In this study, we retrospectively reviewed clinical data of patients who were treated with an anal fistula plug for trans-sphincteric anal fistulas, and evaluated the long-term therapeutic effect of an anal fistula plug and the risk factors impacting anal fistula healing. In addition, we assessed the effects of post-operative changes on anal function, as well as the risk factors affecting anal function.

Treatment of anal fistulas, especially involving significant anal sphincters, continues to represent a challenge for surgeons. Surgery has been the mainstay of treatment, and the ideal goal of anal fistula treatment is to obliterate the fistulous tract, while preserving the anal sphincter and avoiding fecal incontinence. The anal fistula plug is a sphincter-sparing procedure that uses biological substances to close an anorectal fistula. Several studies have preliminarily shown that the anal fistula plug had advantages of simple and repeatable application, preservation of sphincter integrity, minimal patient discomfort, and subsequent surgical options if needed. The healing rate of anal fistula plug varied widely, which range from 14% to 88%, and no significant effect on anal function in the short term. Therefore, long-term observation and a large sample size are needed to evaluate the long-term healing rate of an anal fistula plug, and the effect on anal function. The aim of this study is to assess the long-term therapeutic effect of an anal fistula plug in patients with trans-sphincteric fistula-in-ano, as well as the impact on anal function.

Inclusion Criteria:

• Patients with trans-sphincteric anal fistula.
• The case information was complete.
• Not receive other treatment previously.

Exclusion Criteria:

• Fistulas related to Crohn's disease, ulcerative colitis or anorectal tumors.
• Underwent surgical incision and drainage for acute perianal infections within 3 months.
• Multiple fistula tracts > 2.
• Poor underlying condition and unable to tolerate surgery.