In patients with Crohn's disease, anal fistulas are usually treated in three stages: 1) close examination of the fistula and drainage with a seton, 2) pharmacological treatment of the inflammatory component, and 3) closure of the fistulous tract by a sphincter-sparing technique. Setons are used to ensure the permeability of the fistulous tract, to decrease the rate of re-intervention due to the formation of new abscesses or tracts. A seton is a small, often elastic, thread used for drainage. It is inserted into the fistulous tract, passing from the external orifice of the fistula (close to the anus or, in some cases, the vaginal) through the fistula and exiting via the anal orifice.

Seton use seems to minimize colonization of the mucosa of the fistulous tract by the intestinal flora, leukocyte infiltration, and the spread of inflammation within the fistulous tract. Most clinical practice guidelines advocate the use of a seton, but the level of evidence for the efficacy of this approach remains low (D, EL5). Indeed, only a few open studies have reported seton use to be potentially beneficial. In the retrospective study of 32 patients by Regueiro et al., a surgery group with seton insertion before treatment with infliximab was compared with a group on infliximab, without a seton, from the outset. Response rates were better in the group of patients with a seton, with a lower rate of recurrence and a longer time to recurrence than for the seton-less group. Another retrospective study by Schwartz et al. compared two groups - seton (n = 326) and no seton (n = 1519) - in patient with at least six months of biotherapy in three states of the USA. There were more hospitalizations and higher costs generated by greater use of the healthcare system in the group treated without a seton than in those with a seton.

The systematic use of setons in the context of Crohn's disease was inspired by the management of cryptoglandular fistula. However, the protective value of setons in this context remains far from clear, due to a lack of studies providing high-level evidence. Furthermore, the impact of seton use on patient quality of life has been little evaluated.

Investigators aim to determine whether the insertion of one or more setons in anal fistulas in Crohn's disease patients significantly alters patient quality of life. Investigators will perform a randomized controlled trial comparing two strategies: drainage surgery with and without seton use.

Inclusion Criteria:

• Patients with an anal fistula requiring surgical management in the context of Crohn's disease, with or without anti-TNF treatment (infliximab or adalimumab)
• Patient over 16 years of age (for minors, the consent of one of the parents will be requested)
• Patient with health insurance coverage
• French-speaking patient
• Signed written informed consent

Exclusion Criteria:

• Patient already included in a type 1 interventional research protocol (RIPH1)
• Patient under guardianship or curatorship
• Patient incarcerated
• Patient under legal protection
• Patient refusing randomization or follow-up
• Patient refusing the medical protocol for anti-TNF treatment (infliximab or adalimumab)
• Patient already experiencing treatment failure on optimized infliximab treatment; by contrast, those experiencing treatment failure on adalimumab alone may be included
• Patient allergic or intolerant to the two anti-TNF agents (infliximab and adalimumab)
• Patient with a stoma
• Patient with an ano-recto-vaginal fistula
• Patient with anal or rectal stenosis
• Patient with ileo-anal anastomosis
• Patient without preoperative MRI