This injury is caused by hyperextension and axial loading. Typically these injuries widen the spinal canal and therefore rarely produce neurological damage. The traditional 'Hangman's fracture' (extension in association with distraction) is seldom seen today. Spondylolisthesis of the axis was classified by Effendi and later modified by Levine:
• Type I: a stable injury with <3 mm displacement, treated in a collar for 6 weeks.
• Type II: an unstable injury, with >3 mm C2/3 displacement and angulation. Traction in slight extension usually achieves reduction, followed by application of a halo for 6 to 8 weeks.
• Type IIA: Levine proposed 5% of patients have this pattern of injury, from flexion-distraction and resultant C2/3 disc disruption. Angulation between C2 and C3 is more severe. These injuries mimic the traditional Hangman's fracture and with traction the cord can be distracted. A halo in slight compression and extension is required.
• Type III: a pars fracture, with uni- or bi-facet dislocation of C2/C3 and associated neurological injury. Treatment is again with traction, followed by halo immobilization. If the dislocation is irreducible, MRI is required to exclude disc herniation. A posterior fusion is performed between the inferior facet of C2 and the spinous process of C3. If the reduction of the body of C2 cannot be maintained, anterior fusion should be considered.
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