Elbow Motion Induces Greater Median Nerve Excursion and Lower Shear Strain Than Wrist or Finger Motion in Healthy...

Previous ultrasound (US)-based assessments of median nerve (MN) displacement within the carpal tunnel have shown inconsistent results due to methodological variability. Quantitative data on how different upper-limb movements affect MN displacement and shear strain at the wrist remain scarce. This study aimed to quantify MN longitudinal displacement and shear strain during finger, wrist, and elbow movements in healthy individuals to establish normative patterns of nerve gliding and deformation.

Twenty healthy subjects (13 females; mean age: 31.9 years, range: 27-36 years) were prospectively recruited. US videos captured MN motion during middle finger, wrist, and elbow movements. A custom robotic device ensured consistent wrist motion and forearm stability. Speckle-tracking software was used to analyze MN absolute longitudinal displacement, relative displacement to adjacent deep and superficial tissues, and normalized shear strain at both interfaces.

Elbow motion resulted in significantly greater MN absolute displacement (3.8 ± 1.2 mm) and displacement relative to deep tissue (3.6 ± 1.2 mm), compared to finger or wrist motion. No significant differences were observed in MN displacement relative to superficial tissue across motions. Normalized shear strain at the deep interface was lowest during elbow motion (41.8 ± 16.6 mm^-1). Significant differences were found for wrist-to-elbow and finger-to-elbow motions, but not for finger-to-wrist motions.

Presented findings highlight the importance of joint-specific contributions to MN motion and suggest that proximal joint movements, such as at the elbow, may promote more effective nerve excursion while minimizing shear strain. This knowledge may help refine nerve current mobilization approaches.