Acute apatite arthritis of the shoulder in a young woman

We describe the case of a 40-year-old-woman with an acute arthritis of the left shoulder. Synovial fluid aspirated from the joint cavity appeared purulent but contained few leucocytes and no birefringent crystals. It was, however, rich in apatite crystals. A communication between the subacromial bursa and the gleno-humeral cavity through the rotator cuff could be demonstrated by sonography. The acute arthritis was secondary to the intra-articular rupture of a peri-articular calcification.