What are C2 odontoid fractures?

Updated: Nov 21, 2018
  • Author: Igor Boyarsky, DO, FACEP, FAAEM; Chief Editor: Jeffrey A Goldstein, MD  more...
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Incidence of odontoid fractures approaches 15% of all C-spine fractures. Usually, these fractures are secondary to MVAs or falls. [3]  When an odontoid fracture is suspected, it is important to rule out concomitant associated C-spine injuries. For example, C1 anterior ring fractures are not an uncommon finding, and a prevertebral soft-tissue shadow of more than 10 mm on plain films is highly suggestive of such a fracture. Anderson and D'Alonzo classified odontoid fractures based on the anatomic location of the fracture (see the image below).

Three types of C2 odontoid fractures: type I is an Three types of C2 odontoid fractures: type I is an oblique fracture through the upper part of the odontoid process; type II is a fracture occurring at the base of the odontoid as it attaches to the body of C2; type III occurs when the fracture line extends through the body of the axis.

A type I fracture (< 5% of cases) is an oblique fracture through the upper part of the odontoid process. This type of fracture occasionally is associated with gross instability due to traction forces applied to, and subsequent injury of, the apical and/or alar ligaments. This is an avulsion injury to the tip of the odontoid and usually is stable.

A type II fracture (>60% of cases) is a fracture occurring at the base of the odontoid as it attaches to the body of C2 (see the image below).

Odontoid type II fracture Odontoid type II fracture

A type III fracture (30% of cases) occurs when the fracture line extends through the body of the axis. The fracture line can extend laterally into the superior articular facet for the atlas.

Another type of odontoid process fracture is a vertical fracture through the odontoid process and body of the axis (< 5% of cases). This type of fracture often is considered a variant of a traumatic spondylolisthesis of C2, which is discussed below.

The precise mechanism of odontoid fractures is unknown. However, the mechanism most likely includes a combination of flexion, extension, and rotation. In addition to pain and inability to actively move the neck, most patients complain of a sensation of instability, described as a feeling of the head being unstable on the spine. Patients may present by holding their head with their hands to prevent any motion. Clinical findings range from quadriplegia with respiratory center involvement to minimal upper-extremity motor and sensory deficits secondary to loss of one or more cervical nerve roots. Radiographic findings are based on the type of fracture.


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