PAO was designed as a joint preserving surgical procedure to compensate for a shallow acetabulum by re-orienting the acetabulum into a position that provides better coverage of the femoral head. Although the overall theory that increasing load bearing area (improving coverage of the femoral head) results in reduced joint stress is intuitive, the complex bony surface may not behave in this manner. It is possible that joint stress may increase when the acetabulum is reoriented into a position that increases load bearing area if post-operative joint congruency is worse than pre-operative.