The purpose of this study is to determine whether the outcome of anal fistula repair with a collagen plug is comparable to that of repair by a mucosal advancement flap.

Perianal fistula can occur as a complication to a perianal abscess. A perianal fistula is associated with significant morbidity and reduced quality of life. Anal fistulas seldom heal spontaneously and may require surgical intervention. The main purpose of the operation will be to close the fistula and preserve anal continence. The traditional surgical fistula closing techniques often show disappointing results. Today, a collagen plug for fistula treatment is commercially available. The mounting of this plug is technically easy and less invasive than the traditional closure of the fistula by making a lid of anal mucosa (advancement flap). The purpose of this study is to determine whether the outcome of anal fistula repair with a collagen plug is comparable to that of repair by a mucosal advancement flap, with regard to healing of fistula, anal continence and pain. Plug treatment has so far shown promising results, but prospective, randomised controlled trials are needed.

Inclusion Criteria:

• Patients with fistula involving > 1/3 of the external anal sphincter
• Single, continuous fistula tract at time of inclusion (implies pre-treatment with seton)
• Patients with previous fistula surgery can be included (max. 1 lambeau or 1 plug)
• All patients included must be able to fill in an informed, written consent and to understand its implications and contents and to participate in the follow-up

Exclusion Criteria:

• Fistula tract shorter than 2 cm
• Complex fistula tract system (branching of the fistula tract)
• Age < 18 years
• Pregnancy
• HIV-positivity
• Fistula caused by malignancy
• Tuberculosis
• Hidrosadenitis suppurativa
• Pilonidal sinus disease
• No internal fistula opening found
• Unable/contra indications to go through MRI scanning
• Crohn´s disease
• Ulcerative proctitis