Outcomes after revision of metal on metal hip resurfacing to total arthroplasty using the direct anterior approach

BackgroundFunction after revision total hip arthroplasty (THA) in failed metal-on-metal (MoM) hip resurfacing arthroplasty (HRA) is variable, but post-operative complication rates are reportedly high. We hypothesized HRA conversion to THA using the direct anterior approach (DAA) would be associated with optimal outcome.MethodsSeventeen MoM-HRAs in 15 patients (seven males, eight females) were revised through the DAA. The mean age was 45years (28-59yrs). The most common indications for revision were aseptic loosening of the acetabular component or of the femoral component and femoral neck fracture. In 16 hips, a conversion to a ceramic-on-ceramic (CoC) (13 hips) or to a metal-on polyethylene (MOP) (2), or to a large-head MoM (1) THA was done. An isolated femoral revision was done in one hip.ResultsAfter 6.73years, no hip had required a re-revision. The Postel-Merle d'Aubigne (PMA) functional score improved from 9 (4-14) to 16 (12-18) (p<0.001). An intra-operative fracture of the greater trochanter (one hip) and dysesthesia of the lateral femoral cutaneous nerve (four hips) were reported. Mean serum chromium concentration decreased from 33.2g/L (11.8-62g/L) pre-operatively to 5.8g/L (0.4-35.5g/L) post-operatively (p<0.001), and mean serum cobalt concentration decreased from 35.8g/L (6.3-85.5g/L) to 4.7g/L (0.26-25.7g/L) (p=0.003).Conclusion Revision of failed MoM-HRA using the DAA resulted in an acceptable clinical outcome, no specific complication and no further surgery. A consistent decline in serum ion levels may be expected following HRA conversion to THA.