Spontaneous rupture of extensor pollicis longus tendon was first reported by Dupley in 1876. This rupture has been reported after distal radius fracture (Colles fracture), rheumatoid arthritis, steroid injections or systemic steroid treatment, and occupational tenosynovitis. The main etiologies of this rupture are the fracture of the tendon over the irregular bone surface following the fracture or inflammatory processes as in rheumatoid arthritis. Most ruptures are usually found at Lister's tubercle. Some authors suggested ischemic etiology in the cases following wrist trauma with no residual fracture. We describe a case of rupture of the extensor pollicis longus tendon 1 month after a blunt wrist trauma with no residual fracture. The rupture was at the myotendinous junction (MTJ). To highlight on this rupture, we believed it was caused from both vascular and mechanical factors. The mechanical factor was the position of the myotendinous junction under the extensor retinaculum. The vascular factor was the nature of the myotendinous junction being the most sensitive to ischemia. Level of Evidence: Level V, diagnostic study.