Internal Validation of Preoperative Inflammation-Nutrition Markers for Predicting Complications After Complex Lower-Extremity Wound Reconstruction.

Background: Complications after complex lower-extremity wound reconstruction remain common in clinically heterogeneous adult patients, many of whom are older and multimorbid. We evaluated whether adding the C-reactive protein-to-albumin ratio and prognostic nutritional index to a prespecified clinical baseline model improves internally validated prediction of 30-day clinically significant reconstruction-related complications. Methods: In a prospective single-center cohort from 2021 to 2024, consecutive adults undergoing complex lower-extremity reconstruction were enrolled. The C-reactive protein-to-albumin ratio and prognostic nutritional index were calculated from routine preoperative laboratories. A ridge-penalized logistic regression clinical baseline model was compared with an augmented model adding log-transformed C-reactive protein-to-albumin ratio and prognostic nutritional index. Internal validation used 5-fold cross-validation with out-of-fold predictions. Performance was assessed by area under the receiver operating characteristic curve (AUC) and Brier score; calibration and decision-curve analyses were interpreted descriptively from the internally validated predictions. Log-transformed C-reactive protein-to-albumin ratio was used as a monotonic skewness-reducing transformation rather than as a broader nonlinear biologic model. Results: Among 693 patients (median age 70.7 years; 62.3% male), 139 (20.1%) met the composite endpoint. Infection, necrosis, and additional unplanned interventions occurred in 12.1%, 7.6%, and 10.2%, respectively (non-mutually exclusive). The C-reactive protein-to-albumin ratio was higher (median 0.55 vs 0.19) and the prognostic nutritional index lower (43.2±4.2 vs 46.1±4.5) in patients with complications. With the augmented model, higher log-transformed C-reactive protein-to-albumin ratio and lower prognostic nutritional index shifted predicted risk in the expected direction. The augmented model improved discrimination from AUC 0.71 (0.65-0.75) to 0.79 (0.75-0.83), reduced Brier score (0.132 vs 0.147), and showed higher net benefit than the baseline model across an approximate 10-35% threshold range in exploratory decision-curve analysis. Conclusion: Routine preoperative C-reactive protein-to-albumin ratio and prognostic nutritional index may provide potentially useful incremental prognostic information for early complications after complex lower-extremity wound reconstruction, should be interpreted alongside clinical judgment, and external validation is warranted.