Many classifications are used to define vertebral injuries. Some surgeons believe that using a classification system based on mechanisms is beneficial in planning surgical reduction and stabilization. Two of the earliest classifications were by Whitley and Forsyth [1] and Holdsworth [2], who emphasized mechanisms of injury. Roaf [3] made a plea to classify vertebral injuries according to the principles of classic dynamics. Unfortunately, this scholarly approach is not useful to radiologists. Gehweiler and coworkers [4] addressed the needs of radiologists by stressing the radiographic features of the Holdsworth classification.

In 1982, Allen and associates [5] reviewed a series of their own cases and observed a spectrum of injuries in the cervical vertebral column that they called phylogenies. They expanded the existing classifications along mechanistic lines and defined six common groups:

• compressive flexion

• vertical compression (pure axial loading)

• distractive flexion

• lateral flexion

• compressive extension

• distractive extension.

These investigators also proposed that the probability of an associated neurologic lesion was directly related to the type and severity of the lesion [5].

Ferguson and Allen [6] applied a similar mechanistic classification to thoracolumbar fractures and established the following categories:

• compressive flexion, comprising three subcategories:

• anterior wedge fracture

• anterior wedge with posterior distraction, with facet fracture or dislocation, or with both

• burst with middle element failure and retropulsion of bone fragments (classic burst fracture)

• distraction flexion injuries, in which the abnormalities are primarily posterior (Chance-type fractures)

• lateral flexion

• torsional flexion (rotary “grinding”)

• translational (shearing)

• vertical compression (pure axial loading).