Abstract / Summary
Background/Objectives: Classical descriptions of median nerve motor anatomy often emphasize muscle-specific destinations, although a single muscular branch may divide to supply several muscles. This can obscure the hierarchical relationship between branch origin and downstream ramification. We therefore quantified the two-dimensional topography of muscular branches arising directly from the median nerve and analyzed each branch origin as a single spatial event linked to its subsequent muscular destinations. Methods: Sixteen fresh, non-frozen right upper limbs from 16 independent adult body donors (8 male and 8 female; mean age, 82.2 ± 9.6 years) underwent standardized dissection. Cartesian coordinates were assigned only to the origin of each first-order muscular branch from the median nerve. Branches were ordered proximodistally and linked to downstream subbranch count and target muscles. Coordinates were normalized to bistyloid distance (RPX) and forearm length (RPY). Donor-clustered bootstrap confidence intervals and mixed-effects models with donor-specific random intercepts summarized spatial variation across branch rank, with the longitudinal association interpreted descriptively because rank was defined proximodistally. Results: Seventy muscular branches generated 274 recorded downstream subbranches and 146 unique branch–muscle associations. Limbs contained a median of 4 muscular branches (range, 2–6), and 32/70 branches (45.7%) supplied two or more target muscles; this proportion includes the anterior interosseous nerve when its origin met the study’s branch-centered definition. The first branch participated in pronator teres innervation in all 16 limbs and was exclusive to that muscle in 11 (68.8%); all five sixth-ranked branches observed in this sample supplied flexor digitorum superficialis. As expected from the ranking definition, increasing branch order was descriptively associated with a more distal origin (β = 0.084; 95% CI, 0.063–0.104) and was associated with a higher normalized transverse coordinate (β = 0.077; 95% CI, 0.050–0.103; p < 0.001). Branch order explained substantially more longitudinal than transverse variance (marginal R2, 0.444 vs. 0.183). Conclusions: Proximodistally ranked median nerve branch origins were associated with frequent and variable downstream multi-muscle pathways. The rank–longitudinal coordinate association does not independently establish anatomical reproducibility. Treating the muscular-branch origin as the coordinate-level unit preserves the anatomical hierarchy, prevents pseudoreplication of shared coordinates, and provides an anatomical framework with potential relevance to peripheral nerve surgery; clinical benefits remain untested.