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Odontoid C2 Fracture


KEY FACTS

Terminology

  • Type I: Avulsion fracture from tip of odontoid at insertion of alar ligament

    • Usually stable injury

    • Usually seen in conjunction with more extensive craniocervical injury

  • Type II: Transverse fracture through base of odontoid

    • Most likely to progress to nonunion without surgical fusion

  • Type III: Oblique fracture extending from base of odontoid into body of C2

Imaging

  • Direct visualization of fracture line on radiography

    • Soft tissue swelling anterior to C2 in acute cases

    • Displacement of dens, C1 on lateral film

  • CT protocol: Thin-slice (1 mm or less) multidetector CT, fast scan time to minimize motion

    • Sagittal and coronal reformatted images mandatory

  • MR

    • Effacement of thecal sac on MR due to displaced fracture

    • Cord injury, if present, hyperintense on T2WI

    • Fractures without compression &/or fractures with distraction do not reliably generate marrow edema and can lead to false-negative MR imaging

Top Differential Diagnoses

  • Os odontoideum

  • Congenital variation: 3rd occipital condyle (condylus tertius)

  • Rheumatoid arthritis: C1/C2 subluxation

  • Pathologic C2 fracture

  • Ossiculum terminale persistens

Pathology

  • Osteoporosis in elderly predisposes to type II fracture and nonunion

Anterior graphic shows an avulsion fracture through the tip of the odontoid (type I), transverse fracture at the base of the odontoid (type II), and an odontoid fracture extending through the body of C2 (type III).

Sagittal reformatted bone CT shows a nondisplaced fracture through the tip of the odontoid (type I odontoid fracture).

Sagittal reconstructed CT shows a fracture extending through the base of the dens (type II). The dens is moderately displaced anteriorly.

Coronal reformatted CT shows a type III fracture extending from the right of the base of the odontoid through the C2 body and into the left lateral mass .

TERMINOLOGY

Synonyms

  • Dens fracture

Definitions

  • Type I: Avulsion fracture from tip of odontoid at insertion of alar ligament

  • Type II: Transverse fracture through base of odontoid

  • Type III: Oblique fracture extending from base of odontoid into body of C2

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