Osteoarthritis (OA) is the most common form of arthritis. The aches and pains of this type of arthritis can be easy to dismiss as normal aging, but the chronic pain and disability can often prevent people from living a full life.

OA is caused by breakdown of cartilage in joints, and by bone changes at the edges of joints. Cartilage is the elastic material that covers and protects the ends of bones where they meet in joints such as the knee and hip.

Osteoarthritis causes pain and swelling in one or more joints. Although OA can affect any of the joints in the body, it most commonly affects weight-bearing joints such as the hips, knees, feet, and spine, or the hands. Osteoarthritis can affect any joint on either side of the body. This is different from rheumatoid arthritis, which affects the whole body and causes problems on both sides of the body (e.g., both hands) equally.

Although OA can happen at any age, the risk increases rapidly after a person reaches 45 years of age. After age 40, some 90% of people have changes in their weight-bearing joints, visible by X-ray, that suggest OA. It is associated with considerable amounts of lost working time and may contribute to early retirement.

Wondering if you might have OA? Read "Are you at risk" and "Symptoms of OA" to learn more. Then see your doctor to find out whether your symptoms may be caused by OA.