Grip Force Modulation on Median Nerve Morphology Changes

Compression on the median nerve can lead to carpal tunnel syndrome (CTS), and median nerve indicators measured from ultrasound images can be used for CTS diagnosis. The aim of this study was to investigate the relationship between grip force modulation and dynamic morphological changes of the median nerve. We used a digital grip dynamometer to measure grip force while simultaneously conducting ultrasound examinations. Ultrasound images were sampled for both the dominant and nondominant hands of all participants (n = 20) during a baseline condition at approximately 0% maximum voluntary force (MVF), during sustained grip force conditions at 25%, 50%, 75%, and 100% MVF, and during the return to a relaxed state (≈0% MVF) directly following each grip force condition. Regardless of hand dominance, grip force level, and grip force modulation, median nerve cross-sectional area (MNCSA) during the grip tasks was smaller relative to the initial baseline condition without grip force. With respect to shape change, the median nerve became more flattened, including increased longitudinal diameter (D1) and decreased vertical diameter (D2), when grip force was relaxed compared to the preceding sustained grip force condition for the dominant hand; however, there were no significant shape changes for the nondominant hand. As morphological changes to tissue result in strain, our results indicate that median nerve injury development may be associated with more hand usage (dominant hand, grip exertion, and grip force modulation), and further suggests the evaluative potential for median nerve dynamics within the carpal tunnel.