ACUTE ANTEROLATERAL ROTATORY INSTABILITY OF THE KNEE

Thirty-six consecutive knees with acute anterolateral rotatory instability were reviewed to document the ligamentous and meniscal injuries and to evaluate the value of the jerk test and anterior drawer test in diagnosing anterolateral rotatory instability. At surgery, the anterior cruciate ligament and the midthird of the lateral capsular ligament were found to be torn in twenty-one knees; the lateral capsular ligament alone, in six knees; the anterior cruciate ligament alone, in four knees; the anterior cruciate ligament, lateral capsular ligament, and fibers of the iliotibial tract, in three knees; and the anterior cruciate ligament and iliotibial tract fibers, in two knees. The lateral meniscus tear was the sole meniscal injury in fourteen knees, and the tear of the medial meniscus was the sole meniscal injury in five knees. Both the medial and the lateral menisci were torn in six knees, and eleven knees had no meniscal injury. The anterior drawer test done with the tibia in neutral rotation was the most sensitive test for anterolateral rotatory instability and was prevented by hamstring spasm. The jerk test was frequently guarded against by the patient, and was positive on the initial examination in only nine of thirty-six knees. The anterior drawer test was positive in fourteen of thirty-six knees on initial examination. Each test was markedly positive at examination under anesthesia prior to surgery. Four knees with acute anteromedial rotatory instability had unexpected anterolateral instability demonstrated on examination under anesthesia prior to surgical repair of the acute medical-compartment injury. Knees that demonstrate acute anteromedial rotatory instability should also be examined for anterolateral rotatory instability under anesthesia prior to surgical repair of the medial ligaments.