Injury Basics 3 "Slipped Disc" – What does that mean?

My doctor tells me I have a “slipped disc” What is it?

slipped disc

In my experience, when people are told they have a “slipped disc”, it is rare that it is actually a genuine injury to the intervertebral disc.

Most of the time the pain is caused by an awkward movement, leading to inflammation in the spinal joints triggering a severe muscle spasm.

Disc structure

Intervertebral discs are composite structures. They have an outer section with layers of tough, stretchy fibres. The fibres are made of collagen, much like ligaments and tendons. Each layer lies in the opposite orientation to the previous layer, providing strength and resistance in rotation, compression and tension.

The outer layers surround a shock absorbing gel. This gel has a high water content which helps to cushion any compression the spine goes through.

intervertebral disc

Courtesy of wikipedia. https://en.wikipedia.org/wiki/Intervertebral_disc No Permissions Granted

During the day, the compression of the disc as we stand upright pushes the water content out of the disc. When we lie down at night, the comparative traction in the disc causes fluid to re-enter the disc. This also brings in the nutrition that the disc needs.

Disc analogy

A lot of people find it easier to understand the outer layers a bit like the layers in an onion made of elastic. Fibres stretch and then return to their original shape due to the highly elastic collagen. The inner section is like a water balloon filled with toothpaste. (Don’t worry, there isn’t any toothpaste in your spine, the fluid just has a similar consistency to toothpaste.)

Disc ageing

Discs spend a lot of time in compression while we are upright, reducing the water content in the intervertebral disc over time.
The gel-like fluid becomes much thicker from the age of about 65 onwards, as most of the water has been squashed out of the disc.

Alex Green

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