Axial loading with hyperflexion injury to the atlas resulting in crushed lateral masses.

A 40-year-old man was involved in an ATV accident, in which he landed on the top of his head. There was no neurological deficit. A plain radiograph showed prevertebral soft tissue swelling at the atlas and axis level. Computed tomography (CT) demonstrated vertical fractures of the anterior aspects of both lateral masses of the atlas, extending to the junction of the lateral mass with the anterior arch bilaterally. There was no lateral offset of the lateral masses. The mechanism of injury is believed to be axial loading along with hyperflexion.