Spinal accessory nerve injury: A potentially missed cause of a painful, droopy shoulder.

BACKGROUND: Spinal accessory nerve (SAN) injury can be an overlooked cause of scapular winging and shoulder dysfunction. The most common etiology is iatrogenic injury following surgical procedures at the posterior triangle of the neck. We present three cases of isolated injury to the SAN following trauma.

OBJECTIVE: To improve detection of SAN injuries through highlighting the clinical presentation, diagnosis and treatment via three cases in which the injuries were initially missed.

METHODS: Clinical case series and narrative review.

RESULTS: Three (3) patients were evaluated by history, physical exam and electrodiagnostic study (EMG). Clinical symptoms included, a painful, droopy shoulder and difficulties with overhead activities. Clinical signs included the observation of scapular winging, and focal atrophy of the trapezius and in some cases the sternocleidomastoid (SCM). Novel clinical signs such as the active elevation lag sign and triangle sign were also helpful clinically to highlight the SAN as the site of pathology. EMG revealed denervation and reduced motor unit recruitment in the trapezius and SCM.

CONCLUSIONS: Early detection of SAN injuries can be improved through appropriate clinical suspicion, a detailed history and careful physical exam. EMG testing can help guide prognosis, direct conservative and surgical treatment, and reduce patient morbidity.