Rotational motion of the knee

This study deals with the quantitation of axial rotation at the knee. Passive rotation of the knee was measured at various degrees of flexion on 17 subjects with normal knees and 19 patients with unilateral anterolateral ro tatory instability. Normal subjects were found to have bilateral sym metric rotational knee motion at each angle of flexion tested. When the knee is in a position of flexion be tween 30 and 90°, there are approximately 45° external and 25° internal rotation. Rotatory motion decreases with further extension and, at 5° of flexion, the knee has 23° external and 10° internal rotation. The knee with a torn anterior cruciate ligament and anterolateral rotatory instability was found to have an arc of rotation similar to the contralateral knee and to the control knees between 30 and 90° flexion. At 15° of flexion, a slightly greater arc of rotation was meas ured compared to normal knees. At 5° of flexion, a significantly greater range of external (to 41 °) as well as internal (to 14°) rotation was measured.