Association between triglyceride glucose–body mass index and nonunion in older patients following limb fracture surgery: a multicenter retrospective cohort study

Introduction: Metabolic syndrome (MetS) is increasingly recognized as an emerging risk factor affecting fracture healing. We sought to investigate the association between the metabolic abnormality indicator triglyceride glucose-body mass index (TyG-BMI) and postoperative nonunion in older patients with limb fractures. Methods: In a multicenter retrospective cohort study across five tertiary hospitals, we included older patients (≥60 years) undergoing limb fracture surgery between January 2020 and December 2022. The exposure of interest was the post-injury TyG-BMI, derived from fasting plasma glucose, triglyceride levels, and body mass index. The outcome was nonunion, defined as persistence of the fracture for 9 months or longer without evidence of healing for 3 months. Restricted cubic spline (RCS) model and multivariable logistic regression were used to evaluate the association between TyG-BMI and nonunion. Sensitivity analyses and subgroup analyses were conducted to evaluate the robustness and population heterogeneity of the primary outcome. Results: Among 8,499 eligible patients [median age 75.0 (67.0, 83.0) years; 60.5% male], 141 cases (1.66%) developed nonunion. RCS revealed a U-shaped, nonlinear relationship between TyG-BMI and nonunion, with risk-protective thresholds at 173.9 and 213.0. Compared with the reference range, both low (<173.9) and high (>213.0) TyG-BMI levels were independently associated with increased risk [TyG-BMI < 173.9: adjusted relative risk (aOR), 1.358; 95% confidence interval (CI), 1.016-1.816; TyG-BMI > 213.0: aOR, 1.233; 95%CI, 1.030-1.475], which remained robust across multiple sensitivity and exploratory analyses. Significant interactions were observed between TyG-BMI levels and perioperative blood transfusion and bone grafting type (P for interaction < 0.05). Conclusion: Both low and high TyG-BMI levels are significantly associated with increased nonunion risk in older patients following limb fracture surgery, serving as a potential biomarker for risk stratification and individualized management.