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Odontoid fracture

Odontoid process fracture, also known as the PEG or dens fracture, occurs where there is a fracture through the odontoid process of C2.


The mechanism of injury is variable, and can occur both during flexion or extension with or without compression 5


The commonest classification of these fractures is the Anderson and D'Alonzo classification 5:

  • type I
    • rare
    • fracture of the upper part of the odontoid peg
    • above the level of the transverse band of the cruciform ligament
    • usually considered stable
  • type II
    • most common
    • fracture at the base of the odontoid
    • below the level of the transverse band of the cruciform ligament
    • unstable
    • high risk of non-union
  • type III
    • through the odontoid and into the lateral masses of C2
    • relatively stable if not excessively displaced
    • best prognosis for healing because of the larger surface area of the fracture

Differential diagnosis

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