Synovial osteochondromatosis: an unusual cause for subacromial impingement.

Impingement syndrome is usually caused by encroachment on the rotator cuff of the acromion, coracoacromial ligament, acromioclavicular joint or coracoid process. Bursal causes of impingement are rare but include rheumatoid thickening, and thickening from previous and iatrogenic causes such as sutures, pins, or wires left from previous surgery. We report a case of synovial osteochondromatosis presenting as chronic impingement syndrome. Synovial osteochondromatosis may be difficult to differentiate from chronic calcific tendinitis, but we describe a radiological sign and its anatomical basis that can differentiate between the two. If densities are seen on plain radiographs distal to the greater tuberosity, then loose bodies within the subacromial bursa should be considered.