Tests for posterolateral instability of the knee in normal subjects. Results of examination under anesthesia.

Abstract

An apparently normal knee was examined in each of 100 subjects while they were under general or epidural anesthesia for an unrelated operation. The Lachman, anterior drawer, posterior drawer, and pivot-shift tests were negative in all knees. All knees were stable to varus and valgus stress at both 0 and 30 degrees of flexion. The external-rotation recurvatum test also was negative in all knees. A positive reversed pivot-shift sign was present in 35 per cent of the knees, suggesting that it may not signify abnormality, at least not without a negative test on the contralateral knee. The results of the posterolateral drawer test were variable, difficult to quantify, and did not always have a firm end-point. The amount of maximum external rotation of the tibia, measured from the reference line of the medial border of the foot, was extremely variable at both 30 and 90 degrees of flexion of the knee. External rotation, as determined by this reference, was slightly greater (averaging 9 degrees) at 90 than at 30 degrees of flexion. The normal range of maximum external rotation of the foot was 10 to 45 degrees at 30 degrees of flexion of the knee and 15 to 70 degrees at 90 degrees of flexion. The presence of a large angle of external rotation and a positive reversed pivot-shift sign correlated strongly with increased ligamentous laxity and mild varus alignment of the knee.