Learning Objectives:After participating in this continuing professional development activity, the provider should be better able to:
1. Identify the risk factors for and incidence of obstetric anal sphincter injuries (OASIS) and possible strategies to prevent them.
2. Describe perineal anatomy and surgical repair of OASIS.
3. Explain short- and long-term complications of OASIS and postpartum care after repair.
Lacerations are a common complication at the time of vaginal birth and affect the majority of parturient women.1 Perineal lacerations are classified according to the involvement of the skin and musculature, and range in degree of severity from first to fourth2 (Table 1). Third- and fourth-degree lacerations are commonly referred to as obstetric anal sphincter injuries (OASIS), given their involvement of the anal sphincter and mucosa, respectively. Risk factors that predispose patients to OASIS include operative delivery, midline episiotomy, large fetus, primiparity, Asian ethnicity, labor induction and augmentation, use of epidural analgesia, and persistent occiput posterior position.3
Although difficult to estimate, the incidence of OASIS is as high as 11%.4 The relatively low rate of third- (3.3%) and fourth-degree (1.1%) lacerations in the United States limits provider exposure, familiarity, and comfort with repair techniques.5 Because OASIS may incur significant morbidity, including wound complications, chronic perineal pain, dyspareunia, fistulae, and incontinence of fecal and urinary origin, prompt recognition and repair is essential to optimal functional outcomes.6,7 Herein, we review basic, relevant perineal anatomy, and detail techniques for repair of OASIS.
Anatomy of the Perineum
The perineum encompasses the diamond-shaped, superficial, and deep spaces demarcated anteriorly by the pubic symphysis, posteriorly by the coccyx, anterolaterally by the ischiopubic rami and ischial tuberosities, and posterolaterally by the sacrotuberous ligaments8 (Figure 1). Familiarity with the bulbocavernosus, superficial transverse perineal, and anal sphincter muscles is of utmost importance during OASIS repair. These muscles, in addition to the pubococcygeus muscle and perineal membrane, converge in the midline between the rectum and the vagina to form a fibromuscular mass called the perineal body. The perineal body is a major structural support element of the pelvis.
The anal sphincter is located immediately below the perineal body and extends approximately 4 cm into the anal canal. It is composed of internal (IAS) and external anal sphincter (EAS) muscles, and is responsible for fecal and flatal continence (Figure 2). The EAS is composed of skeletal muscle and responsible for voluntary control. The IAS is a 5-mm-thick, ring of smooth muscle that partly overlaps the EAS and provides 80% of anal resting tone. Underlying the IAS are the rectal mucosa, and lumen. Familiarity with perineal anatomic structures in the form of an idyllic representation of a fourth-degree laceration is helpful at the time of repair (Figure 3A).
Identification of OASIS
Severe perineal lacerations are not always symmetrical along the midline. Poor visualization, bleeding, and patient discomfort challenge the repair. In our practice, repair of OASIS routinely takes place in the operating suite, where lighting, instrument availability, and anesthetic choices are greater. Satisfactory patient comfort can be achieved with continued use of an already existing epidural catheter, with infiltration of 1% lidocaine or 0.25% bupivacaine along the margins of the tissues to be reapproximated (maximum doses: lidocaine 4.5 mg/kg/dose not to exceed 300 mg, bupivacaine 2.5 mg/kg/dose not to exceed 125 mg), or with a combination of both modalities.9 In patients with no labor analgesia that incur OASIS, neuraxial analgesia is often most effective in allowing for a comfortable and efficient repair for both the provider and the patient, and is administered upon arrival to the operating suite. The patient is placed in dorsal lithotomy position using boot stirrups; lighting and position are optimized. The perineum is prepared with Betadine and draped in sterile fashion, and a Foley catheter is placed to decrease bladder distension. In accordance with recommendations from the American College of Obstetricians and Gynecologists (ACOG), a dose of prophylactic antibiotics is administered at the time of repair.2
Ensuring cessation of bleeding from uterine sources is helpful for both visualization and maintenance of future repair integrity, as bimanual examination can break down a previously completed repair. Gently placing a laparotomy sponge in the posterior vagina can be helpful for exposure and absorption of blood coming from the uterus and cervix. This frees the operator's hands to allow rectal examination with the nondominant index finger, and close examination of perineal tissues with the aid of another laparotomy sponge on the dominant hand. The use of surgical retractors can be advantageous: Sims, Deaver, and lateral vaginal retractors (if repairing with an assistant), or Gelpie or Weitlaner retractors (if repairing alone).
Repair of Fourth-Degree Perineal Lacerations
Digital rectal examination is important in assessing for damage to the anal sphincter complex and mucosa. Although fourth-degree lacerations are often easiest to identify given the extent of structural damage, mucosal defects are not always contiguous with the anal verge and may be missed if digital examination is not performed. Identification of the different subtypes of third-degree lacerations is often more challenging. Thus, a thorough digital examination should be performed before attempting any part of the repair.
Repair of the most severe perineal laceration requires reapproximation of the rectal mucosa, anal sphincter complex, perineal body, vaginal mucosa, and perineal skin. Next, we review a common approach to this repair, and 2 options for reapproximation of the EAS. In the event of provider discomfort or lack of experience with repair of advanced lacerations, it may be appropriate to pack the vagina and call for more experienced providers or subspecialists.
Reapproximation of the Rectal Mucosa
The rectal mucosa can be reapproximated with 4-0 poliglecaprone 25 (MONOCRYL) or polyglactin 910 (VICRYL) sutures in a running or interrupted fashion (Figure 3B). The sutures can be placed through the mucosa, or only partially to avoid entry into the lumen. We prefer using a monofilament suture placed partially through the mucosa in a running, unlocked fashion. The rectovaginal fascia overlaying the mucosal repair is then reapproximated separately, in a running, unlocked fashion, before repair of the anal sphincter complex.
Reapproximation of the Anal Sphincter Complex
The IAS can be identified over the distal rectal mucosa under the EAS. It is light red, shiny, thinner than the EAS, and frequently retracts laterally. To identify the IAS, we grasp the EAS with Allis clamps and pull medially to expose the laterally retracted, underlying IAS fibers. We prefer using 3-0 poliglecaprone or polyglactin 910 sutures for end-to-end reanastomosis of the IAS in a running, unlocked fashion (Figure 3C).
The EAS is often easier to identify as a thicker, distinct, dark red muscle and can be reapproximated via end-to-end or overlapping techniques. Long-term studies have not shown clinically significant differences in outcomes between the 2 techniques.10 Repair is performed with 1-0 or 2-0 polyglactin 910 or polydioxanone sutures. To perform the end-to-end technique, the cut ends of the EAS are reapproximated to restore normal anatomy. Allis clamps and forceps with teeth can aid with the approximation of the EAS. Commonly, 4 individual, interrupted stitches are placed through the muscle and its capsule in the following order: posterior, inferior, superior, and anterior (Figures 3D and 4A-E). The mnemonic "PISA" can be used to remember the order. As the sutures are placed, individual hemostat clamps can be used to secure the cut ends of the sutures to the sterile drapes. Once all stitches are placed, the sutures are tied in the order in which they were placed.
An alternative method of repair overlaps the cut ends of the EAS by 1 to 2 cm at the midline. Single interrupted stitches (usually 2-4) are placed through the overlapping muscles and tied over the EAS (Figure 4F). This method requires a full-thickness defect and usually requires further dissection of the retracted EAS to provide an ample segment for overlap. As such, we prefer the end-to-end technique for most repairs. Partial-thickness (Figures 3A and 3B) lacerations should always be repaired in end-to-end fashion. After repair of the anal sphincter complex, a rectal examination should be performed to assess the integrity of the repair.
Reapproximation of Vaginal Mucosa, Perineal Body, and Skin
Immediately above the anal sphincter complex are the fibers of the transverse perineal and bulbocavernosus muscles. We use 3-0 or 2-0 polydioxanone or polyglactin 910 sutures to reapproximate these muscles in what, essentially, is now a second-degree laceration. We first anchor and run the suture in a running, locked fashion from the apex of the vaginal tear to the hymen (Figure 3E). At this point, we change the orientation of the needle by penetrating the mucosa at 90 degrees, protect this needle within the needle driver, and place it aside without cutting the suture. We continue by placing interrupted stitches through the muscle fibers of the transverse perineal and bulbocavernosus, and cut and tie each, individually, using the 2-handed technique (Figure 3F). The first stitch is placed as cephalad as possible to obliterate any empty spaces. Subsequent stitches (usually 1-2 more) are placed caudally. Note that the angle at which the needle is inserted into the bulbocavernosus muscle is not horizontal, but closer to 45 degrees from the horizontal to allow appropriate acquirement of the muscle fibers. A gentle tug on the suture should elicit movement in the ipsilateral labium majus and confirms adequate placement. After repair of the perineal body, we run the previously protected stitch in a subcutaneous fashion to the posterior end of the laceration (closest to the rectum; Figure 3G), and return in a subcuticular fashion back to the hymen, behind which we tie our stitch and finish the repair (Figure 3H).
Postpartum Care
Postpartum care after OASIS is critical to achieving optimal functional outcomes. A multifaceted approach should include provision of adequate pain control, avoiding constipation, close-interval postpartum physical examinations, and screening for anal incontinence.2 Pain management can be achieved with cold packs, nonsteroidal anti-inflammatory drugs, local anesthetics, and opiates. Due to the constipating side effect of opiates, we try to restrict their use after OASIS repairs. If opiates are needed during the initial postpartum window, additional stool softeners and laxatives should be provided to maintain regular, soft stools. Avoiding constipation is essential for reducing tension on the repair and improving pain.11 This can be achieved with behavioral changes, including increased fluid and fiber intake, along with a bowel regimen that may include stool softeners and/or oral laxatives. Adjunctive supportive care measures such as sitz baths should be discussed, and if possible, initiated during the hospitalization.
Before discharge, patients should be counseled on the importance of pelvic rest for at least 6 weeks.12 Education on general wound care should be provided verbally and documented in the discharge instructions for referencing at a later time. Patients should be scheduled for an early postpartum visit, usually within 2 weeks, to assess for signs of infection and wound breakdown. A thorough examination including a digital rectal examination is repeated at 4 to 6 weeks postpartum to reevaluate the integrity of the repair.
Complications
Immediate and long-term complications of OASIS include blood loss, urinary retention, wound infection, wound dehiscence, fistula formation, anal incontinence, chronic perineal pain, and sexual dysfunction.2 Increased blood loss is common at the time of delivery, but most bleeding can be controlled with swift repair of the laceration. For friable tissue that continues to bleed after reapproximation, vaginal packing can provide compression, allowing time for intrinsic clotting factors to take effect. Rarely, hematoma formation occurs within 24 hours after delivery. Presentation and treatment of hematomas vary and are outside the scope of this review.
Women with severe perineal trauma have an increased risk of postpartum urinary retention. Spontaneous voiding should be monitored in the immediate postpartum period. Patients who are unable to void should have a Foley catheter placed with repeat voiding trial after bladder rest. Most postpartum urinary retention is self-limited and will resolve spontaneously within several days.13
The perineum should be evaluated at 1 to 2 weeks, and again at 4 to 6 weeks postpartum, to assess for infection and wound breakdown.12 Reported rates of these complications are high as 25%.2 Most superficial infections will resolve with routine perineal wound care alone including sitz baths at least 4 times daily or after bowel movements. Abscess formation warrants systemic oral antibiotics along with intentional disruption of the repair to allow for drainage. Superficial wound breakdowns not involving anal sphincter or rectum can be treated with conservative management, which allows for closure through spontaneous healing. For more extensive wound breakdown, primary closure should be attempted, as inadequately repaired lacerations can lead to fistula formation. If a concurrent infection is noted, repair should be delayed until all signs of infection have resolved.2
Anal incontinence, the involuntary loss of feces or flatus, is a rare but an emotionally distressing complication of severe perineal lacerations. Unfortunately, no interventions have been shown to prevent anal incontinence after OASIS repair. Pelvic floor exercises and biofeedback physiotherapy have overall mixed results. Screening for symptoms of anal incontinence should be performed at all postpartum visits. If the patient screens positive, she should be referred to a specialist for treatment.2
Prevention Strategies
Several studies have examined the role of interventions thought to decrease the risk and/or severity of perineal lacerations. These include maternal perineal massage, manual perineal support, warm compresses, varying birthing positions, and delayed pushing. The only interventions with sufficient clinical evidence to warrant routine recommendation are the use of perineal massage and warm compresses.14,15 Perineal massage decreases muscular resistance. When performed starting at 34 weeks' gestation, it has been found to decrease rates of perineal trauma that required repair. During the second stage of labor, perineal massage and warm compress have both independently been found to decrease the rate of OASIS.
Midline episiotomy is a strong risk factor for OASIS. The ACOG currently recommends restrictive episiotomy practices. Midline episiotomy has been shown to increase risk of severe perineal lacerations and anal incontinence. Mediolateral episiotomy increases risk of perineal pain and dyspareunia.2 If an episiotomy is necessary, mediolateral rather than midline episiotomy may be preferred to decrease risk of OASIS.
Operative delivery is also an independent risk factor for OASIS. Forceps-assisted delivery is associated with more severe perineal lacerations when compared with vacuum-assisted delivery.12 In the appropriate clinical context, it may be reasonable to preferentially use vacuums when operative delivery is necessary.
Women with a history of OASIS are at increased risk for repeat severe lacerations with an absolute risk up to 6%.2,16 Prenatal counseling should include the overall low risk of recurrence and the significant morbidities associated with cesarean delivery. Women without complications from prior OASIS should generally be counseled toward vaginal delivery. However, for women who had postpartum complications, such as wound infection, breakdown, anal incontinence, or experienced psychological trauma, it may be reasonable to undergo cesarean delivery at patient request.2 Shared decision-making should be used when deciding on route of delivery.
Conclusion
Perineal lacerations are common at the time of vaginal delivery. Although third- and fourth-degree lacerations occur less frequently, they are of particular concern given the significant short-and long-term morbidity that can result. The relative rarity of OASIS has led to limited training in the recognition, repair, and care of these advanced lacerations. Providers should be familiar with diagnostic criteria, repair strategies, preventive techniques, and postpartum care measures, to ensure the most optimal functional outcomes for our patients.
Acknowledgments
The authors thank Alejandro Fernandez for artistic rendition of the relevant anatomic structures.
REFERENCES