Approach

The aim of spinal imaging in acute trauma is to detect fractures, evaluate their stability, and identify associated soft tissue injuries. Other emergent indications include atraumatic pain (usually in the setting of an underlying malignancy or predisposition to infection) and acute myelopathy or radiculopathy.

CT with multiplanar reconstructions is significantly more sensitive and specific for detection and exclusion of cervical spine fractures than plain radiography and is now considered the standard of care in acute trauma. Five specific clinical criteria—validated by the National Emergency X-ray Utilization Study (NEXUS) and widely used in emergency departments and trauma centers—permit the emergency physician to exclude cervical spine fracture without imaging:

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  No midline tenderness

  
  
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  No focal neurologic deficit

  
  
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  Normal alertness

  
  
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  No intoxication

  
  
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  No painful distracting injuries

MRI is indicated for patients with neurological deficits, prolonged obtundation, or unstable spinal injuries. Flexion and extension radiographs are never indicated in the emergency setting, as muscle spasm can mask ligamentous instability and truly unstable injuries can be made worse.

Both the thoracic and lumbar spine are normally included on chest and abdomen CT in the setting of polytrauma, and as long as high-quality reformations are available, a separate dedicated spinal examination need not be performed. Plain radiographs are usually adequate to screen for thoracic and lumbar spine injuries in patients with low-energy mechanisms, with CT to follow if an abnormality is identified.

To avoid missing craniocervical dissociation injuries, which can be subtle, several measurements in the cervical spine are useful. The tip of the basion should be within 9.5 mm of the tip of the dens on CT (12 mm on lateral radiograph). The tip of the basion should be between 6 and 12 mm from a line drawn along the posterior cortex of C2 (the posterior axial line). This is referred to as the basion–axial interval. Injury to the transverse ligament, which affixes the dens to C1, increases the atlantodental interval, which should be less than 3 mm in adults and 5 mm in children on both CT and radiographs.

In the lower thoracic and lumbar spine, the interspinous distance and interpedicular distances on frontal radiographs and coronal CT increase by about 2 mm at each level from craniad to caudad. Isolated widening of either of these distances at a single spinal level should raise suspicion for fracture. Disk herniations should be identified when present and can be practically described as either (1) broad-based disk bulge, (2) central, paracentral, foraminal, or lateral protrusion, or (3) extruded or sequestered disk, in which disk material is separated from the body of the disk.

Anterior compression and burst fractures can be described by the ratio of the affected vertebral body height to the average height of the adjacent superior and inferior vertebral bodies; for example, if the adjacent vertebral body height average is 25 mm and the affected vertebra is 20 mm, it has a 20% loss of height. Canal compromise can similarly be expressed as a percentage of the expected canal diameter at the affected level.

Imaging

Clinical Presentations and Differential Diagnosis

Craniocervical Junction Injuries

Atlantooccipital dislocation (AOD) is a consequence of very high-energy trauma; usually diagnosed at autopsy rather than on imaging studies. In AOD, the skull is dislocated with respect to the lateral masses of C1, and this can be directly assessed on CT by evaluating the congruity of the atlantooccipital articulations. Displacement can be along either the transverse or craniocaudal axis and is usually associated with marked prevertebral soft tissue swelling.

Complete AOD (dislocation) is a fatal injury, but partial AOD (subluxation) may be compatible with life. To ensure detection of an unstable but potentially survivable injury, the atlantooccipital articulation should be specifically evaluated on any lateral radiograph or cervical spine CT obtained for trauma. The most useful measurements are the basion–dens interval, the basion–axial interval, and the atlantodental interval, which assesses integrity of the transverse C1 ligament.

Occipital condyle fractures, considered rare prior to the advent of CT, are diagnosed with increasing frequency. Depending on the mechanism of injury, several types of occipital condyle fracture have been identified.

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  Type I: impaction fracture of the occipital condyle due to axial loading

  
  
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  Type II: basilar skull fracture, usually due to direct impact, that extends to the occipital condyle

  
  
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  Type III: avulsion injury at alar ligament attachment due to bending and rotation

In Type I and II injuries the alar ligaments and tectorial membrane are intact, and these fractures are generally stable. Because the alar ligament is disrupted in Type III fractures, they are potentially unstable. Type III fractures are more likely to be associated with lower cranial nerve deficits ( Fig. 4.1 ).

Atlantoaxial Rotatory Subluxation

Atlantoaxial rotatory subluxation is a consequence of motor vehicle accidents and sports-related injuries in older adolescents and adults but may be nontraumatic in children. In trauma, disruption of the alar ligament, atlantoaxial joint capsule, and transverse ligament permits hyperrotation of C1 relative to C2 with widening of the atlantodental interval. Patients present with their head tilted to one side and rotated toward the opposite side.

AP or odontoid radiographs will show asymmetry of the lateral atlantodental intervals. CT is diagnostic and demonstrates rotation of the C1 ring with respect to the C2 lateral masses. If not clinically obvious, dynamic imaging with scanning before and after voluntary head turning can establish whether or not subluxation is fixed.

Fixed subluxation can be reduced by cervical traction followed by active range of motion (ROM) exercises. Rarely, C1–C2 fusion can be considered for persistently fixed and painful rotation ( Fig. 4.2 ).

C1 Burst (Jefferson) Fracture

Axial forces transmitted through the occipital condyles to the C1 lateral masses result in multipart fractures of the C1 ring with radial displacement of the fragments away from the C2 odontoid. A common injury mechanism is diving headfirst into shallow water. Because the fracture widens rather than narrows the spinal canal, patients often present with pain but without neurologic dysfunction. Associated spinal cord injury is usually absent unless there is a retropulsed fragment. Stability of this fracture depends on whether or not the transverse atlantal ligament is intact.

The “classical” Jefferson fracture is a four-part fracture with bilateral anterior and posterior arch fractures. Two- and three-part fractures are common variants reflecting eccentric loading and usually involve one lateral mass and the adjacent occipital condyle.

Coronal CT reformations will show displacement of the C1 lateral masses away from the odontoid. If the combined lateral atlantodental intervals are > 7 mm, transverse ligament rupture is possible. Sagittal CT reconstructions will show prevertebral soft tissue swelling as well as a widened atlantodental interval. The normal atlanto-dental interval is ≤ 3 mm in adults and ≤ 5 mm in children. An atlantodental interval > 6 mm indicates definite transverse ligament disruption. Associated cervical spine fractures, especially of C2, should be excluded.

Multidetector CT more precisely delineates the C1 ring fractures, their extent of displacement, and any other synchronous fractures of the cervical spine. Minimally displaced fractures may be treated conservatively with hard collar immobilization. If the transverse atlantal ligament is disrupted, the injury will likely require halo placement or C1–C2 surgical fixation ( Fig. 4.3 ).

Odontoid (Dens) Fracture

C2 fractures are common and are frequently seen in elderly patients who fall from standing or sitting. Hyperflexion, hyper-extension, and lateral flexion mechanisms can all result in fractures that separate the odontoid from the vertebral body.

Type I fractures are avulsions of the odontoid tip at the attachment of the alar ligaments. These are rare but sometimes seen in patients with atlantooccipital dislocation. Type II fractures traverse the odontoid base. Because the dens is mainly composed of dense cortical bone, they are prone to non-union, and patients often require operative repair. Type III fractures separate a fragment that includes both the dens and a portion of the C2 body. Thanks to the larger area of cancellous bone-to-bone contact, type III fractures tend to heal with immobilization and do not usually require surgical fixation. Types II and III are also referred to as “high” and “low” dens fractures, respectively ( Fig. 4.4 ).

Traumatic C2 Spondylolisthesis

Traumatic C2 spondylolisthesis results from the combined effects of axial loading and either hyperextension or hyperflexion. Both C2 pedicles fracture with varying degrees of angulation and anterolisthesis of C2 on C3. Historically referred to as a “hanged man′s” fracture or “hangman” fracture because of its similarity to the injury caused by judicial hangings, traumatic C2 spondylolisthesis most frequently results from high-speed motor vehicle accidents. Neurologic sequelae are uncommon. Because the fracture tends to widen, rather than narrow, the spinal canal, the spinal cord and nerve roots are not usually damaged. The “atypical” hangman fracture is a variant in which the coronal fracture traverses the posterior C2 body, rather than the pedicles.

CT is necessary for accurate evaluation of displacement and angulation, which impact classification and treatment decisions, as well as identification of vertebral foraminal fractures and potential vascular injury. As in all cervical spine fractures, CTA should be considered to exclude vertebral or carotid artery injury.

Fractures that do not show disk widening, angulation, or subluxation are considered stable (Type I) ( Fig. 4.5 ).

Effendi/Levine and Edwards Classification

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  Type I: Bilateral pedicle fractures with intact disk and ligaments. No angulation or translation

  
  
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  Type II: C2/3 disk disruption with angulation but no translation

  
  
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  Type III: C2/3 disk disruption with angulation, translation, and facet subluxation or dislocation

Type I fractures are stable, types II and III are unstable ( Fig. 4.6 ).

Cervical Hyperflexion Injury 1

Cervical spine hyperflexion injuries result from whiplash mechanisms in which abrupt extension is followed by flexion or from axial loading forces acting upon a flexed neck. The latter are seen in head-on motor vehicle collisions and diving accidents. Hyperflexion injuries range, with increasing severity, from the stable hyperflexion sprain, in which only the posterior ligamentous complex is disrupted, to anterior vertebral subluxation, bilateral facet dislocation, and flexion “teardrop” or burst fractures.

Hyperflexion sprains may only show subtle spinous process distraction on lateral radiographs or sagittal CT reformations. If the injury is limited to the interspinous and nuchal ligaments, it is considered stable. Any degree of anterior vertebral subluxation, facet subluxation, or facet dislocation, however, indicates instability. MRI and/or delayed flexion and extension radiographs (after muscle spasm related to the acute injury has resolved) can be used to assess ligamentous injury and stability better.

The clay shoveler fracture is a horizontal fracture of a lower cervical spinous process originally described in workers who would abruptly contract their cervical muscles and flex the neck while shoveling heavy clay. The fracture may also result from direct impact and other complex mechanisms. Clay shoveler fractures are stable, as they do not involve the vertebral ring and are often incidentally discovered years after a forgotten injury.

Bilateral interfacet dislocation (BID) is a hyperflexion injury characterized by disruption of the anterior, middle, and posterior spinal ligaments. It is uncommon, extremely unstable, and associated with a high risk of spinal cord damage. On lateral cervical spine radiograph or sagittal CT reformation, the inferior articulating facet of the upper vertebra is displaced and locked anterior to the superior articulating facet of the lower vertebra. The upper vertebral body is anteriorly displaced by up to 50% relative to the lower one. Disk space and interspinous widening reflect the ligamentous nature of this injury. Small facet fractures may be seen ( Fig. 4.7 ).