Understanding a herniated disc begins with understanding the disc itself.
The intervertebral or spinal disc is a structure in the spine whose primary purpose is to act as a shock absorber between adjacent vertebrae.
Spinal discs also act as ligaments that hold the vertebrae of the spine together and as cartilaginous joints that allow for slight mobility in the spine.
There are a total of twenty-three intervertebral discs in the spinal column. The most common discs in the lower back to become injured or degenerated are at the levels between L4-L5, and L5-S1.
Spinal discs are composed of two parts: a tough outer portion and a soft inner core. The design has been likened to that of a jelly donut.
The annular fibers hydraulically seal the gelatinous nucleus and evenly distribute pressure and force imposed on the structure.
portion and inner core of the spinal disc fit together like two
concentric cylinders and are interconnected by cartilaginous end-plates.
At birth, eighty percent of the disc is composed of water. In order for the disc to function properly, it must be well hydrated.
The nucleus pulposus is the major carrier of the body’s axial load and relies on its water-based contents to maintain strength and pliability.
Over time, spinal discs dehydrate and become stiffer, causing the disc to be less able to adjust to compression.
While this is a natural aging process, as the disc degenerates it can become painful in some individuals.
The most likely reason for this is that the degeneration
can produce micromotion instability and the inflammatory proteins (the
soft inner core of the disc) probably leak out of the disc space and
inflame the well-innervated structures next to the disc (e.g. nerve
Sometimes a twisting injury damages the disc and starts a cascade of events that leads to degeneration.
The spinal disc itself has very few nerve endings and no blood supply. Without a blood supply the disc does not have a way to repair itself, and pain created by the damaged disc can last for years.
In general, as we age there are less inflammatory proteins in the disc space and discogenic pain rarely occurs after 60 years of age.
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