Absorptive Functions of the Synovial Membrane

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Abstract
The fine structure of the synovial membrane of the knee joint of young adult rabbits was studied between 1 and 24 hours after the injection of a suspension of Thorotrast (thorium dioxide). Particles were found in vacuoles of synovial cells and histiocytes, and there were free particles in the subsynovial tissue within 1 hour of the injection. The amount of thorium dioxide had increased after 2 hours; some of the cells containing ingested particles now showed a prominent Golgi apparatus, separation of the constituent layers of the nuclear membrane and complicated multlvesicular bodies; the tissue showed a polymorph infiltration but these cells did not absorb the particles. The cells showed further enlargement of the Golgi apparatus and the endoplasmic reticulum was hypertrophied by 24 hours after injection. The mechanism by which synovial cells absorb particulate matter is discussed; the later changes within the cells may be due to the toxicity of the injected material.