Authors of section

Authors

Alex Vaccaro, Frank Kandziora, Michael Fehlings, Rajasekaran Shanmughanathan

Executive Editor

Luiz Vialle

General Editor

German Ochoa (in memoriam)

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Rationale for fracture classification: A0, A1, A2, A3, A4, B1, B2, B3, C

1. Preliminary remarks

The classification system described here exists in order to provide surgeons from different institutions with a common language to discuss various injuries. It provides consistency in injury diagnosis and treatment.

The AOSpine thoracolumbar fracture classification system aims to achieve international acceptance.

The subsequent sections elaborate on how to assess the fracture type based on the flow chart shown in the figure.

To make a diagnosis, imaging studies are required.

Thoracic and Lumbar fractures: Algorithm for morphologic classification

2. Step 1: Displacement/Dislocation

First, the physician must see if there is a translational injury. This is considered a type C injury.

X-ray/CT images are examined to determine if displacement and dislocation exists.

Thoracic and Lumbar Fractures: Rationale for fracture classification

3. Type C injuries

Type C injuries are segmental injuries. They involve an interruption or separation of both the anterior and posterior components of the vertebral segments. The disruption of the anterior component may be through the disk or vertebral body. The disruption of the posterior elements may be through the spinous process, lamina, pars interarticularis, or posterior ligamentous complex.

These injuries can be associated with any A-type fracture (vertebral body).

Thoracic and Lumbar Fractures: Rationale for fracture classification

4. Step 2: Tension band injury

The treating physician now determines if there is a tension band injury to the spinal column.

Thoracic and Lumbar Fractures: Rationale for fracture classification

5. Step 2.1: Disruption of anterior tension band

If there is disruption of the anterior tension band only, then this is classified as a B3-hyperextension injury.

Thoracic and Lumbar Fractures: Rationale for fracture classification

6. Type B3 injury

Subtype B3 is characterized by a tension injury of the disc or vertebral body, or both, resulting in a hyperextended position of the vertebral column.

The anterior longitudinal ligament is ruptured.

This is commonly seen in ankylotic disorders.

This injury can be associated with any A-type fracture (vertebral body).

Type B, such as type C injuries are segmental injuries (except B1).

Thoracic and Lumbar Fractures: Rationale for fracture classification

7. Step 2.2: Disruption of posterior tension band

If there is disruption of the posterior tension band without translation, then the injury is classified as either B1 or B2, depending on involvement of the structures disrupted.

Thoracic and Lumbar Fractures: Rationale for fracture classification

8. Type B2 injury

Subtype B2 is a posterior tension band disruption with failure through both soft tissue and bony elements.

This injury can be associated with any A-type fracture (vertebral body).

Type B, such as type C injuries are segmental injuries (except B1).

Thoracic and Lumbar Fractures: Rationale for fracture classification

9. Type B1 injury

Type B1 is a monosegmental bony posterior tension band injury.

There is complete osseous failure of the posterior tension band at one level that extends into the vertebral body. These are also known as seatbelt or "Chance" fractures (named after George Quentin Chance, a British radiologist who first described it in 1948).

This injury can be associated with any A-type fracture (vertebral body).

Thoracic and Lumbar Fractures: Rationale for fracture classification

10. Step 3: Vertebral body fracture

The presence of a vertebral body fracture should be determined. This can be seen in addition to both B and C type injuries.

Thoracic and Lumbar Fractures: Rationale for fracture classification

11. Step 3.1: Posterior wall involvement

If there is a vertebral body fracture, it is determined whether the fracture involves the posterior vertebral body wall. If yes (burst fracture), it is assessed whether both or only one endplates are fractured.

Thoracic and Lumbar Fractures: Rationale for fracture classification

12. Type A4 injury

Type A4 burst injuries are fractures of both endplates.
A vertical fracture of the lamina does not imply posterior tension band rupture. It is a sign of compression forces.

Thoracic and Lumbar Fractures: Rationale for fracture classification

13. Type A3 injury

Type A3 burst injuries are fractures of a single endplate. There may be a vertical fracture of the lamina. The posterior tension band is maintained.

Thoracic and Lumbar Fractures: Rationale for fracture classification

14. Step 3.2: Vertebral body fracture without posterior wall injury

A-type fractures are injuries without posterior wall injury.

Thoracic and Lumbar Fractures: Rationale for fracture classification

15. Type A2 injury

Type A2 injuries are vertebral body fractures in which the fracture involves both endplates.

These can be called split- or pincer-type fractures.

Thoracic and Lumbar Fractures: Rationale for fracture classification

16. Type A1 injury

Type A1 injuries are vertebral body fractures with one or both endplates involved but the fractures do not connect with one another.

These can be called wedge compression or impaction fractures.

Thoracic and Lumbar Fractures: Rationale for fracture classification

17. Type A0 injury

Type A0 is used to describe all other insignificant fractures not affecting the spinal stability in a significant way, such as an isolated fracture of the spinous process, the transverse process, or the lamina.

Thoracic and Lumbar Fractures: Rationale for fracture classification

18. Modifiers

The classification system uses modifiers M1 and M2 to assist in treatment recommendations.

M1 is used to designate fractures with an indeterminate injury to the tension band based on spinal imaging or clinical examination.

M2 is used to designate a patient-specific comorbidity, which might argue either for or against surgery for those patients with relative indications for surgery.

Thoracic and Lumbar Fractures: Rationale for fracture classification

M1 assessment: Feeling the gap between two spinous processes.

Thoracic and Lumbar Fractures: Rationale for fracture classification

19. Neurology

Neurology is assessed as seen on the grid following a neurological evaluation.

Thoracic and Lumbar Fractures: Rationale for fracture classification

20. Nomenclature

Because type B and C are segmental injuries, the level must be described as follows:

Type B, T11/12

If there is a fracture, then it will be described between brackets as follows:

Type B, T11/12 (T12: A4)

Example 1:

Type C, T11/12 (T12: A3) N1

A translational injury with an incomplete burst fracture in a patient who is neurologically intact.

Thoracic and Lumbar Fractures: Rationale for fracture classification

Example 2:

Type A4, L1
N3, M1

A complete burst fracture in the setting of an incomplete spinal cord injury with possible disruption of the posterior ligamentous complex.

Thoracic and Lumbar Fractures: Rationale for fracture classification