Comparison of Femoral Head Translation following Eccentric Rotational Acetabular Osteotomy and Rotational Acetabular Osteotomy

Purpose Eccentric rotational acetabular osteotomy (ERAO) is a modification of rotational acetabular osteotomy (RAO); it has been reported that ERAO allows the femoral head to translate medially and distally. However, no study has compared femoral head translation following RAO or ERAO. The purpose of this study was to compare immediate postoperative translation of the femoral head after RAO and ERAO in comparison with the pre-operative position by radiological methods. Methods Patients treated by RAO or ERAO between 2006 and 2014 were retrospectively evaluated. 19 hips (17 patients) were treated with RAO, and 25 hips (22 patients) were treated with ERAO. The acetabular roof angle and the location of the femoral head were measured on anteroposterior pelvic radiographs. Results The mean pre-operative acetabular roof angle was 20.9° in the RAO group and 22.0° in the ERAO group, showing no significant difference. The mean acetabular roof angle immediately postoperatively was −0.5° in the RAO group and −0.4° in the ERAO group, again showing no significant difference. The mean femoral head translation immediately postoperatively was 3.1 mm (95% confidence interval (CI), 1.5-4.7 mm) laterally and 3.0 mm (95% CI, 1.3-4.7 mm) proximally in the RAO group and 0.8 mm (95% CI, −0.7-2.3 mm) medially and 2.8 mm (95% CI, 1.5-4.1 mm) distally in the ERAO group; this difference was very highly significant (p≤0.001). Conclusions In contrast with RAO, ERAO resulted in significant femoral head translation both medially and distally immediately postoperatively.