Acute synovitis with intra-articular apatite deposits in an osteoarthritic metacarpophalangeal joint.

A patient was shown to have acute arthritis in a metacarpophalangeal joint, with local calcification indicated by x-rays. Surgical and pathological examinations showed strictly intra-articular apatite crystal deposits and an erosive osteoarthritis. These crystal deposits could account for the synovial inflammation; they are thought to be related to bone fragments embedded in the synovium. The predisposing role of previous local injections of corticosteroids is debatable.