Other conditions for which the procedure may be indicated and which predispose to the development of secondary osteoarthritis include developmental dysplasia of the hip, Paget's disease. trauma, and osteonecrosis of the femoral head. Patients with rheuma- toid arthritis, other collagen diseases such as systemic ankylosing spondylitis may benefit as well. The large number of operations per formed each year reflects the fact that more than 90% of appropriately selected patients achieve complete pain