Hip resurfacing requires larger acetabular cups than conventional hip replacement: A comparative analysis of 100 hips, based on radiographic templating

Acetabular bone loss is a matter for concern in hip resurfacing arthroplasty (HRA), as preservation of the femoral head and neck might demand a larger acetabular cup than in total hip arthroplasty (THA). Using radiographic templating, the cup size required for either THA or HRA was calculated on 100 pelvic films. First, the cup size was determined based on the dimensions of the acetabulum. Then, the cup size for HRA was evaluated taking into account the dimensions of the femoral head/neck. The average cup size required for HRA was larger than for THA (Delta + 1.1 mm). The cup size for HRA and THA was similar in 49% of hips; in 51% of the hips the cup required for HRA was larger : one size larger in 31%, two sizes larger in 18% and three sizes larger in 2% of the cases. The greatest difference and highest bone loss were observed for the large sizes (between 52 and 56 mm) and thus predominantly in men (Delta + 1.5 mm male, Delta + 0.7 mm female). This study shows that HRA requires a larger acetabular cup in more than 50% of the cases compared to THA. When planning HRA surgeons should remember that cup size is determined by the size of the matching femoral component and that size difference with THA increases with increasing hip sizes.