# Third- and Fourth-Degree Perineal Lacerations: Repair and Prevention
## Classification of Perineal Lacerations
### First Degree
First-degree lacerations involve injury to the vaginal mucosa and/or perineal skin only, with no involvement of the underlying muscle.
### Second Degree
Second-degree lacerations extend into the perineal body muscles, including the bulbospongiosus and transverse perineal muscles, but do not involve the anal sphincter complex.
### Third Degree
Third-degree lacerations involve the anal sphincter complex and are further subdivided. A 3a laceration involves less than 50% of the external anal sphincter thickness. A 3b laceration involves 50% or more of the external anal sphincter thickness. A 3c laceration involves both the external and internal anal sphincters.
### Fourth Degree
Fourth-degree lacerations extend through the external anal sphincter, internal anal sphincter, and anal or rectal mucosa, creating a full-thickness injury from the vaginal lumen to the rectal lumen.
| Degree | Structures Involved | Subdivisions |
|---|---|---|
| First | Vaginal mucosa and/or perineal skin only | None |
| Second | Perineal body muscles (bulbospongiosus, transverse perineal) | None |
| Third | Anal sphincter complex | 3a: <50% EAS; 3b: ≥50% EAS; 3c: EAS + IAS |
| Fourth | EAS + IAS + rectal mucosa | None |
## Anatomy of the Anal Sphincter Complex
The external anal sphincter is a striated (voluntary) muscle that is tonically contracted and encircles the anal canal. The internal anal sphincter is smooth (involuntary) muscle that represents a continuation of the circular smooth muscle of the rectum and provides 70 to 80% of resting anal tone. The perineal body is the central tendon where the bulbospongiosus, superficial and deep transverse perineal muscles, external anal sphincter, and rectovaginal fascia converge. The internal anal sphincter lies deep to the external anal sphincter and appears as a pale or white glistening band, distinct from the striated reddish-brown external anal sphincter. The anorectal mucosa consists of columnar epithelium lining the anal canal.
Cross-sectional anatomy of the perineal body and anal sphincter complex showing the spatial relationship of the external anal sphincter (striated, red-brown), internal anal sphincter (smooth, pale white band), perineal body with converging muscles, and rectal mucosa, with labels for each degree of laceration depth
## Incidence and Risk Factors
### Epidemiology
Third- and fourth-degree lacerations, collectively referred to as obstetric anal sphincter injuries or OASIS, occur in 3 to 5% of vaginal deliveries. Rates are higher in primiparous women, reaching 6 to 8%. Fourth-degree tears account for approximately 1% of vaginal deliveries.
### Risk Factors
Nulliparity is the strongest risk factor. Midline episiotomy increases OASIS risk 3 to 4 times compared to no episiotomy. Operative vaginal delivery is a significant risk factor, with forceps carrying greater risk than vacuum. Other risk factors include fetal macrosomia above 4,000 g, persistent occiput posterior position, prolonged second stage of labor, shoulder dystocia, Asian ethnicity (related to anatomic differences in perineal body length), short perineal body length, and previous OASIS with a recurrence rate of 5 to 7%.
## Prevention
### Perineal Support Techniques
Warm compresses applied to the perineum during the second stage reduce OASIS risk. Manual perineal protection using the modified Ritgen maneuver involves supporting the perineum with one hand while controlling the fetal head with the other during crowning. Some evidence favors an active perineal support approach over a hands-off technique.
### Episiotomy Considerations
A restrictive episiotomy policy is preferred over routine episiotomy based on Cochrane evidence. Midline episiotomy increases the risk of OASIS by 3 to 4 times and should be avoided when possible. Mediolateral episiotomy, cut at 60 degrees from the midline, reduces OASIS risk compared to midline, particularly during operative vaginal delivery. Mediolateral episiotomy is the standard practice in many European countries but is less common in North America.
### Operative Delivery Modifications
Forceps carry a higher OASIS risk than vacuum extraction. When forceps are indicated, a mediolateral episiotomy should be considered. The number of instrument applications and the duration of traction should be limited.
## Examination and Identification
### Systematic Approach
Every vaginal delivery requires systematic inspection of the perineum, vagina, and cervix. A digital rectal exam is mandatory if any perineal laceration extends beyond superficial skin. The examiner places an index finger in the rectum to palpate the integrity of the rectal mucosa and sphincter. The internal anal sphincter is identified as a pale, glistening smooth muscle band that is distinct from the external anal sphincter. The extent of external anal sphincter disruption is classified as less than 50% versus 50% or more. Missed OASIS is a significant source of long-term morbidity, and a high clinical suspicion should be maintained.
### Common Pitfalls
The most common pitfalls include failure to perform a rectal exam, confusing a buttonhole tear (an isolated rectal mucosal tear with an intact sphincter) with a fourth-degree laceration, not recognizing internal anal sphincter injury when the muscle retracts laterally, and inadequate lighting or exposure.
Step-by-step examination technique for suspected OASIS: the examiner performing a rectal exam with the index finger while inspecting the perineal wound, demonstrating identification of the pale white IAS band retracted laterally, the torn red-brown EAS ends, and assessment of rectal mucosal integrity
## Surgical Repair Technique
### General Principles
Repair is performed in the delivery room or operating room with adequate lighting and exposure. Regional anesthesia through epidural top-up, spinal block, or pudendal block with local infiltration provides adequate analgesia. The patient is positioned in dorsal lithotomy with stirrups. Good surgical lighting and retractors are essential for visualization. All tissue planes should be identified and tagged before beginning the repair.
### Fourth-Degree Repair: Rectal Mucosa
The rectal mucosa is repaired first, starting at the apex of the mucosal tear. Interrupted or continuous 3-0 or 4-0 polyglactin sutures are placed through the submucosal layer, avoiding full-thickness sutures through the rectal lumen. The closure is performed in a tension-free manner with knots tied on the vaginal side, away from the rectal lumen.
### IAS Repair
The retracted ends of the internal anal sphincter are identified as pale smooth muscle. Repair is performed with interrupted 3-0 polyglactin or polydioxanone sutures using end-to-end approximation. Because the internal anal sphincter provides 70 to 80% of resting anal tone, meticulous repair is essential.
### EAS Repair
End-to-end repair involves grasping the retracted sphincter ends with Allis clamps and approximating them with interrupted 2-0 or 3-0 polyglactin or polydioxanone sutures placed through the sphincter capsule. For complete external anal sphincter tears (3b and 3c), the overlap technique is an alternative that may provide equivalent or superior outcomes. In the overlap method, each end of the sphincter is mobilized, overlapped, and sutured in a double-breasted fashion. Randomized trial data from Fernando in 2006 showed similar outcomes between overlap and end-to-end repair at 12 months, with some studies suggesting lower incontinence rates with the overlap technique. Sutures must incorporate the sphincter capsule or sheath for a secure repair.
### Perineal Body and Remaining Layers
The perineal body is reconstructed by reapproximating the transverse perineal muscles. The vaginal mucosa is closed with continuous 2-0 or 3-0 polyglactin suture. The perineal skin is closed with subcuticular or interrupted sutures.
Surgical repair illustration showing the layered approach: first panel shows interrupted sutures closing the rectal mucosa from apex to dentate line, second panel shows end-to-end approximation of the pale IAS with fine sutures, third panel demonstrates overlap repair of the EAS with the two ends overlapped and secured, and fourth panel shows completed reconstruction of the perineal body
## Postoperative Management
### Immediate Postpartum
Antibiotics are administered as a single dose of a broad-spectrum agent at the time of repair, such as cefoxitin or a second-generation cephalosporin. Some protocols recommend a short 7-day course for fourth-degree tears. Stool softeners, typically docusate sodium 100 mg twice daily for 2 to 4 weeks, are essential to prevent constipation. Adequate analgesia with acetaminophen and NSAIDs is provided, minimizing opioids and avoiding rectal suppositories. Laxatives such as lactulose or polyethylene glycol are used to keep stools soft for 2 weeks. A high-fiber diet with adequate fluid intake is recommended.
### Follow-up
The 6-week postpartum visit should include specific assessment of continence and wound healing. Patients should be asked directly about flatal incontinence, fecal urgency, and fecal incontinence, as many will not volunteer these symptoms. A digital rectal exam assesses sphincter tone. Pelvic floor physical therapy referral is appropriate for all OASIS patients. Endoanal ultrasound is considered if symptoms of incontinence develop, and anorectal manometry provides objective sphincter function assessment when needed.
## Long-Term Outcomes
### Anal Incontinence
Flatal incontinence occurs in 15 to 30% of patients after OASIS repair. Fecal incontinence occurs in 3 to 10% after primary repair. Occult sphincter defects are detected on endoanal ultrasound in 30 to 50% of patients even after apparently successful primary repair. Symptoms may worsen with subsequent vaginal deliveries or with aging.
### Subsequent Deliveries
The recurrence risk of OASIS in a subsequent vaginal delivery is 5 to 7%. Shared decision-making regarding mode of delivery is appropriate. Elective cesarean may be offered if the patient has persistent anal incontinence symptoms, abnormal endoanal ultrasound findings, abnormal anorectal manometry, or a strong preference after thorough counseling. Many women with a successful primary repair can have a safe subsequent vaginal delivery.
## Clinical Pearls
A digital rectal exam must be performed after every perineal laceration repair to confirm sphincter integrity and to rule out an unrecognized fourth-degree extension.
The internal anal sphincter is the single most important structure for resting anal continence. It should be identified separately and repaired meticulously.
Midline episiotomy increases OASIS risk 3 to 4 fold. Mediolateral episiotomy at 60 degrees is protective.
Warm perineal compresses and manual perineal support during crowning are simple, evidence-based interventions that reduce the incidence of severe tears.
Missed OASIS that is unrecognized at the time of delivery is associated with significantly worse long-term outcomes than injuries recognized and repaired primarily.
Stool softeners and a high-fiber diet are essential postoperatively. A hard first bowel movement can disrupt the repair.
Clinicians should always ask about flatal and fecal incontinence at the postpartum visit. Patients often feel embarrassed and will not volunteer these symptoms.
## References
- ACOG Practice Bulletin No. 198: Prevention and Management of Obstetric Lacerations at Vaginal Delivery (2018, reaffirmed 2023)
- RCOG Green-top Guideline No. 29: Third- and Fourth-Degree Perineal Tears (2015)
- Fernando RJ et al. Repair techniques for obstetric anal sphincter injuries: a randomized controlled trial. Obstet Gynecol. 2006;107:1261-1268
- Aasheim V et al. Perineal techniques during the second stage of labour for reducing perineal trauma. Cochrane Database Syst Rev. 2017
- Sultan AH et al. Anal sphincter trauma during instrumental delivery. Int J Gynaecol Obstet. 1998;63:263-270
- Jha S, Parker V. Risk factors for recurrent obstetric anal sphincter injury. Eur J Obstet Gynecol Reprod Biol. 2016;205:110