Sound touch viscosity in the evaluation of median nerve in healthy volunteers-a preliminary study.

Background: Quantitative assessment of peripheral nerve viscoelasticity is important for understanding nerve physiology and detecting early neuropathic changes. However, reference values for the viscosity and stiffness of the median nerve in healthy adults are lacking.

Materials and methods: A total of 98 healthy volunteers (58 females, 40 males; mean age: 35 ± 12 years) were assessed using the Sound Touch Viscosity and shear wave elastography modules integrated into the Resona A20S ultrasound system. Viscosity and stiffness were measured at three anatomical locations: the carpal tunnel (MN1), mid-forearm (MN2), and 5 cm proximal to the elbow joint (MN3). Paired bilateral measurements were obtained, and demographic factors were analyzed for their influence.

Results: No significant differences were found between the left and right median nerves (p > 0.05). MN1 showed the highest viscosity 1.83 Pa·s (1.48-2.13) and stiffness of 30.24 kPa (28.46-33.65) significantly greater than MN2 and MN3 (p < 0.001). Viscosity and stiffness were moderately correlated at all sites ((r = 0.39, 0.56, and 0.36; all p < 0.001). Males showed higher stiffness at all locations (p < 0.001) and higher viscosity at MN1 and MN2 (p = 0.039 and 0.011). While age and body mass index (BMI) showed no significant effects.

Conclusion: STVi is a feasible and reproducible modality for quantifying median nerve viscoelasticity. Viscoelastic parameters vary significantly by anatomical location and sex, with no influence from age and BMI. These findings establish normative values and support the clinical applicability of Sound Touch Viscosity in peripheral nerve assessment.