Differential Impact of Body Mass Index on Postoperative Complications in Orthognathic Surgery: A retrospective study of 1,309 patients

Background : Body Mass Index (BMI) is a well-established predictor of postoperative complications in various surgical fields; however, its specific role in orthognathic surgery has not been sufficiently investigated. This study aimed to comprehensively analyze the association between BMI and postoperative complications in orthognathic surgery to enhance surgical safety and establish practical clinical guidelines. Methods : A retrospective study was conducted on 1,309 patients who underwent orthognathic surgery performed by a single surgeon from 2012 to 2024. BMI was classified according to the World Health Organization Asia-Pacific criteria: underweight (<18.5 kg/m²), normal (18.5–23.0 kg/m²), overweight (23.0–25.0 kg/m²), and obese (≥25.0 kg/m²). Complications were categorized into intraoperative events, such as bad split and excessive bleeding, and postoperative issues, including hardware failure, infection, and relapse. Statistical analyses were performed using Chi-square or Fisher’s exact tests for categorical variables and One-way ANOVA or Kruskal-Wallis tests for continuous variables. Results : Statistically significant differences were observed in complication patterns across BMI categories. Among major complications, the transfusion rate was significantly highest in the underweight group (3.6%, p=0.0181). Conversely, fixation hardware failure (8.0%, p<0.001) and skeletal relapse (3.3%, p=0.0051) were significantly more prevalent in the obese group. While initial surgical overjet change increased with higher BMI (p=0.0011), postoperative overjet changes showed no significant differences among groups. No significant association was observed between BMI and infection rates. Conclusions : This study suggests that distinct pathophysiological and biomechanical risk factors are involved according to BMI categories in orthognathic surgery. Underweight patients show an increased risk of transfusion due to reduced physiological reserve, while obese patients face elevated risks of hardware failure and relapse due to biomechanical instability. Personalized clinical management strategies based on BMI are necessary, including enhanced fixation methods and long-term follow-up for obese patients. Trial registration: Clinical Research Information Service KCT0011570, February 3, 2026. Retrospectively registered.