Anal preservation surgery for low to intermediate rectal cancer includes: anterior rectal resection: this procedure preserves the anal sphincter, thus avoiding permanent colostomy, and although it may result in poor defecation function after surgery, the quality of life after surgery is much higher compared to patients with permanent colostomy. It was gradually accepted by surgeons in the mid-20th century. Two determinants of successful anterior resection are a safe manual anastomosis and a clean distal margin. Early studies considered 5 cm to be the “safe” distal resection border, and some later studies showed that a distal margin of 2 cm or less did not affect survival or recurrence rates. Nowadays, the widely accepted safe margin is 2 cm from the lower edge of the tumor. Combined transabdominal perineal resection: This procedure became the standard of care for low-grade rectal cancer. anterior resection was first routinely used in the 1940s for malignant tumors in the upper third of the rectum, but many surgeons still believe that APR should be the surgical approach for low-grade rectal cancer because anterior resection involves the development of anastomotic fistula and increases postoperative mortality and recurrence. and increases the postoperative mortality of patients as well as some defecation dysfunction caused by low anastomosis. Total rectal mesenteric resection: anterior resection for rectal cancer is now the gold standard for anus-preserving surgery for low- to mid-level rectal cancer. It is a surgical procedure to remove the entire rectum and the modified mesentery completely and precisely by sharply separating the avascular zone under direct vision. As long as the rectal mesentery is completely removed, it is safe to limit the extent of resection of the distal bowel wall to preserve the anal sphincter. This technique has reduced the recurrence rate of rectal cancer to less than 10% at 5 years after surgery. Because of the high incidence of anastomotic fistula after low anterior resection, especially after TME, some surgeons recommend that patients with risk factors for developing anastomotic fistula should have a protective temporary stoma. Factors affecting anus-preserving surgery for low to mid-level rectal cancer: With the widely accepted principle of 2-cm distal margin and the development of anastomosis technology, many patients with low-level rectal cancer can complete anus-preserving surgery, but there are still 20% to 38% of patients who cannot complete anus-preserving surgery, and the main factors limiting the successful completion of anus-preserving surgery are: 1. gender Due to the physiological difference in pelvic anatomy, men are more likely to have anus-preserving surgery than women. Due to the physiological difference of pelvic anatomy, the male pelvis is narrower than the female pelvis, and the space available for surgical operation is more limited, which makes the surgical operation more difficult. Therefore, it is more likely for male patients with low and middle rectal cancer to undergo APR. 2. Body mass index (BMI) obesity also affects the successful completion of anal preservation surgery. One study showed that 37.2% of patients with normal weight failed to preserve the anus, while 46.7% of obese patients failed to preserve the anus. 3.Surgeon’s surgical technique There is a significant difference in the success rate of anal preservation surgery among different surgeons. 4.The functional status of the patient’s local tissues Poor functional status of the local tissues often leads to anastomotic fistula after resection of low and middle rectal cancer, thus affecting the successful completion of anal preservation surgery. a. During the TME anal preservation surgery, the rectum and the left hemicocele or sigmoid colon need to be fully freed so that the tension-free anastomosis of the rectum and colon can be safely completed to reduce the occurrence of postoperative anastomotic fistula. b. The relative ischemia of the rectal stump after completion of TME makes the anastomosis heal poorly and prone to anastomotic fistula, while the blood supply to the anal canal is relatively abundant, so the incidence of coloanal anastomotic fistula is relatively low. c. Some studies have shown that the risk of postoperative anastomotic fistula is significantly higher in patients who receive preoperative radiotherapy. 5.Patients’ systemic status When patients with low rectal cancer have intestinal obstruction, intestinal perforation, peritonitis, and systemic infection, often the anastomosis cannot be completed in one stage, and even if the anastomosis is completed, the incidence of postoperative anastomotic fistula is higher, which leads to failure of anus-preserving surgery. If the patient has severe anemia, diabetes, or malnutrition, the anastomosis does not heal well, which also increases the incidence of postoperative anastomotic fistula. In addition, long-term smokers and alcoholics are at significantly higher risk of postoperative anastomotic fistula. Problems of anastomotic fistula after anastomotic surgery for low and intermediate rectal cancer A major problem after anastomotic surgery for low and intermediate rectal cancer is rectal or anal canal anastomotic fistula, and low anastomosis is now considered to be a significant factor in the occurrence of anastomotic fistula. 2. Postoperative recurrence With the widespread use of TME surgery and preoperative adjuvant radiotherapy, the recurrence rate of rectal cancer after surgery has decreased significantly and the survival rate has increased significantly. A study in Sweden showed that the postoperative recurrence rate of rectal cancer patients who underwent preoperative radiotherapy was only 9%, while the postoperative recurrence rate of patients who did not undergo preoperative radiotherapy reached 26%. TME surgery combined with radiotherapy can improve the prognosis, but sometimes it can increase the serious toxic side effects. 3. Anal function After TME anal preservation surgery for low and middle rectal cancer, patients with anastomosis using end-to-end anastomosis have disordered bowel function and have many bowel movements, especially in the first postoperative year. In order to improve the function of the anus after surgery, an “J” type storage bag can be made with the colon intraoperatively, and then anastomosed with the rectum or anal canal. 4. Autonomic nerve injury Some patients with middle and low rectal cancer will have sexual dysfunction and urinary dysfunction after surgery, mainly because the lower abdominal nerves and pelvic visceral nerves are injured during surgery, and the incidence of postoperative impotence is as high as 40% in male patients. tME advocates sharp dissection of the rectum, thus preserving the autonomic nerve trunk, so that the incidence of postoperative impotence in male patients is significantly reduced, but there are still some patients with decreased maximum postoperative urinary flow rate and decreased penile erectile function index.