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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