DAMAGING EFFECTS OF ANAL STRETCHING ON THE EXTERNAL ANAL-SPHINCTER

PURPOSE: This study was undertaken to investigate the effects of anal stretching on anal pressures and damage to the external anal sphincter . METHODS: This study was performed on 37 guinea pigs. Animals were di vided into three groups: control group, quick stretching group, and co ntinuous overstretching group. Anal stretching was conducted by an 8-F Foley(R) catheter balloon. RESULTS: It was found that if the muscle w as stretched from 100 to 300 percent of its original length, anal rest ing pressure (ARP) kept relatively steady, but anal contracting pressu re (ACP) gradually increased; from 300 to 370 percent, a sharp ARP inc rease was developed, but ACP gradually decreased to zero; beyond 370 p ercent, ARP remained unchanged (plateau phase). By histologic examinat ion, it was revealed that when the muscle was stretched at the ARP pla teau phase, an ischemic zone of necrosis and an edematous zone of necr osis could be clearly identified in the muscle. CONCLUSION: This study shows that length of the external anal sphincter definitively influen ces muscle strengths, and severe anal stretching will result in muscle damage. These results imply that the sphincteric muscle complex in hi gh or intermediate anorectal anomalies may be injured during present c onventional surgical approaches.