Osteoarthritis (OA), which is also known as osteoarthrosis or degenerative joint disease (DJD), is a disorder of the joints that worsens over time. It results from deterioration or loss of the cartilage that acts as a protective cushion between bones, particularly in weight-bearing joints such as the knees and hips. As the cartilage wears away, the bone forms hardened areas called spurs and fluid-filled pockets in the marrow, known as subchondral cysts. The deformed bones and fluid accumulation in the joints cause pain, which is made worse by moving the joint or putting weight on it. Rest usually relieves the pain.

People with osteoarthritis may have joint pain on one or both sides of the body. It affects mainly the knees, hands, hips, feet, and spine.

Osteoarthritis usually appears after age 40. About 90% of Americans will show some signs of the disorder in their weight-bearing joints by that 40. In...