Abstract
BACKGROUND: Obesity is often associated with worse outcomes after lumbar fusion surgery, but its impact on patient-reported 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.