The correct answer is:

Anterior two-thirds of the vertebral body, the posterior third of the vertebral body, and the posterior elements.

Educational Objective:

Review the determination of stability of spinal fractures using the 3-column method of Denis.

Key Point:

By determining which columns are disrupted, it is possible to assess fracture stability in most cases.

Explanation:

The Denis 3-column theory is classically described as follows (see Figure 1):

Anterior column: anterior two-thirds of the vertebral body and the anterior longitudinal ligament

Middle column: posterior one-third of the vertebral body, the posterior longitudinal ligament, and the arch elements (eg, transverse processes)

Posterior column: spinous processes and the posterior ligaments (eg, interspinous, nuchal)

Figure 1:

It can seem difficult to use the theory if reviewing the original literature, because there are 20 subtypes. A principle that makes this easier is to remember that the 3 major ligaments count as much as anything.

The question to ask is: Is the anterior longitudinal ligament, the posterior longitudinal ligament, and/or the posterior interspinous ligaments likely disrupted? If the answer is yes to any two, then there is an unstable fracture.

A simple example can clarify this further. A small, simple anterior wedge fracture is caused by hyperflexion. It is an anterior column injury only. It is stable.

An anterior wedge fracture caused by severe flexion will also disrupt the middle column and the posterior ligaments (see Figure 2). This violates all 3 columns and is unstable.

Figure 2:

It is worth noting that it is common to find incorrect explanations of the theory, eg, the columns defined by equal halves of the vertebral body or the "tree column" instead of the "three column" theory.