Radiology pearls 3 --> subaxial cervical spine and thoracolumbar spine

subaxial cervical spine - C3 to C7

The classification of injury is based on the mechanism of injury. The patterns are distraction, compression, flexion and extension. Then there are distractive flexion, distractive extension, compressive flexion and compressive extension injuries.

A. On sagittal reconstructions, check for the following:

• anterior and posterior vertebral body lines and spinolaminar line are uninterrupted
• vertebral body height is the same anteriorly and posteriorly
• no prevertebral swelling
• no widening of distances between spinous process
• facet joints aligned, appearing as stacked parallelograms
• disc spaces intact

B. On coronal images check the following:

• height on each side of the vertebral body is the same
• disc spaces are intact
• facet joints are aligned

C. On axial images check the following:

• no soft tissue swelling
• facet joints aligned
• no significant rotation

i. compressive extension injury:

there is damage to the vertebral arch but the body remains intact. The vertebral arch fractures may be unilateral or bilateral, involving the pedicle, articular process, the lamina or a combination of these. In more severe injuries, the affected vertebra may be displaced anteriorly relative to the subjacent vertebra. The antero superior aspect of the subjacent vertebra may be sheared off.

ii. compressive flexion injury:

• stage 1 - there is blunting of the anterior-superior vertebral margin.
• stage 2 - there is a beak like appearance to the anterioe vertebral body with loss of anterior vertebral height and oblique contour.
• stage 3 -there is fracture extending from anterior surface of the vertebral body into the disc space.
• stage 4 - there is posterior displacement of the inferoposterior aspect of the vertebral body less than 3 mm.
• stage 5 -displacement relative to the vertebra below is more than 3 mm

iii. distractive extension injury

• stage 1 -abnormal widening of the disc space, representing disruption of the anterior longitudinal ligament and disc
• stage 2 - posterior ligaments are disrupted and the cephalad vertebtrae are displaced into the spinal canal

iv. distractive flexion injury:

range from facet subluxation, through unilateral facet fracture or dislocation to bilateral facet joint fracture or dislocation.

v. vertical compression

• stage 1: there is central fracture of either the superior or inferior endplate with a cupping deformity of the endplate.
• stage 2: bothe endplates are involved.
• stage 3: the vertebral body is fragmented with fragments displaced in multiple directions. The vertebral arch may not be involved.

Thoracolumbar spine

Classification of injury is based on three column concept. Columns of thoracic spine are anterior, middle and posterior. common injury patterns are compression fractures, burst fractures, flexion distraction (seat belt type), and fracture dislocations.

The anterior column:is formed by the anterior longitudinal ligament, the anterior half of the vertebral body and the anterior annulus fibrosus.

Middle column: posterior longitudinal ligament, the posterior half of the vertebral body and posterior annulus fibrosus.

Posterior column: posterior osseous arch, supraspinous and interspinous ligaments, the ligamentum flavum and the facet joint capsule.

The features sought on sagittal, coronal and axial images of the T-L spine are similar to those described for lower cervical spine injuries.

i. compression fracture:

the anterior column fails under compression. The middle column remains intact and acts as a hinge. The posterior column is usually intact but with severe injuriew it may partially fail in distraction. This injury may be anterior or lateral.

ii. burst fractures:

there is failure of compression of the anterior and middle columns, but no posterior column. Failure in compression of the anterior column is shown by fracture of the cortex of the anterior vertebral body, which loses height. Failure in compression of the middle column is shown by similar findings in the posterior vertebral body. Characteristically the pedicles are spread apart by the posterior vertebral body fracture. There is commonly a vertical fracture of the lamina, and splaying of the facet joints, without which there could not be significant widening of the interpedicular distance.

iii. flexion distraction "seat-belt type" injury:

there is failure in distraction of the middle and posterior columns with either no injury to the anterior column or minor compression. The injury may be through bone, through the ligaments or a combination of the two. When injury is through the bone at one level, it is known as "chance" fracture. There is a high incidence (around 60%) of intra-abdominal injury in association with flexion-distraction injuries.

iv. fracture dislocation:

failure of all three columns leading to translational deformity (sublaxation or dislocation) which may be in the sagittal or coronal plane. Fracture dislocation of thoracic spine occur with high energy trauma.

Fracture dislocations involve all three column making them extremely unstable injuries, commonly associated with neurological damage.

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Clearing the C-spine

The best approach to clearing the cervical spine with multiple trauma remains controversial. In this group of patients, plain XRay miss a significant proportion of bony cervical injuries. A single cross table lateral view missed 37% of significant injuries. A three view series missed 10% while cervical spine CT missed none. Ligamentous injuries are not well imaged with CT scan. When multiple trauma patients are imaged with CT scan, 6% have discoligamentous injuries that are not detected.

CT is the imaging modality of choice in this group of patients with supplementary MRI when spinal cord of ligamentous injury is suspected.