Which of the following is the most common site of anal fissure?

Explanation

## Anatomical Location of Anal Fissure **Key Point:** Anal fissures occur in the midline of the anal canal, with the posterior midline being the most common site (90% of cases). The anterior midline is the second most common site, particularly in women. ### Why Posterior Midline is Most Common The posterior midline location is due to: 1. **Vascular anatomy** — The posterior anal canal has relatively poor blood supply compared to lateral and anterior regions, making it more prone to ischemia and delayed healing. 2. **Mechanical trauma** — During defecation, the posterior anal canal experiences maximum shear stress due to the anatomy of the pelvic floor and direction of straining. 3. **Sphincter pressure** — The internal anal sphincter has higher resting pressure posteriorly, leading to greater mucosal trauma during passage of hard stool. ### Location Variations by Gender | Location | Frequency in Males | Frequency in Females | Clinical Note | |---|---|---|---| | Posterior midline | 90% | 85% | Most common overall | | Anterior midline | 8% | 15% | More common in women, especially postpartum | | Lateral walls | 2% | < 1% | Rare; suggests secondary fissure or Crohn's disease | **Clinical Pearl:** A fissure located in the lateral anal canal or at an unusual site should raise suspicion for secondary causes such as Crohn's disease, tuberculosis, or malignancy. Always investigate atypical presentations. **High-Yield:** The posterior midline location is so characteristic that it is considered a diagnostic feature of primary anal fissure. Deviation from this location warrants investigation for underlying pathology. [cite:Sabiston Textbook of Surgery Ch 31]