Measurement of anterior-posterior motion of the knee in injured patients using a biomechanical stress technique.

We performed biomechanical stress tests preoperatively on the knees of fifty-one patients with an injury to the knee. We measured the amount of anterior and posterior tibial translation at 90 degrees of knee flexion using a roentgenographic technique and a fifty-newton joint load. Knees with an isolated meniscal tear exhibited no abnormal motion. There was no difference in motion of the knee between patients with a rupture of the anterior cruciate ligament and patients with this injury who had had a prior medial meniscectomy. We found that prior knee surgery that was not associated with stability did not adversely affect the test procedure. A significant finding, however, was that only nineteen of twenty-five patients with a ruptured anterior cruciate ligament had greater excursion on the injured side compared with the uninjured knee. Because of this inconsistent result, a biomechanical stress test at 90 degrees of knee flexion measuring anterior and posterior translation under a fifty-newton joint load appears insufficient in itself to be of clinical use.