Hi Bellasmommy,
so sorry you're in pain.
I have the exact same as you and I am having the seton placed on wednesday.
I had a fistula before that was just laid open - they basically just cut it and leave it to heal. If the fistula has tracked through the sphincter muscle then to cut it would leave you incontinent, so they insert a seton to slowly cut it - like a cheese wire through cheese. Then they tighten it so that the track closes behind it.
Before you get it tightened take some painkillers about half hour beforehand and soak in a sitz bath to ease the pain afterwards.
There isn't much info anywhere about this - I googled for ages and just read horror stories which upset me. I did find a website called Fistula friends, but I cant remember how I got to it!
Was it a painful operation? I'm totally freaking out about it!
Welcome to the forum - this is a problem that is so much better shared with people who understand butt-troubles!