AO classification of upper cervical injuries

Dr Craig Hacking et al.

The AO classification of upper cervical injuries aims to simplify and universalise the process of classifying upper cervical injuries and improve interobserver and intraobserver reliability.

Injuries are based on location specific patterns and divided into:

  • type 1: occipital condyle and occipital cervical joint complex injuries
  • type 2: C1 ring and C1-2 joint complex injuries
  • type 3: C2 and C2-3 joint complex injuries
  • A: bony injury only - considered stable injuries
  • B: tension band injuries - considered potentially unstable injuries
  • C: translation injuries - considered unstable injuries
  • Nx: the patient cannot be examined
  • N0: no neurological deficits
  • N1: transient neurological injury
  • N2: nerve root injury
  • N3: incomplete spinal cord injury
  • N4: complete spinal cord injury
  • +: continued spinal cord compression
  • M1: injury at high risk of non union with nonoperative treatment
  • M2: injury with significant potential for instability
  • M3: patient specific factors affecting treatment (e.g. ankylosing spondylitis)
  • M4: vascular injury or abnormality affecting treatment 
Spinal trauma
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rID: 63414
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