Obliques and Flexion/Extension Views
Flexion/Extension (F/E) views are most often obtained for patients with an acceleration-deceleration mechanism who have neck pain/cervical tenderness but normal plain radiographs. In these patients, there is potential for ligamentous injury that may not be seen on a static, neutral view of the cervical spine.71 Small retrospective studies have suggested this approach might be of diagnostic benefit in certain patients.72,73 Patients must have a normal mental status, have a normal neurologic examination, and be able to cooperate with the neck movement that is required. Pollack et al reviewed the NEXUS data to attempt to determine if there is benefit to the use of F/E views in this setting.71 F/E views were obtained in 10.5% of the 818 patients in NEXUS who were ultimately found to have cervical spine injury. In only 4 of these patients, standard imaging failed to identify a cervical spine subluxation or dislocation, but in every such instance, these views were positive for some injury that routinely prompts additional imaging.71 Where there is concern about ligamentous instability, MRI is preferable to F/E. The overall use of F/E in the acute setting of blunt cervical trauma should be very limited; in fact, the ability of F/E views to reliably diagnose significant injury is questionable.71 A recent cadaver study demonstrated that, with less than 60 degrees of flexion or extension, intervertebral rotation or displacement was almost never greater than the 95% confidence interval established for asymptomatic people. Even with adequate motion, intervertebral rotation and displacement were within normal limits after excessive damage to the soft-tissues.74
The addition of supine oblique views is thought to enhance the visualization of the lower cervical spine and posterior elements and to detect injury that may not be identified with standard views alone. However, Offerman et al demonstrated that the addition of oblique views did not increase the sensitivity and specificity for fracture detection.75 While some centers may not have CT readily available, addition of oblique views to the standard 3 view series does not always improve diagnostic accuracy. The clinician may have a false sense of security about the absence of a fracture when the oblique views are normal; therefore, these views are not recommended for regular use.
Interpretation Of Plain Radiographs
Ensure that the films are good quality and that the lateral view visualizes the C7-T1 junction. One of the most common reasons for missed cervical spine fracture is technically inadequate plain films. In one retrospective review of 216 trauma patients, failure to visualize C7 and the C7-T1 junction was the most common error made in the radiographic assessment of cervical spine injury.76 In another retrospective review of 740 patients with cervical spine injuries, the diagnosis of cervical spine injury was delayed or missed in 34 patients (4.6%). In this study, the single most common error was failure to obtain an adequate series of cervical spine radiographs.77 Interpretation of cervical spine radiographs should be undertaken in a systematic manner each time. A useful technique is to remember the ABCs of cervical spine film evaluation: A=alignment, B=bony abnormalities, C=cartilage/space assessment, and S=soft tissues. (See Tables 5 and 6.)
Anterior and posterior cervical lines are imaginary lines that connect the anterior and posterior margins of the vertebral bodies. The spinolaminal line connects the bases of the spinous processes extending to the posterior aspect of the foramen magnum. The 3 lines should form a lordotic curve without disruption. Any disruption suggests bony or ligamentous injury. An exception to this is pseudosubluxation in children at C2-C3, which will be discussed in a subsequent section.49
Evaluate the bones for obvious fractures and loss of height of the vertebral bodies. Any small fragment may represent a fracture. Closely inspect the odontoid and its relationship to C1. Fractures commonly missed on plain films include fractures of C1, fractures of the odontoid, facet fractures, and C7-T1 injuries.78
Anterior or posterior widening of the intervertebral space can be seen in a dislocation, but this may be subtle. Intervertebral disc spaces should be uniform in height and length. Narrowing of the disk space may represent acute disk herniation or adjacent vertebral fracture. Widening could represent injury of the posterior ligamentous complex.
Abnormal size of prevertebral soft tissues suggests an adjacent fracture. To evaluate the size of the retropharyngeal space, measure from the anterior border of C2 to the posterior wall of the pharynx. This distance should be no greater than 6 mm in children and adults. The space from the anterior border of the body of C6 to the posterior wall of the trachea should not exceed 22 mm in adults and 14 mm in children < 15 years old or should be less than the width of the vertebral body at each level. In children less than 2 years old, the retropharyngeal space may normally appear widened during expiration, thus requiring an inspiratory film.49 In a retrospective study of 106 study patients and 93 control patients, the patients were divided into 2 groups: those with fractures at C1-C4 and those with fractures at C4-C7. A C2 prevertebral soft tissue measurement of more than 6 mm had a sensitivity of 59% and a specificity of 84% for fractures at C1-C4. A C6 prevertebral soft tissue measurement of more than 22 mm had a sensitivity of 5% and a specificity of 95% for fractures at C4-C7. The authors concluded that the cutoffs of 6 mm at C2 and 22 mm at C6 as a marker of cervical spine injury fails to identify a large proportion of patients with cervical spine fractures.79
On the lateral view, the predental space (distance between the anterior aspect of the odontoid process and the posterior aspect of the anterior ring of C1) should not exceed 3 mm in an adult or 5 mm in a child.61 Widening of this space is concerning for a Jefferson burst fracture.49 Proper evaluation of the soft tissues in an intubated patient is not possible as the normal air and soft tissue interface is obscured.
First determine if the film is adequate. All 7 cervical vertebrae must be seen, including the top of the first thoracic vertebra. Check the alignment of the ante2009rior, middle, and posterior arcs. These arcs should be present in smooth unbroken lines. Figure 5 demonstrates
a single lateral view of the cervical spine.
Examine the bones; the vertebral bodies C2 through C7 and spinous processes should have uniformity and similar height. The anterior height of the vertebral body should be no more than 3 mm shorter than the posterior height. The "double facet" sign indicates a fractured articular facet. The sign is caused by a display of the anterior margin of the inter-faceted joints overlapping the horizontal rotation
of the fractured facet. (See Figure 6.)
Examine the cartilage; the intervertebral disk space height and length should be uniform. Finally, examine the prevertebral soft-tissue width. Focal prevertebral or retropharyngeal soft tissue edema or hematoma can indicate an otherwise radiographically undetected fracture.4
Missed injuries on lateral view film can include overlapping of bone (especially involving the cervicocranial junction, the articular masses, and the laminae) and non-displaced or minimally displaced fractures (especially C1 and C2).78
This view is often obtained to visualize the cervicothoracic junction when it is obscured by the density of the shadows produced by the shoulders on the true lateral. Optimal positioning requires that one of the patient's arms be abducted 180 degrees and extended above the head while the opposite shoulder is extended posteriorly to decrease the overlapping of skeletal structures. If a swimmer's view cannot be obtained, oblique views or CT is needed.
The AP view includes C3-T1 as the mandible obscures C1 and C2. (See Figure 7
.) Evaluate the alignment of the spinous processes and the distance between the spinous processes as well as the uniformity and height of the vertebrae. The spinous processes should form a straight line down the middle of the vertebral body and should be equidistant apart. If one spinous process is out of line compared to the others, a jumped facet may be present.78
The lateral masses should form smoothly undulating margins without abrupt interruption, and the disc spaces should be uniform in height from anterior to posterior.78
Open Mouth Odontoid (Atlantoaxial View)
This view requires the cooperation from the patient for optimal studies. Problems with this view may occur due to overlap from the mandible or dentition. A normal open-mouth odontoid (OMO) view demonstrates the lateral margins of the C1 ring aligned within 1 to 2 mm of the articular masses of the axis. The articular masses of C2 should appear symmetric, as should the joint spaces between the articular masses of C1 and C2 as long as there is no rotation of the head. The distance between the odontoid and the C1 medial border (lateral atlantodental space) should be equal, but a discrepancy of 3 mm or greater is often seen in patients without pathology. A vertical line bisecting the odontoid process should form a 90-degree angle with a line placed across the superior aspect of the C2 articular masses.78
CT Versus Plain Films
In the past decade, helical CT scanning with or without multidetector technology has been replacing radiography as the method of choice for cervical trauma screening in most large U.S. trauma centers among moderate-risk to high-risk patients.80-82 This is due to CT's ease of performance, speed of study, and greater ability to detect fractures.83,84
The sensitivity of plain films is inversely correlated with the severity of trauma sustained.9,85 Multiple studies have demonstrated the limitations of plain radiography in the cervical spine, particularly at the craniocervical and cervicothoracic junctions.85,86 In a study of 102 patients, Widder et al reported plain films to have a sensitivity of 39% compared to CT.86 In a retrospective study of 245 patients with 309 cervical spine injuries, Daffner et al demonstrated that plain radiography detected just 44% of injuries whereas CT detected 99.2% of injuries.88
Many centers have reported CT scanning in moderate-risk to high-risk trauma patients to be a more cost-effective screening modality than plain radiography when the costs of missed injuries are taken into account.90-92
The main reasons to get a CT scan in blunt trauma patients include inadequate plain films, abnormal plain films, fractures or dislocations seen on plain films, or high suspicion of injury despite a normal plain film series. Patients with multi-system injuries who need CT of the brain often have CT of the cervical spine performed as well. Patients who are intubated cannot be evaluated with only plain ce vical spin radiographs. Evaluation of the soft tissues of the upper cervical spine requires the presence of an air column in the trachea to help delineate the curvature and width of the soft tissues. The presence of an endotracheal tube diminishes the magnitude of this air column thus rendering the soft tissue evaluation inaccurate. If there is any doubt about an abnormality on the plain radiograph or if the patient has disproportionate neck pain, a CT is warranted. Be familiar with your scanner. CT cuts need to be 3 mm or less to reliably detect occult fracture.
Low-risk patients are those who have low prevalence of injury. Plain radiographs are an effective tool in these patients.55 A 2.4% prevalence of cervical spine injury was reported in NEXUS. This low revalence of injury makes it extremely unlikely that an individual patient with blunt trauma will have an injury missed on screening radiography.55 Plain radiography has its limitations in the high-risk patient group. It is difficult to obtain adequate films in severely injured patients, especially those who are intubated. High-risk patients would include those who have a significant closed head injury, neurologic deficits, high-energy trauma, unreliable examination secondary to intoxication, and neck pain out of proportion to plain film findings.93 These patients need CT evaluation.
Presently, the American College of Radiology's 2007 Appropriateness Criteria recommends that patients who need imaging have a thin-section CT examination that includes sagittal and coronal multiplanar reconstructed images. CT of the cervical spine with sagittal and coronal reformats is given a rating of 9, considered most appropriate. Three-view cervical spine plain radiographs are given a rating of 2, with 1 being least appropriate.94
Table 7, lists the 5 cardinal findings on CT that indicate instability.
How to detect significant cervical spine instability in the absence of bony injury remains a controversial issue. This injury is uncommon, with a reported incidence of 0.1% to 0.5% of patients with blunt trauma.77,85,95,96
MRI is considered to be the gold standard to make this diagnosis.
MRI is a highly sensitive non-invasive imaging modality that is unique in its ability to detect acute injury of the spinal cord as well as injury to the ligamentous structures and intervertebral disks. It is the study of choice for detecting neurologic injury secondary to trauma. The advantages of MRI include superior resolution in the detection of soft tissue injuries (such as contusions, hematomas, or laceration) and no requirement for IV contrast material or ionizing radiation.
Hemodynamically-unstable patients are not appropriate for MRI as intensive monitoring and resuscitation are difficult in the MRI suite. MRI is time-consuming, taking much longer than CT, and it is not universally available. In addition, some patients have medical implants that preclude the use of MRI. Additionally, cortical bone contains essentially no hydrogen atoms so it is not well visualized by MRI. Only major bone injuries are seen on MRI. The indications for emergent MRI include the presence of neurological deficits attributable to a spinal cord injury or suspicion of ligamentous injury as evidenced by subluxation on plain films or CT.
See Table 8
for a list of MRI findings that indicate cervical spine ligamentous injury.