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What is the actual function of intervertebral discs?

Verfasst von Theresia Lechner
Bandscheibe mit Wirbelsäule gezeichnet

If you are diagnosed with a slipped disc, it is essential that you lose no further time in becoming better acquainted with your spine’s ingenious shock absorbers. Have you maybe often asked yourself what exactly the function of an intervertebral disc actually is? Then you’re in just the right place. In this article you will find out what your intervertebral discs have to do with astronauts in space, how they are supplied with nutrients, and why your intervertebral discs are extremely resistant.

So much more than just discs

To give you a rough overview, we’ll first start with the construction and the position of your intervertebral discs. Your intervertebral discs (also called discus intervertebralis) always lie between two neighbouring vertebral bodies in your spine. Their main task is to absorb pressure and impact – caused through running, jumping or simply moving, for example. In this way they also protect, for example, your brain against too heavy shock. Any resultant weight is evenly distributed across your spine.

It is also the function of the intervertebral discs, together with the small vertebral joints, to make it possible for your spine to move smoothly and freely [1,2].

As a general rule, an intervertebral disc can be split into three components [1]:

  • centrally located gelatinous core (nucleus pulposus) (1*)
  • An outer fibre ring (annulus fibrosus) (2*)
  • Two cartilaginous endplates (3*)
Bestandteile der Bandscheibe: Gallertkern, Faserring und Knorpelplatte mit Wirbelkörper gezeichnet
Intervertebral disc construction with centrally located gelatinous core (nucleus pulposus) (1*), outer fibre ring (annulus fibrosus) (2*) and two cartilaginous endplates (3*)

It is not just what is inside that counts

The inner core of your intervertebral disc consists of up to 85% water and has a slimy and thick-flowing consistency. A bit like gelatine.  It doesn’t have a fixed form, but rather changes depending on pressure. This make it the ideal cushion [3,4].

In 2-year-old children, the inner core of the intervertebral disc does, in fact, consist of a fluid, like water. If you cut through the outer fibre ring, the fluid runs out and you can wash it away with a cloth. However, as we age, the inner core becomesharder and more granular [3,4].

The outer fibre ring (annulus fibrosus) of your intervertebral discs consists of several lamellae-like layers, which go around the inner core (nucleus pulposus) in circles.  Within these lamellae, there are also a lot of very strong, connective tissue-like fibres that pull in all directions [3,4].

Sometimes our lumbar spine has to bear the weight of up to 150 kilograms, such as when sneezing or coughing [2].

But don’t worry. This ingenious and extremely resistant system is, itself, incredible at withstanding complex and heavy loads [3,4]. An intervertebral disc is also situated like a sandwich between two cartilaginous plates and the bones of your vertebral bodies [1].

Nothing jumps out and nothing slips around

However, unlike with a sandwich, an intervertebral disc cannot be budged and is conjoined with the cartilaginous endplates and the bones in your vertebral bodies. It is also strengthened at the back and at the front with corresponding ligaments [2,3,4].

So don’t pay any attention to people who claim that one of their intervertebral discs has jumped out or slipped. This isn’t possible. An intervertebral disc stays where it is.

Lendenwirbel mit Bandscheibe und Bändern und Fasern
Intervertebral discs are firmly anchored between the vertebral bodies with ligaments and fibres (blue)

It is only the outer fibre ring that can become brittle and lose tension. In some cases, this can cause the fluid from the inner core to seep out. This is known as a slipped disc (more on this in this hyperlinked article). In principle though, your intervertebral disc is an extremely strong system that can even withstand the most violent impacts. So any violent external impact is more likely to result in a vertebral body fracture, than in an injury to your intervertebral disc [3].

Your intervertebral discs are hungry

Unlike with muscles and bones and other connective tissue, the inner core of an intervertebral disc does not have its own vascular supply system. Of course, your intervertebral discs still need nutrients and oxygen. Any waste produced, such as old cells, have to be carried away again, as well. For this reason, your body uses two mechanisms from the realm of physics: diffusion and osmosis. More simply put, this means that there is a pressure-dependent exchange of fluids between an intervertebral disc and its environment [3,4].

So if intervertebral discs experience pressure, such as when we are sitting down, then fluid is pressed out of them. This means waste can be transported away. Conversely, when pressure is taken off intervertebral discs, for example when lying down, they fill up again with new fluid and nutrients [3,4].

Change in position – a little treat for your intervertebral discs

That means for healthy and load-resistant intervertebral discs, there is a magic potion: movement. Each time you change position, the pressure on your intervertebral discs changes. This means that when you move, you are feeding your intervertebral discs and are helping to maintain their important function.

Don’t allow your intervertebral discs to starve, but rather make sure you move a lot throughout the day.

After a maximum of 30 minutes in one position, it is imperative that you move (e.g. go from sitting to walking). And at least every few minutes there should be small micro movements (for example, shift your weight from left to right) [5,6].

If you are finding it hard to fit in these moving-about breaks and to really implement active sitting, you can use the 8clip in the office. This clip gives you feedback about how much you move. In addition, it motivates you throughsmall vibrations to move more if you have been in one position for too long.


What you have learnt in this article about the function of intervertebral discs

You now know that your intervertebral discs cannot slide around or jump out, as they are firmly conjoined with the vertebral bodies through ligaments and connective tissue fibres. You have also learnt that these intervertebral discs literally starve if you do not feed them regularly by moving about. Hurrah! You’re now a veritable intervertebral disc whiz!

Back up your knowledge

Due to the pressure loads experienced through day-to-day activities, each person loses about 1.7 cm in height throughout the day due to the reduction of fluid in their intervertebral discs. One of the things that causes this is gravity. Scientists were able to prove that, when astronauts from Skylab 4 were in zero gravity in space, they grew by more than 4 cm. However, this effect was immediately reversed as soon as the astronauts were back on Earth [4].

Important to note:
This article contains general recommendations only and must not be used for self-diagnosing or self-treatment. It is not a replacement for visiting your GP.

[1] Schünke, M. ; Schulte, E.; Schumacher,U.(2007): Prometheus. LernAtlas der Anatomie. 2. Aufl. Stuttgart: Georg Thieme Verlag.

[2] Streeck, U.;  Focke, J.; Klimpel, L.; Noack, D. (2007): Manuelle Therapie und komplexe Rehabilitation. Band 2: Untere Körperregionen. Heidelberg: Springer Medizin Verlag.

[3] Frost, B.; Camarero-Espinosa, S.; Foster, E. (2019): Materials for the Spine: Anatomy, Problems, Solutions. In: materials(Basel). 12(2): 253. 

[4] Krämer, R.; Matussek, J.; Theodoridis, T. (2013): Bandscheibenbedingte Erkrankungen. Ursachen, Diagnose, Behandlung, Vorbeugung, Begutachtung. 6. Auflage. Stuttgart: Georg Thieme Verlag.

[5] Sorensen, C.J.; Norton, B.J.; Callaghan, J.B.; Hwang, C.T.; Van Dillen, L.R.: Is lumbar lordosis related to low back pain development during prolonged standing? Man. Ther., 20 (2015): 553-557.

[6] Womersley, L.; May, S.: Sitting posture of subjects with postural backache. J. Manip. Physiol. Ther., 29 (2006): 213-218.