Novel insight into the site-specificity of Hegu (LI4): morphological, biomechanical, and histological analyses.

Objective: To investigate the site specificity and differences of the Hegu (LI4) located on the midpoint of the second metacarpal and the point where the bases of the first and second metacarpal bones on the dorsum was historically used as Hegu (LI4) in Japan, through morphological, biomechanical, and histological analyses.

Methods: We defined distally located Hegu (LI4) as Hegu (LI4)-D and proximally located Hegu (LI4) as Hegu (LI4)-P. The distance from the skin surface to the blood vessels as well as the biomechanical properties of the two Hegu (LI4) samples were measured using an ultrasound device and MyotonPRO (MyotonAS, Tallinn, Estonia), respectively, in 20 healthy adult volunteers. Sympathetic fibers under the two Hegu (LI4) samples were histologically observed using tyrosine hydroxylase (TH) immunostaining in 10 cadavers.

Results: Hegu (LI4)-D was classified into type 1 with blood vessels < 4 mm away from the skin surface, and type 2 with blood vessels > 10 mm away from the skin surface. In Hegu (LI4)-P, blood vessels were approximately 10 mm away from the surface. Further, Hegu (LI4)-P had significantly higher tone, stiffness, and elasticity than Hegu (LI4)-D (P < 0.0001). TH-positive fibers were present near the artery in Hegu (LI4)-P.

Conclusion: Hegu (LI4)-D and Hegu (LI4)-P differed in terms of hardness and the distance between the skin surface and blood vessels. Furthermore, sympathetic nerve fibers were present near the artery in Hegu (LI4)-P. Taken together, these results suggest that there is site specificity of morphological, biomechanical, and histological differences between the Hegu (LI4)-D and Hegu (LI4)-P.