Kinematics of the distal radioulnar joint in rheumatoid arthritis: an in vivo study using centrode analysis.

The kinematics of the distal radioulnar joint were examined using the method of centrode analysis in vivo. A group of normal subjects was studied along with a group of rheumatoid arthritis patients who had distal radioulnar joint involvement. Serial computed tomographic scans were obtained through the distal radioulnar joint of nine subjects (10 wrists) in varying degrees of pronation and supination. For normal subjects, the movement that occurs in a stable distal radioulnar joint is not erratic and the center of rotation lies within a well-defined area. When subjects with rheumatoid arthritis were analyzed, it was determined that early in the disease process bone erosions may occur in the sigmoid notch of the distal radius. When the joint contour in this region is maintained, the kinematics are not markedly altered. Erosion involving the dorsal border of the sigmoid notch of the radius is associated with subluxation of the distal radioulnar joint. The ulna becomes dorsally positioned relative to the radius, and significant alteration in the kinematics of the distal radioulnar joint occurs.