Medialization of the Cup During Total Hip Arthroplasty

Abstract

Background: Placement of the acetabular cup, particularly regarding medialization of the cup, remains debated today. The purpose of this study was to evaluate whether medialization of the acetabular cup during total hip arthroplasty (THA) using modern day implants affects the outcome of aseptic loosening.

Methods: Retrospective analysis of patients who underwent THA between 2007 and 2013 was done. Acetabular offset (AO) was measured on preoperative and postoperative radiographs. Change in AO was defined as the postoperative minus the preoperative measurement.

Results: One hundred forty-nine total patients were included, consisting of 117 patients with long-term (10 years minimum) follow-up who did not require revision surgery and 31 patients who required revision due to aseptic loosening of the cup an average of 7.7 years after THA. Patients with no change or increase in AO (corresponding to no change or lateralization of hip center) had 2.9 times (95% confidence interval, 1.3 to 6.6; P = 0.0097) increased odds of aseptic loosening compared with those with a decrease in AO (corresponding to medialization of hip center). Patients who underwent revision for aseptic loosening had significantly greater change in AO compared with patients without revision surgery by 2.6 mm (0.7 mm increase in the revision group vs. 1.9 mm decrease in the nonrevision group; P = 0.013). Similarly, multivariate regression controlling for diabetes and Body Mass Index demonstrated a difference of 2.6 mm in mean AO change (P = 0.018).

Conclusion: Aseptic loosening was markedly associated with increased AO after THA, with nearly three times increased odds of aseptic loosening compared with those with decreased AO after THA.

Figure 1

A, Radiographic parameters, preoperative. B, Radiographic parameters, postoperative. AB = acetabular offset (AO), BC = femoral offset (FO), AC = combined (global) offset, BD = vertical offset (VO), AE = acetabular floor width (AFW)