The active pivot shift: the role of the popliteus muscle.

Ligament insufficiency due to athletic injury is widely recognized and reported as an etiological factor in knee joint instability. It was recognized that a patient presenting with knee joint instability due to past hockey injury to the anterior cruciate ligament, subsequently verified surgically, was able to voluntarily and actively perform the pivot shift maneuver with his knee as a result of his anterolateral rotatory instability. During a subsequent 6 month period, three other patients with similar anterior cruciate deficiencies presented with this same active pivot shift maneuver phenomenon. A study was designed to determine the active muscle or muscles involved in this abnormal active motion in the knee joint with anterolateral rotatory instability. Electromyographic studies with needle electrodes were conducted on a variety of muscles in four subjects presenting with the instability. Results indicated that the popliteus muscle plays a major role in the active performance of the pivot shift maneuver.