Some aspects of knee joint kinematics in rheumatoid arthritis as studied with roentgen stereophotogrammetry.

Kinematic studies of the rheumatoid knee joint with the aid of roentgen stereophotogrammetry were performed in 4 patients (6 knees). Three kinds of experiments were carried out. The screw axis of rotation between various flexion angles was determined. The displacement of the screw axis indicated pathological function in all cases. Using different treatment techniques the effect of traction was studied. A separation between the femur and the tibia of 1.3-3.8 mm was found in 3 knees which were slightly flexed during the traction. The compression effect of isometric knee extension was determined in 4 knees. Compression of 0.5 mm at a medial point and of 0.3 mm at a lateral point of the femoral condyle were found in one knee. The present study indicates that roentgen stereophotogrammetric analysis may give additional information on the development of internal derangement of the rheumatoid knee joint.