Post-injury TyG–BMI shows U-shaped link to nonunion in older limb fracture patients

IntroductionMetabolic 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.MethodsIn 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.ResultsAmong 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 (213.0) TyG-BMI levels were independently associated with increased risk [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).ConclusionBoth 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.