The Lumbar Disc - Lumbar Spine Anatomy

I think the lumbar 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 discs.

X-Ray of a lumbar spine - side view

lumbar disc anatomy
X-Ray of a lumbar spine showing the space that a lumbar disc would occupy


In Western society we fear this structure. We think its a real area of weakness in the lower back, we worry that it will slip about and cause a pinched nerve (sciatica). Worse than that we think that it can happen at any moment, that it is just waiting to slip right out if we make the wrong moves.

spine diagramNearly all of us have got a story to tell of someone we know whose disc slipped, when he was getting the shopping out of the car for example..

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). However, the nucleus becomes flatter and contains less water as we age, this is normal.

Diagram of human spine

  • 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.

I have made a slideshow to explain the difference between disc bulges and herniations (prolapses) here.

However, only 5% of people with lower back pain will have a problem with their spinal disc. Most people with back pain have got the more common simple lower back pain.

Why do so many of us worry about 'slipping' a lumbar disc?

Simply calling the problem a slipped disc imediatly creates a worry. the idea that something could slip about is alarming and makes lose confidence with movemnet if we have this problem.

If you have ever seen anyone with a real lumbar disc bulge causing sciatic pain then you will know that it really, really hurts. The pain can be excruciating, it often interferes with sleep and it may knock you flat for several weeks. If you have had it or seen someone in pain with it you won't forget it. The experience can be dramatic and alarming and I think this increases our fear of the problem.

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 may make us feel like we have really slippy, vulnerable backs.

The bottom line is that disc bulges are rare (less than 5%) and if you do have one you need to gently get moving as soon as you are able. Your doctor or physiotherapist will guide you in your recovery.

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