Influence of pelvic incidence–lumbar lordosis mismatch on surgical outcomes of total hip arthroplasty: a retrospective cohort study

Abstract

Purpose: Pelvic incidence–lumbar lordosis (PI-LL) mismatch has been widely studied in spinal disorders; however, its impact on total hip arthroplasty (THA) outcomes remains unclear. This study evaluated the impact of preoperative PI-LL mismatch on postoperative functional recovery and spinopelvic dynamics in patients undergoing THA. Methods: This retrospective cohort study included 167 patients who underwent primary unilateral THA. Patients were categorised into two groups based on a PI-LL mismatch threshold of 10°: mismatch group (PI-LL ≥ 10°) and matched group (PI-LL < 10°). Preoperative characteristics, spinopelvic parameters, and clinical outcomes were analysed. The Numerical Rating Scale (NRS) for pain, modified Harris Hip Score (mHHS), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) were used to assess the hip condition preoperatively and 6 months postoperatively. Results: The mismatch group exhibited a significantly higher pelvic tilt (PT) and lower sacral slope (SS) than the matched group. Furthermore, the mismatch group demonstrated reduced spinal flexibility, as indicated by a significantly smaller difference in spinopelvic angle between maximum lateral flexion positions. The spinopelvic parameters (PI, LL, PT, and SS) remained stable from preoperative to postoperative assessments. Preoperative mHHS and WOMAC scores were significantly worse in the mismatch group. However, no significant differences in postoperative outcomes were observed between the groups at 6 months. Conclusion: PI-LL mismatch was associated with altered spinopelvic parameters and poorer preoperative functional scores. However, short-term outcomes after THA remained comparable. These findings underscore the importance of individualised preoperative assessment while supporting the efficacy of THA, irrespective of spinopelvic alignment.