Accessory nerve distribution for aesthetic botulinum toxin injections into the upper trapezius muscle

Abstract

The descending part of the trapezius muscle is clinically associated with neck pain and aesthetic applications. The innervation of the trapezius muscle is not well described in the medical literature for clinicians. The aim of study was to analyze the perforating branch pattern of the accessory nerve in the descending part of the trapezius muscle with the aim of describing the most efficient and reproducible botulinum toxin (BoNT) injection sites for aesthetic treatment of shoulder contouring. Twenty-six specimens (five male and eight female) from embalmed Korean cadavers were used in this study. The trapezius muscle was dissected scrupulously and then reflected to enable examination of the locations of the perforating points. The dense arborization of the perforating accessory nerve branches was confined mostly to section b (66.7%, 54/81) and section c (33.3%, 27/81) above a line divided into four sections between the 7th spinous process of the vertebra prominens and the acromion. Therefore, we recommended injecting into six points separated by 2 cm in sections b and c of the upper trapezius muscle to optimize the outcome of BoNT injection.