Risk factors and a predictive nomogram for nonunion following intramedullary nailing of femoral shaft fractures.

BACKGROUND: While fracture nonunion has been widely studied, nonunion after femoral intramedullary nailing (IMN) remains under-researched, with limited clinical translation of findings. This study aims to identify risk factors for nonunion after IMN of femoral shaft fractures and to develop a predictive nomogram. METHODS: A retrospective study was conducted on patients treated from January 2018 to December 2023. Cases of nonunion were designated as the nonunion group, with a 1:3 ratio of matched controls selected from patients who achieved union during the same period. Demographic and surgical variables were collected. Univariate and multivariate logistic regression analyses were conducted to determine independent risk factors.A predictive nomogram was developed and evaluated by the area under the receiver operating characteristic curve(AUC), calibration curve, 1000 bootstrap resamples, and decision curve analysis(DCA). RESULTS: Among 144 patients, 36 experienced nonunion. Multivariate analysis revealed that older age (OR = 1.04,P = 0.04), fracture end displacement > 4 mm (OR = 5.07, P = 0.00), multiple fractures (OR = 4.11, P = 0.01), intramedullary nail instability (OR = 5.07, P = 0.00), and delayed weight-bearing (OR = 4.67, P = 0.00) were independent predictors of nonunion. The nomogram demonstrated good discriminative capacity (AUC = 0.82), with a validated C-index of 0.79. Calibration and DCA confirmed the model’s clinical utility and accuracy. CONCLUSION: Advanced age, fracture end displacement > 4 mm, multiple fractures, intramedullary nail instability, and delayed weight-bearing are independent predictors of nonunion following IMN for femoral shaft fractures. The developed nomogram offers a practical tool for individualized risk assessment and may inform early clinical decision-making.