Anatomical Entrapment of the Dorsal Scapular and Long Thoracic Nerves Secondary to Brachial Plexus Piercing Variation
Authors: Williams Avery A. , Smith Heather F. 
Published: June 2021

Understanding and documenting anatomical variation plays a vital role for furthering the ability of a physician to diagnose, care, and treat patients. Despite the textbook definition of the typical or classical pattern of the brachial plexus as emerging between the anterior and middle scalene muscles, variants involving different patterns are becoming well documented, especially the high frequency of “piercing” variants, in which the superior and/or middle trunk of the brachial plexus courses through the belly of the anterior scalene muscle. While this variation is now widely acknowledged, it is currently unclear how these variants may influence branching patterns distally along the brachial plexus in branches such as the dorsal scapular and long thoracic nerves.

This project strived to identify and quantify the types of variations (piercing and non‐piercing variants) of the brachial plexus trunks, and assess the frequency of corresponding anomalies in the dorsal scapular nerve (DSN) and long thoracic nerve (LTN). Human cadavers used in gross anatomy courses at Midwestern University's Glendale Campus were utilized in this project to examine a total of ninety‐one cadaveric brachial plexuses (46F/45M) with the right and left sides being examined independently. In the majority of specimens (89.71%), at least one neural structure (brachial plexus, DSN, or LTN) pierced one of the scalene muscles. The most common condition for the brachial plexus was piercing the anterior scalene muscle (59.34%), while the most common piercing condition for both the DSN and LTN was through the middle scalene (41.89% and 38.1% respectively). Of the specimens with a DSN piercing pattern, 64.44% also had the brachial plexus piercing variant. Similarly, of the specimens with piercing LTNs, 72.97% also had trunk(s) of the brachial plexus piercing a scalene muscle. Thus, the anomalous brachial plexus piercing variants are associated with higher frequencies of distal nerve branches also coursing through the scalene musculature, and specifically, there is a statistically significant correlation between brachial plexus piercings and LTN piercing (p = 0.0412).

Circumscapular pain is a frequent complaint in clinical practice. While numerous etiologies exist, DSN entrapment is a common underlying cause. It is well documented that the DSN courses through the scalene region as it exits the neck, where it may become entrapped between or even within adjacent scalene muscles. Similarly, compromise of the LTN can result in debilitating paralysis or paresthesia of the serratus anterior muscle, often resulting in winging of the scapula. As a primary stabilizer of the scapula, serratus anterior is crucial in maintaining the normal position of the scapula against the thoracic wall and in sustaining proper scapulohumeral function. This study demonstrated that anatomical entrapment of the DSN and LTN are both quite common, and occur in higher frequency in individuals with brachial plexus piercing variants. Additionally, individuals with these compounded neural piercing patterns may be at greater risk for nerve impingement in the cervical, pectoral, and/or scapular region.

Support or Funding Information

Support provided by Midwestern University.

This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.