Cranial Nerve Co-activation and Implication for Nerve Transfers to the Facial Nerve

Summary: In reanimation surgery, effortless smile can be achieved by a non-facial donor nerve. The underlying mechanisms for this smile development, as well as which is the best non-facial neurotizer, need further clarification. The aim of the present study was therefore to further explore the natural co-activation between facial mimic muscles and muscles innervated by the most common donor nerves used in smile reanimation. The study was conducted in 10 healthy adults. Correlation between voluntary facial muscle movements and simultaneous electromyographic (EMG) activity in muscles innervated by the masseter, hypoglossal and spinal accessory nerves was assessed. The association between voluntary movements in the latter muscles and simultaneous EMG activity in facial muscles was also studied. Smile co-activated the masseter and tongue muscles equally. During the seven mimic movements, the masseter muscle had fewer EMG-measured co-activations compared to the tongue (2/7 vs. 5/7). The trapezius muscle demonstrated no co-activation during mimic movements. Movements of the masseter, tongue and trapezius muscles induced EMG-recorded co-activation in the facial muscles. Bite resulted in the strongest co-activation of the zygomaticus major muscle. We demonstrated co-activation between voluntary smile and the masseter and tongue muscles. During voluntary bite, strong co-activation of the zygomaticus major muscle was noted. The narrower co-activation pattern in the masseter muscle may be advantageous for central re-learning and the development of a spontaneous smile. The strong co-activation between the masseter muscle and the zygomaticus major indicates that the masseter nerve may be preferred in smile reanimation. This study was supported by Uppsala County Council Research and Developmental Funding, Uppsala University, Acta Otolaryngologica Foundation and ALF Funding. The authors would like to thank Nermin Hadziosmanovic, Uppsala Clinical Research Center for help with statistical analysis. Products and devices used in this research: Needle electrode (Dantec™ DCF 25) Surface electrode (Ambu® NF-50-K/W/12) Ground electrode (Ambu® Neuroline Ground electrode 71410-M/1) Routine clinical EMG equipment (Keypoint®) None of the authors has a financial interest in any of the products, devices, or drugs mentioned in this manuscript. Correspondence: David Jensson, MD. Department of Surgical Sciences, Plastic and Maxillofacial Surgery, Uppsala University, SE-75185 Uppsala, Sweden. E-mail: davidjensson81@gmail.com ©2017American Society of Plastic Surgeons