Chondral abrasion is followed by vertical fissuring and cartilage loss. Eventually, large areas of the joint may be denuded of articular cartilage, exposing the subchondral bone.
Deterioration is accompanied by aberrant attempts at repair.
Proliferation of chondrocytes adjacent to the cartilage fissures creates a pattern of sporadic clusters of cells, some of which are necrotic. Bone growth at the joint margins produces exophytic protuberances, or osteophytes, which are capped with new hyaline cartilage. Subchondral bone also proliferates and thickens, especially in denuded areas, forming a dense, eburnated bony plate. Localized cystic areas may develop in the subchondral bone, leading to structural weakening. All of these changes usually are accompanied by little synovial reaction, in sharp contrast to the synovial changes typical of rheumatoid arthritis.