ORIGINAL ARTICLE Effect of myogenic stem cells on the integrity and histomorphology of repaired transected external anal sphincter Joseph L. Fitzwater & Kathryn B. Grande & Joseph L. Sailors & Jesus F. Acevedo & R. Ann Word & Clifford Y. Wai Received: 3 July 2014 /Accepted: 24 August 2014 /Published online: 25 September 2014 # The International Urogynecological Association 2014 Abstract Introduction and hypothesis The objective was to evaluate the effect of myogenic stem cells on histological properties and the volume of striated muscle of the external anal sphincter after transection and repair. Methods Histological analysis was performed on the external anal sphincters of 40 young female rats euthanized at 7 or 90 days after transection and repair and randomization to injection of either phosphate buffered solution (PBS) or myo- genic stem cells (SC) at the transection site. Sphincter com- plexes, previously evaluated for neurophysiological function, were processed for histology and analyzed for possible dis- ruption, amount of inflammation, and volume of striated muscle. The relationship between the muscular disruption and contractile force of sphincters was evaluated. Results Disruption was seen in 100 % of sphincters 7 days after repair for both SC and control animals. Eighty-nine percent of controls and 78 % of SC-administered animals had intact sphincters at 90 days. Significant inflammatory infiltrate was seen in repaired anal sphincters for both the PBS and the SC groups at 7 days, and persisted at 90 days, with no difference between treatment groups. Striated muscle volume increased from 7 to 90 days for both control and SC- administered animals. Although there was no difference in volume between treatments, there was substantial temporal improvement in contractile force generation of the sphincters receiving SC compared with those receiving PBS. Conclusion In this animal model, administration of myogenic stem cells to transected/repaired anal sphincters did not alter the amount of inflammation nor the volume of striated muscle, suggesting that stem cells might improve contractile function through other cellular processes. Keywords Myogenic stem cells . External anal sphincter . Histology Introduction One of the major causes of anal incontinence in women is the mechanical disruption of the external anal sphincter [1–3]. Under most circumstances, healing of the external anal sphincter, which is composed mainly of striated muscle, is unremarkable, providing certain conditions are met and select processes involved with healing take place. Events that occur during healing include angiogenesis, fibroblast in-growth and collagen deposition, formation of granulation tissue, epithelial cell proliferation and migration, and wound contraction [4]. In addition to these, the ends of the healing muscle must be in close apposition, myofibroblast proliferation and collagen deposition must occur appropriately, and the necessary growth factors should be present for optimal wound healing. Failure of any one, or a combination, of these criteria can compromise healing and result in persistent disruption or functional im- pairment of the anal sphincter complex. There are instances where wound healing is impaired from either a functional or morphological standpoint and enhancing the healing process is desirable. Although stem cell therapy has been shown to be beneficial in the treatment of urinary incontinence secondary to a deficient urethral sphincter [5, 6] J. L. Fitzwater : K. B. Grande : J. F. Acevedo : R. A. Word : C. Y. Wai(*) Division of Female Pelvic Medicine and Reconstructive Surgery, Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas, TX, USA e-mail: clifford.wai@utsouthwestern.edu J. L. Sailors Division of Female Pelvic Medicine and Reconstructive Surgery, Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX, USA Int Urogynecol J (2015) 26:251–256 DOI 10.1007/s00192-014-2496-5