Sexual Dimorphism and Population Variation in Median Nerve Morphometry: A Multi-Institutional Cadaveric Analysis

Background/Objectives: The median nerve exhibits clinically relevant anatomical variability, with critical implications for surgical exposure, regional anesthesia, peripheral nerve repair, and diagnostic imaging. Despite extensive descriptive reports, quantitative morphometric analyses incorporating biological sex and donor record population classification remain limited, particularly among Hispanic cadaveric cohorts. Methods: This multi-institutional cadaveric study evaluated median nerve formation and segmental morphometry in 82 anatomical donors, each contributing paired bilateral upper limbs (164 upper limbs total), classified in institutional records as Puerto Rican, Caucasian, or African American. Standardized dissections were performed from the brachial plexus to the distal forearm, and linear measurements were obtained between predefined anatomical landmarks using digital calipers. Results: Mixed-effects modeling was used to evaluate morphometric differences associated with biological sex, donor record population classification, and anatomical location. Male specimens demonstrated localized differences in proximal median nerve formation, including a longer medial cord contribution on the left side. Population group comparisons identified greater measured morphometric distances in the Puerto Rican cohort compared with Caucasian and African American cohorts. Normalized LEH/MEH ratios did not differ between sexes, suggesting that some absolute differences may reflect limb-size scaling rather than proportional shifts in nerve position. Conclusions: These findings provide standardized landmark-based morphometric data and support the value of population-sensitive anatomical reference data for surgical planning and imaging-based interpretations of median nerve morphology.