SYNOVIAL OSTEOCHONDROMATOSIS OF THE DISTAL RADIO-ULNAR JOINT H. P. von SCHROEDER and T. S. AXELROD From the Division of Orthopaedic Surgery, Universityof Toronto, and Sunnybrook Hospital, Toronto, Canada Synoviai osteochondromatosis is an uncommon lesion characterized by cartilagenous and osseous metaplasia of joint synovium. It is typically monarticular, affecting large joints such as the knee and hip, although it has also been described in the ankle, elbow and shoulder. It is exceptionally rare in the hand, but has been reported involving the tenosynovium of the digits and the wrist. We report a rare case of synovial osteochondromatosis involving the distal radio-ulnar joint in a 16-year-old man. Journal of Hand Surgery (British and European Volume, 1996) 21B: 1." 30-32 CASE REPORT A 16-year-old man was seen with a 2-month history of progressive discomfort in the dominant right wrist which was aggravated by pronation and supination. He also developed a tender fullness on the palmar and dorsal aspects over the distal radio-ulnar joint. There was no history of trauma or overuse. The discomfort, tenderness and decreased range of motion interfered with his daily activities and sports. On examination, the right forearm was tender in the region of the distal radio-ulnar joint. A mass was palpable on the volar aspect of the joint, and there was ill-defined thickening on the dorsal aspect. The mass and joint were tender to palpation. Pronation and supination were limited to 45 ° and 35 ° respectively, and there was a solid end-point to motion in both directions. Radio-carpal motion was normal and was not tender, and there were no other joint or systemic abnormali- ties evident on physical examination and laboratory investigations. Radiographs of the right wrist revealed a nodular, calcified tumour proximal and anterior to the distal radio-ulnar joint (Figs la and b). There were no degenerative changes in the radio-ulnar or other joints of the hand. At surgery, the joint capsule of the radio- ulnar joint was hypertrophic. The joint space was sig- nificantly larger than normal and was occupied by 13 separate bodies which were adherent to the synovium and loose within the joint. The bodies ranged in size from 3 mm in diameter to 10 x 10 x 4 mm (Fig 2). The articular surface of the joint was normal and the triangu- Fig 1 (a) Radiograph of the right wrist showing a calcified tumour adjacent to the distal radio-ulnar joint. (b) Lateral radiograph of the tumour which was palpable over the anterior aspect of the joint. 30