I have a degenerative disc disease. Is my spine really that old?
There are numerous factors that contribute to disc degeneration, of which ageing is only one component. Other factors include, disc nutrition, mechanical forces (including compression, torsion and vibration), toxic factors, metabolic and genetic factors. As can be seen, degeneration is not only an ageing process but can have many underlying factors which we can try and influence or reduce.
In a healthy disc there is a continuous process of disc hydration, which means that the water that makes up the majority of the gel like nucleus pulposus is pushed out and reabsorbed as stresses are placed on the disc. If anything effects this balancing process, it leads to a dehydration of the disc and, as such, the disc will loose some of its core characteristics like shock absorption and joint function. However, it is not only the gel like inner substance that can be effected, but also the outer fibres of the annulus as well as the 2 vertebral end plates.
An adult intervertebral discs is the largest avascular tissue in the human body, with the cells at the centre of the disc being up to 8mm away from the nearest blood supply. As such, the disc is vulnerable to any changes to the blood supply that provides oxygen and nutrition to the disc and helps in recovery. Most of this blood supply comes from the vertebral end plates above and below the disc.
Father time moves slowly forward and we all undergo the ageing process. Time, therefore, also effects what is happening to all our processes on a cellular level. The rate at which the body produces the vital proteins (proteoglycans) starts to slow down, especially in the outer annulus fibres. These proteoglycans are also smaller and less aggregated. This leads to a decrease in the cells ability to reabsorb water and thus loosing some of its hydration and function.
Three main forces have a direct impact on the disc: compression, torsion and vibration.
Compression is the most obvious force influencing the disc as this is its main function. In fact, loading of the disc is healthy and helps stimulate normal disc metabolism – a reason physiotherapists love to give weight bearing exercises! The problem comes in when we start to overload the discs, especially the lumbar discs. Prolonged or repeated excess compression can damage the vertebral end plates, causing inflammation and scar tissue or callus formation. We have seen that the disc gets most of its blood supply from here and this leads, unfortunately, to impaired nutrition and healing.
Torsion is when we apply a rotation force to the discs. When we rotate our spine, half of the circular fibres of the annulus are put under tension as the other half are slackened. If we get excessive rotation, especially when we twisted and bend at the same time, the fibres can tear. This leads to a weakend outer layer that can predisose the disc to further damages.
Vibration is the one mechanical force we tend to forget has a role to play in degenerative disc disease. This is often seen in pilots and long distance drivers and occurs at frequencies of 4-6 Hz. This can have an effect on the compression of the end plates as well as influencing normal cell nutrition and metabolism.
Nicotine is the biggest toxic factor involved in degenerative disc disease. Smoking can decrease the amount of oxygen carried in the blood, supplying less to the tissues of the disc and slowing normal recovery. It can slow down the production of the vital protein and collagen production needed to keep the annulus fibres strong, thus leading to increased oppertunities for a disc bulge or herniation
- Metabolic and genetic factors
Metabolic conditions, such as diabetes, can also contribute to degeneration of the disc and can occur via many different pathways. Firstly, the blood supply can be compromised due to changes in the circulation process. Secondly, the effect the sugars can have on the formation of the proteoglycans and collagen fibres changes the normal metabolism of the disc and can slow the healing and recovery process required after we load our spine normally throughout the day.
When it comes to genetic factors, twin studies have shown us that there may be a hereditary component to degenerative disc disease. Mostly, the proposed way that genes may encode how the make up of the cellular substance is set up. This predisposition is worth to keep in mind during the assessment.
All these factors may sound daunting, but it also allows us to change and prevent so much. A well hydrated and healthy disc allows the compression and rotation we need to work and play, even to the extremes of running, jumping and picking up weights. Any changes that occur due to the factors described above can cause a loss of disc height and also mobilty. These changes can lead to irritation of the nerves around the disc and cause inflammation and pain. Loss of mobility can also be seen as we cannot touch our toes or reach up to the roof to change a light bulb. All this can lead to irritation of the surrounding muscles causing spasm and pain.