Crystal deposition disease of the shoulder (including calcific tendonitis and milwaukee shoulder syndrome).

Calcific tendinitis of the shoulder is a dynamic process. Osteopontin is present in cells surrounding tendon calcifications. Resorption is probably mediated by cathepsin K-containing multinucleated giant cells. Rotator cuff tears are associated with an inflammatory response based on the presence of interleukin-1 and a proliferative synovitis. Metalloproteinases are found in the synovial fluids of patients with rotator cuff tears. Some patients with large rotator cuff tears progress to a severe destructive arthropathy characterized by large joint effusions, which are noninflammatory but contain basic calcium phosphate crystals. These crystals stimulate metalloproteinase production in vitro and also suppress metalloproteinase inhibitor production. Mutations in the ank gene result in decreased extracellular inorganic pyrophosphate in murine progressive ankylosis, and increased extracellular inorganic pyrophosphate in some cases of familial chondrocalcinosis.