Ultrastructural study of articular cartilage in experimental pyogenic arthritis.

Ultrastructural changes of the articular cartilage at the early stage of experimental pyogenic arthritis were studied by electron microscopy. The superficial zone of the cartilage at the site of the cartilage-synovium junction demonstrated far more changes than those at the site of the free surface of the articular cartilage. Changes were observed at the cartilage-synovium junction as early as four hours after the intraarticular injection of the infecting organism. The most interesting finding was migration of erythrocytes and polymorphonuclear leucocytes into the superficial zone of the cartilage at the early stage. The pericellular matrix in the middle zone became so loose in some areas that collagen fibrils were partially exposed after three days. The naked collagen fibrils were tapered, nicked and irregular in size after seven days.