The Cellular and Molecular Biology
of the Intervertebral Disc: A Clinician’s Primer
SOURCE: J Can Chiropr Assoc. 2014 (Sep); 58 (3): 246–257
W. Mark Erwin, DC, PhD and Katherine E. Hood, DC
Assistant Professor, Divisions of Neurological and Orthopaedic Surgery,
University of Toronto, Toronto Western Hospital;
Scientist, Toronto Western Research Institute;
Associate Professor, Research Canadian Memorial Chiropractic College.
Clinicians routinely encounter patients suffering from both degenerative and acute spinal pain, often as a consequence of pathology affecting the intervertebral disc (IVD). The IVD is a complex structure essential to spinal function and is subject to degenerative disease and injury. However, due to the complexity of spinal pain syndromes it is often difficult to determine the extent of the IVD’s contribution to the genesis of spinal pain. The location of the IVD is within close proximity to vital neural elements and may in the event of pathological change or injury compromise those structures. It is therefore important that clinicians performing manual therapy understand the cellular and molecular biology of the IVD as well as its clinical manifestation of degeneration/injury in order to safely manage and appreciate the role played by the disc in the development of mechanical spinal pain syndromes.
Keywords: spine, degenerative, pain, disc, intervertebral
The Full-Text Article:
The intervertebral disc (IVD) is a complex structure positioned between two adjacent vertebrae where in addition to protecting the spinal cord and segmental spinal nerves it confers flexibility, multi-axial spinal motion and load transmission to the spine. The IVD is vulnerable to injury and degeneration often leading to pain syndromes however much remains to be discovered concerning the development of axial and radicular pain syndromes, the biology of the disc and the capacity of the IVD to repair itself after injury.  From the clinician’s perspective, familiarity with the biology of the IVD is vital in order to understand the natural history of disc-related injury/illness and to develop appropriate therapeutic strategies. The purpose of this review is to provide an overview of the salient characteristics of IVD pathology with a particular emphasis upon degenerative disease and its role in the generation of clinical spinal pain syndromes.
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The disc as an organ:
Capping the IVD superiorly and inferiorly, the cartilaginous vertebral end plates (VEP) are thinnest in the central region contiguous with the NP and may be up to 1mm thick at their outer edge. Much like hyaline cartilage found within appendicular joints, VEPs are typically without vasculature or neural elements and although a minute arrangement of vessels exists at early stages, these will fade as skeletal maturity is reached and undergo calcification and significant loss of function with degenerative disease. [2-4] Although the VEPs are without direct vascular supply, there are capillary networks abutting the central portion of the VEP that are directly connected with the vasculature of the vertebral body. Interestingly the capillary density is 4 times denser at the centre of the VEP (over the nucleus pulposus or ‘NP’) than the periphery; suggesting the importance of diffusion from these networks into and out of the NP.