Secondary osteochondromatosis in the subacromial bursa: a report of two cases and review of the literature.

Osteochondromatosis is classified into primary and secondary lesions; primary osteochondromatosis is a tumor-like lesion, whereas secondary lesions are due to such joint or bursal disorders as osteoarthritis and osteochondral fractures. There is no clinical distinction between these two conditions. Only the pathological findings of loose bodies and synovium can clearly distinguish between them. In this report, we present two patients with secondary osteochondromatosis in the subacromial bursa. Both had shoulder pain and were treated surgically. We discuss methods of differentiating between primary and secondary lesions and elucidate the pathogenesis of osteochondromatosis in the subacromial bursa by analyzing findings for 17 shoulders with this condition reported in the literature. We also present two more cases. We reviewed the 12 cases of osteochondromatosis in the literature for histopathological findings of loose bodies and the presence or absence of acromial osteophytes. Our findings suggest that osteochondromatosis of the subacromial bursa is secondary in most cases, and that osteocartilaginous fragments from acromial osteophytes can be shed into the subacromial bursa and grow into loose bodies.