Experimental study on external tibial rotation of the knee.

Using biplanar roentgenographic photogrammetry, we investigated posterolateral rotatory instability of the knee joint both before and after sectioning of posterolateral structures, the posterior cruciate ligament, and the lateral collateral ligament. Fifteen fresh-frozen cadaveric knees were used. Compared with the intact state, sectioning of the posterior cruciate ligament alone did not increase the amount of external tibial rotation, but the axis of external tibial rotation shifted when the anterolateral bundle of the posterior cruciate ligament was cut. When the posterior cruciate ligament was cut after sectioning of the posterolateral structures and the lateral collateral ligament, external tibial rotation increased and the axis of external rotation shifted. The results demonstrated that sectioning of the anterolateral bundle of the posterior cruciate ligament is associated with a change in the location of the axis of tibial rotation. Therefore an isolated posterior cruciate ligament injury can alter the kinematics of the knee joint by changing the axis of external tibial rotation. The present results also demonstrate that the posterior cruciate ligament serves as a kind of secondary restraint to posterolateral rotatory instability in knees with injured posterolateral structures. Helical motion analysis using biplanar roentgenographic photogrammetry is a useful method for evaluating knee kinematics.