Changes in low back pain, global sagittal alignment, and spinopelvic parameters following primary total hip arthroplasty: results of a prospective observational study with two-year follow-up

Abstract Purpose The hip-spine relationship is increasingly recognized as clinically relevant in patients undergoing total hip arthroplasty (THA), yet associations between THA and changes in low back pain (LBP), sagittal alignment, and functional disability remain incompletely understood. This prospective study evaluated two-year changes in LBP (primary clinical endpoint) and radiographic alignment, with global sagittal alignment and spinopelvic alignment defined as primary radiographic endpoints, as well as their associations with postoperative pain and disability. Methods This prospective observational cohort study included 197 patients undergoing primary unilateral THA. LBP was assessed using the Numeric Rating Scale (NRS) preoperatively and at two-year follow-up. Standing lateral radiographs evaluated global sagittal alignment (sagittal vertical axis SVA) and spinopelvic parameters at both timepoints. The Oswestry Disability Index (ODI) assessed postoperative functional disability. Associations between radiographic alignment parameters and clinical outcomes were examined using univariable and multivariable regression analyses. Results Of 197 patients enrolled, 144 (73.1%) completed clinical follow-up at a mean of 29.1 months, and 120 had complete clinical and radiographic data. LBP improved significantly from a median NRS score of 5 (IQR 1–8) preoperatively to 2 (0–4) at two years ( p < 0.001). Both SVA and pelvic incidence–lumbar lordosis (PI–LL) difference improved significantly ( p < 0.001 and p = 0.038, respectively). In multivariable analysis, preoperative LBP was the strongest predictor of postoperative LBP ( p = 0.002; η²=0.14). Postoperative PI–LL difference ( p = 0.009) was independently associated with functional disability, whereas SVA showed no significant association with either postoperative LBP ( p = 0.422) or functional disability ( p = 0.096). Conclusions Primary THA was associated with significant improvement in LBP, sagittal and spinopelvic alignment at two years. Preoperative LBP was the strongest predictor of postoperative pain, while postoperative PI-LL difference was independently associated with functional disability at two years. These findings support preoperative spinopelvic assessment for risk stratification and interdisciplinary management in patients with coexisting hip and spine symptoms.