Classification of knee ligament instabilities. Part I. The medial compartment and cruciate ligaments.

Based on the clinical and operative findings in sixty-eight knees with acute tears of the medial compartment and cruciate ligaments, a standardized terminology and classification of knee ligament instability is presented. With an intact posterior cruciate ligament, anteromedial, anterolateral, or posterolateral rotatory instability may occur, but not true posteromedial rotatory instability. With the posterior cruciate ligament ruptured, straight anterior, posterior, medial, or lateral instability may be found.