The relationship between functional prognosis in patients with infection after upper limb trauma: a predictive model based on HbA1c stratification and the mediating role of delayed rehabilitation

OBJECTIVE: To investigate the association between preoperative glycated hemoglobin (HbA1c) and upper limb function (Disabilities of the Arm, Shoulder and Hand [DASH] score) at 6 months post-surgery in patients with fracture-related infection (FRI) after upper limb trauma, and to test the mediating role of rehabilitation initiation time. METHODS: This retrospective cohort study included 100 patients with FRIs after upper limb trauma surgery (September 2020 to August 2025). Demographic characteristics, fracture features, HbA1c levels, time to initiate rehabilitation, and debridement frequency of patients were collected. With the DASH score at 6 months after surgery as the outcome variable, multiple linear regression was used to analyze the association between HbA1c and functional prognosis, and the Bootstrap method was used to test the mediating effect of rehabilitation initiation time. RESULTS: HbA1c was significantly positively correlated with the DASH score (β = 6.90, 95% CI 3.91-9.89, p < 0.001). Recovery initiation time played a partial mediating role between the HbA1c and the DASH scores, with a mediating ratio of 27% (indirect effect 2.04, 95% CI 0.63-3.59, p = 0.004). There was no significant interaction between HbA1c and recovery initiation time or debridement frequency (p > 0.05). Thresholding effect analysis did not find a definite breakpoint (log-likelihood ratio test p = 0.220), and HbA1c was linearly related to the DASH score. CONCLUSION: Preoperative HbA1c is independently associated with 6-month upper limb function in patients with post-traumatic infection, with rehabilitation initiation time playing a partial mediating role. Clinicians should prioritize glycemic control and initiate rehabilitation as early as safely possible.