www.PRSJournal.com 370e Disclosure: None of the authors has a financial interest in any of the products or devices mentioned in this article. Alison K. Snyder-Warwick, M.D. Adel Y. Fattah, Ph.D., F.R.C.S.(Plast.) Leanne Zive William Halliday, M.D. Gregory H. Borschel, M.D. Ronald M. Zuker, M.D. St. Louis, Mo.; Liverpool, United King- dom; and Toronto, Ontario, Canada Background: Free functional muscle transfer to the face is a standard of facial animation. The contralateral facial nerve, via a cross-face nerve graft, provides spontaneous innervation for the transferred muscle, but is not universally avail- able and has additional shortcomings. The motor nerve to the masseter pro- vides an alternative innervation source. In this study, the authors compared donor nerve histomorphometry and clinical outcomes in a single patient popu- lation undergoing free muscle transfer to the face. Methods: Pediatric patients undergoing dynamic facial (re-)animation with intraoperative nerve biopsies and gracilis transfer to the face powered by either the contralateral facial nerve via a cross-face nerve graft or the motor nerve to the masseter were reviewed over a 7-year period. Myelinated nerve counts were assessed histomorphometrically, and functional outcomes were evaluated with the Scaled Measurement of Improvement in Lip Excursion software. Results: From 2004 to 2011, 91 facial (re-)animation procedures satisfied study inclusion criteria. Average myelinated fiber counts were 6757 per mm2 in the do- nor facial nerve branch, 1647 per mm 2 in the downstream cross-face nerve graft at the second stage, and 5289 per mm 2 in the masseteric nerve. Reconstructions with either innervation source resulted in improvements in oral commissure excursion and smile symmetry, with the greatest amounts of oral commissure excursion noted in the masseteric nerve group. Conclusions: Facial (re-)animation procedures with use of the cross-face nerve graft or masseteric nerve are effective and result in symmetric smiles. The mas- seteric nerve provides a more robust innervation source and results in greater commissure excursion. (Plast. Reconstr. Surg. 135: 370e, 2015.) CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, III. From the Facial Nerve Institute, Department of Surgery, Division of Plastic and Reconstructive Surgery, Wash- ington University School of Medicine; the Facial Nerve Program, Regional Pediatric Burns and Plastic Surgery Service, Alder Hey Children’s NHS Foundation Trust; the Department of Surgery, Division of Plastic Surgery, and the Department of Pediatric Laboratory Medicine, Division of Pathology, The Hospital for Sick Children; and the Divi- sion of Plastic and Reconstructive Surgery, University of Toronto. Received for publication June 15, 2014; accepted August 26, 2014. Presented in part at the 2011 Chang Gung Mayo Sympo- sium in Reconstructive Surgery, in Linkou, Taiwan, Octo- ber 27 through 30, 2011; the Group for the Advancement of Microsurgery Canada 2012 Annual Meeting, June 6, 2012; the American Society for Reconstructive Microsurgery Annual Meeting, in Naples, Florida, January 12 through 15, 2013; the 17th World Congress of the International Confederation of Plastic, Reconstructive and Aesthetic Sur- The Degree of Facial Movement following Microvascular Muscle Transfer in Pediatric Facial Reanimation Depends on Donor Motor Nerve Axonal Density Supplemental digital content is available for this article. Direct URL citations appear in the text; simply type the URL address into any Web brows- er to access this content. Clickable links to the ma- terial are provided in the HTML text of this article on the Journal ’s Web site (www.PRSJournal.com). Copyright © 2015 by the American Society of Plastic Surgeons DOI: 10.1097/PRS.0000000000000860 gery, in Santiago, Chile, February 24 through March 1, 2013; and the 12th International Facial Nerve Symposium, in Boston, Massachusetts, June 28 through July 1, 2013. PEDIATRIC/CRANIOFACIAL