The cause of osteoarthritis is unknown, but metabolic, genetic, chemical, and mechanical factors may play a role in development. It is associated with the aging process and is the most common form of arthritis . It may first appear without symptoms between 20 and 30 years of age and is present in almost everyone by the age of 70.
Symptoms appear in middle age.
Approximately 4 out of 100 people are affected. The cartilage of the affected joint is roughened and becomes worn down. As the disease progresses, so much of the cartilage is worn down that the bone ends start to rub against each other. Bony spurs may develop around the joint, causing pain and inflammation. Systemic symptoms, sometimes associated with other arthritic conditions, are not associated with osteoarthritis.