Randomized trial comparing anorectal myectomy and controlled anal dilatation for outlet obstruction

A randomized controlled study has compared anorectal myectomy (n = 13) with anal dilatation (n = 10) using Park's anal retractor for patients with constipation. No patient was able to defaecate spontaneously more than three times a week before the operation. Of the 13 patients, 7 were able to defaecate spontaneously more than three times a week after anorectal myectomy, compared with none after anal dilatation (P less than 0.05). None of the patients in either group became incontinent. There was a significant fall of anal canal pressure after anorectal myectomy at rest, during maximum pelvic floor contraction, and attempted defaecation: median, 100 (range, 21-200) to 43 (20-133) cmH2O, P less than 0.01; 140 (79-238) to 86 (43-153) cmH2O, P less than 0.01; 127 (79-208) to 86 (29-167) cmH2O, P less than 0.005. A significant improvement in rectal emptying occurred after anorectal myectomy (median, 0 per cent/min (range, 0-83) to 50 (0-100) per cent/min, P less than 0.025). On the other hand, anal dilatation was not associated with any significant change in rectal emptying or anal pressure. Pre-operative anal pressures during attempted defaecation in patients who achieved a good result after anorectal myectomy were significantly higher than those that did not (median, 136 (range, 120-208) versus 114 (79-129) cmH2O, P less than 0.025). Patients having a good result after anorectal myectomy had a significantly shorter history of constipation (median, 4 (range, 2-14) versus 38 (4-72) years, P less than 0.01) and normal colonic transit (median, 100 (range, 4-100) versus 10 (0-90) years, P less than 0.05) compared with those who had no benefit after operation.