Metal on metal total hip resurfacing has recently gained tremendous popularity as another method of performing hip replacements. Metal-on-metal resurfacing in general involves a one-piece acetabular cup that is similar to what is used in total hip replacement and a femoral cap. The resurfacing femoral component is applied to the top of the femoral head with a minimum loss of bone. Some patients with extra-articular bony deformities of the proximal femur or retained hardware in the proximal femur will end up needing a hip replacement. These extra-articular deformities and obstructive pieces of metal in the proximal femur may make a standard total hip replacement very difficult. They will necessitate in the first case (deformity) various osteotomies (extensive surgical procedures where sequential cuts are made to the bone) in addition to the hip replacement and in a second case removal of retained hardware, which in some cases can be technically difficult. By utilizing a resurfacing hip arthroplasty, which just caps the proximal femur, dealing with the deformity or retained hardware can be avoided.