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Jefferson C1 Fracture


KEY FACTS

Terminology

  • Fracture(s) of C1 ring

Imaging

  • Multiple fractures of C1 arch (2-, 3-, and 4-part fractures)

  • Combined offset of lateral masses of C1 relative to lateral margins of C2 ≥ 7 mm suggests interruption of transverse ligament

  • Avulsion fragment off inner C1 pillar at insertion of transverse ligament indicates unstable fracture

  • Widening of atlantoaxial interval

    • ≥ 4 mm concerning for interruption of transverse ligament

    • ≥ 7 mm presumed interruption of transverse ligament

  • Associated C2 fracture (hangman's fracture, odontoid fracture)

    • Fractures at lower levels not uncommon

  • May see T2 hyperintense edema if cord contusion present

Top Differential Diagnoses

  • Congenital variants, clefts, malformations of atlas

  • Rotational malalignment of atlas, axis pillars

  • Pseudospread of atlas in children

Pathology

  • Force transmitted down through occipital condyles onto sloped C1 pillars with head and neck rigidly erect

  • Transverse ligament often intact

  • If transverse ligament is interrupted, stability of fracture depends on integrity of alar ligaments

Clinical Issues

  • Neurologic signs uncommon unless unstable fracture, injury at another level, or vascular injury

Diagnostic Checklist

  • Important to evaluate lower levels for additional fractures

Lateral radiograph of the craniovertebral junction shows faint lucencies in the posterior arch of C1.

Coronal radiograph, in which the interval between the dens and the lateral masses of C1 is obscured by the occipital bone, shows lateral displacement of the outer margins relative to C2.

Axial NECT shows fractures extending through the anterior and posterior arches of C1. A small bony fragment demonstrates the site of an avulsion fracture at the attachment of the transverse ligament.

Coronal reformatted CT shows lateral displacement of both C1 lateral masses relative to the occipital condyles and C2 lateral masses. Also seen is a bony fragment due to transverse ligament tubercle avulsion .

IMAGING

General Features

  • Best diagnostic clue

    • Lateral displacement of both articular masses of C1 relative to margins of C2 on open mouth radiograph

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