Effects of Body Mass Index on Spondylolisthesis Surgery and Associated Patient-Reported Outcomes: A Retrospective Review

Background: Obesity is often associated with worse outcomes after lumbar fusion surgery, but its impact on patientreported outcomes in spondylolisthesis remains unclear. This study assesses the effect of body mass index (BMI) on outcomes for degenerative and isthmic spondylolisthesis patients undergoing lumbar fusion. Methods: We conducted a retrospective analysis of 86 patients with low-grade lumbar degenerative and isthmic spondylolisthesis, categorized by BMI into nonobese (<30 kg/m²), obesity class I (30.0–34.9 kg/m²), obesity class II (35.0–39.9 kg/m²), and obesity class III (≥40.0 kg/m²). Outcomes were measured using the visual analog scale (VAS) for pain and the Oswestry Disability Index (ODI) at baseline and 12 months postoperatively. Statistical analyses included a 1-way analysis of variance, Bonferroni post hoc comparisons, and Kruskal-Wallis tests. Results: Significant disability improvements (mean ODI improvement: 15.6 points, P < 0.001) were observed across all BMI categories, while pain improvements were less pronounced (mean VAS improvement: 2.1 points, P < 0.001). Nonobese and class II patients maintained improvements at 12 months. Degenerative spondylolisthesis patients showed better ODI outcomes compared with isthmic patients (P = 0.019), while VAS outcomes were similar (P = 0.251). Conclusion: Lumbar fusion results in significant disability reduction across BMI categories, with sustained improvements in nonobese and obesity class II patients. These findings suggest that obesity should not be a contraindication for lumbar fusion in well-selected patients, as meaningful improvements can be achieved, particularly in disability outcomes. Clinical Relevance: Clinically, this supports a more individualized approach to surgical candidacy, emphasizing functional goals and symptom burden over BMI alone, thereby promoting equitable access to care and helping guide preoperative counseling and shared decision-making. Level of Evidence: 3.