Enzymatic release of microspheroids containing hydroxyapatite crystals from synovium and of calcium pyrophosphate dihydrate crystals from cartilage.

Incubation of minced, focally calcified, chondromatosis tissue obtained at operation from a patient with Milwaukee shoulder (rotator cuff defect and glenohumeral osteoarthritis associated with synovial fluid, hydroxyapatite crystals in microspheroidal masses, collagenase, and neutral protease) with partially purified mammalian synovial cell collagenase released masses of hydroxyapatite crystals of the same size as those originally found in the patient's synovial fluid. Incubation of mineral articular cartilage obtained from a shoulder joint at arthroplasty for a destructive arthropathy in a patient with generalised calcium pyrophosphate dihydrate (CPPD) crystal deposition with partially purified synovial cell collagenase freed CPPD crystals from their matrix. These data are compatible with a previously postulated mechanism linking microcrystals to destructive arthropathies, that is, crystal endocytosis by synovial cells stimulating collagenase secretion with subsequent enzymatic crystal "strip-mining', releasing additional crystals into the synovial fluid in a self-perpetuating cycle.