Snapping of the Thumb Caused by Supernumerary Extensor Pollicis Longus Tendon

Supernumerary extensor tendons of the hand are relatively common, whereas supernumerary extensor pollicis longus (EPL) tendons are rarely reported. Herein, we present the case of a 17-year-old boy with painful snapping at the anatomical snuffbox after repetitive pushups. Preoperative dynamic ultrasonography and magnetic resonance imaging revealed the bifurcation of EPL tendons. Through explorative surgery under wide-awake anesthesia, we found 2 EPL tendons with a single EPL muscle, which pass through the single extensor compartment and EPL canal distally. Intraoperatively, after releasing the extensor compartment and EPL canal, each EPL tendon was rerouted to a separate gliding plane to resolve the snapping symptom and recurrence. Six months postoperatively, the snapping symptom was resolved, and the patient resumed activities of daily living without any complications. This clinical case may be useful for examining anatomical variations of the thumb extensor tendon and detecting extraordinary pathological symptoms.