Statistical analysis
Patients were randomly divided into a training group and a validation group (3:1). The data from the training group were used to search for independent risk factors to establish nomogram model. Data from the validation group were used to evaluate the prediction effectiveness of the nomogram model. Measurement data are expressed as mean ± standard deviation, and count data are expressed as n (%). In the training group, univariate analysis using Mann–Whitney U and Chisquared tests as appropriate was performed to assess the association between different variables and SSI. Multivariate analysis of variables with Discrimination of dichotomous result was most often evaluated by calculating the area under the curve (AUC) of the receiver operating characteristic (ROC) curve. Generally, an AUC between 0.5 and 0.7 indicates low accuracy, 0.70–0.9 is considered acceptable, and AUC > 0.9 means that the model has excellent discriminative power [