The anatomy of the perineal membrane: its relationship to injury in childbirth and episiotomy.

Background: Episiotomy during childbirth, intended to protect the anal sphincter, may fail to do so. Furthermore damage to the anal sphincter complex may occur without complete perineal tear. We hypothesise that these particular injuries may occur due to posterior displacement of the anus leading to distraction of the anal sphincter complex from an anterior attachment to the perineal membrane.