Hangman's Fractures

Etiology

Schneider et al. coined the term hangman’s fracture in 1965. Despite the term implying a hyperextension and distraction injury, such as in the case of a judicial hanging, the more common mechanism of action is hyperextension and axial loading.[6] These injuries are most commonly seen in motor vehicle accidents, diving injuries, or contact sports.

Epidemiology

Fractures of the cervical spine are present in 1% to 3% of all trauma cases, of which 9% to 18% are of the C2 vertebrae. The incidence of C2 fractures has doubled from 3 per 100,000 to 6 per 100,000 from 1997 to 2014 in data reported from the Swedish National Patient Registry. Fractures of the odontoid process are much more common, representing 35% to 78% of all C2 fractures in the general population and 89% of patients older than 70 years old. Meanwhile, hangman’s fractures represent 11% to 25% of all C2 vertebrae fractures.[7] In a study comprising 58 patients, the mean age of the cohorts was 62.7 ± 25 years, with male to female ratio of 1:1.2. Motor vehicle accidents accounted for the most common cause of the same.[2]

Pathophysiology

It is vitally important to keep in mind the unique anatomy of the atlas-axis complex when treating their associated injuries. Unlike the subaxial cervical spine, the C1 to C2 complex does not contain an intervertebral disc; there are unique ligaments that allow for support of the cranium and provide the majority of cervical rotation. There is also a close relationship between the transverse foramen, which carries the vertebral artery through the cervical spine, with the C2 pedicle/pars interarticularis, which may slightly weaken this area allowing for a fracture to occur.

Two hypotheses have been presented for the pathogenesis of Hangman’s fracture:

1. Internal gear hypothesis: The presence of a trabeculae void and acute transition from the bi-columnar to tri-columnar unit  places the isthmus of the Axis at  increased risk of injury
2. Leaf spring hypothesis: C2 pedicle is like the shackle in the assembly and therefore the weak link within the same.[3]

The extension compression subtype of Hangman's fracture results from pincer-like compression of the C2 pedicle between adjoining articular processes of C1 and C3. The flexion subtype of Hangman's fracture results following the bending failure of the pedicle over the fulcrum formed by the superior facet of C3.[3] The flexion type of injury harbingers the risk of injury to the C2–C3 disc anteriorly and C1–C2 posterior ligament complex (PLC) posteriorly.[3] 

Multiple grading systems for hangman’s fractures exist; however, the Levine and Edwards classifications are the most widely used.

Levine and Edwards Classification

Specifics

Angulation in this system is measured as the angle between the inferior endplate of C2 and C3. Anterior subluxation of C2 on C3 greater than 3 mm is a marker for C2 to C3 intervertebral disc disruption. It is important to recognize that this grading system does not apply to the pediatric population.[8]

Grading

• Type 1: Less than 3 mm subluxation of C2 on C3, due to axial loading, stable, rigid cervical collar treatment
• Type 2: Disruption of the C2 to C3 disc, posterior longitudinal ligament, greater than 4 mm subluxation, greater than 11 degrees angulation, less than 5 mm requires a reduction in axial traction and halo fixation for 6 to 12 weeks while that greater than 5 mm can require surgery
• Type 2a: Less displacement more angular deformity, flexion injury, unstable, not suitable for axial traction, treatment in halo
• Type 3: C2 to C3 facet capsule disrupted, anterior longitudinal ligament disruption, unstable, may have a deficit, surgical candidates

Francis Grading System

Specifics

Two factors are considered for the Francis Grading system: angulation and displacement. Angulation is measured by the degree of anterior angulation off the posterior vertebral line drawn straight from the C3 vertebral body. The magnitude of anterolisthesis that measures displacement is graded as either greater than or less than 3.5 mm.[9]

Grading

• Type 1: Less than 11 degrees of angulation and less than 3.5 mm of displacement
• Type 2: Greater than 11 degrees of angulation and less than 3.5 mm of displacement
• Type 3: Less than 11 degrees of angulation and greater than 3.5 mm displacement
• Type 4: Greater than 11 degrees of angulation and greater than 3.5 mm of displacement
• Type 5: Complete disc disruption

Typical versus Atypical Fractures

It is important to recognize that not all C2, hangman’s type fractures can be described using these classification systems. A typical hangman’s fracture allows for the separation of the anterior elements from the posterior elements of the C2 vertebrae, therefore increasing the available space for the spinal cord. However, in the case of an atypical hangman’s fracture, the posterior aspect of the C2 vertebral body, not the bilateral pars, is involved. This leads to a higher risk of neurologic injury as the space remaining for the spinal cord does not increase secondary to the fracture.

Typical "Hangman's fractures" lead to the separation of the neural arch from C2 bilaterally.[10]

Atypical Hangman's fractures include:

• Coronal vertical fractures involving the posterior aspect of the C2 body.[11]
• Isolated C2-C3 facet dislocation.[12]
• C2-C3 spondylolisthesis following injury to the capsular ligament of the facet joint and posterior spinous ligamentous complex.[13]
• Fractures involving the pedicles.[14]

History and Physical

It is important to recognize that outside of the obvious motor vehicle collisions and high-impact falls, low-energy and blunt trauma, especially in the elderly population, can induce significant unstable injury. History should also entertain fracture risk factors such as osteoporosis, metastatic burden, or vitamin D deficiencies. Physical exam findings include pain with palpation in the posterior portion of the neck, radiculopathy, myelopathy, and possible posterior fossa findings secondary to vertebral artery injury. A strict neurologic exam including cranial nerves, sensory, motor, and rectal tone is mandatory.

Evaluation

Laboratory tests should be ordered as an adjunct to overall medical status.  Normalized hemoglobin, hematocrit, PT/PTT, INR, and platelet counts will be needed for operative intervention.

X-ray

Evaluation with X-rays will provide limited but important information. Care must be taken to ensure proper radiographic imaging creates a picture from the occiput to the C7 through the T1 disc space. This is essential in reviewing cervical spine trauma. Lateral, anteroposterior (AP), and open-mouth odontoid views are necessary. Approximately 93% of cervical spine injuries appear with combined, lateral, AP, and odontoid view radiographs. X-rays are an excellent modality for determining alignment during the immediate injury, post-operative period, as well as long-term follow-up.

CT Scan

Computed tomography is the mainstay of radio imaging.[10] CT scan is the most important modality for determining fracture etiology and ruling out an injury regarding a C2 fracture. A CT scan is warranted even if plain films are negative and clinical suspicion is high. CT scan does not directly evaluate the spinal cord, soft tissue, or ligamentous construct. It is important to recognize the importance that complete imaging will require dedicated thin-cut CT reconstructions. Non-contrast CT scan is adequate for evaluating the bony anatomy for fracture. This can be coupled with a CT angiogram (see below) for evaluation of the vascular anatomy.

MRI

Evaluation with MRI is essential for analyzing the ligamentous construct, disc space, spinal cord, nerve roots, and other soft tissue injuries. MRI is also useful for determining the acute nature of the fracture when this is otherwise unknown. This is done via non-contrasted imaging. T2 signal hyperintensities and STIR changes within the dens, ligaments, or soft tissue can illustrate a critical component.  MRI is less dangerous than flexion-extension cervical injury.

The Effendi, Levine, and Francis classifications are solely based on static radiographs.[1] The management algorithm however is also dependent upon the integrity of the C2/3 disc, the anterior and the posterior longitudinal ligaments.[10] The MRI is an important armamentarium to connote concurrent instability which is determined by:

• C2-3 angulation of ≥11°.
• C2-3 translation of ≥3.5 mm.
• Teardrop fracture involving C2 or C3.
• Associated C disco-ligamentous injury.[1][15]

Vascular Imaging

Vascular imaging may be indicated. The vertebral artery’s second segment (V2) runs through the transverse foramen of C2 to C6, while V3 runs extradurally, exiting the C2 foramen across the sulcus arteriosus.  This can place it at risk for injury. Indeed, in one series, 15% of patients with C1 to C2 fractures had vertebral artery injuries. Of which, type-III odontoid fractures posed the greatest risk. It is important to note that an untreated vertebral artery injury has a 24% stroke rate. CT angiography can be coupled to CT imaging upon fracture evaluation with consideration of kidney function. Level-III evidence suggests that patients with C1 to C3 fractures can be screened with multi-slice multi-detector CT angiography. At this time, MR angiography cannot be listed as the sole imaging modality for the evaluation of vertebral artery injury. The first-line investigation with percutaneous angiography is overly aggressive.[16][17]

Treatment / Management

Treatment options include conservative management, cervical orthosis, halo-vest orthosis, and surgical procedures.

External Fixation

A rigid cervical collar represents the immediate first treatment. Nonunion may occur as frequently as 50% of odontoid fractures, but nonunion is rare in hangman’s fractures, with approximately 90% healing with immobilization alone. Level III evidence shows that a hangman’s fracture may be initially managed with immobilization with a halo-vest or collar alone. This produces a reduction rate of 97% to 100% and a fusion rate of 93% to 100%. External orthosis should be maintained for 8 to 14 weeks. It is important to remember that halo-vest orthosis is not very well tolerated in the elderly population, and therefore collar is recommended as first-line management.[18][19][20](B3)

Non-operative treatment is advocated for extension type Levine-Edwards type I and type II hangman's fracture whereas flexion type Levine type IIa and type III  fractures invariably require surgical intervention.[2][4][10][21](B2)

A systematic review has shown that conservative treatment failed sequentially for Levine-Edward's type I (fusion rate of almost 100%) to III fractures (fusion rate of only 30%).[1] This approach is also time-consuming and harbingers high-risk risks of nonunion. In one study comprising 625 patients who were managed with halo-vest immobilization (HVI), cohorts aged>80 had higher risks of complications, mortality, and readmissions. [22] Another similar study comprising 189 patients with 71.1% sustaining C2 fractures and managed with halos showed a mortality of 8.3%, a failure rate of 10.7%, and a complication rate of 46.3%.[23]

Internal Fixation

Surgical fixation may be considered in the following scenarios:

• Severe angulation of C2 on C3 (Francis II and IV, Levine II).
• Disruption of the C2 to C3 disc space (Francis V, Levine II).
• Anterior displacement of C2 greater than 50% on C3.
• Inability to establish or maintain alignment with external immobilization.
• Nonunion after the use of external immobilization.

The main mandate of surgical intervention is to achieve early anatomical stability while preserving the maximum range of neck movements.[24]

Abnormal angulations and incomplete reduction impair biomechanical loading thereby leading to a heightened risk for persistent neck pain, nonunion, and implant failure.[1]

The different patterns of surgical strategies include:

• Halo traction.
• Anterior stand-alone fusion.
• Posterior stand-alone fusion, and
• Global (anterior-posterior) fusion.[1]

Internal fixation can be achieved via anterior fixation or by a variety of posterior constructs.

Anterior

C2 to C3 anterior cervical discectomy and fusion may be used with anterior plating to stabilize the C2 to C3 vertebral bodies. The main benefit of the anterior approach is preserving the C1 motion, which drastically decreases the morbidity compared to posterior fixation.[9]

Posterior

• C1 to C2 transarticular screws
• C1 lateral mass and C2 pedicle screws
• C1 lateral mass and C2 pars interarticularis screws
• C1 to C2 wiring (also as an adjunct technique)
• Extension to C3 lateral mass if there is a disruption of the C2 to C3 intervertebral disc or facet joint capsules.[25]
(A1)

Posterior fixation technique selection requires significant review by a neurosurgeon or orthopedic spine surgeon. It considers a variety of factors, including surgeon experience, fracture location, vertebral artery location, biomechanical suitability, and anatomical variations. Vascular imaging is mandatory to illustrate the location of the vertebral artery in the V2 and V3 segments. The patient’s overall functional status, medical optimization, and bone health must be evaluated in the operative decision-making.

Flexion injury damaging the posterior ligamentous complex requires C1–2 posterior fixation per the tension band law. The extension injury needs either anterior or posterior C2–3 fixations.[3] Levine-Edwards type II fractures are mostly managed by anterior C2/3 fusion.[10] Levine-Edwards type III fractures, if reducible following traction, can be managed by anterior C2/3 fusion. If irreducible, they most often have to undergo posterior fusion.[10] They may necessitate global fixation.[1] An anterior stand-alone approach with a longer cantilever beam technique to include C4 has also been shown to achieve good reduction and stability for Levine Edward's Type III Hangman's fractures.[1] The prerequisites for posterior pars screw fixation include reduction of fracture translation to <3 mm, and intact anterior longitudinal ligament.[1] However, pars screws should have concurrent C3 lateral mass fixation for type II fractures. This also hampers C1-2 motion and cannot address the anterior disc.[1] Anterior fixation is advocated in C2-3 disc disruption. C3 corpectomy may be required to decompress the cord.[1][26] The accuracy of screw placements can be enhanced by newer adjuncts such as Robot-assisted methods and intra-operative navigation systems.[24][27][28][29] The course and the integrity of the vertebral artery can be ascertained by preoperative angiography.[10] The intraoperative risk of arterial injury can be nullified by the use of color-coded duplex ultrasound.[30][31] C2 spinous muscle complex graft, compared to iliac bone, minimize donor site morbidities and complications.[32] A zero profile minimizes dysphagia and spares the motion at the atlantoaxial joint.[33] C2 pedicle reformation (osteosynthesis with Herbert's compression and lag screws) preserves neck movements.[34][35] A longer construct encompassing C4 might be required to prevent kyphosis.[36][37] The posterior approach has a better recovery of cervical sagittal balance compared to the anterior approach.[38] Minimally invasive approaches have also been described through tubular retractor systems aided with neuronavigation.[39][40](B3)

Hangman's fractures most often show excellent clinical outcomes.[4] Management of Hangman's fracture has low risks of mortality and procuring neurological complications.[21](B2)

Differential Diagnosis

Differential diagnoses include pseudosubluxation (generally C2 on C3) and the Mach effect.

Prognosis

Successful repair of the fractured bone(s) can lead to excellent recoveries with a good long-term prognosis. Some cases require fusion of the C2 and C3 vertebrae. Researchers studied fusion surgery performed via the posterior approach; this method demonstrated excellent results in 3-part fractures of the axis.[41]

In another study of over 30 people with a hangman’s fracture, researchers found that 85 percent of patients with a hangman's fracture experienced a full recovery within a year.[42]

Complications

Complications of the Hangman's fracture include:

• Vertebral artery arteriovenous fistula (AVF).[43][44]
• Occlusion and dissection of the vertebral artery.[45][46]
• Brown-Sequard syndrome (BSS).[47]
• Concurrent spinal cord injury especially in atypical, Type IIa, and III fractures.[2]

Complications of different management strategies include:

• Post-operative dysphagia has a reported incidence of 22.6% in 1st week and 9.7% at 3 months. The risk is higher with anterior plating and minimized with zero profile implants.
• Post-operative dysphonia has a reported incidence of 24.5% in 1st week and 3.8% at 3 months.[48]
• Intraoperative vertebral artery injury.[30]
• Halos complications include pin site infections, loosening of the pins, and restricted neck movements.