Computed Tomography is usually the first imaging modality in the assessment of a potential traumatic spinal injury, particularly in demonstrating injuries of the bony skeleton. Magnetic Resonance Imaging adds vital information regarding the integrity of the pre-vertebral soft tissues, intervertebral disc and spinal ligamentous structures. This will determine the stability of the injury, but more importantly will aid in the formulation of a management plan, both conservative, surgical and the potential surgical approach. 

Figures 1 and 2 demonstrate the normal spinal anatomy on Computed Tomography.

Figure 3 demonstrates the normal spinal anatomy on Magnetic Resonance Imaging.

The definition of spinal instability remains debatable, however an  injury should be considered unstable when there is risk of further skeletal or neurological injury without stabilisation. 

Several concepts have been developed in an attempt to identify unstable injuries. The 3 column spine and its classification described by Denis in 1983 is still widely used for the assessment of the thoracolumbar spine. 

• The anterior column comprises of the Anterior Longitudinal Ligament (ALL), the anterior two thirds of the vertebral body and its associated intervertebral disc. 
• The middle column consists of the posterior one third of the vertebral body, its associated intervertebral disc and Posterior Longitudinal Ligament (PLL). 
• The posterior column includes the posterior neural arch, the ligamentum flavum, interspinous ligaments, supraspinous ligaments and facet joint capsules (Posterior Ligament Complex -PLC). 

For a spinal injury to be deemed unstable, there should be disruption of two adjacent columns in the same vertebra or damage to the Posterior Longitudinal Ligament and posterior third of the intervertebral disc.

The same principle applies for the C3 to C7 cervical spine levels. In the sub-axial cervical spine, the injuries are classified based on the mechanism of injury. Hyperflexion may result in injury of the posterior and middle column with progression of the injury anteriorly and bilateral facet joint dislocation, in more severe cases. Hyperextension may result in injury to the anterior and middle column, with progression of the injury posteriorly resulting in dislocation and disc herniation. The injuries of the cranio-cervical junction will not be analysed on this presentation.