Long-term Effects on Pressure and Electromyography in a Rat Model of Anal Sphincter Injury

Purpose: The goal of this research was to study the chronic effects of pudendal nerve transection and sphincterotomy on the anal sphincter, because there is no good animal model investigating anal sphincter injury. Clinically, anal sphincter dysfunction impacts a cohort of women who have fecal incontinence; conclusions from the study can benefit research for new effective treatments.

Methods: Sixty-eight virgin Sprague-Dawley rats were allocated into control (n = 12), sphincterotomy (n = 28), and pudendal nerve transection (n = 28) groups and were evaluated before injury and immediately, 4 days, 14 days, and 28 days after. Anal pressures and electromyography were recorded and statistically compared. The anal sphincter was submitted to histology.

Results: : Sphincterotomy data showed anal pressure recovery 14 days after injury and were comparable to controls after 28 days. Pudendal nerve transection showed a significant decrease in anal pressure 4 days after injury (P < .001), and this continued until 28 days after injury (P = .01). Electromyography showed significant loss of activity after nerve transection compared with controls. Twenty-eight days after sphincterotomy and nerve transection, fibrosis and muscle atrophy of the external anal sphincter muscle were demonstrated, respectively.

Conclusion: Anal pressures recover significantly after sphincterotomy. Pudendal nerve transection caused atrophy of the external anal sphincter that was reflected by decreased pressures and electromyography. The results of this study can contribute to a better understanding of the mechanisms that lead to fecal incontinence and can be used to test the efficacy of therapies.