This study of the human brachial plexus quantifies and compares the total number of fibers, fiber diameter, and fiber density within the lateral and medial roots of the median nerve in twenty-seven adult human cadavers (IRB Ref #1030 V.0). The lateral and medial cords give rise to the lateral and medial roots of the median nerve, which join to form the median nerve. In this study, the fiber ratios of small-diameter Group III and IV sensory fibers as well as large-diameter Group I and II sensory fibers composing the lateral and medial roots of the median nerve of the brachial plexus were investigated. Peripheral nervous tissue sections of the lateral and medial roots were surgically removed from the axilla region of formalin-fixed cadavers. Excised tissue sections were fractured using liquid nitrogen-based freeze-cracking, and subsequently viewed using scanning electron microscopy. ImageJ 1.x, Microsoft Excel, and Statistica software were used to analyze fiber count, diameter, and density, plus fascicular bundle count. Results revealed a higher ratio of large-diameter Group I and II sensory fibers for the lateral root, and a higher ratio of small-diameter Group III and IV fibers for the medial root. Understanding the fiber composition of the lateral and medial roots of the median nerve can aid in interpreting why avulsive injury of the upper or lower roots of the brachial plexus can lead to different pain experiences post-injury.
Walters, B.N., Brandt, L.S.E., and Kunigelis, S.C. Exploring sensory fiber composition in the lateral and medial roots of the median nerve. Translational Research in Anatomy, 35 (2024), https://doi.org/10.1016/j.tria.2024.100288