surgical technique - 3 templating x-ray templating templating the anterior/posterior (a/p) x-ray...
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Our surgeon design team first implanted the Preservation™ Unicompartmental Knee System in 2001. The system was developed with over 100 years combined unicompartmental knee replacement experience.
In its design, our objective was to develop specialist instruments and a new concept of specific technique that allowed the surgeon to achieve accurate, reproducible alignment and balance for long-term clinical results. Since its launch, this technique has evolved with the experience of our designing surgeon team and is incorporated into this Surgical Technique manual.
Appropriate implant alignment and articulation, as well as flexion and extension space balancing must be achieved to obtain optimal results. The relatively small working area available for unicompartmental surgery means that the cementing technique is also critical to long term fixation. If these fundamentals are respected, excellent outcomes can be achieved with early return of function, outstanding range of motion, and a very high level of patient satisfaction.
The clinical results to date have been enlightening and rewarding. With 5 years of clinical experience, we continue to follow hundreds of patients enjoying ongoing clinical success with the Preservation™ Unicompartmental Knee.
We believe the implant will continue to perform well for years to come.
The Preservation™ Design Group
Dr. Dave Dalury - Baltimore, USA
Dr. Dave Fisher – Indianapolis, USA
Dr. James McAuley – London, Canada
Dr. Wolfgang Herzberg – Hamburg, Germany
Dr. Greg Keene – Adelaide, Australia
Dr. Ed Newman – Christchurch, New Zealand
Dr. Gerry Engh – Arlington, USA
FOREWORD PRESERVATION™ UNICOMPARTMENTAL KNEE SYSTEM
Approach and Exposure 5
Tibial Jig Alignment 7
Proximal Tibial Resection 10
Extension Gap 12
Flexion Gap 13
Alignment and Femoral Resection 14
Femoral Sizing and Rotation 15
Femoral Chamfer Cuts 18
Trial Reduction 19
Femoral Fin Slot 21
Femoral Peg 22
Tibial Keel Preparation 23
Component Trial 24
Cementing Preparation 25
Cementing the Tibial Components 26
Cementing the Femoral Component 30
Possible Flexion/Extension Gap Adjustment 32
Implant Product Codes 33
Instrument Product Codes 35
INTRODUCTION PRESERVATION™ UNICOMPARTMENTAL KNEE SYSTEM
Precise Alignment The exposure for the Preservation™ Unicompartmental Knee System leaves the patella in its natural position over the femoral condyles and avoids disruption of the extensor mechanism.
Varus/valgus alignment The key to precise varus/valgus alignment is the approach to femoral resection. For the Preservation™ Unicompartmental Knee System, the distal femoral cut is made with the leg in extension, with the cutting block resting on the resected tibia. This allows the surgeon to assess the joint for natural balance and alignment with the patella close to it’s normal position, before the final cut is made.
True component to component alignment Adjustment to medial/lateral alignment at the trial stage ensures that the femoral and tibial component are truly aligned for optimum articulation, throughout the range of motion.
Preserved Natural Balance Preventing over correction The joint balance is checked in natural alignment to ensure even load distribution across the joint, using the Preservation™ Unicompartmental Knee System distal cutting block and shims. This avoids over correction of the unaffected compartment.
Balanced flexion and extension The flexion and extension gaps are checked before any femoral cuts are made. This allows fine adjustments to be made to balance the knee.
Joint line restoration Positioning the implant based on a joint line reference with the distal femoral cutting block allows good function throughout gait.
Restores Joint Function Established articulating geometry The Preservation™ Unicompartmental Knee System “J” curve sagittal geometry, with its anterior kick-back, provides good coverage of the femoral condyle. This allows smooth, pain free kinematic patella function. Its coronal profile is curved to optimise bearing contact, avoiding edge loading in varus or valgus lift off.
Optimal, intra-operative bearing selection to suit each patient The Preservation™ Unicompartmental Knee System offers a range of all-polyethylene, modular fixed and mobile bearing options, to suit the needs of each patient.
GUR 1020 Cross-linked bearing material GUR 1020 cross-linked, ‘closed’ foil pack sterilised polyethylene is used in the Preservation™ Unicompartmental Knee System for its resistance to oxidation and wear.
Keeled tibial fixation The keel design ensures the tray or bearing is mechanically stable on the tibial plateau. It also adds strength to the tibial component and allows a minimum bearing thickness of 7 mm for the all-polyethylene option.
Indications Unicompartmental Knee Replacement (UKR) is indicated for patients with osteoarthrosis that is isolated to the medial or lateral tibial-femoral compartment. In these cases, the remaining opposite compartment articular cartilage is physically and biomechanically intact and capable of bearing normal loads.
In very young and active patients, a high tibial osteotomy may still remain the treatment of choice for advanced single compartmental disease.
Contraindications UKR is contraindicated for patients with inflammatory arthritis, significant chondrocalcinosis of the articular surface, advanced involvement of the other compartments or a significant extra-articular deformity.
X-ray Templating Templating the Anterior/Posterior (A/P) X-ray will indicate the amount of tibia to be resected (Figure 1). The lateral X-ray is used to determine the size of the femoral component and the angle of the posterior tibial slope. It is recommended that each patient is X-ray templated prior to the procedure.
Anterior Posterior Template: Tibia The A/P template is placed over the A/P X-ray with the thick red horizontal line 2 mm above the lowest point of the superior tibial bone on the non-arthritic side (Figure 2). This indicates the new joint line on the arthritic side.
Select the thinnest tibial prosthesis that will remove the defect. The minimum thickness of a fixed bearing all-polyethylene is 7 mm. A fixed bearing modular metal backed or mobile bearing minimum thickness is 9.5 mm. This thickness will determine the tibial resection. If the gap from the joint line to the lowest point of the worn side is 3 mm, then only 4 mm of tibia is resected. If there has been greater wear of the tibia and a thicker tibial component is necessary, simply adjust the measurements accordingly. This predicted tibial resection must be checked intra-operatively before tibial resection.
Anterior posterior X-ray and template
Joint Line 3 mm
4 mm tibial resection
New Joint Line
7 mm tibial component
4 mm tibial resection
Figure 1 Figure 2
Lateral Template: Femur The lateral template is positioned in the coronal plane at a right angle to the long axis of the femur (Figure 3). Align the template with the planned distal femoral cut to remove the defect. The template outline should be 1-2 mm larger than the bony margin of the X-ray, and should match the outline of the articular surface (2 mm thick). The posterior condyle of the prosthesis must not excessively overlap the superior bony margin of the adjacent posterior condyle of the femur.
The posterior slope of the upper tibia should also be templated on the lateral X-ray as this is set at the time of tibial resection (Figure 4). This can vary from 0 to 15˚ and affects tightness of the prosthesis in flexion.
A preliminary arthroscopy may also be used at an earlier stage to provide an initial assessment.
Femoral sizing on the lateral X-ray Posterior tibial slope on the lateral X-ray
Figure 3 Figure 4
The Approach - Medial or Lateral Compartment An antero-medial or antero-lateral skin incision is performed. The incision should begin 1 cm proximal to the superior border of the patella. It should extend 6 -10 cm distally along the edge of the patella and patella tendon, and end 2 cm distal to the joint line (Figure 5). A longer incision is advised when first starting to use the procedure or if the patient is obese. The joint capsule is entered with a parapatellar incision (Figure 6). Once the joint is exposed, a final assessment can be made of the extent of arthritic damage and the suitability of the joint for this procedure.
Exposure The deep menisco-tibial layer of the medial or lateral capsule should be carefully retracted to provide good access to any tibial osteophytes and allow accurate wound closure. Any excess deep synovium is excised to provide clear sight of the joint. If required, all or part of the fat pad may also be excised to improve vision and allow inspection of the opposite compartment. Two large rake or ‘z’ retractors are then introduced to maintain access to the capsule during all stages of the procedure. Retraction of skin edges should be avoided. No ligament releases should be performed as part of this procedure as th