>>862160"The surgical treatment of chronic anal fissure is basically done by therapeutic controlled damage to the internal anal sphincter. While fecal incontinence is a well-documented early complication of anal fissure surgery, few data are available about delayed incontinence. The aim of the present study was to assess whether surgical treatment of anal fissures may contribute to the development of delayed anal incontinence."
"Fecal incontinence may present as a late complication of anal fissure surgery. Incontinence may be associated with other cofactors accumulating over time or, more likely, anal fissure surgery may accelerate the physiologic age-related weakening of the anal sphincter mechanism."
International Journal of Colorectal Disease. 2011 Dec; 26(12): 1595-9.
https://www.ncbi.nlm.nih.gov/pubmed/21805112"Fecal continence applies to normal stool consistency and volume. Its maintenance requires normal colonic transit time, a compliant rectum as well as innervation of the pelvic floor and anal sphincters. The interplay between the puborectalis muscle, rectum, the internal anal sphincter (IAS) and the external anal sphincter (EAS) is of primary importance in the maintenance of fecal continence. Although continence is multifactorial, the IAS contributes to approximately 70% of resting anal canal pressure. Damage to the neuromuscular integrity of the IAS, age related weakness of the sphincteric smooth muscle, surgical or obstetric trauma, etc. can result in fecal incontinence."
Surgery. 2014 Apr; 155(4): 668–674.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4017655/