Multimodal Location-Dependent Biomechanical Characterization and Numerical Modeling of Inhomogeneous Median Nerve in Carpal Tunnel

This study assessed location-dependent inhomogeneity in the intracarpal median nerve of healthy subjects using a multimodal framework integrating subject-specific finite element analysis (FEA), ultrasound, and diffusion tensor imaging (DTI). Dynamic B-mode ultrasonography tracked segmental nerve displacement during finger flexion in subjects, with axial strain quantified via speckle cross-correlation. Cross-sectional ultrasound measured nerve cross-sectional area and flattening ratio. Twelve subject-specific FEA models analyzed stress distributions in the nerve, while DTI evaluated diffusion tensor of the median nerve indicating microstructural properties. Correlations between biomechanical and microstructural parameters were examined. Results showed that cross-sectional area, axial strain, von Mises stress, maximum principal stress, and frictional anisotropy of the median nerve decreased from the carpal tunnel inlet to outlet. Strong and significant correlations (r>0.8, P<0.05) were found among these parameters. Our findings in healthy individuals suggest that segmental nerve displacement creates localized strain, particularly at the carpal tunnel inlet. These potential biomechanical vulnerabilities could contribute to the initiation or progression of Carpal Tunnel Syndrome, a hypothesis requiring further clinical investigation.