Does BMI Impact Spinopelvic Alignment After Lumbar Fusion Surgery?

Study Design. Retrospective cohort. Objective. Evaluating the impact of elevated BMI on perioperative sagittal alignment parameters among patients undergoing single-level lumbar fusion. Summary of Background Data. Sagittal malalignment affects postoperative outcomes after fusion for spine deformity. It is unclear what role elevated BMI plays in attaining and maintaining proper spinopelvic parameters postoperatively. Methods. Adult patients who underwent one-level lumbar fusion (2010–2019) with preoperative, immediate, and 2- to 3-year postoperative lateral lumbar radiographs were retrospectively identified. Spinopelvic parameters [lumbar lordosis (LL), segmental lordosis (SL), posterior disc height (DH), sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI)] were collected. Patients were dichotomized based on PT and PI–LL cutoffs indicative of spinopelvic instability (PT >20° and PI–LL >10). Patients were classified based on BMI (normal: 18.5–24.9; overweight: 25–29.9; obese ≥30). Demographic and surgical outcome data were compared between groups. Multivariate analysis was utilized to assess independent predictors of PI–LL mismatch >10° at 2 to 3 years follow-up. Results. A total of 832 patients were included—132 normal BMI, 267 overweight, and 433 obese. As BMI categories increased (normal vs. overweight vs. obese), the female percentage decreased (69.7% vs. 46.1% vs. 48.5%, P <0.001), and the Elixhauser comorbidity index increased (ECI) (0.99±1.04 vs. 1.15±1.14 vs. 1.60±1.29, P <0.001). At baseline, patients with greater BMI had greater PT (21.5°±8.05° vs. 22.8°±8.19° vs. 24.0°±9.24°, P =0.025) and were more likely to have PT >20° (59.1% vs. 68.7% vs. 71.2%, P =0.036). Logistic regression found BMI (OR: 1.06, CI: 1.01–1.12, P =0.024) and preoperative PI–LL mismatch (OR: 1.17, CI: 1.14–1.21, P <0.001) to be independent predictors of PI–LL >10° at 2 to 3 years postoperatively. Conclusion. This study indicates that increasing BMI is associated with increasing incidence of male sex, comorbidity burden, and worse preoperative sagittal balance. In addition, increasing BMI was independently predictive of failure to attain ideal, long-term postoperative PI–LL mismatch.