Human intervertebral disc: structure and function.

This review begins with a brief introduction in which the development, blood supply and innervation of the intervertebral disc is considered, particularly as these may influence the following sections on structure and function. The three regions within the disc--that is, the nucleus pulposus, annulus fibrosus, and cartilage end plates--are considered in some detail. There appears to be no distinct border between the central nucleus pulposus and the outer annulus fibrosus, the main difference being in their fibrous structure. The fluid space is important in the nutrition of the disc, showing plastic deformation and recovery characteristics. The structural elements, both macroscopically and microscopically, together with the biochemical elements, are intimately related to function. The intervertebral disc should not be though of as a homogeneous and static structure; it has a heterogeneous composition and responds dynamically to applied loads. Neither should it be considered as an isolated structure because it interacts with the vertebral bodies, together constituting the vertebral unit. Furthermore, changes within the disc can, and do, have dramatic effects on vertebral column kinematics. The intervertebral disc is not inactive; it is capable of self-maintenance; in injury it can repair itself and has considerable regenerative properties.