Functional Differentiation in the Spinal Column

Abstract

The structure of the spine suggests that functional specialisation occurs radially in both the vertebral centra and the intervertebral discs. Vertebrae are covered by a thin layer of cortical bone which is attached to the outer lamellae of the discs. These outer lamellae have a high collagen concentration. Thus the outer margins of both the discs and the vertebral centra are strengthened to withstand the tensile stresses generated by torsion and bending of the spine. Inner lamellae of the disc are attached to cartilage end-plates to form a closed system which can withstand the high pressure generated in the nucleus pulposus during compression of the spine. Compression also deforms the cancellous bone of the vertebrae; the inner regions of the discs and vertebral bodies thus appear to be coupled to form a continuous pressure-bearing column. Blood flow from the cancellous bone provides a possible mechanism for dissipating compressive energy. However under some circumstances compression may fracture the cancellous bone; in contrast the disc is more likely to be damaged by torsion and flexion.