h1 class=”calibre8″>7 Odontoid and Hangman’s Fractures

Megan M. Jack, Domenico A. Gattozzi, and Paul M. Arnold

Keywords: odontoid fractures, hangman fractures, C1–C2 fusion, external immobilization

7.1 Odontoid Fractures

7.1.1 Introduction

Due to the unique biomechanics of the C1 region, the upper cervical spine is highly susceptible to bony fractures and ligamentous injuries following trauma, which can lead to fracture of the dens. Odontoid fractures range from 10 to 20% of cervical spine fractures. ¹ These most commonly occur in older adults and the prevalence is increasing substantially with the growth rate of the elderly population. Odontoid fractures more frequently affect men with a sex ratio of nearly 3:1. Odontoid fractures generally are classified based on their anatomical fracture patterns. While many types of odontoid fractures can be treated conservatively, surgical intervention including posterior C1–C2 fusion and anterior odontoid screws, are options for the management of unstable fractures or those unlikely to heal with external immobilization alone. Rates of mortality following odontoid fractures in the elderly population have been reported to be as high as 30%. ²

7.1.2 Mechanism of Injury

Trauma accounts for majority of odontoid fractures. Motor vehicle accidents and low-velocity falls are the most frequent traumas associated with odontoid fractures for younger and older patients, respectively. The main forces that result in dens fractures are flexion, extension, lateral bending, and rotation forces, or a combination of these. The direction of the forces applied during trauma dictate the fracture pattern. It has been suggested that high-energy mechanisms account for fractures in younger patients, while low-energy impacts produce similar anatomic injuries in the geriatric population due to reduced bone density. ^3,4,5

7.1.3 Classification

The Anderson and D’Alonzo classification is the most frequently utilized classification scheme (▶ Fig. 7.1). It categorizes C2 dens fractures based on their location within the odontoid: type I fractures are limited to avulsions of the odontoid tip, type II fractures occur through the neck, and type III fractures involve the odontoid base. Type I odontoid fractures are relatively rare in comparison to the other types of C2 fractures. ⁴ Type II and III fractures are frequently seen in busy trauma centers. Type II fractures are by far the most common of the three in young and elderly patients. ⁴ Based on this classification scheme, Hadley et al proposed the addition of the IIA communition fracture pattern, referring to chip-fracture fragments of the odontoid base.

While the Anderson and D’Alonzo classification is the most commonly used system, multiple other classification systems do exist. The Schatzker’s, the Althoff’s, and the Mourgues’s classifications systems are based on the direction of the fracture. The Schatzker’s classification distinguishes two fracture types based on their location either above or below the attachment of the accessory ligaments. ⁶ The Althoff classification also describes four types of fractures based on anatomic location including fractures at the neck, the superior body, the lateral masses, and the inferior body. The Mourgues classification proposes two fracture types based on fractures either through the neck or through the base of the odontoid process. The Korres classification, on the other hand, is an anatomically based delineation of four fracture types that occur resulting from hyperflexion and produce teardrop formations. The Roy-Camille classification describes three types of fractures that are based on the direction of the fracture line through the odontoid, correlating with the biomechanical stress applied during the trauma. Each classification has been linked with prognosis of union or fracture healing.

7.1.4 Physical Exam

The primary and secondary trauma surveys help identify clinical features that are suggestive of underlying injuries. Particularly in the case of upper cervical fractures, such as odontoid fractures, patients may report tenderness to palpation, neck pain with motion, and exhibit ecchymosis indicative of underlying traumatic injury. Dysphagia may also indicate an odontoid fracture with the development of a large hematoma which compromises surrounding structures. Neurological examination is also key to determining the need for further cervical imaging. Though neurological compromise is rare following odontoid fractures, weakness or sensory changes may indicate a concomitant fracture at another spinal level.

7.1.5 Imaging

The choice of imaging following cervical trauma is influenced by numerous patient factors, including age, stability of the patient, the mechanism of injury, presence of neurological deficits, and the existence of confounding injuries. Cervical radiographs with odontoid views are preferred for patients that do not require advanced imaging or are too unstable for advanced imaging to be obtained, and for younger patients to reduce radiation exposure. Plain films that reveal asymmetry between the dens and lateral masses of C1 are indicative of transverse ligament injury. While routine films achieve the diagnosis, computed tomography (CT) scans allow for much more detailed classification of the fracture and remain the study of choice for traumatic odontoid fractures. Magnetic resonance imaging (MRI) of the cervical spine would be indicated if the patient has neurological compromise. Similarly, CT angiogram may be useful in determining the course of the vertebral artery for surgical planning, but it is typically unnecessary.

7.1.6 Treatment Considerations

Treatment of odontoid fractures begins with appropriate management following an acute trauma with principles of advanced trauma and life support. Following diagnostic imaging, the appropriate treatment varies depending on the classification of the odontoid fracture. There are numerous important factors that influence surgical considerations and patient outcomes which include the fracture pattern, age, degree of comminution, fracture displacement, angulation, and nonunion, as well as patient comorbidities.

Age is an important predictor of outcome following traumatic fracture of the dens. Elderly patients suffer higher rates of odontoid fractures; however, they also experience higher rates of complications depending on the type of treatment. Similarly, they are at higher risk for nonunion, while younger patients with better bone quality are less likely to experience pseudarthrosis or fibrous nonunion. Thus, younger patients may be successfully treated with conservative measures, while elderly patients may require surgical intervention to achieve fracture healing.

The degree of angulation and/or displacement also influences clinical decision-making and treatment options. Greater than 5 mm of displacement may influence the decision to recommend surgical fixation of a type III fracture in order to reduce the risk of nonunion. ⁷ Nonunions are often considered treatment failure, however they are often clinically insignificant. ⁸ Type II fractures have an average rate of pseudarthrosis of 36%. ⁶ Pseudarthrosis is often a feared result, but rarely causes cervical myelopathy. ⁹ Similarly, fibrous union likely provides sufficient stability. However, nonunion remains a reason for delayed surgical intervention in approximately 20 to 30% of cases.

Finally, the fracture type greatly influences the decision to undergo surgical intervention. Based on the Anderson and D’Alonzo classification, type I and III fractures are known to be stable fractures and can be treated conservatively. The management of type II fractures, however, remains controversial. Generally, surgical intervention is reserved for type IIA fractures or those associated with transverse ligament injury or severe dens displacement. ¹⁰ Chapman et al reviewed 322 elderly patients with type II odontoid fractures and found nonoperative management was associated with a higher 30-day mortality risk. ¹¹ On the other hand, other studies have found significant mortality indices and high rates of complications with surgical intervention in older adults. ^9,11 This variability in outcome data has contributed to the controversy surrounding the optimum treatment of type II odontoid fractures.

7.1.7 Nonoperative Management

Cervical spine immobilization is a common treatment for type I and III odontoid fractures. Halo vests or hard cervical collars are rigid immobility techniques that allow for bony fusion to occur following injury. Pseudarthrosis can occur if limited mobility is not successfully preserved. Koller et al demonstrated comparable limitations in flexion and extension with either a halo vest or Philadelphia collar. ¹² However, halo vests showed a superior ability to limit axial rotation and coronal bending compared to rigid collars. ¹³

One systematic review compared failure rates of odontoid fractures following treatment with either halo placement or immobilization with a hard collar. Treatment failure was defined as the need for surgical intervention. There were no differences in failure rates between halo and collar treatment for type II odontoid fractures. However, halo treatment was associated with significantly higher rates of complications. ¹ The most common complications included pin-site infections, hardware failure, pneumonia, and respiratory failure. ¹ Other studies have demonstrated impaired swallowing and reduced mobilization with halo vest treatment. ^14,15 It is important to note neurological decline is rarely reported. Halo vests are especially poorly tolerated in the elderly.

Type I and most type III fractures generally are managed conservatively or with external immobilization. Evidence has shown patients are able to achieve high fusion rates without neurological decline for these types of fractures. Type I fractures have a nearly 100% fusion rate independent of the specific immobilization device chosen. ⁷

7.1.8 Operative Management

The patients’ comorbidities and neurological function coupled with regional practice patterns are all considerations when determining the appropriate treatment course for individual patients with odontoid fractures as discussed above. The risk of nonunion must be weighed against potential surgical complications. Relative indications for surgical fixation include > 5 mm of fracture dislocation, > 10 mm of angulation, and the inability to reduce the fracture through conservative measures. ³ The rate of surgical intervention on elderly patients is near 15%. ⁹

Type II fractures have significant controversy surrounding the appropriate management. There are no clear guidelines regarding which type II fractures necessitate surgery as both conservative and operative management techniques have proven effective. ¹⁶ Due to limited blood supply and poor bone quality, fractures through the base of the dens are at high risk for nonunion. ¹¹ Thus, some advocate for surgical intervention due to the high rate of pseudarthrosis with nonoperative management. Others consider conservative management more appropriate, particularly in patients with significant medical comorbidities that are also associated with adverse outcomes following surgery. Therefore, due to the frail nature of those that suffer odontoid fractures, operative intervention is often viewed as too risky compared to nonoperative management. Low hemoglobin, neurological deficits on presentation, type III odontoid fractures, and elderly nursing home patients were all found to be independent predictors of mortality following traumatic odontoid fractures in older adults. ² However, there remains evidence to suggest that patients, particularly the elderly, have improved 30-day and long-term survival following surgery compared with nonoperative management. ⁴

Anterior odontoid screw placement is considered the treatment of choice for type II and certain rostral shallow type III fractures. ¹⁷ The benefits of anterior screw placement include immediate fracture stabilization, increased fusion rates compared to rigid collar treatment, and sparing of atlantoaxial rotation. The key to determining if anterior odontoid screws are the appropriate surgical approach is verifying the transverse ligament has not been ruptured resulting from the trauma. Anterior screw placement should be avoided in cases involving fractures with an oblique orientation or large gap, severe osteopenia, fractures older than 6 months, irreducible fractures, and in patients with large barrel chests that make the surgical approach difficult. Anterior odontoid screw placement is associated with higher failure rates than posterior cervical fusion. ¹⁸

Posterior C1–C2 fusion should be considered for type III odontoid fractures at risk for nonunion and for type II fractures. Class II medical evidence supports early surgical fixation and fusion for elderly patients with type II odontoid fractures. ⁷ Other considerations for posterior atlantoaxial fusions include type IIA fractures with significant comminution that are unlikely to heal without operative management, and fractures in which the dens is significantly displaced. While an anterior approach may be considered, evidence of transverse ligament compromise, comminution of the fracture, or anteroinferior to posterosuperior type II fracture lines are clear indications that posterior C1–C2 fusion is the definitive treatment.

A variety of different techniques has been described to achieve C1–C2 fusion. All posterior fixation techniques achieve a high fusion rate. ⁷ While much more infrequently encountered in the modern management of spine fractures, wiring techniques may be used as rescue procedures or supplementation to other internal fixation methods to improve fusion outcomes. ⁷ Stereotactic navigation has been popularized in spinal surgery. The Harms technique has become popular in the past few years for managing these lesions and has largely supplanted the use of transarticular screws. ⁹ Stereotactic navigation has been utilized for anterior odontoid screw placement and for posterior C1–C2 fusions, with success. ^19,20 This technique is purported to improve the safety of screw placement in the upper cervical spine. The use of stereotactic navigation following traumatic odontoid fractures may help improve outcomes particularly for elderly patients.

While posterior atlantoaxial fixation achieves high fusion rates, there remains some drawbacks to the procedure. Nearly 50% of axial rotation occurs at the atlantoaxial complex; thus, posterior C1–C2 fusion greatly limits movement of the head following fixation. This often drastically limits patients’ activities of daily living and quality of life. This limited neck motion remains a consideration for posterior surgical stabilization, particularly in the elderly.

7.1.9 Conclusion

Odontoid fractures are a commonly occurring fracture following significant trauma. While they can occur at any age, elderly patients are at particular risk given their propensity to fall coupled with poor bone quality. The Anderson and D’Alonzo classification categorizes odontoid fractures based on the anatomical fracture pattern. It is generally agreed upon that type I and III fractures can be managed using noninvasive strategies such as rigid cervical collar or halo immobilization. There remains much clinical controversy surrounding the treatment of type II fractures. Surgical intervention including posterior C1–C2 fusion and anterior odontoid screws are options for unstable fractures or those unlikely to heal with conservative measures.

7.2 Hangman’s Fractures

7.2.1 Introduction

Traumatic spondylolisthesis of the axis is the second most common C2 fracture after odontoid fractures. It comprises approximately 20% of C2 fractures that present for clinical attention, accounting for approximately 5% of all cervical spine fractures. ²¹ This type of fracture has been described historically in numerous studies. In 1913, a postmortem anatomical study of judicial hangings described bilateral pars fractures of the axis, and distraction as cause of injury and death. A series reported by Schneider et al in 1964 commented on traumatic spondylolisthesis of the C2 vertebra and paralleled the radiographic findings with the anatomical description of the hanging victims. It is from the title of this manuscript that the colloquial eponym of “hangman’s fracture” for this type of injury is derived. ²² With increasing awareness of the frequency of this injury, further studies were performed to classify this fracture into clinical grades for prognosis and for guidance on treatment.

7.2.2 Anatomy

Hangman’s fractures of the C2 vertebra are classically described as bilateral pars interarticularis fractures of the ring of C2 with varying degrees of anterolisthesis of C2 on C3, and varying degrees of angulation of the odontoid process. The second cervical vertebra is often described as a “transitional vertebra” due to its location between the atlas and the subaxial spine. ²³ The superior and inferior facets are not vertically in-line, due to the need for support to the atlas and occipital condyles above, and fixation in-line with the C3 facet joints and remainder of the cervical spine below. This creates a weak point, especially as axial loading from hyperextension creates a force to the superior articular processes of C2, driving force into the facets posteriorly and the disc space anteriorly. ²² This distributes the forces during axial loading from a lateral and posterior position at the occipital condyles to a medial and anterior position on the axis, through the C1–C2 lateral masses. Compression of the posterior elements leads to fracture at the relatively weaker pars interarticularis of C2 bilaterally, with anterior displacement of the C2 vertebral body. ^21,24,25

7.2.3 Mechanism of Injury

The mechanism of injury resulting in hangman’s fractures is typically hyperextension with axial loading. It is important to note that this fracture can also occur with hyperflexion with rebound extension and axial loading as well. ^21,26 The two most common traumatic events leading to this injury are falls and motor vehicle accidents. The key distinction between trauma as opposed to judicial hanging is that with traumatic injuries the mechanism of action does not include distraction, which is thought to be the key factor along with hyperextension resulting in fatality from hanging. ²⁷ In fact, it was noted from early studies that the incidence of neurological deficits in isolated traumatic spondylolisthesis of the axis were low, and, when present, were often transient. ^22,27,28 This effect has been attributed to the fact the spinal canal is wider in the high cervical spine, as well as the fact that the hangman’s fractures widen the spinal canal after injury. ^{21,24,25,28,29} Examples of neurological symptoms can include paresthesias, hemiparesis, and occipital neuralgia. It is not uncommon for concurrent head, face, and/or chest trauma to be present. ³⁰ Concomitant cervical fractures can occur in up to 34% of hangman’s fracture cases, with a reported 5 to 6% rate of concurrent odontoid fractures. ^30,31

7.2.4 Imaging

Historically, due to ease of access, lateral cervical plain films were the initial imaging modality for diagnosing cervical spine fractures after trauma. While plain films provide information regarding anterolisthesis or odontoid angulation, and demonstrating bilateral C2 pars fractures, unilateral C2 pars fractures may be missed up to 40% of the time. ²¹ CT of the cervical spine has increased the sensitivity in identifying this lesion and can be used in the mid-sagittal plane to identify odontoid angulation or anterolisthesis of C2 on C3. MRI is a useful tool for identifying disc retropulsion, longitudinal ligamentous disruption, or other soft-tissue injury. Dynamic studies, such as flexion-extension films, can identify laxity of the C2–C3 disc space in apparently stable fractures on static images. Vertebral artery injury may result from high cervical fractures, including hangman’s fractures. The rate of radiographically identified vertebral artery injury can approach 27%. ²¹ Given that unilateral vertebral artery injury is usually asymptomatic it may be important to identify this comorbidity with vascular imaging such as magnetic resonance angiography (MRA) or computed tomography angiography (CTA). ³² Vertebral artery injury should be considered in patients with neurological symptoms referable to the brainstem or cerebellum or with fractures extending to the transverse foramen of C2, especially if comminuted. ³³

7.2.5 Classifications

There have been several grading scales proposed for hangman’s fractures. Francis et al graded traumatic spondylolisthesis of the axis in 1981 on a scale from I to V, with increasing grade indicating increasing severity. The appearance on lateral radiographs was used to calculate anterior displacement of the C2 vertebral body on the C3 vertebral body, the angulation of the dens, and concern for disc disruption. ²⁷ Effendi et al classified spondylolisthesis of the axis into a three-tiered grading system with a case series of 131 patients, and provided the basis for the most commonly used clinical classification today. Effendi Class I patients had ring fractures with a stable disc space at C2–C3, identified by minimal anterior displacement of C2 (▶ Fig. 7.2, ▶ Fig. 7.3, and ▶ Fig. 7.4).

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