AIM: Reconstruction of severe lower extremity trauma with extensive soft tissue defects remains a major microsurgical concern. Unlike elective procedures, emergency reconstruction is plagued by higher rates of necrosis and failure. Current preoperative assessments predominantly focus on local vascular patency, often neglecting systemic physiological disturbances. This gap in the assessment process highlights the need to incorporate whole-body resuscitation indicators. This study aimed to evaluate the predictive value of combining a modified computed tomography angiography (CTA) Run-off Score with systemic resuscitation indices—specifically Central Venous Oxygen Saturation (ScvO2) and preoperative lactate (Lac_Pre)—for emergency flap prognosis.

METHODS: A retrospective cohort study was conducted on 180 patients undergoing emergency free flap transfer for high-energy lower limb trauma between February 1, 2022, and March 31, 2025. Systemic monitoring involved ScvO2 measurement via central venous catheterization and serial lactate analysis. Anatomical assessment included a modified CTA Run-off Score and the measurement of the distance from injury zone to anastomosis site (Dist_Anastomosis). The dataset was divided into the training and validation sets at a 6:4 ratio, which does not represent random clinical allocation. A multivariate logistic regression model was built in the training cohort, with candidate predictors selected based on univariable analyses, collinearity assessment and the clinical relevance supported by previous literature. The model’s performance was evaluated through discrimination (Area Under the Curve [AUC]), calibration (calibration curve), and clinical utility (decision curve analysis). For the secondary aesthetic analysis, a total of 163 patients were ultimately included in the 6-month VISIA/Vancouver Scar Scale (VSS)-based analysis after excluding patients with complete flap failure, for whom scar-based assessment was not applicable.

RESULTS: Multivariate logistic regression analysis identified three variables independently associated with flap failure: CTA Run-off Score (p < 0.001), Dist_Anastomosis (Odds Ratio [OR] 0.76, p = 0.006), and preoperative lactate (Lac_Pre; OR 1.54, p = 0.014). The combined prognostic model demonstrated acceptable to good discrimination, with an Area Under the Curve (AUC) of 0.89 (95% Confidence Interval [CI]: 0.82–0.97) in the training set and 0.79 (95% CI: 0.66–0.92) in the validation set. Calibration analysis, assessed via the Brier Score, yielded values of 0.103 for the training set and 0.165 for the validation set, indicating acceptable predictive error and robust model calibration. Secondary analysis revealed that flaps experiencing early adverse events showed significantly higher VISIA-7 Complexion Analysis System–derived “Redness Index” scores at 6 months after surgery (p = 0.006).

CONCLUSIONS: Integrating anatomical characteristics and perioperative physiological indicators may provide a useful approach for risk stratification in emergency reconstruction. In this internally validated retrospective cohort, preoperative lactate demonstrated a significant association with adverse acute flap outcomes and should be interpreted as a stratification marker rather than a definitive predictor. Further prospective studies with external validation are required to confirm these findings and evaluate functional recovery outcomes.