| C1 | Jefferson fracture (Figures 6 and 7) | Moderately unstable | Burst fracture; occurs with axial load or vertebral compression | Displaced lateral aspects of C1 on odontoid view, predental space more than 3 mm |
| Atlantoaxial subluxation | Highly unstable | Occurs in patients with Down syndrome, rheumatoid arthritis and other destructive processes | Asymmetric lateral bodies on odontoid view, increased predental space |
| C2 | Odontoid fracture (Figures 1 and 9) | Highly unstable | Mechanism poorly understood | May be difficult to see on plain films; high clinical suspicion requires CT scanning |
| Hangman's fracture (Figure 8) | Unstable | Occurs with sudden deceleration (hanging) and with hyperextension, as in motor vehicle accidents | Bilateral pedicle fracture of C2 with or without anterior subluxation; lateral view required |
| Any level | Flexion teardrop injury | Highly unstable | Sudden and forceful flexion | Large wedge off the anterior aspect of affected vertebra; ligamentous instability causes alignment abnormalities |
| Bilateral facet dislocations | Highly unstable | Flexion or combined flexion/rotation | Anterior displacement of 50% or more of one cervical vertebra on lateral views |
| Unilateral facet dislocations (Figure 5) | Unstable | Flexion or combined flexion/rotation | Anterior dislocation of 25 to 33% of one cervical vertebra on lateral views; an abrupt transition in rotation so that lateral view of affected vertebra is rotated; lateral displacement of spinous process on anteroposterior view |
| Lower cervical or upper thoracic | Clay shoveler's fracture | Very stable | Flexion, such as when picking up and throwing heavy loads (such as snow or clay) | Avulsion of posterior aspect of spinous process; frequently an incidental finding |