IntroductionPrevious studies have found mixed associations between body mass index (BMI) and adolescent idiopathic scoliosis (AIS) incidence and progression. The aim of this study was to examine the association between BMI and the incidence of posterior spine fusion (PSF) among pediatric patients with AIS.MethodsThis was a retrospective cohort study of patients diagnosed with AIS at a single large tertiary care center between January 1, 2014 and December 31, 2020. BMI-for-age percentiles were used to categorize BMI into four categories: underweight (<5th percentile), healthy weight (≥5th to <85th percentile), overweight (≥85th to <95th percentile), and obese (≥95th percentile). Chi-square and t-tests were used to compare distributions of baseline characteristics by incident PSF outcome status. Multivariable logistic regression assessed the association between BMI category at baseline and incident PSF adjusting for sex, age at diagnosis, race/ethnicity, health insurance type, vitamin D supplementation, and low vitamin D levels.ResultsA total of 2,258 patients met the inclusion criteria with 2,113 patients (93.6%) who did not undergo PSF during the study period and 145 patients (6.4%) who did undergo PSF. At baseline, 7.3% of patients were categorized as underweight, 73.2% were healthy weight, 10.2% were overweight, and 9.3% were obese. Compared to those in the healthy weight group, there was no significant association between PSF and being underweight (adjusted odds ratio [AOR] 1.64, 95% CI 0.90–2.99, p = 0.107), being overweight (AOR 1.25, 95% CI 0.71–2.20, p = 0.436), or being obese (AOR 1.19, 95% CI 0.63–2.27, p = 0.594).ConclusionsThis study did not find a statistically significant association between underweight, overweight, or obese BMI category and incident PSF among patients with AIS. These findings add to the current mixed evidence on the relationship between BMI and surgical risk and may support the recommendation of conservative treatment to patients regardless of BMI.