This randomized controlled trial will compare closed versus open lateral internal sphincterotomy (LIS) under spinal anesthesia in patients with chronic anal fissure. The study will evaluate wound healing rates, postoperative pain, return to work, anal incontinence, and recurrence. A total of 160 patients will be randomized equally to either closed LIS or open LIS. The primary outcome will be complete wound healing at 6 weeks. Secondary outcomes include pain at 24 hours measured by Visual Analog Scale (VAS), return to work (days), anal incontinence at 6 weeks and 1 year, and recurrence at 1 year. Multivariate analysis will identify independent predictors of non-healing.

Inclusion Criteria:

• Diagnosis of chronic anal fissure (symptoms > 6 weeks)
• Failure of conservative medical management (dietary fiber, stool softeners, topical lignocaine, and at least 4 weeks of topical glyceryl trinitrate 0.2%)
• Willing to provide informed consent

Exclusion Criteria:

• Multiple fissures
• Concomitant anorectal pathology (anal fistula, abscess, significant hemorrhoids, rectal cancer)
• Inflammatory bowel disease
• Previous anorectal surgery
• History of anoreceptive intercourse
• Psychiatric disease or inability to consent

Informed consent did not explicitly include permission for sharing de-identified data with external researchers

Institutional ethical approval was obtained only for the primary analysis and publication, not for data sharing