Femoral neck narrowing after metal-on-metal hip resurfacing

We reviewed 40 Corin Cormet 2000 (Corin, Cirencester, UK) metal-on-metal resurfacing hips, in 36 patients, for the presence of femoral neck narrowing. A neck-to-prosthesis ratio was calculated by dividing the diameter of the femoral neck with that of the implant. This ratio was measured on plain anteroposterior pelvis radiographs taken immediately and 2 years postoperation. Subsequent radiographs were measured up to a maximum 7 years (mean, 5.3 years) postoperation. Femoral neck narrowing was observed in 90% of hips at 2 years, with the average neck narrowing ranging from a ratio of 0.865 to 0.811. Importantly, no further narrowing occurred beyond this point up to 7 years postoperation. We described a simple reproducible method of measuring neck narrowing on plain radiographs and discuss possible causal factors for neck narrowing after hip resurfacing.