Answers

Short answers

1. Anteroposterior lateral and anteroposterior odontoid peg views.

2. Anterior spinal line, posterior spinal line, spino-laminar line, posterior pillar line, and spinous process line.

3. There is bilateral facet joint subluxation with splaying of the spinous processes.

4. This injury is an unstable injury.

5. Computed tomogram and magnetic resonance image of the cervical spine.

Long answers
1. Standard views
According to the National Institute for Health and Clinical Excellence ¹, the standard trauma series consists of three views—namely, anteroposterior, lateral, and anteroposterior odontoid peg views. The two large evidence based studies on imaging guidelines—the Canadian cervical spine (c spine) rules² and the NEXUS (National Emergency X-Radiography Utilization Study) rules³—were also based on the standard three-view series, with additional views (for example, oblique views) at the doctor’s discretion.

It is essential that a technically adequate examination is performed. The top of the T1 vertebra must be included on the lateral image and the odontoid peg view should show the lateral masses of the atlanto-axial articulation. Further views are required to supplement the lateral view (for example, Swimmer’s view) if the T1 vertebral body cannot be visualised. Computed tomography of the cervical spine may be required if this cannot be achieved after two attempts. Remember that most missed spinal injuries occur in the upper and lower cervical regions, areas which are poorly visualised in suboptimal films.⁴ Where doubt exists, computed tomography is recommended.

2. Lines for evaluation
On the lateral views, alignment should be assessed along five anatomical lines. They are the anterior and posterior spinal lines, which run along the anterior and posterior aspects of the vertebral bodies along the line of the longitudinal ligaments, and the spinolaminar line, which runs at the bases of the spinous processes. This line marks the posterior margin of the spinal canal. The bony spinal canal where the spinal cord sits lies between the posterior longitudinal line and spinolaminar line. Other additional lines have been described—namely, the posterior pillar line, which runs along the posterior margins of the articular pillars, and the spinous process line, which joins the tips of the spinous processes.⁵

The described lines must run in a smooth arc, without any step in them (fig 2). Also look for prevertebral soft tissue swelling, which may give a clue to the presence of an injury. This sign, however, is insensitive and its absence should not provide any degree of reassurance. Above the level of the laryngeal inlet, the width of the prevertebral soft tissue should not exceed 7 mm. Below the level of the laryngeal inlet, the width of the soft tissue layer should not exceed the width of the adjacent vertebral body.^{5 6} (fig 2 )

View larger version (72K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 2

 
3. Abnormalities present
The expected smooth lines have been disrupted by a step at the level of the C3 and C4 vertebrae posteriorly. The posterior pillar line is also disrupted. Both the superior articular facets of the C4 vertebrae are subluxed with widening of the spinous processes (fig 3) The radiographs suggest that there has been injury involving the anterior longitudinal ligament, posterior longitudinal ligament, supraspinous ligament, interspinous ligament, and ligamentum flavum. Note also the widened interspinous distance between C3 and C4 of more than 50% compared with the adjacent interspinous distance of C4 and C5 indicating hyperflexion injury (fig 4).⁶

View larger version (71K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 3

 

View larger version (85K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 4

 
4. Clinical importance
The radiographic/computed tomography signs of major injury include displacement of more than 2 mm in any plane, wide vertebral body in any plane, wide interspinous space, wide facet joint, disrupted posterior vertebral body line, wide disc space, vertebral burst fractures, and locked facets (unilateral or bilateral). Only one of these signs needs to be present to make a radiographic diagnosis of an unstable injury. An unstable injury is one where further movement or force applied to the injured neck can cause added deformity, risking spinal cord injury. Relatively minor injuries include isolated spinous process or transverse process fracture and simple wedge compression fracture.⁷

5. Further imaging
Computed tomography is the next appropriate step to take. This technique is more sensitive than plain radiography in detecting fractures with a reported sensitivity of 100% and specificity of 99%.⁸ According to the NICE guidelines, computed tomography is indicated if plain films are technically inadequate, suspicious, abnormal or if clinical suspicion of spinal injury continues despite normal radiographs.¹

Several studies have advocated the use of computed tomography as a primary screening tool, although the substantial radiation burden it places particularly to radiosensitive organs such as the thyroid gland, suggest that this test should be performed after appropriate clinical stratification. The additional nominal lifetime risk of cancer following spiral computd tomography of the cervical spine are between 1 in 2400 to 1 in 4500.⁹

Computed tomography may be considered the first line imaging investigation in patients with suspected spinal injuries who are obtunded or uncooperative, have altered mental status, distracting injuries, or neurological injuries.^{10 11} Moreover, patients with multisystem or significant head injuries have a high incidence of cervical spine injuries and computed tomography of the cervical spine should also be considered.¹² When scanning other body regions in the context of trauma, it is helpful to scan the cervical spine during the same examination.

Magnetic resonance imaging of the cervical spine would be required to evaluate the extent of ligamentous injury and determine if other injuries are also present, in particular within and around the spinal cord. It allows superior depiction of soft tissue structures with reported sensitivities for intervertebral disc injury of 93%, posterior longitudinal ligament injury of 93%, and interspinous ligament injury of 100%.¹³ Spinal cord contusions can be identified by signal changes within the cord itself. Other pathologies identifiable include acute disc herniation, epidural haematomas, and vertebral artery injury.¹⁴ Both disc herniations and haematomas may result in cord compression and neurological sequelae.

Cite this as: BMJ 2008;337:a207