Saturday, July 25, 2009

Fracture of the Dens (Type 1)

24 Year old male came with motor vehicle accident with pain in neck, Sagittal T1 W and Coronal STIR MRI images of cervical spine shows an oblique fracture in the tip of odontoid process (arrow). No cord compression.


  • Most dens fractures are caused by motor vehicle accidents and falls
  • About 1/3 of C-spine injuries occur at C2 and about ½ at C6-C7
  • As expected, most fatal cervical spine injuries occur at C1 or C2
  • Most odontoid fractures occur with flexion, extension and rotation.
  • Classification of dens fractures:
    • About 15% of all cervical spine fractures
    • Classified by location (Anderson and D’Alonzo classification)
      • Type I (<5%)
        • Tip of dens at insertion of alar ligament which connects dens to occiput
        • Usually stable but may be associated with atlanto-occipital dislocation
      • Type II (>60%)
        • Most common dens fractures
        • Fracture at base of dens at its attachment to body of C2
      • Type III (30%)
        • Subdentate—through body of C2
        • Does not actually involve dens
        • Unstable fracture as the atlas and occiput can now move together as a unit
    • Other fractures include a rare longitudinal fracture through dens and body of C2
  • Imaging findings
    • Conventional radiography is frequently first used as it tends to be most available
    • CT is better at demonstrating fractures
    • MRI is used for evaluation of ligamentous, disk, spinal cord and soft tissue injuries
    • Posterior displacement of the fractured dens into the spinal canal is more common than other displacements
    • Lateral view on conventional radiography is most useful as most (85-90%) of injuries can be seen on lateral view
    • Cervicothoracic junction visibility assures that the entire cervical spine is visualized
    • Soft tissue findings may include >5 mm of prevertebral soft tissue at C3 or less than half of the AP diameter of the adjacent vertebra
      • At level of C6, prevertebral soft tissue should be no more than 22 mm in adults and 14 mm in children younger than 15 years
    • Widening of the predentate space to greater than 3 mm is abnormal
  • Pitfalls
    • A mach line may appear to traverse the base of the dens on the open-mouth (aka as the atlantoaxial or odontoid) view but should be recognized by the superimposed base of the occiput
      • The mach line will not be present on the lateral view of the dens
    • A smooth and sclerotic edge to the “fracture” usually indicates either congenital non-union or acquired non-union of the dens to the body of C2
  • Treatment
    • Type I fractures are usually treated with a hard collar for 6-8 weeks
    • Type II fractures can be treated with
      • Immobilization for 12-16 weeks
      • Operative fixation (odontoid screw)
      • Arthrodesis of C1 to C2
    • Type II fractures can be treated with a halo or surgically, as Type II fractures
  • Complications
    • Non-union
      • Due to limited vascular supply
      • May occur in 30-50% of Type II fractures, especially in elderly
    • Malunion
    • Pseudarthrosis
    • Affected by age of patient, amount of displacement.

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