Ultrasound Assessment After Surgery for Chronic Anal Fissure

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.