Transanal Total Mesorectal Excision for Rectal Cancer on Anal Physiology + Fecal Incontinence

Low Anterior Resection (LAR) surgery can be done using various techniques. The traditional technique for performing the surgery is through one or multiple incision(s) in the muscular wall of the abdomen. This will allow the surgeon to gain access to inside the belly (Abdominal cavity). The surgeon will start from above and go down until reaching the rectum located low in the pelvis. The surgeon will then cut out the rectum along with some of the tissue surrounding it and reconnect the bowel. An alternative new approach to perform Low Anterior Resection is called the Trans-anal approach. In this technique, a tube containing special surgical tools is introduced through the anus (back passage), while the patient is asleep. These tools are used to free the rectum up from its surroundings so that it can be removed. Taking out the rectum via the opening of the anus (Trans-anal) is a relatively new surgical approach. This new technique enables the surgeon to better see deep in the pelvis which makes it easier to remove the rectum and its surrounding outer tissues while protecting other important nerves and organs located in the pelvis. However, it also involves inserting a tube through the opening of the anus to perform the rectal dissection. The alternative traditional way of doing the operation does not involve inserting such a tube because the access to the pelvis and rectum is gained from above through incision(s) in the abdominal wall. The anal sphincter is the medical name for the muscle layers surrounding the opening of the anus. The anal sphincter functions as a seal that can be opened to discharge body waste and allow the passage of stool. A damage to the anal sphincter can result in inability to fully control bowel movements, causing stool (feces) to leak unexpectedly. Because the Trans-anal approach involves inserting a tube through the opening of the anus for the duration of the surgery, this can lead to a certain degree of stretch and damage to the anal sphincter muscles. The main aim of this study is to compare the effect of the these two possible approaches to perform "Low Anterior Resection" operation on the muscles of the anal sphincter and whether they are associated with stool seepage from the anus after the operation. Whether the patient is receiving the traditional or trans-anal approach is not related to the subject's participation in the study and is decided by the treating surgeon based on medical and surgical reasoning.