Osteoarthritis is characterized by progressive erosion of articular cartilage, which results from the breakdown of protein and collagen by enzymes. Increased water is absorbed because of disruption in pumping action, so the cartilage becomes less able to tolerate weight bearing and loses some of its tensile strength. As osteoarthritis progresses, bits of articular cartilage flake off and longitudinal fissures develop. The cartilage becomes thin or absent, leaving the bone unprotected. Subchondral bone thickens and becomes sclerotic with potential of cyst formation. Osteophytes (bone spurs) develop at the joint margin, which can also break off, causing synovitis and joint effusion. The joint capsule becomes thickened and may adhere to underlying structures. Knees, hips, vertebrae, and fingers are the most common sites. Pain associated with osteoarthritis arises from a combination of articular distension, inflammation, and fibrosis.

Osteoarthritis is managed by a combination of rest and exercise, including range of motion exercises to maintain joint mobility. Weight reduction is important if indicated. Ambulation aids may be necessary to reduce stress on weight-bearing joints. Pain management with acetaminophen and other nonsteroidal antiinflammatory drugs (NSAIDs) is the mainstay of therapy. Cyclooxygenase-2 inhibitors are used sparingly and in those patients without risk of vessel disease or bleeding abnormalities. Patient education is important in the management of this chronic condition. Surgery and joint replacement is sometimes indicated.