Postero-lateral Internal Sphincterotomy vs Botulinum Toxin Injection in the Treatment of Chronic Anal Fissure: A Randomized Controlled Trial

2.1 Trial design This trial will be designed as a prospective randomized, controlled, intervention, open label trial with two parallel groups, and a primary endpoint of fissure healing during 6 months after initial intervention, with the randomization will be performed by an online software with a 1:1 allocation.

2.3 Pre-enrollment After careful history and clinical examination, the diagnosis of chronic anal fissure will be considered when a wider and deeper ulcer with keratinous edges, presence of a sentinel tag at the external apex, hypertrophy of the anal papillae, and exposed internal anal sphincter (IAS) smooth muscle fibers, will be exist. As a routine in Mansoura colorectal surgery unit, any patient above 50 years old will be scheduled for colonoscopy to rule out colorectal cancer, as well as, those associated with bleeding per rectum or other risk factors. Additionally, patients will be evaluated for constipation by preoperative and 6th-months postoperative Wexner Constipation Score and for their continence status by preoperative and 6th-months postoperative Fecal Incontinence Severity Index (FISI) and Anorectal Manometry. Preoperative mechanical bowel preparation will not be indicated, however, single enema in the day of the procedure will be advised in order to facilitate examination under anesthesia (EUA) which is a mandatory initial step in all begin anorectal procedures in our unit. Appropriated thromboembolic prophylaxis will be prescribed based on the patient risk stratification.

2.4 Interventions Eligible patients will be randomized in equal proportions between Botulinum Toxin (BT) injection and Posterolateral Internal Anal Sphincterotomy (PIAS). All procedures will be performed under spinal anesthesia with the patient in modified lithotomy position by senior consultant colorectal surgeons or under their direct supervision. At the time of the anesthesia induction, 500 mg metronidazole will be administrated. All procedures will be preceded by gentle anal dilatation, insertion of an anal retractor, and EUA. Subsequently, the surgeon will proceed to the allocated intervention.

In group I (BT injection), 21 U will be injected in 3 divided doses through the internal anal sphincter at 3,9, and 12 o'clock. In the Egyptian market two commercial forms are available; botulinum toxin type A (Botox 100 IU/vial; Coolock, Dublin, Ireland), and abobotulinumtoxin A (Dysport 500 U/vial; Ipsen Biopharm Ltd, Wrexham, UK). In case of Dysport it should be remembered that dosing is on a ratio of approximately 1 to 3, meaning that 50 IU of Botox have the same effect as 150 IU of Dysport.

In group II (PIAS), A 1.5 to 2-cm circumferential skin incision will be placed at 5 o'clock position outside the anal verge using an electrocautery device. Dissection will be proceeded through the intersphincteric groove to separate both IAS and external anal sphincter (EAS). Then, the IAS will be identified by its characteristic white fibers, separated from the anal mucosa, and assessed under direct vision. Subsequently, about 50 % of the IAS will be divided at 5 o'clock position and any skin tags or hypertrophied anal papillae will be removed leaving the skin incision open to allow drainage.