The deposition of basic calcium phosphate and calcium pyrophosphate dihydrate crystals in articular tissues is probably an under-recognized event. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Measurements of putative markers of cartilage breakdown suggest that these crystals magnify the degenerative process. In vitro studies reveal two potential mechanisms by which crystals cause degeneration. These involve the stimulation of mitogenesis in synovial fibroblasts and the secretion of metalloproteinases by cells that phagocytose these crystals. Approaches that may ameliorate the degenerative process may ensue from new information about how crystals form and how they exert their biologic effects.
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