Osteoarthritis (OA) is a common and disabling disease. Because of improved treatment of chronic diseases and lower mortality from infectious diseases, the US population is aging, and older Americans are living with disabling conditions, including hip OA. The projected number of older adults with arthritis or other chronic musculoskeletal joint symptoms is expected to nearly double, from 21.4 million in 2005 to 41.1 million by 2030. The burden of hip OA is increasing due to the aging population and the obesity crisis; as a result, the need for total hip arthroplasty (THA) is expected to grow 174%, to 572,000 primary THAs per year by 2030 in the United States. Prior projections appear to have underestimated the actual number of primary and revision THAs that are in demand.