Osteoarthritis-also known as degenerative joint disease-is the gradual age-related deterioration of cartilage within the joints, causing pain and sometimes deformity. (Joint inflammation is uncommon.) It is the most common form of arthritis: nearly all people have developed some degree of osteoarthritis in one or more joints by the age of 60. It can occur in any joint, but most commonly osteoarthritis affects the fingers, neck, spine, hips, knees, and feet.

As the elastic cartilage that serves as a cushion between bones breaks down, bone ends may rub together, causing them to develop uneven outgrowths called osteophytes, or spurs, that may grind against each other as the joint moves. Damage usually develops gradually over a period of years. In some people, symptoms remain mild or even fade; in others, symptoms grow progressively worse until they are severely disabling. Affected joints may begin to lose their shape and alignment. Weakness and wasting of the muscles surrounding the joints may occur if pain and stiffness prevent normal motion.

Osteoarthritis has no impact on longevity (unlike some other forms of arthritis), but it can diminish overall quality of life. There is no cure, but a number of treatments can ease pain and minimize disability.