Three Columns of the Spine
The three-column model of spinal stability, often attributed to Denis refers to the following:
Anterior Column (Column 1): This includes the anterior longitudinal ligament, the anterior half of the vertebral body, and the anterior part of the intervertebral disc (annulus fibrosus).
Middle Column (Column 2): This consists of the posterior longitudinal ligament, the posterior half of the vertebral body, and the posterior part of the intervertebral disc (annulus fibrosus).
Posterior Column (Column 3): This comprises the bony elements posterior to the middle column (pedicles, facets, laminae, spinous process) and the posterior ligamentous complex (ligamentum flavum, interspinous ligaments, supraspinous ligament, and facet joint capsules).
Injury to two or more of these columns typically indicates an unstable spinal injury.
The sternal-rib complex acts as a fourth column, providing additional structural support (See Ribcage Biomechanics)
