AO Spine classification of upper cervical injuries

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

Usage

Although in routine clinical practice, at least in many institutions, injuries will be described using more 'traditional' terminology (e.g. hangman's fracture of C2, type II dens fracture, etc...) rather than by specifying exact AO nomenclature, these classifications highlight important unifying principles and use increasingly universal terminology. As such, familiarity with them is worthwhile.

Classification

Injuries are broadly divided into three types based on location-specific patterns and then further subdivided according to injury type and presence of neurological signs and/or modifying factors.

Location

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

Injury types (A, B or C)

A: bony injury only - considered stable injuries
B: tension band injuries - considered potentially unstable injuries
C: translation injuries - considered unstable injuries

Neurological signs (N)

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

Modifiers (M)

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