An internally validated nomogram for predicting impaired wound healing after calcaneal fracture surgery in patients with type 2 diabetes Mellitus

Abstract

Impaired wound healing remains a major complication following calcaneal fracture surgery in patients with type 2 diabetes mellitus (T2DM), yet reliable tools for individualized risk prediction are lacking. Of 553 T2DM patients screened, 360 were eligible and randomly allocated to a training set ( n  = 269 after excluding 1 for incomplete outcome adjudication; 66 outcome events) and an internal validation set ( n  = 90; 22 outcome events, 24.4%). A nomogram was developed using multivariable logistic regression based on predictors selected via LASSO. Model performance was assessed by area under the ROC curve (AUC), calibration (evaluated by the Brier score and the Hosmer-Lemeshow goodness-of-fit test), and decision curve analysis (DCA). The final model incorporated five predictors: HbA1c, insulin use, diabetic peripheral neuropathy, C-reactive protein, and platelet count. In the training set, the nomogram achieved an apparent AUC of 0.886 (95% CI: 0.846–0.925),with an optimism-corrected AUC of 0.875 (optimism estimate = 0.011). In the internal validation set, the AUC was 0.891 (95% CI: 0.789–0.965). The model showed favorable calibration in the training set [Brier score = 0.113 (95% CI: 0.088–0.140); Hosmer–Lemeshow test, χ 2  = 7.215, df = 8, P = 0.514] and good calibration in the validation set (Brier score = 0.106 (95% CI: 0.067–0.147);calibration slope = 1.27 (95% CI: 0.75–2.89),intercept = 0.44 (95% CI:–0.24–1.85); Hosmer–Lemeshow test, χ 2  = 10.552, df = 8, P = 0.228), and provided higher net benefit than treat-all or treat-none strategies across threshold probabilities from 0.01 to 0.95in both the training and validation sets. At a threshold of 0.4, it identified approximately one-fifth of patients as high-risk, with a high proportion of events among them. The internally validated nomogram provides a promising tool for risk stratification of postoperative wound complications in T2DM patients with calcaneal fractures. The model is exploratory and limited to internal validation; external validation in multicenter cohorts is required before routine clinical adoption.