Abstract
An important goal of total knee replacement is deformity correction. Arthritic narrowing can be accompanied by a fixed shortening of the collateral ligament on the same side of the narrowing. There can also be ligamentous laxity that develops in the opposite compartment. Flexion contracture can develop with tightening of the posterior capsule. Successful total knee replacement requires proper bone resection along with gap balancing and balanced collateral ligament tensioning. Beware of correctable deformities, as the collateral ligament may have kept its resting length and therefore the knee becomes stable after the bone resections are made and the spacer block is inserted to test the stability of the knee in flexion and extension.
In the varus knee, the MCL may be contracted. A medial release of the superficial medial collateral ligament may be necessary. This can be done by stripping the periosteal insertion of the MCL. A stretch may be accomplished by placing a laminar spreader in the narrow medial joint space and opening the space until the MCL stretches from its insertion. This maneuver will require a further increase in polyethylene thickness height of 2 – 4mm. Krackow has also on occasion done a surgical imbrication of the LCL, if it appears attenuated on the lateral side of a severe varus deformity.
For valgus deformities, the LCL, arcuate ligament and popliteus and ITB can be contracted. At this time, most authors recommend preservation of the popliteus tendon as it affects primarily the flexion gap. In extension there has been consensus that the surgeon should release what is tight. This may include the ITB release in a pie-crust fashion, or off the Gerdy's tubercle and then a selective release of the arcuate ligament complex. Krackow has also utilised tightening imbrication of the MCL if it is severely attenuated and lax. This has been used infrequently, however. To avoid overlengthening of the knee by referencing balance off of the lengthened, attenuated MCL in cases of severe valgus deformity, less release is performed and a CCK implant may be used.
For severe flexion contractures, the posterior osteophytes should be first aggressively removed. The posterior joint capsule can be stripped off the distal femur and sometimes the gastrocnemius muscle insertions can be dissected free. After these maneuvers, proximal raising of the joint line by resection of the distal femur can be utilised. In ankylosis with severe flexion contracture, constrained implants will be needed if the proximal resection extends above the insertion of the collateral ligaments.
Recurvatum is a rarely seen deformity that is usually associated with an extraordinarily weak or paretic quadriceps. The joint capsule has become stretched over time. Careful balancing of the knee is necessary. But, if the recurvatum still persists, distally augmenting the femur is an option. And no releases are required.
