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In the present understanding of joint pathology, the exact pathogenic role of hydroxyapatite crystals, both periarticularand intraarticular, is not yet completely clear. An association between rapidly destructive osteoarthritis (OA) andhydroxyapatite or basic calcium crystals was confirmed. This is a case report of a 78-year old female patient presentingwith a five-month history of shoulder pain with swelling of both AC joints. Imaging showed a large bursitis starting in theAC joints of both shoulders. Synovial fluid analysis showed many hydroxyapatite crystals and no calcium pyrophosphateor sodium urate crystals, which confirmed the diagnosis of crystal-induced periarthropathy and AC arthritis. Theseperiarticular radiographic and synovial fluid findings are a frequent and known manifestation of hydroxyapatite crystaldeposition disease, similar to the intra-articular destructive “Milwaukee shoulder syndrome”. Surgical intervention wasthe only therapeutic option to reduce the patient’s shoulder pain.