Impact of spinopelvic parameters on acetabular cup positioning and patient-reported outcomes following total hip arthroplasty

Abstract

Background: Hip instability is one of the most common complications after total hip arthroplasty (THA). While prior research has explored patient factors, surgical technique, soft tissue dynamics, implant design, and spinopelvic parameters. In particular, the relationship between spinopelvic alignment and acetabular cup positioning is not yet fully understood. Therefore, we aim to evaluate the association between spinopelvic parameters, acetabular cup positioning, and 12-month postoperative PROMs.

Methods: This study included 90 patients undergoing primary THA at a single institution from March 2019 to May 2023. Pelvic parameters (acetabular inclination, acetabular version, pelvic incidence, pelvic tilt, sacral slope, flexion, and obliquity) were assessed using EOS imaging and radiographs. Additional data were obtained from the Veterans RAND-12 survey and the FORCE-TJR database. PROMs were collected preoperatively, at 3 months, and at 12 months postoperatively, along with postoperative hospital metrics. Statistical analysis included Pearson's correlation to evaluate associations between pelvic parameters and PROMs.

Results: Postoperatively, 1.1 % of patients required reoperation, 2.2 % experienced dislocation, 5.5 % were readmitted within 90 days, and 12.1 % had complications, though none were associated with spinopelvic parameters or cup positioning. Acetabular cup inclination was significantly correlated with pelvic tilt (R = 0.30, p = 0.003), while acetabular version showed negative correlations with pelvic incidence (R = -0.23, p = 0.02) and sacral slope (R = -0.31, p = 0.002). At 12 months, acetabular inclination predicted improvement in MCS (R = 0.28, p = 0.02), and obliquity predicted improvements in activities of daily living (R = 0.29, p = 0.02), pain (R = 0.28, p = 0.03), and quality of life (R = 0.30, p = 0.002).

Conclusion: In the first year after THA, acetabular inclination was linked to improved patient-reported outcomes, while greater pelvic obliquity was associated with better scores in activities of daily living, pain, and quality of life. Post-operative acetabular cup version had weak correlations with pelvic incidence, sacral slope, and pelvic tilt. No other associations were found between spinopelvic parameters, cup positioning, and instability or complications.

Keywords: Acetabular cup positioning; Hip instability; Patient-reported outcome measures; Postoperative complications; Spinopelvic parameters; Total hip arthroplasty.