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ABSTRACT
TKR is one of the greatest inventions of the last century and is one of the widely accepted and successful surgeries in modern orthopaedics. The most important step in primary TKR is the correct approach and correct incision, which does not affect the vascularity of the flaps. Anterior midline incision with medial parapatellar capsular approach is the most widely accepted method. But this may weaken the medial soft tissue structures. The incision should not be lateral to the lateral margin of the patella. Undermining of the skin is dangerous and heavy retraction affects the vascularity of the flaps. Interrupted loose sutures are used to close the wounds. In subvastus approach, the vastus medialis is seperated and retracted from the capsule. But the exposure is less extensive, when compared to the medial parapatellar approach. But the medial soft tissue structures are not weakened. In midvastus approach, the vastus medialis is split at the superomedial corner. In this, exposure is better and this approach is becoming more popular now. Patella evertion is easier and exposure is adequate. Majority of the valgus knees can be operated through medial parapatellar capsular approach, but in severe valgus deformity, a lateral capsular approach is used. Care should be taken to avoid the avultion of the tibial tubercle, which is a disasturous complication. In stiff knees without any range of movements, extensile approach with quadriceps v-y plasty, or a rectus sniff is used.
J.Orthopaedics 2004;1(1)e6
SKIN INCISION
The anterior midline is the most commonly used one. It can be just lateral to the anterior midline but never be medial to it because majority of the blood vessels to the flaps come from the medial side. The incision should never be lateral to the lateral margin of the patella
The incision of any previous surgeries around the knee should be aways taken into account. Never undermine the skin, always raise fasciocutaneous flaps. There is no role for minimally invasive approach, use a liberal incision and avoid heavy retraction which will definitely delay wound healing. In nut shell the best incision is midline anterior approach with a starting point 7 cm superior to the proximal pole of patella, the distal end point being 6 cm distal to the inferior pole of the patella. During closure it is better to use interrupted mono filament suture material for the skin with the knots tied loosely
CAPSULAR APROACHES
Medial parapatellar approach: Compared to any approach gives maximum exposure for bone cuts, ligament balancing and prosthesis fitting.
The medial approach is started at the medial 1/3rd of the patellar tendon 3 cm above the superior pole of patella, curves round the medial aspect of patella with at least 1 cm of the medial retinaculum attached to the patella for facilitating late repair. The approach ends 1 cm medial to the tibial tubercle.
Patella is then dislocated laterally with the knee flexed; the patella should not be everted forcefully because avulsion of the ligamentum patellae from the tibial tubercle could be a disastrous complication. This risk should be reduced by division of patellar ligament, with a piece of bone at the tibial tuberosity and release of adhesions under the patellar tendon and the quadriceps tendon. Closure is made by interrupted sutures applied loosely so that flexion is not restricted.
Subvastus approach: The medial margin of the vastus medialis is freed and retracted and the tendinous insertion of this muscle is separated from the medial capsule(5). The distal part of the approach is the same as that of the medial parapatellar approach. The vastus medialis, extensor mechanism and the patella are retracted laterally and then the patella is dislocated laterally. Muscle need not be retracted. Advantage of this approach is that extensor mechanism as such is minimally disturbed, the tracking of the patella is not affected and the blood supply to the patella is preserved(1,3,5). Scarring patellar fixity, severe flexion deformity and previous surgery are however contraindications.
Midvastus approach:
The vastus medialis muscle is split at the superomedial corner of the patella(2). Distal part of the approach is the same as medial parapatellar approach. Split in the muscles needs only few sutures for approximation
Compared to the subvastus approach the patellar eversion is easier, the blood supply to the patella is unaffected, and the extensor mechanism is least disturbed. Contraindications are the same as that of subvastus approach.
Lateral approach: This is used in valgus knees. Upper part of the anterior compartment muscles and ITB are elevated(4,5). Popliteus tendon may be released, lateral patellar retinaculum is incised and patella everted medially. Care should be taken to avoid avulsion of the ligamentum patellae from the tibial tubercle, which is a catastrophic complication. Main advantage is that this approach helps in lateral release in valgus knees.
Midline approach: Capsular incision starts at the middle of the quadriceps tendon. The distal part of the approach is the same as that of medial parapatellar approach. This is not routinely used nowadays.
Extensile approach: When patellar eversion is difficult in stiff knees and patellar fixity is there, extensile approach is needed. Tibial tubercle division, quadriceps V-Y plasty, rectus snip and medial epicondyle osteotomies are used. Rectus snip involves medial parapatellar approach and cutting either transversely or of ohliquely the rectus tendon and then followed by inferolateral eversion of the patella
Quadriceps V-Y plasty helps in lengthening of the quadriceps tendon and this during surgery helps in the turning down the patella inferolaterally
The medial epicondylar osteotomy is done through medial parapatellar approach with an osteotome from distal to proximal 1 cm thick bone is elevated, the attachment of the collaterals and the adductors should not be disturbed; the elevated bone piece is fixed with screws.
Another method is to skeletonise the femur by subperiosteally elevating the muscles and the ligaments. One should be careful not to produce mediolateral instability.
References:
1.Bindeglass DF, Vince KG:Patellar tilt and subluxation following subvastus and parapatellar approach in total knee arthroplasty: Implication for surgical technique. J Arthroplasty 11:507-511, 1996
2. Engh GA, Parks NL, Ammeen DJ: Influence of surgical approach on lateral retinacular releases in total knee arthroplasty. Clin Ortho 331:56-63, 1996
3.Faure BT, Benjamin JB, Lindsey B, et al: Comparison of the subvastus and paramedian surgical approaches in bilateral knee arthroplasty. J Arthroplasty 8:511-516, 1993.
4. Fiddian NJ, Blackway C, Kumar A: Replacement arthroplasty of the valgus knee. J Bone Joint Surg Br 80:859-861, 1994.
5. Instability after Major Joint Replacement:The Orthopedic Clinics of North America: Vol 32, Number 4, Oct 2001.
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