Internal sphincterotomy for chronic anal fissure: long term effects on anal pressure.

In 28 patients with chronic anal fissure the median anal canal pressure was 98 cmH2O, significantly higher than in control subjects (P less than 0.001). After lateral internal sphincterotomy the pressure dropped by 50 per cent to normal levels and the fissures healed with no change in pressure over 12 months. Ten patients also had normal anal pressures and were asymptomatic 4-6 years after internal sphincterotomy. Adequate internal sphincterotomy appears to reduce permanently anal canal pressure, suggesting that abnormal activity in the sphincter contributes to the development of a fissure.