Modified anal fistula clip: A safe and effective alternative to incision and thread hanging for anal fistula

Abstract

BACKGROUND

Anal fistula is a common anorectal disorder, for which incision and thread hanging (ITH) remains a widely used treatment. However, ITH is often associated with substantial postoperative discomfort and carries a risk of anal sphincter injury, potentially compromising functional outcomes. The anal fistula clip (AFC) is a novel surgical technique designed to occlude the internal orifice of the fistula, eliminate infection source, and preserve anal sphincter function.

AIM

To compare the efficacy and safety between AFC and ITH in a randomized, single-center study focusing on short-term postoperative outcomes.

METHODS

A total of 70 patients with anal fistula who underwent surgery from August 2019 to January 2025 were randomly assigned to the ITH or AFC group. The primary outcomes included cure rates, pain scores, anal sphincter function, and complications. Patients were followed up postoperatively for 6 months.

RESULTS

All surgeries were successfully performed, with postoperative cure rates exceeding 90% in both groups. No severe complications or postoperative fecal incontinence occurred. Compared with the ITH group, the AFC group demonstrated better outcomes in early postoperative pain (P < 0.01), wound healing time (P < 0.01), and anal sphincter function preservation (P < 0.05).

CONCLUSION

Compared with ITH, AFC may reduce postoperative pain, shorten healing time, preserve function, and minimize complications. AFC may be safe and effective; however, larger studies with longer follow-up are needed.

Key Words: Anal fistula clip; Incision and thread hanging treatment; Anal fistula; Anal sphincter function; Postoperative pain; Complications

Core Tip: This exploratory study compared the anal fistula clip (AFC) with conventional incision and thread hanging in 70 patients with anal fistulas. Both techniques achieved high short-term cure rates, with AFC demonstrating early postoperative pain reduction, faster wound healing, and better sphincter function preservation. No recurrences were observed during the follow-up period, although these findings were preliminary. By directly closing the internal orifice through sustained centripetal compression, the AFC interrupts infection source while minimizing sphincter injury. Therefore, AFC may be a safe, minimally invasive, and function-preserving alternative for anal fistula management, warranting further investigation in larger and long-term studies.

INTRODUCTION

Anal fistula (AF) is an abnormal tract connecting the anorectal canal to the perineal skin that most commonly results from infection of the anal crypt glands. Symptoms include recurrent purulent discharge, erythema, anorectal pain, and perianal pruritus. Severe cases may present with defecation difficulty, substantially impairing the patients’ quality of life[1-3]. AF pathogenesis is associated with multiple conditions, including Crohn’s disease (CD), prior anorectal abscesses, trauma, hidradenitis suppurativa, and sexually transmitted infections[4,5]. Its incidence ranges from 26% to 38%, with a prevalence of approximately 1.69 per 100000 people in Europe[6-8].

The cornerstone of AF management is surgical intervention, and conventional approaches, such as incision and thread hanging (ITH), are widely used because of their effectiveness in eliminating infection and facilitating drainage. However, these procedures may cause considerable trauma to the anal canal and sphincter complex, particularly in high or complex fistulas, thereby increasing the risk of fecal incontinence, anal deformity, and prolonged postoperative recovery[9]. To overcome these limitations, various sphincter-preserving techniques, such as AF plug[10], video-assisted AF treatment[11], fistula tract laser closure[12], and ligation of intersphincteric fistula tract[13], have been developed. These methods have improved functional outcomes to varying degrees; nevertheless, their healing rates remain variable. Furthermore, no single technique has been accepted as a universal standard that reliably balances fistula eradication and continence preservation.

Increasing evidence has indicated the important role of the internal fistula orifice in disease persistence and recurrence, and its effective closure is considered a key determinant of surgical success[14,15]. In 2012, the application of an endoscopic over-the-scope clip (OTSC) system to close the internal AF orifice was first reported, demonstrating promising efficacy by sealing the primary source of infection while preserving sphincter integrity[16]. By interrupting the ongoing contamination pathway, this approach provides a mechanistic advantage over conventional procedures that solely focus on tract excision[17].

Building on the principles of the OTSC system, a nickel-titanium memory alloy AF clip (AFC) was subsequently developed. This device exerts continuous centripetal compression on the internal orifice, thereby facilitating durable closure, obstruction of the fistula tract, and resolution of infection (Figure 1). The AFC system was obtained from Fulltai Medical Technology Co., Ltd. (Shanxi, China)[18]. Variable but generally favorable healing rates have been reported for AFC, ranging from 47% to 96%[19].

Figure 1 Schematic illustration of the anal fistula clip system. The device comprises an elastic nitinol clip and a dedicated applicator designed for precise placement at the internal orifice of the fistula.

Considering these findings, we aimed to evaluate the clinical efficacy and safety of AFC for AF treatment at our institution. Specifically, we compared postoperative pain, wound healing time, anal sphincter function, and complication rates between patients who underwent procedures using AFC and conventional ITH. Our findings can provide further evidence to inform clinical decision-making and expand therapeutic options for AF management.

MATERIALS AND METHODS

Patients and study design

Patients diagnosed with AF who were admitted to the Department of Anorectal Surgery at the First Affiliated Hospital of Anhui University of Chinese Medicine from August 2019 to January 2025 were enrolled in the study. Overall, 70 eligible patients were included in this study. The hospital’s Medical Ethics Committee approved the study protocol, and all participants provided written informed consent.

Patients were randomly assigned in a 1:1 ratio to either the AFC or ITH group using a computer-generated randomization sequence. The allocation was concealed using sequentially numbered, sealed, opaque envelopes prepared by an independent researcher who was not involved in patient recruitment or outcome assessment. The envelopes were opened only after patient enrollment and baseline data collection. Owing to the nature of the surgical interventions, the operating surgeons were aware of the group allocation. However, postoperative outcome assessors and data analysts were blinded to treatment assignments to minimize detection and reporting bias.

The inclusion criteria were AF diagnosis confirmed by transrectal biplane ultrasound or magnetic resonance imaging and aged 18 years to 75 years. The exclusion criteria were as follows: AF with acute infection; AF associated with rectal cancer and extensive inflammatory involvement; AF that has been surgically treated; and patients with hematological disorders, inflammatory bowel disease, tuberculosis, decompensated liver, or kidney failure.

Surgical procedure

Experienced physicians performed all surgeries. Under epidural anesthesia, the patients were placed in the lateral decubitus position, and a U-shaped anoscope was inserted. Hydrogen peroxide was injected through the external fistula orifice to identify the internal orifice. The probe was advanced from the external to the internal orifice to confirm the fistula tract. Any necrotic tissue and epithelialized tract lining were thoroughly debrided using a fistula brush. The fistula tract and area surrounding the internal orifice were then irrigated two to three times with povidone-iodine, followed by normal saline. The internal orifice was elevated using tissue forceps. Centered on the internal orifice, an area of mucosa and submucosa of approximately 1.0 cm in diameter was marked and excised using an electrocautery device to expose the underlying muscular layer. A 3-0 absorbable suture was placed in a cross-shaped (“+”) configuration to approximate the internal orifice. The suture ends were lifted and positioned within the deployment head of the clip-closure device, ensuring alignment between the central aperture of the clip and internal orifice. With the device oriented perpendicularly to the orifice and traction applied to the sutures, the clip was deployed and left in place for 30 seconds to ensure complete closure. The external orifice was appropriately enlarged via electrocautery to facilitate postoperative drainage (Figure 2).

Figure 2  Key operative steps of the anal fistula clip procedure in a representative patient with anal fistula, illustrating identification of the internal orifice, tract preparation, and precise placement of the anal fistula clip to facilitate drainage and promote healing.

The ITH procedure was performed according to a standardized surgical protocol. Procedures were performed by experienced attending surgeons who had completed the learning curve for this technique, ensuring procedural consistency and stable outcomes. Postoperative pain management was standardized in both groups. All patients routinely received nonsteroidal anti-inflammatory drugs, with additional analgesics as needed. The type, dosage, and timing of analgesic administration were consistent between the two groups.

Evaluation parameters and follow-up

Intraoperative details and relevant surgical parameters were carefully recorded. Postoperative follow-up was conducted within the first week and subsequently at 1, 3, and 6 months. Postoperative pain, wound healing time, anal sphincter function, and complications were assessed. Pain was evaluated using the visual analog scale (VAS) on postoperative days 1, 5, and 28. Wound healing was defined as complete epithelialization of the surgical site without discharge, as confirmed by an experienced anorectal specialist. Anal sphincter function was assessed using the Wexner incontinence score (range, 0-20). In addition, anorectal manometry was performed to measure the resting anal sphincter pressure and maximum squeeze pressure preoperatively and at 1 and 6 months postoperatively. Postoperative complications included infection, bleeding, incisional edema, anal stenosis, and fistula recurrence. All assessments were conducted by investigators blinded to the group allocation.

Statistical analysis

Statistical analyses were performed using IBM SPSS Statistics for Windows, version 28.0 (IBM Corp., Armonk, NY, United States). All tests were two-sided, and P < 0.05 was considered statistically significant. Continuous variables were assessed for normality using the Shapiro-Wilk test and homogeneity of variance before analysis. Normally distributed data are presented as mean ± SD and were compared using a Student’s t-test. Welch’s t-tests were used when the assumption of equal variance was violated. Non-normally distributed data are expressed as median (interquartile range; P25-P75) and were compared using the Mann-Whitney U test. Categorical variables are presented as n (%) and were compared using a χ² test or Fisher’s exact test, as appropriate.

RESULTS

In total, 70 patients were included in the final analysis, with 35 patients in each group. There were no significant differences in baseline demographic or clinical characteristics between the AFC and ITH groups (all P > 0.05) (Table 1). The postoperative resting VAS pain scores were significantly lower in the AFC group than in the ITH group on postoperative days 1 and 5 (both P < 0.001). However, no significant between-group difference was observed on postoperative day 28 (P = 0.73) (Table 2).

Table 1 Baseline demographic and clinical characteristics of the patients, n (%)/mean ± SD.

Characteristic	AFC (n = 35)	ITH (n = 35)	P value
Age (years)	35.00 ± 9.70	37.83 ± 11.16	0.30
Sex
Male	31 (88.6)	32 (91.4)	0.65
Female	4 (11.4)	3 (8.6)
Fistula type
Transphincteric	23 (65.7)	22 (62.9)	0.98
Intersphincteric	12 (34.3)	13 (37.1)
Simple	21 (60.0)	21 (60.0)	0.76
Complex	14 (40.0)	14 (40.0)
Disease duration (months)	6.0 ± 5.1	8.2 ± 10.2	0.81

AFC: Anal fistula clip; ITH: Incision and thread hanging.

Table 2 Comparison of resting visual analog scale pain scores between the anal fistula clip and incision and thread hanging groups at different postoperative time points.

Group	n	Resting VAS pain score
		Day 1	Day 5	Day 28
AFC	35	3.18 ± 2.43	2.76 ± 2.47	0.63 ± 0.58
ITH	35	5.90 ± 1.31	4.50 ± 1.13	0.71 ± 1.24
Test statistic		Welch t = 5.84	Welch t = 3.76	t = 0.34
P value		< 0.001	< 0.001	0.73

AFC: Anal fistula clip; ITH: Incision and thread hanging; VAS: Visual analog score.

None of the patients in either group experienced postoperative fecal incontinence. In the AFC group, the mean Wexner score increased from 0.04 ± 0.23 preoperatively to 0.09 ± 0.29 at 1 month (P < 0.01) and decreased to 0.03 ± 0.17 at 6 months, with no significant difference compared with baseline. Preoperative Wexner scores were comparable between the two groups. However, at both 1 and 6 months postoperatively, the AFC group demonstrated significantly lower Wexner scores than the ITH group (both P < 0.05), indicating better preservation of anal sphincter function, although the absolute differences were small (Figure 3).

Figure 3 Wexner incontinence scores in the anal fistula clip and incision and thread hanging groups at baseline, 1 month, and 6 months postoperatively. ^aP < 0.05 vs anal fistula clip group at the same time point; ^bP < 0.01 vs preoperative value in the anal fistula clip group. AFC: Anal fistula clip; ITH: Incision and thread hanging.

We compared the preoperative anal resting and maximum squeeze pressures, which reflect internal anal sphincter tone the and voluntary contraction strength of the external anal sphincter, respectively, between the AFC and ITH groups. Postoperative analyses demonstrated that both resting and maximum squeeze pressures were significantly higher in the AFC group than in the ITH group (P < 0.05). Within the AFC group, there were no significant differences between the preoperative and 6-month postoperative pressures, suggesting better preservation of anal sphincter function (Figure 4).

Figure 4 Comparison of anal sphincter pressures between the anal fistula clip and incision and thread hanging groups before surgery, at 3 months, and 6 months postoperatively. A: Resting anal sphincter pressure; B: Maximum squeeze pressure. ^bP < 0.01 vs incision and thread hanging group at the same time point. AFC: Anal fistula clip; ITH: Incision and thread hanging.

Neither group experienced fistula recurrence. Overall, complications were mild and clinically insignificant. In the ITH group, one patient (2.86%) experienced mild wound edema, two (5.71%) developed anal stenosis, and one (2.86%) experienced postoperative bleeding, which was managed conservatively without reoperation. No severe complications occurred. Notably, there were no reported complications in the AFC group. In addition, the AFC group demonstrated a significantly shorter wound healing time than the ITH group (P < 0.001), indicating faster postoperative recovery. Although the sample size was limited, these findings suggest that AFC may be associated with fewer complications and accelerated healing (Table 3).

Table 3 Comparison of primary endpoints, including postoperative complications and wound healing time, between the anal fistula clip and incision and thread hanging groups, n (%).

Complications	AFC (n = 35)	ITH (n = 35)	Analysis	P value
Total healed	33 (94.3)	32 (91.4)	Fisher’s exact test	0.63
Any complications	0 (0.0)	4 (11.4)	Fisher’s exact test	0.02
Bleeding	0	1 (2.86)	-	-
Edema	0	1 (2.86)	-	-
Stenosis	0	2 (5.71)	-	-
Healing time (days)	26.0 ± 2.5	34.5 ± 3.1	Welch t-test	< 0.001

AFC: Anal fistula clip; ITH: Incision and thread hanging.

Collectively, compared with ITH, AFC was associated with favorable clinical outcomes, including reduced early postoperative pain, shorter wound healing time, better preservation of anal sphincter function, and lower incidence of complications. These findings suggest that AFC may be a safe and effective alternative for AF management, with potential benefits for postoperative recovery and functional preservation. Nonetheless, considering the relatively small sample size and limited follow-up duration, larger prospective studies with extended follow-up periods are warranted to validate these findings and comprehensively evaluate the long-term efficacy and safety of this approach.

DISCUSSION

In this study, we compared the clinical outcomes of the AFC and ITH techniques for AF treatment in 70 patients over a 6-month postoperative follow-up period. The AFC technique was associated with favorable outcomes, such as early postoperative pain relief, faster wound healing, better preservation of anal function, and lower incidence of complications. No cases of fistula recurrence were observed in either group, suggesting that AFC may represent a promising alternative to conventional ITH, offering potential benefits for postoperative recovery and preservation of sphincter function.

In the present study, postoperative pain control significantly improved in the AFC group compared with the ITH group, as evidenced by lower VAS scores, particularly during the early postoperative period. Early pain reduction is clinically meaningful because it can enhance patient mobility, facilitate wound care, and improve overall recovery. This analgesic advantage of AFC is likely attributable to its mechanism of action: Continuous compression of the internal orifice without progressive tissue cutting and sphincter traction inherent to conventional seton-based procedures. By avoiding repeated mechanical trauma to the sphincter complex, this technique minimizes the inflammatory response and postoperative discomfort. Although pain is inherently subjective, we minimized potential bias by using a standardized postoperative analgesia protocol in both groups. Future studies incorporating objective pain assessments or stratified analyses may further validate these findings.

Our findings on functional outcomes further supported the potential advantages of AFC. Compared with the ITH group, the AFC group demonstrated better preservation of sphincter integrity and more rapid functional recovery, as indicated by improved Wexner incontinence scores, anal resting pressure, and maximum squeeze pressure and minimal changes from baseline at 6 months. Additionally, the wound healing times were significantly shorter in the AFC group, suggesting that effective closure of the internal orifice may accelerate the resolution of infection and tissue repair. In contrast, patients treated with ITH generally required longer recovery periods, and their functional restoration was more frequently affected by postoperative complications. Therefore, AFC may provide clinically meaningful benefits in terms of both functional preservation and postoperative recovery.

Furthermore, we observed that the incidence of postoperative complications was lower in the AFC group than in the ITH group. No cases of anal stenosis, wound edema, postoperative bleeding, or fecal incontinence were observed after AFC. Meanwhile, a small number of such complications occurred in the ITH group, all of which were managed conservatively without the need for reoperation. The absence of continence impairment is particularly noteworthy, as the preservation of sphincter function remains a central challenge in the surgical treatment of AF. Additionally, the AFC group exhibited significantly shorter wound-healing times, suggesting accelerated postoperative recovery. Collectively, AFC may provide a more favorable balance between therapeutic efficacy and functional preservation.

The primary goal of AF surgery is complete eradication of the internal orifice and epithelialized tract while preserving anal sphincter function. The ITH technique can effectively control infection but is often associated with substantial postoperative pain, prolonged recovery, and potential sphincter injury. These limitations prompted the development of sphincter-preserving strategies aimed at improving functional outcomes without compromising cure rates. In this context, the AFC technique has emerged as a minimally invasive approach designed to achieve effective closure of the internal orifice while minimizing trauma to the sphincter complex[20,21].

The AFC is a modification of the OTSC concept that achieves durable internal orifice closure through sustained centripetal compression. By sealing the primary infection source, AFC interrupts the cycle of persistent contamination and chronic inflammation while preserving sphincter integrity. This technique reportedly yields high healing rates and minimal risk of fecal incontinence. Eid et al[22] reported an overall healing rate of 67.7%, exceeding 75% for cryptoglandular fistulas[23]. Deng et al[24] showed that AFC exhibited superior clinical outcomes in terms of fistula healing rate, hospitalization duration, and postoperative anal pain. Promising prospects for AFC in minimally invasive treatments, particularly for preserving sphincter function, have also been reported[25]. Li et al[18] observed a healing rate of over 85%, including cases of CD-related or multiple fistulas. In a prospective study, Wang et al[26] demonstrated that AFC provided superior outcomes in terms of clinical symptoms and radiologic healing compared with endorectal advancement flap procedures. Meta-analyses have indicated that fistula closure can be achieved in approximately two-thirds of patients, with healing rates exceeding 75% for cryptoglandular fistulas, including inflammatory bowel disease-related cases.

Other clinical series have reported overall cure rates above 85%, including in patients with CD-associated or multiple fistulas. Concerns regarding the potential damage to the normal anal sphincter have driven the development of novel sphincter-preserving techniques. As a modified OTSC approach, the AFC achieves permanent closure of the internal orifice through continuous clamping pressure, providing significant advantages for sphincter preservation. The AFC can achieve high cure rates for AFs without inducing fecal incontinence[27]. Compared with conventional sphincter-dividing procedures, clip-based sphincter-preserving approaches appear promising for selected complex fistulas, with acceptable healing and functional outcomes[28]. Clip-based sphincter-preserving strategies have also been explored in CD-associated fistulas within the broader framework of multidisciplinary management[29]. Recent reviews suggest that minimally invasive clip-based closure techniques are promising, although their indications and patient selection still require refinement[30]. Prospective comparisons further suggest that AFC may outperform endorectal advancement flap procedures in terms of symptom improvement and radiological healing.

In addition to clinical efficacy, AFC offers several practical advantages. As a minimally invasive technique, it can be repeated if necessary, without compromising sphincter integrity or complicating future surgical interventions. Reproducible operative steps can facilitate broader clinical adoption. These characteristics make AFC particularly attractive for the management of complex fistulas, including those associated with CD, for which the preservation of continence is paramount.

The present study has some limitations. First, the sample size was relatively small, and no formal power calculation was performed, which may have limited the ability to detect small but clinically meaningful differences. Second, the 6-month follow-up period may be insufficient to capture late fistula recurrence or long-term functional outcomes. Previous studies have suggested that recurrence may occur 1-2 years postoperatively. Although we did not observe recurrence in this study, this finding should be interpreted with caution. Third, unmeasured confounding factors may have influenced early pain outcomes despite the standardized postoperative analgesia across groups. Another important consideration is the learning curve associated with the AFC technique. While all procedures were performed by experienced surgeons, the learning process has not yet been systematically evaluated. As a critical determinant of adoption and generalizability, the learning curve may influence operative efficiency, complication rates, and clinical outcomes, particularly during early implementation. Future prospective multicenter studies with consecutive cases are warranted to systematically assess the AFC learning curve. Notably, key parameters including operative time, complication rates, and treatment success should be analyzed to define the number of cases required to achieve technical proficiency. Based on our clinical experience, approximately 8-12 cases may be needed to reach proficiency; however, this estimate requires validation in well-designed prospective studies. Future studies should evaluate AFC application across diverse fistula phenotypes, including high, branching, recurrent, and CD-associated fistulas. Identifying predictors of treatment success, such as fistula anatomy, baseline disease activity, and prior interventions, is essential for optimizing patient selection and refining surgical strategies.

CONCLUSION

In summary, compared with ITH, AFC was associated with favorable outcomes, including reduced early postoperative pain, shorter wound healing times, better preservation of anal function, and lower complication rates. These results suggest that AFC may be a safe, minimally invasive, and effective alternative for AF management, potentially improving postoperative recovery while preserving sphincter function. Nonetheless, larger, adequately powered studies with longer follow-up periods are needed to confirm these results and fully evaluate the long-term safety, durability, and efficacy of this approach.