Dynamic ultrasound evaluation of median nerve mobility at the wrist: implications for surgical safety

To evaluate the dynamic position of the median nerve (MN) relative to the palmaris longus (PL) and flexor carpi radialis (FCR) tendons at the distal forearm during finger, wrist, and forearm movements, and to assess how the individual range of motion influences MN displacement in positions relevant for anterior wrist surgery.

Both upper limbs of 27 healthy volunteers were examined prospectively using high-frequency ultrasound, yielding 53 limbs for analysis after applying exclusion criteria. Transverse images were obtained at the distal insertion of pronator quadratus in five standardized positions combining neutral, radial, and ulnar wrist deviation; finger flexion/extension; and forearm pronation/supination. The distances from the medial margin of the MN to the medial margin of the PL and from the lateral margin of the MN to the lateral margin of the FCR were measured using image-analysis software. Correlations between the range of motion and MN displacement were analyzed using Pearson correlation.

The MN had a mean height of 1.8 ± 0.4 mm and width of 4.7 ± 0.9 mm. The nerve changed position relative to PL and FCR in all tested positions. The medial margin of the MN was found medial to the PL at least once in every wrist position and most frequently during finger flexion. The lateral margin of the MN extended beyond the lateral margin of the FCR only rarely. A statistically significant negative correlation was found between maximum radial deviation and MN displacement toward the lateral border of the FCR.

The MN demonstrates measurable positional changes at the distal forearm during finger, wrist, and forearm movements. These dynamic shifts reduce the reliability of assuming a constant "safe" location between PL and FCR and should be considered when planning volar wrist approaches and performing percutaneous or minimally invasive procedures around the MN.