Osteoarthritis (OA) is the most common joint disorder.

In osteoarthritis, the cushioning (cartilage) between the bones wears away in the joints. As osteoarthritis gets worse, the cartilage disappears and bone rubs on bone. Bony spurs or growths usually form around the joint. The ligaments and muscles around the joint loosen and become weaker.

Often, the cause of OA is unknown. It is mainly related to aging, but other factors can also lead to OA.

• Osteoarthritis tends to run in families
• Being overweight increases the risk
• Fractures or other joint injuries can lead to osteoarthritis later in life
• Long-term overuse at work or in sports can lead to osteoarthritis

Medical conditions that can lead to osteoarthritis include:

• Bleeding disorders that cause bleeding in the joint, such as hemophilia
• Disorders that block the blood supply near a joint, such as avascular necrosis
• Other types of arthritis, such as chronic gout, pseudogout, or rheumatoid arthritis

The symptoms of osteoarthritis usually appear in middle age and almost everyone has them by age 70. Before age 55, the condition occurs equally in men and women. After age 55, it is more common in women.