Long thoracic nerve: Anatomy and functional assessment

Background: The anatomy and function of the long thoracic nerve are not fully understood. The purposes of this study were to clarify the anatomy of the long thoracic nerve and to propose a clinical test to assess the function of the upper division of the long thoracic nerve. Methods: The long thoracic nerve and the serratus anterior muscle were studied in fifteen fresh cadavera. Six patients had an operation to treat a brachial plexus injury, and the long thoracic nerve was electrically stimulated. The resulting shoulder motion was then observed. Results: The long thoracic nerve was formed by branches arising from the C5, C6, and C7 nerve roots. The C5 and C6 branches joined beneath the scalenus medius muscle to form the upper division of the long thoracic nerve, which was located 1 cm posteriorly and superiorly to the upper trunk origin. The union of the upper division with the branch from C7 occurred caudally, in the axillary region. Two branches from the upper division of the long thoracic nerve to the upper portion of the serratus anterior muscle were consistently identified. After electrical stimulation of the upper division branches, shoulder protraction was observed. Conclusions and Clinical Relevance: In the supraclavicular region, the long thoracic nerve has a trajectory parallel to the brachial plexus, which is contrary to the schematic representation in most textbooks. The upper division of the long thoracic nerve can be assessed by the shoulder protraction test.