This prospective randomized controlled trial compares three lateral internal sphincterotomy (LIS) techniques in patients with chronic anal fissure refractory to medical treatment: (1) Spasm-Controlled LIS (serial small sphincterotomies using an anal calibrator until 30 mm anal caliber is achieved, under local anesthesia plus sedation), (2) LIS up to the Fissure Apex (spinal or general anesthesia), and (3) LIS up to the Dentate Line (spinal or general anesthesia). The primary outcomes are fissure healing rate and fecal incontinence incidence at 12 months, assessed using the Wexner Incontinence Score. Secondary outcomes include postoperative pain (VAS), recurrence rate, patient satisfaction, and complications. A total of 150 patients (50 per group) will be enrolled and followed for 12 months.

Chronic anal fissure (CAF) is a longitudinal tear in the anoderm persisting for more than 8 weeks. Lateral internal sphincterotomy (LIS) is the gold-standard surgical treatment for CAF refractory to medical management, achieving healing rates of 90-98%. However, postoperative fecal incontinence remains its most significant complication, with rates ranging from 1-15% for permanent incontinence.

To reduce incontinence risk, various techniques limiting the extent of sphincterotomy have been proposed. Mentes et al. (2005) demonstrated that LIS up to the dentate line provided faster healing but caused significant continence disturbance, while LIS limited to the fissure apex was associated with lower incontinence but a higher treatment failure rate. Mentes et al. (2008) subsequently showed that spasm-controlled LIS using anal calibrators achieved faster pain relief with lower early incontinence rates compared to fissure apex sphincterotomy. However, no randomized trial has compared all three techniques simultaneously.

This single-center, prospective, three-arm RCT will enroll 150 adult patients with CAF refractory to at least 6 weeks of medical treatment. Patients will be randomized (1:1:1) to one of three groups: Group 1 (Spasm-Controlled LIS): serial small sphincterotomies under local anesthesia plus sedation until anal caliber reaches 30 mm using an anal calibrator. Group 2 (LIS up to Fissure Apex): open sphincterotomy extended to the proximal end of the fissure under spinal or general anesthesia. Group 3 (LIS up to Dentate Line): open sphincterotomy extended to the dentate line under spinal or general anesthesia.

All procedures will use the open technique with patients in lithotomy position. Randomization will be performed using computer-generated block randomization (block size 6), stratified by sex and fissure location. Outcome assessors will be blinded to group allocation.

Patients will be evaluated preoperatively and at postoperative day 1, week 1, week 2, month 1, month 2, month 6, and month 12. The Wexner (Cleveland Clinic) Incontinence Score will be used to assess continence at each visit. Fissure healing will be defined as complete epithelialization with no symptoms. Statistical analysis will follow the intention-to-treat principle, with Bonferroni correction applied for multiple comparisons.

Inclusion Criteria:

• Age 18 years or older
• Diagnosis of chronic anal fissure (duration ≥8 weeks)
• Failure to heal after at least 6 weeks of appropriate medical treatment (topical agents, fiber supplementation, sitz baths)
• Complete preoperative fecal continence (Wexner Incontinence Score = 0)
• Primary anal fissure (posterior or anterior midline location)
• Written informed consent

Exclusion Criteria:

• Any degree of preoperative fecal incontinence
• Secondary anal fissure (associated with Crohn's disease, tuberculosis, HIV, syphilis, or other systemic conditions)
• Previous anal sphincter surgery
• History of obstetric sphincter injury
• Active anorectal infection (abscess or fistula)
• Pregnancy or breastfeeding
• Uncorrectable coagulopathy or current anticoagulant use
• Inability to cooperate with study procedures or attend follow-up visits

The surgeon performing the procedure is aware of the group allocation as blinding is not feasible for surgical technique trials. Patients are aware of their anesthesia type but are not informed of their specific group assignment until after the study. Data analysts will be blinded to group allocation during statistical analysis.