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 rotatory instability. Normal subjects were found to have bilateral symmetric rotational knee motion at each angle of flexion tested. When the knee is in a position of flexion between 30 and 90 degrees, there are approximately 45 degrees external and 25 degrees internal rotation. Rotatory motion decreases with further extension and, at 5 degrees of flexion, the knee has 23 degrees external and 10 degrees 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 degrees flexion. At 15 degrees of flexion, a slightly greater arc of rotation was measured compared to normal knees. At 5 degrees of flexion, a significantly greater range of external (to 41 degrees) as well as internal (to 14 degrees) rotation was measured.