After vaginal delivery, the vagina, perineum, and anorectum are examined to identify and repair significant injuries. In particular, occult injury to the anal sphincter complex occurs frequently at the time of an otherwise uncomplicated delivery and, if neglected, can contribute to anal and fecal incontinence . Even when recognized and repaired, persistent sphincter dysfunction is considered to be the most common cause of postpartum anal incontinence [2,3].
Evaluation and repair of episiotomy incisions and perineal lacerations associated with childbirth will be reviewed here. Evaluation and management of vaginal lacerations are discussed separately. (See "Evaluation and management of lower genital tract trauma in women", section on 'Vagina'.)
The muscles of the female pelvic floor and perineum are shown in the following figures (figure 1 and figure 2). The perineal body is the central point of the perineum and separates the urogenital triangle from the anal triangle. Within the perineal body are the interlacing fibers of the superficial transverse perineal muscles, bulbocavernosus, and fibers of the external anal sphincter. The anorectal sphincter complex is comprised of two structures with different, but overlapping, roles for maintaining continence (figure 3). The external anal sphincter (EAS) is a thick, circular, predominantly striated muscle that surrounds the anal orifice, and is responsible for continence of solid and liquid stool, as well as flatus, both at rest and at times of rectal distension. The internal anal sphincter (IAS) lies between the external sphincter and the anal canal and represents a thin condensation of the longitudinal smooth muscle fibers of the colon submucosa (figure 3). The IAS extends more than a centimeter above the cephalad margin of the external sphincter . It is entirely under involuntary control and contributes to maintaining anal continence at rest . The puborectalis portion of the levator ani complex also plays an important role in continence of solid stool. The external anal sphincter is innervated by the pudendal nerve, which may be susceptible to injury during delivery.
In 1999, Sultan proposed refining the traditional classification system for obstetric perineal lacerations . The revised system provided a subclassification for third degree lacerations:
●First degree lacerations involve injury to the skin and subcutaneous tissue of the perineum and vaginal epithelium only. The perineal muscles remain intact.