Fig. 8.1
Schematic of the perineal muscles (With kind permission from Springer Science + Business Media: Thakar and Fenner [12], p. 1–12)
Obstetric anal sphincter injury involves the muscles of the anal triangle. The anal canal is 3–4 cm long and is lined by an epithelial cell layer with the anal sphincter complex being situated externally. The anal sphincter complex is separated into external (EAS) and internal (IAS) components by a layer of fibromuscular and connective tissue. The EAS consists of striated muscle fibres and permits voluntary squeeze (via the pudendal nerve) as well as reflex contractions. The IAS consists of circular smooth muscle under autonomic control, and is responsible for the majority of the resting tone of the sphincter complex. The anatomical configuration of the anal sphincter complex is illustrated in Fig. 8.2.
Fig. 8.2
The anal sphincter complex (With kind permission from Springer Science + Business Media: Sultan and Kettle [13], p. 13–19)
The term “pelvic floor” is used to refer to a muscular layer that spans the pelvic outlet and is comprised mainly of the paired levator ani muscles, which are found deep to the muscles of the perineum and anal sphincter complex. These muscles arise from the arcus tendineous fascia pelvis on each side and are subdivided according to their bony attachments into three main portions- iliococcygeus, pubococcygeus and ischiococcygeus. Medial fibres from the pubococcygeus are arranged to form a hammock-like configuration around the rectum, and are designated the puborectalis.
Perineal trauma may occur spontaneously with vaginal delivery, or it may be iatrogenic, i.e., an episiotomy. An episiotomy may also extend to involve other structures. Although perineal trauma is conventionally thought of as incorporating trauma to the posterior vaginal wall and the muscles of the perineum and anal sphincter complex, tears may also be seen which involve the anterior vaginal wall, urethra, clitoris or labia. Tears can sometimes be highly complex, involving multiple compartments of the vagina in a “spiral” fashion, or with complete detachment of the vaginal epithelium from underlying structures.
The following classification has been recommended for use in the assessment of perineal trauma [2]:
First degree: Injury to the vaginal epithelium or perineal skin only
Second degree: Involvement of the superficial perineal muscles (bulbospongiosus, transverse perineal) and sometimes the pubococcygeus muscle, but with no involvement of the anal sphincter.
Third degree: Involvement of the anal sphincter complex (Fig. 8.3). Can be further subdivided into:
Fig. 8.3
External view of a third-degree tear
3A
Less than 50 % thickness of external anal sphincter torn
3B
More than 50 % thickness of external anal sphincter torn
3C
External and internal anal sphincters torn
Fourth Degree: A third-degree tear with additional involvement of the anorectal mucosa
A buttonhole tear refers to an isolated tear of the rectal mucosa into the vagina, without involvement of the anal sphincters. These sit outside of the classification above as they do not involve the muscles of the perineum. They may be difficult to detect without a thorough assessment including a digital rectal examination. Detection is essential in order to avoid debilitating consequences such as rectovaginal fistula, although there is no association between buttonhole tears and continence outcomes.
Prior to assessment for genital tract trauma, it is recommended that the examining clinician ensures the following criteria are met [5]:
- 1.
The woman understands what will be done and why (including specific verbal consent for a vaginal and rectal examination).
- 2.
Effective analgesia has been provided (epidural or inhalational).
- 3.
Lighting is adequate.
- 4.
The woman is positioned comfortably such that the genital structures can be clearly visualized; the lithotomy position may be necessary to facilitate good visualization if there are deep or complex tears.Related posts:
Pelvic Floor Physiotherapy for the Prevention and Management of Childbirth Trauma
Childbirth and Lower Urinary Tract Complications
Types of Pelvic Floor Injury During Childbirth
The Effect of Pregnancy on the Pelvic Floor
Female Pelvic Anatomy
Further Investigations and Follow-Up: Pelvic Floor Ultrasound
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