Recovery of external anal sphincter contractile function after prolonged vaginal distention or sphincter transection in an animal model

OBJECTIVE:: To estimate the effect of prolonged vaginal distention and anal sphincter transection on contractile properties of the external anal sphincter as a function of time. METHODS:: One hundred thirty-nine young female virginal rats were randomly assigned into four treatment groups (sham, vaginal distention, transection of anal sphincter plus repair, or combined distention and transection plus repair). After 3 days, 3 months, or 6 months, the anal sphincter complex was analyzed for peak force of twitch tension, peak tetanic force, fatigue, and maximal responses to electrical field stimulation. Statistical analysis was performed using analysis of variance (Student-Neuman-Keuls). RESULTS:: After 3 days, vaginal balloon distention, anal sphincter transection with repair, and combined distention and transection plus repair resulted in compromise of maximal tetanic contraction and electrical field stimulated force generation. Twitch tension, and resistance to fatigue were also significantly decreased in animals with anal sphincter disruption and repair with and without vaginal distention at 3 days. Contractile function of the external anal sphincter, however, was fully recovered by 3 months and was sustained at 6 months in all treatment groups. The time course of repair was slower in animals with sphincter laceration. CONCLUSION:: Anal sphincter transection with or without antecedent prolonged vaginal distention results in severe compromise of external anal sphincter function in the immediate period after injury. In this animal model, complete recovery of external anal sphincter function occurs 3 months after initial insult.