A prospective manometric study of the effect of anal fistula surgery on anorectal function.

In 31 adults consecutively undergoing surgery for anal fistula (opening of fistulous tract), anorectal manometry was performed before and 7 months after the operation. The resting pressure was significantly reduced in the distal 3 cm of the anal canal postoperatively. Voluntary sphincter contraction was less markedly affected. Maximal squeeze pressure and maximal contractile power were significantly reduced, however, especially in women and after division of the external sphincter muscle. The pressures were significantly lower in women than in men, particularly after operation, and defective anal control was associated with reduced squeeze pressure. It is therefore suggested that in selected cases, primarily women, anal pressure should be measured preoperatively and division of the external sphincter muscle avoided if the pressure is low. Constant rectoanal inhibitory reflex was elicited by a significantly smaller distending volume and lower rectal pressure postoperatively than preoperatively which, like the reduced resting pressure, indicated impaired function of the internal sphincter muscle.