Hip resurfacing and conventional THA: comparison of acetabular bone stock removal, leg length, and offset

The purpose of this study was to compare total hip arthroplasty (THA) and hip resurfacing arthroplasty (HRA) with regard to the amount of acetabular bone stock removed and the ability to restore leg length and offset. Anteroposterior pelvis radiographs of 153 consecutive THAs and 84 consecutive HRAs were compared. Excluded patients were those with prior hip surgery, those in which a best-fit circle could not be adequately matched to the femoral head, and those with preoperative radiographic findings that precluded consideration for HRA (ie, disease severity, deformity, leg-length discrepancy). A significant difference was found between THA and HRA with regards to age and sex but not primary diagnosis. Relative differences in acetabular bone removal were compared using a ratio of acetabular implant diameter to preoperative ipsilateral femoral head diameter measured with a best-fit circle. The ratio of acetabular cup diameter to preoperative ipsilateral femoral head diameter was significantly greater following THA than following HRA, indicating relatively more acetabular bone removal in THA procedures. Mean leg-length discrepancy was significantly greater following THA than following HRA. Offset was increased to a greater extent following THA than following HRA. Overall, HRA was associated with relatively less acetabular bone stock removal and less alteration in leg length and offset than was THA.