Emergency Radiology (2000) 7: 3±6
Ó American Society of Emergency Radiology 2000
O R I GI N A L A RT IC LE William R. Mower ´ Jerome R. Hoffman ´ Michael I. Zucker
Odontoid fractures following blunt trauma
Abstract Fractures of the odontoid process typically result from forceful blunt trauma. They often produce instability of the cervical spine, and may be associated with neurologic impairment. This study was designed to examine the epidemiology and demographics of odontoid injuries, including their incidence and prevalence relative to other spine injuries, the prevalence of associated injuries, and the likelihood of neurologic impairment. Of 34,069 enrolled blunt trauma victims, 818 (2.4 %) sustained a cervical spine injury, 94 of whom had a fracture of the odontoid. The relative prevalence of odontoid fractures varied by age, ranging from less than 3 % among individuals under age 20 years, to greater than 20 % in patients over 80 years old. Classification by Anderson±D'Alonzo criteria revealed 6 type I injuries, 60 type II injuries, and 27 type III injuries; one vertical injury could not be categorized. Over half of the odontoid fracture victims sustained additional cervical spine injuries, with 90 % of these injuries involving the atlanto-axial complex. In addition, non-spine-related injuries were found in 52 % of odontoid injury victims, over one-third (34 %) presented with an altered level of alertness, and almost one-quarter (23 %) exhibited some form of focal neurologic deficit associated with their injury. Fractures of the odontoid are among the most frequently encountered cervical spine injuries, and increase in prevalence with increasing patient age. Odontoid fracture victims often have other spine injuries, particularly to the atlanThe authors wrote on behalf of the NEXUS group
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W. R. Mower ( ) ´ Jerome R. Hoffman ´ M. I. Zucker The UCLA Emergency Medicine Center, UCLA School of Medicine, 924 Westwood Blvd., Suite 300, Los Angeles, CA 90024, USA e-mail:
[email protected] Tel.: + 1-3 10-7 94 05 82 Fax: + 1-3 10-7 94 05 99 M. I. Zucker Department of Radiology, UCLA School of Medicine, Los Angeles, California, USA
to-axial complex, and may harbor other non-spine-related injuries and neurologic pathology. Key words Cervical spine ± Radiography ± Odontoid fractures ± Dens
Introduction Fractures of the odontoid process typically result from forceful blunt trauma. They are known to produce instability of the cervical spine in many cases, and may be associated with neurologic impairment. This study, by far the largest ever done on patients with blunt trauma to the neck, was designed to provide relatively definitive information regarding the incidence and prevalence of these injuries relative to other spine injuries, and to investigate the prevalence of associated injuries, neurologic impairment, and the epidemiology and demographics of odontoid injuries.
Methods The methods for this multicenter study have been described in detail elsewhere [1]. Briefly, the primary goal of the National X-radiography Utilization Study (NEXUS) was to evaluate the performance of a decision instrument in identifying patients with blunt trauma who can be safely managed without obtaining any imaging studies. In the course of this prospective observational study, we obtained plain X-rays of the cervical spine, as well as any necessary ancillary studies, in 34,069 blunt trauma patients evaluated in participating centers. Participating centers We conducted this prospective observational study at 21 centers distributed across the United States, including university and community hospitals, public and private hospitals, centers with and without residency programs, large and small hospitals, institutions with wide variation in their Emergency Department (ED) census, and representing all levels of trauma categorization.
4 Patient inclusion criteria We enrolled all blunt trauma patients who underwent cervical spine radiography in the participating EDs. We excluded nontrauma patients 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. Cervical spine radiography Clinicians ordered standard three-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 cases where they felt such imaging would enhance injury detection and diagnosis, and in cases where it was impractical or impossible to obtain plain films.
Table 1 Distribution of nonodontoid injuries sustained by odontoid fracture victims Spine level
Number of injuries
C1 C1±C2 interspace C2 C3 C4 C5 C6 C7 Spinal cord
18 11 20 1 1 2 0 1 4
Table 2 Distribution of odontoid fractures by age (excludes seven patients with type II injuries for whom age was unknown) Age Odontoid injuries (years)
Injury assessment and data collection All radiographic studies were formally interpreted by site radiologists. We used the final interpretations of all imaging studies to determine the injury status for individual patients. In instances where reports were ambiguous, study radiologists reviewed both the reports and original radiographs to determine final injury classification. We sequestered data on all patients diagnosed with odontoid fractures for separate analysis. Because the study has the potential for verification bias, we reviewed neurosurgical and risk management logs 3 months after the close of the study to determine whether any injuries may have been missed on initial evaluations.
< 20 20±29 30±39 40±49 50±59 60±69 70±79 80 + a
Total no. of other spine injuries
Type I
Type II
Type III Total no.
Percent of all spine injuries
0 1 1 2 0 0 2 0
2 2 6 5 6 6 13 13
1 5 2 3 2 5 6 3
2.86 3.00 3.42 4.33 6.45 14.1 16.5 20.2
3 8 9 10 8 11 21 17a
105 267 263 231 124 78 127 84
One 87-year-old patient had a coronal odontoid fracture
Institutional approval and patient consent 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, using unique identifiers, prior to 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.
Results The entire study enrolled 34,069 patients, of whom 818 (2.4 %) had one or more cervical spine injuries. These injury victims sustained a total of 1,496 distinct injuries to 1,285 different cervical spine structures, including 94 odontoid fractures. Thus, odontoid fractures were found in 0.28 % of all blunt trauma patients suspected of being at risk for cervical spine injury, and occurred in 11.5 % of spine injury victims. These injuries represent 6.3 % of all cervical spine injuries. Overall, these 94 patients with an odontoid injury sustained a total of 152 cervical spine injuries, or 1.65 injuries per patient. This value is slightly less than the 1.83 injuries per patient seen among all spine injury victims in the study.
Table 1 lists the 58 non odontoid injuries sustained by odontoid fracture victims. Most of these additional injuries involved the atlanto-axial complex with five injuries (8.6 %) involving other areas of the spine. Only three patients exhibited noncontiguous lesions, including two individuals with injuries to the fifth cervical vertebra (a laminar fracture and a spinous process fracture), and one patient with a fracture of the C7 lateral mass. Of the 94 odontoid fracture victims, 58 (61.7 %) were male; this distribution is similar to the 64.8 % male predominance among all injury victims in the entire cohort. Twenty-two (23.4 %) of the odontoid fracture victims exhibited some form of neurologic deficit as a result of their injury, 49 (52.1 %) sustained some additional, nonspine injury, and 32 (34.0 %) presented with altered levels of alertness. Ages for all cervical spine fracture victims ranged from 1 month to 101 years, with an average of 37.0 years. In contrast, odontoid fracture victims tended to be older, with an average age of 58.7 years (range 2±99 years). Table 2 presents the distribution of odontoid fractures by age. The prevalence of odontoid fractures, and type II injuries in particular, increases with increasing age and is highest in the very elderly. In terms
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of the Anderson±D'Alonzo classification [2], 6 injuries (6.4 %) were categorized as type I, 60 (63.8 %) as type II, 27 (28.7 %) as type III, and one coronal injury could not be categorized by the Anderson±D'Alonzo classification. Screening radiographs provided diagnostic visualization of 60 odontoid fractures, including 28 injuries not visualized by other modalities. CT visualized 52 fractures (32 of which were independently visualized on plain radiographs). MRI detected 8 fractures, including 3 injuries that were not visualized with other modalities. Eleven injuries were detected on combined readings of multiple modalities. In one patient, screening radiographs failed to demonstrate evidence of a type II injury; this patient's injury was subsequently detected by review of risk management logs (the injury was detected at an outside institution using an undisclosed type of imaging).
Discussion Odontoid fractures are among the most frequently seen cervical spine injuries with prevalence rates of 8±18 % [3, 4] among spine injury victims. These injuries are important to detect, because immediate treatment and long term prognosis depend on the accurate diagnosis and classification of the injury [2, 5, 6]. This study represents the first prospective multicenter investigation of the acute presentations of odontoid injury. Other, earlier studies have focused on patients from single institutions [2, 6], subsets of patients [7, 8, 9] or patients hospitalized following injury [5]. While these studies contain important information on odontoid injuries, they fail to capture the spectrum of injury seen in general emergency radiology. Findings from this study indicate that slightly more than 10 % of spine injury victims sustain a fracture of the odontoid. This rate of injury is very age-dependent, odontoid injuries being rare in the very young and increasingly common in the elderly and very elderly. Patients under age 20 sustained only 3 of the 94 (3.2 %) odontoid injuries found in this study, and odontoid injuries accounted for only 2.9 % of all spine injuries seen in this age group. These findings confirm those of other recent reports [4, 9]. In contrast, patients older than 80 years sustained over 18 % of all odontoid injuries, and odontoid fractures accounted for over one-fifth of all spine injuries in this age group. Odontoid injuries in the elderly are of particular concern because they frequently occur despite a relatively minor mechanism of injury, such as a fall [5, 7, 8, 10, 11], but are often associated with significant complications, including malunion and nonunion [7, 8, 11]. In addition, older individuals frequently suffer other medical complications, including death, as a result of their injury and inability to tolerate prolonged periods of immobility [7, 8]. The long-term prognosis following an odontoid fracture is best predicted by the Anderson±D'Alonzo classi-
fication of injury [2]. This scheme recognizes three variants of injury. Type I lesions represent fractures through the tip of the odontoid, and typically do not involve disruption of the transverse ligament. These injuries are usually mechanically stable and tend to heal with conservative treatment. In contrast, type II injuries occur when the fracture line extends through the base of the odontoid at the junction of the odontoid and vertebral body. Such injuries have a high incidence of malunion and nonunion, particularly if the odontoid process is displaced or angulated relative to the vertebral body [2, 5, 6, 11]. Conservative treatment, including prolonged immobilization, is often effective in treating favorable fractures. Alternatively, surgical repair, such as anterior screw fixation, may be more effective in treating displaced or angulated injuries, particularly among elderly individuals [5, 12]. Type III injuries represent fractures of the vertebral body. Although some sources suggest that these injuries are stable, and produce low complication rates [6], the prognosis for this type of injury actually depends on multiple characteristics of the injury [3, 5]. Unfavorable fractures, characterized by shallow encroachment into the vertebral body, or angulation or marked displacement of the odontoid fragment, frequently result in malunion or nonunion, particularly among elderly patients treated conservatively[3, 5]. Emergency radiologists must be familiar with the features that predict instability and unfavorable outcomes in these injuries, particularly if they wish to avoid generating false reassurances among naïve clinicians. The distribution of injuries found in this study contains a higher proportion of type I injuries than many other studies [5, 6, 7]. This difference undoubtedly reflects the referral bias of such studies, which are based on inpatient populations, since patients with stable type I injuries are rarely admitted for neurosurgical management. This study also enrolled one patient having a vertical odontoid fracture. Only a handful of these rare injuries have been described in the medical literature [13, 14]. They are typically well visualized using CT, and if the transverse ligament is intact, may be considered stable and treated in a manner similar to stable type I injuries [13]. Nearly half the odontoid fracture victims in this study had additional cervical spine injuries. The majority of these lesions involved the atlanto-axial complex, with less than 10 % involving the lower five cervical vertebra. Fractures to the bony elements of the first and second vertebra accounted for the majority of these additional injuries, but nearly 20 % were associated with ligamentous instability, and 10 % involved radiographically demonstrable cord lesions. Radiologists must be cognizant of this high prevalence of associated injury, and focus careful attention on the region of the atlanto-axial complex. This study also confirms a previous report which found that a significant proportion of fracture victims
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have evidence of other pathology [15]. Nearly onefourth of the patients in this study exhibited a focal neurologic deficit, one-third had an abnormal level of alertness, and over half had other injuries not associated with the cervical spine fracture. Responsible clinicians will be alert for evidence of such additional problems, in order to be able to institute appropriate evaluation and treatment as indicated. In summary, fractures of the odontoid are among the most frequently encountered cervical spine injuries. The prevalence of injury increases with age; the elderly are most likely to sustain an odontoid fracture. Optimal management depends on correct categorization according to the Anderson±D'Alonzo classification scheme, as well as recognition of characteristics associated with favorable and unfavorable outcomes. Patients with odontoid fracture often have other spine injuries, particularly injuries to the atlanto-axial complex, and may harbor other nonspine injuries and neurologic pathology. Acknowledgements This work was funded by Grant # RO1 HS08239 from the Agency for Health Care Policy and Research. The authors wish to 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. The following centers and investigators collaborated in this study. Principal Investigator: W. Mower. Co-Investigator: J. Hoffman. Steering Committee: J. Hoffman, W. Mower, K. Todd, A. Wolfson, 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.
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