Factors associated with the progression of sagittal spinal deformity after total hip arthroplasty: a propensity score-matched cohort study

Purpose The functional interaction between the hip and spine in patients undergoing total hip arthroplasty (THA) is clinically significant, as it impacts post-operative outcomes. Therefore, this study aimed to identify factors associated with the progression of sagittal spinal deformity and assess the association with patient-reported outcomes. Methods This retrospective case–control study included 200 patients who underwent primary THA and completed a mean follow-up duration of 42.2 months (range, 24.0–78.0). We employed a multivariate logistic regression to identify variables predictive of a post-THA sagittal vertical axis (SVA) ≥ 50 mm, which was indicative of a spinal sagittal imbalance. Propensity score-matched cohorts for age, sex, body mass index, follow-up duration, hip flexion contracture, developmental dysplasia, pelvic incidence (PI), and SVA were created, and the outcomes were compared between the two groups. Results PI (odds ratio 1.39; 95% confidence interval 1.04–1.86, p = 0.033) was associated with an SVA ≥ 50 mm. After successfully matching patients with ( n = 50) and without ( n = 50) an SVA ≥ 50 mm, the minimum clinically important difference showed significant differences between the 50 matched pairs ( p = 0.016 for EuroQol-5D, p = 0.003 for Hip Disability and Osteoarthritis Outcome Score Joint Replacement, and p