Hi Sore Tum,
I've had the setons in for over a year. The doctor called it a Stage 1 fistulectomy. He explained that setons keep the fistula open, which allows "stuff" to drain out and not get trapped and abscess. With things draining, and usually with antibiotics, any infected tissue around the fistula and old abscess can heal. The next stage of the fistulectomy procedure is when they cut open teh fistula. This distroys the fistula tube and then it can heal like normal tissue. They don't sew it closed, rather it is allowed to heal from the inside out. If they sitch it closed, bacteria usually gets in and then -- abscess!!!
But if the origin/start of the fistula is high in the rectum, then cutting the fistula open would require cutting through sphincter muscle. You would be immediately be incontinent because the sphincter muscle will never heal properly. That is the case with mine -- too much "sphincter involvement."
There are two other procedures my colorectal surgeon said were options for me. The first is the fistula plug, where they thread a wick-like string through the fistula. Your tissue grows into the wick and so the fistula closes. This procedure is successful only about 60-70% in non-Crohn's people and only 40-50% in Crohn's (we just don't heal as well). The other option for me is the Advancement Flap Procedure, where they cut a flap of tissue right beside the fistula opening, fold it over the opening, and stick it closed. Success rate is 80-90% in non-CD and only 60-70% in CD.
Here are two good websites that provide information about fistulae:
http://emedicine.medscape.com/article/190234-overview --- this continues on several pages, so be sure to click on the sections, especially "Treatment"