MRI Analysis of the Wrist: Does the Presence of Palmaris Longus Affect Median Nerve Position?

Abstract

Background: Understanding the median nerve's position relative to surrounding anatomy is essential; however, there are many variations among individuals. This study assesses differences in median nerve position with or without palmaris longus (PL). We hypothesize that PL presence alters median nerve position, resulting in a greater distance to the skin volar surface, a decreased distance to the radius volar surface, and an increased distance to the flexor carpi radialis (FCR).

Methods: 1193 wrist magnetic resonance imaging (MRI) studies were retrospectively reviewed from 2019 to 2023. One hundred adults ages 18 to 50 meeting criteria were included for a power > 80%: 50 wrist axial plane MRIs (distal radial-ulnar joint level) with PL and 50 without PL. Measurements included the distance from the median nerve center to the skin volar surface, radius volar surface, and FCR center. Statistical analysis included Fisher exact tests and Mann-Whitney U Test (median, ranges), with significance at P-value < 0.05.

Results: Individuals with PL had a greater distance between the median nerve and skin volar surface. The presence of PL exhibited no discernable difference in the distance between the median nerve to the radius volar surface or the FCR center. Palmaris longus presence or absence did not affect the radial/ulnar positioning of the median nerve to the FCR center.

Conclusions: PL presence results in a deeper median nerve position within the wrist in relation to the skin volar surface. This knowledge is crucial for musculoskeletal specialists, especially during volar approach wrist surgeries and when administering anesthetic or therapeutic injections to the median nerve.