Spinal discs are comprised of fibrocartilaginous tissues that connect two adjacent vertebral bodies, forming the spinal column. These are also known as intervertebral discs.
Shaped like circular capsules, spinal discs consist of a tough outer layer (the annulus fibrosus), and an elastic inner core (the nucleus pulposus).
The nucleus pulposus is made up of a substance rich in proteoglycans, a small amount of collagen type II and elastin fibers.
The main function of this inner core is to facilitate the smooth distribution of hydraulic pressure within each disc under compressive loads.
The annulus fibrosus consists of a type I collagen-based concentric lamellar structure.
Within this structure, the collagen fibers are arranged in such a manner that they are approximately 30 degrees aligned to the transverse plane of the vertebral endplates.
Among these vertebral endplates, are two thin endplates that extend over the annulus fibrosus and the nucleur pulposus with the purpose of supplying nutrients to the discs by diffusion.
The vertebral endplates consist of osseous and hyaline-cartilaginous layers that connect the intervertebral disc to the vertebral bodies.
There are different types of cells located in various regions of the intervertebral discs, including the vertebral endplates, the annulus fibrosus and the nucleus pulposus.
These cells remain relatively constant in the endplates and the annulus fibrosus but the cells in the nucleus pulposus undergo substantial cell type changes in life.
There are two common types of disc problems that originate from intervertebral discs - disc degeneration and herniated disc.
Intervertebral Disc Degeneration is a common cause of low back pain. It involves a structural dysfunction of the intervertebral disc and factors such as ageing, genetics or injuries can facilitate its development.
With growth and skeletal maturation, the boundary between the nucleus pulposus and annulus fibrosus becomes less distinct; the annular lamellae becomes irregular and the collagen and elastin networks become less organised.
Degeneration of the annulus fibrosus, seen in intervertebral disc degeneration, allows the nucleus pulposus to push out towards the outer edge causing disc bulge.
A complete rupture of the annulus fibrosus allows the nucleus pulposus to protrude beyond the boundary of the disc, leading to herniation of the disc.
This increases pressure on the spinal cord or the nerve root, depending on where the herniation has occurred.
The complete aetiology of intervertebral disc degeneration is complex and requires further research. This is the reason why current treatment modalities primarily focus on symptomatic relief through the use of non-steroidal or steroidal medication for inflammation.
Surgical intervention is usually recommended for late-stage intervertebral disc degeneration which presents severe neurological symptoms.
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