The Voluntarily Evoked Posterolateral Drawer Sign in the Knee with Posterolateral Instability

Posterolateral instability of the knee refers to a ligamentous lesion that allows abnormal posterior and posterolateral subluxation of the tibial plateau. This condition is caused by injuries of the posterolateral structures (arcuate ligament complex) and the posterior cruciate ligament. Ten patients could produce the instability voluntarily by active muscle pull. Electromyographic studies clearly demonstrated that the biceps femoris muscle acted as a major subluxor and the popliteus as a reducer. The operative findings of the patients were not different from those of the patients who could not subluxate voluntarily. The active muscle pull of the popliteus is a key to treatment of posterolateral instability.