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.

Discussion:

• 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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