# Ultrasonograhic Identification of the Entrapment of a Transligamentous Sensory Branch of the Ulnar Nerve

## TL;DR

This paper describes a rare case where ultrasound was used to identify an unusual entrapment of a sensory branch of the ulnar nerve at the wrist.

## Contribution

The study presents a novel ultrasound-based identification of a transligamentous sensory branch entrapment of the ulnar nerve.

## Key findings

- High-resolution ultrasonography revealed an aberrant sensory branch piercing the palmar carpal ligament.
- Focal nerve flattening and proximal enlargement were observed, consistent with entrapment.
- The case emphasizes the importance of extending sonographic evaluation beyond conventional wrist entrapment sites.

## Abstract

Anatomical variations of the ulnar nerve at the wrist are uncommon and may lead to diagnostic confusion or iatrogenic injury if unrecognized. We present an ultrasound-based identification of a rare transligamentous ulnar nerve sensory branch entrapment in an elderly male with chronic ulnar-sided hand paresthesia. High-resolution ultrasonography revealed an aberrant sensory branch deviating from the ulnar nerve, piercing the palmar carpal ligament, and coursing superficially rather than entering Guyon’s canal. Further assessment demonstrated focal nerve flattening within the ligament with proximal enlargement, consistent with entrapment. This case highlights the value of ultrasound in detecting rare peripheral nerve variants and their entrapments. Therefore, it is also noteworthy to extend the sonographic evaluation beyond conventional entrapment sites at the wrist.