Experimental cholesterol crystal arthropathy.

To understand the role of cholesterol crystals in the pathogenesis of synovial effusions, we studied the articular tissue reaction to an intraarticular injection of cholesterol crystals in rabbits' knees. With the right knee as control, the left knees of 14 adult male, white, New Zealand rabbits were injected with 11 mg of cholesterol crystals suspended in 0.5 ml of saline. At 4, 8, 24, 48 h and at 7, 14, 28 and 56 d postinjection, the animals were autopsied and these tissues, including synovial fluid (SF), examined by light and transmission electron microscopy. Crystal injection produced an acute synovitis which peaked at 24 h coincident with phagocytosis of crystals in SF. Cholesterol crystals persisted within the synovium throughout the experiment resulting in cholesterol granulomata, synovial lining cell hyperplasia and synovial fibrosis. Relative to urate and pyrophosphate crystals, cholesterol crystals appear to have weak phlogistic potential. Because of their insolubility and resistance to cellular degradation, crystals persist within the synovium for prolonged periods. This results in a chronic proliferative synovitis and fibrosis.