In vivo recovery of the injured anal sphincter after repair and injection of myogenic stem cells: An experimental model

OBJECTIVE: This study aims to evaluate in vivo function of the external anal sphincter after transection and repair augmented with myogenic stem cells, and to establish normative electromyography parameters of the rodent external anal sphincter. DESIGN AND SETTING: Thirty-three Sprague-Dawley rodents underwent baseline needle electromyography of the external anal sphincter. Motor unit action potentials were obtained and normative parameters established. Animals were randomly assigned to a myogenic stem cell group (n = 24) or control group (n = 9). All underwent proctoepisiotomy. The control group underwent layered repair with phosphate-buffered saline injection to the external anal sphincter. The treatment group underwent identical repair with injection of myogenic stem cells 5.0 × 106. Baseline anal pressure recordings were collected and repeated 2 weeks postintervention, and electromyography was repeated at 2 and 4 weeks. Groups were compared across 3 time points with the use of repeated measures ANOVA. MAIN OUTCOME MEASURES: The primary outcomes measured were the functional recovery of rat anal sphincters after stem cell transplantation as assessed by objective electromyography and anal pressure measures. RESULTS: A mean of 17 motor unit action potentials were sampled per animal. At 2 weeks postrepair, there was a significant difference between control and transplant groups with respect to amplitude, duration, turns, and phases (p < 0.01 for each). No significant electromyography differences were seen at 4 weeks. Resting and peak anal pressures declined significantly at 2 weeks postinjury in the control but not in the stem cell group. LIMITATIONS: Use of a murine animal population limited the subjective feedback and wider applicability. CONCLUSIONS: In vivo functional studies show recovery of anal sphincter pressures and electromyography to preinjury levels by day 14 in the myogenic stem cell group but not controls. At 4 weeks, all electromyography parameters returned to baseline irrespective of group. Restoration of function may be accelerated by the transplantation of myogenic stem cells and associated trophic factors.