Spinal Anatomy

The discs are fibrocartilagenous structures positioned between the vertebrae. Discs consist of a central core called the nucleus pulposus, a thick, gelatinous substance comprised of water and protein molecules. The nucleus pulposus is surrounded by multiple layers of fibers that comprise the ligamentous outer layer, or the annulus fibrosus. The annulus connects the discs to the vertebral bodies, and helps cushion the spine and control motion. (25-26)

Facet joints bilaterally allow articulation between the vertebrae and provide stability for the spine. (25) The spine is surrounded anteriorly and posteriorly by many ligaments that provide support and constrain motion within safe anatomic limits (Figure 1).

Figure 1. Spinal Ligaments

The trunk muscles provide stability and produce movement, and play a role in protecting the spine in trauma.

The spinal cord runs posterior to the vertebral bodies and is protected posteriorly by the neural arch, comprised by the pedicles and laminae. At each level of the spine, nerve roots exit bilaterally via the neural foramen to enervate the trunk and extremities.

Biomechanically, 80% of weight bearing occurs through the discs and vertebral bodies, with 20% of weight bearing occurring through the facet joints. (26-27)