# Dynamic Ultrasound Imaging of Extensor Pollicis Brevis Hypertrophy in Proximal Intersection Syndrome: A Case Report and Literature Review

## TL;DR

This case report uses dynamic ultrasound to show how extensor pollicis brevis muscle changes can cause wrist pain in non-athletes due to repetitive tasks.

## Contribution

The study introduces a novel friction-based mechanism for proximal intersection syndrome identified via dynamic ultrasound.

## Key findings

- Dynamic ultrasound showed extensor pollicis brevis hypertrophy displacing second compartment tendons.
- The condition was linked to repetitive lifting with a wide grip, not athletic activity.
- The findings suggest mechanical friction between dorsal compartments may cause overuse wrist pain.

## Abstract

This case report presents an atypical presentation of proximal intersection syndrome and provides ultrasound‐based evidence of extensor pollicis brevis muscle belly hypertrophy with associated edema in a non‐athletic population. While occupationally induced PIS has been previously documented, the patient's symptoms in this case were linked to repetitive lifting tasks involving prolonged extension of the first metacarpophalangeal joint with a wide grip. Dynamic ultrasound assessment revealed radial displacement of the second compartment tendons by the extensor pollicis brevis muscle during the aggravating movement. This finding suggests a novel pathomechanism, potentially driven by mechanical friction and stress between the first and second dorsal compartments, warranting further investigation.

Dynamic ultrasound revealed extensor pollicis brevis hypertrophy displacing second compartment tendons, suggesting a novel friction‐based mechanism for proximal intersection syndrome. This case highlights the role of dynamic sonography in identifying motion‐dependent tendon interactions underlying overuse‐related wrist pain.