I found an article last night that I hadn't come across before in my reading, and have cited one section below. What I find most interesting, is #2. Maybe some people on this board have had a lot of spasming even after LIS because their surgeon didn't get through the entire thickness?
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2048592/
There are certain principles that should be noted:
1. The sphincterotomy should be away from the fissure site so that intact mucosal bridges fill the gap between divided muscle fibres to allow rapid healing.
2. The entire thickness of the lower internal sphincter must be divided, as any remaining intact fibres go into intense spasm to compensate for the divided fibres.
3. The mucosa over the sphincterotomy site should not be breached as this would predispose to infection.
4. The upper one-third of the sphincter must remain intact for continence.
5. The length of the sphincterotomy should be ‘tailored’ to the length of the anal fissure.