Comparative Analysis of Directional Snare vs Cutting Seton for High Anal Fistula Treatment

Introduction

Fistula-in-ano is an abnormally infectious tract that connects the perianal skin with the anal canal [1]. The inner wall of the fistula is glandular epithelial tissue or granulation tissue. Some 80% to 90% of anal fistulas are caused by primary or secondary infection of anal glands, which forms anorectal abscesses, epithelialized fistulas, or chronic infectious lesions left after abscess rupture or incision and drainage [1–3]. Patients with an anal fistula often experience discharge of pus, feces, or blood, and intermittent pain and itching [4]. A small number of patients with anal fistula do not have obvious anorectal abscesses, and anal fistulas caused by special reasons, such as Crohn’s disease, special infections, trauma, and malignant tumors, should be given appropriate attention. Anal fistulas can occur at any age, with most occurring between 20 to 40 years of age, and the incidence rate is higher in men than in women [5–7].

It is important to get a detailed understanding of the medical history and symptoms and to conduct a physical examination. Based on the patient’s history of spontaneous rupture of perianal abscesses, drainage through incision, or repeated rupture after healing, combined with physical signs, such as the subcutaneous hard cord between the rupture and the anus, and anal sphincter fibrosis, a clear diagnosis can be made for most anal fistulas. If the diagnosis is unclear or it is necessary to determine the relationship between the fistula and the anal sphincter, further auxiliary examinations, such as computed tomography, ultrasound, magnetic resonance imaging (MRI), or fistula angiography are recommended.

There are many classification methods for anal fistula, but all of them are based on anatomy, specifically in relation to the internal and external anal sphincters. Among them, the Parks classification is still widely used [8]. Four types were described: intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric. Anal fistula are commonly categorized as “high” and “low” on the basis of their anatomical course relative to the external anal sphincter [9–11]. High anal fistulas include transsphincteric fistulas, which involve greater than 30% of the external anal sphincter, and suprasphincteric, extrasphincteric, or horseshoe fistulas. Low anal fistula include intersphincteric or low transsphincteric fistulas, which cross less than 30% of the external anal sphincter.

Treatment of anal fistula depends on the basis of anatomical complexity relative to the external anal sphincter, as well as patient factors. Surgery, which can be divided into those that damage the sphincter and those that preserve the sphincter function, is the best way to cure cryptoglandular fistulas. The former includes fistulotomy and cutting seton (CS); the latter includes endorectal advancement flap, ligation of intersphincteric fistula tract, fibrin plug and glue, and minimally invasive approaches using endoscopic or laser closure techniques [12]. High anal fistula has the characteristics of prolonged or recurrent attacks, and the treatment is relatively difficult [4,13,14]. Although several alternative treatments for high anal fistula have been proposed, it is difficult to treat high anal fistula, due to their long-lasting or recurrent characteristics, resulting in an extremely low healing rate after surgery [15–18].

The CS method plays an important role in the treatment of high anal fistula in China [14]. The method of CS to treat anal fistula with tightening rubber bands is to ligate slowly, to irritate and drain the abscess. After the process, the relationship between the fistula and anal sphincters is marked [19–21]. Although CS is effective, because of the stress mode of centripetal cutting, there are some shortcomings, such as severe postoperative pain, long wound recovery time, large anal sphincter injury, many postoperative complications, and high recurrence rate [22,23]. Therefore, the CS technique should be appropriately selected to ensure that the function of the anal sphincter is protected. Directional CS is used to reduce the force on the distal end by changing the area of the distal end of the hanging tissue, to produce a directional force from top to bottom and from deep to shallow, to give priority to cutting and growth of the deep and basal tissue [24] (Figure 1). The advantage of the technique is that it could avoid cutting off a whole anorectal ring at one time, which is able to reduce the occurrence of serious complications, such as anal “keyhole” deformity and anal incontinence [25–27]. The disposable fistula snare is a device that integrates all tools of the CS. In other words, the entire surgical procedure can be completed using the disposable fistula snare alone (Figure 2). Therefore, this study aimed to compare outcomes in 60 patients with high anal fistula treated with a disposable directional snare or a CS method.

Material and Methods

STUDY DESIGN:

This study was single-blinded, randomly controlled, and conducted according to the ethical standards of the Helsinki Declaration. All patients signed an informed consent form. This study was approved by the Ethics Committee of the Third Affiliated Hospital of Liaoning University of Traditional Chinese Medicine (No. 20220928011).

SAMPLE COLLECTION:

Sixty patients with high anal fistula treated in the Third Affiliated Hospital of Liaoning University of Traditional Chinese Medicine from October 2022 to October 2023 were randomly divided into a treatment group (n=30, treated with disposable fistula snare for directional CS [DFCS group]) and a control group (n=30, treated with CS [CS group]).

DIAGNOSTIC CRITERIA:

The relevant diagnostic criteria of high anal fistula in the guidelines developed by the American Society of Colon and Rectal Surgeons in August 2022 were followed [28]: (1) previous perianal abscess; (2) clinical symptoms include perianal pus, dampness, pain, itching, and defecation; (3) opening of a wound or hard lumps caused by perianal collapse could be seen; digital rectal examination reveals perianal hard lump and their tracking, anal sphincter fibrosis, and other physical signs; and (4) computed tomography, B ultrasound, MRI, and other ancillary tests clarify the diagnosis, and the main fistula ran above the deep layer of the external sphincter.

INCLUSION AND EXCLUSION CRITERIA:

The inclusion criteria were as follows: (1) the above diagnostic criteria were met; (2) age of 18–65 years; (3) patient in good health and able to undergo surgery; (4) patient had an anus with normal function and normal shape before surgery; (5) no history of anal surgery; (5) no serious primary diseases, such as of the heart, cerebrovascular, liver, kidney, and hematopoietic systems; and (6) patients and their families have accepted informed consent and could cooperate with follow-up surveys.

The exclusion criteria were as follows: (1) patients with non-cryptoglandular fistulas; (2) high anal fistula caused by trauma or iatrogenic injury; (3) patients with inflammatory bowel disease or malignant tumors; (4) patients with diseases such as diabetes that can affect wound healing; (5) sexually transmitted diseases; (6) women during pregnancy or lactation; (7) patients with mental illness; and (8) those who have history of any allergy.

BEFORE SURGERY:

Endoanal ultrasonography or anorectal MRI was used to pinpoint the internal opening area of the fistula, scope of the fistula, and number and tracking of the fistula, and analyze its correlation with anorectal ring and internal and external anal sphincter. Patients underwent preoperative fasting and water restriction for 8 h. Patients underwent enema cleaning before surgery. Patients were underwent surgery with epidural and spinal anesthesia and were placed in the lithotomy position. After routine disinfection, the operation towel was laid down.

PROCEDURES: For the DFCS group (Figure 3). First, hydrogen peroxide was injected through the external, superficial opening to delineate the tract and help localize the deep internal opening. Second, the upper wire device was used to pass the rubber ring or elastic fixing line through the head end of the disposable fistula snare and install it into the card slot to a preset state. Then, the head end of the disposable fistula snare was removed, and the probe and elastic cutting line were pulled out of its cavity. After selecting a silicone gasket of the appropriate size, the probe in the fistula snare was set to pass through a fixed hole in the gasket, and the probe was probed around from the external openings of fistula. Next, through the thinnest part of the internal opening of the fistula or rectal mucosa, the electric knife was used to remove the skin and subcutaneous tissue between the probes. The top end of elastic line for the drainage tube was transected and separated from the spacer, and then, the tail end of elastic line for the drainage tube was also cut. The top end was fixed with the tail end. The drainage tube was laid at the deepest part of the fistula. Then, the probe was set to pass through another fixed hole on the gasket, the gasket was adjusted to a suitable position, and the probe was put back into the cavity of the disposable fistula snare, the rubber ring or the elastic fixing line, which had been preset, and was tied to the elastic cutting cord through the pusher. The next step was to cut the end of the elastic cord, and then the 2 ends of the elastic cord were pulled to push the elastic fixing line of elastic cutting cord toward the cutting tissue of patients until no tension existed (Figure 4). The edge of wound was repaired properly, was formed in a shape of “V”, and the drainage was made more smooth. After no active bleeding, the patients’ wounds were filled with Vaseline gauze, bandaged, and fixed with aseptic gauze.

For the CS group, the preoperative preparation was the same as that of the DFCS group, and the surgical steps were as follows: probe around from the external openings of fistula, penetrate from the thinnest part of the internal openings of fistula or rectal mucosa, cut off the fistula and fibrotic tissue under the anorectal ring along the direction of the probe, and scratch and scrape the fistula and sinus above the anorectal ring. Scrape, rinse, and debride until there are no hard lumps on the wound. Continue to use silk thread to fix the tail of the probe, and connect the rubber band to draw out from the internal openings of fistula, tighten the rubber band to maintain tension, and the tightness should be tolerated by the patient and cut slowly. After clamping with a curved vascular clamp, ligate and fix it with No. 7 wire. The follow-up operation was consistent with that of the DFCS group.

POSTOPERATIVE TREATMENT:

Postoperative treatment consisted of daily dressing change, prophylactic use of antibiotics for 3 days, no use of the analgesic pump, and regular follow-up and reexamination. During dressing change, the tension at both ends of the elastic cutting line for the DFCS group was adjusted to maintain in a slow cutting state. The drainage tube was removed 7 days after the surgery. On the contrary, during dressing change in the CS group, if the rubber bands were loose and lack of tension, the rubber band was tightened, and the tightness should be acceptable to the patients and suitable for slow cutting. After clamping with the curved vascular clamp, it was re-ligated and fixed with No. 7 silk thread.

OBSERVATIONAL INDEXES:

After surgery, the following 9 observations were recorded.

STATISTICAL ANALYSIS:

IBM SPSS Statistics version 25 was used for data analyses. Mean±standard deviation was presented to calculate numerical data, and the categorical variables were presented in numbers and percentages. The independent t test was used to compare the numerical data. The chi-square test compared Garg classification, sex, clinical efficacy, and recurrence rate of the groups. All effects of tests were conducted with a 2-sided α level of 0.05 and 95% confidence intervals. The difference was statistically significant at P<0.05).

Results

PATIENT CHARACTERISTICS:

There were 6 women and 24 men, aged 19 to 60 years (mean age 36.3 ±12.5 years), who, according to the Garg classification [34], included 22 cases of high linear transsphincteric fistula (grade III), 6 cases of high transsphincteric fistula with either abscess, multiple or horseshoe tract (grade IV), and 2 cases of suprasphincteric fistula (grade V). There were 3 women and 27 men, aged 19 to 58 years (mean age 37.4±12.1 years), including 26 cases of high linear transsphincteric fistula (grade III) and 2 cases of high transsphincteric fistula with either abscess, multiple or horseshoe tract (grade IV). There were no significant differences in age, sex, and type of anal fistula between the 2 groups (P=0.744, P=0.470, P=0.255; Table 1).

CLINICAL EFFICACY:

After the 3-month follow-up, the total effective rate was 100% in the DFCS group and 90% in the CS group. There was no significant difference in the clinical efficacy between the 2 groups (P=1.000; Table 2).

OPERATION TIME, ELASTIC CUTTING CORD OR RUBBER BAND FALLING OFF TIME, AND WOUND HEALING TIME:

The operation time and wound healing time in the DFCS group were significantly shorter than those in the CS group (25.5±4.6 vs 29.9±5.1, P =0.001; 29.5±9.2 vs 37.2±10.7, P =0.004), but the elastic cutting cord falling off time in the DFCS group was not significantly different from the rubber band falling time in the CS group. (11.8±1.2 vs 11.3±1.6, P=0.176; Table 3).

VAS SCORE:

On the day 1 after the operation, there was no significant difference in VAS score between the 2 groups (7.1±0.2 vs 7.1±0.1, P=0.196), but on day 7 after the operation, the VAS score of the DFCS group was significantly lower than that of the CS group (3.4±0.2 vs 4.9±0.1, P=0.000; Table 4).

ANAL FUNCTION:

Before surgery, there was no significant difference in the scores of Wexner incontinence, anal resting pressure and anal maximal contraction pressure between the 2 groups (P>0.05). However, 3 months after the operation, the scores of Wexner incontinence in both groups were higher than those before the operation, while anal resting pressure and anal maximal contraction pressure were lower than those before the operation, and the Wexner score in the DFCS group was lower than that in the CS group (3.9±1.3 vs 5.0±1.3, P=0.001). Anal resting pressure and anal maximal contraction pressure were higher than those in the CS group (58.3±1.6 vs 54.5±2.5, P=0.000; 145.1±9.2 vs 131.2±8.7, P=0.000; Table 5).

RECURRENCE:

After the 12-month follow-up, 1 patient had recurrence in the DFCS group (3.33%), and 3 patients had recurrence in the CS group (10%). There was no significant difference in the recurrence rate between the 2 groups (χ²: 0.268).

PATIENT SATISFACTION:

The satisfaction scores of patients in the DFCS group were better than those in the CS group, and there was a significant difference between the 2 groups (8.83±0.79 vs 5.51±0.37, P=0.000; Table 6).

Discussion

LIMITATIONS:

There are some limitations in this study. First, because of the short follow-up time, the recurrence rate of high anal fistula may have increased with time. Further studies are needed to observe the long-term results of the disposable fistula ligature in the treatment of high anal fistula. Second, the study had a small sample size and may not have included enough patients to support the result. Third, this study was mainly a clinical observation and lacked some more convincing objective indicators. Therefore, a clinical trial consisting of a large number of patients with a longer follow-up period is needed to confirm the initial positive results of the trial.

Conclusions

The application of the disposable fistula snare in the clinical treatment of high anal fistula can simplify the surgical procedure, shorten the operation time, protect the fine anal function, and make the thread-tightening procedure more convenient and less painful after surgery. Therefore, it provides an excellent option for seton as a new type of medical equipment that is more convenient and beneficial to patients.