Effects of an anal fistula plug on anal function after surgery for treatment of a trans-sphincteric anal fistula

Purpose The aim of this study was to evaluate the anal function in patients with trans-sphincteric anal fistulas who underwent an anal fistula plug procedure, and analyze risk factors that might affect post-operative anal function. Methods This was an observational, retrospective study of patients diagnosed with trans-sphincteric anal fistulas and initially underwent anal fistula plug procedures between August 2008 and September 2012 at our institute. The analysis includes clinical characteristics, anal fistula healing, and the Wexner score for pre- and post-operative anal function (0 = no incontinence to 20 = complete incontinence). Results A total of 123 patients who had an adequate follow-up in the end were included. The median duration of follow-up was 8 years (range 72-121 months). The overall healing rate was 56% (69/123), and 33 (26.8%) patients had decreased anal function after surgery. The post-operative Wexner score on anal function was significantly higher than that before the operation (p < 0.001), as well as scores of gas, liquid stool, solid stool incontinence, and alteration in lifestyle (p < 0.05). Based on multiple logistic regression analysis, a high body mass index (p < 0.001) and long distance between the external opening and anal verge (p = 0.003) were significantly associated with a decline in post-operative anal function. Conclusions As a sphincter-preserving technique for the treatment of anal fistulas, the anal fistula plug procedure might impair the anal function. Especially for patients with obesity or long distance between the external opening of anal fistula and anal verge, the reduced anal function is more likely to occur after treatment with anal fistula plug therapy.