Cholesterol crystals in osteoarthritic joint effusions.

Cholesterol crystals were demonstrated in synovial fluids from 4 patients with knee osteoarthritis and recurrent synovial effusions. Large crystals (10-80 micros) were readily identifiable by their characteristic plate-like morphology. Some fluids also contained numerous smaller (1-5 microns) irregular, rod and needle shaped crystals. Identification of these crystals as cholesterol was established by x-ray diffraction analysis (2 fluids) and by ultrastructural studies (1 fluid). This study documents the occurrence of cholesterol crystals in osteoarthritic effusions, but their precise pathogenetic significance remains unclear.