Authors: S.V. Mahadevan, MD, FACEP, Assistant Professor of Surgery/Emergency Medicine, Stanford University School of Medicine; Associate Chief, Division of Emergency Medicine, and Medical Director, Stanford University Emergency Department, Stanford, CA; and Misty Navarro, MD, Senior Emergency Medicine Resident, Stanford-Kaiser Emergency Medicine Residency, Stanford, CA.
Reviewer: Andrew D. Perron, MD, FACEP, FACSM, Residency Program Director, Maine Medical Center, Portland, ME.
Cervical spine injuries, although uncommon (0.9-6% of blunt trauma patients),1-5 have the potential to result in permanent neurologic devastation for the patient. Appropriate suspicion for cervical spine injury, immobilization, and the decision to obtain radiographic imaging are all important aspects of the acute care of an adult who has sustained a blunt traumatic injury (as discussed in Part 1 of this series); but the responsibilities of emergency department (ED)/trauma physicians do not end with the decision to obtain radiologic imaging.
The physician must then decide the most appropriate initial imaging modality (plain radiographs, computerized tomography [CT], or magnetic resonance imaging [MRI]) for the patient and when an adequate evaluation has been performed. Understanding the indications, advantages, and limitations of each radiographic modality is critical to obtaining a diagnostic evaluation that effectively identifies or excludes a cervical spine injury.
This issue presents the physician with a thorough discussion of the imaging alternatives available and facilitates clinical decision-making for diagnostic imaging. The author also provides a comprehensive discussion of the evaluation of a patient with a potential ligamentous injury to the cervical spine. —The Editor
Although cervical spine injury is uncommon, the implications of a missed injury are profound and may result in many serious complications for the patient and the physician. In one series, missed spinal injuries were responsible for 3% of malpractice claims and 9% of total dollars paid in claims.6 A portion of these missed injuries resulted from inaccurate interpretation of radiographs or failure to obtain the appropriate imaging required to make the diagnosis. Trauma care providers must have a thorough understanding of imaging modalities, their indications, and more importantly, their limitations. Alternatives available include plain radiographs, CT, and MRI. Formulating an imaging approach to a patient with a potential cervical spine injury allows the trauma care provider to achieve an accurate diagnosis in a timely manner with minimal risk to the patient. Understanding the roles and risks with flexion-extension radiographs and fluoroscopy allows the trauma care provider to accurately identify ligamentous injury to the cervical spine, without placing the patient at risk for neurologic complications.
Radiographic Cervical Spine Clearance
Plain Films vs Computed Tomography. Although there is increasing consensus among clinicians as to which patients re-quire cervical spine imaging, extensive variation still exists in the approach.1 Once the decision to perform radiographic clearance has been made, the question remains: What study should I order: plain radiography, CT, or both? The ideal strategy is one that accurately and inexpensively identifies all cervical spine injuries. Unfortunately, no current approach singularly fits that bill.
Conventional radiography remains the most commonly employed approach to traumatic spine assessment in most hospitals in the world.7 Most trauma physicians agree that at least a three-view series (i.e., lateral, open mouth, and anteroposterior) is the minimally acceptable standard for radiographic evaluation of most blunt trauma patients. A consensus agreement among emergency physicians, radiologists, and trauma surgeons states that, in an alert patient with cervical tenderness in the absence of neurologic injury, an adequate three-view series is sufficient for excluding cervical spine injury.8 The addition of oblique views (five-view series) to improve sensitivity and improve detection of the lateral and posterior spinal elements adds little to the overall evaluation and simply prolongs the diagnostic work-up of these patients.9 However, the swimmer’s or oblique view may improve visualization of the cervico-thoracic junction when the lateral view fails to display these areas adequately.10 The routine addition of flexion-extension views to the standard plain films is not necessary unless there is specific concern for ligamentous injury.
A single lateral view of the cervical spine is insensitive for excluding cervical spine injury. A survey of more than 100 hospitals in the mid-1990s revealed that 33% of their physicians were clearing the cervical spine using only lateral radiographs.11 As many as 15-46% of cervical fractures were missed when cross-table lateral radiographs solely were used to exclude cervical spine injury.6,11,12
Although obtaining plain radiography is inexpensive, poses a low radiation risk, and is available widely, it has several distinct limitations and disadvantages. The diagnosis of significant cervical spine injury using plain films in the severely injured or un-conscious patient is challenging. In many cases, the cervico-cranium (C1-C2) and cervicothoracic junction (C7-T1) are shown inadequately, or the quality of the portable films is poor. Plain films are repeated in almost 50-70% of those patients to obtain a complete study.13,14 The result is more time lost, additional x-rays taken, and higher cost.15,16 Moreover, the frequency of inadequate or false-positive plain radiographs increases with injury severity.16
In recent years, the diagnostic efficacy of cervical plain radiographs for demonstrating and excluding injury has come under increasing scrutiny. Results from a number of studies have ex-posed the limitations of conventional radiography. Fractures that are clearly evident on CT are not always evident on plain films. In a series comparing plain films with CT, Woodring and Lee showed that plain films revealed only 33% of all fractures and 55% of subluxations or dislocations.11 They also found that 23% of patients (half of whom had unstable injuries) initially were diagnosed as normal.11 Nunez et al found that 42% of injuries were not seen on plain films, including 10 patients with unstable fractures.14 When pooling the data from several retrospective series (recognizing potential design limitations), the overall sensitivity of plain films in detecting cervical spine injury is only 53%, while that of CT is 98%.6,14,17-19
The availability of such an effective imaging strategy raises the question: Shouldn’t everyone be screened using CT? The initial role of cervical CT was an adjunct to plain films, not a screening tool. CT was reserved for further delineation of areas suspicious for injury and areas poorly defined on plain films.20-22 However, the widespread use of this imaging modality led to the identification of fractures and subluxations not readily apparent on plain film radiographs.
Helical CT represents an advance from the older approach of single acquisition CT. Advantages of helical CT include faster acquisition and image reconstruction times, reduction of artifacts, and a higher quality of reformatted and three dimensional images.23 In the multiple-trauma patient, helical CT can assess several body regions in less time. Before helical CT, the time required for the scan itself and heating and cooling of the tube made screening of the entire cervical spine impractical.24
Rather than adopting CT as the primary screening modality, an early approach advocated limited use of CT to examine portions of the spine that were anatomically difficult to see on plain films, such as the cervicocranial and cervicothoracic junctions.25 These guidelines recommended standard plain radiography supplemented by regional CT of the cervicocranium and areas of suspicion. However, results of a recent study revealed that the approach would have missed 71% (29/41) of injuries that occur-red below the C2 level and did not show up on plain films.17
Some centers routinely obtain cervical spine CT in all patients who are getting a CT scan of the head or body. That practice is supported by several small studies and is in keeping with the most recent American College of Radiology (ACR) Guidelines (2002), which recommend cervical spine CT in patients with paresthesias, altered level of consciousness, and in whom cranial CT will be obtained.8 When CT of the head and cervical spine are obtained together, the overall time for cervical spine evaluation was reduced by an average of 17 minutes, and the estimated additional cost was only $184.42 per patient.6,18,26-28 That app-roach also identified a significant number of fractures (occipital condyle fractures and C1/C2 fractures) not seen on plain films.29
An additional advantage of obtaining a cervical spine CT is its ability to provide information about surrounding anatomical structures. In one series, other injuries were detected in 9% of patients undergoing CT of the cervical spine, including fractures of the upper thoracic spine, proximal ribs, mandible, and skull base.30 Small, apical pneumothoraces and airway injuries also may be detected.26
Considering the ease of obtaining a CT, the time saved, and the diagnostic sensitivity, there is a propensity to use it routinely for cervical spine clearance instead of conventional radiography. Advantages of helical CT compared with plain radiographs include improved accuracy and faster diagnosis; disadvantages include greater expense and higher radiation doses.19,30 It is well known that the risk of thyroid cancer increases with radiation exposure, especially in children.18,31,32 Estimates of radiation risk from a complete cervical CT scan vary depending upon the technique and type of scanner. Rybicki et al found that helical CT exposed the thyroid to 14 times the radiation of standard cervical spine plain radiographs, even when accounting for the need for repeat radiographs.33
With the radiation risk and cost of CT in mind, a number of authors have attempted to define high-risk patients who should be screened primarily with cervical CT.6,18,26,30,34 High-risk patients as described by Hanson and Blackmore are patients with a probability of cervical spine injury exceeding 5-10%.26,30 This definition included patients suffering a high-energy mechanism injury or presenting with a high-risk clinical parameter.30,34 (See Table.) In their small prospective study, Berne et al defined high-risk patients as those who had an altered mental status, were unconscious, or required an admission to an intensive care unit.18 Screening high-risk patients with CT has been shown to be cost-effective, time efficient, and clinically efficacious.15,35
Table. Harborview High-Risk Criteria
Although Blackmore et al did not find CT to be cost-effective in low-risk patients (less than 4% chance of injury),35 Griffin et al suggest there is a growing body of evidence that CT should replace plain films for the screening evaluation of the cervical spine in all blunt trauma patients.17 In their recent, retrospective review of 1,199 trauma patients, they found that plain radio-graphs—interpreted as normal by the radiologists without recommendation for further radiography—failed to identify 41 of 116 cervical spine injuries detected by CT. A number of factors made it difficult to draw any firm conclusions from their study: 1) the retrospective nature of data collection; 2) types of injuries missed (including transverse process and spinous process fractures); 3) types of patients evaluated (including patients with neurologic deficits or deaths); and 4) absence of missed injuries (patients with normal plain films still were scanned). Before adopting a strategy of screening all patients with CT, further prospective research is needed.
Before abandoning plain films completely, it is important to understand that screening radiography is not intended to detect every cervical spine injury.36 Rather, when plain films reveal an injury or area of suspicion, or prove to be inadequate, other modalities such as CT or MRI should be used to evaluate for cervical spine injuries. In a review of 34,069 patients screened with plain radiography, Mower et al found that screening radiography only missed three injuries associated with spinous instability, or one unstable injury for every 11,000 screening evaluations.36
No radiological modality—including CT— is 100% sensitive in the detection of cervical spine injuries. Brohi et al describe a patient with a C6-C7 bilateral facet dislocation missed on CT scan.37 Schenarts et al revealed that CT had a sensitivity of 96% and missed three injuries seen on plain films (an atlanto-occipital dislocation and two subluxations).19 They also describe the case of a patient with a C4 fracture—missed on both CT and plain films—who suffered a severe neurologic injury after removal of the cervical collar. Berne et al showed that helical CT of the entire cervical spine had a sensitivity of 90% and missed two stable injuries (a ligamentous injury and spinous process fracture).18 The rationale for missed ligamentous injuries on CT is that moderate subluxation may be noted only when evaluating the spine in profile.23 Though the addition of the lateral radiograph allows for detection of fractures or subluxation that might be subtle or overlooked on axial CT images (See Figure 1.), the improved technology of multi-detector scanners and reformatting may make this practice unnecessary.38
The identification of a cervical spine injury on plain films or CT mandates evaluation of the remainder of the cervical spine and the thoracic and lumbosacral spine to exclude concomitant spinal injuries.37 The incidence of multiple level, non-contiguous fractures has been reported to be 15-24%.39,40 Recent use of MRI reveals that percentage could be much higher (42%).41
Magnetic Resonance Imaging. MRI has several advantages as an imaging modality: high-resolution capabilities; the lack of ionizing radiation; multiplanar imaging capabilities; and the ability to visualize soft-tissue structures including intervertebral discs, ligaments, and the spinal cord. Disadvantages of MRI include prolonged acquisition time, impaired monitoring abilities, and several absolute contraindications (e.g., pacemakers, aneurysm clips, and metallic foreign bodies). In addition, MRI is not available universally, and patient transfer might be required to obtain this study.
In the acute trauma patient with potential cervical spine in-jury, the indications for MRI as part of the ED evaluation in-clude: 1) complete or incomplete neurologic deficits with radio-graphic evidence of fracture or subluxation; 2) neurologic deficits not explained by plain films or CT findings (i.e., spinal cord injury without radiographic abnormality [SCIWORA]); 3) deterioration of neurologic function; and 4) suspicion of ligamentous injury following inadequate or negative flexion-extension film findings.42
Will MRI replace CT as the primary adjunct to plain film imaging? The ability of MRI to visualize cervical spine fractures (in addition to spinal cord and soft-tissue injuries) has been variable.43-44 Holmes et al found that MRI missed 45% of osseous fractures identified on CT.45 While MRI is clearly superior to CT in identifying spinal cord and ligamentous injuries, CT remains the preferred adjunct to plain radiography for the identification of bony injuries.
Diagnosis of Ligamentous Injury
Awake and Alert Patients. Patients without cervical spine fractures still may harbor unstable ligamentous injuries. Al-though the prevalence of isolated ligamentous injury in the absence of a cervical spine fracture is thought to be low—a reported frequency of 0.04-0.2% in all blunt trauma patients—the consequences of a missed ligamentous injury can be devastating for the patient.46,47 The true incidence of such injury is actually unknown; a gold standard for such diagnosis currently does not exist. Although traditional cervical spine radiography is useful for detecting fractures and subluxation, the detection of ligamentous injury is less precise.48 For that reason, a patient with normal cervical spine radiography still may remain in a cervical collar until his or her ligaments can be cleared clinically or definitive imaging is obtained.
If a patient has negative results on radiographic studies, is alert and awake, and denies neck pain, the cervical spine is considered clear. However, the persistence of cervical pain while initial radiographs are normal requires the exclusion of ligamentous injury. While ligamentous injury may be inferred on the basis of an injury seen on CT or plain radiographs, the possibility of ligamentous injury causing instability in the absence of fracture may be excluded through the use of flexion-extension films or MRI.
Flexion-extension radiographs generally are obtained by asking an upright patient to actively flex and extend the neck during cervical spine imaging. This action should be performed only by patients under their own power; the physician should never forcibly assist the patient with flexion or extension. Flexion-extension radiographs should be obtained only in awake, alert, cooperative patients without neurologic symptoms or deficits. Under those circumstances, the risk of neurologic compromise produced by flexion and extension of the cervical spine is very unlikely. When performed voluntarily by the patient, no serious adverse events have been reported.37,43,48-51
The goal in interpreting flexion-extension radiographs is to identify or exclude signs of soft-tissue ligamentous injury, such as abnormal subluxation, angulation, or uncovering of facet joints.52,53 However, following an acute injury, pain associated with motion or muscle spasm may limit a patient’s ability to flex and extend adequately. A patient must have a range greater than 30° in each direction from the neutral position for flexion-extension radiographs to be considered adequate.54 The inability to flex and extend adequately may lead to masking of abnormalities (e.g., subluxation) and result in false-negative studies. Results from a number of series have revealed that 28-59% of flexion-extension radiographs obtained in acutely injured patients were deemed inadequate.53,55-57
For that reason, the practice of obtaining flexion-extension radiographs in the acutely traumatized patient has been questioned by numerous studies.53,57-60 Most recently, the American College of Radiology stated in its guidelines that those views in general are not very helpful and should be reserved for follow up of symptomatic patients 7-10 days after initial injury.8 In such cases, patients are discharged with a semi-rigid collar and pain medications, and asked to return when they can cooperate actively for flexion-extension radiographs. In a case series by Wilberger et al, 8 of 62 patients (13%), who returned 2-4 weeks after initial flexion-extension films for a repeat set, had significant ligamentous instability requiring cervical fusion.55
Do flexion-extension radiographs have any role in the acutely injured patient? Rather than completely abandoning them, a logical approach may be to screen the patient first for the ability to flex and extend the neck adequately. In patients with an adequate range of motion (i.e., greater than 30° in each direction from the neutral position), films may be warranted. In such patients with adequate mobility and negative radiographs, the cervical spine would be cleared effectively. This strategy is supported by the findings of Insko et al, who found that in patients with adequate imaging, flexion-extension radiographs had a false-negative rate of 0%.57
In cases of inadequate flexion-extension radiographs, patients also may be studied with an MRI to exclude ligamentous in-juries. A negative MRI in the first 48 hours post injury combined with normal plain films and/or CT is sufficient to clear a patient.
Obtunded Patients. The evaluation of ligamentous injury in the obtunded or intoxicated individual is somewhat more difficult. In these patients, a detailed neurologic examination often is not feasible, and the physical exam may be unreliable. For that reason, obtunded, impaired, or distracted patients should not have flexion-extension studies performed in the ED, as such a practice is unsafe and potentially dangerous.
However, obtunded patients who are admitted to the hospital and subject to prolonged immobilization are at risk for detrimental consequences. Prolonged application of a cervical collar in obtunded patients has been associated with skin ulceration, interference with care of neck and shoulder wounds, difficulty with the placement of central lines, increased risk of aspiration, and patient discomfort.56,61,62 Additionally, the use of cervical collars alone is not sufficient for immobilizing the cervical spine.63,64
For those reasons, clearance of the cervical spine and removal of the collar should be performed in a timely manner. No clear consensus exists as to how to evaluate these patients, and practice varies greatly as to how to exclude ligamentous injury.1 If a patient shows clinical improvement, has a clear sensorium, and can be examined reliably, then a ligamentous injury could be excluded either clinically or with flexion-extension radiographs. In a patient who remains obtunded, recommendations vary from removal of the collar after 24 hours in patients with normal radiographs, to indefinite immobilization in the cervical collar, to MRI and dynamic flexion-extension under fluoroscopy.47
MRI is highly sensitive for the recognition of ligamentous injuries, identifying soft-tissue injuries in 25% of obtunded patients with negative radiographs.51,65 MRI has the added benefit of being able to exclude spinal cord injuries. A negative MRI study within 48 hours of injury implies the absence of ligamentous injury. However, MRI may be overly sensitive for the detection of ligamentous injuries and may reveal injuries of unclear clinical significance.56 In addition, MRI may not be feasible in unstable patients due to prolonged scanning times and impaired monitoring abilities.62
Dynamic fluoroscopy may be used to evaluate for ligamentous injury in obtunded patients who are not candidates for MRI due to contraindications or instability. (See Figures 2A and 2B). Unlike MRI, this test may be performed in the critical care unit.37 Unfortunately, dynamic fluoroscopy often is labor intensive and has the potential to induce secondary neurologic injury. Active flexion-extension under fluoroscopy places patients at risk for neurologic impairment due to subluxation at non-visualized segments or disc abnormalities not demonstrated by radiographs or CT.66 There are reports of patients who developed quadriplegia following dynamic fluoroscopic evaluation.47,67
Due to the exceedingly low incidence of isolated ligamentous instability in obtunded patients with normal radiography, some authors have suggested that the cervical spine can be cleared with an adequate lateral view of the cervical spine and a helical CT from the occiput to T4 with sagittal and coronal reconstructions.56 That practice has yet to be validated in a large clinical trial and is in contrast to the most current Eastern Association for the Surgery of Trauma (EAST) Guidelines.68
Spinal Cord Injury without Radiographic Abnormality (SCIWORA)
Pang and Wilberger defined the term SCIWORA (spinal cord injury without radiographic abnormality) in 1982 to describe a syndrome of post-traumatic neurologic injury without evidence of fracture or ligamentous instability on plain radiographs or CT.69 Although this syndrome classically is associated with children—playing a role in as many as 50% of pediatric spinal cord injuries—it also may occur in adults.46,62-77 While the clinical presentations of this syndrome in children and adults may be similar, the hypothesized mechanisms by which they occur differ.
In the pediatric population, highly elastic ligaments in the juvenile spine are thought to allow transient intersegmental vertebral dislocation followed by spontaneous reduction, resulting in damage to the spinal cord, but a normal-appearing, bony vertebral column.71 Adult patients with degenerative cervical spine conditions and stenosis of the spinal canal also are at risk for SCIWORA. In such patients with pre-existing cervical spon-dylitic changes, hyperextension can lead to pinching of the spinal cord between vertebral osteophytes and the inward bulging of the ligamentum flavum. (See Figure 3.) However, Bhatoe reported another mechanism for SCIWORA in young adult patients who lacked features of pre-existing cervical spine disease.78 He concluded that acute stretching of the spinal cord from hyperflexion and torsional strain leads to SCIWORA in these patients.
Figure 3. Adult SCIWORA
Figure 3. MRI image revealing spinal cord contusion in a patient with spinal canal narrowing at C5-C6 and an osteophyte causing mild impression on the thecal sac. There was no evidence of ligamentous injury or prevertebral hematoma. The patient’s CT scan revealed no acute fractures or dislocation.
Image courtesy of S.V. Mahadevan, MD.
Patients with SCIWORA often present with profound or progressive paralysis, either immediately or within 48 hours of a traumatic incident. While a significant number of patients have demonstrable neurologic deficits at time of presentation, others may present with transient or delayed symptoms. Pang et al found that almost 52% of the patients in their study with SCIWORA had a delayed onset of neurologic deficits ranging from 30 minutes to 4 days.70 A number of these children had transient warning symptoms immediately following their trauma that had been ignored initially.70 The observation of delayed deterioration by different investigators highlights the importance of screening patients for SCIWORA warning signs, such as transient weakness, paresthesias, numbness, shock-like sensations, or focal clumsiness following a traumatic event.71,79 Although the initial neurologic exam may be unremarkable, frequent patient re-assessment may detect an evolving neurologic condition. Results from one study showed that several adult patients had normal initial neurologic exams and later developed neurologic deficits.46
Hendey et al in their review of the NEXUS database found that the NEXUS criteria also were useful in identifying all 27 patients with SCIWORA.77 The criteria may have a role in identifying patients at reduced risk for SCIWORA, although that has not been validated prospectively.
When Pang and Wilberger originally defined SCIWORA, MRI did not exist.80 With its advent, some authors note that the term SCIWORA now may be a misnomer because most patients actually have a demonstrable radiographic spinal cord abnormality seen on MRI.74 MRI has revealed such findings as spinal cord hemorrhage or edema, intervertebral disc herniation, and spinal cord transection. Occasionally, the MRI may be normal.
In their series, Pang and Wilberger reported that the primary predictor of neurologic outcome in SCIWORA was the presenting neurologic status.69 More recent studies have revealed that the appearance of the spinal cord on MRI provides better prognostic information regarding the patient’s ultimate neurological outcome.79 A normal-appearing spinal cord (i.e., absence of signal change) portends an excellent outcome; the presence of edema or microhemorrhages without frank hematomyelia (hemorrhage into the spinal cord) is associated with significant im-provement of neurologic function over time; and the presence of hematomyelia or cord transection is associated with severe, permanent neurologic injury.80-82
The evaluation and clearance of the cervical spine in adult trauma patients are challenging and evolving aspects of trauma care. Trauma care providers should have a thorough understanding of risk factors for cervical spine injury, techniques for protecting patients from exacerbation of their injuries, advances in the practice of clinical and radiographic clearance of the cervical spine, and the diagnosis of such conditions as isolated ligamentous injury and SCIWORA syndrome.
With adequate training, improved detection, and proper care, physicians can prevent the life-altering complications of cervical spine injury such as neurologic injury, severe disability, and death.
Special thanks to Kathryn Stevens, MD, FRCR, BSc (hons), Assistant Professor of Radiology, Department of Radiology, Stanford University School of Medicine, for her contributions to this article.
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