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Structure and Function of the Low Back

The spinal column extends from the base of the skull to the pelvis and consists of the cervical spine (neck), thoracic spine (upper back, from which the ribs attach) and the lumbar spine (low back).

Illustration showing the location and basic anatomy of the lumbar spine within a female body - anterior (front) and posterior (rear) views. © Louise Carrier 2007.

The lumbar spine consists of 5 separate bones called vertebrae, which rest on top of a triangular bone that forms part of the pelvis called the sacrum.

Illustration showing the location and basic anatomy of the 5 lumbar vertebrae and sacrum. © Louise Carrier 2007.

The sacrum is joined to the pelvis either side by the sacroiliac joints. These joints are rugged and strong, supported by strong ligaments and therefore contribute significantly to the stability of the lumbar spine and pelvis. In addition, by allowing small movements they act as a suspension system between the spine and the legs when walking.

Illustration showing the location of the sacroiliac joints, anterior and posterior views. © Louise Carrier 2007.

The spine consists of three columns which have different functions:

Anterior Column:The vertebrae comprise a solid, broad, cylindrical body at the front. Each vertebra sits on top of another vertabra separated at the front by intervertebral discs.

Illustration showing the anterior column; including the 5 lumbar vertebrae and anterior and posterior views of am individual vertebrae. © Louise Carrier 2007. Illustration showing the axial and lateral views of am individual vertebrae. © Louise Carrier 2007.

The disc is made up of a soft, pliable, spherical centre called the nucleus pulposus and a firmer, fibrous outer ring called the annulus fibrosis. The discs contribute to a weight bearing, suspension between the vertebrae as well as to maintaining uniform and smooth movement about an axis.

Illustration showing a lateral view of 2 lumbar vertebrae and an intervertebral disc with it's structural features. © Louise Carrier 2007.