Original article
Traumatic Injuries of the C1/C2 Complex: Computed Tomographic Imaging Appearances

https://doi.org/10.1067/j.cpradiol.2007.07.001Get rights and content

Cervical spine fractures occur in 1 to 3% of trauma cases and account for two-thirds of spinal cord injuries. Injury to the C1/C2 complex accounts for 19 to 25% of cervical spine injuries. Fractures of C2 occur most frequently, 55% of which involve the odontoid peg. The unique anatomical relationship between the atlas and axis produces a variety of injury patterns not seen elsewhere in the spine. Numerous developmental anomalies also occur which can mimic trauma. Well-described fracture patterns include posterior arch fractures of the atlas, Jefferson type fractures, fractures of the odontoid process, and Hangman’s fractures. Traumatic subluxation of C1 on C2 and rotatory fixation also occur with or without associated bone injury. Computed tomography is an important tool for accurately assessing injuries to the C1/C2 complex, occasionally supplemented by dynamic computed tomography in cases of rotatory fixation. A description of the anatomy, common anatomical variants, and injury patterns of the atlas and axis illustrated by computed tomography is presented along with the relevant injury classifications.

Section snippets

Embryology and Anatomy of the Atlantoaxial Complex

In utero, the vertebral column develops as a series of hyaline cartilaginous rings from the mesodermal tissue lying adjacent to the notochord. Centers of ossification develop in each lateral mass of the atlas in the seventh fetal week. From each lateral mass, ossification extends into the posterior arch and the ossification centers unite in the midline at 4 years of age. A third ossification center develops in the anterior arch of the atlas in the first year of life which fuses with each

Atlas Fractures

Fractures of the atlas account for 2 to 13% of cervical spine fractures and are generally not associated with neurological deficit.1 C1 fractures are frequently associated with fractures elsewhere in the cervical spine particularly at the C2 and C7 levels.3 A variety of fracture patterns of the atlas have been described by Levine and coworkers and Gehweiler and coworkers (Table 1).1, 4, 5 Gehweiler and coworkers classified C1 fractures into five types including fractures of the anterior arch,

Axis Fractures

There are a variety of fracture patterns encountered at C2. The most common injury is fracture of the odontoid process, which accounts for approximately 55% of axis fractures.16

Summary

The wide range of C1/C2 complex injuries is described. The common posterior arch fracture of the atlas, the well-described Jefferson and Hangman’s fractures, odontoid peg fractures, and rarer injuries including atlantoaxial rotatory fixation and Plough fracture are discussed. The appearance of anomalies and fractures, in particular, posterior arch clefts of the atlas, is compared.

The key points are as follows:

  • 1

    The C1/C2 complex produces a variety of injury patterns, most of which are not seen

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