What is primary osteoarthritis (OA)?

Osteoarthritis is classified as primary (idiopathic) when the exact cause is unknown, and secondary if it is associated with a specific disease or condition such as diabetes. Most primary OA is related to aging. Approximately 80-90 percent of men and women have evidence of OA by the time they reach age 65.

In the vast majority of cases, OA develops silently before causing noticeable pain and stiffness. Affected individuals often do not have any symptoms until after age 50.