Morphological analysis of the median nerve in the carpal tunnel during wrist movements, finger pinching and palm loading

Abstract

The aim of this study was to analyze the morphology of the median nerve (MN) in the carpal tunnel during hand motion and palmar load in healthy participants using ultrasound. Twenty healthy participants (10 men and 10 women) were enrolled in the study. Wrist flexion angle is negatively correlated with cross-sectional area (CSA) and perimeter, and positively correlated with circularity, whereas wrist extension angle is negatively correlated with MNCSA and circularity. At 15°, 45°, and 60° wrist flexion and extension, both MNCSA and perimeter were significantly smaller than at neutral (all P < 0.05). MN circularity was significantly greater at 30°, 45°, and 60° wrist flexion than at neutral (all P < 0.05). At 30° ulnar deviation of the wrist, MNCSA and perimeter were significantly smaller than the neutral position, while circularity was significantly larger (all P < 0.05). At 15° of wrist radial deviation, MNCSA and perimeter were significantly smaller than at the neutral position (all P < 0.05). Compared to the 40 % maximum voluntary effort (MVE), thumb-ring finger pinch (10 %MVE) resulted in significantly higher MNCSA and perimeter, while circularity was noticeably smaller (all P < 0.05). In the neutral position, no differences were observed in MNCSA, perimeter and circularity unloaded at 100 g, 200 g, 300 g, 400 g and 500 g palmar loads (all P > 0.05). The results indicate that wrist positions involving flexion, extension, and deviations, as well as finger pinch, can significantly impact the morphology of the MN. This is an important step in understanding the biomechanics of MN compression within the carpal tunnel.