Endorectal Advancement Flap Procedure for Anal Fistula

An endorectal advancement flap is a sphincter-sparing surgical technique used to close complex anal fistulas, the abnormal tunnels that form between the anal canal or rectum and the surrounding skin. The procedure involves raising a flap of tissue from inside the rectum, cleaning out the fistula tract, and pulling the flap down to cover the internal opening so it can heal from the inside out. Across pooled data, success rates for cryptoglandular fistulas sit around 75%, though the numbers vary widely depending on the type of flap used, the patient’s history, and whether Crohn’s disease is involved. The operation has been a workhorse in colorectal surgery for decades, but understanding when it works best and what influences the outcome requires digging into the specifics.

Who Needs This Procedure

The endorectal advancement flap is designed for fistulas that cannot safely be treated with a simple lay-open procedure (fistulotomy) because too much sphincter muscle is involved. If a fistula runs through a large portion of the external sphincter, cutting it open risks permanent incontinence. The flap avoids this by approaching the problem from inside the rectal wall rather than cutting through the muscle from the outside. It is most commonly used for trans-sphincteric and suprasphincteric fistulas of cryptoglandular origin, meaning they started from an infected gland inside the anal canal rather than from inflammatory bowel disease or other systemic conditions.

Beyond standard anal fistulas, the technique is used for rectovaginal fistulas, the tunnels that form between the rectum and the vagina. An early series of 35 women with low or mid-level rectovaginal fistulas from traumatic or infectious causes reported healing in about 91% of cases.¹ The procedure has also been adapted for pediatric patients with congenital fistula types. A small case series described its use in children with H-type rectovestibular fistulas and a normal anus, with favorable results in all three patients.²

How the Procedure Works

The patient is positioned prone (face down) under general or regional anesthesia, and the surgeon works through the anal canal using a retractor for visibility. The internal opening of the fistula tract is identified first. The surgeon then excises or curettes the granulation tissue lining the tract to remove infected or scarred material. The external opening is left open to allow drainage.

A flap of tissue is then mobilized from the rectal wall, starting above the internal opening and extending broad enough at its base to maintain a good blood supply. The flap is freed from the underlying muscle, pulled downward to cover where the internal opening was, and sutured in place. The goal is to create a well-vascularized barrier between the inside of the rectum and the fistula tract so that stool and bacteria can no longer feed the tunnel.

One of the most consequential decisions the surgeon makes is how thick to cut the flap. This sounds like a small detail, but it substantially affects both recurrence and continence. A mucosal flap takes only the innermost lining. A partial-thickness flap includes the mucosa, submucosa, and some of the internal sphincter muscle. A full-thickness flap takes the full rectal wall including muscle. A systematic review and meta-analysis found that full-thickness flaps had a recurrence rate of about 7%, compared with 19% for partial-thickness and 30% for mucosal-only flaps.³ One comparative study put the difference even more starkly: 5% recurrence for full-thickness versus about 35% for partial-thickness flaps.⁴

The tradeoff is continence. Thicker flaps are more durable but involve more manipulation of the sphincter complex. The same meta-analysis found that mucosal and partial-thickness flaps had similar incontinence rates (about 9-10%), while full-thickness flaps disturbed continence in about 20% of patients, though most of these changes were minor.⁵ That said, the comparative study found that full-thickness flaps did not pose a greater threat to continence than partial-thickness ones, with about 11% of all patients showing significant continence changes.⁶ The inconsistency across studies reflects a broader theme in this literature: individual surgeon technique and patient selection matter a great deal, and published series can look quite different from one another.

What Drives Success and Failure

The headline success rate for endorectal advancement flaps in cryptoglandular fistulas is roughly 75% when pooled across studies, but this average conceals important variation. A large systematic review comparing the flap to another sphincter-sparing technique (LIFT) reported a weighted success rate of about 75% for flap repair of cryptoglandular fistulas.⁷ Individual series range widely. One recent study reported primary closure in only 43% of patients, with 57% having an unhealed fistula after the procedure, including about 22% classified as true recurrences.⁸

Several patient-level factors influence outcomes:

Prior surgeries: Patients who have had four or more previous anal operations are at the highest risk of the flap failing.⁹ Repeated operations scar the tissue, compromising the blood supply that the flap depends on.
Smoking: Tobacco use is associated with increased fistula recurrence after flap repair. A study specifically examining this found that smoking history was linked to higher failure rates.¹⁰ Smoking impairs microvascular circulation, and the flap’s survival depends on blood flow from its base.
Crohn’s disease: Having Crohn’s disease significantly reduces the chances of healing after flap repair.¹¹ The ongoing intestinal inflammation can undermine the repair from within. Rectovaginal fistulas also had lower healing rates in the same analysis.
Body weight: Higher BMI has been associated with worse healing. A study of salvage flap repair after a prior failed procedure found that patients with lower BMI had significantly higher healing rates.¹²

What Happens to Continence After Surgery

One of the main reasons surgeons choose the advancement flap over a fistulotomy is to protect the anal sphincter and preserve continence. The procedure does achieve this goal in most cases, but it is not risk-free. A study that measured sphincter pressures before and after flap repair found significant drops in both resting and squeeze pressures at three months. Before surgery, about 9% of patients reported incontinence symptoms. Afterward, roughly 79% had normal continence, about 13% had minor symptoms like occasional soiling, and 9% had more substantial continence disturbance.¹³

These changes are often temporary. A randomized trial comparing the flap to LIFT found that some patients had flatus incontinence at six months after either procedure, but all were continent at two years.¹⁴ It is worth noting, though, that the pooled incontinence rate after advancement flap was about 8% in the meta-analytic data, compared with under 2% for the LIFT procedure.¹⁵ For patients who already have borderline sphincter function, this difference could matter.

How the Flap Compares to the LIFT Procedure

The main competitor to the endorectal advancement flap is the LIFT (ligation of the intersphincteric fistula tract) procedure. LIFT approaches the fistula through the intersphincteric space rather than from inside the rectum, tying off and dividing the tract between the two sphincter muscles. Both are sphincter-sparing, but they work through different anatomical planes and have different strengths.

The evidence comparing them is genuinely mixed. When pooled across studies, the two procedures show similar overall success and recurrence rates for cryptoglandular fistulas. The systematic review found success rates of about 75% for the flap and 69% for LIFT, with recurrence rates of about 26% and 22% respectively, and none of these differences were statistically significant.¹⁶ A separate meta-analysis of randomized trials reached a similar conclusion, finding no significant differences in healing, recurrence, or complications between the two.¹⁷

Where the two procedures do diverge is in the perioperative experience and continence profile. LIFT was associated with shorter operating times and less postoperative pain in the meta-analysis of randomized trials.¹⁸ LIFT also trended toward lower odds of fecal incontinence, though this difference was borderline.

But context matters. One study that looked specifically at outcomes when either procedure was performed after a preliminary seton drain found the flap had a significantly higher success rate than LIFT: about 94% versus 63%.¹⁹ And one randomized trial found LIFT had a better healing rate than the flap (about 76% versus 55%), though continence disturbances in both groups resolved by two years.²⁰ The contradictions across studies are a good reminder that these procedures are highly operator-dependent, and the individual surgeon’s experience with a particular technique likely matters more than the theoretical advantages of one approach over another.

The Role of Preoperative Seton Drainage

Many surgeons place a seton, a thin loop of material threaded through the fistula tract, weeks or months before definitive repair. The idea is that the seton keeps the tract draining, reduces the septic burden, and conditions the tissue for a better repair. It sounds logical, and it is standard practice in many centers. But the evidence supporting it is surprisingly thin. A study examining whether preoperative seton drainage improved flap outcomes found that it did not improve the success rate of the repair.²¹

This does not mean setons are useless. They are still valuable for controlling acute infection and defining the anatomy before deciding on a definitive approach. The finding does suggest, however, that a prolonged seton drainage phase specifically to improve flap outcomes may not be necessary. Surgeons may be adding weeks of discomfort for the patient without a measurable benefit on the final success rate.

Advancement Flap in Crohn’s Disease

Perianal fistulas are one of the most debilitating complications of Crohn’s disease, affecting roughly a third of patients with the condition at some point. The endorectal advancement flap can work in this population, but the results are less predictable, and careful patient selection becomes critical.

A study from a specialized center reported an overall failure rate of about 20% for Crohn’s patients who underwent the flap, with a final healing rate of roughly 93% when secondary procedures were included. All patients who were diverted (had a temporary stoma) at the time of surgery healed successfully, and longer preoperative immunotherapy was associated with better outcomes.²² That result is remarkably good, but it came from a center with extensive experience and a protocol that involved optimization of medical therapy before surgery. It underscores the point that in Crohn’s, medical control of the disease is as important as the surgical technique.

Not all series are that encouraging. A tertiary center treating Crohn’s-related rectovaginal fistulas reported a success rate of only about 32% with the flap, much lower than the results seen in cryptoglandular disease.²³ A retrospective comparison of LIFT and the flap for Crohn’s perianal fistulas showed a trend toward higher healing with LIFT (about 90% versus 60%), though the difference did not reach statistical significance in the small sample studied.²⁴ The pooled success rate for the flap in Crohn’s fistulas sits around 61% across systematic review data.²⁵

When the First Attempt Fails

If you are reading about this procedure, there is a reasonable chance you or someone you know has already had a failed fistula repair. The good news is that a failed initial procedure does not close the door on the advancement flap. It can be performed as a salvage procedure after other techniques have failed, and it can be repeated.

A recent study examined the flap specifically as a rescue operation after a failed LIFT procedure. The success rate was about 71%, which is actually comparable to what the flap achieves as a first-line procedure.²⁶ Continence scores did not significantly change between before and after the salvage flap, suggesting the tissue tolerates a second procedure reasonably well. The same study found that lower BMI predicted better healing, which may be worth discussing with your surgeon if this scenario applies to you.

The reverse approach works too. Patients who fail the advancement flap can go on to have a LIFT procedure, a biologic plug, a video-assisted fistula treatment (VAAFT), or other sphincter-sparing options. The key is that these techniques address the fistula through different tissue planes, so a failure of one does not necessarily doom the next.

Healing Speed and Quality of Life

A five-year retrospective study compared the advancement flap directly with the cutting seton, an older technique that slowly cuts through the sphincter over weeks. The flap group healed faster, but recurrence rates, continence outcomes, and quality-of-life scores were similar between the two groups at long-term follow-up.²⁷ The physical and mental health scores were broadly comparable. This is reassuring in one sense, as the flap does not sacrifice long-term quality of life, but it also means the flap’s main advantage over the cutting seton is getting to healing sooner rather than producing a fundamentally better outcome years later.

From a cost perspective, the flap tends to be more expensive than some alternatives. A cost-effectiveness analysis comparing the flap to the anal fistula plug found that the plug saved roughly $1,600 per healed fistula and about a day and a half of hospital stay, though the two procedures had similar healing rates in that particular small series.²⁸ The fistula plug has since fallen out of favor at many centers due to high failure rates in larger studies, so this comparison may be less relevant today. Still, the point stands that the advancement flap is a more involved operation with longer operating time and hospital stay than several competing approaches.

Stem Cell Therapy as an Emerging Alternative

One of the more intriguing developments in fistula treatment is mesenchymal stem cell therapy, where stem cells are injected into and around the fistula tract to promote healing from within. This approach has gained traction for Crohn’s-related fistulas in particular. A study comparing the advancement flap to stem cell therapy in patients with complex Crohn’s perianal fistulas found no significant difference in healing rates between the two methods. Complete healing was achieved in roughly 87% of patients in the flap group, including a high proportion with vaginal fistulas.²⁹

The two approaches do have complementary strengths. The flap can be used for vaginal fistulas where stem cell therapy is generally not performed. Stem cell therapy can be used in situations where the rectal mucosa is too diseased, the anorectal canal is narrowed, or the fistula has two internal openings, all of which make flap construction difficult or impossible.³⁰ In practice, this means the two are not really competitors but rather tools suited to different anatomical and clinical scenarios. Stem cell therapy remains expensive and is not yet widely available outside specialized centers, but it represents a genuinely new treatment pathway for patients who are not good candidates for conventional surgery.