The rotational angle in osteoarthritic knees.

The angle of rotation of the knee joint during weight-bearing in osteoarthritic knees has not been fully determined. The authors aimed to examine the nature and extent of rotation during weight-bearing by means of ultrasonic investigation. There was a highly significant correlation between the rotational angle measured by ultrasound and that determined by CT. The dynamic rotatory movement during weight-bearing was measured in 107 osteoarthritic and 40 control knees. At 20 degrees of flexion the internal rotation of the early grade I osteoarthritic knees (-1.6 degrees) was significantly less than that of the control knees (-4.8 degrees, P = 0.004). This abnormality was the initial pathological rotational change in osteoarthritis of the knee joint. The external rotation at maximal extension and the rotation of the screw-home movement proportionately decreased with progression of medial compartment osteoarthritis. By virtue of these observations we have clarified the dynamic rotatory movement in osteoarthritic knees during weight-bearing.