Rotatory instability of cadaver knees after transection of collateral ligaments and capsule.

The importance of the medial and lateral compartment ligaments of the knee in relation to valgus-varus and axial rotation instability was investigated. Mobility patterns were drawn from 20 osteoligamentous knee preparations after successive transections of the structures. Cutting of the medial collateral ligament resulted only in slight valgus instability and modest anteromedial instability. When the medial posterior joint capsule was also cut, both types of instability increased, and moreover, the knee became posteromedially unstable. Cutting of the lateral collateral ligament produced only a little varus instability and anterolateral rotatory instability, but varus instability increased considerably when the posterior lateral capsule was also transected. In this latter situation, even marked posterolateral rotatory instability was found. Isolated transection of the medial or lateral collateral ligament did not cause any major valgus or varus instability, but when the posterior capsule was also transected, a considerable degree rotatory instability could be found even though the cruciate ligaments were intact.