Normal Cervical Posterior Line Alignment on X-ray, CT, MRI
The cervical posterior line (posterior vertebral body line) is an imaginary line connecting the posterior cortical margins of the cervical vertebral bodies on a lateral projection. It serves as a reliable anatomical reference for assessing spinal alignment and canal integrity. Displacement of this line is a critical indicator of fracture, ligamentous instability, or subluxation requiring prompt clinical attention.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Lateral | <2 mm |
Clinical Significance
In a normally aligned cervical spine, the posterior vertebral body line forms a smooth, continuous curve on the lateral view. Any single vertebral body stepping anteriorly or posteriorly beyond <2 mm relative to adjacent levels is considered abnormal and raises concern for structural instability. Minor variations may occur at C2–C3 in children due to physiologic pseudosubluxation, a pitfall that must be recognized to avoid misdiagnosis.
Disruption of the posterior line can reflect a spectrum of pathology ranging from acute trauma to degenerative or inflammatory disease. Posterior line displacement combined with other imaging findings — such as widened interspinous distances or prevertebral soft tissue swelling — substantially increases suspicion for significant injury.
- Flexion teardrop fracture with retropulsion
- Unilateral or bilateral facet dislocation
- Hangman’s fracture (C2 traumatic spondylolisthesis)
- Degenerative spondylolisthesis or disc herniation with retrolisthesis
- Physiologic pseudosubluxation at C2–C3 or C3–C4 in pediatric patients
Reference: Frymoyer JW, Wiesel SW. The Adult and Pediatric Spine. (2004).
Imaging Notes
On lateral radiography, the posterior vertebral line is assessed by tracing the posterior cortical margin of each cervical body from C1 to C7. Adequate lateral positioning with full visualization of C7–T1 is essential; a swimmer’s view may be required if the cervicothoracic junction is obscured. On CT, sagittal multiplanar reconstructions provide the most reliable assessment, allowing precise sub-millimeter measurement of any step-off. MRI sagittal sequences (T1 and T2) complement CT by simultaneously evaluating associated cord compression, disc injury, and ligamentous disruption that may not be apparent on bony imaging alone. Consistent measurement from mid-posterior cortex to mid-posterior cortex at adjacent levels minimizes inter-observer variability across all modalities.