In the United States NTDB data between January 2014 to December 2019, overall mortality rate in all odontoid fractures was low at 0.7%, with lower mortality in those undergoing operative management in either the mild-moderate and severe GCS groups. Outpatient follow-up and care is not tracked through the NTDB, but longer-term odontoid fracture mortality has been reported as 10-20% in 30-day, and 20-50% in 1-year post-injury with most mortalities related to patient comorbidities and not sequelae from odontoid fracture injuries [4]. Therefore, the immediate mortality of the odontoid fracture is associated with the index admission and management therein. The data demonstrates that mortality is improved with operative management, having a mortality rate of 0.1% compared to non-operative management mortality rate at 0.9%. ISS scores between the two groups were very similar, but GCS was found to be a significant indicator of mortality in this study with OR of 21.9 (14.8, 32.4 95% CI) for severe GCS compared with mild to moderate GCS. Severe GCS in traumatic injuries is likely due to acute brain injury and not a chronic comorbidity of pre-existing conditions for determining pre-operative suitability for which the Charlson Comorbidity Index (CCI) [10] or the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) [11] were designed to aid in clinical decision making. Decisions on whether to operate then become based on weighing the clinical stability of the patient in front of the surgeon and the risk of the non-operative and surgical intervention options.
Non-operative management techniques have been presented as viable options to mitigate patient complications with studies providing evidence of fracture fusion in selected patients. These selected patients are typically of lower severity (lower ISS) and more mild-moderate GCS score. Patients that are deemed too high risk for surgery are also managed non-operatively as the patient comorbidity, frailty, or other perioperative risks lend greater risk to the patient than the injury itself. In these cases, cervical immobilization using one of the methods listed above are utilized. Historically, the halo vest was used for maintaining cervical in-line stabilization for healing but require precise pin placement and have risks of infection, nerve/brain damage, and provide the patient with pain and tissue breakdown beneath the torso, and functional limitation and poor compliance [4, 6–8]. Semi-rigid collars were shown to have fewer complications, with similar or improved fracture union (>70% semi-rigid vs 40% HV) [4, 6, 8, 9]. Differing opinions exist to whether only full osseous fusion or including asymptomatic pseudoarthrosis are considered sufficient in goals of care with these fractures. Measures of quality of life, pain, and neck mobility are taken into consideration for cessation of non-operative management with cervical orthosis, with some still requiring surgery for failure of non-operative management. Stable nonunion or asymptomatic mobile nonunion have been deemed appropriate for clinical outcome in geriatric patients whose operative morbidity and mortality associated with undergoing surgery [4].
Patient comorbidities in odontoid fractures can be misleading as deciding factors for surgery as occult injuries can be missed on radiological studies alone. Stability of injury by measuring anteroposterior displacement >3.5 mm and perceived spinal canal invasion are insufficient for injury severity. Agunbiade, et al. described a patient with complete cervical cord transection from a ground-level fall in a patient with minimal radiological evidence for spinal cord injury from mildly displaced odontoid fracture [12]. Disruption of the ligamentous tissues and re-alignment in cervical collar during emergency evaluation with routine imaging could miss neurological injury. Suspicion is usually low of severe spinal cord injury as it is typically rare and patients may be intubated, but this must always be considered in seriously sick patients. When taken for MRI, ligamentous injuries may then be found with even minor fractures. Ligamentous injuries may still cause significant comorbidity themselves as sub-failure injury to soft tissues can still cause persistent pain, headaches, dizziness, and chronic spine pain [13].
Cervical ligaments placed under stress during the traumatic injury but not rupturing can still create structural damage causing spinal instability and chronic pain leading to increased future falls or injury. Therefore, even when odontoid fractures are managed non-operatively with fracture union, patients may be left with persistent cervical instability [13]. Lending to cervical instability in these patients is a study by Kepler, et al. that demonstrated 30% of acute traumatic injury with initial findings of type II odontoid fractures had chronic C2 injuries with obvious nonunion from poor primary healing, with 17.5% of these showing new neurologic deficits on secondary injury [14]. These patients in that study were new to the hospital where this study was performed and did not state whether the patient had known of prior diagnosis of odontoid fracture or treatment non-operatively. The number of chronic type II odontoid fracture patients and their likelihood of returning to the emergency department for subsequent injuries found in this single institution may demonstrate an underrepresentation of morbidity for non-operative management causing increased evidence for early operative management.
Operative management techniques for odontoid fractures are divided between anterior and posterior approaches. Anterior cannulated screw fixation (ACSF) is the gold-standard for odontoid fracture surgery and has shown union rates of 88-100% [15, 16]. The operation requires anterior exposure through the prevertebral fascia to place screw through the body of C2 into the dens fragment to pull it towards the fracture line for fusion. This approach provides immediate stabilization, reduced post-operative pain, no bone grafting, and preservation of the atlanto-axial rotational movement [15]. The neck disability index (NDI) measuring the subjective pain and discomfort of the patient was rated as better than posterior instrumentation of C1-2 without fusion (PIWF) but showed decreased union rates (90.9% ACSF vs 96% PIWF; not statistically significant in that study) [15]. Both approaches demonstrate much higher successful union rates compared to non-operative management (90.9-96% vs 40-70%) [4, 6–9, 14, 15]. PIWF involves a second operation to remove the instrumentation, so the patient is put at risk for surgical complications again in order to return some of the axial rotation of the cervical spine, but still not as much as present in ACSF. Another posterior approach is a posterior instrumentation with fusion (PIF) where bone graft is used to fuse the C1-C2 vertebrae to achieve immediate cervical stability but a loss of approximately 50% of axial rotation [4], however it requires only a single operation with 90.5% union rate compared to 96% union rate in PIWF [17]. This approach reduces functionality but saves the patient from additional surgery if patient comorbidity and risk of reoperation is a deciding factor. Another approach is an occipito-cervical fusion (OCF) which is typically used when a posterior decompression is needed. This significantly reduces in cervical mobility, increases risk of dysphagia, has lower fusion rates, and significant post-operative complications as the procedure requires instrumentation along the occiput through C1 and C2 [18].
Comparing all odontoid fractures in this large national database, low mortality in operative management for all types has shown better outcomes than non-operative management. Given that the standard management of type I and type III odontoid fractures are nonoperative with cervical collars, the operative patients are likely the unstable fractures and type II odontoid fractures. Patients undergoing surgery have demonstrated longer hospital length of stay and increased likelihood of ICU admission. This may represent the time required for post-operative recovery as an operation was associated with longer ICU and hospital LOS for each level of ISS and GCS groups. Longer hospital and ICU LOS in severe GCS compared to mild to moderate GCS, and similarly with more severe ISS scores, likely is associated to other injuries as operative fixation of the fracture immediately stabilizes the odontoid injury. Wagner, et al. reported that non-operative management of type II odontoid fractures led to hazard ratios for mortality at follow-up was 1.35 and an eventual delayed operation of 22% of patients [19].
In the elderly population incurring these injuries, the bone quality and blood supply necessary for non-operative fracture healing was a comorbid risk to optimal healing [19]. Physiology and pre-existing comorbid conditions might be indications toward operative management due to chronic pain and complications leading to eventual and costly continued management. Surgery was not found to have a negative impact on survival with adjusted comorbidities in the AOSpine North America study by Chapman, et al [20]. Mitigating cost and risk associated with prolonged non-operative management in elderly patients 65-84 would be more beneficial to undergo an operation when considering cost at $100,000/quality-adjusted life year (QALY) as a surgical benchmark [19]. The longer hospital and ICU LOS associated with surgical healing and management of acute injuries may be marginal financial cost by operating on type II odontoid fractures relative to the opportunity cost of prolonged outpatient clinic hours, subsequent operative time to the surgeon and chronic pain, medication effects, and quality of life lost by patients.