If a large transsphincteric fistula involving a significant amount of external sphincter muscle is present, a seton should be placed. The probe is first passed from the external opening to the internal opening, and a 0 silk suture is tied around the groove in the probe (Figure 14). The probe with the suture is then pulled back through the fistula track, and the 0 silk suture is tied tightly around the muscle. All fat and skin are removed leaving the seton compressing sphincter muscle only. Silk is an irritant, and with time the silk will cut through the sphincter muscle. However, the fistulotomy will be performed incrementally giving time for the sphincter to heal. The fistula is slowly drawn out by the seton. This protects against incontinence, by preventing the sphincter muscle from separating, as would happen during a fistulotomy. A non-cutting seton using a vessel loop is indicated in chronic perianal disease.
The patient may be out of bed as soon as the anesthesia has worn off. The patient is allowed a light diet, and there is no attempt to restrain bowel movements. Stool softeners are prescribed. Sitz baths may be started on the second day following operation. Patients may be discharged the day of surgery and are seen within one week.
An alternative therapy for a complex fistula is an endorectal advancement flap (Figure 15). A flap with mucosa and submucosa is created to include the internal opening (Figure 16). The dissection is carried far enough proximal until the flap can be advanced distally without tension. The internal opening is excised, and then the flap is matured to the intersphincteric groove (Figure 17). The external sphincter may be plicated to close the fistula opening and then ...