Type of tear
Definition
First degree
Injury to the perineal skin
Second degree
Injury to the perineum involving the perineal muscles, but not involving the anal sphincter
Third degree
Injury to the perineum involving the anal sphincter complex:
3A
<50 % of the EAS thickness involved
3B
>50 % of the EAS thickness involved
3C
Both the EAS and the IAS involved
Fourth degree
Injury to the perineum involving the anal sphincter complex (both the EAS and the IAS) and anal epithelium
Occult Anal Sphincter Injury
Occult sphincter injury rates ranging between 6.8 and 28 % have been reported in the literature [19, 20]. Andrews et al. speculated whether these were truly “occult” injuries or simply missed clinically at the time of delivery [21]. The diagnosis of anal sphincter damage is often delayed for many years because the symptoms of fecal incontinence are not commonly reported in the immediate postpartum period and many patients remain asymptomatic for many years.
The importance of early diagnosis of sphincter injury cannot be emphasized enough. Faltin et al. showed a reduction in fecal incontinence symptoms at 12 months, in women who had surgical repair of sphincter injury at the time of delivery when compared with women who had no repair [20].
The role of endoanal ultrasound in the long-term management of patients who have undergone anal sphincter repair and in those presenting with symptoms following delivery is undisputed. However, in the immediate postpartum period, its role is debatable due to poor patient acceptability and poor image quality resulting from edema and should not be used on a routine basis.
Risk Factors for Anal Sphincter Injury
A number of risk factors have been identified by retrospective studies for third-degree tears [22]. These include:
Primiparity (up to 4 %): the first vaginal delivery carries the greatest risk of new-onset fecal incontinence according to population-based studies.
Induction of labor (up to 2 %).
Epidural analgesia (up to 2 %).
Birth weight over 4 kg (up to 2 %).
Persistent occipitoposterior position (up to 3 %).
Second stage longer than 1 h (up to 4 %).
Forceps delivery (up to 7 %).
Evidence for other suggested risk factors, such as shoulder dystocia and episiotomy is contradictory. Though the rationale for the practice of episiotomy was that it protects the perineum from uncontrolled injury during delivery, data is conflicting. Evidence does report a significantly lower risk of sphincter injury with mediolateral episiotomy when compared with a midline episiotomy (2 % versus 12 %) [23, 24]. However, these studies may not have accounted for various confounding variables including differences in clinical practice and the experience of the obstetrician. Current evidence does not support the routine use of episiotomy as a method to prevent anal sphincter injury. However, in a recent large retrospective analysis of 17,094 women who underwent operative vaginal delivery between 2000 and 2010, it was found that the use of mediolateral episiotomy when performing operative vaginal delivery is associated with a large reduction of the risk of anal sphincter injury [25].
There have been various attempts at developing an antenatal risk scoring system for sphincter injury [26]. But they have been unsuccessful as many of the risk factors identified are components of normal vaginal delivery and a majority of women with these risk factors deliver without sphincter injury.
A significant fact in recent years is that though the incidence world over has shown an upward trend, it has essentially remained stable at 0.3–0.6 % over the past 15 years in Finland [27]. This has been attributed to the use of traditional methods of perineal support during delivery of the fetal head and shoulders. When Laine et al. introduced this method of delivery, combined with restricted use of episiotomy, the rate of OASIS fell significantly from 4 to 1 % in four Nordic hospitals who adopted this method [28, 29].
Recommended Guidelines
The RCOG national guidelines [30] and the Cochrane systematic review [31] provide recommendations on every aspect of sphincter repair. The salient points are highlighted in this chapter.
All women with perineal trauma after childbirth need to have an assessment of anal sphincter integrity immediately following delivery by visual inspection, digital vaginal and rectal palpation. If sphincter injury is identified, appropriate counseling is an ideal precursor to repair. Patient information booklets which discuss the repair and the outcomes in a reader-friendly manner with clear diagrams are very helpful to prepare the patient.
Technique of Repair
Repair of sphincter injury needs to be performed in an operation theater, in lithotomy position, under aseptic conditions, with adequate light and an assistant. Regional or general anesthesia is preferable as it enables the sphincter muscle to relax, thus making it easier to retrieve the retracted torn ends and bring them together without tension [32–34].
The internal anal sphincter lies between the anal epithelium and the external sphincter, and its muscle fibers are paler than those of the external sphincter and run in a circular fashion. The original description of sphincter injury repair included separate repair of the internal anal sphincter [32]. However identification of the internal sphincter may often be difficult. In fact it was not identified separately in the RCTs conducted on the two methods of repair of EAS [33–36]. However, though the evidence for the same is not yet concrete, it is advisable that if identified, any tears in the IAS should be repaired separately from the external sphincter using an end-to-end technique.
External Anal Sphincter (EAS) Repair
There has been considerable debate on the right method of repairing the EAS: the traditional end-to-end approximation method or the overlap technique (Fig. 17.1). A retrospective study by Sultan et al. in 1999 suggested an improved outcome with the overlap technique [32]. Since then, four RCTs have compared the two techniques [33–36]. The number of recruited women in these studies varied between 41 and 112 with a follow-up duration of 3–12 months. The outcomes assessed included, anal continence scores and quality of life, together with a combination of ultrasound and anal manometry assessment. All studies except one showed no significant difference between the two groups, in terms of fecal incontinence rates. It is important to note that in the study by Fernando et al. [36] in which better outcomes were obtained with overlap technique, only patients with 3B and 3C injuries were included as opposed to the other studies in which all EAS injuries (3A, 3B, and 3C) were included. Also in the Fernando et al. study, in patients with 3B tears, the remaining EAS fibers were divided to perform an overlap technique unlike in the other studies where the overlap was performed without division of the EAS fibers. Significantly, the repair was performed by only three trained clinicians in the Fernando et al. study, in contrast to other studies in which the repair was performed by a larger pool of trained clinicians. Thus, it needs to be considered that the improved outcome of overlap repair shown by Fernando et al. may not be applicable to other obstetric units throughout the world.
Fig. 17.1
End-to-end anastomosis of external anal sphincter (a) and overlap technique (b)
Choice of Suture Material
Only one RCT has assessed suture materials in which no difference was found between 2-0 coated polyglactin (Vicryl) and 3-0 polydioxanone (PDS), when anal incontinence, perineal pain, and suture migration were considered at 12 months follow-up [34]. PDS and Vicryl are both recommended for sphincter repair, as both are absorbable with absorption in 180 and 70 days, respectively.
Monofilament suture materials such as polydioxanone (PDS) or polyglyconate (Maxon) are commonly used for repair of the external anal sphincter muscle because of their longer half-life, increased strength retention and decreased tissue reactivity. They are also less likely to get infected as compared with braided sutures such as polyglactin (Vicryl). However, these long-acting materials are associated with suture migration which can often lead to discomfort when the ends of the suture impinge on the perineal skin [10]. Use of a fine suture such as 3-0 PDS may cause less irritation and discomfort. Burying of the surgical knots beneath the superficial muscle is recommended to prevent knot migration to skin. Internal anal sphincter damage should be repaired with a fine suture such as 2-0 Vicryl. In the presence of a fourth-degree tear, the torn anal epithelium is repaired with interrupted 3-0 Vicryl sutures with the knots tied in the anal lumen. A subcuticular repair of the anal epithelium via the transvaginal approach can also be performed [37].
Who Should Undertake the Repair?
The sequelae associated with third- and fourth-degree perineal tears are of sufficient significance, that it is recommended that sphincter repair needs to be performed by appropriately trained obstetricians under optimal conditions [10]. While repairs performed by inexperienced trainee obstetricians may not be adequate, delay in the repair so that it can be undertaken by colorectal surgeons in a secondary sitting is also not advisable [5]. An audit of obstetric trainees showed that only 13 % of them were satisfied with their level of experience prior to performing their first unsupervised repair [21]. Hence it is recommended that hands-on workshops are conducted that bridges the gaps in the training of obstetricians. Such workshops have been shown to increase both the awareness of perineal anatomy and recognition of anal sphincter injury [38].
Postoperative Care
Antibiotics
There are no published RCTs regarding the use of perioperative and postoperative antibiotics for third- and fourth-degree tears. The Cochrane review found insufficient data to support administration of prophylactic antibiotics routinely [31]. However third-degree and particularly fourth-degree tears can become contaminated with bacteria from the rectum, significantly increasing the chance of perineal wound infection leading to a higher risk of wound dehiscence, fistula formation and anal incontinence. Given the seriousness of these potential sequelae, it is prudent to prescribe both aerobic and anaerobic antibiotic cover following primary repair. Typically most studies have used intraoperative intravenous antibiotics (cefuroxime 1.5 g and metronidazole 500 mg), followed by a 7-day course of oral broad-spectrum antibiotics (cephalexin and metronidazole).
Pain Relief
Rectal diclofenac is the primary choice of pain relief for obstetric anal sphincter and other perineal injuries [39]. It significantly reduces pain on sitting, walking and defecation, within the first 48 h after delivery.
Use of Laxatives
Traditionally colorectal surgeons, who undertake secondary sphincter repair on patients with fecal incontinence, have recommended the use of constipating agents as it is advisable to avoid the contamination of the wound site by liquid fecal matter. However, primary repair is not associated with preexisting fecal incontinence at the time of repair. Delayed and painful defecation due to hard stools, can lead to considerable discomfort and stress for the patient. It is advisable to use postoperative laxatives and stool softeners following primary repair to ensure significantly earlier and less painful first bowel motion. This helps in early discharge from hospital and reduces the incidence of postoperative wound dehiscence. In the published RCTs, stool softeners (lactulose 10 ml three times a day) along with a bulking agent (ispaghula husk, Fybogel, one sachet twice a day) were used for 10 days following repair [10]. The dose and type of laxatives used should be tailored to the individual and should be customized based on the patient’s diet, gut transit time and stool consistency.
Postoperative Physiotherapy
There is very limited data regarding the importance of pelvic floor exercises in the postpartum management of women with OASIS. RCOG guidelines are not very clear and the hospitals world-wide differ in the policy they follow. One study has reported lower anal incontinence rates at 1 year, in women who were taught pelvic floor muscle exercises by a physiotherapist, following third-degree tear. The study however lacked a control group [40].
Outcomes
Endoanal ultrasound and neurophysiological tests, along with patient symptoms of anal incontinence have been used to assess the outcome of primary anal sphincter repair. Poor outcomes have been shown to be related to persistent sphincter defect detected on endoanal ultrasound [41]. The four RCTs described earlier [33–36] comparing end-to-end approximation with overlap repair have shown that 60–80 % of women will be asymptomatic at 12 months after primary repair of obstetric anal sphincter injury. Based on these results, RCOG guidelines recommend that patients who have had either of the two repairs can be counseled that the outcome of primary repair is likely to be good. However, 19–36 % of women in these studies have been shown to have persistent defects, most of which affect the EAS. The most common symptom experienced is incontinence to flatus.
Long-Term Follow-Up and Future Delivery
Women should be followed up at 6 weeks postpartum by a trained obstetrician. It is valuable to set up a dedicated multidisciplinary perineal clinic to ensure that patients receive dedicated care postoperatively. In addition to discussing the delivery details and the injury, the patient should be specifically questioned about bladder, bowel, and sexual function, symptoms of fecal incontinence, fecal urgency, dyspareunia, and perineal pain. Since these questions are embarrassing to ask, structured questionnaires of bladder, bowel, and sexual function are useful [41, 42]. A careful vaginal and rectal examination should be performed to check for complete healing, scar tenderness and sphincter tone. Ideally, anorectal investigation (i.e., endoanal ultrasound, anorectal manometry, and EMG) should be part of follow-up of every patient who has undergone anal sphincter repair. Hence if these facilities are not available at the primary hospital, at least the symptomatic women and those who have clinically reduced anal tone or contraction should be referred to an appropriate center where these investigations can be conducted.
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