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

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.