Finger Position Alters the Median Nerve Properties within the Carpal Tunnel: A Pre-Post MRI Comparison Study

PURPOSE: The purpose of this study was to compare the properties of the median nerve and the flexor retinaculum within the carpal tunnel with Magnetic Resonance Imaging (MRI) under two conditions: (a) fingers extended, and (b) fingers in an isometric squeeze grip. METHODS: Thirty-Four volunteers participated in this experimental study. The flexor retinaculum and median nerve characteristics were measured during both conditions using MRI. RESULTS: The isometric squeeze grip condition resulted in significant palmar bowing of the flexor retinaculum (t = 7.67, p<.001), a significant flattening-ratio of the median nerve (t = 4.308, p<.001), and no significant decrease in the cross-sectional area of the median nerve (t = 2.508, p = 0.017). CONCLUSION: The isometric squeeze grip condition resulted in anatomical deformations within the carpal tunnel, possibly explained by the lumbrical muscles incursion into the carpal tunnel during finger flexion.