Normal variations in position and relations of the median nerve in the carpal tunnel: A cross-sectional observational study using clinical magnetic resonance imaging.

A standard relationship of the median nerve to neighboring tendons in the carpal tunnel has been described, but descriptions of normal variations are limited. The aim of this study is to describe the variation in position of the median nerve within the carpal tunnel and the variability in relation to adjacent tendons on clinical MR studies. A retrospective study was performed, analyzing 37 wrist MR examinations performed on a 3T MR machine. Primary endpoints involved measuring the four coordinates of the median nerve in relation to anatomical bony landmarks performed on a single-slice image. The secondary endpoints were anterior, posterior, medial, and lateral relations of the median nerve. The mean distance from hook of hamate to trapezium was 21.8 mm with a mean depth of 9.6 mm. The mean position of the median nerve from the hook of the hamate was 12.5 mm with a depth of 2.9 mm. The most common radial relations to the median nerve in descending order of frequencies were FPL, FDS 2, and FDS 3, the most common dorsal relations were FDS 2 and then FDS 3, and the most common ulnar relations were FDS 3 and then FDS 2. The position of the median nerve in the carpal tunnel is variable both in ulna-to-radial and dorsal to palmar directions, and variations in relation to neighboring tendons are also common. Clin. Anat. 33:598-604, 2020.