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Chronic renal failure is known to be associated with secondary hyperoxalemia and the deposition of calcium oxalate in visceral organs, bones, and cartilage. We report the identification of calcium oxalate crystals in the synovial fluid of three patients with chronic renal failure. In one patient, calcium oxalate crystals were also identified within synovium and cartilage. Crystals were pleomorphic and bipyramidal. Some crystals were rod-like and had positive birefringence, thus tending to be confused with calcium pyrophosphate dihydrate when observed with only compensated polarized light microscopy. In one patients asymptomatic effusions were associated with joint capsule calcification, but otherwise normal knee radiographs. The other two patients had bilateral knee pain, one having coexistent features of osteoarthritis and the other chondrocalcinosis. Samples of proliferative synovium, joint capsule, and cartilage from the patient with chondrocalcinosis showed abundant calcium oxalate crystals, and not calcium pyrophosphate dihydrate or calcium hydroxyapatite. Thus, radiographically typical chondrocalcinosis may be due to calcium oxalate. Joint disease in chronic renal failure may be associated with calcium oxalate as well as the previously recognized apatite deposition.

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