Osteoarthritis (OA) is a degenerative joint disease due to wear and tear of the joint cartilage and the formation of new bone (bone spurs) at the edges of the joints. The cartilage of the affected joint wears down until there is none left and the opposing bones rub together. The joints most commonly affected are those of the hips, knees, big toe, and spine. Risk factors for osteoarthritis include age, female sex, obesity and joint injury.

Blood tests are not used to diagnose the disease but may be used to monitor side effects of various treatments.
X-rays of the affected joints will show loss of cartilage and narrowing of the joint space.

Osteoarthritis cannot be cured, but there are several types of treatment available to alleviate the symptoms. Exercise, particularly in water, and weight loss, as well as good nutrition and the use of heat and cold treatments may increase mobility. Pain due to OA can be treated with pain killers and anti-inflammation drugs. Sometimes steroid drugs are injected directly into the affected joint to help relieve pain. The dietary supplements glucosamine and chondroitin are available 'over-the-counter' in many pharmacies though their effectiveness is unproven.

Surgical treatment to replace or repair damaged joints may be needed in severe cases.