Where are anal fissures most commonly located?

Anal fissures are most commonly found at the posterior midline, specifically at the 6 o’clock position. This prevalence can be attributed to several factors, including the anatomy and blood supply of the anal canal. The posterior midline area is less well perfused compared to other parts of the anal region, making it more susceptible to trauma from passing stools, especially if they are hard or large. Additionally, the location is subjected to greater mechanical stress during bowel movements, contributing to the development of fissures.

Fissures in the 12 o'clock position (anterior midline) are much less common and often associated with specific conditions or anatomical abnormalities. Lateral fissures at the 3 and 9 o'clock positions might suggest underlying disease processes, such as inflammatory bowel disease or sexually transmitted infections, rather than the typical presentation of simple anal fissures. Anal fissures are typically localized rather than circumferential, which supports the focus on the posterior midline as the primary site for their occurrence.