Postoperative posterior pelvic tilt progression is a risk factor for cup revision after total hip arthroplasty with a conventional polyethylene liner: a 25-year follow-up study

Background: Whether postoperative posterior pelvic tilt progression is an independent risk factor for cup revision after total hip arthroplasty (THA) with a conventional polyethylene (PE) liner is unclear. This long-term follow-up study assessed the association between posterior pelvic tilt and cup revision after THA using the porous-coated anatomic (PCA) total hip system. Methods: This retrospective cohort study included 94 patients who underwent THA using the PCA total hip system and participated in postoperative follow-up for a mean of 25 years. The Japanese Orthopaedic Association (JOA) hip score was the clinical outcome, and prosthetic alignment and the change in pelvic tilt were measured as radiological outcomes. Prosthetic survival rates for revision as the endpoint were evaluated, and risk factors for cup revision were identified using a multivariate logistic regression analysis. Results: The JOA hip score improved significantly (p < 0.001) after THA (before THA: 41 +/- 6.3 points; after THA: 86 +/- 8.9 points). The postoperative posterior pelvic tilt progressed 3.6 +/- 3.2 degrees. Survival rates of the cup and stem at 27 years postoperatively were 60.8% and 87.5%, respectively (p < 0.001). The main reason for revision (81% of all revisions) was aseptic loosening. Postoperative posterior pelvic tilt progression was an independent risk factor for cup revision (odds ratio, 1.53; 95% confidence interval, 1.06-2.20; p = 0.022). Conclusions: When the PCA total hip system was used, the stem exhibited good longevity during a mean follow-up period of 25 years; however, the cup was vulnerable because of aseptic loosening. Postoperative posterior pelvic tilt progression was an independent risk factor for cup revision.