Residual sagittal imbalance is associated with early hip degeneration after long lumbosacral fusion: an EOS-based study of 119 patients.

Abstract

To determine clinical and radiographic factors associated with early progression of hip osteoarthritis following long lumbosacral fusion, and to identify independent predictors of rapid joint space narrowing. This retrospective single-centre study included 119 patients (mean age 67.4 ± 8.6 years) who underwent long posterior fusion (≥ five levels across L5-S1). The most affected hip-defined by the smallest preoperative joint space width (JSW)-was analysed on standing EOS radiographs. Rapid progression was defined as JSW loss > 0.5 mm/year. Clinical, surgical, and spinopelvic parameters were compared between progression and non-progression groups. Variables with p < 0.10 in univariate analysis were entered into a multivariate logistic regression model. Rapid progression occurred in 37.8% of patients. The progression group showed higher BMI (27.9 ± 5.8 vs 25.1 ± 4.4, p = 0.018), greater pelvic incidence (PI) (58.1 ± 9.8 vs 51.4 ± 10.6°, p = 0.014), and higher postoperative sagittal vertical axis (SVA) (61.2 ± 46.9 vs 42.8 ± 33.7 mm, p = 0.012). In multivariate analysis, a one-standard deviation increase in postoperative sagittal vertical axis (SVA) was independently associated with rapid hip joint space narrowing (OR = 2.20; 95% CI 1.22-3.96; p = 0.009). Residual postoperative sagittal imbalance after long lumbosacral fusion is independently associated with early radiographic hip joint degeneration. Optimizing sagittal alignment may help reduce mechanical overload on the hip joints. IV - Retrospective analytical study.