Ultrasound Assessment After Surgery for Chronic Anal Fissure

Chronic anal fissure is a painful tear in the lining of the anal canal that may not heal with medication or other non-surgical treatments. Lateral internal sphincterotomy is a commonly used surgical treatment. However, the amount of internal anal sphincter muscle divided during surgery may affect both fissure healing and the risk of impaired bowel control. The purpose of this prospective observational study is to assess whether the extent of internal anal sphincter division, measured using three-dimensional endoanal ultrasound, is associated with fissure healing and changes in anal continence during the first year after surgery. The study will include 66 adults with chronic anal fissure undergoing open or closed lateral internal sphincterotomy as part of their usual clinical care. The surgical technique will be selected by the treating clinical team and will not be assigned by the researchers. Participants will be assessed before surgery and at 3, 6, and 12 months after surgery. At the 3-month visit, they will undergo two-dimensional and three-dimensional endoanal ultrasound. Two independent observers will separately review the stored ultrasound images. Follow-up assessments will evaluate fissure healing or recurrence, bowel control, faecal soiling, pain, bleeding, postoperative complications, and quality of life. The findings may help identify the extent of sphincter division that provides effective fissure healing while limiting the risk of postoperative anal incontinence.

Inclusion Criteria: * Age 18 years or older. * Primary chronic anal fissure, defined as symptoms lasting more than 6-8 weeks and failure of complete conservative treatment, irrespective of the presence of anatomical signs of chronicity. * Clinical indication for open or closed LIS. * Capacity to understand the study, complete the questionnaires and provide written informed consent. Exclusion Criteria: * Acute anal fissure of less than 6-8 weeks' duration. * Secondary anal fissure associated with Crohn's disease, ulcerative colitis, tuberculosis, HIV infection, anal malignancy or another identified secondary cause. * Neurological or neuromuscular disease that may affect continence. * Moderate or severe anal incontinence at baseline. * Concomitant anorectal disease requiring another procedure, including symptomatic haemorrhoids or anal fistula. * Previous or current circumstances that prevent reliable completion of patient-reported measures. * Anticipated inability to attend postoperative follow-up. * Incomplete conservative treatment before the decision for surgery. * Participants may withdraw consent at any time without affecting their care. Investigators may discontinue study follow-up if eligibility was incorrectly assigned or if a clinical event prevents completion of study procedures. Data collected before withdrawal will be handled in accordance with the consent form and applicable legislation.