BACKGROUND: Sphincterotomy is used to treat chronic anal fissure, but the length of the sphincterotomy is associated with incontinence.
OBJECTIVE: We used 3-dimensional anal ultrasonography to determine the proportion of the internal anal sphincter that may be divided during lateral internal sphincterotomy in women without predisposing them to a high risk of fecal incontinence.
DESIGN AND SETTING: This was a prospective, observational cohort study conducted at a tertiary-care hospital.
PATIENTS: Women treated for chronic anal fissure with high anal resting pressure and no symptoms of fecal incontinence were selected. Asymptomatic women recruited from different departments of the same hospital served as controls to provide reference values for anal canal measurements.
INTERVENTION: Patients underwent a standardized technique of lateral internal sphincterotomy.
MAIN OUTCOME MEASURES: Three-dimensional ultrasonography was used to measure sphincter lengths. Continence was assessed with the Cleveland Clinic Florida (Wexner) score. The relationship between the extent of the surgically divided portion of the internal anal sphincter and the continence score was evaluated.
RESULTS: Successful healing was achieved in all patients within 2 months. Follow-up continence scores were significantly correlated with the extent of sphincter division. The proportion of patients with a continence score of 0 was significantly greater in patients in whom sphincter division was less than 25% in comparison with patients with a division of 25% or more. Anal canal and sphincter lengths in patients after sphincterotomy did not significantly differ from those in asymptomatic women.
LIMITATIONS: The study is limited by its nonrandomized nature and the lack of preoperative ultrasound assessment.
CONCLUSIONS: Based on data from this study, the safe extent of division is less than 25% of the total sphincter length, which in women corresponds to less than 1 cm.