THE indications for and benefits and limitations of modern total hip replacement have been well defined by the years of experience since the first operation in 1962.1 The operation, which is by far the most successful surgery for patients with advanced osteoarthritis and rheumatoid arthritis of the hip, is now performed an estimated 120,000 times a year in North America. Total hip replacement, in contrast to other major hip surgery, including hip fusion, osteotomy, and cup arthroplasty, is an entirely biomechanical rather than biologic solution to severe arthritis of the hip. The femoral head and part of the femoral neck . . .