Use of Plain Radiography to Screen for Cervical Spine Injuries

ORIGINAL CONTRIBUTION

Use of Plain Radiography to Screen for Cervical Spine Injuries

From the UCLA Emergency Medicine Center and Department of Medicine, UCLA School of Medicine, Los Angeles, CA*; the Department of Emergency Medicine, Maricopa Medical Center, Phoenix, AZ‡; the Department of Radiology, UCLA School of Medicine, Los Angeles, CA§; the Department of Emergency Medicine, University of Maryland, Baltimore, MDII; and the Department of Emergency Medicine, University of Pittsburgh, Pittsburgh, PA.¶

William R. Mower, MD, PhD* Jerome R. Hoffman, MA, MD* Charles V. Pollack, Jr., MA, MD‡ Michael I. Zucker, MD*§ Brian J. Browne, MDII Allan B. Wolfson, MD¶ For the NEXUS Group

Author contributions are provided at the end of this article. Received for publication September 5, 2000. Revision received March 6, 2001. Accepted for publication March 14, 2001. This work was funded by grant No. RO1 HS08239 from the Agency for Healthcare Research and Quality, formerly the Agency for Health Care Policy and Research. Address for reprints: William R. Mower, MD, PhD, UCLA Emergency Medicine Center, 924 Westwood Boulevard, Suite 300, Los Angeles, CA 90024; 310-794-0582, fax 310-794-0599; E-mail [email protected]. Copyright © 2001 by the American College of Emergency Physicians. 0196-0644/2001/$35.00 + 0 47/1/115946 doi:10.1067/mem.2001.115946

See related articles, p. 8, p. 12, p. 17, and p. 22. Study objective: Standard radiographic screening may fail to reveal any evidence of injury in some patients with spinal injury. The purposes of this investigation were to document the efficacy of standard radiographic views and to categorize the frequencies and types of injuries missed on plain radiographic screening of the cervical spine. Methods: All patients with blunt trauma selected for radiographic cervical spine imaging at 21 participating institutions underwent a standard 3-view series (cross-table lateral, anteroposterior, and odontoid views), as well as any other imaging deemed necessary by their physicians. Injuries detected with screening radiography were then compared with final injury status for each patient, as determined by review of all radiographic studies. Results: The study enrolled 34,069 patients with blunt trauma, including 818 patients (2.40% of all patients; 95% confidence interval [CI] 2.40% to 2.40%) having a total of 1,496 distinct cervical spine injuries. Plain radiographs revealed 932 injuries in 498 patients (1.46% of all patients; 95% CI 1.46% to 1.46%) but missed 564 injuries in 320 patients (0.94% of all patients; 95% CI 0.94% to 0.94%). The majority of missed injuries (436 injuries in 237 patients [representing 0.80% of all patients]; 95% CI 0.80% to 0.80%) occurred in cases in which plain radiographs were interpreted as abnormal (but not diagnostic of injury) or inadequate. However, 23 patients (0.07% of all patients; 95% CI 0.05% to 0.09%) had 35 injuries (including 3 potentially unstable injuries) that were not visualized on adequate plain film imaging. These patients represent 2.81% (95% CI 1.89% to 3.63%) of all injured patients with blunt trauma undergoing radiographic evaluation. Conclusion: Standard 3-view imaging provides reliable screening for most patients with blunt trauma. However, on rare

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ANNALS OF EMERGENCY MEDICINE

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SCREENING CERVICAL SPINE RADIOGRAPHY IN BLUNT TRAUMA Mower et al

occasions, such imaging may fail to detect significant unstable injuries. In addition, it is difficult to obtain adequate plain radiographic imaging in a substantial minority of patients. [Mower WR, Hoffman JR, Pollack CV Jr, Zucker MI, Browne BJ, Wolfson AB, for the NEXUS Group. Ann Emerg Med. July 2001;38:1-7.] INTRODUCTION

Timely and accurate recognition of cervical spine injury is essential to the optimal management of patients with blunt trauma. Standard radiographic evaluation of the cervical spine in such patients typically consists of cross-table lateral, anteroposterior, and open-mouth odontoid views, supplemented at some centers with oblique imaging.1,2 These initial views are used to screen for the presence of injury or abnormalities associated with injury, and further radiographic search for cervical spine injuries is often terminated if these views are determined to be normal. Reports from several institutions suggest that standard 3-view radiography may be unreliable, missing up to 53% of all cervical spine fractures and yielding completely normal results in up to 8% of patients with bony cervical spine injury.3-5 Although others have failed to confirm these findings,6 such reports have prompted some authors to call for a reappraisal of screening radiography and for development of criteria to identify individuals whose injuries might be missed with plain film imaging.7,8 The purposes of this study are to examine prospectively the reliability of standard plain film screening of the cervical spine in patients with blunt trauma in a variety of institutions and to categorize the frequencies and types of injuries missed by screening radiography. M AT E R I A L S A N D M E T H O D S

The methods for this multicenter study have been described in detail elsewhere.9 Briefly, the primary goal of the National Emergency X-Radiography Utilization Study (NEXUS) was to evaluate the performance of a decision instrument in identifying patients with blunt trauma who can be managed safely without obtaining any imaging studies. In the course of this prospective observational study, we obtained plain radiographic films of the cervical spine, as well as any necessary ancillary studies, in 34,069 patients with blunt trauma evaluated in the participating centers. We conducted this prospective observational study at 21 centers distributed across the United States, including university and community hospitals, public and private

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hospitals, centers with and without residency programs, large and small hospitals, and institutions with wide variation in their emergency department censuses. All levels of trauma categorization were represented. We enrolled all patients with blunt trauma who underwent cervical spine radiography in the participating EDs. We excluded patients without trauma and those undergoing cervical spine imaging for any other reason. There were no other exclusion criteria. We allowed treating physicians to order films at their own discretion, using whatever criteria they ordinarily use. The decision to order films was not dictated by study protocol. Clinicians ordered standard 3-view cervical spine radiography (cross-table lateral, anteroposterior, and odontoid views) on all patients. Other studies, such as oblique views, flexion-extension radiographs, and plain tomography, were ordered at the discretion of the treating physician. Clinicians ordered computed tomography (CT) or magnetic resonance imaging (MRI) as adjunctive studies in patients in whom they believed such imaging would enhance injury detection and diagnosis and in patients in whom it impractical or impossible to obtain plain films. All radiographic studies were interpreted formally by site radiologists. We used the final interpretations of all imaging studies to determine the injury status for individual patients. If reports were ambiguous, study radiologists reviewed both the reports and original radiographs to determine final injury classification. Using these final interpretations, we assembled a list of all radiographically diagnosed spine injuries for each patient. We then reviewed individual imaging reports to determine whether any injuries were evident on the associated study. On the basis of our review of these reports, we assigned each enrolled patient to one of the following groups: 1. No injury detected on any imaging study 2. Injuries present and at least one injury detected with screening radiography 3. Injuries present but none detected with screening radiography and screening images interpreted as normal 4. Injuries present but none detected with screening radiography and screening images interpreted as abnormal (eg, abnormal soft tissue contour, straightening of the spine, and similar findings that suggest injury but are not diagnostic) 5. Injuries present but none detected with screening radiography and images classified as inadequate or complete series not obtained. We counted uninjured patients who had negative screening radiographs as having true-negative results


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(group 1). We counted plain radiographic reports that revealed any injuries as true-positive results (group 2). Reports on injured individuals that were interpreted as normal were classified as false-negative results (group 3). Reports on injured individuals that were interpreted as abnormal (but not diagnostic of injury) or inadequate were classified as indeterminate results (groups 4 and 5). The study was conducted as a prospective observational study, and the study protocol neither mandated nor directed any element of patient care and thus posed no risk to patients. For purposes of confidentiality, data were transformed by using unique identifiers before concatenation with the central data bank. Thus, it is impossible for individual patients to be identified from study data. Waivers of informed consent were granted to each institution participating in the study. Because we did not perform exhaustive imaging on all patients with blunt trauma, it is possible that injuries in some patients may have gone undetected. Clinicians may have failed to obtain screening radiographs in some patients with injuries or terminated imaging when screening radiographs were interpreted as normal. Thus, the study has the potential for workup or verification bias. To protect against this bias, we reviewed neurosurgical and risk management logs of each participating center 3 months after the completion of the study to identify any case of missed cervical spine injury. R E S U LT S

The entire study enrolled 34,069 patients, of whom 818 (2.40% of all patients; 95% confidence interval [CI] 2.40% to 2.40%) had 1 or more cervical spine injuries. Ages ranged from 1 month to 101 years, with an average age of 37.0 years. The majority of the patients were male (58.7%; 95% CI 58.7% to 58.7%), as were the majority of injury victims (64.8%; 95% CI 64.8% to 64.8%). Injury victims sustained a total of 1,496 distinct injuries at 1,285 cervical spine sites. Plain films identified at least 1 injury in 498 patients (1.46% of all patients; 95% CI 1.46% to 1.46%). These patients were found to have a total of 932 injuries. An additional 564 injuries in 320 patients (0.94% of all patients; 95% CI 0.94% to 0.94%) were not identified by plain film imaging. The majority of missed injuries, 436 lesions in 237 patients (representing 0.80% of all patients; 95% CI 0.80% to 0.80%), occurred in patients in whom it was impossible to complete adequate plain film imaging (radiographs were inadequate); the injuries were diagnosed by means of other imaging modalities. The remaining 83

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patients had complete 3-view images that missed a total of 128 injuries. In 36 of these patients (0.11% of all patients; 95% CI 0.07% to 0.14%) with 66 associated injuries, the radiographs were interpreted as abnormal, with no specific injury diagnosis. Overall, plain film images were deemed indeterminate (inadequate or abnormal but not diagnostic for the specific lesion) in 237 patients (0.80% of all patients; 95% CI 0.80% to 0.80%) involving 502 injuries. The figure details the distribution of radiographic findings among the enrolled patients. Radiologists interpreted 3-view plain images as normal in 47 patients who ultimately were found to have 62 injuries. Twenty-four of these patients (0.07% of all patients; 95% CI 0.05% to 0.09%) had MRI documenting 27 spinal cord injuries without radiographic abnormality (SCIWORA). The remaining 23 patients had 35 injuries that were not visualized on adequate plain film imaging. These patients represent 2.81% of all patients with injuries (95% CI 1.89% to 3.63%), 2.3% of all injuries, and 0.07% (95% CI 0.05% to 0.09%) of all patients undergoing radiographic evaluation. Patients with missed injuries were predominantly male (19 [82.6%]), with ages ranging from 14 to 81 years (average age, 39.4 years). Two patients with missed injuries were older than age 65 years, and 1 victim was older than 80 years. The number of patients with injuries that were not visualized on adequate plain film imaging varied by site, ranging from a minimum of 0 to a maximum of 5 (median, 1; interquartile range, 0 to 3). The number of missed patients at each site was closely related to the total number of patients enrolled (Spearman rank correlation coefficient, r = 0.78). Similarly, the number of patients with injuries that were not detected as a result of inadequate radiographs also varied by site from a minimum of 0 to a maximum of 53 (median, 7; interquartile range, 1 to 16). The number of missed patients associated with inadequate radiographs was also related to institutional volume (Spearman rank correlation coefficient, r = 0.85). Of the 35 missed injuries, 8 (in 6 patients) were identified on flexion-extension imaging, 3 (in 2 patients) were seen on MRI, and 29 (in 18 patients) were diagnosed by means of CT. The total number of detected injuries exceeds 35 because several injuries were evident on multiple modalities. A single injury was detected by means of risk-management review (on the basis of unspecified imaging from an outside institution) in a patient who had no additional imaging beyond plain films at the time of initial presentation. Adequate screening radiography was obtained in 557 patients without SCIWORA and detected injuries in 498

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patients. Thus, the functional sensitivity (ie, ability to detect at least 1 lesion in an injured patient) of an adequate 3-view series was 89.4% (95% CI 86.9% to 91.4%). The negative predictive value of normal screening films for any injury was 99.9% (35 missed injuries among 33,286 negative films; 95% CI 99.9% to 100.0%) and 99.99% (95% CI 99.9% to 100.0%) for unstable injuries. However, screening radiographs were indeterminate (abnormal or inadequate) in 273 (33.4%) of the 818 patients (95% CI 33.3% to 33.4%).

Table 1 lists the injuries missed by plain film radiography. The most common sites of missed injury were the lamina and posterior elements (excluding the spinous processes). Three of the missed injuries were of a type associated with clinical instability, including one type II odontoid fracture, one atypical traumatic spondylolisthesis, and one subluxation. The spine levels associated with missed injuries are presented in Table 2. This table also lists the number of missed injuries, as well as the total number of injuries

Figure.

Classification of enrolled patients by means of injury status and findings from screening radiography.

Total number of enrolled patients 34,069

Patients without cervical spine injury 33,251 (97.6% of all patients)

Patients having cervical spine injury 818 (2.4% of all patients)

At least one injury visualized on screening radiography 498 patients (1.5% of all patients) (932 injuries)

No injury visualized on screening radiography 320 patients (0.9% of all patients) (564 injuries)

No injury visualized, screening radiographs inadequate 237 patients (0.7% of all patients) (436 injuries)

No injury visualized on adequate imaging 83 patients (0.2% of all patients) (128 injuries)

No injury visualized, but radiographs interpreted as abnormal 36 patients (0.1% of all patients) (66 injuries)

No injury visualized, radiographs interpreted as normal 47 patients (0.1% of all patients) (62 injuries)

No injury seen, SCIWORA victim 24 patients (0.07% of all patients) (27 injuries)

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No injury seen with adequate normal radiographs in non-SCIWORA victims 23 patients (0.07% of all patients) (35 injuries)


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detected at each level. Injuries to C6 and C7 accounted for 17 (48.6%) of the missed injuries, and 7 injuries to C2 and the odontoid represent 20% of all missed injuries. Injuries to C6 were the most likely to be missed in terms of absolute magnitude (total of 10 injuries) and relative magnitude (4.1% of these injures were missed). DISCUSSION

The NEXUS project is the first large-scale, prospective multicenter study to examine the reliability of standard plain film radiography in detecting cervical spine injuries in patients with blunt trauma. Our sites were selected carefully to be representative of all types of EDs across the country. Hence, the results of this study should be applicable to the majority of institutions evaluating patients with blunt trauma. The observed 2.40% prevalence of cervical spine injury is similar to rates reported in other studies.10,11 This low prevalence of injury makes it extremely unlikely that an individual patient with blunt trauma will have an injury that is missed on screening radiography. In fact, screening radiographs missed all injuries in only 23 (0.07%) of 34,069 enrolled patients with blunt trauma or once in every 1,481 blunt trauma evaluations. Nevertheless, patients with missed injuries represented 2.81% of all injured patients and 4.13% of the 557 patients who had adequate screening radiographs (3-view series). These values are similar to the miss rates reported in singleinstitution studies.3-5 Our patients with missed injuries represent instances in which screening radiography failed to detect any evidence of injury. Most of our patients with fractures had

multiple injuries, and many of these additional injuries were not detected by screening radiography. We did not include these additional injuries among our missed injury counts because screening radiography by its very nature is not intended to detect every injury. Rather, the role of screening radiography is to detect any evidence of injury. Other modalities, such as CT and MRI, can then be used to carefully evaluate for additional injuries.3,4,12 Furthermore, we have not counted patients with SCIWORA as missed injuries because patients with SCIWORA, by definition, do not have bony injury. Many of the missed injuries, such as isolated spinous process fractures, are trivial and require no specific treatment.13 However, a number of the missed injuries are potentially significant, including 3 injuries associated with spinous instability. Fortunately, unstable injuries were missed infrequently, representing only 0.20% of all injuries and occurring in only 0.008% of all blunt trauma presentations (or less than once in every 11,000 screening evaluations). An additional concern associated with screening radiography is inadequate imaging. In this series, injuries were missed in 237 (30%) patients because screening radiographs were technically inadequate. Although this rate may vary slightly from the rate of inadequate radiographs among all patients with trauma (particularly those without spine injuries), it is similar to the rates reported in other studies.4,14 Inadequate films are of concern because incomplete visualization of crucial cervical anatomy necessitates the use of other imaging modalities, such as CT and plain tomography.12,15-17 These additional modalities increase the cost of radiographic clearance, as well as exposure to ionizing radiation.4 In addi-

Table 2. Table 1.

Cervical spine levels associated with missed injuries.

Injuries missed by plain film radiography. Injury Location

No. of Missed Injuries Spine Level

Lamina and posterior elements Spinous process Lateral mass and facet Vertebral body Transverse process Intraspinous ligament Odontoid Atypical traumatic spondylolisthesis Uncinate process Subluxations

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12 6 5 4 2 2 1 1 1 1

C1 C2 (nonodontoid) Odontoid C3 C4 C5 C6 C7 Interspinous

No. of Injuries in All Patients

No. of Missed Injuries

% of Injuries Missed

105 194 92 51 84 179 242 228 231

1 6 1 2 1 4 10 7 3

1.0 3.1 1.1 3.9 1.2 2.2 4.1 3.1 1.3

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tion, inadequate films can interfere with the acute care and management of patients with trauma, particularly when prolonged or repeated imaging delays other aspects of care.18 Concern about missed injuries and the costs and delays associated with inadequate standard radiographs has led some investigators to examine the possibility of developing criteria to identify patients with trauma at greatest risk of injury, particularly those having injuries most likely to be missed by standard radiography.7,8 Proposed high-risk criteria include focal neurologic deficit, severe head injury or high-energy mechanism, and age of 50 years or younger.8 Whether these strategies will prove effective, while simultaneously limiting cost and radiation exposure, remains to be seen. This study enrolled all patients with blunt trauma for whom physicians ordered radiographic cervical spine imaging. It is possible that clinicians failed to identify some injured patient and did not obtain screening radiography. It is also possible that some such patients would have had normal radiographs, although there is no evidence that this is particularly likely. More importantly, because we did not perform exhaustive imaging (including CT) on all patients, it is possible that some injuries went undetected after plain films were interpreted as normal. This potential verification bias may have led us to underestimate the number of missed injuries and overestimate the reliability of standard screening radiography. On the other hand, our review of neurosurgical and risk-management logs revealed only a single case of missed injury not picked up during the study. This suggests that additional missed injuries are probably rare, and even if several other cases occurred but went undetected, this would not significantly change the overall study results. In addition, it is possible that radiologists may have used results from adjunctive imaging in making their final interpretations of screening studies. This would also increase the apparent performance of screening radiography and underestimate the number of missed injuries. The standard practice at many of the study institutions (particularly those that contributed the greatest number of cases), however, is to have plain films interpreted before CT scans are completed. In these same institutions, plain radiographic films and CT scans typically are read by separate individuals. Alternatively, because we considered CT (and MRI) readings to be correct whenever they were interpreted differently than were the plain films, it is possible that some injuries diagnosed by means of CT actually repre-

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sent false-positive CT scans rather than false-negative plain films. Such cases would increase the number of missed injuries and decrease the apparent utility of screening radiography. Although this type of bias may exist in the study, any such effect is likely to have been minimal, given the accepted accuracy of such gold standard imaging. Overall, the potential for bias is small and should not greatly affect the ultimate findings of the study. In summary, the evidence from this large prospective study strongly suggests that adequate screening radiographs identify the large majority of patients with bony cervical spine injuries and that the overwhelming majority of patients with blunt trauma with an adequate screening series that shows no injury are indeed without bony injury. Nevertheless, in a small number of patients with blunt trauma, important cervical spine injury can be missed, even on adequate screening plain films. Furthermore, in many patients with blunt trauma, plain films are not adequate, and adjunctive studies are required before cervical spine injury can be excluded. Any strategy designed to improve the identification of such injuries must attempt to achieve a balance between detecting a small number of additional injuries and exposing large numbers of patients with trauma to the costs and radiation associated with additional imaging. Author contributions: WRM, JRH, CVP, MIZ, BJB, and ABW participated in the project development, data collection, interpretation, authorship, and critical review. WRM and JRH performed the interpretation and statistical analysis. WRM takes responsibility for the paper as a whole. We thank Guy Merchant, NEXUS Project Coordinator, for his outstanding contributions to the project, as well as the house officers and attending physicians at each of the participating NEXUS sites, without whose cooperation and hard work the study would not have been possible.

REFERENCES 1. American College of Radiology. Appropriateness Criteria for Imaging and Treatment Decisions. Reston, VA: American College of Radiology; 1995. 2. Mirvis SE, Diaconis JN, Chirico PA, et al. Protocol-driven radiologic evaluation of suspected cervical spine injury: efficacy study. Radiology. 1989;170:831-834. 3. Woodring JH, Lee C. The role and limitations of computed tomographic scanning in the evaluation of cervical trauma. J Trauma. 1993;34:32-39. 4. Acheson MB, Livingston RR, Richardson ML, et al. High-resolution CT scanning in the evaluation of cervical spine fractures: comparison with plain film examinations. AJR Am J Roentgenol. 1987;148:1179-1185. 5. Streitwieser DR, Knoop R, Wales LR, et al. Accuracy of standard radiographic views in detecting cervical spine fractures. Ann Emerg Med. 1983;12:538-542. 6. Davis JW, Phreaner DL, Hoyt DB, et al. The etiology of missed cervical spine injuries. J Trauma. 1993;34:342-346. 7. Blackmore CC, Emerson SS, Mann FA, et al. Cervical spine imaging in patients with trauma: determination of fracture risk to optimize use. Radiology. 1999;211:759-765.


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8. Blackmore CC, Ramsey SD, Mann FA, et al. Cervical spine screening with CT in trauma patients: a cost-effectiveness analysis. Radiology. 1999;212:117-125.

APPENDIX

9. Hoffman JR, Wolfson AB, Todd K, et al. Selective cervical spine radiography in blunt trauma: methodology of the National Emergency X-Radiography Utilization Study (NEXUS). Ann Emerg Med. 1998;32:461-469.

The following centers and investigators collaborated in this study. Principal Investigator: W. Mower Coinvestigator: J. Hoffman Steering Committee: J. Hoffman, W. Mower, K. Todd, A. Wolfson, and M. Zucker Site Investigators Antelope Valley Medical Center (Los Angeles): M. Brown and R. Sisson; Bellevue Hospital (New York): W. Goldberg and R. Siegmann; Cedars-Sinai Medical Center (Los Angeles): J. Geiderman and B. Pressman; Crawford Long Hospital (Atlanta): S. Pitts and W. Davis; Egleston Children’s Hospital (Atlanta): H. Simon and T. Ball; Emory University Medical Center (Atlanta): D. Lowery and S. Tigges; Grady Hospital (Atlanta): C. Finney and S. Tigges; Hennepin County Medical Center (Minneapolis): B. Mahoney and J. Hollerman; Jacobi Medical Center (Bronx): M. Touger, P. Gennis, and N. Nathanson; Maricopa Medical Center (Phoenix): C. Pollack and M. Connell; Mercy Hospital of Pittsburgh (Pittsburgh): M. Turturro and B. Carlin; Midway Hospital (Los Angeles): D. Kalmanson and G. Berman; Ohio State University Medical Center (Columbus): D. Martin and C. Mueller; Southern Regional Hospital (Decatur): W. Watkins and E. Hadley; State University of New York at Stonybrook (Stonybrook): P. Viccellio and S. Fuchs; University of California, Davis, Medical Center (Sacramento): E. Panacek and J. Holmes; University of California, Los Angeles, Center for the Health Sciences (Los Angeles): J. Hoffman and M. Zucker; University of California, San Francisco, Fresno University Medical Center (Fresno): G. Hendey and R. Lesperance; University of Maryland Medical Center (Baltimore): B. Browne and S. Mirvis; University of Pittsburgh Medical Center (Pittsburgh): A. Wolfson and J. Towers; University of Texas Health Sciences Center/Hermann Hospital (Houston): N. Adame, Jr., and J. Harris, Jr.

10. Hoffman JR, Schriger DL, Mower WR, et al. Low-risk criteria for cervical spine radiography in blunt trauma: a prospective study. Ann Emerg Med. 1992;12:1454-1460. 11. Roberge RJ, Wears RC, Kelly M, et al. Selective application of cervical spine radiography in alert victims of blunt trauma: a prospective study. J Trauma. 1988;28:784-788. 12. Borock EC, Gabram SG, Jacobs LM, et al. A prospective analysis of a two-year experience using computed tomography as an adjunct for cervical spine clearance. J Trauma. 1991;31:10011005. 13. Stiell IG, Lesiuk HJ, Vandemheen K, et al. Obtaining consensus for a definition of “clinically important cervical spine injury” in the CCC study [abstract]. Acad Emerg Med. 1999;6:435. 14. Blackmore CC, Deyo RA. Specificity of cervical spine radiography: importance of clinical scenario. Emerg Radiol. 1997;4:283-286. 15. El-Khoury GY, Kathol MH, Daniel WW. Imaging of acute injuries of the cervical spine: value of plain radiography, CT, and MR imaging. AJR Am J Roentgenol. 1995;164:43-50. 16. Clark CR, Igram CM, El-Khoury GY, et al. Radiographic evaluation of cervical spine injuries. Spine. 1988;13:742-747. 17. Link TM, Schuierer G, Hufendiek A, et al. Substantial head trauma: value of routine CT examination of the cervicocranium. Radiology. 1995;196:741-745. 18. Nunez DB, Ahmad AA, Coin CG, et al. Clearing the cervical spine in multiple trauma victims: time-effective protocol using helical computed tomography. Emerg Radiol. 1994;1:273-278.

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