Abstract
Articular cartilage and subchondral bone of spontaneous osteoarthritis of ICR mouse knees were studied by transmission electron microscopy. The most characteristic finding of this mouse knee was chondrocyte necrosis of calcified cartilage before apparent osteoarthritic changes of cartilage. Early ultrastructural changes of the osteoarthritic cartilage included degeneration and disappearance of superficial discoid chondrocytes, microscar formation in the superficial layer, degeneration of deep-layer chondrocytes, and atrophy or degeneration of osteocytes in the subchondral bone. In advanced osteoarthritis, there was a various degree of cartilage loss and most of the cells in remaining cartilage and subchondral bone were necrotic. These findings resembled aging changes of the articular cartilage, however, the changes seen in osteoarthritic cartilage were thought to be severer, more frequent and more extensive than those in aging cartilage. Though proliferative changes such as chondrocyte clusters and osteophyte formation were not observed, there were some chondrocytes with abundant rough endoplasmic reticulum, mitochondria and Golgi complex. Densely packed thick collagen fibrils were often seen in contact with those cells. These thick collagen fibrils, which are similar to fibrils found in microscars, may be formed as a result of reparative reaction of cartilage chondrocytes.
