Perineal injury is common during vaginal delivery (up to 75% of parturients) (1). It may be iatrogenic (episiotomy), accidental (spontaneous laceration), or a combination (episiotomy with extension surrounding tissues).
Episiotomy is a surgical enlargement of the posterior aspect of the vagina by an incision in the perineum during the last part of the second stage of labor (2).
The routine use of episiotomy to hasten delivery is no longer recommended by most national and international Ob/Gyn organizations because of its associated complications.
Current individualized indications include the need to:
Rapidly widen the introitus for delivery for fetal reasons
Direct an impending laceration away from the anal sphincter
The type of episiotomy recommended differs according to country of practice with a recommendation for mediolateral episiotomy at an angle of 60 degrees away from the midline in the Royal College of Obstetricians and Gynaecologists (RCOG) Green Top Guideline #29 and no specific guidance on median versus mediolateral in the American College of Obstetricians and Gynecologists (ACOG) Practice Bulletin (3).
The anatomy of the pelvic floor is shown in Figure 4.1.1.
The anatomy of the anus and rectum is shown in Figure 4.1.2.
The anal canal (Figure 4.1.3) is ˜2.5 to 3.5 cm long and extends from the puborectalis sling in the rectal ampulla to the intersphincteric groove (which separates the anal margin externally from the anal verge internally).
Collectively, the perianal margin and the anal verge comprise the anoderm, with the skin of the anal verge being hairless and smooth and that of the perianal margin being pigmented and having follicles and glands.
The anal canal is surrounded by the internal and external anal sphincter (EAS) muscles (Figure 4.1.3).
There are a series of longitudinal ridges called the anal columns (of Morgagni) in the superior portion of the anal canal, extending from the anorectal junction superiorly to the anal valves inferiorly.
The anal valves are arranged in an irregular (dentate or pectinate) line (colored purple in the diagram) dividing the anal canal into two different regions (superior and inferior).
Each region has completely different arteries, veins, lymphatics, nerve connections, and even different epithelial linings.
The classification (Table 4.1.1) (1) has been adopted by the International Consultation on Incontinence (4) and the RCOG (1) and differs slightly from that of ACOG (4). The most significant difference is that the ACOG classification does not include the vaginal mucosa in first-degree injuries and limits this designation to the perineal skin only. The RCOG classification includes the vaginal mucosa and thus, by definition, would have a lower rate of second-degree injuries as compared to that defined by the ACOG classification in which any injury to the perineal skin and vaginal mucosa is classified as a second-degree laceration. This complicates efforts to understand true incidences of injury on either side of the Atlantic.
Table 4.1.1 Classification of Perineal Lacerations
First degree: Injury to perineal skin only
Second degree: Injury to perineum involving perineal muscles but not involving anal sphincter
Third degree: Injury to perineum involving anal sphincter complex
3a: <50% of external anal sphincter thickness torn
3b: >50% external anal sphincter thickness torn
3c: Both external anal sphincter and internal sphincter torn
Fourth degree: Injury to perineum involving anal sphincter complex (external anal sphincter and internal anal sphincter) and anal epithelium
Reprinted with permission from American College of Obstetricians and Gynecologists. Revitalize Obstetric Data Definitions. American College of Obstetricians and Gynecologists; 2014.
Second-degree tear: Injury to the perineum involving perineal muscles but not involving the anal sphincter
Third-degree tear: Injury to perineum involving the anal sphincter complex:
Grade 3a tear: <50% of EAS thickness torn
Grade 3b tear: >50% of EAS thickness torn
Grade 3c tear: Both EAS and internal anal sphincter (IAS) torn
Fourth-degree tear: Injury to the perineum involving the anal sphincter complex (EAS and IAS) and anorectal mucosa
Injuries involving the anal sphincter and/or rectum are called obstetric anal sphincter injury(s) (OASIS). The rate in the United States is 3% to 11% (3).
Rectal button hole tear: If there is a tear into the rectal mucosa without damage to the anal sphincter, the injury should not be classified as a fourth-degree tear. The RCOG recommends that this should be documented as a rectal button hole tear (1).
The Cochrane Pregnancy and Childbirth Group state: “There is limited evidence available from RCTs to guide the choice between surgical or nonsurgical repair of first- or second-degree perineal tears sustained during childbirth.