disorder of the joints (joint) characterized by progressive deterioration of the articular cartilage. It is the most common joint disease, affecting more than 80 percent of those who reach the age of 70. Although its suffix indicates otherwise, osteoarthritis is not characterized by excessive joint inflammation as is the case with rheumatoid arthritis. The disease may be asymptomatic, especially in the early years of its onset. As it progresses, however, pain, stiffness, and a limitation in movement may develop. Common sites of discomfort are the vertebrae, knees, and hips—joints that bear much of the weight of the body.

The cause of this disorder is not completely understood, but biomechanical forces that place stress on the joints (e.g., bearing weight, postural or orthopedic abnormalities, or injuries that cause chronic irritation of the bone) are thought to interact with biochemical and genetic factors to contribute to osteoarthritis. In its early stages there is softening and roughening of the cartilage, which eventually wears away. The bone, deprived of its protective cover, regenerates the destroyed tissue, resulting in an uneven remodeling of the surface of the joint. Thick bony outgrowths called spurs sometimes develop. Articulation of the joint becomes difficult.

Depending on the site and severity of the disease, various treatments are employed. Individuals who experience moderate symptoms can be treated by a combination of the following: analgesic medications, periodic rest, weight reduction, corticosteroid injections, and physical therapy or exercise. Surgical procedures such as hip or knee replacement or joint debridement (the removal of unhealthy tissue) may be necessary to relieve more severe pain and improve joint function.