The goal of this pilot clinical study is to learn whether radiofrequency ablation (RFA) can safely and effectively treat perianal fistulas in adults. It will also evaluate procedure-related safety and changes in symptoms over time. The main questions it aims to answer are:

• How many participants achieve fistula closure by 6 months after RFA treatment?
• How often do fistulas recur during follow-up?
• What medical problems or adverse events occur after the RFA procedure (for example, pain, bleeding, infection, urinary retention, or changes in continence)?
• How do patient-reported outcomes (such as pain and quality of life) change after treatment? This is a prospective, multicenter, single-arm pilot study. All participants will receive RFA treatment; there is no comparison (control) group.

Participants will:

• Be screened and enrolled at one of the participating hospitals
• Undergo a standardized RFA procedure for the perianal fistula
• Attend follow-up visits with clinical assessments at regular time points up to 6 months (including key assessments around 3 and 6 months)
• Report symptoms and any adverse events during the follow-up period

Perianal fistula is a chronic inflammatory tract that can cause persistent discharge, pain, recurrent abscess formation, and substantial impairment in daily activities and quality of life. While definitive surgical management aims to eradicate the fistula while preserving sphincter function, conventional approaches may be limited by variable healing rates, risk of recurrence, and concerns regarding sphincter injury and subsequent continence disturbance-particularly in complex fistulas or in patients at higher risk of incontinence. As a result, sphincter-preserving, minimally invasive techniques have been actively explored to improve clinical outcomes while minimizing functional compromise.

Radiofrequency ablation (RFA) is a thermal energy-based modality that can induce controlled tissue coagulation and remodeling. For perianal fistula treatment, RFA has the potential to ablate the fistula tract internally and promote tract closure without dividing sphincter muscles. However, a key challenge in energy-based fistula treatments is achieving consistent and uniform ablation along the entire tract length, because uneven energy delivery may lead to insufficient ablation in certain segments and treatment failure or recurrence. To address this limitation, a novel, dedicated RFA fistula device has been developed to deliver thermal energy in a standardized manner along the tract, with the intent of achieving more uniform ablation across tract segments (ie, segment-by-segment energy delivery rather than focal "dot" ablation). Prior preclinical work using a porcine perianal fistula model was performed to establish feasible operating parameters and to support translation to a first-in-human clinical pilot study.

Objectives The primary objective of this prospective multicenter single-arm pilot study is to evaluate the clinical efficacy of a novel RFA device for the treatment of perianal fistula in adult participants, with clinical fistula closure assessed at 6 months after the procedure. Secondary objectives are to evaluate safety (procedure- and device-related adverse events), recurrence patterns during follow-up, and changes in symptom burden and functional outcomes over time. In addition, this pilot study aims to assess procedural feasibility and to generate data that will inform the design of larger confirmatory studies, including refinement of outcome definitions, follow-up strategy, and operational standardization across sites.

Methods This is a prospective, multicenter, single-arm pilot interventional study enrolling adult participants with perianal fistula who are considered appropriate for a sphincter-preserving approach. All enrolled participants will receive RFA treatment using the dedicated fistula RFA device under a standardized procedural framework across participating sites.

Intervention (RFA procedure):

RFA will be delivered intraluminally to the fistula tract using the dedicated RFA catheter introduced via the external opening according to the standardized technique. The procedure is designed to apply controlled thermal energy along the tract to promote tract closure while minimizing injury to surrounding sphincter structures. Periprocedural management and post-procedure care will follow a harmonized protocol across sites to support consistent implementation and safety monitoring.

Follow-up and assessments:

Participants will be evaluated longitudinally after the procedure, with key clinical assessments at approximately 3 and 6 months post-procedure (in addition to immediate post-procedure assessment per routine clinical care). Clinical evaluation will include inspection and digital rectal examination to assess fistula healing status and to identify any signs of persistent or recurrent disease. Safety monitoring will include collection and documentation of adverse events from the time of the procedure through the final follow-up assessment, including severity and relationship to the procedure/device. Patient-reported symptoms (including pain) and functional outcomes (including continence-related measures and quality-of-life measures when applicable) will be captured at predefined time points.

Endpoints overview:

The primary endpoint is clinical fistula closure at 6 months after RFA treatment, based on standardized clinical criteria. Secondary endpoints include recurrence during follow-up, safety outcomes (adverse events/serious adverse events), symptom trajectories (eg, pain), functional outcomes (eg, continence), quality of life measures, and the need for additional fistula-related interventions.

Data analysis:

As a pilot study, analyses will primarily be descriptive and estimation-focused to characterize preliminary efficacy and safety signals. Outcome measures will be summarized using appropriate descriptive statistics, and clinically relevant proportions (eg, closure and recurrence rates) will be reported with confidence intervals where applicable. The resulting data will be used to inform sample size assumptions, endpoint operationalization, and protocol optimization for subsequent larger-scale studies.

Inclusion Criteria:

• Adults aged 20 to 74 years

• Able and willing to provide written informed consent after receiving explanation of the study purpose, procedures, potential benefits, and risks

• Diagnosed with one or more of the following perianal fistula types:

  1. High trans-sphincteric fistula
  2. Low trans-sphincteric fistula with high risk of fecal incontinence (sphincter injury risk)
  3. Fistula with seton placement (seton in situ or previously placed per protocol)
  4. Crohn's disease-associated perianal fistula
  5. Complex fistula, including cases with a history of perineal or gynecologic surgery and/or recurrent fistula

Exclusion Criteria:

• Superficial fistula that is expected to be curable with simple fistulotomy with minimal risk of sphincter injury
• Fistula related to malignancy
• Any contraindication to RFA, including: History of stapled hemorrhoidopexy, Presence of endoscopic clips (or similar metallic clips) within the anal canal, Fecal diversion with stoma (diverting stoma in place), Pregnancy