Leg Length and Offset following hip Resurfacing and Hip Replacement

Abstract

We measured and compared critical parameters on antero-posterior radiographs from 28 patients who had undergone hybrid hip replacement (CPS/EPF), with 28 patients who had undergone cemented hip resurfacing (Cormet). All operations were performed by a single surgeon or under his supervision. We measured the femoral offset, acetabular offset, cup height and leg length on pre and post operative radiographs. The mean difference in femoral offset post-operatively was 3.52 mm (95% CI: -1.10 to 8.14 mm) in the hybrid group and -1.30mm (95%CI: -2.88 to 0.29 mm) in the resurfacing group. Using the independent sample t test (two-tailed), the difference between these means was significant, test statistic t 2.025, p<0.05. This suggests that resurfacing restored the femoral offset more accurately than hybrid hip replacement. The mean difference in leg length post-operatively was 11.91 mm (95% CI: 8.21 to 15.62 mm) in the hybrid group and 4.87 mm (95% CI: 3.32 to 6.42 mm) in the resurfacing group. Using the independent sample t test (two-tailed), the difference between the means was significant, test statistic t 3.597, p<0.001. This suggests that resurfacing produced less change in leg length post-operatively than hybrid hip replacement. We found no statistically significant difference in ideal pre and post operative centre of rotation in the two groups. Proximal femoral anatomy was restored during hip resurfacing by resecting bone of a thickness determined by corresponding preoperative templating and implant thickness rather than relying on placement of the cutting ring at the head-neck junction. No femoral neck fractures occurred in the resurfacing group.