The effect of medial release on flexion and extension gaps in cadaveric knees: implications for soft-tissue balancing in total knee arthroplasty.

This cadaver study examined the effects of medial structure release for varus deformity correction during total knee arthroplasty. Twelve specimens were used to investigate the amount of varus correction achieved with sequential release of medial structures. Varus-valgus and internal-external rotation angles were measured using the Isotrack II motion tracking system. Each release sequence was tested at full extension and 45 degrees and 90 degrees of flexion to compare any differences obtained in the joint gaps. After release of the posteromedial capsule oblique ligament complex, superficial medial collateral ligament (MCL), pes anserinus, and semimembranosus tendons, valgus rotation increased to 6.9 degrees in full extension and 13.4 degrees in 90 degrees of flexion. The largest increase (3.2 degrees) in valgus rotation occurred after the superficial MCL was released. Initial release of the superficial MCL led to a more gradual correction with release of subsequent structures. Changes seen in 90 degrees flexion were significantly greater than those in full extension. While the cadaveric model is limited by the lack of deformity in the specimens, the data provide several clinically relevant conclusions. In many cases requiring major medial release for severe varus deformity, potential flexion-extension differences in the resulting tibiofemoral gaps may require new consideration. These data may help explain the heightened interest in and variety of approaches for addressing femoral component rotation and issues of flexion stability since a significantly larger correction is obtained in flexion. Minimal changes in internal-external rotation of the tibia occurred until both the pes anserinus and semimembranosus tendons were released (4 degrees of external rotation).