Some upper cervical spine norms.

Lateral cervical spine films from 175 normal examinations of adults performed in the emergency room of North Carolina Baptist Hospital were analyzed to establish some norms and relationships in the upper cervical spine. The predens angle was found to be between 0 degree-13 degrees (mean 5.57 degrees) in neutral position and 0-18 degrees (mean 9.27 degrees) in flexion in most persons. Ninety-two percent of persons have angles greater than 3 degrees in flexion. A V-shaped predens space is not indicative of injury to the cruciate ligament. Virtually every person has posterior slanting or tilting of the dens and the range of values is up to 35 degrees (mean 17.43 degrees). Ninety-eight percent of persons have an angle greater than 6 degrees. A tilted dens does not indicate acute or remote trauma. No relationship was identified between the predens angle and the dens tilt angle. The posterior arch of the atlas can be found at any position between the occiput and spinous process of C2 in all positions of the head and neck. Hence, fanning or widening of the C1-C2 interspinous distance is not a reliable index of ligamentous injury in the upper cervical spine.