There is nothing slippery about a disc. Discs are living adaptable force transducers that are firmly connected to the bones in your back and supported by really powerful ligaments. Diffs slip, soap slips, disc definitely don’t slip.
- G Lorimer Mosely and David S Butler
Discs have a bad reputation. We associate them with the ideas of slipping, bulging, herniating, protruding, extruding and degenerating. But we have twenty three of them in our spines- surely they don’t all do this? And even if they do bulge, protrude or extrude this does not always mean that we have pain as a result. In scans of 98 asymptomatic subjects 52 percent had a bulge at at least one level, 27 percent had a protrusion, and 1 percent had an extrusion. This lead the researchers to conclude that the discovery by MRI of bulges or protrusions in people with low back pain may frequently be coincidental.
Our discs are amazing structures. They act as joints between our vertebrae, they separate and connect the many bones of our spine. They help our body absorb force and transfer it, they create mobility and hold us upright. They are more efficient than bone because they are not constantly building and breaking down in the way that our bones are. They don’t need the same fuel as our highly vascularised bones do either. Instead of giving support through a strong structure, they give us support through their ability to stretch and spread load.
Discs are made up of connective tissue (or fibrocartilage) that contains collagen and proteoglycans (or glucosaminoglycans); these are water binding proteins that bind 10,000 times their weight in water. The outside of the disc is called the annulus fibrosus. Which is made up several layers of strong and stiff collagen designed to withstand compressive forces. Here is a gorgeous image from the University of Exeter of a polarised light microscope slide of the fibres of the annulus.
The centre of the disk holds the nucleus pulposus which has much looser collagen fibres suspended in a mucoprotein gel. Imagine that each disk is like a water bed or an inner tube. When we push down on the centre the sides stretch or expand and create an evenly distributed tensile force. Here is a much less beautiful (but informative) image for you (thank you Wikipedia):
Under load the pressure moves from the nucleus pulposus to the annulus to the endplates then to the vertebrae. This serves to spread load over time and slows any impact of weight through the body. Our endplates are the interface between the disc and the vertebrae. They are made from hyaline and fibrocartilage and serve as the medium through which blood and nutrients flow from capillaries in the bone to cells in the discs. This is important because intervertebral discs do not receive their own blood supply. Nutrients get to disc cells through diffusion. When the disc is compressed fluid moves out into the endplate and is returned during decompression.
Why is this important? It shows us that the more movement there is at the disc the more diffusion there is. Without movement, cells don’t get oxygen and nutrients to the disc. The disc then stops producing collagen at that point and the annulus becomes weak. A bulging disc is a weakening to the structure of the annulus. A herniated disc happens when the annulus tears and the nucleus pulposus moves beyond its normal position inside the disk.
Imagine how this could happen over time. Let’s say an average office worker spends eight hours a day sitting hunched over a desk. They are compressing the front of their discs. Unless they then spend another eight hours compressing the back and sides of their discs and decompressing their spines there will be uneven nutrition distribution to the cells of the discs. This is a picture of two vertebrae in flexion. Imagine that the sponge between them is a disc compressed at the front, lifted at the back.
For healthy discs we need to move all parts of our spine in every direction every day. This is twisting, side bending, flexing, extending, compressing and distracting. Here is a photo of me showing different parts of the Franklin Method spine dance.
You could do this but if it doesn’t tickle your fancy know that walking is one way to actively practice disk compression and decompression. Walking also incorporates small amounts of rotation, side bending, flexion and extension in the lumbar and thoracic spine.. I’ve said it before. I will say it again. If you can’t do any other movement today - just walk. Your discs will thank you.
PS: Just a little extra note for those who want to go a little deeper (and possibly weirder). Franklin method uses the mind to improve our movement. This requires that we really visualise what is actually happening at the discs. The Franklin Method embodiments for the discs involve visualising the posterior annulus stretching like ropes of a boxing ring (or fish net tights) when curling forward, visualising the anterior annulus stretching when extending back and seeing the contralateral annulus stretching when side bending. We then layer this imagery with the metaphor of water swishing in a tub. As we curl forward we see the fluid in our discs swishing back and we extend we see it swishing forwards and as we side bend we see it swishing to the opposite side. We do the same with the nucleus imagining that it is a ball floating in the water following the water’s path, rebounding off the walls of the annulus and returning to centre. To embody compression and decompression of our discs we bend and straighten our knees, imagining the wide disks as we bend and the tall disks as we straighten. When we twist we imagine our discs doing the same thing, compressing as we turn and re-plumping as we return.
Notice once you have finished how centred yet energised you feel after deeply experiencing the movement of your disks.