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. 2021 May 8;25(7):761–830. doi: 10.1007/s10151-021-02452-5

Heterogeneity in outcome selection, definition and measurement in studies assessing the treatment of cryptoglandular anal fistula: findings from a systematic review

A J H M Machielsen 1,2,#, N Iqbal 3,4,✉,#, M L Kimman 5, K Sahnan 3,4, S O Adegbola 3,4, G Kane 6, R Woodcock 7, J Kleijnen 8, U Grossi 9, S O Breukink 10, P J Tozer 3,4
PMCID: PMC8187216  PMID: 33963945

Abstract

Background

Treatment for cryptoglandular anal fistula (AF) is challenging and a lack of uniform outcomes in the literature prevents direct comparison of treatments. This can be addressed by developing a core outcome set, a standardised set of outcomes reported in all interventional studies for a specific condition. The aim of this systematic review is to assess the range of outcomes, their definitions, and the measurement instruments currently utilised in interventional studies for adult patients with AF. This will inform the development of an AF core outcome set.

Methods

Medline, Embase and The Cochrane Library were searched to identify all patient- and clinician-reported outcomes in studies assessing medical, surgical or combination treatment of adult patients with AF published from January 2008 to May 2020. The resulting outcomes were categorized according to the Core Outcome Measurement in Effectiveness Trials (COMET) taxonomy to better understand their distribution.

Results

In total, 155 studies were included, 552 outcomes were extracted, with a median of three outcomes (interquartile range 2–5) per study. Only 25% of studies demonstrated high-quality outcome reporting. The outcomes were merged into 52 unique outcomes and structured into four core areas and 14 domains, with the majority in the domain of physiological or clinical (gastrointestinal) outcomes. The most commonly reported outcomes were healing (77%), incontinence (63%), and recurrence (40%), with no single outcome assessed across all studies. There was a wide variation in outcome definitions and measurement instruments used.

Conclusions

There is substantial heterogeneity in outcomes, definitions, and measurement instruments reported in interventional studies for cryptoglandular anal fistula. This emphasises the need for standardised outcome reporting and measurement.

Keywords: Cryptoglandular anal fistula, Systematic review, Outcome assessment, Core outcome set

Introduction

Cryptoglandular anal fistula (AF) is a challenging condition to manage. The symptom burden can be severe and can have wide-ranging impact on physical functioning and quality of life [1]. For clinicians, the difficulties of balancing treatment efficacy with minimal impairment of continence have been well documented [2, 3], particularly for complex and recurrent cases. In an attempt to address the dichotomy in achieving these key treatment aims, numerous sphincter-preserving procedures have been developed in recent decades. These procedures have now made their way into common clinical practice, leading to wide variation in the techniques used according to surgical expertise, preference, and geographical area [4]. Along with the expansion of procedures, numerous interventional studies have been conducted to assess success rates and determine treatment superiority. Attempts have been made to meta-analyse data from multiple studies, however, difficulties in doing so reliably are frequently reported, due to inadequate follow-up, lack of randomized controlled trials, and non-uniform reporting of outcomes [46]. This limits the development of treatment guidelines for AF.

The selection of relevant and appropriate outcomes is crucial to any study on treatment effectiveness [7], however, the lack of a systematic approach results in the reporting of numerous outcomes with varied definitions, multiple measurement instruments, and inconsistencies in the timing of assessment. Furthermore, selective reporting of outcomes based on significant results is a recognised problem and can overestimate the size of the treatment effect [8, 9]. Such outcome reporting bias can lead to ill-informed decisions with the potential to cause patient harm [10].

One way of addressing such issues is to develop a core outcome set (COS); an agreed, standardised set of outcomes to be measured in all interventional studies for a specific health condition [9]. The importance and value of a COS in disease areas with heterogeneity in outcome reporting is being increasingly recognised. However, a COS has not yet been developed for cryptoglandular AF. We believe that this is an important step in addressing the challenges in developing evidence-based management strategies.

According to the Core Outcome Measurement in Effectiveness Trials (COMET) initiative, the first stage in the development of a COS is to determine what to measure, which can be partially achieved by identifying potential outcomes from the existing literature [7]. The primary aim of this systematic review was to identify all patient- and clinician-reported outcomes in studies assessing medical, surgical or combination treatment of adult patients with cryptoglandular AF, to inform the development of a cryptoglandular Anal Fistula Core Outcome Set (AFCOS) [11]. The secondary aim is to assess outcome definitions and identify the measurement instruments used.

Materials and methods

A systematic review of studies assessing medical, surgical, and combined interventions for cryptoglandular AF was performed in accordance with a registered protocol (PROSPERO-ID CRD42018102778).

Search strategy

An electronic search strategy was developed by an information specialist prior to execution. The following electronic databases were searched, adjusting vocabulary and syntax for each: Medline (Ovid), Embase (Ovid), and The Cochrane Library. Validated terms for ‘Perianal Fistula’ were used, ensuring that all interventional studies for AF could be captured. If MeSH terms or subject headings existed, these were included in the search strategy and supplemented with free-text searches of the same databases. To avoid limiting the scope of outcomes identified, no study design filter was applied. The search was restricted to full-text articles in English published from January 2008 to May 2020 and to studies conducted in human subjects aged ≥ 18 years. The full search strategy can be found in Table 1.

Table 1.

Search strategy

Embase (Ovid)
 1 Anus fistula/
 2 Rectum fistula/
 3 ((Anus or anal or anorectal or rectal or rectum or perianal) adj4 fistul*).m_titl
 4 Fistula ani.m_titl
 5 Fistula-in-ano.m_titl
 6 1 or 2 or 3 or 4 or 5
 7 Limit 6 to (full text and human and year = “2008–current”)
The Cochrane library
 1 MeSH descriptor: (rectal fistula) this term only
 2 (Anus or anal or anorectal or rectal or rectum or perianal) near/4 (fistul*):ti
 3 Fistula ani:ti
 4 Fistula-in-ano:ti
 5 #1 or #2 or #3 or #4
Publication date from January 2008 to May 2020
Medline (Ovid)
 1 Rectal fistula/
 2 ((Anus or anal or anorectal or rectal or rectum or perianal) adj4 fistul*).m_titl
 3 Fistula ani.m_titl
 4 Fistula-in-ano.m_titl
 5 1 or 2 or 3 or 4
 6 Limit 5 to (full text and humans and year = “2008–current”)

Study selection

Four members of the study management group (AM, NI, KS, SA) identified and screened titles and abstracts using Covidence Systematic Review Software (Veritas Health Innovation, Melbourne, Australia, available at https://www.covidence.org/home), with each abstract and full-text publication screened by two independent group members. The following predefined selection criteria were used: (1) Prospective [including randomised controlled trials (RCTs), cohort comparisons, case controls and case series], retrospective, and observational studies including ≥ 10 patients and systematic reviews published between January 2008 and May 2020; (2) including ≥ 10 adult patients (aged ≥ 18 years) with cryptoglandular AF; (3) assessing medical, surgical, or combined interventions for cryptoglandular AF; (4) and reporting ≥ one outcome. Studies were excluded if they were abstract only or if they reported on interventions that were only assessed on fistulas that were not perianal or not of cryptoglandular origin. Systematic reviews were included and individual studies were checked for eligibility. Disagreements were resolved through discussion with recourse to the senior authors (PT, SB) if necessary.

Data extraction

Two members of the study management group (AM, NI) extracted data from eligible studies using a predefined data extraction sheet created in Microsoft Excel. Extracted data included study publication year, design, interventions, patients, outcomes (primary and secondary), outcome definitions and measurement instruments used. In keeping with COMET recommendations, all data were extracted verbatim [7]. The quality of describing and reporting outcomes was assessed using Harman’s criteria [12], which are presented in (Table 2). Disagreements were resolved through discussion with recourse to the senior authors (PT, SB) if necessary.

Table 2.

Overview of the included studies

First author Title Year of publication Study design Intervention(s) Number of participants Number of outcome(s) Primary outcome clearly stated? Primary outcome clearly defined? Secondary outcomes clearly stated? Secondary outcomes clearly defined? The use of the selected outcomes explained? Methods used to enhance the quality of outcome measurement?
A ba-bai-ke-re Randomized controlled trial of minimally invasive surgery using acellular dermal matrix for complex anorectal fistula 2010 RCT

ADM

ERAF

90 6 Yes Yes Yes Yes No Yes
Abcarian Ligation of intersphincteric fistula tract: early results of a pilot study 2012 Prospective study LIFT procedure 40 3 Yes No Yes No No No
Abdelnaby Drained mucosal advancement flap versus rerouting seton around the internal anal sphincter in treatment of high trans-sphincteric anal fistula: a randomized trial 2019 RCT

Advancement flap and drainage seton around EAS

Seton around IAS

97 6 Yes Yes Yes Yes No No
Aboulian Early result of ligation of the intersphincteric fistula tract for fistula-in-ano 2011 Retrospective review LIFT procedure 25 5 Yes No Yes No No No
Adams Long-term outlook after successful fibrin glue ablation of cryptoglandular transsphincteric fistula-in-ano 2008 Retrospective review Fibrin glue 36 2 Yes No Yes No No No
Adamina To plug or not to plug: a cost-effectiveness analysis for complex anal fistula 2010 Prospective study

AFP

ERAF

24 2 Yes Yes N/A N/A Yes No
Altomare Seton or glue for trans-sphincteric anal fistulae: a prospective randomized crossover clinical trial 2011 RCT

Fibrin glue

Seton

64 5 Yes No Yes Yes No No
Alvandipour Efficacy of 10% sucralfate ointment after anal fistulotomy: a prospective, double-blind, randomized, placebo-controlled trial 2016 RCT

Fistulotomy and 10% sucralfate

Fistulotomy and placebo

41 2 Yes Yes Yes Yes No No
Anan Fistulotomy with or without marsupialisation of wound edges in treatment of simple anal fistula: a randomised controlled trial 2019 RCT

Fistulotomy

Fistulotomy and marsupialization

60 5 Yes Yes Yes Yes No No
Arawatti Standardization and clinical evaluation of nimba ksharsutra in the management of bhagandar (fistula in ano) 2012 RCT

Seton

Seton

40 5 Yes Yes No N/A No No
Arroyo Photodynamic therapy for the treatment of complex anal fistula 2017 Prospective study Photodynamic therapy 10 4 Yes Yes Yes Yes No No
Arroyo Fistulotomy and sphincter reconstruction in the treatment of complex fistula-in-ano: long-term clinical and manometric results 2012 Prospective study FISR 70 2 Yes No Yes No No Yes
Atkin For many high anal fistulas, lay open is still a good option 2011 Retrospective review

EUA

Drainage of abscess

Fistulotomy (and marsupialization)

Seton

Fibrin glue

Advancement flap

Transperineal core-out and repair

Martius flap

Sphincter repair

Defunctioning stoma

Proctectomy and permanent colostomy

180 3 Yes No Yes No No No
Attaallah Should we consider topical silver nitrate irrigation as a definitive nonsurgical treatment for perianal fistula 2014 Prospective study Irrigation and 1% silver nitrate 56 3 Yes Yes Yes Yes No Yes
Bleier Ligation of the intersphincteric fistula tract: an effective new technique for complex fistulas 2010 Retrospective review LIFT procedure 39 3 Yes No Yes No No No
Boenicke Advancement flap for treatment of complex cryptoglandular anal fistula: prediction of therapy success or failure using anamnestic and clinical parameters 2017 Prospective study Advancement flap 61 2 Yes Yes Yes Yes No No
Bondi Randomized clinical trial comparing collagen plug and advancement flap for transsphincteric anal fistula 2017 RCT

AFP

Advancement flap

94 4 Yes Yes Yes Yes No Yes
Browder Modified Hanley procedure for management of complex horseshoe fistulae 2009 Retrospective review Modified Hanley procedure, drainage and setons 23 4 Yes No Yes No No No
Chalya Fistulectomy versus fistulotomy with marsupialisation in the treatment of low fistula-in-ano: a prospective randomized controlled trial 2013 RCT

Fistulectomy

Fistulotomy and marsupialization

162 9 Yes Yes Yes Yes No No
Chan Initial experience of treating anal fistula with the Surgisis anal fistula plug 2012 Prospective study AFP 44 2 Yes Yes Yes No No No
Chen High ligation of the fistula track by lateral approach: a modified sphincter-saving technique for advanced anal fistulas 2012 Prospective study Modified LIFT procedure 10 4 No N/A No N/A Yes No
Chowbey Minimally invasive anal fistula treatment (MAFT)—an appraisal of early results in 416 patients 2015 Prospective study MAFT 416 3 Yes No No N/A No No
Chung Anal fistula plug and fibrin glue versus conventional treatment in repair of complex anal fistulas 2009 Retrospective review

AFP

Fibrin glue

Advancement flap

Seton

232 1 Yes Yes N/A N/A No No
Choi Patient-performed seton irrigation for the treatment of deep horseshoe fistula 2010 Retrospective review

Seton

Seton

24 4 Yes Yes No N/A No No
Choi Autologous adipose tissue-derived stem cells for the treatment of complex perianal fistulas not associated with Crohn’s disease: a phase II clinical trial for safety and efficacy 2017 Prospective study ASC 15 5 Yes Yes Yes Yes No Yes
Christoforidis Treatment of complex anal fistulas with the collagen fistula plug 2008 Retrospective review AFP 47 1 Yes No N/A N/A No No
Christoforidis Treatment of transsphincteric anal fistulas by endorectal advancement flap or collagen fistula plug: a comparative study 2009 Retrospective review ERAFAFP 80 3 Yes Yes Yes Yes No No
Cintron Treatment of fistula-in-ano using a porcine small intestinal submucosa anal fistula plug 2013 Prospective study AFP 73 2 Yes Yes Yes Yes No No
Daodu Draining setons as definitive management of fistula-in-ano 2018 Retrospective study Seton 76 2 Yes Yes No N/A No No
De La Portilla Platelet-rich plasma (PRP) versus fibrin glue in cryptogenic fistula-in-ano: a phase III single-center, randomized, double-blind trial 2019 RCT

PRP

Fibrin glue

56 5 Yes Yes Yes No No Yes
De La Portilla Treatment of transsphincteric fistula-in-ano with growth factors from autologous platelets: results of a phase II clinical trial 2017 Prospective study PRGF 36 5 Yes Yes No N/A No No
De La Portilla Evaluation of a new synthetic plug in the treatment of anal fistulas: results of a pilot study 2011 Prospective study AFP 19 4 Yes No No N/A No No
Dubsky Endorectal advancement flaps in the treatment of high anal fistula of cryptoglandular origin: full thickness vs mucosal rectum flaps 2008 Retrospective review

Advancement flap

Advancement flap

54 2 No N/A No N/A No No
Dozois Early results of a phase I trial using an adipose-derived mesenchymal stem cell-coated fistula plug for the treatment of transsphincteric cryptoglandular fistulas 2019 Prospective study AFP 15 3 Yes No Yes Yes No Yes
Ege Hybrid seton for the treatment of high anal fistulas: results of 128 consecutive patients 2014 Retrospective review Seton 128 5 Yes No No N/A No No
Eitan The use of the loose seton technique as a definitive treatment for recurrent and persistent high trans-sphincteric anal fistulas: a long-term outcome 2009 Retrospective review Seton 41 3 Yes Yes No N/A No No
Ellis Outcomes with the use of bioprosthetic grafts to reinforce the ligation of the intersphincteric fistula tract (BioLIFT procedure) for the management of complex anal fistulas 2010 Retrospective review BioLIFT procedure 31 2 Yes Yes N/A N/A No No
Ellis Long-term outcomes with the use of bioprosthetic plugs for the management of complex anal fistulas 2010 Retrospective review AFP 63 1 Yes No No N/A No No
Fabiani Permacol collagen paste injection for the treatment of complex anal fistula: 1-year follow-up 2017 Prospective study Collagen paste injection 21 3 Yes No Yes No No No
Fung Operative strategy for fistula-in-ano without diversion of the anal sphincter 2013 Retrospective review Partial fistulotomy and seton 46 3 Yes Yes Yes Yes No Yes
Garcia-Arranz Autologous adipose-derived stem cells for the treatment of complex cryptoglandular perianal fistula: a randomized clinical trial with long-term follow-up 2020 RCT

ASC and fibrin glue

Fibrin glue

57 4 Yes Yes N/A N/A No Yes
Garcia-Olmo Expanded adipose-derived stem cells for the treatment of complex perianal fistula: a phase II clinical trial 2009 RCT Fibrin glueFibrin glue and ASC 49 4 Yes No No N/A No No
Garg PERFACT procedure (Proximal superficial cauterization, emptying regularly of fistula tracts and curettage of tracts): A new concept to treat highly complex anal fistula 2015 Prospective study PERFACT procedure 51 3 Yes No No N/A No No
Garg To determine the efficacy of anal fistula plug in the treatment of high fistula-in-ano: an initial experience 2009 Prospective study AFP 21 7 No N/A No N/A No No
Gautier Easy clip to treat anal fistula tracts: a word of caution 2015 Retrospective study Clip 17 10 Yes No No N/A No No
Giamundo Fistula-tract laser closure (FiLaC): long-term results and new operative strategies 2015 Retrospective study FiLaC 45 5 Yes Yes Yes Yes No No
Gottgens Ligation of the intersphincteric fistula tract for high transsphincteric fistula yields moderate results at best: is the tide turning? 2019 Retrospective study

LIFT

BioLIFT

46 5 Yes Yes Yes No No No
Gottgens Long-term results of mucosal advancement flap combined with platelet-rich plasma for high cryptoglandular perianal fistulas 2014 Retrospective study Advancement flap and platelet-rich plasma 25 2 Yes Yes Yes Yes No No
Grolich Role of video-assisted anal fistula treatment in our management of fistula-in-ano 2014 Retrospective review VAAFT 30 2 Yes No No N/A No No
Gupta Topical sucralfate treatment of anal fistulotomy wounds: a randomized placebo-controlled trial 2011 RCT

Fistulotomy and 7% sucralfate

Fistulotomy and placebo

80 3 Yes Yes Yes Yes No No
Haim Long-term results of fibrin glue treatment for cryptogenic perianal fistulas: a multicenter study 2011 Retrospective review Fibrin glue 23 3 Yes Yes Yes Yes No Yes
Hall Outcomes after operations for anal fistula: results of a prospective, multicenter, regional study 2014 Retrospective review

Fistulotomy

LIFT procedure

Seton

Advancement flap

AFP

240 2 Yes No No N/A No No
Hammond Management of idiopathic anal fistula using cross-linked collagen: a prospective phase 1 study 2011 Prospective study

Collagen paste injection

Fibrin glue

29 6 Yes Yes Yes Yes No No
Han Ligation of intersphincteric fistula tract vs ligation of the intersphincteric fistula tract plus a bioprosthetic anal fistula plug procedure in patients with transsphincteric anal fistula: early results of a multicenter prospective randomized trial 2016 RCT

LIFT procedure

LIPT-plug procedure

237 5 Yes Yes No N/A No No
Han Long-term outcomes of human acellular dermal matrix plug in closure of complex anal fistulas with a single tract 2011 Retrospective study ADM 114 2 Yes Yes No N/A No No
Han Ligation of the intersphincteric fistula tract plus bioprosthetic anal fistula plug (LIFT-Plug): a new technique for fistula-in-ano 2013 Prospective study LIFT-plug procedure 21 3 Yes Yes Yes Yes No No
Herold Results of the Gore Bio-a fistula plug implantation in the treatment of anal fistula: a multicentre study 2016 Prospective study AFP 60 6 Yes Yes Yes Yes No Yes
Herreros Autologous expanded adipose-derived stem cells for the treatment of complex cryptoglandular perianal fistulas: a phase III randomized clinical trial (FATT 1: fistula advanced therapy trial 1) and long-term evaluation 2012 RCT

ASC

ASC and fibrin glue

Fibrin glue

183 4 Yes Yes No N/A No No
Hirschburger Fistulectomy with primary sphincter reconstruction in the treatment of high transsphincteric anal fistulas 2014 Retrospective review FISR 50 4 No N/A No N/A No No
Han Ligation of the intersphincteric fistula tract plus a bioprosthetic anal fistula plug (LIFT‐plug): a new technique for fistula‐in‐ano 2013 Prospective study LIFT-plug procedure 46 5 No N/A Yes No No No
Heydari Bioabsorbable synthetic plug in the treatment of anal fistulas 2013 Retrospective review AFP 48 3 Yes No No N/A No No
Hyman Outcomes after fistulotomy: results of a prospective, multicenter regional study 2009 Prospective study

Fistulotomy

Seton

Fistulotomy

AFP

Fibrin glue

Advancement flap

245 3 Yes Yes Yes Yes No No
Jain Comparison of a fistulectomy and a fistulotomy with marsupialization in the management of a simple anal fistula: a randomized, controlled pilot trial 2012 RCT

Fistulectomy

Fistulotomy and marsupialization

40 9 Yes No No N/A No No
Jivapaisarnpong Core out fistulectomy, anal sphincter reconstruction and primary repair of internal opening in the treatment of complex anal fistula 2009 Prospective study FISR 33 4 No N/A No N/A No No
Jarrar Advancement flap repair: a good option for complex anorectal fistulas 2011 Retrospective study Advancement flap 98 3 Yes No Yes No No No
Jayne Anal fistula plug versus surgeon’s preference for surgery for transsphincteric anal fistula: the FIAT RCT 2019 RCT

AFP

Surgeon’s preference (fistulotomy, seton, advancement flap or LIFT)

304 6 Yes Yes Yes No Yes No
Jiang Video-assisted anal fistula treatment (VAAFT) for complex anal fistula: a preliminary evaluation in China 2017 Retrospective review VAAFT 52 4 Yes Yes No N/A No No
Kalim Comparison of mean healing time and mean pain scores between fistulectomy and fistulotomy for the treatment of low fistula in ano 2017 RCT

Fistulectomy

Fistulotomy

304 3 Yes No Yes No No No
Ky Collagen fistula plug for the treatment of anal fistulas 2008 Prospective study AFP 45 3 Yes Yes No N/A No No
Kelly The role of loose seton in the management of anal fistula: a multicenter study of 200 patients 2014 Retrospective review Seton 200 3 Yes No No N/A No No
Khafagy Treatment of anal fistulas by partial rectal wall advancement flap or mucosal advancement flap: a prospective randomized study 2010 Prospective study

Advancement flap

Advancement flap

40 5 Yes No No N/A No No
Kochhar Video-assisted anal fistula treatment 2014 Retrospective review VAAFT 82 5 Yes Yes Yes Yes No No
Lara Platelet-rich fibrin sealant as a treatment for complex perianal fistulas: a multicentre study 2015 Prospective study PRF 60 3 Yes Yes No N/A No Yes
Lawes Early experience with the bioabsorbable anal fistula plug 2008 Retrospective review AFP 20 2 Yes No No N/A No No
Leventoglu Treatment for horseshoe fistula with the modified Hanley procedure using a hybrid seton: results of 21 cases 2013 Prospective study Modified Hanley procedure 21 7 Yes No Yes No No Yes
Liu Long-term results of ligation of intersphincteric fistula tract (LIFT) for fistula-in-ano 2013 Retrospective review LIFT procedure 38 5 Yes Yes No N/A No No
Lupinacci Treatment of fistula-in-ano with the Surgisis AFP anal fistula plug 2010 Prospective study AFP 15 2 Yes Yes Yes Yes No No
Lo Ligation of intersphincteric fistula tract procedure for the management of cryptoglandular anal fistulas 2012 Prospective study LIFT procedure 25 5 Yes Yes No N/A No No
Lehman Efficacy of LIFT for recurrent anal fistula 2013 Prospective study LIFT procedure 17 2 No N/A No N/A Yes No
Lobo A comparative clinical study of Snuhi Ksheera Sutra, Tilanala Kshara Sutra and Apamarga Kshara Sutra in Bhagandara (fistula in ano) 2012 Prospective study

Seton

Seton

Seton

33 3 Yes Yes No N/A No No
Madbouly Ligation of intersphincteric fistula tract versus mucosal advancement flap in patients with high transsphincteric fistula-in-ano: a prospective randomized trial 2014 RCT

LIFT procedure

Advancement flap

70 6 Yes Yes Yes No No No
Malakorn Ligation of intersphincteric fistula tract for fistula in ano: lessons learned from a decade of experience 2017 Retrospective review LIFT procedure 251 1 Yes Yes N/A N/A No No
Mansour Medical interventional treatment of adult fistula-in-ano. A pilot study for curative response of intra-tract injections of Ceftazidine and Metronidazol 2016 RCT Ceftazidime and Metronidazole injection 25 2 No N/A No N/A No No
Mascagni OTSC proctology vs. fistulectomy and primary sphincter reconstruction as a treatment for low trans-sphincteric anal fistula in a randomized controlled pilot trial 2019 Retrospective study

Clip

Fistulectomy

30 3 No N/A No N/A No No
Mascagni Total fistulectomy, sphincteroplasty and closure of the residual cavity for transsphincteric perianal fistula in the elderly patient 2017 Retrospective review FISR 86 6 No N/A No N/A No No
McGee Tract length predicts successful closure with anal fistula plug in cryptoglandular fistulas 2010 Prospective study AFP 41 2 Yes No No N/A No No
Meinero Video-assisted anal fistula treatment: a novel sphincter-saving procedure for treating complex anal fistulas 2011 Retrospective review VAAFT 136 3 No N/A No N/A No No
Meinero Video-assisted anal fistula treatment: a new concept of treating anal fistulas 2014 Retrospective review VAAFT 203 5 No N/A No N/A No No
Mennigen The OTSC proctology clip system for the closure of refractory anal fistulas 2015 Retrospective review Clip 10 4 Yes Yes No N/A No No
Mishra The role of fibrin glue in the treatment of high and low fistulas in ano 2013 Prospective study Fibrin glue 30 4 No N/A No N/A No No
Mitalas Does rectal mucosal blood flow affect the outcome of transanal advancement flap repair? 2009 Prospective study Advancement flap 54 3 No N/A No N/A Yes No
Mushaya Ligation of intersphincteric fistula tract compared with advancement flap for complex anorectal fistulas requiring initial seton drainage 2012 RCT

LIFT procedure

Advancement flap

39 6 No N/A No N/A No Yes
Nazeer Better option for the patients of low fistula in ano: fistulectomy or fistulotomy 2012 RCT

Fistulotomy

Fistulectomy

150 5 No N/A No N/A No No
Nordholm-Carstensen Treatment of complex fistula-in-ano with nitinol proctology clip 2017 Retrospective review Clip 35 2 Yes Yes Yes Yes Yes No
Omar Drainage seton versus external anal sphincter-sparing seton after rerouting of the fistula tract in the treatment of complex anal fistula: a randomized controlled trial 2019 RCT

Seton

Rerouting of fistula tract and seton around internal anal sphincter

60 6 Yes Yes Yes Yes No No
Ommer Gore BioA fistula plug in the treatment of high anal fistulas - initial results from a German multicenter-study 2012 Retrospective review AFP 40 1 No N/A N/A N/A Yes No
Ortiz Randomized clinical trial of anal fistula plug versus endorectal advancement flap for the treatment of high cryptoglandular fistula in ano 2009 RCT

AFP

ERAF

32 2 Yes No Yes Yes Yes No
Ortiz Length of follow‐up after fistulotomy and fistulectomy associated with endorectal advancement flap repair for fistula in ano 2008 Prospective study

Fistulotomy

Fistulectomy and ERAF

206 2 No N/A No N/A No No
Owen Plugs unplugged. Anal fistula plug: the Concord experience 2010 Retrospective review AFP 32 1 Yes Yes N/A N/A No No
Ooi Managing fistula‐in‐ano with ligation of the intersphincteric fistula tract procedure: the Western Hospital experience 2012 Prospective study LIFT procedure 25 2 Yes Yes Yes Yes Yes No
Ozturk Treatment of recurrent anal fistula using an autologous cartilage plug: a pilot study 2015 Prospective study AFP 10 5 No N/A No N/A Yes No
Ozturk Laser ablation of fistula tract: a sphincter-preserving method for treating fistula-in-ano 2014 Retrospective review Laser ablation 37 1 Yes Yes N/A N/A Yes No
Prosst Short-term outcomes of a novel endoscopic clipping device for closure of the internal opening in 100 anorectal fistulas 2016 Retrospective review Clip 96 2 No N/A No N/A No No
Ratto Fistulotomy with end-to-end primary sphincteroplasty for anal fistula: results from a prospective study 2013 Prospective study FISR 72 2 No N/A No N/A No No
Roig Changes in anorectal morphologic and functional parameters after fistula-in-ano surgery 2009 Prospective study

Fistulotomy

FISR

Seton

Fistulectomy and advancement flap

120 4 No N/A No N/A Yes No
Roig Fistulectomy and sphincteric reconstruction for complex cryptoglandular fistulas 2010 Retrospective review

ERAF

FISR

146 7 No N/A No N/A No No
Safar Anal fistula plug: initial experience and outcomes 2009 Retrospective review AFP 35 1 No N/A No N/A Yes No
Sanad A randomized controlled trial on the effect of topical phenytoin 2% on wound healing after anal fistulotomy 2019 RCT

Fistulotomy and phenytoin

Fistulotomy

60 6 Yes Yes Yes Yes No No
Schulze Management of complex anorectal fistulas with seton drainage plus partial fistulotomy and subsequent ligation of intersphincteric fistula tract (LIFT) 2015 Prospective study

Seton

Fistulotomy and LIFT procedure

75 5 Yes Yes N/A N/A No No
Schwandner Surgical treatment of complex anal fistulas with the anal fistula plug: a prospective, multicenter study 2009 Prospective study AFP 60 4 No N/A No N/A No No
Schwandner Randomized clinical trial comparing a small intestinal submucosa anal fistula plug to advancement flap for the repair of complex anal fistulas 2018 RCT

AFP

Advancement flap

82 5 Yes Yes Yes Yes No No
Seneviratne Quality of life following surgery for recurrent fistula-in-ano 2009 Prospective study

Fistulotomy

Fistulectomy

Seton

21 1 No N/A No N/A No No
Seow-En An experience with video-assisted anal fistula treatment (VAAFT) with new insights into the treatment of anal fistulae 2016 Retrospective review VAAFT 41 3 Yes Yes N/A N/A Yes No
Shafik Combined partial fistulectomy and electro-cauterization of the intersphincteric tract as a sphincter-sparing treatment of complex anal fistula: clinical and functional outcome 2014 Prospective study Fistulectomy and electro-cauterization 53 4 No N/A No N/A No No
Shanwani Ligation of the intersphincteric fistula tract (LIFT): a sphincter-saving technique for fistula-in-ano 2010 Prospective study LIFT procedure 45 4 No N/A No N/A No No
Sileri Surgery of fistula-in-ano in a specialist colorectal unit: a critical appraisal 2011 Prospective study

Seton

Fistulotomy

LIFT procedure

Advancement flap

247 6 No N/A No N/A No No
Sileri Ligation of the intersphincteric fistula tract (LIFT) to treat anal fistula: early results from a prospective observational study 2011 Prospective study LIFT procedure 18 4 No N/A No N/A No No
Stamos Prospective multicenter study of a synthetic bioabsorbable anal fistula plug to treat cryptoglandular transsphincteric anal fistulas 2015 Prospective study AFP 93 5 No N/A No N/A No No
Stroumza Surgical treatment of transsphincteric anal fistulas with the Fat GRAFT technique: a minimally invasive procedure 2017 Prospective study Fat grafting 11 3 Yes Yes Yes No Yes No
Sugrue Sphincter-sparing anal fistula repair: are we getting better? 2017 Retrospective review

LIFT procedure

Fibrin glue

Advancement flap

AFP

Advancement flap and AFP

Advancement flap and advancement flap

462 1 Yes No N/A N/A Yes No
Shanwari Ligation of the intersphincteric fistula tract (LIFT): a sphincter-saving technique for fistula-in-ano 2010 Prospective study LIFT procedure 45 4 Yes Yes No N/A No Yes
Schwandner Initial experience on efficacy in closure of cryptoglandular and Crohn’s transsphincteric fistula by the use of the anal fistula plug 2008 Prospective study AFP 19 3 Yes Yes Yes Yes No No
Sirikurnpiboon Ligation of intersphincteric fistula tract and its modification: results from treatment of complex fistula 2013 Prospective study

LIFT procedure

LIFT procedure and fistulectomy

41 6 No N/A No N/A No No
Sungurtekin Loose seton: a misnomer of cutting seton 2016 Prospective study Seton 50 3 Yes Yes Yes Yes No No
Tan To LIFT or to flap? Which surgery to perform following seton insertion for high anal fistula? 2012 Retrospective review

ERAF

LIFT procedure

31 2 No N/A No N/A Yes No
Tan The anatomy of failures following the ligation of intersphincteric tract technique for anal fistula: a review of 93 patients over 4 years 2011 Retrospective review LIFT procedure 93 3 No N/A No N/A Yes No
Terzi Closing perianal fistulas using a laser: long-term results in 103 patients 2018 Retrospective review FiLaC 103 2 No N/A No N/A No No
Tobisch Total fistulectomy with simple closure of the internal opening in the management of complex cryptoglandular fistulas: long-term results and functional outcome 2012 Retrospective review Fistulectomy and closure of internal opening 252 2 No N/A No N/A Yes No
Tokunaga Clinical role of a modified seton technique for the treatment of trans-sphincteric and supra-sphincteric anal fistulas 2013 Retrospective review Seton 239 2 No N/A No N/A Yes Yes
Tozer Fistulotomy in the tertiary setting can achieve high rates of fistula cure with an acceptable risk of deterioration in continence 2013 Retrospective review Fistulotomy 50 3 No N/A No N/A No No
Tan Early experience of reinforcing the ligation of the intersphincteric fistula tract procedure with a bioprosthetic graft (BioLIFT) for anal fistula 2014 Retrospective study BioLIFT procedure 13 4 No N/A No N/A No No
Thekkinkattil Efficacy of the anal fistula plug in complex anorectal fistulae 2009 Prospective study AFP 43 2 Yes Yes No N/A No No
Tsunoda Anal function after ligation of the intersphincteric fistula tract 2013 Prospective study LIFT procedure and seton 20 3 No N/A No N/A Yes No
Van Koperen The anal fistula plug versus the mucosal advancement flap for the treatment of anorectal fistula (PLUG trial) 2008 RCT

AFP

Advancement flap

60 4 No N/A No N/A Yes No
Van Koperen Fibrin glue and transanal rectal advancement flap for high transsphincteric perianal fistulas; is there any advantage? 2008 Retrospective study Fibrin glue and advancement flap 80 2 Yes Yes Yes No Yes No
Van Koperen The anal fistula plug treatment compared with the mucosal advancement flap for cryptoglandular high transsphincteric perianal fistula: a double-blinded multicenter randomized trial 2011 RCT

AFP

Advancement flap

60 5 No N/A No N/A No No
Van Koperen Long-term functional outcome and risk factors for recurrence after surgical treatment for low and high perianal fistulas of cryptoglandular origin 2008 Retrospective review

Fistulotomy

Advancement flap

179 3 No N/A No N/A No No
Van Onkelen Treatment of anal fistulas with high intersphincteric extension 2013 Retrospective review Advancement flap and drainage of abscess 14 3 No N/A No N/A Yes No
Van Onkelen Is it possible to improve the outcome of transanal advancement flap repair for high transsphincteric fistulas by additional ligation of the intersphincteric fistula tract? 2012 Prospective study LIFT procedure and advancement flap 41 2 No N/A No N/A Yes No
Van Onkelen Ligation of the intersphincteric fistula tract in low transsphincteric fistula: a new technique to avoid fistulotomy 2013 Retrospective study LIFT procedure 22 2 Yes Yes No N/A No No
Van Onkelen Predictors of outcome after transanal advancement flap repair for high transsphincteric fistulas 2014 Retrospective review Advancement flap 252 2 No N/A No N/A Yes No
Visscher Long-term follow-up after surgery for simple and complex cryptoglandular fistulas: fecal incontinence and impact on quality of life 2015 Retrospective study

Fistulotomy

Sphincter-preserving procedures

116 2 No N/A No N/A Yes Yes
Walega VAAFT: a new minimally invasive method in the diagnostics and treatment of anal fistulas-initial results 2014 Prospective study VAAFT 18 5 No N/A No N/A No No
Wallin Does ligation of the intersphincteric fistula tract raise the bar in fistula surgery? 2012 Retrospective review LIFT procedure 93 4 No N/A No N/A No No
Wang Traditional Chinese surgical treatment for anal fistulae with secondary tracks and abscess 2012 RCT

Suture dragging and pad compression

Fistulotomy

60 6 Yes No Yes No No No
Wang Management of low transsphincteric anal fistula with serial setons and interval muscle-cutting fistulotomy 2016 Retrospective study

Seton

Fistulotomy

26 2 Yes Yes N/A N/A No No
Wang Treatment of transsphincteric anal fistulas: are fistula plugs an acceptable alternative? 2009 Retrospective study

AFP

Advancement flap

55 1 No N/A No N/A No No
Wilhelm A new technique for sphincter-preserving anal fistula repair using a novel radial emitting laser probe 2011 Retrospective study FiLaC 11 2 Yes Yes Yes Yes Yes No
Wilhelm Five years of experience with the FiLaC laser for fistula-in-ano management: long-term follow-up from a single institution 2017 Prospective study FiLaC 117 2 No N/A No N/A Yes No
Yan Clinical effect of tunnel-like fistulectomy plus draining seton combined with incision of internal opening of anal fistula (TFSIA) in the treatment of high-transsphincteric anal fistula 2020 RCT

TFSIA

Seton

80 7 No N/A No N/A No No
Ye Early experience with the modificated approach of ligation of the intersphincteric fistula tract for high transsphincteric fistula 2015 Retrospective review Modified LIFT procedure 43 3 Yes Yes Yes Yes Yes No
Yuan Clinical study on herbal fumigation of detumescence and pain relieving shengji decoction in wound repair after anal fistula surgery 2017 RCT

Shengji decoction

Potassium permanganate

90 6 No N/A No N/A No No
Zarin VAAFT: video-assisted anal fistula treatment: bringing revolution in fistula treatment 2015 Prospective study VAAFT 40 3 Yes Yes N/A N/A Yes No
Zubaidi Anal fistula plug in high fistula-in-ano: an early Saudi experience 2009 Prospective study AFP 22 1 Yes No No N/A No No
Zwiep Comparison of ligation of the intersphincteric fistula tract and BioLIFT for the treatment of transsphincteric anal fistula: a retrospective analysis 2020 Retrospective review

LIFT

BioLIFT

119 4 Yes Yes Yes Yes No No
Total 11,819 patients 552 outcomes 65.8% 67.6% 39.7% 64.3% 20.0% 11.0%
Adegbola Short-term efficacy and safety of three novel sphincter-sparing techniques for anal fistulae: a systematic review 2017 Systematic review
Alasari Overview of anal fistula and systematic review of ligation of the intersphincteric fistula tract (LIFT) 2014 Systematic review
Cirocchi The treatment of anal fistulas with biologically derived products: is innovation better than conventional surgical treatment? An update 2013 Systematic review
Cirocchi Meta-analysis of fibrin glue versus surgery for treatment of fistula-in-ano 2010 Systematic review
Garg The efficacy of anal fistula plug in fistula-in-ano: a systematic review 2010 Systematic review
Hong Ligation of intersphincteric fistula tract (LIFT) to treat anal fistula: systematic review and meta-analysis 2014 Systematic review
Jacob Surgical intervention for anorectal fistula 2010 Systematic review
Malik Incision and drainage of perianal abscess with or without treatment of anal fistula 2010 Systematic review
O’Riordan A systematic review of the anal fistula plug for patients with Crohn’s and non-Crohn’s related fistula-in-ano 2012 Systematic review
Pu Fistula plug versus conventional surgical treatment for anal fistulas: a systematic review and meta-analysis 2012 Systematic review
Ratto Fistulotomy or fistulectomy and primary sphincteroplasty for anal fistula (FIPS): a systematic review 2015 Systematic review
Ritchie Incontinence rates after cutting seton treatment for anal fistula 2009 Systematic review
Sirany The ligation of the intersphincteric fistula tract procedure for anal fistula: a mixed bag of results 2015 Systematic review
Soltani Endorectal advancement flap for cryptoglandular or Crohn’s fistula-in-ano 2010 Systematic review
Vial Faecal incontinence after seton treatment for anal fistulae with and without surgical division of internal anal sphincter: a systematic review 2010 Systematic review

RCT randomized controlled trial, ADM acellular dermal matrix, ERAF endorectal advancement flap, LIFT  ligation of intersphincteric fistula tract, EAS external anal sphincter, IAS internal anal sphincter, AFP anal fistula plug, FISR fistulectomy/fistulotomy and immediate sphincter reconstruction, EUA examination under anaesthetic, MAFT minimally invasive anal fistula treatment, ASC adipose-derived stem cells, PRP platelet-rich plasma, PRGF plasma-rich growth factor, PERFACT proximal superficial cauterization, emptying regularly fistula tracts and curettage of tracts, FiLaC fistula laser closure, VAAFT video-assisted anal fistula treatment, PRF platelet-rich fibrin, TFSIA tunnel-like fistulectomy plus draining seton combined with incision of internal opening of anal fistula

Data synthesis

Outcome categorisation

The resulting list of outcomes was reviewed by the study management group, including patient representatives (AM, NI, GK, RW, HG, MK, UG, PT, SB) to enable those with similar wording or meaning to be reduced to a single outcome. These were then mapped according to the COMET taxonomy developed for outcomes in medical research [13]. In this taxonomy, the measurable aspects of health conditions can be structured into five core areas, namely death, physiological or clinical, life impact, resource use, and adverse events, and further subdivided into 38 domains.

Data analysis

Primary, secondary, and overall outcome reporting were analysed. Results were summarized using frequencies and percentages. The frequency of outcome domain reporting was calculated. The interventions studied, number of outcome definitions and measurement instruments used were collated and analysed.

Results

Search strategy and study selection

The electronic databases Medline (Ovid), Embase (Ovid), and The Cochrane Library were searched in May 2018, followed by an updated search in May 2020, identifying a total of 2583 records. A schematic overview of the inclusion and exclusion of articles, including reasons provided for exclusion, is presented in Fig. 1. Full-text screening resulted in the inclusion of 143 articles, including 15 systematic reviews. The systematic reviews were individually screened for any additional studies that were not captured by the initial search and this yielded 27 articles, resulting in a final number of 155 articles from which data were extracted.

Fig. 1.

Fig. 1

Preferred reporting items for systematic reviews and meta-analyses flow chart of study selection

Study characteristics

An overview of the 155 included studies is presented in Table 2. Interventions for cryptoglandular AF were assessed on a total of 11,819 patients (mean 76, range 10–462 participants per study). The majority of studies were prospective studies (52%) and assessed the effectiveness of sphincter-preserving procedures, of which fistula plugs (19%) and ligation of intersphincteric fistula tract (LIFT) procedures (19%) were assessed most frequently. The characteristics of the included studies are presented in Table 3. The quality of outcome reporting for each individual study was assessed using Harman’s criteria [12] and reported in Table 2. The criteria involve assessing whether: (1) The primary outcome for a study is clearly stated, (2) The primary outcome is clearly defined so that other researchers can reproduce its measurement, (3) The secondary outcomes are clearly stated, (4) The secondary outcomes are clearly defined, (5) The authors explain the use of the outcomes they have selected and (6) Any methods were used to enhance the quality of outcome measurement. The average number of criteria met across all studies was two, with only 38 of 155 studies (25%) meeting ≥ four criteria, indicating high-quality outcome reporting in just a quarter of the studies assessed.

Table 3.

Study characteristics

n (%)
Total included 155 (100)
Study types contributing to data synthesis
 Retrospective studies 66 (43)

 Prospective studies

(RCT)

89 (57)

30 (19)

Publication year
 2008–2010 40 (25)
 2011–2013 50 (32)
 2014–2016 35 (23)
 2017–2019 27 (17)
 2020 3 (2)
Intervention(s) Control(s) n (%)
AFP

No control

Advancement flap

ERAF

Fistulotomy or cutting seton or advancement flap or LIFT

30 (19)

LIFT

LIFT-plug

BioLIFT

Modified LIFT

LIFT and seton

LIFT and advancement flap

LIFT and fistulectomy

No control

LIFT-plug

Advancement flap

LIFT and fistulectomy

BioLIFT

29 (19)
Seton

No control

Seton(s)

Fistulotomy

Fistulotomy and LIFT

Rerouting of fistula tract and seton around internal anal sphincter

12 (8)

Fistulotomy

Fistulotomy and sucralfate

Partial fistulotomy and seton

Fistulotomy and phenytoin

No control

Advancement flap

Fistulectomy

Fistulotomy and placebo sucralfate

Fistulectomy and ERAF

Fistulectomy and seton

Fistulotomy and marsupialization

Fistulotomy

10 (7)

Advancement flap

Advancement flap and platelet-rich plasma

Advancement flap and drainage of abscess

Advancement flap and drainage seton around external anal sphincter

No control

Advancement flap

Seton around internal anal sphincter

9 (6)
VAAFT No control 8 (5)

Fibrin glue

Fibrin glue and advancement flap

No control

Seton

Fibrin glue and ASC

6 (4)

Fistulectomy

Fistulectomy and electro-cauterization

Fistulectomy and closure of internal fistula opening

TFSIA

No control

Fistulotomy

Fistulotomy and marsupialization

Seton

6 (4)
FISR No control 5 (3)
FiLaC or laser ablation No control 5 (3)
Clip

No control

Fistulectomy

5 (3)
ERAF

AFP

LIFT

FISR

3 (2)

ASC

ASC and fibrin glue

No control

ASC, fibrin glue, and fibrin glue

Fibrin glue

3 (2)
ADM

No control

ERAF

2 (1)

Modified Hanley

Modified Hanley, drainage, and setons

No control 2 (1)
Collagen paste injection

No control

Fibrin glue

2 (1)
PRGF No control 1 (1)
PERFACT procedure No control 1 (1)
PRF No control 1 (1)
MAFT No control 1 (1)
Irrigation and silver nitrate No control 1 (1)
PRP Fibrin glue 1 (1)
 ≥ 4 interventions compared 7 (5)
Other 5 (3)
Total 155 (100)

AFP anal fistula plug, ERAF endorectal advancement flap, LIFT ligation of intersphincteric fistula tract, VAAFT video-assisted anal fistula treatment, ASC adipose-derived stem cells, TFSIA tunnel-like fistulectomy plus draining seton combined with incision of internal opening of anal fistula, FISR fistulectomy/fistulotomy and immediate sphincter reconstruction, FiLaC fistula laser closure, ADM acellular dermal matrix, PRGF plasma-rich growth factor, PERFACT proximal superficial cauterization, emptying regularly fistula tracts and curettage of tracts, PRF platelet-rich fibrin, MAFT minimally invasive anal fistula treatment, PRP platelet-rich plasma

Study outcomes

In total, 552 patient- and clinician-reported outcomes were extracted from 155 studies, with studies reporting a median of three outcomes (interquartile range 2–5) per study. Duplicate and analogous terms were merged to form 52 outcomes, of which healing (77%), incontinence (63%), recurrence (40%), and pain (26%) were reported most frequently (Table 4). Outcomes such as healing and recurrence were sometimes measured at different time points within the same study but referred to as primary or secondary outcomes. This resulted in some studies reporting outcomes of healing and recurrence more than once.

Table 4.

Frequency of outcome reporting

Outcome Reported as primary outcome (n) Reported as secondary outcome (n) Unstated (n) Number of studies reporting outcome (n) (%)
Healing 80 12 38 120 (77)
Incontinence 24 35 39 98 (63)
Recurrence 16 21 27 62 (40)
Pain 12 16 12 40 (26)
Complications 15 10 11 36 (23)
Closure time 13 3 9 25 (16)
Treatment failure 4 4 14 22 (14)
Quality of life 6 12 4 22 (14)
Duration of treatment 4 7 1 12 (8)
Morbidity 1 3 7 11 (7)
Return to work 2 2 3 7 (5)
Patient satisfaction 2 2 3 7 (5)
Anorectal manometry 0 0 6 6 (4)
Pus discharge 2 3 0 5 (3)
Hospital stay 1 2 2 5 (3)
Adverse effects 2 3 0 5 (3)
Fistula persistence 3 1 0 4 (3)
Reinterventions 0 1 3 4 (3)
Safety 1 3 0 4 (3)
Plug dislodgement rates 1 2 0 3 (2)
Symptoms 3 0 0 3 (2)
Unit cutting time 2 0 0 2 (1)
Size of operative wound 0 2 0 2 (1)
Postoperative perineal sepsis 1 0 1 2 (1)
Postoperative bleeding 0 0 2 2 (1)
Cost-effectiveness 1 1 0 2 (1)
Difficulty of technique 2 0 0 2 (1)
Impact on daily life 0 2 0 2 (1)
Endoanal ultrasound 0 0 2 2 (1)
Radiological healing 0 1 0 1 (1)
Anorectal deformity rate 0 1 0 1 (1)
Burning sensation 0 1 0 1 (1)
Itching 0 1 0 1 (1)
Length of time until seton removal 0 1 0 1 (1)
Fraction of patients showing ≥ 50% decrease in fistula size 0 1 0 1 (1)
Investigator’s satisfaction score 0 1 0 1 (1)
Amount of mucosal covering 0 1 0 1 (1)
Asymptomatic 1 0 0 1 (1)
Subjective parameters 0 1 0 1 (1)
Glue reaction 0 0 1 1 (1)
Median mucosal blood flow 0 0 1 1 (1)
Problems related to sexual function 0 0 1 1 (1)
Pudendal nerve terminal motor latency 0 0 1 1 (1)
Duration for return to normal activity 1 0 0 1 (1)
Duration of immobilisation 1 0 0 1 (1)
Emerging of a secondary abscess 1 0 0 1 (1)
Need for a new wave of drainage 1 0 0 1 (1)
Removal or migration of the clip 1 0 0 1 (1)
Perianal incision wound healing 1 0 0 1 (1)
Analgesic requirement 0 0 1 1 (1)
Keyhole like anomaly 0 0 1 1 (1)
Conversion into intersphincteric perianal fistula 0 1 0 1 (1)

Outcome categorisation

The outcomes were categorized into core areas and domains according to the COMET taxonomy, with guidance from a member of COMET. The frequency of these outcomes and their categorisation is shown in Table 5. Adverse event outcomes are categorised under their appropriate taxonomy and identified as a harm outcome [13]. Cryptoglandular AF treatment rarely impacts lifespan, therefore the core area death was excluded from categorisation. Some outcomes were categorised in multiple domains, as the study management group considered their impact to be broad. For instance, ‘problems related to sexual function’ was included in the domains physical, social and emotional functioning and well-being. Outcomes belonging to the core area of ‘physiological or clinical’ were placed in domains according to their underlying cause or affected body system [13]. Whilst categorisation highlighted the spread of outcomes across all relevant domains, the majority focused on the physiological or clinical impact, particularly in the domain of gastrointestinal outcomes (99%), whereas only 12% of outcomes were related to the impact on physical, role and social functioning and emotional functioning and wellbeing (Table 5).

Table 5.

Outcome categorisation and frequency of outcome reporting according to the COMET taxonomy

Core area Domain Outcomes No. studies reporting outcomes (%)
Physiological or clinical Gastrointestinal outcomes Healing 154 (99)
Incontinence (harm)
Recurrence (harm)
Pain
Treatment failure (harm)
Closure time
Pus discharge
Anorectal manometry
Fistula persistence (harm)
Plug dislodgement rates (harm)
Unit cutting time
Symptoms
Radiological healing
Anorectal deformity rate (harm)
Burning sensation
Itching
Fraction of patients showing ≥ 50% decrease in fistula size
Amount of mucosal covering
Asymptomatic
Subjective parameters
Glue reaction (harm)
Endoanal ultrasound
Pudendal nerve terminal motor latency
Removal or migration of the clip (harm)
Perianal incision wound healing
Conversion into intersphincteric fistula (harm)
Keyhole like anomaly (harm)
General outcomes Morbidity (harm) 11 (7)
Infection and infestation outcomes Postoperative perineal sepsis (harm) 3 (2)
Emerging of a secondary abscess (harm)
Vascular outcomes Median mucosal blood flow 2 (1)
Postoperative bleeding (harm)
Life impact Physical functioning Problems related to sexual functioning 5 (3)
Duration for return to normal activity
Duration of immobilisation
Impact daily life
Social functioning Problems related to sexual functioning 3 (2)
Impact daily life
Role functioning Return to work 8 (5)
Impact daily life
Emotional functioning or well-being Problems related to sexual functioning 3 (2)
Impact daily life
Global quality of life Quality of life 22 (14)
Delivery of care Treatment failure 32 (22)
Duration of treatment
Patient satisfaction
Size of operative wound
Length of time until seton removal
Investigator’s satisfaction score
Difficulty of technique
Resource use Economic Cost-effectiveness 2 (1)
Hospital Hospital stay 5 (3)
Need for further intervention Reinterventions 6 (4)
Need for a new wave of drainage
Analgesic requirement
Adverse events Adverse events and/or effects Complications 44 (28)
Adverse effects
Safety

Outcome definitions

Significant heterogeneity in outcome definition and overlap between definitions was noted in the outcomes of ‘healing’, ‘recurrence’, and ‘treatment failure’.

Healing

Healing was reported in 120 studies (77%) and was synonymous with terms such as ‘healing rate’, ‘fistula closure’, ‘success’, ‘cure’, ‘effectiveness’, and ‘complete clinical response’. There was considerable heterogeneity in the definitions of healing, however, overlap between the components of each definition meant that all could be defined by using one or more of the components presented in Table 6. Considering the ways in which components could be combined, 34 different definitions were found. Healing was most frequently defined as ‘healing of the external fistula opening and absence of symptoms’ (n = 16). In nine studies, a radiological assessment was needed to confirm or refute healing [1422], whereas another study identified ‘radiological healing’ as a separate outcome [23]. Five of these 10 studies included the radiological description required to demonstrate healing [14, 15, 18, 21, 22]. In 21 studies, the definition of healing was dependent upon a time period after which the fistula should be assessed, or for the duration of which the components of healing should be present, which in themselves demonstrated significant variation, ranging from 2 weeks [24] to 12 months [16, 25] after the procedure.

Table 6.

Components used, in varying combinations, to define the outcome ‘healing’

Component Times used
Absence of symptoms 70
Closure of the external fistula opening 61
Absence of abscess or infection or inflammation or sepsis 27
Closure of the (surgical) wound 24
Closure of the internal fistula opening 15
Closure of the fistula tract 14
No additional intervention required 8
Absence of recurrence or persistence or treatment failure 8
Absence of anal sphincter injury 1

Recurrence, treatment failure and persistence

The terms recurrence, treatment failure, and persistence were used interchangeably to describe a spectrum of clinical manifestations, ranging from no evidence of closure or persistence of fistula and symptoms [2629], to temporary closure followed by re-appearance of the original fistula [26], to the development of additional fistulas [20, 3032]. Similar to healing, the definitions were broken down into components which are presented in Table 7. The most frequently used definitions were ‘persistence or recurrence of symptoms’ (n = 21), followed by ‘persistence or reappearance of the external fistula opening’ (n = 13). There were 19 different definitions of recurrence and treatment failure. In 10 studies, the definition was qualified by a time period at or after which the fistula had to be assessed, ranging from within the first month [20] to 12 months after treatment [33].

Table 7.

Components used, in varying combinations, to define the outcomes ‘recurrence’ and ‘treatment failure’

Component Times used
Persistence or recurrence of symptoms 21
Reappearance of the fistula after healing 16
Persistence or reappearance of the external fistula opening 13
Absence of wound healing 8
Abscess or infection 6
Absence of fistula closure or persistence 6
Non-healing fistula 3
Additional intervention required 3
Additional fistula 2

Outcome measurement instruments

Heterogeneity was noted amongst the measurement instruments used for the most frequently reported outcomes (Table 8). Combinations of measurement instruments were frequently used. Furthermore, the instruments for each outcome were not always clearly stated and many studies used unspecified questionnaires.

Table 8.

Measurement instruments used, in varying combinations, to assess the most frequently reported outcomes

Outcome Instruments (used in various combinations) Times used
Healing Clinical examination, including digital rectal examination 88
(Telephone) interview 16
MRI 9
(3D) endoanal ultrasound 7
Medical record review 7
Anoscopy or proctoscopy or rectoscopy 7
(Un)specified questionnaire 6
Digital photograph of the external fistula opening 2
Transanal ultrasound 1
Examination under anaesthetic 1
Anal endosonography 1
Incontinence/sphincter function Wexner Cleveland Clinic Florida incontinence score 48
Patient-reported 9
Vaizey incontinence score 9
Fecal Incontinence Quality of Life Scale 6
(Un)specified questionnaire 5
Anorectal manometry 5
Endoanal ultrasound 4
Specified grading system 3
Clinical examination, including digital rectal examination 3
Colorectal functional outcome questionnaire 3
(Telephone) interview 3
Medical record review 2
German Society of Coloproctology score 1
Williams grade 1
Fecal Incontinence Severity Index 1

Recurrence

Treatment failure

Clinical examination 43
(Telephone) interview 7
MRI 6
Medical record review 6
(Un)specified questionnaire 3
Endorectal ultrasound 2
Anoscopy or proctoscopy 2
3D endoanal ultrasound 1
Anal endosonography 1
Patient-reported 1
Quality of life Fecal Incontinence Quality of Life Scale 6
Short Form-36 health survey (SF-36) 6
EQ-5D 4
Short Form-12 health survey (SF-12) 2
Cleveland global quality of life 2
Gastrointestinal Quality of Life Index 2
(Un)specified questionnaire 2
Quality of Life Scale 1
Visual Analogue Scale (VAS) 1
Fecal Incontinence Severity Index 1
Pain VAS 31
Patient-reported 2
Specified grading system 1
Medical record review 1
Number of analgesics used 1

MRI magnetic resinance imaging, VAS Visual Analogue Scale, EQ-5D EuroQol five-dimensions questionnaire

Discussion

This systematic review is the first study to provide an overview of the outcomes reported in interventional studies for AF. We identified 552 outcomes from 155 studies published in the last 12 years, which were merged into 52 unique outcomes, of which healing was reported most frequently (77%). Our results demonstrate heterogeneity in outcome definition and measurement, making the use of such studies to supplement current understanding of fistula management and guide treatment pathways much more challenging.

The lack of consistency and clarity in definitions of success, treatment failure, and recurrence after fistula treatment has been previously noted [34]. Despite being one of the most frequently reported outcomes, healing was variably defined in terms of anatomical features, absence of a specific set of symptoms or healing of the (surgical) wound. This highlights the difficulty of data synthesis across different studies, particularly when a fistula has healed in one study simply by closure of the external fistula opening [35], but would be considered persistent in another, where both the external and internal fistula openings, and an absence of symptoms are required [36]. The addition of radiological healing provides additional complexity, as it is well documented that deep tissue healing of perianal fistula as assessed on magnetic resonance imaging lags behind clinical healing by a period of months [3739]. Nevertheless, radiological outcomes and objective measures of the disease have been frequently used in studies of AF, and their potential inclusion in a COS warrants further discussion and involvement of radiological expertise.

The various definitions of recurrence, persistence, and treatment failure demonstrated overlap, however, in line with previous suggestions [34], we determined that treatment failure and persistence of the fistula, i.e. no change in the morphology and symptomatology of the original fistula, should be differentiated from fistula recurrence, which describes reappearance of the fistula after a period of resolution, and that development of new fistulas should be considered separately. However, persistence and recurrence of fistulas could simply be the same problem viewed at different time points, and from a patient’s perspective 1 year after the intervention, the difference is probably minimal. This would be an interesting area to explore during the generation of the COS.

The quality of studies eligible for data extraction was assessed using Harman’s criteria [12], however, only a quarter of the studies demonstrated high-quality outcome reporting using this method. Whilst the majority of studies clearly stated their measured outcomes, few went as far as defining whether the outcomes were primary or secondary. Only 20% of the studies explained their reasoning for selecting their outcomes. This may be due to the fact that healing, incontinence, and recurrence, the most commonly reported outcomes, require little explanation for their selection to fistula surgeons or patients, as the ultimate aim of any fistula treatment is frequently cited as healing with minimal impact on continence, and minimal risk of recurrence.

The outcomes summarised in this systematic review were categorised according to the COMET taxonomy. Although all relevant domains are represented, the vast majority of outcomes are related to the pathophysiology of disease and treatment. Only 10% of the outcomes reported by all studies in the last 12 years were related to the impact of disease in terms of its influence on patients’ physical, social and role functioning, in other words their quality of life. Whilst the inclusion of outcomes such as these is encouraging and should be recognised, their use is infrequent and gives a narrow reflection of the wide-ranging impact that fistula symptoms or treatments have for patients. For example, whilst the impact on sexual functioning has been recognised, the wider effects on personal and social relationships have not been recorded, as well as the influence of symptoms on non-work-related activities. Whilst the pathophysiological aspects of the disease are inevitably interrelated with life impact and use of resources, focusing only on the physical symptoms fails to address adequately the wider impact of living with AF. Earlier studies have identified that patients and surgeons allocate importance to different aspects of quality of life associated with anal fistula and its treatment. Surgeons rated continence, leakage, pain, cure and sepsis, whereas patients identified independent activity, good health, pain, continence, psychological health and leakage as their most important aspects of quality of life [40]. We are currently conducting further qualitative work to explore patients’ experiences of disease further, and patient involvement in deciding the final COS and how these outcomes should be prioritised is crucial to ensure that the COS remains representative of all stakeholders [7] and centred around relevance to patients.

The current study reported the range of outcome measurement instruments used for the most frequently reported outcomes. Validated measures were largely used for outcomes such as incontinence and quality of life, allowing the benefit of comparison across studies, as well as with other chronic health conditions [41]. However, the broad range of validated measures across studies for AF makes it difficult to compare these specific outcomes across interventions. This supports the need for a systematic method of selecting appropriate Outcome Measurement Instruments (OMIs) once the final COS is established [7, 42]. Furthermore, most measurement instruments of quality of life were generic. Disease-specific measures are known to be more sensitive to change and can directly detect the specific concerns of particular clinical groups, which may be underrepresented in generic measurement instruments [43]. Planned qualitative work will help to determine whether the concerns of patients with AF are adequately addressed by these instruments, or whether the development of a disease-specific Patient-Reported Outcome Measure (PROM) is needed.

The strength of this systematic review is that with the range of studies reviewed, it is well placed to inform a long list of items for the development of a COS. However, it is limited by the lack of outcomes related to the quality of life, suggesting that the additional qualitative feedback from patients required by COMET to supplement this longlist is crucial. Although it is possible that not all relevant studies have been captured due to the eligibility criteria used, the sheer number of outcomes extracted from the included studies make it likely that saturation has been reached and that any additional outcomes would be procedure specific, and, therefore, not eligible for a generic COS representing a minimum set of outcomes to be adopted by all studies, regardless of intervention used. A further limitation is the English language inclusion criterion, although no abstracts or full texts were excluded based on the language criterion alone, rather they studied the wrong population or were review articles or commentaries. The lack of non-English papers may limit the generalisability of these findings across cultural and ethnic groups. This may be effectively countered through the subsequent longlisting and consensus processes, which will include a broad ethnic and cultural diversity.

Conclusions

This systematic review highlights the need for consensus amongst researchers and clinicians regarding the outcomes that are essential in determining successful fistula treatment, and how they should be defined and measured. The underrepresentation of outcomes relating to the quality of life needs to be challenged, and qualitative exploration of the patient experience, as well as active engagement of patients in determining a COS are crucial.

Funding

NI is supported by a Royal College of Surgeons of England Research Fellowship.

Data availability

Registered protocol is available on Prospero (CRD42018102778).

Code availability

Not applicable.

Declarations

Conflict of interest

The authors have no relevant financial or non-financial interests to disclose.

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

A. J. H. M. Machielsen and N. Iqbal should be considered joint first author.

Contributor Information

A. J. H. M. Machielsen, Email: ajhmmachielsen@gmail.com

N. Iqbal, Email: niqbal@doctors.org.uk

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

Registered protocol is available on Prospero (CRD42018102778).

Not applicable.


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