[A biomechanical study of osteoarthritis of the knee with special reference to the rotatory movement of the knee joint].

Clinical picture of osteoarthritis of the knee (OA) was investigated from the viewpoint of dynamic rotatory movement of the knee. With regard to 140 normal knee joints and 263 OA joints, dynamic rotatory movement of the knee was measured and analyzed on serial lateral X-ray films of the knee during loading. In normal knee joints, the femur showed internal rotation on the tibia from a 90 degrees flexion to maximal extension. In OA joints, rotatory movement on terminal extension of the knee, i.e., screw home movement, was disturbed in the early stage. With progress of osteoarthritis, the previously mentioned rotatory movement of the knee joint was reduced, and finally adverse rotatory movement appeared. The measured results of the rotatory movement of the knee in normal and every grades of OA joints were analyzed by the least squares method and subsequently depicted in an approximate curve of the fifth degree. Consequently, osteoarthritis of the knee was graded into 4 groups, on the basis of rotatory movement of the knee. Thus, it is concluded that disturbed rotatory movement of the knee may be a key factor in the progress of osteoarthritis of the knee.