The spinal accessory nerve and its entry point into the posterior triangle of the neck

The course of the spinal accessory nerve in the neck is long and superficial rendering it at high risk of injury during procedures performed in the posterior triangle. The majority of spinal accessory nerve injuries are iatrogenic in nature. This is associated with significant morbidity including reduction in shoulder movements, drooping of the shoulder, winging of the scapula and neuropathic pain. Knowledge of the nerve anatomy reduces the risk of intra-operative nerve injury. Traditional teaching describes the point of entry into the posterior triangle as the intersection between the upper and middle third of the posterior border of sternocleidomastoid. The aim of this study was to determine whether this is in fact the case and if so, whether this landmark can reliably be used to identify the spinal accessory nerve in order to improve patient outcomes.