Osteoarthritis, also known as "wear and tear" arthritis, is a common problem for many people after they reach middle age.

Knee osteoarthritis is a leading cause of disability in the United States. In 2005, approximately 9 million American adults were diagnosed with knee osteoarthritis. About 55% of people with knee osteoarthritis are older than 65.

For more statistical information on osteoarthritis and other musculoskeletal conditions, visit Orthopaedic StatisticsOrthopaedic Statistics (http://www.aaos.org/research/stats/patientstats.asp).

Orthopaedic Statistics is maintained by the American Academy of Orthopaedic Surgeons. It presents the most recent data from the U.S. Department of Health and Human Services; Centers for Disease Control and Prevention; and the National Center for Health Statistics.