Thirty-seven studies were included (n=1,460; range 3 to 397). The study designs included were unclear, but three were prospective randomised trials (n=235), 15 were prospective (one-armed), case reports or consensus drafts (n=796) and 19 were retrospective (one-armed) (n=429).
The average rate of incontinence was 12% (range 0% to 67%) (37 studies). Incontinence rates were 20.5% for trans-sphincteric (18 studies, n=348 patients), 67% for supra-sphincteric (five studies, n=15 patients) and 37% for extra-sphincteric fistulae (five studies, n=25 patients). Liquid stool was the most common type of incontinence (69%, 19 studies) followed by flatus incontinence (46%, 14 studies). Incontinence associated with the treatment of non-specific cryptoglandular fistulas was 16% (13 studies).