With the progress of anus-preserving technology and the recognition of the optimal and safe distal margin and acceptable tumor results, total ISR has become the ultimate anus-preserving approach27. Moreover, long-term studies have shown that complete ISR does not increase the local recurrence rate of patients with ultra-low rectal cancer after surgery compared with APR, and its safety has been recognized by the majority of surgeons14, 28. Colon-anal anastomosis was performed manually in both groups. And there were no significant differences in operation time, intraoperative blood loss, postoperative drainage tube removal time, postoperative feeding time, postoperative length of hospital stays and hospitalization costs between the two groups (P > 0.05). Except for the control group, the operating methods of the two groups were similar, so there was no significant difference in the surgical results. The surgical approaches were similar in both groups, except that the observation group received an additional PGOT. However, there was no significant difference in operation time between the two groups, which was due to the fact that the patients in the control group were enrolled earlier and the maturity of early total ISR surgery skill was not high, which also prolonged the median operation time of the patients in the control group. In addition, the procedure of PGOT is simple and time-consuming. As a result, there was no significant difference in the median operation time between the two groups.
All patients in the two groups underwent laparoscopic surgery successfully, without conversion to laparotomy. The incidence of postoperative complications was not high, which was similar to that reported by other centers29, 30. Moreover, through data review, the postoperative complications of the patients in this study mainly occurred in the early stage of initiating total ISR, and the incidence of postoperative complications in the later stage was relatively low, which may be caused by the improvement of surgical proficiency and surgical skills of the surgeons. In addition, no complications such as omental infection or necrosis were observed in the observation group.
With the application of total ISR, ULRC patients are able to avoid APR and permanent colostomy, but severe anorectal dysfunction will occur after surgery, which also brings low or very low quality of life to the patients. Multiple studies have shown that up to 50%-80% of patients will suffer from anorectal dysfunction of varying degrees after surgery31–33, which has an impact on their quality of life and may even offset the benefits brought by preserving intestinal continuity34.
In order to improve defecation function after complete ISR, many scholars have done sufficient research and exploration on the physiological function of original rectum, the pathogenesis of LARS, and the reconstruction method of digestive tract35–38. However, there is no existing data providing us with direct evidence to improve LARS39, 40. In other words, in clinical practice, the choice of digestive tract reconstruction method may be influenced by anatomical and technical possibilities as well as the willingness of the surgeons39, which also indicates that surgeons need to improve the digestive tract reconstruction method after total ISR.
In the past, our center tried to transplant pedicled greater omentum to the rear of the neo-rectum after TME in patients with middle and low rectal cancer, and the postoperative follow-up found that the defecation function of these patients was better, which provided us with inspiration for improving postoperative LARS21. This suggests that we should pay attention to the physiological differences between the dilatation characteristics of sigmoid colon or descending colon used to construct the neo-rectum and the original rectum, and pay attention to the influence of changes in volume, pressure41, compliance42, 43 and movement of the neo-rectum on postoperative anorectal function.
On the one hand, postoperative poor defecation function is thought to be associated with the combined effect of smaller neo-rectal volume and higher neo-rectal pressure when anal sphincter function is weakened44. The patients in this study had a small volume of the now-rectum in the early postoperative period, which was confirmed by the decrease in the first sensation volume and the discomfort volume in the anorectal manometry. Due to the small volume of the neo-rectum, the pressure is prone to rise, leading to the loss of the role of the rectal reservoir, and the patient will have frequent defecation even in the presence of a small amount of stool.
On the other hand, postoperative poor defecation function is also believed to be associated with severe pelvic floor tissue adhesion and poor intestinal compliance after digestive tract reconstruction44, 45. In order to ensure radical resection, TME is the standard surgical method46, 47. However, due to removal of the whole mesorectum, the neo-rectum lacks the matting and buffering of the surrounding mesangium, and the postoperative scar traction caused by pelvic tissue adhesion, the spastic hypermotility of the neo-rectum is easy to lead to increased pressure and decreased compliance. This is also believed to be closely related to the occurrence of LARS42, 45, 48.
In this study, patients in the observation group received pedicled omentum transplantation. Greater omentum is an ideal material for repair. At present, pedicled omental flap, as a source of biomaterials, has been widely used in the prevention or treatment of complications, such as rectovaginal fistula and vesicovaginal fistula, cerebrovascular reconstruction, tissue damage repair, and as a carrier to promote regeneration, etc.49–52, which has solved many clinical treatment problems. The pedicled omentum was free and transplanted to the pelvic floor to simulate the reconstruction of the mesentery around the neo-rectum and the presacral tissue, which avoided the intestinal stiffness caused by the adhesion between the neo-rectum and the presacral tissue, reduced the pressure of the neo-rectum, improved the compliance of the neo-rectum, and increased the defecation buffer.
Through follow-up of postoperative anorectal function of the two groups of patients, it was found that the intestinal dysfunction of the patients was at the level of severe LARS within 1–3 months after surgery. In addition to the symptoms of postoperative difficulty in defecation (constipation), other patients in both groups had symptoms related to anorectal dysfunction, such as increased frequency of defecation, fecal incontinence, multiple defecation within 1 hour, gas-stool confusion, and defecation after eating. This is due to the removal of the rectal ampulla and all the internal anal sphincter during total ISR operation, which destroyed the original physiological structure of the rectum and the anorectal ring53, 54. Anal sphincter function, rectal fecal storage capacity and sensory ability of rectal mucosal receptors are important features to maintain fecal abstinence. Anorectal ring also plays an important role in anal self-control function. Therefore, short-term postoperative intestinal dysfunction, defecation and stool control dysfunction are common and serious phenomena after total ISR.
As observed by the LARS curves of the two groups after surgery, although the patients were in a stage of severe LARS within 1–3 months after surgery, the anorectal function of the two groups was slightly improved from the 3rd month after surgery, showing a gradual recovery trend. In addition, the LARS score of the observation group was significantly lower than that of the control group at the time points of 3rd, 4th, 5th, 6th, 9th, 12th month and > 12th month after surgery, and the difference was statistically significant. It shows that the recovery time and speed of anorectal function in the observation group are better than those in the control group. Furthermore, patients in the observation group showed defecation frequency within 3 months after surgery, and the intestinal function was poor, or some patients showed symptoms of postoperative defecation difficulty (constipation). However, after 3 months of surgery, the patients' defecation function can gradually recover, and their fecal abstinence ability is better. On the 9th month after surgery, most of the patients were in mild LARS, even no LARS in some patients. On the contrary, the recovery of the defecation function in the control group occurred mainly 6 months after surgery, and the overall recovery was still not ideal. Some patients had frequent defecation after 6 months or even 2–3 years after surgery. The difference of postoperative anorectal function recovery between the two groups was earlier and faster in the observation group, which was considered to be related to the low neo-rectal pressure and good improvement of compliance in the observation group under the active assistance of pedicled omentum.
Another important point is that under the matting of pedicled omentum, the thickness of posterior rectal mesangium in the observation group was significantly greater than that in the control group, and also greater than the preoperative level. Accordingly, the mean RRP of patients in the observation group was significantly lower, the neo-rectum of patients in the observation group regained a buffer force, reduced the occurrence of spasmodic movement, significantly reduced RRP, and maintained the pressure gradient formed by ARP and RRP, which played an important role in maintaining the anal self-restraint of patients in the resting state55. However, it should not be ignored that some patients show symptoms of constipation and weak defecation in the early postoperative period, which is not only due to the pelvic floor muscle trauma leading to poor active defecation, but also due to low rectal resting pressure, which causes the weakening of intestinal movement. However, about 3 months after surgery, the symptoms of constipation can be improved, which also reflects the recovery of the patient's anorectal function.
In this study, only part of the patients underwent rectal MRI defecography, which resulted in limited reference significance, but it also preliminarily showed the anorectal morphological characteristics of patients after surgery. In the force phase of rectal MRI defecography, the coordination of neo-rectum peristalsis was poor in the control group. In contrast, the greater omentum behind the neo-rectum in the observation group was well scalable, and with its help, the compliance and coordination of the neo-rectum were good.
There were some limitations in this study, which did not fully and comprehensively assess the anorectal function of the patients after surgery. First, the rectal MRI defecography data in the study were usually obtained in the prone position, which may produce poor physiological results compared to the sitting position. Secondly, the sample size of this study was small, which leads to the lack of credibility of the statistical results. Finally, not all of the subjects received anorectal manometry detection and rectal MRI defecography in this study. Although patients' intestinal function was assessed by various methods, the data integrity was insufficient to further analyze postoperative anorectal function and morphological changes.
In conclusion, due to the destruction of anorectal physiological structure and surgical trauma, almost all patients with ULRC will have LARS symptoms such as increased defecation times and poor stool control ability after complete ISR. Over time, the postoperative anorectal function of patients will recover to a certain extent. Compared with the control group, patients in the observation group were combined with PGOT, and the new rectal compliance of patients in the observation group was better, peristalsis was more coordinated, and the postoperative anorectal function recovery was faster and more ideal.
Therefore, PGOT has a positive effect on LARS after total ISR in ULRC patients and is expected to be an effective strategy for the prevention and improvement of LARS. However, the selection criteria for the implementation of PGOT have not yet been formulated, and the filled omentum has not been quantified and standardized, which needs further study. At the same time, we encourage more clinical centers to join our study.