Anal fistula has always been a problem for surgeons (1). Surgeons are forced to choose between two bad options: an effective treatment of the fistula tract or risk of fecal incontinence (2). To seek therapeutic effects and to maximize the protection of anal function have become the constant pursuit of anorectal doctors.

The internal orifice has been found to play an important role in the genesis, development, and treatment of anal fistula diseases (3). Both anal fistula caused by anal gland infection and anal fistula accompanied by inflammatory bowel disease are believed to originate from anal sinus or ulceration of the intestinal wall (4). Based on this concept, blocking the internal orifice to prevent intestinal bacteria from entering tissues has become a strategy for surgeons to create new procedures (5). However, injecting Salvecoll-E (6), fistula-tract laser closure (7), slide flap (8), and stem cells (9) in the treatment of fistula pay too much attention to the internal orifice and fistulas that had formed but do not pay attention to the operability of the technique. They are difficult for beginners to master. Therefore, the focus seems to be shifting to operational and effective technologies that can better serve more patients.

In this study, the use of disposable titanium nickel alloy anal fistula stapler can be easily mastered according to the instructions. An alloy anal fistula clamp has ultrahigh elasticity and continuous centripetal pressure closure of the internal orifice. The internal orifice was kept closed to eradicate the entrance of infection and completely heal the fistula (Figure 1). Because the external sphincter is preserved during surgery, the risk of fecal incontinence is expected to be minimal. The aim of our study was to report treatment results of this simple novel procedure and to explore the factors promoting anal fistula healing.

A prospective study was performed in which patients operated in our hospital between 1 May 2020 and 1 November 2020 were included. The study was approved by the hospital ethical committee. Each patient was informed of the principle, associated risks, and significance of the study and signed written consent (Figure 2).

Twenty-one patients with fistula-in-ano underwent surgery. The median follow-up was 6 months (range: 5–11 months). The mean age was 39.7 ± 10.5 years, and the male-to-female ratio was 18/3. In total, 33.3% (7) patients had trans-sphincteric anal fistula, and the others had intersphincteric anal fistula. In total, 38.1% (8) had multiple tracts, and 9.5% (2) had high anal fistula. In total, 23.8% (5) of anal fistula patients were complicated by Crohn’s disease. The anal canal wound and the fistula healed completely in 85.7% (18/21) patients; the healing time was 56 ± 8 days after surgery. The anal canal wound and the fistula did not heal in 14.3% (3/21) patients (Table 1). Three patients who did not heal had conventional surgery reperformed and eventually healed at 94, 103, and 108 days after primary surgery, respectively. Anorectal ultrasound also found that the healed fistula emitted a stronger echo than the surrounding tissue when the surgeon considered the anal fistula to be clinically healed.

The result of the samples sent for histological analysis was chronic inflammatory changes, with a large number of lymphocytes and plasma cells infiltrating, and no tumor cells were found.

The five patients with coexisting Crohn’s disease were treated with different treatments for Crohn’s disease according to their condition. All of them went into remission from Crohn’s disease.

Before the alloy clamp fell off, anal pain gradually decreased with time. When the alloy clamp came off, the pain score was 0. There was no significant bleeding in the anus postoperatively, including during defecation.

Except for three patients undergoing additional traditional anal fistula surgery, the Wexner incontinence scores of other patients did not change after surgery compared with those before surgery. Preoperative incontinence scores were 0.12 ± 0.2, and postsurgery incontinence scores after 3 months were 0.36 ± 0.4 (p = 0.24, unpaired t-test). No major complications or adverse reactions occurred during the treatment of all patients. In our retrospective analysis, 103 patients who underwent anal fistulotomy, including rubber band tightening during the same period, had varying degrees of anal incontinence, with an incontinence score of 3.93 ± 1.7 at 3 months after surgery (p < 0.001, compared with IOAC).

A new surgical procedure for anal fistula, IOAC, has been found by our current study to be simple, inexpensive, effective, and protective of the sphincter.

Although many surgical methods have been innovated in recent years, treating anal fistula is still a huge challenge. Traditional methods such as direct fistula resection and chronic rubber band resection have a high risk of incontinence in these fistulas (12). The newer methods are relatively safe but have a low success rate and are a complicated surgical procedure for a junior surgeon (13). This results in repeated surgeries for patients with anal fistula, which costs a lot of time and money (14). The principles of these methods include closing internal openings and treating fistulas, as well as treating gaps in fistula running. The corresponding surgical names include rectal mucosal muscle flap propulsion repair and anal fistula laser closure (15); anal fistula resection, anatomy, and placement, the latter including intersphincteric fistula ligation (LIFT) (16); video-assisted anal fistula treatment (17); and transanal incision of the sphincter space [transanal opening of intersphincteric space (TROPIS)] surgery (18). In our retrospective analysis, patients who received IOAC had a significant reduction in incomplete anal incontinence compared with patients who underwent anal fistulotomy in the same period.

Further, IOAC was performed only on the internal and external orifices and tracts, without additional surgical approaches. None of the procedures (rectal mucosal muscle flap propulsion repair and anal fistula laser closure; anal fistula resection, anatomy, and placement; LIFT; and TROPIS) avoids additional damage. Only video-assisted anal fistula treatment avoids additional damage, and pathological tissue is used as the approach (17). Unfortunately, video-assisted anal fistula treatment requires more expensive equipment and more experienced surgeons. The price of the IOAC set is $40, well below the cost of consumables used in other technologies.

The LIFT procedure also stops the infection from ligation of the intersphincteric tract. However, theoretically, IOAC might have a higher success rate than LIFT. First, in LIFT, nothing has been done to internal orifices. Second, fibrotic tracts remain after the LIFT procedure. In addition, the over-the-scope clip (OTSC) system is used for the management of leakage after laparoscopic sleeve gastrectomy and treatment of anal fistula (19, 20). Both OTSC clip and IOAC clamp are made of alloy material, and their therapeutic principle is to clamp the rupture of the digestive tract wall. However, first, OTSC is operated under digestive endoscopy for leakage, and the procedure is relatively complicated. Second, in the treatment of anal fistula, the clamp of OTSC has a symmetrical two-blade structure, while the clamp of IOAC has a three-blade structure. The latter has a continuous centripetal force at the internal orifice in terms of mechanics. This makes the latter clamp self-removable or easier to remove in about 6 weeks if it does not fall off by itself.

Detailed analysis of anorectal ultrasound in all the patients helped significantly to track the fistula tracts. This facilitates the treatment of all fistulas by the anal brush.

Although our study has never been reported before, the principle of treatment is also based on closing the internal orifices, managing fistulas, and expanding drainage of the external orifices. This procedure was quite effective (healing rate of 85.7%) in curing fistula-in-ano, including Crohn’s anal fistula and fistula with multiple tracts. Even in the absence of postoperative primary anal fistula healing, additional conventional surgery does not cause more damage or complicate the disease.

To conclude, the success rate of the IOAC procedure in more than 85% of the fistula is quite impressive. In this study, more than 38% had multiple tracts, and more than 23% patients had Crohn’s disease. This procedure has the advantages of a simple operation and no damage to the external sphincter and normal tissues because the surgical approach is in the internal and external orifices. Although the technique is easy to reproduce, it is associated with little pain and early resumption of normal activities. However, therapeutic effects on acute infectious anal fistula are awaited. Retrospective noncomparative studies have many limitations, such as a small number of patients, selective patients, and short follow-ups.