Rupture of the extensor pollicis longus (EPL) is an uncommon but important cause of wrist and distal forearm pain that may be easily overlooked in clinical practice. Ultrasound-particularly dynamic assessment-offers a reliable and noninvasive method for evaluating musculotendinous integrity. We report the case of a 31-year-old male who presented with a dislocation-like sensation and pain in the left wrist during weight training. Dynamic ultrasound examination revealed a focal anechoic defect with loss of normal fibrillar echotexture within the EPL muscle, confirming muscular rupture. This case underscores the diagnostic value of dynamic ultrasound in detecting EPL injuries and highlights the importance of detailed knowledge of distal forearm sonoanatomy for precise lesion localization.