anal canal. The puborectalis, which is continuous with the levator ani muscles that form the pelvic diaphragm, is best palpated posteriorly and is often referred to as the anorectal ring.

The maximum pressure that can be generated in the anal canal is produced by the voluntary contrac­tion of the external sphincters and the puborectalis. It is called the maximum voluntary squeeze and can be maintained for only a short time. Contraction of the striated sphincteric mechanism is also caused as a refl ex in response to coughing or sneezing. Conti­nence depends on the interaction between the anal sphincters, the type of challenge (solid, liquid, gas), and the compliance of the rectum. The compliance of the rectum can be thought of as its ability to act as a reservoir. Decreased compliance of the rectum produces urgent calls to stool at low intrarectal volumes. Common causes of decreased rectal com­pliance include radiation proctitis, infl ammatory bowel disease, rectal resection, and irritable bowel syndrome. Patients with incontinence often have abnormalities in more than one area. Patients with a sphincter injury may have a good control of formed stool but be incontinent with liquid stool. Subtle abnormalities in sphincter function and continence may be unmasked by anal surgery. This can occur even with procedures that are usually not associated with changes in continence, such as a partial lateral internal sphincterotomy. Therefore it is extremely important to determine any abnormalities in bowel function that would predispose individuals to impaired continence postoperatively. Historical information regarding bowel habits and symptoms of minor sphincter dysfunction such as seepage, pruri­tus, or incontinence of fl atus should be noted and documented.