Internal anal sphincter defect influences continence outcome following obstetric anal sphincter injury

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To date, little correlation has been found between the extent of anal sphincter injury defined by endoanal ultrasound and symptoms of postpartum fecal incontinence. To define this relationship, we assessed a large cohort of women following first recognized obstetric anal sphincter injury.


In all, 500 consecutive women were studied at 3 months following primary repair of a first recognized obstetric anal sphincter injury sustained during vaginal delivery. Assessment included a standardized fecal incontinence questionnaire (modified Jorge-Wexner score), anal manometry, and endoanal ultrasound. Severe fecal incontinence was defined by a score greater than 9. Statistical significance of the relationship between symptoms and factors including age, parity, mode of delivery, and extent of sphincter injury (defined by endoanal ultrasound), was analyzed through multiple logistic regression.


Increasing age (P = .006) and parity (P = .039), instrumental delivery (P < .001), an anal canal resting pressure of ≤35 mm Hg (P = .047), and internal anal sphincter (IAS) injury (P = .002) were significantly related to the presence of fecal incontinence. With multivariate analysis, and adjusting for other factors, instrumental delivery (OR 3.1; 95% CI 1.2–7.9) and IAS defect thickness (partial thickness defect > 1 quadrant or full thickness defect; OR 5.1 95% CI 1.5–22.9) were predictive of severe incontinence, but external anal sphincter defects were not.


Endosonographic evidence of IAS injury is predictive of fecal incontinence following obstetric anal sphincter injury. The presence of an IAS defect should be sought carefully if the anal sphincter is injured during vaginal delivery.

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