Chapter 5 Imaging

Introduction

Imaging of the patient’s cervical region following whiplash trauma, although not routine in mild cases, is necessary when moderate to severe trauma is associated with clinical findings indicating injury more severe than sprain or strain or when a patient’s symptoms become chronic. An acceleration-deceleration mechanism of energy transfer to the neck, which may result from rear-end or side impact collisions or other mishaps, has been used to describe whiplash trauma and is included in the publication of the 1995 Quebec Task Force on Whiplash-Associated Disorders.¹ The energy transfer of this trauma can result in soft tissue injuries (whiplash injury), which may in turn lead to a wide variety of clinical manifestations (whiplash-associated disorders).² This description encompasses the diversity of the injuries occurring from this mechanism of trauma. Because of the wide range of impairment occurring from this injury, diagnosis and determination of the full extent of injury can be difficult, and the condition often creates a chronic problem that can last for years following the initial incident.³

The diagnosis of a whiplash-associated disorder (WAD) is often made clinically, after which the clinician may order imaging, such as radiographs, to further evaluate and determine the extent of the injury. Plain film radiographs are often the first step and are used to rule in (or rule out) more severe injury such as fracture or dislocation. Following a plain film evaluation, the clinician may choose to further investigate through the use of magnetic resonance imaging (MRI), computed tomography (CT), or other forms of advanced imaging. This chapter will cover the findings seen with these modalities and include the reasoning behind ordering advanced imaging for the evaluation of WAD. Although injuries to many areas of the body may occur, the scope of this chapter will be limited to injuries of the cervical spine, as this is the primary region of interest in the evaluation of whiplash injuries.

Acute Injury

The role of imaging in the evaluation of acute whiplash injury is rather limited. Plain film radiographs are most commonly the first step in imaging evaluation. The goal of the x-ray examination is to determine whether there is more serious injury to the cervical spine, which would complicate the diagnosis of WAD.

Plain film radiographs of the cervical spine are routinely used to evaluate patients who have experienced significant trauma. In patients with a working diagnosis of WAD, the primary applications are to rule out fracture or dislocation and to detect evidence of instability.⁴^–⁶ Two notable clinical decision rules have been developed to predict the likelihood of significant spinal injury and provide an indicator of the need for cervical spine radiographs in alert and stable trauma patients. These are the National Emergency X-Radiography Utilization Study (NEXUS) criteria and the Canadian C-Spine Rule (CCR).^7,⁸ Both of these screening tools for significant cervical spine injury have been studied extensively, and comparative evaluations of the two sets of criteria have been done.⁷^–¹¹ Both sets of criteria attempt to identify patients at low risk of significant cervical spine injury with the final goal of avoiding unneeded radiographs. The CCR is applied to alert (Glasgow Coma Scale score = 15) and stable blunt trauma patients and addresses three clinical or history factors:

1 The presence of any high-risk factor indicates a need for radiography. High-risk factors are identified as the following:

• Age = 65 years or older

• Dangerous mechanism of injury (Box 5-1)

• Paresthesias in extremities

3 Inability of the patient to actively rotate the neck 45 degrees to the right and left indicates a need for radiography.⁷

BOX 5-2

Complicated Mechanisms of Injury

MVA not considered simple rear-end:

• Pushed into oncoming traffic

• Hit by bus or large truck

• Rollover

• Hit by high-speed vehicle

The NEXUS criteria also evaluate alert, blunt trauma patients. The rules identify a patient as being at virtually no risk of significant cervical spine injury if they meet four criteria⁸:

1 No neurological abnormality

2 No evidence of intoxication

3 No posterior cervical midline spine tenderness

4 No other distracting painful injury

Evaluation and comparison of these clinical decision criteria demonstrate a high level of sensitivity for both. In a study of over 8,000 patients presenting to emergency departments, the CCR would have missed one clinically significant fracture with sensitivity of 99.4%.⁷ The NEXUS Low-Risk Criteria showed 99% sensitivity in a study of over 34,000 patients. It identified 810 of the 818 patients with cervical spine injury.¹² Application of the NEXUS rules appears to be applicable in geriatric patients, who have a somewhat higher rate of fracture as well.¹³

Although evaluation of these criteria outside the emergency department has not been studied, they could clearly be applied in a primary care setting. One concern for practitioners’ considering manual therapies is the definition of “clinically important cervical spine injuries.” The comparison study by Stiell et al ⁷ considered the following injuries to be “clinically unimportant fractures”: osteophyte avulsion, a transverse process not involving a facet joint, a spinous process not involving lamina, or simple vertebral compression of less than 25% of body height. The overall incidence of significant fractures in the emergency department setting was about 2% of patients in the studies evaluating the CCR and NEXUS clinical guidelines.^7,⁸ In the primary care setting these criteria can be applied to stratify patients as high or low risk of significant cervical injury. The addition of criteria from the manual medicine guidelines for musculoskeletal injuries (Box 5-3) can aid the clinician in evaluating patient risk for other injuries that may contraindicate certain manual therapies. Though some of the specific criteria are debatable and not relevant to the trauma patient, these criteria focus the practitioner on information that may indicate a higher risk of injury (e.g., a patient with ankylosing spondylitis is at greater risk of fracture than the general population). These guidelines also indicate that failure to respond to care in 4 weeks or a significant increase in symptoms or impairment warrants x-rays.⁶

Imaging information is applied in patient management plans to determine when conservative care, manipulation, and rehabilitation can be appropriately applied. In this scenario, plain film radiographs provide a diagnostic tool with good cost-benefit ratio. Radiographs are a readily available and relatively low cost imaging choice, but the potential significance of a missed fracture, dislocation, or instability is great. The minimal diagnostic series of anteroposterior, anteroposterior open-mouth, and neutral lateral views should be obtained in the primary care setting, although the lateral view typically provides the most information in cases of cervical trauma.

Radiographs are the initial imaging modality for ruling out fracture. The presence of fracture in the WAD patient may alter management by requiring surgical referral or by delaying or modifying rehabilitation plans. Clinical indicators of fractures may include increasing pain, pain unresponsive to care, and the development of neurological symptoms. Prior radiographs read as negative do not rule out fracture in the face of strong clinical evidence.¹⁴^–¹⁷ Evaluation of the major or unique forces involved in the injury may guide the clinician to higher levels of suspicion for certain types of fracture. Atlas (C1) fractures are associated with axial loading injuries whereas articular pillar fractures are associated with the combination of extension and rotation. Table 5-1 lists some common fractures with their associated force mechanism. Although the known forces may affect the level of suspicion of a given fracture, a lack of correlation should not rule out diagnoses with positive radiographic findings.

TABLE 5-1 Common Cervical Fractures/Dislocations with Mechanisms and Findings

Fracture Location/Type	Mechanism	Radiographic Findings
C1 burst (Jefferson)	Axial compression	Asymmetrical or widened paraodontoid spaces; lateral mass overhangs C2 by >2 mm; posterior arch fracture line
C1 posterior arch	Compressive hyperextension	Fracture lines may be difficult to detect
Odontoid	Complex and poorly understood; combinations of extreme flexion, extension, rotation, and shearing	Fracture line may be difficult to detect; angulation of odontoid
C2 traumatic pars (Hangman’s)	Hyperextension; possibly flexion-distraction for Type II	Anterolisthesis of C2 possibly without alignment abnormality at spinolaminar junction line
Teardrop	Disruptive hyperextension or compressive hyperflexion	Triangular fragment at anteroinferior body corner
Vertebral body compression	Compressive hyperflexion; lateral hyperflexion	Anterior or lateral wedging of vertebral body
Burst, C3-C7	Axial compression with flexion	Loss of anterior and posterior body height
Articular pillar	Hyperextension and rotation	Oblique or pillar views may be required to visualize
Spinous process	Hyperextension or hyperflexion	Inferior displacement of fragment common
Transverse process	Lateral hyperflexion	Uncommon
Uncinate process fracture	Lateral hyperflexion	Uncommon

Taylor JAM, Resnick D: Skeletal imaging atlas of the spine and extremities, Philadelphia, PA, 2000, W.B. Saunders, pp 78-89.

Fractures involving the vertebral bodies (compression/wedge or burst) are less likely to present with visible fracture lines. Stable compression fractures produce anterior wedging. The step defects and bands of condensation that indicate acute fracture may not be as prominent in the cervical spine as they typically are in the thoracic and lumbar vertebrae. MRI may be required to identify the edema associated with recent fracture. The clinician should be aware that C5 and C6 are common sites for developmental variation that results in a slightly decreased anterior body height. Anterior body height loss of more than 25% should be evaluated more thoroughly with MRI or CT to rule out significant involvement of the posterior elements. Burst fracture is indicated by posterior body height loss compared to the vertebrae above and below. Disruption of the posterior body margin is typically seen.¹⁸ Burst fractures should be evaluated with MRI to identify canal stenosis or evidence of cord edema.

Fractures involving the posterior elements may be difficult to identify. The addition of oblique views may be helpful in better visualizing the posterior elements. Specific views of the articular pillars may be required. A variety of special views are intended to better visualize the odontoid process. Fracture of posterior elements should be evaluated with CT to determine stability and to identify any associated fractures.⁵

Careful attention should be paid to prevertebral soft tissues. Focal distention of soft tissues may be the only evidence of an otherwise occult fracture. As with most radiographic findings, the absence of prevertebral soft tissue distension does not rule out fracture or dislocation.^19,²⁰

Dislocation may occur with or without associated fracture. Assessment of vertebral landmarks on the lateral view (neutral, flexion and/or extension) can identify most dislocations. Initial radiographs may appear normal if spontaneous reduction has occurred. These cases may present later when the significant associated soft tissues damage allows the dislocation to recur. Some common patterns of dislocation are identified in Table 5-2. Cervical spine dislocations should be further evaluated with CT to detect associated fracture and determine effects on the neural foramina.⁵ The forces associated with facet dislocation may lead to serious injury to the vertebral and other arteries as well. Clinical or radiographic findings suggesting vertebral artery injury warrant evaluation with magnetic resonance angiography.^5,²¹

TABLE 5-2 Traumatic Dislocations

Dislocation	Mechanism or Tissue Injury	Radiographic Findings
C1-C2	Transverse ligament rupture	Increased atlantodental interval
Bilateral facet dislocation	Hyperflexion	“Perched facets”; anterolisthesis; interspinous widening
Unilateral facet dislocation	Hyperflexion with rotation	Abrupt, focal intersegmental rotation