Abstract: Objective To investigate the effect of extraperitoneal drainage on incisional complications of laparoscopic-assisted median abdominal surgery.The risk factors related to incisional complications were also analysed separately and a prediction model was constructed.Methods Retrospective analysis included 200 patients with colorectal malignant tumours who were operated with laparoscopy from January 2017 to September 2023 at the Department of Abdominal Oncology of the People's Hospital of the Inner Mongolia Autonomous Region (all of whom were operated using laparoscopically-assisted median incision of the lower abdomen),and were divided into the group of extra-peritoneal negative pressure drain (120 cases) and the group of no negative pressure drain (80 cases),according to whether or not negative pressure drains were placed on the outer layer of the peritoneum intraoperatively.General,intraoperative and postoperative data of patients in the two groups were collected and analysed.Single-factor and multifactor Logistic regression models were used to analyse the influencing factors of laparoscopically assisted median abdominal incision complications,analyse the risk factors related to incision complications,and construct a prediction model.Sixty-three patients with colorectal malignancy in our department from October 2023 to January 2025 were collected as an external validation group according to the same criteria.The predictive model effect was assessed by C-index,receiver operating characteristic (ROC) curve,calibration curve,and decision curve in both modelling and external validation groups.Results There was no statistically significant difference between the two groups when comparing the general and intraoperative data (P>0.05).The results of univariate and multivariate Logistic regression analysis showed that extraperitoneal placement of negative pressure drainage reduced the absolute risk of surgical site infections (SSIs) rate by 6.7% and the relative risk by 53.6%;patients' combination of diabetes mellitus,history of previous abdominal surgeries,abdominal adhesions,and intestinal stomas were the risk of SSIs and fatty liquefaction factors (P<0.05).In the modelling and external validation groups,the C-index of the SSIs model was 0.857,95%CI 0.749 to 0.966,0.959,95% CI 0.909 to 1.008;and that of the fat liquefaction model was 0.868,95%CI 0.797 to 0.939,0.955,95%CI 0.895 to 1.016.The area under the ROC curve AOC of the SSIs The area under the ROC curve AUC for the model was 0.865,95%CI 0.756 to 0.975,0.967,95%CI 0.914-1.000,and for the fat liquefaction model was 0.876,95%CI 0.803 to 0.948,0.964,95%CI 0.904-1.000.The calibration curves of the two models passed the Spiegelhalter test (P>0.05).The clinical decision curve of both models showed a high threshold range.Conclusion Diabetes mellitus,history of previous abdominal surgery,abdominal adhesions,and enterostomy are risk factors for SSIs and fatty liquefaction,and for patients with colorectal malignancies treated with laparoscopically-assisted lower abdominal median incision,extraperitoneal drainage is recommended for the prevention of incisional infections;two columnar-line graphical models can more accurately predict the risk of SSIs and fatty liquefaction in the postoperative period,which has a certain clinical reference value.

Key words: surgical incision； complications; infection; fat liquefaction; extraperitoneal negative pressure drainage; laparoscope