The intervertebral discs consist of
three seperate components - the inner gelatinous nucleus pulposus, the outer annulus fibrosus, and the cartilaginous end plates
superiorly and inferiorly. The entire disc is composed of mainly water, proteoglycans and collagen.
Colagen form the strong fibrous network that anchor the vertebral boides and suspending cells, proteoglycan in the extracellular
matrix. The predominant type of collagen in annulus is type I, and in nucleus is type II.
Proteoglycan which form about 5-10% of dis weight is responsible for maintaing disc height and turgor under the compressive
loads. The primary proteoglycan is aggrecan, other PGs include: large aggregating versicans, decorin, biglycan, fibromodulins
Disc tissue has been shown to derive their nutrition either from vascular plexusof the anulus or through the blood
vessels tha peirce hyaline cartilage of endplate to enter from the subchondral one.
Pathomechaics of Symptomatology in Disc hernaition:
Disc herniation causes mechanical deformation of nerve root and an inflammatory reaction resulting from the presence
of foreign nucleus pulposus in the spinal canal. Herniated Nucleus pulposus(HNP) has shown to cause release of inflammatory
cytokines like Il-1, Il 6, TNF alpha nad G- M CSF. These inflammatory cytokines attract macrophages, fibroblasts, endothelial
cells and chondrocyte.
Nerve root affection:
The nerve roots in lumbar spine usualy lie in the superior half of the disc, thus the symptomatology resulting from root
affection will depend on which direction the disc has herniated. Central posterior HNP leads to compression of the thecal
sac and all of the traversing nerve roots. A posterolateral HNP can lead to compression of the traversing nerve, which is
heading for the foramen of the next vertebral body. A far lateral HNP, which is less common, can lead to compression
of the nerve root that has already exited the same vertebrae foramen.
Disk herniations are described as protrusions, prolapses, extrusions, or sequestered herniations depending on how far
the disk material displaces. A protrusion is a bulging of the nucleus through a weakened annulus. A prolapse is a rupture
of the nucleus through the annulus but not through the posterior longitudinal ligament. An extrusion is a rupture of the nucleus
through the annulus and the posterior longitudinal ligament. Finally, a sequestered herniation is a separation of a herniated
fragment from the disk from which it came.