Traumatic spondylolisthesis of the axis (hangman’s fracture), type 1

Discussion

Traumatic spondylolisthesis is the second most common injury of the axis, following fractures of the odontoid.¹ This injury has been termed "hangman's fracture" due to its similarity to that seen following judicial hangings. The most common causes are motor vehicle accidents and falls.¹

This injury is defined as bilateral avulsion of the neural arches from the vertebral body, with or without subluxation. The fracture is through the pars interarticularis of C2 or through the adjacent portion of the articulating facet. The fracture may extend into the posterior vertebral cortex or vertebral artery foramen. The majority of cases of vertebral artery injury are clinically silent.¹

The pars interarticularis is defined as the parts of the neural arch that lie between the superior and inferior articular facets. This is the site of fracture in traumatic spondylolisthesis, not the pedicles or lateral masses, as is commonly stated.²

The mechanism of injury is most commonly hyperextension with vertical compression, or forced hyperflexion with compression.^1,3 There is a high incidence of facial injuries (commonly from windshields or dashboards) associated with the hyperextension type of injury.^1,4

The only differential diagnosis to consider is chronic spondylolithesis of the axis. This is a rare disorder associated with congenital abnormalities of the cervical spine.¹

Several classification systems have been published; the most widely used is the system devised by Effendi, and modified by Levine and Edwards.^1,5 Type 1 injuries have <3 mm of displacement without angulation. The C2/C3 intervertebral disc is normal. The mechanism of injury is hyperextension with axial loading. Type 2 injuries are anteriorly angulated or displaced fractures with disruption of the disc between C2 and C3. The mechanism is combined hyperextension and axial loading followed by hyperflexion. Type 2A injury is defined as significant angulation without anterior translation. The mechanism is one of flexion and distraction. Type 3 injuries involve anterior displacement with hyperflexion of the axis associated with unilateral or bilateral facet dislocations. The mechanism of the dislocation is flexion and distraction, with hyperextension responsible for the spondylolithesis.^1,5

Lateral radiographs of the cervical spine reveal the fracture in >90% of cases.¹ Supervised flexion and extension views may be helpful to evaluate for displacement or angulation. Computed tomography is used to detect undisplaced fractures, extension into the vertebral foramina and to localize displaced fragments.^1,3,5

Neurological injury is not commonly associated with this pattern of injury, as the spinal canal is decompressed. The chance of neurological damage increases with the severity of the injury. However, significant neurological injury is possible even in type 1 injuries.^1,3,5 If the fracture extends into the transverse foramina, angiography may be indicated to exclude vertebral artery dissection or intimal injury.³

Stability of the injury refers to the integrity of the anterior and posterior ligament complexes. Type 1 fractures are considered stable. The pattern of injury may be considered unstable if there is >4 mm of anterior displacement or 11˚of angulation on the initial radiograph. Further criteria for instability on the lateral flexion extension views include >2 mm of translation or 11˚of angulation.^5,6

Treatment is not universally agreed upon and differs depending on the institution and surgeon. In general, type 1 injuries are treated with a rigid collar for 8 to 12 weeks. Type 2 injuries are initially reduced with traction in slight extension followed by a halo vest for 12 weeks. A halo vest in compression and slight extension is used for type 2A injuries. Immediate surgery is required for type 3 injuries to stabilize the C2/C3 facet joint. Surgery is also indicated in the case of failure of fusion after nonsurgical therapy.^4,7

CONCLUSION

Traumatic spondylolisthesis of the axis, also known as hangman's fracture, is one of the most common cervical spine fractures encountered in the trauma setting. The injury involves fractures through the pars interarticularis of C2 bilaterally. The most common mechanism of injury is hyperextension, and may be seen following motor vehicle accidents or falls. The diagnosis can be made on lateral conventional radio-graphs in the majority of cases. CT is used to better define the extent of the fracture, or to detect non-displaced fractures. Neurologic deficits are rare, but possible. Involvement of the transverse foramina may injure the vertebral artery.

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2. Parke WW. Applied anatomy of the spine. In: Herkowitz HN, ed. The Spine.4th ed. Philadelphia, PA: W.B. Saunders Co.; 1999:30-31.
3. Mirvis SE, Young JWR, Lim C, Greenberg J. Hangman's fracture: Radiologic assessment in 27 cases. Radiology.1987;163:713-717.
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7. Isolated fractures of the axis in adults. Neurosurgery.2002;50(3 suppl):S125-S139.