Factors affecting continence after surgery for anal fistula.

Anorectal physiology and continence were assessed prospectively before and after surgery in 50 patients with chronic perianal sepsis. Functional and physiological parameters were unchanged after surgery in 13 control patients who had sepsis but who did not undergo division of the anal sphincter. Group 1 comprised 22 patients with internal sphincter division alone (15 intersphincteric, seven trans-sphincteric treated by a loose seton technique) and group 2 consisted of 15 patients with a trans-sphincteric fistula laid completely open. In group 1 the median (interquartile range (i.q.r.)) resting pressure in the distal 1 cm of the anal canal was reduced from 68 (60-90) cmH2O before surgery to 44 (35-60) cmH2O after operation (P < 0.001); squeeze pressure was less affected, but function deteriorated in 11 of the 22 patients. The median (i.q.r.) resting pressure in group 2 patients also fell, from 68 (34-84) cmH2O before operation to 28 (20-54) cmH2O afterwards (P = 0.003); median (i.q.r.) maximum squeeze pressure decreased more, from 124 (76-170) cmH2O to 72 (48-112) cmH2O (P = 0.002). Functional deficit occurred in eight of the 15 patients. Incontinence was related to low resting pressure, reflecting internal sphincter integrity, and to local epithelial electrosensitivity (reflecting scarring), but not to squeeze pressure, fistula type or surgical treatment.