The Spinal Disc
I think the spinal disc is possibly the most misunderstood part of the human spine! Hopefully, this page will put that right and restore its reputation.
The spine is made up of large bones called vertebrae. Each vertebra is separated from the next by a disc. Check this page on the human spine for a closer view of a vertebra.
X-Ray of a human spine - side view
In Western society we fear the lumbar disc. We think its a real area of weakness in the lower back, we worry that it will slip about and cause a trapped nerve (sciatica).
Worse than that we think that it can happen at any moment, that the disc is just waiting to slip right out if we make the wrong moves.
Nearly all of us have got a story to tell of a Mr so and so down the road whose disc slipped, when all he was doing was getting the shopping out of the car...etc etc
The truth is very different. These spinal discs are very tough structures that are composed of rings of different tissue.
- The outer area of the spinal disc is called the annulus. It is made up of circular rings of strong, elastic tissue called cartilage.
- If you look at a spinal disc from above with a microscope it would look a bit like a tree trunk cut in half, with circular rings moving outward from the centre.
- In the middle area there is a slightly softer area called the nucleus. When we are young this nucleus contains lots of water (especially in the mornings - this is true!). However, the nucleus becomes flatter and contains less water as we age, this is normal.
- In the lower back the discs are fatter and larger than elsewhere in the spine, helping them to act as very good shock absorbers between the different vertebrae.
- Spinal discs are firmly attached to both the vertebra above and below.
Although many people use the term "slipped disc" in fact it can't slip anywhere as it is solidly fixed top and bottom. Occasionally, discs can bulge and cause inflammation of a nerve, even less often the softer, middle area can leak out (called a prolapse). this can be a bit more serious.
However, only 5% of people with lower back pain will have a problem with their spinal disc. Not that many at all. Most people with back pain have got the more common simple lower back pain.
So why do so many of us worry about slipping a disc?
I'm not really sure but I suspect its got something to do with two things.
1. If you have ever seen anyone with a real disc bulge causing sciatic pain then you will know that it really, really hurts. The pain is excruciating, it interferes with sleep, often knocks you flat for several weeks. If you have had it you won't forget it, and if you have seen someone with it you won't want it either. The experience can be pretty dramatic and I think this increases our fear of the problem.
2.I think more importantly, disc bulges are common findings with age. If you scan a group of normal, back pain free people, lots of them will have disc bulges. Our reliance on scans and tests and the way they are often interpreted, I think, makes us feel like we have really slippy, vulnerable discs.
More on tests for lower back pain , including MRI scans, here.
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Lower Back Pain Toolkit Home Page
04-Jul-2008
