Enhancing Evaluation of Cervical Spine: Thresholds for Normal CT Relationships in the Subaxial Cervical Spine

Very little normative computed tomography (CT) scan data exist defining expected relationships of vertebral structures in the intact cervical spine. Better understanding of normal relationships should improve sensitivity of injury detection, particularly for facet subluxation. The purpose of this paper was to describe the normal anatomical relationships and most sensitive measurements to detect abnormal alignment in the subaxial cervical spine.

A group of 30 CT scans with no documented cervical spine injury were utilized from an established database in a trauma population. Twenty-two anatomical measurements were made for each level of the subaxial cervical spine using Microview software. For the purposes of measurement, the upper confidence limit of normal was reported as two standard deviations from the mean.

The novel, CT based measurements of bone articulation were generally smaller and had lower confidence intervals compared to traditional radiographic measurements of midline structures (such as interspinous distance, interlaminar widening, disc space widening). The upper limit of normal of facet joint height was reported (1.54 mm anterior, 1.27 mm posterior, and 2.0 mm midportion), which may help identify distractive-flexion injuries. The upper limit of normal vertebral translation (2.0 mm) was also reported to identify translation/rotation injuries.

Normal CT measurements for the subaxial cervical spine, especially in the facets, were found to have small confidence limits and variation. Based upon these findings, we conclude that facet measurements and translation may be better screening tools than traditional radiographic criteria based upon midline structures. Using these measurements may improve detection of cervical spine injuries warranting further imaging or investigation and reducing missed injuries.

Improved understanding of normal anatomic measures in the subaxial spine will allow for better screening and identification of injuries.