Introduction

Cervical fractures are some of the most frequent spinal injuries in the elderly population today, accounting for 25,000 new hospitalizations every year in the United States [10, 13]. The elderly are particularly predisposed to bony injury as a result of a greater predilection for sustaining low-energy fall injuries coupled with an increased incidence of osteopenia. Compounding the problem is the increasing number of comorbidities in the elderly population [14].

Approximately 10% to 20% of all cervical fractures occur at the odontoid process [7, 10, 16, 17], and the majority of these are classified as Type II fractures [3, 11]. Originally described by Anderson and D’Alanzo, Type II fractures occur at the junction between the body of the axis and the odontoid process [1]. Substantial displacement of the fractured segment may result in cord compression resulting in spinal cord injury (SCI) with possible neurological deficits (ND) [18]. However, this is a rare event with an occurrence rate ranging from 3% to 25% [2, 15] attributable in large part to the capacious spinal canal at this region.

Previous studies [19–21] of patients with Type II odontoid fractures but without ND suggest these injuries are associated with a mortality rate of 12.8% and a major complication rate of 47.8% after a minimum followup of 0 day (average, 15.1 days; range, 0–161 days). However, there is less literature examining patients with ND. One study of 17 patients suggests odontoid fractures are an infrequent cause of SCI with ND, most often occurring in males with congenital stenosis sustaining high-injuries [7]. Another study of 10 patients with ND after Type II fracture reported that six patients died, and SCI is an increasing finding in geriatric patients [18]. These studies contain too few patients to establish the incidence and determine the morbidity and mortality rates. Larger-scale studies specific to Type II odontoid fractures would help describe the hospital course of such patients to better inform treatment decisions. Specific information on the unique complications and causes of mortality associated with Type II odontoid fractures with ND may ultimately improve patient care and survival.

Our purposes were to (1) establish the incidence of neurological deficits with Type II odontoid fractures; and (2) determine if neurologic deficits were associated with increased in-patient mortality and (3) increased morbidity during hospitalization.

Patients and Methods

We searched our institution’s database from June 1985 to July 2008 for patients with Type II odontoid fractures presenting with a ND [19–21]. We included all patients with an American Spinal Injury Association (ASIA) impairment [4] Grade of A, B, C, or D. ASIA A indicates a “complete” SCI in which no motor or sensory function is preserved, ASIA B indicates an “incomplete” SCI in which sensory but not motor function is preserved, ASIA C indicates an “incomplete” SCI in which motor function is preserved and more than half of key muscles below the neurologic level have a muscle grade of less than 3 (active movement with full range of motion against gravity), and ASIA D indicates an “incomplete” SCI in which motor function is preserved and at least half of the key muscles have a muscle grade of 3 or more. The query returned a total of 116 unique cases with a possible ND after an acute Type II odontoid fracture. One patient’s medical record could not be found, and one patient’s record was incomplete, thus excluding them from the study. In the remaining 114 patients, we used radiology reports to confirm the presence of an acute Type II odontoid fracture. We defined a ND as an ASIA Grade A, B, C, or D based on consensus between orthopaedics and neurosurgical consult notes. Of the 114 patients whose charts were reviewed, 35 patients did not have a ND and were excluded. Patients were excluded if the radiology report indicated no C2 fracture (n = 8), C2 body fracture not involving the dens (n = 23), odontoid fractures that were Type I (n = 2) or Type III (n = 19), and chronic fractures (n = 7). These 59 exclusions left 20 patients with an acute Type II odontoid fracture and a ND (“deficit” cohort). Patients were only followed during their acute-care hospitalization (mean, 11.9 days; range, 0–41 days). No patients were recalled specifically for this study; all data were obtained from medical and imaging records. We had prior approval from the Institutional Review Board.

We reviewed the admission records of the 20 patients and extracted the following information: age, date of admission, date of discharge, date of death (if applicable), mechanism of injury (low-energy, high-energy), fracture displacement, comorbidities, associated injuries, ASIA grade, type of treatment (nonoperative or surgical method), estimated blood loss (if surgical treatment), in-hospital complications, and use of traction. Inpatient mortality was defined as a patient death occurring during the course of hospitalization; we did not determine mortality after discharge from our acute-care facility. Comorbidities were quantified using a point system in which one point was assigned for each major organ system (central nervous system, cardiac, respiratory, gastrointestinal, endocrine, vascular, malignancy) with a documented a major comorbidity; this point system was first created and implemented by our institution in a previous study describing Type II odontoid fractures without ND [21]. The data of the 20 patients (Table 1) were compared with data from a previously published cohort of 188 patients with acute Type II odontoid fractures without ND (“intact” cohort) [19–21]. This cohort represents all neurologically intact cases presenting to the same regional SCI center during the same time period serving as a control for this study.

Table 1 Characteristics of patients presenting with neurologic deficits
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Descriptive statistics were calculated, including frequencies for categorical variables and means and ranges for continuous variables. Univariable analysis was performed between the deficit and intact cohorts using the chi-square test for categorical variables and t-test for continuous variables. This demonstrated the presence of ND was associated with younger age (p < 0.001), greater percentage of high-energy mechanism of injury (p < 0.001), and more associated spinal injuries (p < 0.001). There was no difference in the number of comorbidities (p = 0.10), treatment (p = 0.11), or fracture displacement (p = 0.33) between the two cohorts (Table 2). Only the significant (p < 0.05) variables from the univariable analysis (age, mechanism of injury, and associated spinal injuries) were used as control parameters for the multivariable analysis. The outcome measures tested were originally inpatient mortality and the number of complications; however, after further review, the most common complication (respiratory distress) was also included. We used a multivariate logistic regression to determine the relationship between the presence of ND and categorical variables (inpatient mortality, the presence of respiratory distress). We used a Poisson distribution with the same parameters to determine the predictors of continuous variables (number of complications). Finally, a multivariate logistic regression was specifically used to determine correlations between mortality and ASIA grade. Because our study is retrospective in nature, data were missing with certain parameters. Specifically, no data were missing in the deficit cohort data; however, the intact cohort was missing eight values for displacement and 11 values for comorbidities. We did not attempt to impute missing values, and patients were only excluded in models requiring data to preserve our cohort sizes. All statistics were performed using JMP© 7.02 software (SAS, Cary, NC).

Table 2 Comparison of patient characteristics between deficit and intact cohorts
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Results

Combining both the deficit and intact cohorts, the incidence of a ND associated with acute Type II odontoid fractures was 9.6% (20 of 208 patients).

Patients with ND were 4.72 (95% confidence interval [CI], 1.35–16.6) times more likely to die than those who were intact (Table 3). Patients presenting with complete spine injuries (ASIA A) were 9.33 (95% CI, 1.19–73.0) times more likely to die than all other patients. Combining both the deficit and intact cohorts, there was a 16.3% (34 of 208 patients) inpatient mortality rate associated with an acute Type II odontoid fracture (Table 4).

Table 3 Mortality and complications of deficit and intact cohorts
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Table 4 Mortality rates
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Patients with ND had a high number of complications during their hospitalization (Table 5), and the most common complication was respiratory distress. Patients with ND experienced 1.18 (95% CI, 0.54–1.77) times as many complications as those without ND. In the deficit cohort, 18 of 20 (90%) patients experienced respiratory distress and required intubation, of which eight (44%) ultimately required a tracheostomy for respiratory failure. Spine injuries of those who required a tracheostomy were ASIA A (n = 4), ASIA B (n = 1), ASIA C (n = 2), or ASIA D (n = 1). In the intact cohort, 25 (13%) required intubation after respiratory distress, of which 12 (48%) ultimately required a tracheostomy. Patients with ND were 62.3 (95% CI, 13.9–476.3) times more likely to experience respiratory complications.

Table 5 Complications
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Discussion

Type II odontoid fractures are one of the most common cervical spine fractures in the elderly. ND associated with odontoid fractures are rare and generally believed to portend a poor prognosis [5, 6, 14]. However, small case series in previous reports have limited the amount of accurate data available for informed treatment decisions to be made. We therefore (1) established the incidence of ND with Type II odontoid fractures. Then we (2) determined if ND were associated with increased in-patient mortality and (3) increased morbidity during hospitalization.

There are several inherent limitations to our study. First, our study was not prospective or randomized. Because this is a retrospective study in which management decision was at the sole discretion of the surgeon, caution must be taken in establishing causality between treatment method and outcomes. Second, inclusion bias may have existed when classifying patients. Patients were categorized into each cohort based on the presence of a ND, largely determined by the ASIA grade on admission. The ASIA classification is subject to interobserver variance [13]; therefore, we only included patients who had a consensus on neurologic status between the orthopaedic and neurosurgery consult notes. Classification of the type of odontoid fracture in each patient was determined by radiographic reports, and any uncertainty or ambiguity in fracture classification resulted in exclusion of the patient. Third, we had a small number of patients, therefore limiting the power of our study and possibly introducing the risk of Type II error. However, the injuries studied are relatively uncommon with a high rate of early expiration; thus, it is difficult to obtain large single-institution cohorts, even one that is a regional SCI center. Moreover, our multivariable analysis allowed us to control for important variables that may have otherwise confounded our findings. Fourth, our followup was limited to inpatient hospitalization only; therefore, our results may have not captured all mortality or morbidity that would have normally been attained from long-term followup.

We found an incidence of ND among all Type II odontoid fractures of 9.6%. One previous study of 35 cases reported an incidence of 29% with Type II odontoid fractures [18]. Other studies reported an incidence of 7.5% to 13% with all odontoid fractures [7, 15] and 6.9% to 29% [6, 14] with all cervical fractures. Our observations are consistent with the values reported in the literature (Table 6) and represent the largest study specifically observing ND associated with Type II odontoid fractures.

Table 6 Comparison of the incidence of neurologic deficits
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Patients with ND experienced high inpatient mortality. Reported mortality has varied extensively in the literature with fracture type and outcome times (Table 7). One study described a 60% mortality rate associated with Type II fractures with a 21-month followup [18], and another described a 32% mortality rate of cervical fractures with a 3-month followup [6]. Two other studies reported inpatient mortality rates of 14.9% to 53% without followup after discharge [7, 22]. We determined that 10 of 20 patients with a Type II fracture and an associated ND died during inpatient hospitalization. Moreover, patients with deficits had the greatest probability of death with complete injuries (ASIA A). Severe injuries to the spinal cord after trauma have been associated with autonomic dysregulation, oftentimes leading to cardiopulmonary complications [12, 22]. Similarly, all 10 mortalities in the deficit cohort involved cardiac and/or respiratory events during the course of hospitalization.

Table 7 Comparison of mortality with neurologic deficits
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When compared with the intact cohort, the deficit cohort had more complications with stay, in particular respiratory complications. There are several proposed reasons for this finding. Harrop et al. described the pathogenesis of respiratory decompensation as an effect of upper airway obstruction secondary to retropharyngeal edema from soft tissue injury after trauma and unintentional manipulation (ie, positioning for imaging, traction, intubation) [9]. In the deficit cohort, 18 patients were intubated and 10 ultimately were taken off of mechanical ventilation, consistent with the observations of Harrop et al. Conversely, it is important to note that eight patients eventually required tracheostomies. One previous study determined that high cervical injuries normally portend poor respiratory status with all C2 ASIA A patients requiring eventual tracheostomy placement [8]. In our cohort, there was no correlation between ventilator status and the severity of spine injury, and only three of 11 (27%) ASIA A patients required tracheostomies. This finding suggests that in addition to transient airway swelling, there may be a unique feature to the biomechanics of C1–2 injuries that differs from other high-level cervical injuries and merits further study. These results indicate respiratory distress is an extremely common complication of ND in patients with Type II odontoid fractures.

ND with Type II odontoid fractures is a rare event, and it is associated with high inpatient mortality and morbidity. With a growing geriatric population, there may be an increased incidence of this difficult clinical presentation. This study is useful in that it offers valuable prognostic data for the small but formidable population that may present with SCI and possible ND after a Type II odontoid fracture. Odontoid fractures with ND are clinically distinct from neurologically intact fractures and are associated with a high risk of early and rapid clinical decline.