Two unusual cases of the fracture of the first rib resulting from traffic injury are reported. There were no fracture of other ribs, clavicle fracture of the same side, and thoracic injury complications in these cases. We reviewed the mechanism of fracture of these cases. It is suggested that fracture is caused by direct force from the anterior at the posterior portion of the first rib in Case 1, and by the traction force of the muscle in the thinnest portion of the rib in Case 2.
