Comparison of Postoperative Anal Function Between Parks and Bacon Techniques in Low Rectal Cancer

Inclusion Criteria: 1. Men or women, aged between 18 and 75 years; 2. Pathological diagnosis of rectal cancer before operation, with the distance from the lower edge of the tumor to the dentate line ≤ 3cm by MR imaging; 3. No local complications (including complete/ incomplete obstruction, active bleeding, local invasion of sphincter or levator ani, etc.) before operation; 4. Suitable for anal preservation surgery discussed by MDT; 5. Adequate bone marrow, liver, renal and cardiac function meeting the requirements of surgery and anesthesia; 6. R0 resection is expected technically; 7. Provision of written informed consent. Exclusion Criteria: 1. Previous history of malignant colorectal tumors; 2. Complications such as obstruction and gastrointestinal bleeding that need an emergency operation; 3. Unachievable R0 resection due to invasion of adjacent organs by primary tumor; 4. Multiple primary tumors; 5. History of other malignancy; 6. Participation in other clinical trials within the previous 4 weeks of enrollment; 7. ASA physical status score ≥ IV level and/or ECOG performance status ≥ 2; 8. Intolerance of surgery due to liver, renal, cardiopulmonary or coagulation dysfunction, or underlying diseases; 9. History of serious mental disorders; 10. Women in pregnancy or lactation period; 11. Uncontrolled infection before operation; 12. Unsuitable to be included due to other clinical and laboratory conditions by the judgement of investigators.