New Productsfrom AO Development

Norbert P. Haas, AOTK Chairman

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Editors:Univ.-Prof. Norbert P. Haas, AOTK ChairmanE-mail: norbert.haas@ao-asif.chP. SchreitererE-mail: philip.schreiterer@ao-asif.ch

Publisher: AOTKLayout: AO Media ServicesPrint: Gonzen Druck AG, CH-Bad Ragaz

Number of Copies: 20000Issued: May 2002

For further information please contact:TK OfficeClavadeler StrasseCH-7270 Davos PlatzTel.: +41 81 4142-471Fax: +41 81 4142-290E-mail: aotk@ao-asif.ch

Jan. 2001 Dec. 2001- Jan. 2002

Study Start

Clinical Journal (document all distal radius fractures retrospectively)

In- and Exclusion criteria

Fulfilled ⇒⇒ Study case (all plated cases)

Not fulfilled ⇒⇒ Clinical Journal (prospective)

L. HuysseAn outlook on the LCP Distal Radius Studie(Locking Compression Plate)One of the key objectives of AOCID is to organize and conduct clin-ical studies that provide evidence regarding the clinical benefit ofAO methods and implants. The “gold standard” study design toachieve this is a randomized clinical trial (RCT). We therefore con-sidered this design for the LCP distal radius study right from thestart. While simple on paper, the process of randomization met with somepractical obstacles. Which treatment would be optimal to comparethe LCP with? For which indication? Would surgeons be preparedto randomize patients? In fact, we could not find a consensus on thebest control treatment, since the new LCP plate is based on a newconcept and does not replace an existing system on a one by one ba-sis. An RCT was judged inappropriate, in particular because sur-geons were convinced that the LCP will provide a better outcomefor the patient and therefore were not willing to use the conven-tional system any longer. The best compromise was to conduct an observational study wherethe treatment decision remains in the hand of the surgeons. This de-sign allows documentation of the range of indications for treatmentwith the LCP, and both clinical and radiological outcomes, afterplating of the distal radius. By collecting data from a large numberof cases, we will identify different cohorts (e.g. patients treatedwith different plates) that will be compared.

The LCP Distal radius study includes three prospective studies andone retrospective study.❚ ”Conservative” distal radius study in the UK documenting all dis-

tal radius fractures, and all types of treatment (majority of frac-tures treated conservatively).

❚ LCP 3.5mm distal radius study, involving centers mainly usingthe 3.5mm LCP system (10 centers).

❚ LCP 2.4mm distal radius study, focused on the 2.4mm LCP sys-tem (6 centers).

❚ Retrospective study documenting the treatment of all distal radiusfractures in the past year (before the LCP plate was available). Thesame clinical journal form is used, with no follow-up visits, andno collection of X-ray images (7 centers).

We have two types of questionnaires for the prospective studies,one for all plated cases (any type of plate and fulfilling inclusionand exclusion criteria), including follow-up forms up to two yearspost-operatively, and a shorter one for all other cases (making theclinical journal).A schematic overview of the LCP 3.5mm and 2.4mm study, com-bined with the retrospective study is shown in the figure below.The same inclusion and exclusion criteria, as well as clinical (in-cluding the Gartland and Werley, the DASH and the SF-36 scoringsystems) and radiological (centrally evaluated) outcome criteria areused in the different prospective studies. While follow-up is im-plemented for all cases in the "Conservative" distal radius study,only plated cases are followed in the two other prospective studies.

Special attention will be given to the expected advantages of the

new LCP concept as well as to maintenanceof reduction, the additional use of bonegrafting, and the learning curve. The stud-ies are controlled in order allow a compar-ison of the LCP systems to other conven-tional plating systems and conservativetreatment of distal radius fractures. The ret-rospective part of the study (documentingthe situation before the introduction of theLCP system) will show whether any shiftin indication from e.g. external fixator tothe LCP system has occurred and in orderto define a control group accordingly for fu-ture studies.The different studies were started at theend of 2001.

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Dear Reader,

Thank you for the positive feedback to thefirst issue of New Products from AO Develop-ment. We have made several improvementsincluding more X-rays and longer articles onclinical benefits. Nevertheless, we need tostress that none of these articles is a substi-tute for the OP Techniques and our AOteaching tools. This brochure intends to giveyou a first overview only. You can get moredetailed information about these productsfrom your local SYNTHES® representative.

Most of you are receiving New Products fromAO Development as a removable supplementto the AO Dialogue. We hope that this wayof distribution is most convenient to you. Itenables us to provide you with further in-formation about development related infor-mation, e.g. the article about the TK-Systemin this issue of AO Dialogue. The TK-Sys-tem is an organization of medical-technicalcommittees responsible for the developmentof all new AO products. This article pro-vides you with an inside view on what’s be-hind AO Development.

Starting with this issue, we will inform youabout interesting, applied research resultsabout new products presented in thisbrochure or results that are going to influ-ence development in the near future. Fur-thermore, we are aiming to publish more re-sults of clinical studies proving the clinicalbenefit of AO products.

Let me point out to you that all authors aremedical doctors who have participated inthe development of the described products.I would like to thank them for their great en-gagement and contribution to this issue ofNew Products from AO Development.

Yours sincerely,

Norbert P. Haas

Contents

Introduction

Contents

New Concepts in Spine Surgery

New Spine Products

Cervifix/Starlock: Clamp & Holding Sleeve for Screwdriver

Click’X Dual Core Pedicle Screw

New Long Bone Products

Medium External Fixator

Single Pin Clamp, 4 Position Drill Guide & Sleeve

and 8mm Carbon Fiber Rod

DHS: Variable Angle Guide

Distal Femoral Nail with Spiral Blade

High Tibial Osteotomy Device: 70mm Chisel Line Extension

Locking Condylar Plate

Distal Tibia Plate

Locking Compression Plate: Wire Mount

Locking Compression Plate Screw with StarDriveTM Recess

New Knee Products

Tomofix: Osteotomy Chisel

New Paediatric Products

Cannulated Paediatric Osteotomy System

New Craniomaxillofacial Products

2.0 Mandible Locking Plate: Bending/Cutting Pliers with beak

Subcondylar/Ramus Fixation Set

Reversible Battery Powered Screwdriver

MR Safe Instruments

IMF Screw System

New Veterinary Products

3.5mm Broad LC-DCP Plate

New Products from AO Publishing

Research Results

Clinical Studies

Humerus Block

LCP Distal Radius

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Fusion of one or more mobile segmentshas been performed for many decades inthe treatment of degenerative diseases, de-formities and spinal trauma. Circumferential fusion is established asthe most efficient and predictive way tofuse the spine. The use of autologous bonegrafts has been associated with problemsand failures, therefore, various spacers andother devices have been developed in thelast decade and are widely used today.

Cages

The SynCage made of titanium is widelyemployed and very successful in clinicaluse today. The cage design seems to con-form very well with the local anatomy inorder to achieve a stable construction andalso to address the sagittal profile of thespine. Despite its very impressive clinicalperformance, however, there is currentlyno convincing data demonstrating the stateof the autologous bone graft which is im-pacted into the cage. Fusion is only obvi-ous in cases where bony bridging occursout of the cage.

Fig.1 Fusion outside the cage

In most cases we are just “looking” radio-logically through the window of the cagebut do not know whether there is a vitalbony connection running through the cageand connecting the endplates to each oth-er. Different CT-reconstructions producereasonable pictures of trabecular bonyconnections through the cage, but there re-

P. Pavlov

New Developments in Spinal Surgery

mains the need to have a clear view of thebone inside the cage with plain radio-graphs.

Fig.2 Bone running through the cage

Radiolucent materials

Cages made of carbon fiber were employedin spinal fusion in the eighties and resultswere inconsistent. Inflammatory respons-es resulted in many cases of osteolysisaround the cages and establishedpseudarthrosis. The mechanical integrityof the cages was also the subject of criti-cism.

After an extensive search we made thechoice to employ poly-ether-ether-ketone(PEEK) as a material for interbody fusioncages. PEEK is a linear and semi-crystalline ther-moplastic polymer. Medical grade PEEKhas been applied over the past 20 years inmedical devices. Up to now, there are noknown adverse effects in relation to PEEKdevices.

PEEK is a derivative of the PAEK-resigns(poly-aryl-ether-ketone) family. The mostimportant features of PEEK material are itsbiocompatibility, its elastic modulus simi-lar to bone and its radiolucent properties.It is an inert material and its reaction withbone is comparable with titanium.

Different tests show no material cytotoxi-ty. PEEK is registered in the FDA Device

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Masterfile (MAF) and Drug Masterfile(DMF) and is USP class VI approved, ac-cording to FDA regulation. It is also ISOcertified.

Two design concepts were developedbased on the very successful surgical tech-nique for cage impaction in optimal dis-traction; one copying the design of the tita-nium cage with some small modificationsof the contact surfaces named SynCage-LR,and a second one mimicking the configu-ration of the vertebral end plates, namedVisios.

The development of the SynCage-LR (Fig. 3) met two objectives: adaptation ofthe cage design to the specific properties ofL5-S1 intervertebral space and the creationof a larger footprint for improved conform-ity to the endplates of large individuals.

Fig.3 SynCage-LR

Visios has a kidney shaped footprintwhich addresses the strong peripheral partof the end plate. A large central hole facil-itates packing the cage with autologousbone graft or bone graft substitutes.In profile, the Visios uses the same convexcharacteristics as the SynCage and con-forms well with the concave vertebral end-plates.

Fig. 4 Visio

Mechanical testing of cage strength wasvery convincing. In static compressionload testing, structural deformation of theSynCage-LR occurred after loads exceed-ing 44kN. Fatigue testing with a durationof 5 million cycles and a frequency of 6Hz,resulted in only a small deformation of theteeth, without any structural changes tothe construction.

There was no significant difference in bio-mechanical performance between the tita-nium SynCage and the SynCage-LR de-signs when tested in cadavers.

Clinical studies with SynCage-LR and Vi-sios show similar results, as with the tita-nium SynCage. Fig. 5 and 6 show the radi-ological appearance at 3 and 6 months’follow-up. After a year, there is apprecia-ble bony bridging seen through the cages,as shown on CT-reconstructions.

Fig. 5 Fig. 63months p.o., Patient A 6months p.o.

Fig. 7 CT-reconstruction 11 months p.o., Patient B

, Patient A

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Grafts and substitutes

Up to 20% donor site morbidity has beenreported with the use of autologous bonegrafts. For this reason, surgeons in SouthAfrica have used a registered bone graftsubstitute called chronOS, which is madeof tricalcium phosphate (TCP). Difficultieswith filling the individual cages withgranules were encountered, which led to aproject to fabricate cages which are pre-filled with solid chronOS. Mechanicaltests showed satisfactory retention ofchronOS, therefore, a sheep model wasused to compare fusion outcomes betweenthe chronOS granules–filled cages, solidchronOS–filled cages and autologousbone- filled cages.

Fusion using the chronOS-filled cages wasequal to that of autologous bone-filledcages, especially when prefilled with solidchronOS. There is evidence that more than60% of the chronOS filling resorbed after26 weeks being replaced by trabecularbone.

Further, in a small series of cervical cages(Cervios, prefilled with chronOS) the clin-ical results are very convincing.

Fig. 8 C-spine fusion 3 months p.o., Patient C

In conclusion, the generation of new lum-bar and cervical interbody fusion cagesmade from PEEK will be employed exten-sively in the future. The employment ofchronOS as a bone substitute will elimi-

nate donor site morbidity and consider-ably shorten operation time. There is aclear economical benefit, because the elim-ination of donor site morbidity will resultin a shorter hospital stay.

Osteoporotic fractures of the spine

The ageing spine is a very challenging areabecause of the increasing number of seniorcitizens and the lack of impressive resultsfrom the treatment and prevention of os-teoporosis in elderly people.

In the last twenty years, PMMA bone ce-ment has been employed in the treatmentof osteoporosis of the spine. Despite manyenthusiastic reports, however, there is aclear under-reporting of dangers and com-plications when using PMMA for augmen-tation of osteoporotic vertebrae. There is anincreasing number of disastrous complica-tions from the use of PMMA, includingparaplegia and death.

A new concept for augmentation of osteo-porotic and fractured vertebral bodies hasbeen developed. The idea is to create a cav-ity in the osteoporotic vertebral body, to re-duce fragments if fractured, and than injecta biocompatible high viscosity substitute,which may even be slowly resorbable, inorder to achieve high mechanical strengthof the injured vertebra. This so-calledCavitation technique employs newly de-veloped instruments which create a cavityin the affected vertebral body.

Fig.9 Creation of cavity within the vertebral body

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Fig.10 Injection of Norian into cavity

Fig.11 Cadaver specimens half filled with Norian

The major advantage of this technique isthe safety of the procedure; the spinal canaland neural elements cannot be violated.There is also no danger of thermal damagewhen using SRS Norian. The Cavitation technique is already inclinical use. Early results are very encour-aging and it seems to be a safe way to dealwith the increasing number of osteoporot-ic fractures.

Non fusion stabilisation

It is recognized that fusion of the spine al-ters its mechanics and, in the long run, willinduce secondary changes in the adjacentvertebrae. There is a clear tendency for thedevelopment of new techniques to stabi-lize the spine without altering motion.Because of the huge variety of degenerativechanges which occur in the spine over

time, we are looking at a number of differ-ent tailor-made solutions, in order to ad-dress different stages of degeneration.There are different strategies to be fol-lowed, starting maybe with tissue manip-ulation in the very early stages of degener-ation. The aim will be to increase theamount of proteoglycans in the interverte-bral disc and in this way restore consisten-cy and function. In cases of clear degener-ation of the nucleus pulposus, some kindof nucleoplasty may be employed to par-tially restore the mechanical properties ofthe disc.In cases of more pronounced degenerationand extensive distraction of the annulus fi-brosus, total disc replacement may be em-ployed.

Today, different projects have been initiat-ed and some prototypes are already under-going mechanical testing.From a strategic point of view, it is very im-portant to develop a modular approach toproblems of the degenerative spine, withspecial emphasis on well defined secondand third lines of defence. The aim is tocover the entire active life of the individualand to permit normal use of the spine.

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P. Pavlov

New Spine Products

StarLock SystemThe StarLock System was launched inMarch 2000 and has been well received bymany surgeons. On the request of manyconsultants, a modification to the existingclamps has been added to the system; theseare clamps with extended offset and alsoup-going clamps. The new clamps meetthe same functional requirements as theexisting clamps. They will increase theflexibility and the application area of thefixation system.

In order to increase safety of the procedurespecial holding sleeves have been devel-oped. The holding sleeve makes sure thatthe screwdriver does not slip off the screwaccidentally.

Click’X Dual Core Pedicle Screw Features:– constant outer diameter– smaller core diameter in the distal part ➩ optimal purchase in can-

cellous bone– short conical transition to larger core diameter in the proximal

part ➩ minimal loss of grip in case of turning back of the screw– larger core diameter in the proximal part ➩ optimal purchase in

the pedicle– round tip ➩ no danger for segmental vessels in the case of bicor-

tical fixation– double thread starting at the tip ➩ immediate purchase of the

thread, fast insertion

Indications for the new Click’X Dual Core Pedicle Screws are thesame as for the well known cylindrical Click’X Pedicle Screws inthe lower thoracic and the lumbar spine:

❚ Degenerative instabilities❚ Instabilities following decompression❚ Tumours without anterior defect❚ Fractures without loss of ventral support

Deformities, fractures and tumors which primarily effect the ante-rior column should not be treated in the first step with the Click’XDual Core Pedicle Screw. However, an additional posterior fixationafter anterior stabilization might be suitable.

The new Click’X Dual Core Pedicle Screws are available in the fol-lowing diameters: 5.2mm, 6.2mm, 7.0mm, 8.0mm, 9.0mm. Thelast two diameters are thought to serve as emergency/revisionscrews or for sacral fixations.

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C. van der Werken

New Long Bone Products

Variable Angle Guide for DHSThe DHS system is considered the stan-dard implant for the stabilisation of mostproximal femoral fractures. One singleVariable Angle Guide enables surgeons tointroduce the guide wire for the hipscrewunder different angles. The Variable AngleGuide locks in angles of 130°, 135°, 140°,145° and 150°.

D. HöntzschMedium External FixatorThe Modular Tube/Rod External Fixator of the AO is now availablein four sizes: Large (11mm), Medium (8mm), Small (4mm), andMini (2mm).

The Large, Medium and Small Ex Fix have similar clamps, rods andscrews:❚ Single Pin Clamps for pin to rod/tube connection❚ Multi Pin Clamps for multiple pins❚ Combination Clamps

– for rod/tube to rod/tube connection– for pin to rod/tube connection– for pin to pin connection (in future)

Tube and rods are available in steel and/or carbon fiber. The Schanzscrews are self-tapping or self-drilling in steel and titanium. Allclamps will be “open” and “snap on”. The clamps will be colourcoded for each size. The standard frame is the “3 Tube ModularTechnique”.

Lately, the Medium External Fixator was completed. The MediumEx Fix is indicated for the stabilization of medium sized bones: thefoot, forearm, elbow, humerus and small adult’s tibia and children’slong bones. The combination “up” to the Large 11mm and “down”to the Small 4mm System is possible and one of the main indica-tions. Indications for the Medium Ex Fix are identical to the classicindications for external fixation: fractures with severe soft tissuedamage (closed and/or open), polytrauma, septic cases etc.

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Distal Femoral Nail with Spiral Blade (see also article on page 15)In the past years, retrograde femoral nailing has proven to be safeand reliable. The Distal Femoral Nail is becoming increasingly pop-ular and is especially suitable for obese (or pregnant) patients andin osteoporotic metaphyseal bone.

Indications include extra-articular metaphyseal distal femoral frac-tures (32-A1 to C3) and supracondylar fractures and simple articu-lar fractures (33-A1 to A3 and 33-C1 to C3.1).

The Spiral Blade enables significantly more stable distal interlock-ing than with conventional locking bolts due to the large load-bear-ing surface. It reduces cancellous bone compaction and lowers therisk of nail protrusion into the knee joint. The nail diameters are 9.0and 10.0mm for solid nails and 12.0 mm for cannulated nails.Lengths range from 160 to 420mm.

High Tibial Osteotomy (HTO) Device: 70mm Chisel Blade Line ExtensionLonger chisel blades have been requested for performing os-teotomies of the proximal tibia. This extension of the existing SYN-THES® Chisel Blade Line provides the surgeon with 20mm of ad-ditional functional length. The 70mm Chisel blades –from 440AStainless Steel–are available in the standard 5, 10, 16 and 25mmwidths and are compatible with the existing Chisel Handle.

LCP Distal Femur PlateThe Locking Compression Distal Femur Plate or Condylar LockingCompression Plate is indicated primarily for extra- and intra-articu-lar distal femur fractures (32-A1 to C3, 33-A1 to A3 and 33-C1 to C3).

The implant is anatomically pre-shaped and has Locking Compres-sion Holes in the shaft, a limited contact profile and locking screwsin the head. The primary feature of the system is its ability to useeither locking or compression screws. Locking screws in the headof the plate form an angular stable screw-plate construct.

The combination holes are compatible with all AO 4.5mm LCP andconventional screws and technique. The Condylar Locking Com-pression Plate utilises the Locking Periarticular Plating System in-strumentation. The plate is available in Stainless Steel.

Female, 88 y.

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LCP Distal Tibia PlateThe Distal Tibia Plate is anatomically pre-shaped and lockedscrews provide angular stability. In the shaft area this plate has astandard dimension and a limited contact profile, more distally theplate gets thinner to spare the delicate soft tissues over the medialtibia. It is of special advantage in osteoporotic bone, where theanatomical design supports the reduction and allows percutaneousapplication. Indications are extra- and intra-articular fractures ofthe distal tibia (43 A1 to A3 and C1 to C3), especially with osteo-porotic bone and/or with injury to the overlying soft tissues. TheDistal Tibia Plate is available in Stainless Steel and Titanium, theyare fully compatible with all 3.5 conventional screws, with the 3.5Locking Compression Plate System and with the Calcaneus Lock-ing Plate Set.

LCP Wire MountThe Wire Mount for LCP 4.5/5.0 plates fa-cilitates the additional use of cerclagewires in plate fixation of shaft fractures ingeneral, but of periprosthetic fractures inparticular. The Wire Mount is inserted inthe selected plates hole and guarantees afixed position of the wires in direct rela-tion to the underlying plate. It is availablein Stainless Steel and Titanium.

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S. PerrenStardrive™ a new AO screw drive connectionSome 40 years ago the AO selected the hexagonally recessed screwdrive connection. In comparison to single and cruciate slots, theHEX offers a good lateral guidance that allows “blind” insertionand removal. In comparison to Phillips, the torque transmission islargely independent of axial thrust, which may compromise ini-tially unstable reduction of the fracture fragments. Furthermore, toavoid collision of sequentially inserted plate or lag screws the sur-geon knew the inclination of a HEX screw of which only the headprotrudes from the bone because the screw driver by necessityaligns with the screw axis.

Still, the flats of the HEX screw-driver and -recess are orientedrather tangentially to the force applied. Such torque transmissionmay strip and results in a tendency to expand the screw head withapplication of torque. This is the case especially when the screwdriver is worn. The new AO Stardrive™ maintains the advantagesof the HEX but offers a better resistance to stripping, as the flats areorientated more perpendicularly to the force applied. A further ad-vantage of the new AO Stardrive™ is that the size of the drive con-nection now conforms to general technical standards.

The Stardrive has been successfully introduced in the area of max-illo-facial and spine surgery. Further applications such as in thelong bones are under close investigation.

Single slot, cruciate, Phillips HEX Stardrive™

Fig. 1: Different types of screw drive connection.

a b

Fig. 2: Comparison of force transmission upon applicationof torque at insertion/removal between Stardrive™ andHEX

Fig. 2a: Stardrive™: the force is exerted nearly per-pendicularly to the flats of the screw, therefore thetransmission of torque is superior Fig. 2b: HEX: the arrows show that force duringapplication and removal is exerted rather tangentiallyto the flats of the screw drive.

Fig. 3: Appearance of the two different drive connectionsof screws according to the function of the screw used inthe LCP. The locked screws are fitted with Stardrive™, theconventional screws are fitted with HEX drive.

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A. Gächter

New Knee Products

TOMOFIX: Osteotomy ChiselOpen wedge osteotomy ot the tibia seems to have several advan-tages over closed wedge osteotomy, including reduced risk of neu-rologic damage (e.g. peroneal nerve), no shortening of the medialtibial and easier insertion of a future knee arthroplaty if necessary.In addition, the elevation of the proximal tibia can be adjusted moreposteriorly or anteriorly according to needs. On the other hand, itis difficult to maintain the open wedge situation with convention-al implants.For the osteotomy, one can use newly developed chisels withrounded edges and measuring scales to determine the depth of pen-etration. They also come in different widths.The locking plate system creates ideal conditions for a stable situa-tion. The gap can be filled with bone or bone substitute. Normally,a gap up to 1.2 to 1.5 cm fills without the need of bone graft.All osteotomies around the knee achieve optimal fixation with the TOMOFIX system.

J. Hunter

New Paediatric Products

Cannulated Paediatric Osteotomy System (CAPOS)The AO series of angled blade plates for children (infant, toddler,child, adolescent) are essential implants for proximal femoral os-teotomy providing strength, accurate correction, and a good hold,particularly in soft bone such as in cerebral palsy(CP).Users have found placement of the chisel difficult, especially in thedeformed and narrow proximal femur frequently found in CP. TheCAPOS system provides for insertion of the chisel over a guidewire, after insertion of the guide wire through an adjustable angledguide for precision osteotomy. Another feature is a cutting blockthat attaches to the chisel after placement; this ensures that theproximal osteotomy cut is firstly, the correct distance from the chis-el to accommodate the plate offset, and secondly, parallel to thechisel. The plates have not been cannulated at this stage. With a sin-gle chisel track in the femoral neck it was felt that it should be easyto place the implant. We believe that CAPOS will extend the life ofclassical AO implants well into the 21st century and look forwardto users feedback.

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Subcondylar/Ramus Fixation System The Subcondylar/Ramus Fixation System is comprised of instru-mentation to support endoscopic treatment of fractures and orthog-nathic procedures involving the ramus and subcondylar regions ofthe mandible.Open reduction and internal fixation of subcondylar and ramusfractures and osteotomies of the mandible have proven challengingto surgeons; often requiring surgical approaches that provide suffi-cient exposure in order to permit clear visualization of the reduc-tion and application of the fixation device. Open reduction is oftencontroversial due to the difficult access to this area and the poten-tial morbidity related to nerve damage. In addition, large incisionsoften resulting in collateral tissue damage and scarring are regard-ed as costs that must be weighed against the benefits of the proce-dure.Endoscopic technology significantly reduces the invasive aspect ofmany surgical procedures. Synthes Maxillofacial and the AO Max-illofacial Expert Group have developed appropriate instrumenta-tion to support endoscopic, minimally invasive surgical techniquesin treating subcondylar fractures.

R. Schmelzeisen / R. Gutwald

New Craniomaxillofacial Products

1. Panoramic radiograph preopera-tively of a severely dislocated bilateralcondyle fracture. Lag screw fixation ofthe median mandibular fracture wasperformed prior to admission inanother clinic. Note the severely dis-located fragments with medial over-ride on the right and medial displace-ment with shortening of the ascend-ing ramus on the left side.

2. Intraoperative view by a 30degree angled endoscope of thedislocated condyle fracture onthe right side. The condylar frag-ment was dislocated with medi-al override.

3. The condylar fragment wasreduced by the special instru-ments of the Subcondylar / RamusFixation System. Endoscopic viewafter osteosynthesis with a 2.0mmtitanium miniplate. The alignmentof the fragments was controlledendoscopically at the posterioraspect of the ascending ramus.

4. Panoramic radiograph post-operatively after endoscopicassisted reduction and fixationof both condylar fractures.

Bending Cutting Pliers with Beak for 2.0 Mandible Locking PlateThe Bending Cutting Pliers with beak isdesigned for the 2.0 Mandible LockingSystem and combines two features in oneinstrument. Bending over the plane andthe edge as well as cutting of the plates areeasily possible.

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IMF Screw SystemThe IMF Screws are indicated for craniofacial and mandibular trau-ma and reconstruction, plus orthognathic surgery. They are specif-ically used in the occlusion and fracture stabilization of the maxil-la and mandible. IMF (also referred to as maxillo-mandibular fixation, or MMF) is acommonly applied, fundamental technique of wiring the jaws to-gether in trauma and reconstruction procedures. The IMF screw of-fers the advantage of a self-drilling tip and easily identified wireholes that will provide a simple and quick method for achieving in-termaxillary fixation in simple fractures. Generally, between two-and-four screws are placed into each mandible and maxilla andthen connected and tensioned with wire to establish and maintainocclusion.

Battery Powered Screwdriver with ReverseThe Battery Powered Screwdriver (BPS) is a cordless instrument thatassists in the placement of bone fixation screws, tapping and drilling.The handpiece with Reverse is an addition to the BPS system thatcurrently consists of a forward handpiece, Rechargeable BatteryPack and Battery Charger. The addition of a reverse mode on thescrewdriver will enable surgeons to remove screws as well as topower tap. A full line of taps for resorbable screws will be intro-duced with this handpiece.The current method of manual tapping in order to place resorbablescrews is technique sensitive and frequently leads to stripped ornon-functional holes due to excessive wobble caused by surgeonfatigue and motions of the wrist. The Battery Powered Screwdriv-er with Reverse allows the surgeon to tap consistently every timewith little or no wrist action. The combination of self-drilling tapsand a battery driven handpiece offers a clear advantage over thecompetition in the resorbable market in terms of reducing OR timeand surgeon fatigue.

MR Safe InstrumentsMR Safe Instruments, comprised of a vari-ety of taps, screwdriver blades, one drillbit and one screwdriver handle with mini-quick coupling, are to be used in magneticresonance imaging procedures. Most medical device instruments used inan MRI Suite are manufactured from non-magnetic materials such as L605, MP35Nor 316LEH. The MR Safe Instruments willbe manufactured from MP35N (blades,taps and drill bit) and 316LEH stainlesssteel (screwdriver handle) because theyare stronger and have better wear charac-teristics compared to the L605 material. All

of the instrument designs already exist asstandard SYNTHES® products.The MR Safe Instrument Project was initi-ated to meet the needs of those surgeonswho perform operations in a MRI Suite ora MRI Environment, which is highly mag-netic. Instruments made out of materials,such as 440A and X15-TN stainless steelare highly magnetic and can be extremelydangerous to both the patient and thoseperforming or assisting in the operativeprocedure.

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J. Auer /D. Hulse

New Veterinary Products

3.5mm Broad LC-DCPThe Reinforced 3.5mm DCP is a very popular implant in small an-imal surgery because it is stronger than the narrow 4.5mm plate,contains mores plate holes than the same length Narrow 4.5mmDCP and the 3.5mm cortex screw contains more threads than the4.5mm screw. All these parameters result in a stronger construc-tion. The fact that the 3.5mm LC-DCP system did not include abroad plate prevented many small animal surgeons from changingto the LC-DCP system. This was the main reason to develop such aplate.The 3.5mm Broad LC-DCP is made from 4.5mm Narrow LC-DCPplate stock. The LC-DCP looks significantly wider but in realitythere is only a difference of 1.5 mm. Not only were all LC-DCP fea-tures converted but staggered holes to increase torsional stabilityand reduce stress risers from in-line screw holes were added aswell. The only change for veterinary surgeons is the need to adaptto the DCU and Universal Drill Guide.

5year old, 55 lb, male cow.Sustained a low velocity gun-shot wound to the left thigh.Type1 open fracture. No early post operative compli-

cations. Early return og weightbearing function.

R. Egle

New Products from AO PublishingAs you are reading this, the 2001–2 Edition of the AO Image Col-lection–AO Principles of Fracture Management will be released. Itcontains over 1000 images, including LCP, used in the current AOPFxM (edition 2001).

AO Publishing is planning to release the companion to AO PFxM:The AO Manual Series. The first edition will cover Upper Extrem-ities. While the AO PFxM represents a classical text book (illustra-tions supporting the text), the AO Manuals will consist mainly ofillustrations supported by text. The authors are submitting casesdocumented with pictures and intra-operative videos. The publica-tions will be available in print with CD-ROM and Internet-update;as introduced with the AO PFxM. We expect the first edition to beready for the December course.

Visit us on the internet at: www.aopublishing.org

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E. Schneider & K. Ito

Distal Femoral NailA Scientific Study from the AO Research Institute

Objective: Intramedullary nail locking bolts often fail to gain pur-chase or cut out in osteoporotic bone. The biomechanical stabilityof a bladelike device that lowers intraosseous stress levels by dis-tributing the load over a greater volume of bone was compared withconventional locking bolts in osteoporotic bone.

Methods: Standardized simulated comminuted supracondylarfemoral fractures (segmental defect) in fresh-frozen paired osteo-porotic (bone mineral density <200 milligrams per cubic centime-ter) human cadaveric femurs were stabilized with a retrograde un-reamed distal femoral nail and distally interlocked withconventional locking bolts or a bladelike device. The distal por-tions of the fixator-bone constructs were tested under axial load,and the stiffness and strength were compared (pairwise).

Results: Interlocking with a bladelike device was 41 percent stiffer(p = 0.01) and 20 percent stronger (p = 0.02) than that with con-ventional locking bolts. All posttesting radiographs showed com-paction of the cancellous bone distal to the interlocking devices.Even after nail displacements of twelve millimeters, only a fewlocking bolts were plastically deformed and no bladelike deviceshowed gross plastic deformation.

Conclusion: This study showed the biomechanical benefits of in-creasing the bone-implant interface surface for improving the acutestiffness and strength of fracture fixation in osteoporotic cancellousbone. The fixator-bone construct withstood higher forces beforefailure in these fragile bones.

Reference: Ito, K., Hungerbühler, R., Wahl, D., and Grass, R.: Im-proved intramedullary nail interlocking in osteoporotic bone. Jour-nal of Orthopaedic Trauma, Vol. 15, No. 3, pp. 192–196, 2001.

Interlocking with conventional bolts (above) and the bladeplate device (below)

(see also article on page 8)

16

HumerusblockThe “Humerusblock” described in the last issue was made availableto a selection of surgeons in November 2000 as part of a documen-tation series. The aim of this documentation series was to record theresults of first applications with the new implant. In the context of this series 16 cases were documented. The fracturesincluded 7 subcapital humerus fractures, 6 subcapital humerusfractures with additional fracture of the greater tubercle and three4-fragment fractures. A “closed” surgical procedure was performedin all cases. The surgeons generally made use of K-wires with a di-ameter of 2.2mm and no thread. The use of additional screws wasnecessary in 8 cases. Follow-up assessment was carried out in 14 of the 16 cases. In 13cases fracture consolidation was described by the treating physi-cian; in one case delayed healing was suspected. Slight impactionwas observed in four cases and more severe impaction in two cas-es. Impaction can be regarded as a desirable event. In relation to theimplant, the K-wires act as a sort of splint so that impaction occursin a controlled manner. Dislocation of the humeral head was not ob-served in any case. In 11 patients, the K-wires perforated the artic-ular surface; this occurred 6 times intraoperatively and 5 times post-operatively. Primary and secondary perforation of the K-wiresthrough the articular surface indicates that the K-wires need to beplaced in the immediate subchondral region in porotic bone if theyare to find sufficient anchorage. Therefore, implant removal afterfracture healing or prior to mobilization is necessary; the surgeonmay possibly have to withdraw some of the K-wires slightly early on. The following complications occurred during the healing process:local wound irritation above the implant (2 cases; due to incorrect-ly clipped K-wires) and skin perforation by a K-wire (1 case). Inone case, reduction of the greater tubercle was lost in a 4-fragmentfracture; reoperation to stabilize the fragment was necessary. Therewas probably delayed union in one case of a 76-year-old patient.Infections and/or nerve lesions were not observed in any case. In contrast to conventional K-wire osteosynthesis, the “Humerus-block” permitted the surgeons to perform adequate stable fixationof proximal humerus fractures. Compared with fracture treatmentby plate osteosynthesis, this procedure is far less invasive withmaximal conservation of the fracture fragments residual vasculari-ty. The conclusions that can be drawn from this series are limitedby the small number of patients included (n=16) and followed up(n=14). It can be stated that it proved of value in all the participat-ing centers and that with further application a set of suitable indi-cations will no doubt emerge.

H. Resch/M. Müller

Studys

accident

postoperative

fracture healed

62 year old female patient

Jan. 2001 Dec. 2001- Jan. 2002

Study Start

Clinical Journal (document all distal radius fractures retrospectively)

In- and Exclusion criteria

Fulfilled ⇒⇒ Study case (all plated cases)

Not fulfilled ⇒⇒ Clinical Journal (prospective)

L. HuysseAn outlook on the LCP Distal Radius Studie(Locking Compression Plate)One of the key objectives of AOCID is to organize and conduct clin-ical studies that provide evidence regarding the clinical benefit ofAO methods and implants. The “gold standard” study design toachieve this is a randomized clinical trial (RCT). We therefore con-sidered this design for the LCP distal radius study right from thestart. While simple on paper, the process of randomization met with somepractical obstacles. Which treatment would be optimal to comparethe LCP with? For which indication? Would surgeons be preparedto randomize patients? In fact, we could not find a consensus on thebest control treatment, since the new LCP plate is based on a newconcept and does not replace an existing system on a one by one ba-sis. An RCT was judged inappropriate, in particular because sur-geons were convinced that the LCP will provide a better outcomefor the patient and therefore were not willing to use the conven-tional system any longer. The best compromise was to conduct an observational study wherethe treatment decision remains in the hand of the surgeons. This de-sign allows documentation of the range of indications for treatmentwith the LCP, and both clinical and radiological outcomes, afterplating of the distal radius. By collecting data from a large numberof cases, we will identify different cohorts (e.g. patients treatedwith different plates) that will be compared.

The LCP Distal radius study includes three prospective studies andone retrospective study.❚ ”Conservative” distal radius study in the UK documenting all dis-

tal radius fractures, and all types of treatment (majority of frac-tures treated conservatively).

❚ LCP 3.5mm distal radius study, involving centers mainly usingthe 3.5mm LCP system (10 centers).

❚ LCP 2.4mm distal radius study, focused on the 2.4mm LCP sys-tem (6 centers).

❚ Retrospective study documenting the treatment of all distal radiusfractures in the past year (before the LCP plate was available). Thesame clinical journal form is used, with no follow-up visits, andno collection of X-ray images (7 centers).

We have two types of questionnaires for the prospective studies,one for all plated cases (any type of plate and fulfilling inclusionand exclusion criteria), including follow-up forms up to two yearspost-operatively, and a shorter one for all other cases (making theclinical journal).A schematic overview of the LCP 3.5 mm and 2.4mm study, com-bined with the retrospective study is shown in the figure below.The same inclusion and exclusion criteria, as well as clinical (in-cluding the Gartland and Werley, the DASH and the SF-36 scoringsystems) and radiological (centrally evaluated) outcome criteria areused in the different prospective studies. While follow-up is im-plemented for all cases in the "Conservative" distal radius study,only plated cases are followed in the two other prospective studies.

Special attention will be given to the expected advantages of the

new LCP concept as well as to maintenanceof reduction, the additional use of bonegrafting, and the learning curve. The stud-ies are controlled in order allow a compar-ison of the LCP systems to other conven-tional plating systems and conservativetreatment of distal radius fractures. The ret-rospective part of the study (documentingthe situation before the introduction of theLCP system) will show whether any shiftin indication from e.g. external fixator tothe LCP system has occurred and in orderto define a control group accordingly for fu-ture studies.The different studies were started at theend of 2001.

New Productsfrom AO Development

Norbert P. Haas, AOTK Chairman

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Editors:Univ.-Prof. Norbert P. Haas, AOTK ChairmanE-mail: norbert.haas@ao-asif.chP. SchreitererE-mail: philip.schreiterer@ao-asif.ch

Publisher: AOTKLayout: AO Media ServicesPrint: Gonzen Druck AG, CH-Bad Ragaz

Number of Copies: 20000Issued: May 2002

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