Resection of the upper third of the anal sphincters may allow even lower tumours to be safely resected without abdominoperineal resection; the transection of the bowel wall possibly with partial resection of the upper anal canal including the IAS is carried out.
This intersphincteric resection was based on the original Parks technique, which involved complete removal of the rectum . Initial results suggested that there are minimal adverse effects on post-operative continence .
Intersphincteric resection can also provide tumour-free margins for very low rectal tumours, and can be recommended in patients who are candidates for abdominoperineal resection aiming to avoid a permanent colostomy . However, the IAS is resected sometimes with an additional partial external sphincter resection that leads to impaired post-operative continence, with approximately a quarter of patients incontinent to solid stools and half of them with incontinence to liquid stools at least once per week . Functional outcome might be improved with a colonic J-pouch  or by a smooth muscle plastic technique .
A recently developed EMG signal detection and analysis tool  can provide information about the electrophysiology of anal sphincter muscles and computer-simulated motor unit action potentials (MUAPs) (Fig. 8). The EMG anal probe allows the acquisition of EMG from several locations around the anal canal and at different levels from the anal verge. As shown in Figure 9, after intersphincteric resection a reduction of bioelectric activity of the external sphincter could be observed, suggesting damage caused to this muscle during the dissection.
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