The Spinal Accessory Nerve for Functional Muscle Innervation in Facial Reanimation Surgery An Anatomical and Histomorphometric Study

Introduction: Facial reanimation surgery is performed in severe cases of facial palsy to restore facial function. In a 1-stage procedure, the spinal accessory nerve can be used as a donor nerve to power a free gracilis muscle transplant for the reanimation of the mouth. The aim of this study was to describe the surgical anatomy of the spinal accessory nerve, provide a guide for reliable donor nerve dissection, and analyze the available donor axon counts. Methods: Dissections were performed on 10 nonembalmed cadavers (measurements of 20 nerves). Surgical anatomy of the spinal accessory nerve was described and distances to important landmarks were measured. Nerve biopsies were obtained of the main nerve trunk distal to the skull base, caudoposterior to the sternocleidomastoid muscle, proximal to the trapezius muscle and at the level of donor nerve harvest to analyze the myelinated axon count throughout the course of the spinal accessory nerve. The donor nerve length and available donor nerve axon count were the primary outcome parameters in this study. Results: The mean donor nerve length was 11.6 cm. The spinal accessory nerve was transferred to the mandibular angle without tension for ideal coaptation to the free muscle transplant. After retraction of the trapezius muscle, a small distal nerve branch that leaves the main nerve trunk at a 90-degree angle medially was used as a landmark to indicate the level of donor nerve transection. On average, 1400 myelinated donor axons were available for innervation of the gracilis muscle transplant. Conclusions: This study gives a practical guide for spinal accessory nerve dissection for its application in facial reanimation as a motor source for the innervation of a free muscle transplant.