In total knee arthroplasty (TKA) the knee may be found to be too stiff in extension, causing a flexion contracture. One proposed surgical technique to correct this extension deficit is to recut the distal femur, but that may lead to excessively raising the joint line. Alternatively, full extension may be gained by stripping the posterior capsule from its femoral attachment, however if this release has an adverse impact on anterior-posterior (AP) stability of the implanted knee then it may be advisable to avoid this technique. The aim of the study was therefore to investigate the effect of posterior capsular release on AP stability in TKA, and compare this to the restraint from the cruciate ligaments and different TKA inserts. Eight cadaveric knees were mounted in a six degree of freedom testing rig (Fig.1) and tested at 0°, 30°, 60° and 90° flexion with ±150 N AP force, with and without a 710 N axial compressive load. The rig allowed an AP drawer to be applied to the tibia at a fixed angle of flexion, whilst the other degrees-of-freedom were unconstrained and free to translate/ rotate. After the native knee was tested with and without the anterior cruciate ligament (ACL), a cruciate-retaining TKA (Legion; Smith & Nephew) was implanted and the tests repeated. The following stages were then performed: replacing with a deep dished insert, cutting the posterior cruciate ligament (PCL), releasing the posterior capsule using an osteotome (Fig. 2), replacing with a posterior-stabilised implant and finally using a more-constrained insert.Introduction
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