concerns have been raised about the mechanical strength and the debonding of the HA layer from the metal implant [A. El-Ghannam, Expert Review Medical Devices 2(1), 87, 1340, 2005)]. To avert these concerns, we have designed and fabricated ultra-hydrophilic hard nanostructured coatings for bone contacting surfaces. Using ion beam assisted deposition; we have “stitched” the coating to the surface to prevent debonding. Using similar methods, we have also fabricated hydrophobic nano-crystalline silver films. Silver is known to have broad spectrum antibiotic properties, to reduce the probability of biofilm formation. Roughness and grain sizes of these nano-structures have been determined by AFM and TEM and correlated to their wettability as measured by video contact angle measurements. To examine the properties of our coatings we have utilized a cloned bone marrow stromal cell line from C57Bl mice, termed OMA-AD cells. These cells duplicate in vitro all of the characteristics of primary multipotential mes-enchymal stromal cells. Alamar Blue assay and direct cell counting methods were used to determine the growth of OMA-AD on the different nanoengineered surfaces, which included ZrO2, Ta2O5, Al2O3, TiO2, TiN, Ti, CoCr and Ag. Commercially available HA disks were also examined. To assess the impact of the nanocrystalline silver coatings on the growth of bacterial biofilm, we performed continuous flow biofilm assays using a common nosoco-mial pathogen, Staphylococcus aureus. Samples were placed in a flow cell chamber and inoculated with S. aureus strain 15981 and grown for 24 hours. Our results based on multiple sets of samples and runs with Alama blue and direct cell counting clearly indicated that cubic zirconia and tantalum oxide supported the best growth of OMA-AD cells, followed by aluminum and titanium oxides, and then titanium. Silver exhibited the least support for OMA-AD cell growth. A comparative study showed TiO2 is superior to HA. Our results indicate that the characteristics of nano-structures influence the growth of mesenchymal stromal cells. The total number of viable s. aureus cells was reduced on nanocrystalline silver.

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CLINICAL RESULTS OF TOTAL ELBOW ARTHROPLASTY WITH FINE TOTAL ELBOW JOINT SYSTEM Masayuki Sekiguchi, Kazuaki Tsuchiya, Yoshiyasu Miyazaki, Yurika Kanai, Yoshiyuki Ohikata, Ayako Kubota, Hirofumi Kawakami, Muneki Saito, Keitaro Yamamoto, Toru Suguro, Department of Orthopaedic Surgery, Toho University School of Medicine (Institution) Department of Orthopaedic Surgery, Toho University School of Medicine (Address) 6-11-1 Omorinishi, Ota-ku, Tokyo, 143-8541 JAPAN (Phone/FAX/e-mail) +81-3-3762-4151(ext.6635)/+81-3-3763-7539/ [email protected] Purpose: FINE total elbow system (as following FINE ELBOW) of which the basic structure is three components of hume-rus, ulna, and radius was developed, and a clinical application has begun since 2000. Subject and Method: Total elbow joint arthroplasty (as following TEA) was performed by using FINE ELBOW in October, 2000. Pa-tients awere 34 cases 41 elbows, and these were the cases from whom one year or more passed after surgery was performed. The cases were three male cases three elbows, and were 31 female cases 38 elbows. The average age when pa-tients were performed TEA was 62.2 years old, and the passage observation period of after surgery was 46.1 months on the average. Clinical result used and examined the Japanese Orthopaedic Association score (JOA score) and the Mayo clinic performance Index (Mayo Index). Result: JOA score was improved to 80.5 on the average when investigating from 46.0 on the average before TEA, and the improvement of an excellent result was admitted. Excellent results were obtained in the evaluation that used Mayo Index. The evaluation point has been improved from 38.0 to 86.0 points on the average. The dislocation and the sub-dislocation of radio-humeral joint were taken in five cases as postoperative complications. Consideration: Ulna component have the snap structure. This structure is useful so that elbow joint may control the posterior dis-location. Radio-humeral joints are formed with there is radial component. It is useful for obtaining the stability of elbow joint for the stress to the side of enabling elbow joint doing the winding movement smoothly that this joint exists. However, FINE ELBOW has the snap structure. As for humerus, to set up this structure, a large amount of bone is excised. Therefore, it should be careful to use FINE ELBOW for the case with an advanced destruction of the joint surface. The cases from whom the radial component had caused the dislocation or the sub-dislocation were experienced. It is necessary to set up the radial component as agreeing to radial neck axis to prevent this problem. Moreover, it is a method of precede at it simultaneous and do the Sauve-Kapandji method or the Darrach method to TEA for the case with a bad rotation movement of the wrist joint (DRUJ) solving this problem.

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METAL AND POLYETHYLENE PROSTHESIS FOR CMC 1 JOINT ARTHRITIS Taco Gosens, MGFG Schreibers, J. Janssens Sr. Elisabeth Hospital, Hilvarenbeekseweg 60, Tilburg 5022GC Netherlands Phone: 0031135392942 Fax: 00315422547 E-Mail: [email protected] Introduction: Literature shows equal results for all procedures (trapeziectomy, spacer arthroplasty, tendon interposition, ar-throdesis, etc) for CMC 1 joint arthritis. With all operations strength of the operated basal thumb joint will de-crease. The aim of a metal and polyethylene prosthesis is to resurface the joint in order to recreate an anatomical situation so that strength wil not diminish. Material and Methods: Twelve patients were included in a prospective series to judge the results of the TMC prosthesis (Biomet) in which a metal trapezium resurfacing component is combined with a polyethylene metacarpal component. Patients were followed for more than 2 years using strength measurements (Jamar, pinch grip), a mobility score, functional scores (9 hole peg test, SODA) and participation scores (DASH, MHQ). Results: All patients but one significantly improved on all measurements one year after the operation. All but one patients were satisfied. Conclusion: The early results of this operation are satisfying and continued use of this prosthesis seems justifyable.

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TOTAL FINGER ARTHROPLASTY WITH FINE TOTAL FINGER JOINT SYSTEM IN RHEUMATOID ARTHRITIS PATIENTS Masayuki Sekiguchi, Toru Suguro, Yoshiyasu Miyazaki, Yoshiyuki Ohikata, Hirofumi Kawakami, Muneki Saito, Keitaro Yamamoto, Junichi Nakamura, Kazuaki Tsuchiya

(Institution) Department of Orthopaedic Surgery, Toho University School of Medicine (Address) 6-11-1 Omorinishi, Ota-ku, Tokyo, 143-8541 JAPAN (Phone/FAX/e-mail) +81-3-3762-4151 (ext. 6635) / +81-3-3763-7539 / [email protected] Introduction: In order to reconstruct the destroyed MP joints in rheumatoid arthritis patient, we developed FINE total finger joint system (as following FINE finger) of semi-constrain type equipped with the mechanism that is similar to the ana-tomical form and controls dislocation of basal phalanx to palmar side. Clinical application of this system has been started from April, 2004. Materials and Results: The number of cases was fifteen, and eleven cases were females and four cases were males. Age was an average of 63.2 years old. The stage of RA was Larsen's Grade IV or V. The arthroplasty with FINE finger was performed for fifteen cases 43 fingers. The postoperative extension angle of MP joints was an average of -17.2 degrees and the flexion angle was an aver-age of 71.4 degrees. All patient were very much satisfied, in order to be able to perform skill movements, such as writing a character and using chopsticks. Severe case of the ulnar drift deformity of MP joints and the case whose have severe palmar dislocation had poor extension of ring finger and little finger. Moreover, case for which the surgery as simultaneously performed on the rupture of extensor tendons had the bad range of motion. Consideration: It is the trait of this system that proximal phalanx prosthesis has a projection (as following post). This post is snapped into the metacarpal prosthesis. And the tip section of the Post moves so that it may always come to the center of rotation of MP joint. Another trait is that post controls palmar movement of a proximal pha-lanx at the time of a flexion movement. According to these two traits, the smooth joint movement became possi-ble. However, in order to acquire better results, it is necessary to perform reconstruction of soft tissue certainly. The result with which can be satisfied of the clinical results is obtained. However, this system has just begun to be used. Therefore, we fully need to check up the clinical course from now on.

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TOTAL EVOLUTIVE SHOULDER SYSTEM: PRELIMINARY EXPERIENCE OF A NON-DESIGNER WITH A NEW CONCEPT OF SHOULDER PROSTHESIS Taco Gosens, MGFG Schreibers, J. Janssens Sr. Elisabeth Hospital, Hilvarenbeekseweg 60, Tilburg 5022GC Netherlands Phone: 0031135392942 Fax: 00315422547 E-Mail: [email protected] The Total Evolutive Shoulder System is a new shoulder arthroplasty system in which the metaphyseal fixation is obtained with a spider-like, hydroxyapatite coated implant in cases where stemless fixation of a standard or re-versed shoulder prosthesis is possible (some cases of rotator cuff tear arthritis and almost all cases of osteoarthritis of the shoulder). In cases where a stem is needed (fractures) the system provides the possibility of using a stem, combined with the ealier mentioned metaphyseal implant. Here are the preliminary results of the use of this system in rotator cuff tear arthropathy, osteoarthritis, fracture and revision cases using the TESS. A total of 25 patients was operated using this system and after a follow up of 6 months to 3 years, good results were obtained in terms of operation technique, fixation of the prosthesis, union of the tuberosities in fracture cases and function, pain relief and satisfaction of the patient. These preliminary results in the hands of a non-designer justify the continued use of this system (TESS) but longer follow up will be needed and will be conducted.

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COMPUTER-AIDED NAVIGATION FOR SHOULDER ARTHROPLASTY: IMPLICATIONS AS A RESEARCH TOOL Vineet K. Sarin PhD, Matthew D. Williams MD, Hussein A. Elkousy MD, Rodney J. Stanley MD, Gary M. Garts-man MD, T. Bradley Edwards MD Kinamed Navigation Systems LLC 820 Flynn Road Camarillo, CA 93065 USA [email protected] Computer-assisted technologies have been developed to improve implant alignment in hip and knee arthroplasty. Early reports have provided evidence of their efficacy. Like hip and knee arthroplasty, successful shoulder arthro-plasty depends primarily on proper technique because incorrect glenoid and humeral component alignment can lead to premature wear, loosening, and suboptimal function. Computer navigation in shoulder arthroplasty has been validated in cadaveric and clinical studies. We report on the application of computer navigation as a research tool in shoulder arthroplasty.

We have performed fifty shoulder arthroplasties with both unconstrained and reverse total shoul-der prostheses using computer-aided navigation. Data provided by the navigation system includes real-time inclination and version of glenoid components relative to the native glenoid, and inclina-tion and version of the proximal humeral resection in relation to the transepicondylar and humeral long axes. Using computer-aided navigation technology, the impact of glenoid and humeral compo-nent position on radiographic parameters, implant wear, implant longevity, and functional out-comes can now be defined and evaluated prospectively and accurately. Navigation allows us to quantitatively study the effects of specific implant positions in a randomized manner. Such quanti-tative inquiry was not possible prior to the availability of navigation technology in shoulder arthro-plasty.

The effects of implant orientation and position during unconstrained and reverse total shoulder arthroplasty are definable on a prospective and randomized basis using computer-aided navigation. This research allows for the establishment of improved parameters and guidelines for placement of shoulder arthroplasty components.

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3D IN VIVO CONTACT FORCE DETERMINATION OF NORMAL, FUSED AND DEGEN-ERATIVE CERVICAL SPINES Liu F1, Komistek RD1, Cheng JS2, Mahfouz MR1, Sharma A1, Glaser D1 1Department of Mechanical, Aerospace, & Biomedical Engineering, the University of Tennessee, Knoxville, TN, USA 2Vanderbilt University School of Medicine, Nashville, TN, USA 301 Perkins Hall, the University of Tennessee, Knoxville, TN, 37996 USA Office: (865)974-4159, Fax: (865)946-1787, Email: [email protected] Previously, the in vivo kinetics (inter vertebral body forces) of the cervical spine was not completely understood for different subjects performing flexion/extension activities. Therefore, the objective of this study was to deter-mine and compare the 3D in vivo contact forces for subjects having either a normal, degenerative or anterior cervi-cal decompression and fused (ACDF) cervical spine. We hypothesize that this study may lead to a better under-standing of the clinical and biomechanical outcomes for each cervical spine type. In this study, each subject was clinically assessed by the same surgeon at the same facility (Vanderbilt University Medical Center, USA). The ACDF and degenerative (Spondylosis) subjects were symptomatic at the C5-C6 level. Each subject was asked to consent (IRB #060424) to performing a flexion/extension motion under fluoroscopic surveillance (kinematics), to undergo a CT scan (3D bone model creation) and a MRI scan (soft tissue modeling). Then, the motion data derived using fluoroscopy and the CT and MRI scanned data were entered into a mathemati-cal model to determine the in vivo, 3D contact forces of various cervical spine conditions. In vivo 3D contact forces were predicted by using an inverse dynamic model of the entire cervical spine, including 20 ligaments. This model was based on Kane’s dynamics, utilizing a reduction methodology. Contact forces were determined and then a comparison was conducted between the groups. A cadaveric cervical spine (error analysis) experiment was designed and implemented to quantify the accuracy of the inverse dynamic model. The accuracy of the mathematical modeling technique was proved to be highly accurate (10% error). The maxi-mum contact force in the ACDF group was 2.52 times the skull weight (SW) in the transverse direction and 5.93 SW in the vertical direction. In comparison, these forces were only 0.69 SW in the transverse direction, 2.81 SW in the vertical direction for subjects having a normal cervical spine and 1.26 SW in the transverse direction and 2.34 SW in the vertical direction for subjects having a degenerative cervical spine. This was the first study to determine in vivo, 3D forces in the cervical spine using in vivo kinematics, CT and MRI scans as input to a parametric, mathematical model. The results from this study revealed that subjects having a fusion experienced greater contact forces than subjects having either a normal or degenerative cervical spine. These increased forces exhibited by the ACDF group may be responsible for the accelerated degeneration seen at adjacent levels.

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USE OF CHARITE ARTIFICIAL DISC IN COMBINATION WITH SPINAL FUSION IN DOUBLE-LEVEL DEGENERATIVE DISC DISEASE OF THE LUMBAR SPINE (HYBRID CONSTRUCT) A PROSPECTIVE STUDY OF TWENTY FOUR PATIENTS WITH 1 YEAR FOLLOW-UP Author: BITAN, Fabien; HANAN, S; SHEARER, J 130 East 77th street, 7th floor. New York, NY 10021. Telephone: (212) 744-8115 Fax: (212) 744-8407 [email protected] SUMMARY: Twenty-four patients with two level degenerative disc disease in the lumbar spine underwent a hybrid procedure, including a one-level fusion and an artificial disc replacement with the Charité disc. Minimum follow-up is one year, (16 months average). STUDY DESIGN: This is a prospective consecutive non-randomized study. All the surgeries were performed by the same orthopedic spine surgeon and general surgeon. There was no lost of follow-up and the follow-up data was recorded by inde-pendent medical personnel. PURPOSE: Spinal fusions at one and particularly at two levels have been proven to actually stress adjacent discs, which can lead to accentuated pain and disc degeneration at the non-operated levels. As an alternative to double fusion or two-level artificial discs, hybrid surgeries were introduced. These consist of a spinal fusion at one level and an artificial disc replacement at the other, in order to maintain the motion of the spine. METHODS: Of the twenty-four patients followed, eighteen had a disc replacement at L4-L5 and a fusion at L5-S1, two had a disc replacement at L5-S1 and a fusion at L4-L5, and three had a disc replacement at L3-L4 and a fusion at L4-L5. The discectomy for the fusion and the artificial disc placement are performed though an anterior retroperitoneal approach. From the back, a minimally invasive approach with pedicle screws is used. Demographic data was col-lected including age, gender, social history, and surgical history. Data was collected pre- and post-operatively at 2 and 6 weeks, 3, 6, 12, and 24 months. At each clinical follow-up, the patients were given a Visual and Analog Scale (VAS) and an Oswestry Disability Index (ODI) form to complete, to assess the level of their back pain. Also, key radiographic outcome was measured, including range of motion at the 2 treated levels and 1 adjacent level. RESULTS: Data collected from the VAS forms show a 73% reduction in the average score, with an average score of 71 at pre-op, 27 at six months, and 18 at twelve months. The ODI results show a 61% reduction in the average score, with an average score of 55 at pre-op, 30 at six months, and 20 at one year. The average blood loss was 250 cc (100 cc to 700 cc). One patient experienced a shift of the disc during the trans-fer from supine to prone position. The patient was reopened and the artificial disc was readjusted. One patient un-derwent a removal of hardware one year post-op. Radiographically, the ADR maintained at one year a good range of motion, better at L4-L5 than at L5-S1. The adjacent levels maintained the same range than pre-operatively comforting the idea that the ADR prevents the compensatory excess of motion on the adjacent level. CONCLUSION: Hybrid constructs are a valid alternative to 2-level disc replacements. The results at one year are very encouraging and seem to surpass the published results of 2-level disc replacements. Longer follow-up will be required to deter-mine the incidence of adjacent level disease compared to published data.

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B12-3 ESP Lumbar Spine Prosthesis: About a Clinical Series of 50 Patients Hugues Pascal-Moussellard, Jean-Yves Lazennec, Olivier Ricard, Marc Antoine Rousseau, Yves Catonne

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B12-4 Mobidisc Lumbar Spine Prosthesis Evaluation Jerome Allain

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IN VIVO KINEMATICS OF TWO TYPES OF BALL-AND-SOCKET CERVICAL DISC REPLACEMENTS IN THE SAGITTAL PLANE: CRANIAL VERSUS CAUDAL GEOMETRIC CENTER MA Rousseau, Ph Cottin, A Nogier, JY Lazennec, W Skalli Biomechanics Lab. Ecole Nationale Supérieure d’Arts et Métiers. Paris. France Department of Orthopaedics. Hopital Pitié – Salpétière. Paris. France Introduction: Due to disc facets relationships, it has been demonstrated at the lumbar spine that the center of rotation did not match the geometric center of a ball-and-socket total disc arthroplasty after implantation. The goal of our study was to investigate the in vivo kinematics of two opposite types of total disc prostheses at the cervical spine. Methods: Flexion /extension lateral X-rays of the cervical spine of implanted prostheses (Prodisc-C from Synthes, n=25 and Prestige LP from Medtronic, n=26) were analyzed using the Spineview software (Surgiview, France). The range of motion was measured and the mean center of rotation (MCR) was calculated above 3°. Those were compared to 200 normal discs. Results: The range of motion was about 5° for both prostheses (vs. 13° in the Control group, p<0.01). The MCR trended to change with the type of prosthesis: above the center of the disc space with Prestige LP and below with Prodisc-C. Discussion: Both prostheses had similar limited ROM when compared to the intact discs. The position of the MCR changed according the position of the geometric center of the prosthesis.

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DETERMINATION OF IN VIVO, THREE-DIMENSIONAL MOTION OF THE CERVICAL SPINE UNDER VARIABLE CONDITIONS Cheng JS1, Liu F2, Komistek RD2, Mahfouz MR2, Sharma A2, Glaser D2 1Vanderbilt University School of Medicine, Nashville, TN, USA 2Department of Mechanical, Aerospace, & Biomedical Engineering, the University of Tennessee, Knoxville, TN, USA 301 Perkins Hall, the University of Tennessee, Knoxville, TN, 37996 USA Office: (865)974-4159, Fax: (865)946-1787, Email: [email protected] Previously, the in vivo kinematics of the cervical spine has not been determined in three-dimensions (3D). The objective of this research was to adapt a well-known in vivo, 3D fluoroscopic technique that was previously used for the lower extremity to determine the coupled motions for subjects having either a normal, degenerative and fused cervical spine.

One subject have a normal, non symptomatic cervical spine, one subject having a degenerative cervical spine at the C5-C6 level, and one subject who was treated with an anterior cervical decompression and fusion (ACDF) at the C5-C6 level were asked to perform a full flexion/extension (FE) maneuver while under fluoroscopic surveillance. Each subject was also asked to under a CT scan of the cervical spine and segmentation was used to recover the 3D CAD model of each vertebra. Then the in vivo, 3D intersegmental motions were determined by registering the 3D CAD models of the cervical spine onto sequential, two dimensional (2D) fluoroscopic images. An error analysis of this process was performed using a fresh cervical spine cadaver to determine the accuracy of this methodology.

The subject having a degenerative cervical spine experienced relatively smaller intersegmental ROM at each level except at the C4-C5 level, in comparison to the other two groups. The subject having an ACDF cervical spine ex-hibited up to 36.0% of greater intersegmental ROM at the superior adjacent level (C4-C5) and up to 52.5% more at the inferior adjacent level (C6-C7) when compared to the normal subject. The magnitudes of rotation for the cou-pled lateral bending (LB) and axial rotation (AX) between the vertebral bodies was less than 1º in all three sub-jects, except at the C6-C7 level for the ACDF subject. At the full flexion position, the subject having an ACDF cervical spine experienced 1.9º of LB and 7.9º AX, with totally 22.1º flexion/extension rotation at the C6-C7 level.

The subject having a normal cervical spine exhibited the most consistent rotation patterns at each level. The sub-jects have a fusion experienced greater rotation at both adjacent levels, compared to the normal and degenerative subjects. The results from this 3D study are consistent with our previous 2D study, which included 10 subjects for each group. This increased rotation may, in part, be a factor that contributes to degeneration and failure seen at adjacent levels for subjects having a fused cervical spine.

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B12-7 In VIVO 3D INTERVERTEBRAL KINEMATICS AFTER CERVICAL DISC REPLACEMENT USING THE EOS ® STEREORADIOGRAPHY SYSTEM MA Rousseau, S Laporte, L Devun, JY Lazennec, T Dufour, W Skalli Biomechanics Lab. Ecole Nationale Supérieure d’Arts et Métiers. Paris. France Department of Orthopaedics. Hopital Pitié – Salpétière. Paris. France Introduction Intervertebral kinematics studies are usually limited to 2D measurements in flexion / extension. However, the fac-ets / disc relationships are fully engaged in lateral bending and axial rotation. The goal of our study was to use the novel EOS ® imaging system to investigate the actual rotations after total disc replacement at the cervical level in 3D. Methods We have developed the low dose high definition EOS ® stereoradiography system for the assessment of the in-tervertebral kinematics in vivo in 3D at the cervical spine. 16 implanted prostheses (Mobi-C from LDR) were ana-lyzed for measuring the range of motion in flexion / extension, lateral bending and axial torsion of the head. Those were compared to 48 normal discs from volunteers’ radiographs. Results The range of motion was significantly reduced with the prostheses in flexion / extension. The displacement in the main plane of motion was normal in lateral bending and reduced in axial torsion. Coupled motion was reduced in axial torsion and normal in lateral bending. Discussion This study is the first report of in vivo 3D intervertebral kinematics in the case of total disc replacement at the cer-vical level in upright position.

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THE RESULTS OF A ONE STAGE JOINT REVISIONS FOR INFECTED JOINTS USING RADICAL DERBRIDEMENT AND ANTIBIOTIC IMPREGNATED CEMENTED TOTAL JOINT REVISION Authors: Gerhard Maale M.D, Jorge Casas-Gamen M.D., and Allen Rueben M.D. 230 Walnut Hill Lane #514 Dallas, Texas 75231 E-Mail: [email protected] The treatment of infected total joint replacements varies. Popular in the United States is a 2 stage debidement with placement of an intermediate antibiotic loaded cement spacer followed by definitive reconstruction at different timed intervals. Described in this study are the results of a one-stage revision after debridement for infected joints. Seventy eight patients with 2 minimal year follow-up were treated by radical debridement, removal of the joint prosthesis irrigation, changing of drapes and set-ups, re-irrigation and definitive exchange, were analyzed. All pa-tient s were pre-operatively imaged, and staged by the MSIS (Musculoskeletal Infection Society) staging as sub-mitted by McPherson. Radical debribement was defined as removal of all dysvascular hard and soft tissue and re-moval of all prosthesis or related debris for which biofilm formation was possible There were 45 total knees, 33 hips, 1 shoulder, and 1 elbow treated for infection. All patients had local or systemic compromising factors. Sixty six patients were stage IIIC3 by the MSIS Staging. Eight patients had relapse of their infection, 1 with bilateral knee infections with associated with an infected heart valve, done for palliation. An addi-tional patient had a retained Marlex graft after prior pelvic floor reconstruction after resection of a tumor. If these cases are excluded, 92 % remain clinically free of infection. The most common complications were subluxation or dislocation of the patella in total knees secondary to soft tissue resection, and dislocation of total hip secondary to the need of constrained acetalubar prosthesis required by the soft tissue resection in total hips. One recurrence in a knee required amputation. These results for a one-stage treatment of infected joints are better or equal to other published treatment modalities. The authors feel the difference in the success is the oncologig type of surgical resection of the biofilm mediated infection.

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THE VALUE OF A SUBJECTIVE SCORE FOR THE PATELLO-FEMORAL ASSESSMENT IN TOTAL KNEE ARTHROPLASTY Authors: N.Bonin, G.Deschamps, D.Dejour Introduction: Scores which are commonly used to assess total knee arthroplasty are sometimes not sufficient to assess the func-tion of the patellofemoral joint. During a comparative study between 2 series of total knee arthroplasty with and without a resurfaced patella, an objective score referred to as “patellar score” has been designed and assessed on 135 patients clinically reviewed and on 20 patients surveyed on the phone. Score Component: The “patellar score” is based on the assessment of knee pain thanks to Visual Analog Scale (VAS) for items related to patellofemoral joint function: going up or down the stairs, keeping a prolonged seated position, leaving an arm-chair, getting out of a car. A Numerical Scale is used for the patients surveyed over the phone. The pain felt during palpation of the internal and external patellar sides, as well as that of the trochlea, is assessed equally, similarly with a VAS. The total amount is divided by the number of items as to obtain a “patellar score” out of 10. The lower the score the better the result. Score Analysis: The results are compared to the International Knee Society clinical score, to the subjective “clinical anterior knee pain Score” established by Waters and to the patients global satisfaction. Each “patellar score” item is analysed to eliminate non relevant items. A link has been observed between the IKS score, the “patellar score”, and the pa-tients’ satisfaction. The “patellar score” has allowed a finer analysis of the pains undergone by the patellofemoral joint, in detecting a difference in favor of the patellar resurfacing, whereas the more global IKS score was not modified. Besides, the “patellar score” has allowed a more accurate approach of the patient’s pain. Palpation Clini-cal items have not significantly modified the results of the score. By cancelling them a self evaluation file is ob-tained. Conclusion: The “patellar score” is based on the Visual Analog or Numerical Scale, commonly accepted for its value in assess-ing pain. Such a score allows a fairly good evaluation of the PTG since it is connected to the IKS clinical score, and to the patients’ satisfaction. It can be adapted to obtain a subjective self evaluation file.

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CHARACTERIZATION OF THE INFLAMMATORY RESPONSE TO BONE GRAFT SUBSTITUTES USING THE MURINE AIR POUCH MODEL S. Trent Guthrie, M.D., Bin Wu, MD, Zheng Song, MA, Paul H. Wooley, PhD, David C. Markel, M.D. Department of Orthopaedic Surgery 22250 Providence Dr. Southfield, MI 48075 Phone: 248-569-0306 Fax: 248-569-0364 E-Mail: [email protected] Objectives: Bone graft substitutes offer the potential for decreased morbidity with similar efficacy to the gold standard fresh autograft. Recent studies have focused on the efficacy of these new products, but few studies have evaluated their safety. The purpose of this study was to characterize and quantify the inflammatory reaction to different commer-cially available bone graft substitutes. Study Design: Commercially available bone graft substitutes were examined using the in vivo murine air pouch model for inflam-mation. One coralline hydroxyapatite product and three different demineralized bone matrix (DBM) products were tested. Samples were implanted in a murine subcutaneous air pouch and incubated for fourteen days. Pouch fluid was extracted, mRNA isolated and reverse transcription polymerase chain reactions were carried out to detect IL-1 gene expression as a marker for inflammation. Multiple histological characteristics were examined in an attempt to quantify cellular responses to implanted materials. Results: All bone graft substitutes induced a significant inflammatory response compared to control samples. Histology and PCR data suggested a stronger inflammatory reaction in response to DBM products with higher DBM to car-rier proportion. The hydroxyapatite product generated less inflammation than the DBM products. Conclusion: This study used an in vivo model of inflammation to demonstrate and quantify the significant inflammatory reac-tion to implanted bone graft substitutes. When choosing a bone grafting method, surgeons should consider both the efficacy and safety of methods and materials used. Further studies are necessary to determine the ideal bone graft material to maximize efficacy while minimizing morbidity.

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SINGLE USE SURGICAL INSTRUMENTS TO REDUCE THE INCIDENCE OF BONE NECROSIS AND ELIMINATE CROSS CONTAMINATION Dickinson, AS; Taylor, A; Bird, T; Latham, J; Wadey, R; Browne, M. Finsbury Development Ltd, 13 Mole Business Park, Randalls Road, Leatherhead, Surrey, KT22 7BA, UK. Tel: +44(0)1372 360830. Email: [email protected]

The repeated use of surgical cutting instruments has led to a number of concerns, for example, incomplete cleaning may cause cross contamination between patients, and over time, blunting of cutting surfaces may cause sufficient heating to cause bone necrosis, affecting fixation strength. A range of cost-effective single-use acetabular reamers has been designed to address these issues. The aim of a single use device is to cut more efficiently and accurately, and generate lower heat in the surrounding bone. In addition, the risk of patient cross contamination is reduced to zero. The cutting efficiency of a number of conventional reamers which had been used in surgery was compared with that of single use reamers using an analogue bone and bovine bone as test media. A standardised test was developed in which the action of the surgeon preparing a cavity for the acetabular cup in the pelvis was reproduced. The reamer penetration speed, the geometric accuracy of the reamed cup and the heat-ing of the surrounding bone were recorded throughout the investigation. The single-use reamer penetration speed through the analogue bone medium was twice that of the reusable device. The deviation from round of the reamed hemisphere was 41% greater for the reusable device. In bovine bone, the used reamers largely compacted the material rather than cut it. Measurements indicated that the maximum tem-perature increase caused by reaming was at least 18% lower for the single use reamer than for the reusable device.

In conclusion, the tests showed that a new single-use acetabular reamer can cut at twice the speed of a worn reus-able reamer. The use device displayed clear signs of blunting and trapped organic debris. With the new reamer, tests indicated that the cut surface is more accurately shaped and the bone is exposed to a lower temperature for a shorter length of time. Although the reusable device, when new, should in theory have similar cutting characteris-tics to the single use device, repeated application will inevitably lead to poorer performance which can have conse-quences in terms of cross contamination and thermal necrosis. The present study has demonstrated that the single use device presents a viable alternative which carries far lower risk to the patient.

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LASER MELTING TECHNOLOGIES FOR IMPROVED FLEXIBILIY DURING IMPLANT MANUFACTURE Roques, Anne; Taylor, Andy; Sauve, P. Finsbury development, 13 Mole Business Park, Randalls Road, Leatherhead KT227BA, UK Tel: +44 01372 360830, fax: +44 1372 360779, Email:[email protected]

Cobalt chrome implants manufactured using additive methods have been investigated and have shown good bio-compatibility. This type of additive production method is currently used for the manufacture of dental implants. The capability of the technology to fulfil the requirements for orthopaedic implants manufacture was investigated. Proximal interphalangeal finger implants were manufactured using laser sintering of cobalt chrome powder. Post processing inspection results were used to assess the capability of the technology in terms of dimensional accuracy and surface finish on small implants. The laser melting manufacturing technology also offers great design flexibil-ity as intricate shapes which could not be manufactured using current techniques can be built. This is of particular interest for designs that encourage bone ingrowth, for example hollow features. With this increased freedom of manufacturability in mind, a novel acetabular cup was designed. This consists of a rigid articulating surface com-bined to a flexible outer surface (for load transfer improvement) with hollow pyramidal features for improved fixa-tion. Manufacture of the 50 finger joints showed that an average surface finish (Ra) of 5.5 microns could be reproduci-bility obtained. This was in the range of roughness obtained for a standard casting. The dimensional accuracy and technique repeatability were better than 20 microns. The surface could be polished to a mirror finish. The flexible cup design included helicoidal vanes connecting the inner rigid articulating surface to the outer thin metal shell. The outer surface featured hollow pyramids that have been clinically proven to improve bone ingrowth. This could be easily manufactured from the 3 dimensional computer assisted design models using the laser melting technol-ogy. Laser melting technologies offer great design flexibility, and they can be applied to cobalt chrome powders for the manufacture of biocompatible orthopaedic implants. The technology has been shown to offer a high dimensional accuracy and reproducibility for small implants, with the advantage of a great flexibility for complex designs that could not be realised with conventional manufacturing techniques. This opens new avenues for orthopaedic design-ers with the potential realisation of hollow features (eg for bone ingrowth) and 3 dimensional intricate features and sections for tailored stiffness properties. Further developments in post processing treatments are required however to improve the microstructure properties of the built materials for high demand load bearing applications.

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B13-6 COMPLICATIONS ENCOUNTERED WITH THE USE OF CONSTRAINED ACETABULAR PROSTHESES VERSUS LARGE DIAMETER METAL ON METAL MODULAR HEADS IN TOTAL HIP ARTHROPLASTY. A RETROSPECTIVE COMPARATIVE STUDY

Christophe Pattyn, MD¹, Roel De Haan, MD², Georges Van Maele, PhD³, Koen De Smet, MD² 1. Department of Orthopaedic Surgery and Traumatology Ghent University Hospital, Belgium

2. Anca Medical Centre Ghent, Belgium 3. Department of Medical Informatics and Statistics Ghent University Hospital, Belgium Contact Author: Christophe Pattyn, M.D. Department of Orthopaedic Surgery and Traumatology Ghent University Hospital De Pintelaan 185 B 9000 Gent, Belgium Tel. +32.9.2406778 Fax. +32.9.2404975 E-mail: [email protected] At our orthopaedic department, between January 1999 and November 2005, 48 constrained acetabular components and 38 large-diameter head metal-on-metal bearings were placed for similar indications in 40 patients (first group) and 36 patients (second group), respectively, over a period of six years.

Indications included recurrent dislocation, septic and aseptic loosening with extensive bone loss, tumour surgery with extensive bone resection and instability due to neurological impairment.

At 1-7 years of follow-up 3 cup failures and 10 dislocations were observed with the constrained devices versus only one cup failure and one dislocation with the large-diameter metal-on-metal bearings. With the constrained devices, 4 different mechanisms of failure were observed.

In view of the high failure rate with the use of constrained devices (27 %), the authors strongly recommend judicious use of these components and to consider alternative options such as the use of large-diameter femoral heads with a metal-on-metal friction couple.

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A NEW DESIGN OF ANKLE PROSTHESIS TARGETING LIGAMENT ISOMETRY: INTRA- AND POST-OPERATIVE VALIDATION MEASUREMENTS Leardini Alberto, Catani Fabio, Romagnoli Matteo, Bianchi Loris, Miscione Maria Teresa, Giannini Sandro Corresponding Author: Alberto Leardini Istituti Ortopedici Rizzoli, Movement Analysis Lab, Bologna , 40136, Italy Ph: ++39 051 6366522 Fax: ++39 051 6366561 Email: [email protected]

Total ankle (TAA) is still not as satisfactory as total hip and total knee arthroplasty. For TAA to be considered a valuable alternative to ankle arthrodesis, an effective range of mobility must be recovered. The disappointing clini-cal results of the current generation of TAA are mostly related to poor understanding of the anatomical structures guiding joint mobility. A new design has been developed by these authors, potentially able to restore physiologic ankle mobility and a natural relationship between the implanted components and the retained ligaments.

According to extensive prior research, the new design features a spherical convex tibial component, a talar compo-nent with radius of curvature in the sagittal plane longer than that of the natural talus, and a meniscal component fully conforming to these two. In the sagittal plane, the shapes of the tibial and talar components are compatible with a four-bar linkage model formed by the calcaneofibular and tibiocalcaneal ligaments. After computer-based modelling and preliminary observations in trial implantation on anatomical preparations, 75 patients were im-planted in the period July 2003 – May 2007, with mean age 62 years (range 37 – 80), mean follow-up 18 months (range 1 – 46). For the meniscal bearing to slide smoothly on both the components, a special operative technique was designed together with relevant instrumentation in order for the three components to be implanted in an exact position also with respect to the retained ligaments. This was achieved by ensuring that a constant gap is main-tained between the tibial and the talar components throughout the flexion arc. The AOFAS score system was used to assess patient outcome at 3, 6, 12, 24, 36 month follow-ups.

Intra-operatively, the components seated properly onto the prepared osteotomies. Over the entire motion arc, the prosthesis maintained complete congruence at the two articulating surfaces of the meniscal bearing which moved considerably antero-posteriorly. Range of dorsi- and plantar-flexion improved from respectively 0.4 and 15.3 pre-op to 10.1 and 24.2 post-op, maintained at the follow-ups. Radiographs at maximal dorsiflexion and maximal plan-tar flexion and fluoroscanning confirmed the meniscal bearing moves anteriorly during dorsiflexion and posteriorly during plantarflexion, over a distance of 2 to 11 mm. Frontal and lateral radiographs of all patients at all follow-ups showed good alignment of the components, and no signs of radiolucency or loosening. The mean AOFAS score was observed to go from 40.6 pre-op to 78.5 at last follow-up.

Because the meniscal bearing moved in the direction and approximately for the distance predicted by computer-based models, physiological roles of the ligaments must have been restored, i.e. controlling joint mobility by iso-metric fibre rotations and assuring joint stability by appropriate load resistance. As full conformity of the three prosthesis components was observed over the entire motion arc, it is encouraged also the prospect of minimizing wear of these components. Slight misplacement of the bone-anchored components did not affect considerably these observations. The satisfactory though preliminary observations both intra- and post- operatively from this novel TAA encourage continuation of the implantation.

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IN VIVO DETERMINATION OF THE MOBILE BEARING TOTAL ANKLE PROSTHESIS KINEMATICS Leszko Filip1, Komistek Richard D1, Mahfouz Mohamed1, Judet Thierry2, Bonnin Michel3, Colombier Jean-Alain4, Lin Sheldon S5

1University of Tennessee, Knoxville, TN, USA 2Hôpital Raymond Poincarré, Garches, France 3Clinique Saint Anne Lumière, Lyon, France 4Clinique de l'Union, Toulouse, France 5North Jersey Orthopaedic Institute, Newark, NJ, USA Correspondence: Richard D. Komistek, 301 Perkins Hall, University of Tennessee,Knoxville, TN 37996 Email: [email protected] Phone: (865) 974-4159 Fax: (865) 671-2157 Presenting author: Phone: (865) 274 8256, Fax: (865) 671-2157, [email protected] The present study analyses the mobile bearing total ankle prosthesis kinematics under in vivo, weight-bearing con-ditions. 3D range of motion information may help the surgeon assess if the treatment is successful. The relation between rotational and translational components of spatial joint motion gives engineers invaluable knowledge to improve future implant designs. Twenty patients (10 female, 10 male) with an implanted talocrural joint (SaltoTM Total Ankle Prosthesis, Tornier, Saint Ismier, France) were studied using a previously reported method based on fluoroscopy [1]. All subjects were judged clinically successful without pain or ligament instability. Two activities were analyzed; gait and step-up. A 3D-to-2D registration technique [2] was used to determine the medial and lateral anterior/posterior (A/P) transla-tions, plantar/dorsiflexion, eversion/inversion, internal/external rotations and instantaneous axis of rotation. For both activities, the average results showed that the lateral contact point (the closest point between respective talus component condyle and the tibial component) was more anterior than the medial contact point. Both points showed similar average range of translation (2.0 mm and 2.1 mm for gait and 2.8 mm and 2.9 mm for step-up). The translation of medial and lateral contact points is the result of both translational and rotational motion of the tibia relative to the talus. The analysis of pure translation (the distance between centers of tibia and talus implant components) showed that on average the tibia translated anteriorly 1.5 mm for gait and 2.3 mm step-up. In the cor-onal plane the average rotation of the tibia ranged from 0 to 0.5º of eversion. The average range of rotation in this plane was 2.8º and 2.5º for gait and step-up, respectively. During gait, the flexion in the sagittal plane changed almost linearly from 8.1º plantarflexion at heel strike (HS) to 0.4º dorsiflexion at toe off (TO), the average range was 9.2º. For the step-up the pattern was different; tibia flexed from 2.2º plantarflexion at HS, through 1.6º of dor-siflexion at 33% of step-up and returned to 2.1º plantarflexion at TO, the average range was 8.0º. For both activi-ties the internal rotation of the talus was observed and the range of this axial rotation averaged 5.9º and 7.7º for gait and step-up, respectively. The average range of the resultant 3D rotation was 16.1º and 18.5º for gait and step-up, respectively. The analysis also showed that the instantaneous axis of rotation was oriented mainly in the medial-lateral direction, therefore confirming that the dorsiflexion dominates in gait and step-up activities. No significant difference was found between men and women ankle kinematics. The results showed that the SaltoTM TAA has sufficient ROM and the average motion pattern was smooth and con-tinuous. It was further observed that the rotations dominated the motion of ankle joint. Even though the analyzed total ankle replacement was mobile bearing, the measured pure translation was small and may persuade the engi-neers to focus on reproducing the rotational rather than translational motion of the ankle joint. [1] Dennis DA, et al.: Clin Orthop, 1996 [2] Hoff W, et al.: Clin Biomech, 1998

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DESIGN RATIONALE AND MECHANICAL TEST OF 3-COMPONENT MOBILE-BEARING TOTAL ANKLE ARTHROPLASTY Yamamoto, Keitaro., Suguro, Toru., Nakamura, Takashi., Miyazaki, Yoshiyasu., Kogame, Katsunori., Kubota, Ayako., Kuramoto, Koichi., (Address) Department of Orthopaedic Surgery, School of Medicine, Toho University,

6-11-1 Omorinishi, Ota-ku, Tokyo, 143-8541 JAPAN (Phone/FAX/e-mail) +81-3-3762-4151/+81-3-3763-7539/[email protected]

Purpose: Clinical use of Total Ankle Arthroplasty (TAA) began in the 1970’s. A number of different TAA prostheses have been developed in the world. Although TAA currently offers excellent pain relief, there are still significant prob-lems. When compared to the other joints in the lower extremities such as the hip joint and the knee joint, the ta-locrural joint is very small. However, it bears large compressive and shear forces during dorsiflexion, plantar flex-ion, and rotation. The TAA prosthesis is placed in a highly stressful environment, which makes acquisition of long-term clinical results difficult. We therefore developed a new 3-component mobile-bearing TAA prosthesis specifi-cally designed to disperse stress and self-align the talocrural joint under loaded conditions. Materials and Methods: Contact stresses on the tibial articular surface were analyzed using finite element analysis (FEA), which is MSC.Marc2003 made by MSC SOFTWARE to minimize peak contact stresses. Durability test of a new 3-component mobile-bearing TAA prosthesis was performed using the simulator made by MTS. Hyaluronate sodium was used as a lubricant. The program of operation carried out the load of the maximum of 5.0BW (3000N) suppos-ing the time of a walk. Result: FEA showed peak von Mises stress of 13.0 MPa under a 3,000 N load, well below the plastic limit of UHMWPe. The overall contact area of the talocrural joint became a constant 600 mm2 between ±10 degrees of dorsiflexion and plantar flexion. In durability evaluation of UHMWPe by the MTS simulator, the amount of wear of the UHMWPe insert showed about 15mm3 at the time of a 3 million cycle, the clearly marks worn out in the articular surface of UHMWPe were not accepted. Conclusion: A new 3-component mobile-bearing TAA prosthesis was developed for the purpose of stress dispersion and easy self-alignment of the ankle joint. From this investigation, it was shown that TAA of 3-component mobile-bearing prosthesis is excellent in stress dispersion and durability.

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B14-4 FIXED OR MOBILE BEARING TOTAL ANKLE REPLACEMENT DESIGNS: WHAT REALLY MATTERS? Hani Haider, PhD, Lori K. Reed, MD, Ben O’Brien and Kevin L. Garvin, MD Department of Orthopaedic Surgery and Rehabilitation University of Nebraska Medical Center 985360 Nebraska Medical Center - Scott Technology Center Omaha, NE 68198-5360, USA Email: [email protected]

This paper first reviews the history of development of Total Ankle Replacement (TAR) systems, highlighting the challenges in their design, and the less-than-ideal clinical results they appear to have produced so far.

The main question is then posed of how and why so many of the latest designs of ankle replacement systems out-side the United States incorporate mobile bearings. The philosophy and merits of the mobile bearing as an innova-tive concept are described, and the experience of its use and success in the knee is reviewed. This is then placed in the much wider perspective of the overall evolution of TKR, where improvements in many aspects of their de-sign, materials, manufacture and surgical procedure have contributed to their overall success and survivorship in-vivo. The literature is comprehensively probed for those major success factors, which helped conventional fixed-bearing as well as mobile bearing TKRs. Among them was the realization of minimum thresholds of UHMWPE thickness, and its sterilization in inert gases to avoid oxidation and fatigue wear, which helped significantly im-prove TKR survival.

The significant contributions of intramedullary alignment of TKR components, adequate bone coverage and metal backing of polyethylene onto tibial plateaus, and the role of stem fixation, were all also described citing relevant studies. The risks associated with mobile bearings are then described, citing studies which investigated potential extra backside wear, bearing insert stick/slip, the risk of dislocation/subluxation and possibly fracture.

The study concludes by suggesting how the important advances which did bring success in Total Knee Replace-ment can be carried over to the ankle, and questions as to whether the mobile-bearing should be considered an im-portant one of them.

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List of Posters—In alphabetical order by presenting author’s last name ————————————————————————————————— P1 Is Postoperative Periprosthetic Bone Remodeling in Cases Using Cementless Femoral Components

Predictable by Preoperative Planning Using CT-Based 3D Templating System? Tomonari Ando, Tamon Kabata, Toru Maeda, Mitsuhiro Naito, Tadashi Taga, Katsuro Tomita P2 Validation of an ASTM Standard Proposed to assess Localizer Functionality of CAOS Systems: A Joint Effort by Three Laboratories — Andres Barrera, Joel Bach, Peter Kazanzides, Hani Haider P3 Lateral Patellar Retinaculum Release Influence on Total Knee Arthroplastys’ Results N. Bonin, D Dejour P4 Modular Adapters Antonio Croce, Marco Ometti P5 MIS : The Italian Experience in Hip Surgery with Short Stem ( TLS ) - Carmine Cucciniello P6 Total Hip Replacement in Patients with Congental Dysplasia Crowe Type I and II Using Alumina-Ceramic-On-Ceramic Bearings—Stephen Murphy, Timo Ecker P7 Experimental and Theoretical Analysis of Different Bearing Surfaces for THA—Diana Glaser, H Cates, RD Komistek, MR Mahfouz, D Dennis, F Liu P8 Does Separation Vary with Different Surgical Techniques: Traditional Posterolateral vs. Minimally Invasive Anterolateral and Posterolateral THA—Diana Glaser, TM Miner, RD Komistek, MR Mahfouz, DA Dennis, MR Anderle P9 The Conserve-Plus Metal-On-Metal Hip Resurfacing System: Surgical Technique, Clinical Results and Complications on a Consecutive Series—Pier Francesco Indelli, Thomas Parker Vail P10 What is a Normal Kness Laxity? Jean-Yves Jenny, Cyril Boeri, Eugene Ciobanu P11 Does Computer Assisted Surgery Aid in Shortening the Learning Curve in M-O-M Surface Replacement? Thorsten Seyler, William Ward, Denise Sprinkle,Riyaz Jinnah P12 Uncemented Ceramic on Ceramic Articulation Total Hip Replacement for Dysplastic Osteoarthritis—Five or More Year Follow-Up— Atsushi Kusaba, Saiji Kondo, Yoshikatsu Kuroki P13 The EOS 2D-3D X-Ray Scanner: A New Technology to Assess the Tridimensionnal Position of THP Cups—JY Lazennec, A Baudoin, D Mitton, W Skalli, A Rangel, Y Catonne P14 Clinical and Biological Follow-up for a Cemented Titanium Femoral Stem: A Twelve Year Experience—Jean-Yves Lazennec, Patrick Boyer, Joel Poupon, Marc-Antoine Rousseau, Phillipe Ravaud, Yves Catonne P15 Biomechanical Evaluation of Acetabular Component Polyethylene Stresses, Fracture Risk, and Wear Rate During Press-Fit Implantation— Kevin Ong, Steve Rundell, David Markel, Steven Kurtz P16 Knee Arthroplasty Kinematics During Pivoting—How Much Rotation in Extension? P Moonot, G Railton, S Mu, SA Banks, RE Field P17 Analysis of Tantalum Implants Used for Avascular Necrosis of the Femoral Head: A Review of Five Retrieved Specimens—M Montero, A Murcia, M. Fernandez-Fairen P18 Navigated Arthroscopic Percutaneous Osteochondroplasty in Patients with FAI Using a New Method of CT-Fluoro Registration-Preliminary Experience—Stephen Murphy, Timo Ecker

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List of Posters — In alphabetical order by presenting author’s last name ————————————————————————————————— P19 A Novel System for Leg Length Measurement in Computer Assisted Total Knee Arthroplasty Mark Nadzadi, Timo Ecker, Jason Lang, Stephen Murphy P20 16 to21 Year Clinical Results of Total Hip Arthroplasty with HA Granules at Cement-Bone Interface (Interface Bioactive Bone Cement) Oonishi Hironobu, Oonishi Hiroyuki, Jr., Kim Sok Chol, Ohashi Hirotsugu, Ojima Satoshi P21 Computer Assisted Total Knee Arthroplasty: A Novel “Pinless” Technique to Reconstruct a Neutral Mechanical Axis—Lalit Puri, Todd Moen, Nasim Rana, Richard Wixson P22 Computed Tomography to Assess Acetabular Loosening Prior to Revision Hip Arthroplasty Thangamani Vijay B, Pribaz Jonathan R, Puri Lalit, Stulberg S David, Wixson, Richard L. P23 Results of Knee Manipulation for Stiffness After Total Knee Replacement With and Without Intra-Articular Injection of Steroid—Vineet Sharma, Amar Ranawat, Chitranjan Ranawat P24 Does Eversion of the Patella Cause Patella Baja? Vineet Sharma, Amar Ranawat, Chitranjan Ranawat P25 Improvement of Cement Mantle with Pressurized Carbon Dioxide Lavage Wayne Goldstein, Alexander Gordon, Jeffery Goldstein, Kim Berland, Jill Branson, Vineet Sarin P26 Calcium Phosphate Paste for Treatment of Infected TKA Tomotaro Sato, Masami Thukamoto, Atsushi Kaneko, Daihei Kida, Yoshito Eto P27 Lower Incidence and Severity of Heterotopic Ossification With Less Invasive Total Hip Arthroplasty— Nirav Shah, Raju Ghate, S. David Stulberg P28 Hip Arthroplasty: Mini Incision Lateral Approach Versus Standard Approach—Speranza Attilio,

Iorio Raffaele, D’Arrigo Carmelo, Ferretti Andrea P29 Cost-Analysis of the Use of Fibrin Sealant to Minimize Perioperative Allogeneic Transfusion Requirement in Total Knee Replacement — LMG Steuten P30 Alignment of Total Knee Arthroplasty: Implications for Computer Assisted TKA Surgery Nicholas Wegner, Alfred Cook, Joe Feinglass, S. David Stulberg P31 Use of Transverse Acetabular Ligament for Acetabular Cup Placement in Computer-Assisted Total Hip Replacement—Michael Swank, Martha Alkire, Leslie Korbee, Jon Grote P32 Reducing Cardiac Post-Operative Complications After Total Joint Replacement Michael Swank, Martha Alkire P33 The Tibial Slope in Total Knee Replacement—J Tabutin, R Lanza, PM Cambas P34 Full Flexion After Total Knee Using LPS Flex Implant—Samih Tarabichi P35 Total Joint Arthroplasty After Bariatric Surgery for Morbid Obesity: Complications in the Peri-Operative Period —Vijay Thangamani, Lalit Puri P36 In Vivo Changes to Metal on Metal (MoM) Bearing Surfaces—Implications—M Tuke, A Taylor

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P1 Is postoperative periprosthetic bone remodeling in cases using cementless femoral components predictable by preoperative planning using CT-based 3D templating system?

Ando Tomonari, Kabata Tamon, Maeda Toru, Naito Mitsuhiro, Taga Tadashi, Tomita Katsuro Department of Orthopedic Surgery, Kanazawa University School of Medicine 13-1, Takaramachi, Kanazawa, 920-8641, Japan Tel: +81-76-265-2374, Fax: +81-76-234-4261 E-mail: [email protected] Objective When cementless femoral stems are inserted in the femoral canal, a contact state between the stem and femoral canal is estab-lished, but varies between patients due to individual differences in amongst one’s femoral canal configuration. There are also individual differences in postoperative periprosthetic bone remodeling for the same reasons. We hypothesize that the initial contact between stem and femoral canal affects postoperative periprosthetic bone remodeling. Therefore, in this study, 3D-CT templating software is used to test this hypothesis. Materials & Methods Enrollment for this study consisted of a total of 19 hips, which were implanted with Super Secur-Fit HA (Stryker®), in neutral position (within 2 degrees of varus or valgus), and followed for at least 1 year. The preoperative diagnosis for these cases were 14 OA hips, 4 RA hips, and 1 rapidly destructive coxarthropathy. An initial contact area between the implanted cementless stem and the cortex of the femoral canal was retrospectively evaluated using the CT-based surgical planning software called Hip-OP, which has the ability to display the osseous density contacting with stem surface. Periprosthetic bone remodeling, including spot welds in the postoperative radiographs at least one year after surgery, were also evaluated; and lastly, the relationship be-tween initial stem-cortex contact area and postoperative bone remodeling around the stem was examined and analyzed. Results All cases were well functioning without subsidence in spite of full weight bearing immediately after surgery. Contact areas between the inner femoral cortex and the implanted stem was achieved and observed as follows: Gruen Zones 2 to 3 in 5 hips, Zone 3 in 5 hips, Zone 5 in 8 hips, and Zones 5 to 6 in 5 hips. On the other hand, postoperative radiographs showed spot welds in 14 hips (73.4%). The areas showing spot welds were around Gruen Zone 1 in 11 hips, Zone 2 in 11 hips, and Zone 6 in 14 hips. In most cases, spot welds were found proximal to the contact areas between femoral cortex and stem. Only 2 cases showed that both areas were in accord. Discussion In this study, all stems used were proximally hydroxyapatite-coated press-fit stems, in which hydroxyapatite has been reported to promote bony fixation onto an implant’s surface coating. However, the most contact areas between femoral canal cortex and implanted stem, reproduced by Hip-OP, were not on the coating area but just distal to the coating area. On the other hand, most spot welds were found at Gruen Zone 1 (proximal lateral part of the coating area), Zone 2, and Zone 6 (distal part of the coating area), not found on the contact area. From our results, we speculated that the initial contact area of the stem was not necessarily associated with postoperative periprosthetic bone remodeling, which may rather be associated with the stem design and surface coating.

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P2 VALIDATION OF AN ASTM STANDARD PROPOSED TO ASSESS LOCALIZER FUNCTIONALITY OF CAOS SYSTEMS: A JOINT EFFORT BY THREE LABORATORIES Barrera O. Andres; Bach, Joel M.*; Kazanzides, Peter** and Haider, Hani Department of Orthopaedic Surgery and Rehabilitation, University of Nebraska Medical Center, 985360 Nebraska Medical Center - Scott Technology Center, Omaha, NE 68198-5360, USA Phone : (402) 559 5607 – Fax : (402) 559 2575 – E-mail : [email protected] *Colorado School of Mines, Univ. of Colorado at Denver and Health Sciences Center **Johns Hopkins University, Center for Computer-Integrated Surgical Systems and Technology With the increasing popularity and variety of computer-aided orthopaedic surgery systems (CAOS), users need to be able to objectively evaluate the accuracy and performance of different systems. Lack of standardized testing methods has urged ASTM-International and CAOS-International to form a joint task force to draft such standards, involving international members from academia, industry, and medical practice. An initial draft-standard has evolved focusing on testing the “localizer” function as the common factor and most elementary func-tion a CAOS system needs to provide. This standard would be the platform from which to spin-off more complex CAOS-procedure testing (eg. TKR or THR). The proposed test method needed practical testing/validation itself. Three research laboratories have combined to experimentally assess this test-method, and the first round of results is presented here. Three different CAOS systems were used: two customized optical-navigation systems and a surgical-robot (NeuroMate, Integrated Surgical Systems/CA). An aluminum-alloy phantom was designed by the standardiz-ing group, and manufactured according to the draft standard. It comprised an anodized multi-surface 3-D pyramid-like object with 47 fiducial points distributed on its surfaces as identical divots, each a 90º countersunk hole, 0.75mm deep. The phantom had features to attach arbitrary reference frames for navigation. Thirty-three tests were performed by four different users with the same protocol aimed for standardized testing. In each test, after registration/calibration of the pointer and phantom, all 47 divots were visited/digitised with the tip of the pointer keeping the phantom at the center of the measuring volume. At each divot, several inde-pendent readings were taken with various orientations of the pointer (+/-15º, +/-30º, +/-45º, and +/-60º around three different axes). To examine sensitivity to location, experiments were repeated at 13 locations of the phantom around the measurement volume. For one navigation system, many consecutive measurements per-point were made to evaluate the effect of averaging measurements. Due to constraints of the robot, its measurements were taken with the phantom placed at one location, and without pointer pivoting. Both CAOS systems showed a range of three-dimensional errors in point-location of 0.04-1.16mm (mean 0.41mm). Averaging of 5 or 10 consecutive measurements did not significantly improve the results. Errors with the robot were higher, ranging 0.28-2.27mm (mean 1.2mm). We believe this was due to an accidental displacement of the phantom during the testing, which was not detected by the robot system. The results demonstrated similar magnitudes and variability between observers and systems. Overall, our results confirmed that the proposed ASTM-CAOS standard test method could successfully discriminate the localizing accuracy of two infra-red CAOS systems and a surgical-robot. Intra- and inter-observer variability demonstrated that the results were repeatable. The testing process was time-efficient with simple proce-dures for multiple users. Exceptions need to be reported when testing systems (eg. robots) which cannot complete all checkpoints. Future work will include electromagnetic and commercial optical systems. End-users of CAOS systems will want to know the relevant performance parameters in realistic clinical procedures. Evaluation of the localizer functionality will serve as the baseline to be characterized first before confronting more complicated ap-plications.

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P3 LATERAL PATELA RETINACULUM RELEASE INFLUENCE ON TOTAL KNEE ARTHROPLASTYS’ RESULTS N. Bonin, D.Dejour Introduction Release of the lateral patellar retinaculum can be used to treat patellofemoral instability and to balance the extensor mechanism during knee replacement operations. However, the need to perform lateral retinacular release may in-fluence the patient’s subjective and objective results.

Material 94 consecutive knee replacements were performed by the same surgeon, with the same implant (HLS Noetos®, Tornier). All patellas were resurfaced. Surgical approch was trans quadricipital in 79 knees. Lateral retinaculum was preserved in 55 cases (Group 1) and released by section in 24 cases (Group 2). In 15 knees with valgus de-formities or previous tibial osteotomy, lateral approch was performed with lateral retinaculum section (Group 3).

Method

At 3 to 5 years follow-up, 77 patients (80%) were reviewed by an independent observer. International Knee Soci-ety (IKS) score and subjective score were used. Femoropatellar pain was assessed with a specific patellar score based on Visual Analog Scale (VAS). The lower the score the better the result. Merchant view was used to assess patellar tilt or subluxation. Results

IKS Knee score was 83/100 in group 1, 82 in group 2 and 87 in group 3. IKS function score was 75/100 in group 1, 73 in group 2 and 78 in group 3. The « clinical anterior knee pain score » established by Waters was 0.34/3 in group 1, 0.73/3 in group 2 and 0.17/3 in group 3. Patellar specific score was 1.81/10 in group 1, 1.90 in group 2 and 1.63 in group 3. Kneeling was possible for 29% patients in group 1, 5% patients in group 2, 64% patients in group 3. Mean flexion was 118° in group 1, 114° in group 2 and 122° in group 3. All patellas were centered in group 2 and 3. Patellar lateral subluxation was present in 19% patients in group 1. This subluxation lowered the results.

Discussion

This study shows best results when lateral approch, with lateral retinaculum section, is performed. When medial approch, lateral retinaculum release may increase anterior knee pain and compromise kneeling position. Neverthe-less, lateral release reduced the tendency toward lateral subluxation without increasing patellar complications.

This study concerns femoral component in neutral rotation referenced to the posterior condylar axis.

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P4 MODULAR ADAPTERS Croce, Antonio, Ometti, Marco (Istituto Ortopedico G.Pini, Piazza A. Ferrari,1 - 20122 Milano) (3354666648/[email protected])

The hip prosthesis dislocation, in spite of the continuous progress of implants’ materials and design, is again an actual event in the orthopaedic clinical practice, both after a total or endoprosthesis and after total hip replacement. Furthermore, dislocation has an important social-economic impact because of a protracted hospitali-zation and rehabilitation and elevated costs of an eventual revision. Although using heads with a diameter larger than 28 mm we obtain virtually a greater range of motion, with a contemporary increase of degree necessary to cause the head-neck impingement, the risck of dislocation hasn’t a significant increase using head with a diameter of 22 mm. Neck modular adapters (Bioball) allow to correct easily the biomechanics parameters of the dislocated prosthesic joint, avoiding a new important operation. Other indications for the use of the neck modular adapter are total hip replacement and intraoperatory correction of the limb length. Vantages are the possibilty to obtain a great range of motion through a small thickness of the 12/14 adapter, the possibility to extend the limb length up to 21 mm and to use ceramic heads during revisions, because the combination head/neck has a tribological unweared surface. In fact, in normal conditions, if the stem is not mobilizated, the use of ceramic head is rash; the Bioball adapter, instead, can be used with a old stem, so we can set a ceramic head. Every stem with a Biolox cone can be combined with a metal or ceramic head up to the 5XL size (+21 mm) through a Bioball adapter; in this way the cup is not removed. We have two kinds of neck modular adapters: 12/14 allow both to extend the neck and to correct the off-set, and 14/16 that allow to extend only the neck, because of the largest diameter of the prosthesic neck and the small thickness of the adapter. For these neck modular adapters exist different sizes, from M to 5XL (+21mm). We have also proving heads and necks. The proving and defitive heads have to be of the Bioball system because these are inserted on a modular neck with a no-standard diameter.

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P5 MIS: THE ITALIAN EXPERIENCE IN HIP SURGERY WITH SHORT STEM (TLS) Carmine Cucciniello

In order to provide proper solutions for considerable problems as dysplasia and particular/difficult femur shape (curved),research carried on and roved the short stem TLS (Toplock Short) with a proximal metaphyseal anchorage. This solution is the proper one also for easier cases as primary coxoarthrosis. Material used is Titanium alloy (Ti-A16 – 4V ), porous thanks to a corundum treatment; Morse neck is Euro 12/14 and CCD angle is 131,5°. The femoral osteotomic resection cut of the TLS stem allows to save about 2 cm of the medial cortical bone; the primary stability grows thanks to the increased strength to the torsional stresses and to the best mechani-cal features of the medial cortical bone. The stresses on the lateral cortical bone decrease at the tip of the stem too. The longitudinal section of the TLS stem shows a 14° angle: for this reason, the transfer of the proximal load and the strength to the sinking are increased. The TLS stem is about 40% shorter than a traditional stem. It’s so possible to save a big amount of the diaphysis without losing the primary stability. The tapering of the morse neck increases the range of motion, reducing the conflict with the equatorial portion of the cup and the rim-wear.

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P6 TOTAL HIP REPLACEMENT IN PATIENTS WITH CONGENITAL DYSPLASIA CROWE TYPE I AND II USING ALUMINA-CERAMIC-ON-CERAMIC BEARINGS Murphy, Stephen B.; Ecker, Timo M. Center For Computer Assisted and Reconstructive Surgery New England Baptist Bone and Joint Institute 125 Parker Hill Avenue Suite 545 Boston, MA 02120 Phone: 617-232-3040 Fax: 617-754-6436 e-mail: [email protected] Congenital dysplasia of the hip joint is one of the major reasons for development of osteoarthritis and subsequent total joint replacement. THA in patients with developmental dysplasia is associated with an increased complication rate. Pathomorphologic properties of dysplastic hip joints include low lateral and anterior center-edge angles and increased acetabular index as a sign of insufficient acetabular coverage. In addition to a dysplastic acetabulum the femur often exhibits deformities such as narrow femoral canals and the surgeon often encounters the necessity to use smaller diameter implants in many patients. These morphologic abnormalities paired with lower diameter bearings might lead to an increased complication rate. Especially dislocation and osteolysis secon-dary to increased wear are major concerns. We investigated 80 consecutive hips with Crowe type-I (76 hips) and –II (4 hips) dysplasia undergoing ceramic-on-ceramic total hip arthroplasty at a mean age of 45.9 ± 13.2 years (range 17.8 - 74.7). Twenty of the hips had one or multiple previous surgeries including pelvic and femoral osteotomies. At their preoperative consul-tation and their followup visits, patients answered questionnaires assessing their clinical performance. With this information and the findings from the routine physical examinations, patients were evaluated using the Merle d’ Aubigne score. Postoperative radiographs were screened for signs of implant failure, wear and osteoloysis along the Gruen zones. The occurrence of complications was recorded. At a mean followup of 4.1 ± 2.0 years (range 0.1 - 9) there were no radiographic signs of wear or osteoly-sis on plain x-rays. There was one (1.3%) intraoperative femoral calcar crack that was immediately treated in a type-I patient. No other complication, especially no dislocation or prosthetic failure occurred, despite the use of small diameter femoral heads, size 28 in 57.5% and acetabular components, size ≤ 50 in 58.8% of the patients. Furthermore, patients significantly improved clinically, when comparing pre- and postoperative Merle d’ Aubigne scores. Early to mid-term results of Ceramic-on-Ceramic total hip arthroplasty show sufficient safety for patients with low to middle grade developmental dysplasia. The complication rate is low, despite the use of small diameter bearings in many patients and then nonexistence of design modifications such as lipped liners in ceramic implants. The absence of dislocations in this patient cohort was encouraging. Moreover, there was no case of osteolysis at a follow-up interval up to nine years.

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P7 EXPERIMENTAL AND THEORETICAL ANALYSIS OF DIFFERENT BEARING SURFACES FOR THA Glaser D, a, Cates Hb, Komistek RD a, Mahfouz MRa, Dennis Dc, Lui Fa a University of Tennessee, Knoxville, TN, USA b Tennessee Orthopaedics Clinic, Knoxville, USA c Colorado Joint Replacement, Denver, CO, USA Diana Glaser, 301 Perkins Hall, University of Tennessee, Knoxville, TN 37917 Email: [email protected], Phone: 865-974-1936, Fax: 865-946-1787 Sounds generated through the implant interaction are possibly an outcome of a forced vibration induced by a driving force and resulting in dynamic response. The driving force can be associated with the impact follow-ing hip separation and the dynamic response may give insight into implant and bone properties and conditions. It is hypothesized that vibration, in the range of the resonance frequencies, may cause pain, bone degeneration and frac-ture. A further understanding of the physical response resulting from impact during femoral head sliding may lead to valuable insight pertaining to THA failure. Therefore, the objective of the present study was to assess in vivo mechanical properties of implant, bone and fixation for subjects having a total hip arthroplasty with varying bear-ing surfaces and examine hip joint forces associated with the different implants. Gait kinematics and corresponding vibration measurement of twenty subjects following THA were ana-lyzed post-operatively under in vivo, weight-bearing conditions using video fluoroscopy and accelerometer. The subjects included in the study had metal-on-metal, metal-on-polyethylene, ceramic-on-ceramic, ceramic-on-polyethylene or metal-on-metal polyethylene-sandwich THA and performed gait on a level treadmill. The surgical procedure was performed by the same, fellowship-trained surgeon. All patients with excellent clinical results, with-out pain or functional deficits were invited to participate in the study (HHS > 90). Accelerometers, externally at-tached to the pelvic and femoral bony prominences, were used to derive transfer functions across the joint and find resonant frequencies propagated through the hip interaction. A data acquisition system was used to amplify the signal and to filter out the noise. A 3D mathematical model based on inverse dynamics and reduction technique was implemented to determine the in vivo contact and soft tissue forces. In vivo kinematics, obtained using 3D-to-2D image registration technique, were used as input to the model. The maximum bearing surface forces ranged from 2.1 to 3.4 times body weight and was most likely to occur close to 33% of the stance phase. Hip joint separation was also demonstrated by certain subjects in this study and lead to impulse loading conditions. We found statistical difference between the groups as well as a notable difference in the standard deviation among the subjects in each group. The femoral frequency spectrum derived for subjects in this study were similar in nature to previously published data. There is no known published data on the natural frequencies of the pelvis, which were determined in this study and lead to variable results for the different bearing surface material. Frequencies propagating through the hip joint near resonance may lead to undesirable conditions and increased forces. Performance of the different THA designs is usually evaluated using outcomes related to range-of-motion, survi-vorship, and wear. In contrast, our study showed that there are differences in kinematics, kinetics, separation, fre-quencies and intra-group variation between the analyzed implant systems. Force and frequency identification under in vivo conditions for THA generates new possibilities for better understanding of wear and failure modes in THA.


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P8 DOES SEPARATION VARY WITH DIFFERENT SURGICAL TECHNIQUES: TRADITIONAL POSTEROLATERAL VS. MINIMALLY INVASIVE ANTEROLATERAL AND POSTER-OLATERAL THA Glaser D a, Miner TMb, Komistek RD a, Mahfouz MRa, Dennis DAb ,Anderle MRa a University of Tennessee, Knoxville, TN, USA b Colorado Joint Replacement, Denver, CO, USA Diana Glaser, 301 Perkins Hall, University of Tennessee, Knoxville, TN 37917 Email: [email protected], Phone: 865-974-1936, Fax: 865-946-1787 Minimally invasive surgery (MIS) is theorized to have clinical advantages compared to traditional THA. However, concerns related with the smaller incision include: reduced visualization and the following possibility of implant malposition, neurovascular injury, or compromised long-term outcome. Current reports on MIS THA have primarily focused on early functional results, complication rates, amount of blood loss, rehabilitation time, implant position and severity of pain. Therefore, need of objective research on the weight-bearing in vivo kinematics for comparison of subjects implanted with either traditional or MIS approaches has become important. The objective of the study was to determine if the type of surgical technique affects the incidence and magnitude of separation during gait. The post-operative gait characteristics of thirty subjects were evaluated using fluoroscopy while perform-ing gait on a treadmill. Three groups were build based on the surgical approach: 10 patients who underwent THA using traditional THA, 10 patients using MIS anterolateral approach (AL) and 10 patients using a MIS poster-olateral approach (PL). The surgical procedure was performed by the same, fellowship-trained surgeon. All pa-tients with excellent clinical results, without pain or functional deficits were invited to participate in the study (HHS>90) and were evaluated approximately six months following surgery: 6.2 months (3.5-12), 6.9 months (2.3-12) and 5.0 months (3.5-9.5) post-op for the traditional, AL MIS and PL MIS patients, respectively. Groups were matched for age, body mass index, follow-up and femoral head diameter to control for variables possibly having influence on the hip performance and gait kinematics. In-vivo translational and rotational kinematics, derived from 3D-to-2D image registration technique, were used to determine the distance between the femoral head and the acetabular component and diagnose if separation had occurred. Six of ten subjects (60%) having a traditional THA experienced greater than 0.5mm of femoral head slid-ing within the acetabular component. The incidence of separation for the subjects implanted using a minimally invasive approach was much less. Only 1/10 subjects (10%) implanted using an AL-MIS and 2/10 subjects (20%) implanted using a PL-MIS experienced greater than 0.5 mm of separation. The average magnitude in subjects im-planted using a standard approach was 0.59mm (0.38–1.10). The average separation for subjects implanted using a MIS THA was 0.42mm (0.32– 0.64) and 0.47mm (0.35–0.68), for those having an AL-MIS or PL-MIS, respec-tively. There was also a significantly higher hospitalization and variance within the traditional THA subjects, indi-cating more inconsistent results. No significant difference was observed between both MIS procedures. The improved gait kinematics for the MIS patients may be related to a reduction in disruption of soft tis-sue structures important in hip joint stabilization. Objective data pertaining to the benefit of MIS-THA has been limited yet. The present information clearly demonstrates that use of MIS approaches results in more favorable kinematic patterns with a reduced incidence and magnitude of separation. However, whereas the differences be-tween the MIS and traditional approaches early post-operative are statistically significant, further studies are needed to prove if superior results can be maintained over long term.


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P9 THE CONSERVE-PLUS METAL-ON-METAL HIP RESURFACING SYSTEM: SURGICAL TECHNIQUE, CLINICAL RESULTS AND COMPLICATIONS ON A CONSECUTIVE SERIES Pier Francesco Indelli, Thomas Parker Vail Department of Orthopaedic Surgery, Duke University Medical Center, Durham, North Carolina, U.S.A.

This study represents our experience using the Conserve-Plus (Wright Medical) resurfacing system and a postero-lateral approach in a consecutive series of patients. MATERIAL and METHOD: The authors implanted 45 consecutive Conserve Plus resurfacing systems in 40 patients. The study group included 30 males and 10 females with an average age of 47 years (22-64 years). The preoperative diagnosis was arthritis in 36 patients and avascular-necrosis in 9. The procedure was bilateral in 5 cases (3 in one stage). The clinical evalua-tion was done according to the Harris Hip Score. RESULTS: The average length of stay was 3.48 days. All patients were prospectically evaluated at 3, 6, 9, 12, 24 months from surgery. The average Harris Hip Score increased from 48.1 before the operation to 95.5 at 6 months from surgery, to 97.3 at one year, and to 97.0 at two years (min 85-max 100). The pain score moved from 12 to 43 at two years. The radiographic evaluation at two years showed the presence of peri-acetabular radiolucent lines in 5 cases: all of them were non-progressive and less than one millimeter in width. The authors registered 5 postoperative compli-cations: one a-traumatic femoral neck fracture at 6 weeks requiring conversion to a total hip arthroplasty, 3 asymp-tomatic “clicks”, and one eterotopic ossification. The authors did not register any complications linked to the surgi-cal technique. CONCLUSION: The metal-on-metal hip resurfacing system represents an interesting alternative to standard hip replacements, thanks to the improvement of the materials and designs. Our promising results must to be confirmed by larger stud-ies with a longer follow-up.

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P10 WHAT IS A NORMAL KNEE LAXITY ? JENNY Jean-Yves, BOERI Cyril, CIOBANU Eugène Hôpitaux Universitaires de Strasbourg, Centre de Chirurgie Orthopédique et de la Main, 10 avenue Baumann, F-67400 Illkirch-Graffenstaden (France) Tel +33388552145, Fax +33388552146, E-mail [email protected] INTRODUCTION:

To get an optimal ligamentous balance is recommended during total knee replacement. But the goal to be achieved remains unclear, especially because the normal knee laxity in vivo is not well documented. The ligamentous bal-ancing during total knee replacement remains mainly on surgical skill. However, navigation system are very pow-erful tools to measure intra-operative knee laxity and might help achieving an optimal balance. We designed this study to define the normal laxity of the knee in vivo with the same navigated measurement technique than that used in clinical practice for total knee replacement.

MATERIAL:

20 patients operated on for isolated anterior cruciate ligament instability have been documented. The medio-lateral knee laxity has been measured by a non-image based navigation system before the ligament replacement, assuming that there was no significant lesion of the collateral ligaments.

METHODS:

The authors used the OrthoPilot ® navigation system (Aesculap, Tuttlingen, FRG). Infrared trackers were fixed by percutaneous bicortical screws on the distal femur and the proximal tibia, and strapped on the foot. A kinematic and anatomic registration was performed by moving hip, knee and ankle joints and palpating several relevant ana-tomical landmarks with a navigated stylus. Then the mechanical coronal femoro-tibial angle was measured in full extension and at 90° of knee flexion without stress and with a manual maximal stress in varus and valgus. The an-gle variation between the stressless and the varus or valgus measurements was considered as the lateral or medial laxity measurement.

RESULTS:

The mean medial laxity in extension was 3° ± 2° (range, 1° to 6°). The mean lateral laxity in extension was 3° ± 2° (range, 2° to 8°). The mean medial laxity at 90° of flexion was 2° ± 2° (range, 0° to 4°). The mean lateral laxity at 90° of flexion was 4° ± 2° (range, 2° to 8°).

DISCUSSION: The software used allows measuring accurately the ligamentous laxity of the knee, specially in the coronal plane. No controlled force was used, by the previous experience of the authors showed that there was little change in the maximal laxity bu using calibrated spreaders in comparison to manually applied forces. The results of the present study are well fitted to the current literature of in vitro studies. But to transfer in vitro results to the in vivo situation may lead to some errors, if the measurement technique is different in the two situation. This is the first study defin-ing the normal laxity of the knee in vivo with the same navigated measurement technique than that used in clinical practice for total knee replacement. CONCLUSION: To define the physiological knee laxity is a prerequisite when defining the goals to be achieved when balancing a knee during total knee replacement.

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P11 DOES COMPUTER ASSISTED SURGERY AID IN SHORTENING THE LEARNING CURVE IN M-O-M SURFACE REPLACEMENT? Seyler Thorsten, Ward William G, Sprinkle Denise E, Jinnah Riyaz H Wake Forest University Health Sciences, Medical Center Boulevard, Winston-Salem, NC 27157-1070 Phone 336-716-9657, Fax 336-716-6286, [email protected] Resurfacing arthroplasty is again beginning to become popular due to its theoretical advantages of better mechan-ics and bone preservation. However, there is now data available to show that there is a significant learning curve involved in performing M-o-M resurfacing arthroplasty. In an attempt to see if this learning curve could be shortened, we performed ten computer assisted surgeries utiliz-ing the Brain Lab ® System. Radiographic parameters of these patients were compared to the results of ten pa-tients who had surgery performed utilizing the Wright Medical ® instrumentation performed by the same surgeon. Neck shaft angles, anteversion/retroversion, overhang, and seating of the femoral components were compared. The results of these comparisons will be presented.

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P12 UNCEMENTED CERAMIC ON CERAMIC ARTICULATION TOTAL HIP REPLACEMENT FOR DYSPLASTIC OSTEOARTHRITIS – FIVE OR MORE YEAR FOLLOW-UP Kusaba Atsushi, Kondo Saiji, and Kuroki Yoshikatsu Institute of Joint Replacement and Rheumatology, Ebina General Hospital Phone: +81-462-33-1311 Fax: +81-462-32-8934 e-mail: [email protected]

Since the establishment of our institute, mainly we had adapted Spongiosa Metal Hip System (ESKA im-plants, Luebeck, Germany) with polyethylene / ceramic articulation. The long-term stability of the implants was excellent. However, as far as using polyethylene / ceramic articulation, the lifetime pf the implants should be lim-ited because of the polyethylene wear.

Expecting the low wear property, since October 1998, we started to use Spongiosa Metall II Total Hip System

combining with ceramic on ceramic articulation (Biolox Forte, Ceramtec AG, Plochingen, Germany). Until De-cember 2006, we had replaced 524 hips with this type of implants. Among them, we evaluated 102 hips in 97 pa-tients (male 3, female 94) with five years or more follow-up. The preoperative diagnosis was dysplastic os-teoarthritis for all patients, including seven hips of failed pelvic and / or femoral osteotomy, three hips of Perthes like head deformity, two hips of completely dislocated hip. The average age at the surgery was 59 (45 to 75). The average of follow-up period was six years and one month (five to eight years).

The implants have a macro-porous structure on the surface (80% of porosity, 1 to 3 millimeters pore size). The

Harris hip score was improved in all patients. The average amount of the hip score was 62 (30 to 83) points before the surgery and was 91 (69 to 100) points at the final follow-up. A positive Trendelenburg sign was observed in 65 hips (64%) before the surgery and 11 hips (11%) at the final follow-up.

We had no severe postoperative complications, such as deep thrombosis, paralysis, infection, breakage, and

dislocation. No patient required the revision surgery. At the final follow-up, all cups were stable. All stems except one were stable. One stem slightly migrated into a varus position until two years after the surgery. However, after that the stem became stable until the final follow-up. In the acetabulum, the radiolucent line was observed in two hips (2%)(zone I). In the femur the line was observed in 15 hips (14%). All lines existed in the proximal femur. There was no cystic osteolytic lesion. The prevalence of these periprosthetic reactions was less than those in the same type implant with the polyethylene on ceramic articulation. There was no breakage of the ceramic compo-nents. Some authors alerted that ceramic on ceramic articulation should only be applied in the case that optimized implant orientation preventing impingement and dislocation. Fortunately the alignment in this study may be within the safe zone. However, we must always be very careful of the joint alignment, range of motion, and the muscle tension during the surgery to avoid the breakage.

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P13 THE EOS” 2D-3D X-RAY SCANNER: A NEW TECHNOLOGY TO ASSESS THE TRIDIMENSIONAL POSITION OF T.H.P. CUPS JY Lazennec, A Baudoin, D Mitton, W Skalli, A Rangel, Y Catonne Département de chirurgie orthopédique Hopital La Pitié-Salpétrière, 47-83 Boulevard de l’hôpital, 75013 Paris Introduction: Accurate evaluation of pelvis position in functional situations as standing or sitting may help for THP adjustment. EOS" low irradiation 2D-3D X-ray scanner is an innovative technology already used for spinal evaluation. The aim of this study is to compare the data obtained with the EOS" system and the measures from classical CTscan cuts replicating standing and sitting positions for THP with cementless cup. Methods: EOS" system provides simultaneously 2 orthogonal Xrays of the whole body including the lower limbs. Recon-struction cuts are easily obtained to calculate the true anterior opening or anteversion of the acetabulum for stand-ing and sitting positions .The results have been compared to CTscan measures on section planes for the same posi-tions . It has been demonstrated that CTscan cut replicates the horizontal transverse plane in standing position when the inclination of the section plane forms with the upper sacral endplate an angle equal to standing sacral slope. The same principle is used for sitting sacral slope. Results: Mean cup anteversion is 20° for standing position and 41°,2 for sitting position on CTscan ; mean values are re-spectively 19° and 40°,2 for EOS". The mean difference CTscan versus Eos" system is 4,4° with comparable accu-racy and reproductibility. In case of pelvic rotation CTscan measures are inaccurate,as the lying position does not take in account this functional situation ; true cup anteversion can be correlated to the pelvic torsion angle using the Eos". Discussion and Conclusion: EOS" systems brings new perspectives with lower irradiation than classical CT scan measures

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P14 CLINICAL AND BIOLOGICAL FOLLOW-UP FOR A CEMENTED TITANIUM FEMORAL STEM: A TWELVE-YEAR EXPERIENCE Jean-Yves Lazennec PhD, Patrick Boyer MD, Joel Poupon MD, Marc-Antoine Rousseau MD,Phillipe Ravaud PhD, Yves Catonne MD Département de chirurgie orthopédique Hopital La Pitié-Salpétrière, 47-83 Boulevard de l’hôpital, 75013 Paris Introduction: The use of cemented titanium femoral stems remains highly controversial. This study reports our experience with 9 years mean follow-up (7-12). Methods: From 1995 to 2000, 119 total hip replacements (26 bilateral) were enrolled in a prospective study including clini-cal, radiological assessments and titanium serum level determination at regular time-points. The stem was smooth, cemented and made of titanium alloy coated with an anodic oxidation layer. Results: The average Hip Score improved from 29 to 90 at the last review. 7 revisions were performed for cup aseptic loos-ening (4), early recurrent dislocations (2) and one severe stem subsidence. Two other stems showed slowly pro-gressive subsidence, both inferior to 5 millimetres. Non-progressive radiolucencies in zone 1 and 7 were observed in 14 hips at the cement-interface (14/119) without osteolysis. Serum titanium concentrations were recorded until the last time-point: the median values were always below the detection limit (30 nmol/l) in patients with uncompli-cated stem, even with bilateral total hip artroplasties. All patients with failed stems demonstrated values highly above the detection threshold. Discussion and Conclusion: The overall survival rate of the stems was 96,4% at a mean follow-up of 9 years leading to a very acceptable fail-ure rate compared to other series with stainless steel or cobalt chrome cemented stems. We suggest that the protec-tive titanium oxide coating on the smooth stem and the cementing with a homogeneous and thick mantle play a significant role for resistance to aseptic loosening and limit ions serum release. This series confirms clinical results previously reported with cemented anodized femoral stems.

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P15 BIOMECHANICAL EVALUATION OF ACETABULAR COMPONENT POLYETHYLENE STRESSES, FRACTURE RISK, AND WEAR RATE DURING PRESS-FIT IMPLANTATION Ong, Kevin; Rundell, Steve; Markel, David; Kurtz, Steven 22250 Providence Drive Suite 401 Southfield, MI. 48075 Tel: 248-569-0306 [email protected] Acetabular component deformation may occur during press-fit implantation due to cortical bone loading along the anterior-superior and posterior-inferior acetabular margins, resulting in two-point pinching. However, the biomechanical and clinical consequences of liner pinching due to press-fit implantation are unclear. Consequently, we compared the effects of press-fit pinching on the polyethylene fracture risk, potential wear rate, and stresses for two different thickness inserts using computational methods. Finite element models of a Trident® shell (size 50E) with X3™ polyethylene insert wall thicknesses of 5.9 mm (36E) and 3.8 mm (40E) were developed. Line-to-line (“no pinch”) reaming and 2 mm under-reaming press fit (“pinch”) conditions of the acetabulum were examined. The cups were loaded to 3 kN with relevant femoral head rotations. Molecular chain stretch (fracture risk), peak contact stresses, and predicted volumetric wear rate were compared. Volumetric wear rates for X3™ were cali-brated against previous hip simulator experiments (Herrera, 2007). Molecular chain stretch did not exceed the failure threshold in all cases. Pinching was estimated to in-crease the volumetric wear rate from 3.0 to 3.9 mm3 and 3.0 to 5.1 mm3 per 106 cycles for the 36E and 40E compo-nents, respectively. Pinching increased the peak contact stresses from 4.5 to 8.1 MPa (36E) and 4.0 to 13.0 MPa (40E). Although pinching increases insert stresses, particularly for thinner inserts, polyethylene fracture is highly unlikely and the volumetric wear rates are likely to be low compared to conventional polyethylene. Cup deforma-tion depends on many factors including bone quality, reamed bone geometry, and implant design.

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P16 KNEE ARTHROPLASTY KINEMATICS DURING PIVOTING— HOW MUCH ROTATION IN EXTENSION? Moonot P, Railton G, Mu S, Banks SA, Field RE Total knee arthroplasties (TKA) generally are designed to accommodate flexion, axial rotation and anteroposterior translation. The amount of axial rotation allowed near extension varies widely according to design, with some rotating platform devices allowing unrestricted rotation and some conforming fixed-bearing designs allowing al-most none. The purpose of this study was to examine in vivo kinematics of a fixed bearing medial rotation type knee arthroplasty during a standing pivot activity. Eleven patients with medial-pivot TKA were observed during a pivoting maneuver using lateral fluoroscopy. Sub-jects started with their contralateral leg and body rotated away from the stance leg, and then pivoted on their im-planted stance leg to induce maximum axial rotation of the stance leg. Subjects averaged 73 years of age and seven were female. Subjects were an average of 16 months post-operative, and scored 94 points on the Knee Score. Digi-tized fluoroscopic images were corrected for geometric distortion and 3D models of the implant components were registered to determine the 3D position and orientation of the implants in each image. Tibiofemoral axial rotation range during pivoting averaged 8° (2°-19°). The center of rotation was located near the mediolateral and anteroposterior center of the medial plateau (20% of the ML width to the medial side of center, and 10% of the AP width posterior to the AP midline). The amount of axial rotation during pivoting averaged 8 degrees; more rotation than some designs allow. Contact stresses in rotationally conforming articulations must increase to constrain rotation – this may be required for sta-bility, but may also accelerate bearing surface damage. The amount of axial rotation varied considerably, likely due to muscle and ligamentous contributions to joint rotational laxity. In patients with competent collateral liga-ments, a rotationally unconstrained articulation will accommodate varying patient activities and joint laxity without unnecessarily restricting joint motion.

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P17 ANALYSIS OF TANTALUM IMPLANTS USED FOR AVASCULAR NECROSIS OF THE FEMORAL HEAD: A REVIEW OF FIVE RETRIEVED SPECIMENS Montero M. Murcia A., Fernández -Fairén M. Avda. Rufo García Rendueles 6, 11D 33203 Gijón .Asturias. Spain Tel: +34630199143 Fax: +34985131743 E-mail: [email protected] This research was done in the Instituto de Cirugia Ortopédica y Traumatologia de Barcelona. Spain . For this study, five rod implants used for the treatment of avascular necrosis of the femoral head were retrieved following collapse of the femoral head and conversion to total hip arthroplasty. The time of implantation ranged between six weeks and twenty months . Observation during this study has confirmed the effectiveness of osseointegration within this period of time. New bone was observed around and within the porous system of the on rod devices at retrieval date. The bone in-growth however, proved to be of a slower and less intense degree than that resulting within animal species during the first months after implantation. Nevertheless, the results obtained in the quantitative evaluation of this process proved to be similar to those results achieved by other authors in previous experimental work-studies. Our findings included: The effective results shown in the porous systems of tantalum employed for the use of osseointegrates has been demonstrated through animal experimentation. However, there is a total lack of any stud-ies carried out in research on the osseointegration of tantalum implants from retrieval of the same after a period of time whereby the material had been implanted within the human body.


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P18 NAVIGATED ARTHROSCOPIC PERCUTANEOUS OSTEOCHONDROPLASTY IN PATIENTS WITH FAI USING A NEW METHOD OF CT-FLUORO REGISTRATION - PRELIMINARY EXPERIENCE Murphy, Stephen B.; Ecker, Timo M. Center For Computer Assisted and Reconstructive Surgery New England Baptist Bone and Joint Institute 125 Parker Hill Avenue Suite 545 Boston, MA 02120 Phone: 617-232-3040 Fax: 617-754-6436 e-mail: [email protected] Pathomorphologic deformities associated with femoroacetabular impingement are a major cause of early osteoarthritis in young and active patients. These deformities are apparent in over 94% of hips that are at an early arthritic stage, concluding that these findings are not a consequence of endstage arthrosis but rather preexist as prearthrotic deformities. While open osteochondroplasty has been recognized as an effective treatment option in these patients, the current trend to apply arthroscopic techniques has been popularized but is not without risk. Es-pecially limited visualization and recognition of important structures may lead to complications. Combination of arthroscopic techniques with surgical navigation might address this issue. We report on our preliminary experience with a new Fluoro-CT registration method for navigated arthroscopic osteochondroplasty of the hip. We applied this method successfully to 4 patients scheduled for arthroscopic osteochondroplasty for femoroacetabular impingement. The patient is prepped in supine position on the operating table. It is beneficial, but not mandatory, to use a trauma table that permits fluoroscopy. Pelvic and femoral reference frames are affixed. First, the fluoroscopic images are taken with a c-arm equipped with a fluoroscopy kit. The first image is an ap-image including the femoral head and hip center. Then the second image is taken as an oblique image of the pelvis visualizing the pubic symphysis, the obturator foramen and parts of the femoral head. The 2D information of the fluoroscopic images is subsequently registered to a 3D CT dataset obtained preoperatively. For preliminary align-ment, paired-point matching for the femoral condyles and the ipsilateral ASIS are taken. The system then calcu-lates and registers the two-dimensional images to the 3D dataset by knowing the spatial orientation of the images taken. As a final step in registration, accuracy is checked with the navigation system and the digitizing probe by showing the distance of the probe to bony landmarks. After accurate registration has been confirmed, the procedure is performed using navigated instruments. Unlike isolated arthroscopy, the combination with the navigation system enables the surgeon to use the normal arthroscopic images, the images of the navigation system, or a combination of both to have good orientation and to adequately address all pathologic structures. We managed to establish successful and accurate registration in all four cases. Subsequent to confirming registration, the percutaneous arthroscopic osteochondroplasty was carried out in accordance with the detailed pre-operative plan. Our preliminary experience suggests that the new method of CT-Fluoro registration has the potential to improve the precision and safety with which percutaneous osteochondroplasty can be performed. The application of surgical navigation to percutaneous osteochondroplasty may decrease surgical morbidity while ensuring that an appropriate osteochondroplasty is performed.

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P19 A NOVEL SYSTEM FOR LEG LENGTH MEASUREMENT IN COMPUTER ASSISTED TOTAL KNEE ARTRHOPLASTY Nadzadi, Mark E.; Ecker, Timo M.; Lang, Jason and Murphy, Stephen B. Center for Computer Assisted and Reconstructive Surgery New England Baptist Bone and Joint Institute 125 Parker Hill Avenue Suite 545 Boston, MA 02120 Phone: 617-232-3040 Fax: 617-754-6436 e-mail: [email protected] Change of limb length is an important parameter in joint replacement procedures. While this has been investigated for hip arthroplasty in many studies, there are currently no reports in the literature concerning the im-pact of total knee arthroplasty on leg length. Leg length discrepancy leads to unsteady gait and uneven force distri-bution. Besides patient discomfort, this might lead to increased implant wear and early prosthetic failure. Changes in limb length derive from correction of deformities in the coronal or sagittal plane and by change in joint line po-sition of the femur and tibia after implantation of the prosthesis. The current study aims to measure change in limb length resulting from total knee arthroplasty. Seven knees in seven patients underwent computer-assisted total knee arthroplasty. All patients gave con-sent to an IRB-approved protocol. After fixation of tibial and femoral reference frames the navigation system (Achieve CAS, Smith-Nephew, Memphis, TN) was initialized. A second navigation system (the kinematic assess-ment system) was used for simultaneous continuous recording of the positions of the same femoral and tibial skele-tal reference frames. The kinematic assessment system was used to calculate the center of rotation of the hip and to record the ankle landmarks. After recording the preoperative kinematics and landmarks, the limb was held in a fully extended position to allow for calculation of the maximum distance between the hip center and ankle center for leg length assessment. The posterior cruciate ligament preserving total knee prosthesis (Genesis II, Smith-Nephew, Memphis, TN) was then implanted as usual. At the completion of the procedure, the knee was examined again and leg length measured again as done preoperatively. Change in overall limb length was then calculated comparing pre- and postoperative values. Limb length increased for an average of 5.68 mm (range 2.83-9.19 mm). Limb length change due to cor-rection of coronal malalignment, which depended on the degree of coronal malalignment correction, averaged 1.55mm (range 0.27-5.48mm). The preoperative coronal malalignment ranged from 4.83 degrees of varus to 9.38 degrees of valgus, and the postoperative coronal alignment averaged 0.29 degrees of varus (range 2.20 degrees of varus to 1.27degrees of valgus). The pre and post measurements were matched based on sagittal contracture. Therefore, if the patient had a flexion contracture preoperatively that was remedied during the operation the post-operative data is matched for flexion angle. Because of this pairing, no statement can be made on the contribution of sagittal contracture to the overall limb lengthening. The limb length change due to the superior/inferior changes in the joint lines of the femoral and tibial components averaged 4.14mm (range 2.47-6.32mm). Concluding, we found an expected increase in limb length in all cases. While deliberate change in limb length currently cannot reliably be controlled for during primary total knee arthroplasty, our approach offers prom-ising preliminary results. Equalization of length is essential for subjective patient comfort and important for long-term prosthesis survival. However, the current study has only investigated cruciate retaining implants and did not investigate the effect of total knee arthroplasty using posterior cruciate sacrificing prostheses.

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P20 16 to 21 YEAR CLINICAL RESULTS OF TOTAL HIP ARTHROPLASTY WITH HA GRANULES AT CEMENT-BONE INTERFACE (Interface Bioactive Bone Cement) Oonishi Hironobu, Oonishi Hiroyuki Jr., Kim Sok Chol, Ohashi Hirotsugu and Ojima Satoshi (H. Oonishi Memorial Joint Replacement InstituteTominaga Hospital 1-4-48, minato-machi, naniwa-ku, Osaka-shi, 556-0017, Japan) ( 81-6-6568-1601/81-6-6568-1608/[email protected]) Introduction: In THA, implant-bone interface is one of the critical factors for the longevity. Long term after THA spaces will appear at the interface of bone cement and bone or cementless fixation after the onset of osteoporosis due to aging of the bone, and osteolysis will increase due to increasing of wear particles. It would be a revolutionary idea to interpose non-resorbable and osteoconductive HA at the bone and bone cement interface and expect chemical bonding of HA with bone and osteoconduction eternally. Materials and Methods: As a surgical procedure, HA granules are smeared on the bone surface just before the cement insertion. After two weeks, new bone ingrowth into the spaces of HA granules is completed and bone and bone cement are bound chemically by interposing HA granules. We call this “Interface Bioactive Bone Cement” or IBBC. Since 1986, IBBC has been used in THA and TKA. In the first generation (1986 to 1988), HA granules size of 0.3 to 0.5 mm in diameter was used. In the second generation (1989 to 1991), HA granules size of 0.1 to 0.3 mm in diameter was used. We evaluated 16 to 21 year clinical results of THA with IBBC. THAs were performed in 265 joints in the first generation and in 297 joints in the second generation. Diseases were 88% in OA and 10% in RA. Follow-up rates were 90% and 89%, respectively. Results: When IBBC is performed in the bleeding area, mechanical fixation between bone cement and HA is obstacled and “the space” will appear after surgery. When IBBC is performed in the bleeding area without anchor holes as an initial fixation, “the separation” will appear after surgery. After 16 to 21 year follow-up, space was observed in 4 hips (1.8%) in the 1st generation and in 15 hips (6.2%) in the 2nd generation (P < 0.01). Loosening or Separation was observed only 2 cups (0.8%) in the 2nd generation. They appeared only between cement and HA when IBBC was performed in the bleeding area. Osteolysis was ob-served in one hip (0.5%) and 6 hips (1.6%), respectively Discussion: Larger granules can jut out from accumulated blood and do not make space between HA and cement. In conventional bone cement and cementless fixation, radiolucent line will appear after the onset of osteoporosis due to aging, and osteolysis will increase due to increasing of wear particles. When crystalline HA granules exist at the bone interface, new bone formation will be continued even after the onset of osteoporosis and radiolucent lines will never appear, and even after the occurrence of osteolysis, it will be repaired by the osteoconduction of HA and the osteolysis will never progress. IBBC could be expected super long term longevity of THA.

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P21 COMPUTER ASSISTED TOTAL KNEE ARTHROPLASTY: A NOVEL “PINLESS” TECHNIQUE TO RECONSTRUCT A NEUTRAL MECHANICAL AXIS Puri, Lalit; Moen, Todd C.; Rana, Nasim; Wixson, Richard L. Northwestern University Department of Orthopaedic Surgery 645 North Michigan Avenue, Suite 910 Chicago, IL 60611 Phone: (312) 908 7937; Fax: (312) 908 8479; e-mail: [email protected] Introduction: Computer-Assisted Total Knee Arthroplasty (TKA) has been shown to improve clinical outcomes by allowing for more accurate coronal alignment of the components, less variance, and fewer “outliers” than traditional reconstruc-tion techniques. Most computer-navigation systems utilize rigidly-fixed trackers placed on both the femur and tibia in conjunction with a computer workstation and navigation software to determine the mechanical axis of the extremity intraoperatively, in real time. The purpose of this study was to report an initial single-surgeon experi-ence with a novel navigation system that utilizes a “pinless” technique with trackers mounted at the articular sur-face, not rigidly-fixed to the femur and tibia.

Methods: 30 consecutive patients underwent a TKA using a novel “pinless” navigation system. At 4 weeks post-operatively, coronal alignment was assessed with long-standing AP radiographs. Comparison was made with a representative cohort of 30 consecutive patients who underwent a TKA with traditional manual alignment. The Navigated and Traditional groups were compared with the student’s paired t-test.

Results: The average alignment for the Navigated group was 0.3° +/- 1.6° valgus. Variance was 2.5 . The average align-ment for the Traditional group was 1.0° +/- 2.0° varus. Variance was 4.0 . Three traditional knees had a coronal mechanical axis of 4° valgus. All Navigated knees were within 3° of neutral alignment. These results approached but did not achieve statistical significance

Discussion: This study reports an initial single-surgeon experience of a novel “pinless” navigation technique for TKA. These results suggest that this technique is a safe and effective means to reconstruct a neutral mechanical axis. Further investigation is warranted, and ongoing.


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P22 COMPUTED TOMOGRAPHY TO ASSESS ACETABULAR LOOSENING PRIOR TO REVISION HIP ARTHROPLASTY Thangamani Vijay B, Pribaz Jonathan R, Puri Lalit, Stulberg S David, Wixson, Richard L. Northwestern University Feinberg School of Medicine, Department of Orthopaedic Surgery, 645 N. Michigan Ave. Suite 910 Chicago, IL 60611. Phone: 312-908-7937, Fax: 312-908-8479, Email: [email protected] Advanced imaging modalities such as high resolution Computed Tomography (CT) are often used to assess prob-lematic total hip arthroplasties, with particular emphasis on extent of osteolysis. The purpose of this study was to determine if computed tomography (CT) can be used as a tool to diagnose or confirm metal backed acetabular loosening. An IRB approved retrospective study was performed. Thirty five consecutive revision hip arthroplasties without clear radiographic evidence of acetabular aseptic loosening were identified and their hospital and clinic charts re-viewed. All thirty five patients had pre-operative CT scans based on an algorithm developed at our institution spe-cifically aimed at evaluating patterns and amounts of osteolysis. In seven cases, acetabular loosening was found intra-operatively and subsequent acetabular revisions were per-formed at that time. Retrospective review of the CT scans confirmed loosening in all seven cases with evidence of acetabular ingrowth in the remaining twenty eight cases. CT scans can be of great value is assessing osteolysis after hip arthroplasty. We have found that careful review of CT scans can result in high sensitivity and specificity when diagnosing loose acetabular components when radio-graphs cannot confirm this.


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P23 RESULTS OF KNEE MANIPULATION FOR STIFFNESS AFTER TOTAL KNEE REPLACEMENT WITH AND WITHOUT INTRA-ARTICULAR INJECTION OF STEROID

Vineet Sharma, MD, Amar S. Ranawat, MD, Chitranjan S. Ranawat, MD. Stiffness after TKR requiring a manipulation has an incidence of 1.7 to 11 %. The purpose of this study was to report the incidence of stiffness warranting manipulation with 2 different pain management protocols. Also we report the results of manipulation with or without injection of a cocktail of various medications including steroid given at the time of manipulation. Materials and Methods: A total of 286 TKR’s done between January, 2002 and December, 2003 formed the 1st group of patients. No intra-articular injection was given at the time of TKR for pain control and all patients received PCA. The 2nd group con-sisted of 292 TKR’s done between January, 2004 and March, 2006. These patients had an injection of pain control cocktail at the time of surgery. All patients in this group received an injection of steroid and pain medications at the time of manipulation. Only patients with minimum 6 months follow up after manipulation were included in the study. Results: The overall incidence of stiffness requiring manipulation in both groups was 2.45 and 2.05% respectively. The results of manipulation with or without injection showed a significant improvement in final ROM in patients who had an injection along with manipulation. The difference was due to the fact that patients who had an injection lost very little motion from the value achieved at the time of manipulation. Conclusion: We conclude that injection of a pain control cocktail at the time of TKR does not influence the incidence of stiff-ness. Also injection of this control cocktail along with manipulation does have a significant influence on final ROM achieved.

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P24 DOES EVERSION OF THE PATELLA CAUSE PATELLA BAJA?

Vineet Sharma, MD, Amar S. Ranawat, MD, Chitranjan S. Ranawat, MD. There have been claims by some surgeons that eversion of patella leads to patella baja. Studies have shown that decease in patellar tendon length measured by Insall-Salvati ratio (ISR) occurs in 50% of cases and patella baja (defined as ISR < 0.8) in 9.7% cases. The purpose of the present study was to establish if patellar eversion during TKR leads to patella baja. Materials and Methods: A total of 58 consecutive total knee replacements (TKR) were reviewed retrospectively. All knees were operated with a midline incision (10-20 cm) and with eversion of patella. Lateral radiographs (in 30-35 degrees flexion) before surgery and at 6 weeks and 1 year were evaluated for ISR. Two surgeons evaluated the radiographs inde-pendently. For this study, a change in ISR by 0.10 ratio units compared to pre-operative ratio was considered sig-nificant. Results: No patient had pre-operative patella baja. Fifty out of 58 knees had the ISR ratio within 0.10 of the pre-operative value. In 6 knees, the ratio increased and in 2 knees it decreased from the pre-operative value. No patient had post-operative patella baja. There was no difference in KSS for pain and function between patients with decrease in ISR and the rest of the group. Discussion: We conclude that everting the patella at surgery does not increase the risk of patella baja. The reported cases in the literature are probably due to either pre-existing patella baja or surgical errors like elevating the joint line. ISR- Insall-Salvati Ratio TKR- Total Knee Replacement.

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P25

IMPROVEMENT OF CEMENT MANTLE WITH PRESSURIZED CARBON DIOXIDE LAVAGE Goldstein Wayne M, Gordon Alexander, Goldstein Jeffery M, Berland Kim, Branson Jill, Sarin Vineet K Illinois Bone and Joint Institute. 8930 Waukegan Road. Morton Grove, IL 60053 Phone: 805-384-2748, Fax: 805-384-2792, Email: [email protected] Bone-cement interface strength is influenced by cement penetration depth achieved intra-operatively. In ce-mented total knee arthroplasty, implant longevity and resistance to osteolysis depends on the presence of an ade-quate cement mantle. This study evaluated the impact of using pressurized carbon dioxide lavage after pulsatile saline lavage on thickness of the bone-cement mantle. The discarded bone specimens from sixteen anterior chamfer resections performed during total knee arthro-plasty were used for analysis. Both the medial and lateral halves of the bone specimen were irrigated with pulsatile saline lavage and suction using standard methods. Half of each specimen was further cleansed with a pressurized spray of medical-grade carbon dioxide gas. High viscosity bone cement was then applied to each half using thumb pressure. After the cement had cured, the specimens were placed on a digital x-ray cassette which was posi-tioned 90 degrees to the specimen axis for radiographic evaluation of cement penetration depth in each half. The images were developed and printed on photographic paper at known magnification. The cement mantle thickness in each side of each specimen was then measured electronically and compared. The specimens treated with carbon dioxide lavage had an average cement mantle thickness of 1.82 mm ± 0.61mm compared to a thickness of 1.35mm ± 0.42mm for the specimens in which only pulsed lavage was used. The use of carbon dioxide lavage resulted in a 35% increase in cement penetration depth (p = 0.02). The addition of carbon dioxide lavage after pulsed saline irrigation and suction allows for significantly greater cement penetration into cancellous bone. This improvement is thought to be due to the displacement and removal of residual fluid and fatty material that remains in cancellous bone after conventional pulsed saline irrigation and suction. It is believed that by displacing and removing residual fluid and fatty material, carbon dioxide lavage re-sults in lower hydrostatic pressure within the cancellous bone during cementation that would otherwise resist the penetration of cement and ultimately get pushed deeper into the bone. Improved cement mantle thickness in joint arthroplasty through the use of carbon dioxide lavage may enhance bone-cement interface strength and implant longevity.

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P26 CALCIUM PHOSPHATE PASTE FOR TREATMENT OF INFECTED TKA Tomotaro Sato, Masami Thukamoto, Atsushi Kaneko, Daihei Kida, Yoshito Eto Department of Orthopaedic Surgery, Nagoya Medical Center, 4-1-1 Sannomaru, Naka-ku, Nagoya, Aichi, 460-0001, JAPAN Phone: +81-529511111, Fax:+81-529510664, E-mail:[email protected] Infection after Total Knee Arthroplasty (TKA) is one of major problems difficult to solve. We have used Cal-cium Phosphate Paste (CPP) for treatment of infected TJA and followed up minimum one year. CPP is a mix-ture of alpha Tri-Calcium Phosphate, Tetra-Calcium Phosphate, Calcium Hydrogen Phosphate and Hy-droxyapatite. CPP harden in 10 minutes and its stiffness increases to maximum in 3 days. Infected TKA were diagnosed in two osteoarthritis and two rheumatoid arthritis knees from 2001 to 2006. Two were male and two were female, average age were 65.1 years old ranged 39 to 80. Follow-up period were one to 6 years. Two were MRSA infection, one was MSSA, one was unidentified but diagnosed with clinical data. In all cases, CPP (10-12g) with vancomycin hydrochloride or tobramycin were filled on the back side of PMMA articulated surface spacers. In all cases, infection ceased in 2 to 4 month and revision TKA ware performed. No recurrence of infection were observed during follow up and all patients can walk with/without a cane. No VTE were observed CPP filled in the space between articulated spacer and bone is gradually crashed and can release antibiotics during walking and ROM exercise. CPP with antibiotics is useful for the treatment after infected TKA.

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P27 LOWER INCIDENCE AND SEVERITY OF HETEROTOPIC OSSIFICATION WITH LESS INVASIVE TOTAL HIP ARTHROPLASTY

Nirav A Shah MD, Raju S. Ghate MD, S. David Stulberg MD Correspondence: Nirav A. Shah, MD, 701 S. Wells Street, #1603, Chicago, IL 60607 Phone: 312.203.4664, Fax 630.460.2255. E-Mail: [email protected]

Posterolateral Less Invasive THA significantly decreases the incidence and severity of heterotopic ossifi-cation.

Heterotopic ossification (HO) is a frequent complication of THA with a reported incidence of anywhere

from 15 to 90 percent. Decreased soft tissue trauma has been correlated with less invasive THA. The purpose of our study was to compare less invasive and standard posterolateral THA in regards to the radiographic presence and severity of HO.

From 1998 to 2004 we retrospectively reviewed 120 standard incision THA and 120 less invasive THA

with a minimum of two year radiographic follow up. Patients with history of prior THA, diagnosis other then de-generative osteoarthritis, and age greater than 65 years were excluded from the study. Radiographs at one and two year follow up were reviewed and classified for the presence and severity of HO with the Brooker classification. Chi square analysis was performed with p-value set at less than 0.05.

Heterotopic ossification developed in the Standard THA group as follows: Brooker Stage 1 17%, Brooker

Stage 2 13%, Brooker Stage 3 11%, Brooker Stage 4 1.4%. Heterotopic ossification developed in the Less Inva-sive THA group as follows: Brooker 1 10%, Brooker 2 12%, Brooker 3 6%, Brooker 4 0%. 28.2 percent of the less invasive group developed HO. The standard THA group had an incidence of 42.8 percent. This difference was statistically significant. There was also significantly less Brooker 3 and 4 HO in the less invasive group. Ad-ditionally, two patients in the standard group had ankylosed hips (Brooker 4) while there were none in the less in-vasive group.

Posterolateral less invasive THA decreases the risk and severity of HO. With the increase in younger

male patients undergoing THA, less invasive THA may provide a decrease in the occurrence of HO. This is the first study to our knowledge that compares HO in standard and less invasive THA.


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P28 Hip Arthroplasty: mini incision lateral approach versus standard approach Speranza Attilio, Iorio Raffaele, D’Arrigo Carmelo, Ferretti Andrea Speranza Attilio, Iorio Raffaele, In gallina Antonello, D’Arrigo Carmelo, Ferretti Andrea Via F. Marchetti 19, 00199 Roma (RM) Italy; +393391980755 ; [email protected] Orthopaedic Unit, S. Andrea Hospital University “La Sapienza” Rome, Italy Introduction: Minimally invasive surgery has become a trend over the last few years in all aspects of orthopaedic surgery, in-cluding total hip arthroplasty. So called “mini-incision” technique involve limiting the length of the skin incision to ? 10 cm with use of either anterior, lateral or posterior approach. Materials and Methods: Between March 2004 and December 2005 one-hundred and twenty consecutive unilateral total hip replacement were performed by the same senior surgeon in our institute. The diagnosis was of primary osteoarthritis in 101 cases, of osteonecrosis of the femoral head in 8 cases and of femoral neck fracture in 11 cases. In all cases we performed a hip replacement using a direct lateral approach (65 cases using a standard approach / 55 cases using a mini incision approach) In all cases we used a cementless cup (Trident; Stryker Howmedica) and a cementless stem (Hipstar; Stryker How-medica) The following parameters were evaluated: intra and post operative complications, total blood loss, time of surgery, component placement, length of hospital stay and functional outcomes at 3 and 6 months (HHS; Womac). Results: No significant differences were found between the groups with respect to, the average surgical time, the acetabular and stem position, the length of hospital stay and Harris Hip Score (HHS) and the Womac osteoarthritis index at six months. A significant lower blood loss was found in the mini-incision group. A higher percentage of peri-operative complications was recorded in mini incision group (two stupor of sciatic nerve, one fracture of the greater trochanter, one stem malposition). Conclusions: A mini incision lateral approach seems to have a lower blood loss and a shorter length of incision but a higher per-centage of peri – operative complications. On the bases of our experience we could speculate that the minimally invasive surgery should be directed to the new surgical approach with muscle sparing instead of a shorter skin inci-sion using standard approaches.

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P29 COST-ANALYSIS OF THE USE OF FIBRIN SEALANT TO MINIMISE PERIOPERATIVE ALLOGENEIC TRANSFUSION REQUIREMENT IN TOTAL KNEE REPLACEMENT Steuten LMG, Vallejo-Torres L, Buxton MJ.

Fibrin sealants can effectively reduce the need for allogeneic blood transfusions, and herewith the risks for transfusion-related adverse events, and have been associated with shorter length of hospital stay (LOS) after surgery. Since the main potential hurdle for utilisation would be the acquisition costs associated with their use, we developed a health economic model that evaluates the costs of using a commercial fibrin sealant adjuvant to con-ventional haemostatic treatment vs. conventional treatment alone in total knee replacement (TKR) from a UK hos-pital and a NHS healthcare system’s perspective.

The model synthesises data from a number of sources and assesses the proportion of individuals likely to

need blood transfusion, and the implications of this for 1) resource use associated with LOS after TKR and 2) transfusion related adverse events i.e. viral transmissions, bacterial infection, transfusion-related acute lung injury (TRALI) and anaphylactic reaction to human blood products. Two scenarios have been analysed: 1) all patients receiving 10ml product, 2) all patients receiving 5ml product. The first, most conservative scenario to the product was considered the base case.

Base case analyses show that using the fibrin sealant increases the expected cost of one TKR by £72 from

a hospital perspective and £66 when a NHS-UK perspective is adopted. Further information on the proportion of patients that actually require 10ml of product will decrease the net cost of the fibrin sealant strategy up to savings of £306 or £312 respectively from a hospital or NHS-UK perspective. The results are sensitive to the reduction in LOS and the price of an additional day in hospital. Although the model is currently populated with data for TKR taking a UK perspective on costs, it can be used in other areas of orthopaedic surgery and be populated with coun-try specific cost data.

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P30 ALIGNMENT OF TOTAL KNEE ARTHROPLASTY: IMPLICATIONS FOR COMPUTER ASSISTED TKA SURGERY Nicholas Wegner, BS; Alfred Cook, MD; Joe Feinglass PhD; S. David Stulberg, MD Background: Computer assisted surgery (CAS) is beginning to emerge as one of the most important technologies in orthopedic surgery, and many of the initial applications have focused on reconstructive surgery of the knee. However because CAS technologies are still in the early phases of development and implementation, the appropriate roles for these technologies are not yet clear. The purpose of this study is to accurately measure the angle between the anatomical axis and mechanical axis in cadaver femurs in order to determine whether the use of computer assisted total knee arthroplasty (TKA) will result in better mechanical alignment of the leg when compared with the use of a standard distal femoral cutting jig attached to an intramedullary rod placed in the center of the femoral shaft. Methods: Twenty-nine cadaver femurs were removed from 19 bodies and soft tissue about the femur was carefully dissected from the bone. Twelve matched pairs and five unmatched femurs (4 left, 1 right) were obtained. A standard IM rod used for mechanical TKAs was placed at the deepest portion of the trochlear groove and inserted in the in-trameduallary canal as proximal as the femur allowed in order to establish the anatomical axis of the femur. Each bone was then placed in a standardized position and a coronal and sagittal radiograph was obtained. The radio-graphs were digitized and the femoral angle between the anatomical and mechanical axes of the femur was then measured in the coronal and sagittal planes using the measurement feature of a digital x-ray program. Results: The mean femoral axis was 5.25 degrees (range: 3.14 degrees - 7.03 degrees, standard deviation: 1.02 degrees) in the coronal plane and 1.62 degrees (range: 0.19 degrees - 5.21 degrees, standard deviation: 1.09 degrees) in the sagittal plane. There was no significant difference between right and left femurs in either plane. Using current mechanical, intramedullary alignment techniques with a standard femoral cut of 5.25 degrees, 95 percent of TKAs will lie within 2.04 degrees of the mechanical axis of the leg. In the sagittal plane, 95 percent of TKAs will lie within 2.18 degrees of the mechanical axis of the leg using a standard femoral cut of 1.62 degrees. Conclusions: In order to optimize the mechanical alignment of the leg, current mechanical, intramedullary TKA alignment tech-niques should employ a standard distal femoral cut of 5.25 degrees in the coronal plane and 1.62 degrees in the sagittal plane, thereby minimizing the leg’s deviation from its mechanical axis. Using this standardized technique, surgeons can expect 95 percent of postoperative alignments to fall within 2.04 degrees of the mechanical axis in the coronal plane and 2.18 degrees -in the sagittal plane.

The goal when designing a computer assisted TKA system should be to align the leg in the coronal and sagittal plane with less variability than current manual techniques. Thus, in order to improve upon current manual sys-tems, computer assisted TKA systems should align the leg with its mechanical axis so the resulting standard devia-tion is less than 1.02 degrees in the coronal plane and 1.09 degrees in the sagittal plane.

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P31 USE OF TRANSVERSE ACETABULAR LIGAMENT FOR ACETABULAR CUP PLACEMENT IN COMPUTER-ASSISTED TOTAL HIP REPLACEMENT

Michael L. Swank, M.D., Martha Alkire,RN, MSN, ACNP, Leslie Korbee, BS, Jon Grote, PA-C Cincinnati Orthopaedic Reserch Institute BACKGROUND: Multiple studies have looked at different pelvic anatomical references and techniques to optimize acetabular component posi-tioning. Computer-assisted hip replacement with use of the anterior pelvic place for reference has been studied. Efforts to mini-mize the effect of pelvic positioning on anteversion and inclination values have been studied via use of C-arm xray (Muller et al., 2006). Chen et al. (2006) illustrated that in planning for implant positioning, projected coordinates will reflect non-conventional values to account for individual pelvic tilt and rotation. Recent reports in the literature have introduced the use of anatomic referencing of the transverse acetabular ligament (TAL) along with the residual acetabular labrum to determine cup orientation. The TAL-Labrum plane can be defined as coordinates on corresponding arthro-MRI images (Slomczykowski, et al., 2006). It has further been reported that use of TAL as an aid to cup placement has resulted in a decreased dislocation rate as a result of better cup positioning. Use of Computed Tomography in addition to computer navigation has shown promise in improved cup placement but is impractical clinically (Tannast et al., 2005). In this study, computer navigation was used with the TAL-Labrum landmarks as illustrated by MRI to examine anteversion and inclination ranges in comparison to the conventionally defined ranges. METHOD: This descriptive study is a single surgeon series of 61 total hip replacements in which the TAL and labrum identification were used with navigation to optimize acetabular component placement. Data were collected regarding the patients’ preoperative plan for angles of anteversion and inclination, along with the postoperative data for these angles. Intra-operative values were converted by a nomogram equation to radiographic values. Radiographic anteversion and inclination data of a group of 247 patients at 3 months after computer-assisted total hip replace-ment (Non-TAL group) were available for comparison. The Non-Tal group data was collected from January 2004 to April 2006. RESULTS: The range of values for planned anteversion was -10 to 61 degrees, with –16 to 68 degrees post-operatively. The most fre-quently occurring planned anteversion value was 14 degrees in 7 of 61 patients. Results revealed 23% of patients with planned anteversion within five percent of 15 to 25 degrees. Planned inclination values ranged from 19 to 67 degrees; Post-op inclination values within the safe zone were 33% percent. There was a mean deviation from the operative plan of 8 degrees in anteversion and 6 degrees in inclination. Intra-operative computer values were converted by nomogram to radiographic values. Converted planned values for anteversion were –6 to 39 and inclination 20 to 74. Post-operative anteversion ranged from –12 to 39 and inclination 10 to 73. A lesser percentage of converted values (30%) fell in the safe anteversion range versus pre-operative values (39%), post-operative (52%) and 3 month x-ray data (73%). There was a sizeable difference between converted pre and post-operative inclination values (38-39%) to 3 month radiographic data (64%). However, the mean difference from post-operative converted values (x=18.3) to 3 month radiographic values in anteversion (20.9) was only 3 degrees; In inclination, the mean difference from post-operative to xray values was 3 degrees (43.6- 47.1). The dislocation rate was 1.6%. Radiographic anteversion values at 3 months show a higher frequency of TAL patient s (77%) within the safe zone range +/-5 degrees versus Non-TAL patients (61%); inclination was 70% for TAL versus 65% in the Non-TAL. group. DISCUSSION: Use of computer-navigation with the TAL demonstrated a wide range of values for planned inclination and anteversion, ranging from –10-61 degrees of anteversion to 19-67 degrees of inclination (Fig 1). Although a majority of computer navigation values were not within this range, mean deviation from the anteversion-inclination plan was only 6-8 degrees. The 3 month post-operative data showed a higher percentage of TAL patients in the “safe zone.” Computer-generated post-operative values that were converted by nomogram to radiographic values did not differ with significantly in comparing means with 3 month radiographic data. These preliminary findings illustrate that the use of the TAL-labrum landmarks with computer assisted surgery proposes a different set of intraoperative coordinates to achieve desired radiographic values of anteversion and inclination.

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P32 REDUCING CARDIAC POST-OPERATIVE COMPLICATIONS AFTER TOTAL JOINT REPLACEMENT

Michael L. Swank, M.D., Martha Alkire RN, MSN, ACNP Cincinnati Orthopaedic Research Institute BACKGROUND: Post-operative complications occur frequently after total joint replacement surgery. Mortality and morbidity due to cardiovascular disease occurs in over 1 million of 30million noncardiac surgeries performed annually (Mangano, 1996). 50,000 patients annually undergoing elective noncardiac surgery have a perioperative myocardial infarc-tion (Poldermans, 2005). In total joint surgery, overall complication rates for MI, PE and death is documented at 2.2% (Mantilla. 2002) with an increased propensity for myocardial infarction within three days of surgery (Gandhi, 2006). Rates of early death post total hip arthroplasty increase as age increases (Blom, 2006). Complications due to pulmonary embolism and incidence of deep vein thrombosis have been well documented in the literature. Pro-tocols for decreasing incidence of complications due to deep vein thrombosis have been widely studied and devel-oped. Prevention of cardiac complications in general surgical procedures remains a strong area of interest. There is a deficit in standardized pre-operative measures for total joint replacement surgery. Pre-operative cardiac clear-ance is useful to improve outcomes and prevent post-operative complications. The aging population requiring joint replacement surgery is at high risk to undergo anesthesia and have multiple comorbidities that may affect their post-operative outcome. Age greater than 70 has been established as a significant risk factor, as well as chronic obstructive pulmonary disease, congestive heart failure and chronic renal failure (Bhattacharyya, et al, 2002). This retrospective study demonstrates the efficacy of pre-operative cardiac screening of total joint replacement patients after 2004 in reduction of cardiac complications and death. METHOD: This is a single surgeon series of 1694 patients undergoing total joint replacement from 2002 through 2006. In 2004, the author developed a screening protocol to identify patients at risk for major or life threatening cardiac events after total joint replacement. The protocol required all patients over age 70 to undergo cardiac clearance prior to surgery. In addition, all patients under 70 who had a history of cardiac problems or abnormal pre-operative electrocardiogram were also referred for cardiac clearance. It was recommended that diabetic patients should maintain a Hgb A1c level less than 6 mg/dl. Treatment for pulmonary disease was optimized by specialists prior to surgery. Patients were studied in two groups, with the group over 70 or with cardiac history required to have cardiac clearance before surgery was scheduled. Retrospective data of 711 patients between January 2002 through September 2004 was obtained for complications prior to screening. Another group of 943 patients from September 2004 to December 2006 which had received cardiac screening was used in comparison. RESULTS: In the period from 2002 through August 2004, there were 721 total joint surgeries with complete data. The ASA Risk for this group was: I-0.2%; II-6.9%; III-92.7%; IV-0.3%. In the period from September 2004 through the end of 2006 there were 973 total joint surgeries. The ASA Risk for this group was: I-0.5%; II-15.7%; III-83.7%; IV-0.1%. The rate of cardiac post-operative complications prior to the use of the screening protocol was 2%, with 0.42% life threatening complications and 0.28% death rate. All subjects with major cardiac post operative complications were grade III ASA Risk. After the institution of the screening protocol, the complication rate dropped to 1% with a decrease in life threatening complications to 0.21%. All subjects with major cardiac post operative complications were in the grade III ASA risk catagory. Finally, there were no peri-operative deaths after the screening protocol was instituted. DISCUSSION: The majority of our population undergoing joint replacement surgery is an ASA class risk III (up to 92.7%). Ob-taining cardiac clearance prior to joint replacement surgery has identified patients requiring further intervention, thus delaying elective surgery, but decreasing serious complications after joint replacement surgery. The rate of cardiac complications decreased by 50% after the institution of a cardiac screening protocol. This is likely due to early intervention for undiagnosed disease as well as use of beta blockers to offset the sympathetic response of norepinephrine associated with surgical stress. Despite beta blocker therapy, the incidence of cardiac dysrhythmia postoperatively in 2002 was 1 % versus 1 % after cardiac clearance. The death rate also decreased from 0.28% to 0%. Although pre-operative cardiac screening is beneficial, further measures on decreasing post operative cardiac arrhythmia is desired. Optimizing the aging patient with multiple comorbidities prior to surgery presents a chal-lenge to surgeons, specialists and primary care providers in health care delivery to produce the best possible out-

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P33 THE TIBIAL SLOPE IN TOTAL KNEE REPLACEMENT WHAT DO WE GET ?

TABUTIN J., LANZA R., CAMBAS PM. Centre Hospitalier 15 avenue des Broussailles 06401 CANNES Cedex France Obtaining the proper tibial slope in THR is important for the range of flexion of the knee. There are many systems to reach that goal. But do we get what we wish? Material and methods: 247 cases (18 bilateral) were included in this retrospective study : 74 men and 155 women, of an average age of 68 (56 to 82). All were primary cases, without previous high tibial osteotomy. Patients were followed clinically and with X-Rays at regular intervals (2 months, 6 months, 1 year, and then every 2 years). The ancillary was intra medullary either the NexGen with a preset 7° slope or the Miller Galante with a 10° slope. The tibial cut was begun with the tibial IM rod and the saw as oblique in the cutting slot as possible. The implant used was the cementless NexGen prosthesis, with a pegged tibial tray HA-bTCP coated and fixed with resorbable screws (cases from Cannes) or with a standard stemmed tibial tray (cases from Paris). We measured on the lateral X-Rays the tibial slope relative to : the anterior tibial cortex, the intra medullary axis, the posterior tibial cortex and the fibular axis. Measures were done on pre-operative and post-operative (about 2 months and at follow-up) X-Rays. The slope given by the ancillary was also measured. Results:

Pre-operatively measured slope varied from O to 14° with different values according to the reference : anterior cortex : 9.87° ± 0.26, IM axis : 7.44° ± 0.27, posterior cortex : 5.21° ± 0.30, fibular axis : 7.07° ± 0.30

Post-op slopes with the Nex Gen guide were 5.92° ± 0.46 for the tibial IM axis and 3.43 ± 0.23 for the posterior cortex. With the M G 1 guide 8.15° ± 0.24 for the IM axis and 6.44° for the posterior cortex. "Ex vivo" play was between 6.5 to 10° for the Nex Gen guide and 7 to 10.5 for the MG1 guide. Discussion: The values of IM axis and fibular axis were significantly different (p : 0.004). The fibular axis in only an approxi-mation of the tibial IM axis, When using the Nex Gen IM guide we aim at 7° and get 5.92° ± 0.46; with the MGI IM guide we aim at 10° and obtain 8.15° ± 0.24. Our data show that the guides are neither very precise ( shape of the histogram) nor very exact (minus 1 or 2 degrees), although we maintained them as stable as possible by keeping the IM rod in situ for the greater part of the cut. A plane oblique effect does not seem a correct explanation as 10° malrotation will induce 0.3° of slope variation. The deviation from the target value seems to go always in the same direction (less slope) indicating that the saw-blade may be deviated by hard bone or that it should be more rigid. Will Computed As-sisted Surgery improve that ? The orientation of a rigid blade should be navigated rather than the position of the cutting guide.

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P34 FULL FLEXION AFTER TOTAL KNEE USING LPS FLEX IMPLANT Samih Tarabichi, M.D. INTRODUCTION: The majority of implants available in the market today were designed to allow for a flexion up to 130 degree an-gle. The LPS Mobile Flex was designed to accommodate deep flexion, up to 160 degree angle. The purpose of this study is to evaluate the clinical result of the LPS Mobile Flex knee. MATERIALS AND METHODS: From January 1999 to February 2006, 1843 (one thousands eight hundred and forty three) surgeries were per-formed on patients treated for advanced osteoarthritis. All the surgeries were carried out by the same surgeon. The majority of the patients had bilateral total knee replacements simultaneously .Mobile and fixed implants were used. Pre-operative ranges of motion were documented on lateral x-ray. Patients were considered to have full flexion if they were able to flex the knee to at least 140 degree and sit on the ground with calf touching thigh for at least one minute. Data were processed at University of Dundee RESULTS: 61% obtained full flexion as defined above. The majority of the cases with full flexion had full movement pre-operatively; except for 63 cases .Average range of motion was much better than University of Dundee data base. Complications included; 2 cases of peroneal nerve palsy, three of dislocation, and two of infection, a case of rup-ture of MCL ligament, a case of intra-operative tibial plateau fracture, 2of supracondylar femur fracture and 4 pa-tella clunck CONCLUSION: The LPS Flex Implant had a similar complication rate to those reported by other series. There was no complication that could be specifically attributed to deep flexion. However it should be stressed that this exceptional result has to do mainly with careful patient selection.

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P35 TOTAL JOINT ARTHROPLASTY AFTER BARIATRIC SURGERY FOR MORBID OBESITY: COMPLICATIONS IN THE PERI-OPERATIVE PERIOD Thangamani Vijay B, Puri Lalit, Northwestern University Feinberg School of Medicine, Department of Orthopae-dic Surgery, 645 N. Michigan Ave. Suite 910 Chicago, IL 60611. Phone: 312-908-7937, Fax: 312-908-8479, Email: [email protected]. Gastric bypass prior to hip and knee arthroplasty in the morbidly obese is becoming more prevalent. The purpose of this study was to evaluate postoperative complications in total joint arthroplasty patients who have had prior gastric bypass surgery. An IRB approved retrospective study was performed. We reviewed the demographics, histories, surgical procedures, and the 90 day postoperative course of 18 patients that had undergone total knee or hip arthroplasty who were previously treated with gastric bypass surgery. There were 16 females and 2 males. Twenty procedures were performed as 4 patients underwent bilateral joint replacements and 2 patients underwent staged procedures. Twenty knees and 4 hips were replaced. The average length of stay was 4.25 days. In all of the patients, there was either no clinical suspicion of deep venous thrombosis or a negative duplex ultrasound. No patients required the intensive care unit. One patient required prolonged hospitalization for treatment of an ileus. Two patients were later readmitted, one for observa-tion and intravenous antibiotics due to excessive wound drainage and the other for an incision and drainage due to a wound dehiscence. There were no other major complications or adverse events found. Gastric bypass is a popular method of weight loss and can be an effective means of weight reduction in total joint candidates. Overall, we find that patients who have undergone a previous gastric bypass procedure do well postoperatively following total joint replacement, especially if extra vigilance is taken to monitor wound heal-ing.


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P36 IN VIVO CHANGES TO METAL ON METAL (MoM) BEARING SURFACES - IMPLICATIONS Tuke, M.; Taylor, A. Currently, the lubrication regime of MoM hip devices is determined using lubrication theories. These assume unworn perfect geometries and a resulting low contact area. The in-service wear of retrieved MoM bearing sur-faces was characterised; any change, from the original or from the theoretical conditions, will affect the lubrication conditions. The bearing surface of first generation MoM total hip retrievals of various designs which had been in use suc-cessfully for more than 10 years were measured using a Mitutoyo roundness machine, with an accuracy of 0.01 microns. For components under normal conditions of wear (ie no edge wear due to misplacement of the compo-nents), the worn part of the bearing surface was compared to the unworn surface. The wear volumes were derived mathematically from these observations. A significant difference in geometry was observed for all components between worn and unworn parts of the bearing surface. All components showed a linear penetration of the head into the cup and of the cup into the head, resulting in a relatively large, conforming contact patch that could be easily distinguished from the unworn surface. The linear penetration varied between 20 and 35 microns, and the wear patch contact angle varied between 35 and 70 degrees, in good agreement with the literature. The measured contact angle and penetration were similar for each of the two components in a pair. The new surface resulting from wear on the head and cup was essentially spherical, with a diameter part way between the original head and cup diameters. Mathematically, the linear penetration was a function of wear patch contact angle and initial clearance. If the contact patch was assumed as a fully conforming portion of a sphere, the resulting wear volume was a function of initial component dimensions (radius and clearance), contact angle and linear penetration. For the retrievals ana-lysed, this corresponded to wear volumes of 14 to 75mm3. Retrievals analysis shows that MoM components wear. A conforming contact patch forms. It is characterised by new dimensions and surface finish, compared with the initial bearing, with effects on the clearance and entraining geometry. This has implications for wear behaviour prediction using lubrication theories and short term simulator studies.

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