Abstract: Objective To explore the risk factors of “difficult pelvis” in laparoscopic middle and low rectal cancer surgery,and to construct and validate a nomogram prediction model.Methods 143 patients with middle and low rectal cancer who underwent laparoscopic radical resection in our hospital from May 2020 to May 2022 were selected as the training set,and 129 patients treated from June 2022 to June 2024 were selected as the validation set,analyzed its clinical data,and used multi-factor Logistic regression analysis to explore the factors affecting the “difficult pelvis” in laparoscopic middle and low rectal cancer surgery.Based on these risk factors,a nomogram prediction model was constructed and verified.Results Multivariate Logistic regression analysis showed that age,pubic symphysis height,and pelvic depth were independent risk factors for difficult pelvis in patients undergoing laparoscopic surgery for low-lying colon cancer,while the diameter between ischial spines,AB line,A angle,and B angle were independent protective factors for difficult pelvis.Based on The nomogram prediction model was constructed from the above factors.The receiver operating characteristic curve results showed that the areas under the curve of the training set and validation set were 0.870 and 0.843 respectively,and the sensitivity and specificity of the validation set were respectively 81.23%、80.06%,the prediction performance was good.Conclusion The prediction model for “difficult pelvis” in laparoscopic middle and low rectal cancer surgery constructed in this study has good prediction performance

Key words: middle and low rectal cancer, laparoscopy, difficult pelvis, prediction model