The anus is a sphincter at the end of the rectum through which passes stool during defecation. The anal sphincter is a critical mechanism for control of fecal continence.

Anal fissures are tears in the skin overlying the anal sphincter, usually due to increased tone of the anal sphincter muscles, and a failure of these muscle to relax. Anal fissures cause pain during defecation and bleeding from the anus.

Most anal fissures can be treated successfully with conservative measures, which include stool softeners and warm soaks. The goal is to relax the anal sphincter, which allows the fissure to heal. If these methods are ineffective, surgery is necessary. This is called an internal sphincterotomy, a procedure in which the anal sphincter is partially cut, thus allowing it to relax and permitting the fissure to heal.

Sphincterotomy, when properly performed, is very effective in healing anal fissures.