Surface Replacement Conversion: Ensuring an Optimal Total Hip Replacement Outcome

Although hip resurfacing is becoming established as a treatment of hip arthritis in younger, active patients, there has been a greater failure rate in the short term when compared with traditional total hip replacement (THR). Failure modes of hip resurfacing include femoral neck fracture, osteonecrosis of the femoral head, metal hypersensitivity, component malposition leading to metal ion reactivity, and unexplained pain. It is essential to perform a proper workup of these potential failure mechanisms to correct the problem and ensure an optimal THR outcome. Acetabular component condition must be assessed at the time of conversion to THR. If the acetabular socket is well-fixed and well-positioned, a conversion to a stemmed femoral component with a matching large-diameter metal head is an easy, reproducible solution to femoral neck fracture or femoral loosening. Conversion to THR with a large diameter metal ball can also be a solution to impingement by improving the head–neck ratio. If the acetabular component is malpositioned, there can be edge-loading leading to the production of high levels of metal ion. Blood metal ions assessment can be helpful preoperatively to determine the condition of the implants; if substantially elevated, the resurfacing components are likely damaged and should be fully revised. Finally, metal hypersensitivity is a possible failure mechanism. This should be a diagnosis of exclusion, but if thought to be the culprit, the components should be fully revised to a non-metal articulation. Conversion to THR after failed hip resurfacing has been shown to have results comparable with primary THR in most cases. Performing an algorthmic workup preoperatively will help ensure an optimal THR outcome.