Horizontal fracture of the anterior arch of the atlas.

Horizontal fracture of the anterior arch of the atlas can be easily overlooked on lateral radiographs. The fracture is not associated with neurological deficit but may be the cause of severe pain. A review of the literature reveals only 3 previously reported cases. Seven new cases, including 2 without other cervical spine fractures, indicate a much higher incidence than was previously thought. Hypotheses about the mechanism of injury are discussed.