An 85-year-old woman presented with right shoulder pain and swelling and a large hematoma extending into the chest wall. Active range of motion was severely limited, and passive mobility was painful but largely unrestricted. She had had no recent trauma to the shoulder area. Arthrocentesis yielded a hemorrhagic noninflammatory fluid; no crystals were seen on polarized microscopy. Alizarin red staining of the synovial fluid showed rare hydroxyapatite crystals. All cultures were negative, and cancer was not detected by cytologic analysis. Radiography of the right shoulder was suggestive of degenerative arthritis and lateral distention of the subacromial bursa (Panel A). Three . . .