Use of the quadriceps active test to diagnose posterior cruciate-ligament disruption and measure posterior laxity of the knee.

Orthopaedic surgeons routinely use passive tests, in which the displacing force is applied externally, to evaluate the integrity of the ligaments of the knee. Using a quadriceps active test, in which the muscle contractures of the subject served as the displacing force, tibial displacement was measured with an arthrometer in ninety-two subjects: sixty-seven who had an acute or chronic rupture of the posterior or anterior cruciate ligament and twenty-five who had normal knees. With the knee joint in 90 degrees of flexion, contraction of the quadriceps resulted in anterior translation of the tibia in forty-one of forty-two knees that had a documented disruption of the posterior cruciate ligament. This anterior translation did not occur in the contralateral, normal knee of the same subjects; in the knees of the twenty-five normal subjects; or in twenty-five knees that had a known unilateral anterior cruciate-ligament disruption.