 The cause of osteoarthritis in hip dysplasia is thought to be attributable to increased joint contact pressures secondary to decreased acetabular coverage of the femoral head andor incongruity of the articular surfaces. The investigators hypothesis is that when periacetabular osteotomy is performed and contact pressure on cartilage reduced, additional joint degeneration will be slowed or prevented unless irreparable damage to the cartilage has happened at the time periacetabular osteotomy is performed. Hence, the purposes of this study are: 