The spine is an amazing structure which is actually incredibly strong and resiliant. It is made up of 24 vertebrae (bones) with a front (vertebral body) and back compartment (neural arch). Each pair of vertebrae is separated by an intervertebral disc. The disc is a very tough shock absorber that contains a high proportion of water. It holds the spinal segments together improving the flexibility and stability of the spine.
At the back of the vertebrae, the back compartment are the facet joints and the spinous processes. Each vertebra has 2 facet joint at the top and 2 at the bottom. These form the joints with the vertebrae above and below. These joints are important as they ‘guide’ the movement when bending forwards and backwards. The spinous processes are the ‘knobbly’ bits that you can feel running down your back. The bone of the facet joints and the spinous processes forms an arch. These arches when aligned one on top of the other, form the spinal canal. This canal is where the spinal cord sits.
There are also numerous ligaments which hold the bones together, as well as muscles, which give us dynamic support. They help to keep us upright, keeping the trunk in an optimal position, allowing us to function in the most efficient way.
The disc is the largest avascular structure in the body. That means it has a very poor blood supply. The cells in the middle of the disc are therefore a long way from the supply of nutrients and oxygen, which are both essential for the health of all cells.
The disc is essentially made of 2 parts, a tough outer wall made up of very tough, but stretchy fibres. These are laid down in layers, like the layers of an onion.
In the centre is a more jelly like substance. This contains a special protein which has great water attracting properties. The ‘jelly’ centre draws fluid into the disc, bringing with it oxygen and nutrients.
This happens mostly at night when the weight of the body and gravity are at their lowest. Every disc draws in some fluid, making each disc a little ‘fatter’. This is the reason we are all a little taller first thing in the morning.
As soon as we become upright, the downward pressure of gravity and the weight of the body start to squeeze fluid from the discs. This process happens more quickly if we spend long periods sitting. During the day, as we move the discs move. As we bend to touch our toes, the disc is compressed at the front, pushing out fluid and expelling waste products. At the same time the back wall of the disc is stretched, this stretching helps to maintain the elasticity of the disc wall. When we bend backwards it happens in reverse.
If, for whatever reason our backs become stiff, the compression and stretching of the disc wall doesn’t happen. If it is not stretched, the disc wall loses some of its elasticity. Eventually the wall is unable to stretch. Then at bedtime the ‘jelly’ centre tries to ‘suck’ fluid in, but the walls have stiffened and lost some of their elasticity. The ‘jelly’ is not able to absorb as much fluid as it did. Over time the disc gradually gets a little thinner. This means that the bones get a little closer together.