AO classification of thoracolumbar injuries

The AO classification of thoracolumbar injuries aims to simplify and universalise the process of classifying spinal injuries and improve interobserver and intraobserver reliability 3.

The AOSpine thoracolumbar classification system consists of only three classes of thoracolumbar injuries. Unlike the thoracolumbar injury classification and severity score (TLICS) 1, the AOSpine classification system does not aim to determine treatment. 

Classification system

Three separate components to every fracture are considered, with only the first fully assessable on imaging alone 4

  1. morphology of the fracture
  2. presence of neurological signs
  3. presence of ligamentous injuries or co-morbid conditions (referred to as modifiers)
Morphology (A, B or C)

Injuries are broadly categorized into three groups: 

  • A: compression injuries
  • B: distraction injuries
  • C: displacement or dislocation
A: compression injuries

Type A injuries involve the anterior portion of the vertebral column with an intact posterior tension band (the group of muscles, ligaments and processes/pedicles that maintain the integrity of the vertebral column).

  • A0: no or clinically insignificant fractures of the spinous or transverse processes
  • A1: also known as wedge compression injuries; they involve a single anterior or middle endplate of the vertebral body without the involvement of the posterior aspect of the posterior vertebral wall
  • A2: also known as split or pincer type injuries; they involve both endplates without the involvement of the posterior wall
  • A3: also known as incomplete burst injuries; they involve a single end plate along with the posterior vertebral wall; a vertebral laminar fracture is usually also present
  • A4: also known as complete burst injuries; they involve both end plates along with the posterior vertebral wall and are also often associated with a laminar fracture
B: distraction injuries

Type B injuries involve the anterior or posterior tension band.

  • B1: also known as Chance fractures; they involve disruption of the posterior tension band with extension into the vertebral body
  • B2: also known as posterior tension band disruption injuries; involvement of an intervertebral body level with disruption to the posterior +/- anterior tension band
  • B3: also known as hyperextension injuries; they involve injuries to the anterior tension band +/- intervertebral or interosseous injury
C: translation injuries

Type C injuries involve displacement in any direction. No subtypes are present as there are numerous possibilities of dislocating fractures. 

Neurological signs (N)
  • N0: no focal neurological signs present
  • N1: a history of transient neurological signs
  • N2: current symptoms of radiculopathy
  • N3: an incomplete spinal cord or cauda equina injury
  • N4: complete spinal cord injury (complete absence of motor and sensory function) 2
  • NX: cannot be assessed
Modifiers (M)
  • M1: the presence of ligamentous injury in the absence of vertebral body injury which can contribute to poor stability
  • M2: the presence of co-morbid conditions such as ankylosing spondylitis, osteopenia, osteoporosis, overlying burns, etc

Related topics

Spinal trauma
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Article information

rID: 59124
Tag: cases, refs
Synonyms or Alternate Spellings:
  • AO thoracolumbar fractures classification
  • Arbeitsgemeinschaft für Osteosynthesefragen (AO) classification of spinal injuries

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Cases and figures

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  • Case 1: morphology C
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