The Anatomy of the Long Thoracic Nerve Origin, Course, And Branching Pattern: Implications for Long Thoracic Nerve Palsy and Serratus Anterior Dysfunction

Introduction: The long thoracic nerve typically originates from ventral primary rami at the C5, C6, and C7 levels at the root of the neck, and follows a long and superficial course before innervating the serratus anterior muscle. When the long thoracic nerve suffers an insult, it can lead to serratus anterior dysfunction and ensuing scapular winging. However, many cases of serratus anterior dysfunction have been reported without a clear etiology of long thoracic nerve damage; these cases appear to be most common in certain athletes with exaggerated arm movements at the limits of the shoulder’s range of motion and do not appear to have any correlation to athlete traits. To date, no studies have attempted to identify a connection between any specific variant long thoracic nerve anatomy and risk for nerve injury during shoulder movements. Methods: This study describes the origin and branching patterns of 50 long thoracic nerves across 25 cadavers. Serratus anterior dimensions and morphology was also recorded. Results: We describe seven distinct patterns of the long thoracic nerve’s emergence from neck musculature and its branching thereafter, and propose links between certain patterns and their potential susceptibility to nerve injury. The morphologies of the serratus anterior muscle slips are also described, and direct muscular injury to the superior slip is suggested as another potential cause of dysfunction in these athletes. Conclusions: Several etiologies for atraumatic serratus anterior dysfunction are described in this study, with a focus on anatomical variations that may predispose individuals to this pathology especially in the setting of sports with repetitive exaggerated arm movements.

Keywords:Long thoracic nerve; Serratus anterior; Peripheral nerve palsy

List of Abbreviations:AS: Anterior Scalene; IT: Inferior Trunk; LTN: Long Thoracic Nerve; MS: Middle Scalene; MT: Middle Trunk; PS: Posterior Scalene; SCA: Subclavian Artery; ST: Superior Trunk; SSSA: Superior Slip of Serratus Anterior