In the lower back each lumbar vertebra is separated from the one above and below by a disc.
These tough structures are designed to cushion and shock absorb between the vertebrae.
The disc is made up of tough rings of cartilage (the annulus fibrosis) surrounding a softer central area (the nucleus pulposis).
A bulging lumbar disc is caused when the tough outer rings weaken, allowing the softer centre to shift backwards, usually more to one side then another. This shift in the centre creates a bulge in the outer wall of the disc.
This bulging disc can squash or 'pinch' a nerve but more often it causes swelling and inflammation of the nerve which can cause pain. I don't like to use the terms ‘pinched’ or ‘trapped’ nerve very much as often the nerve may be just swollen,irritated and sore.
Many of us will have lumbar disc bulges that show up on scans and we may not even know we had a problem. Very few of us will have symptoms from them, in fact less than 5% of people with lower back pain will have trouble because of lumbar discs.
A bulging lumbar disc causing irritation of the sciatic nerve
A disc herniation or prolapse is where the softer middle bit of the disc breaks through the wall of and escapes out through the tough outer layer.
A lumbar MRI scan showing a disc prolapse
A slipped disc is a layman's term for either a bulge or prolapse (herniation). The disc can't slip as it is firmly attached at the top and bottom to the vertebrae above and below.
So, even if someone has told you that you have a slipped disc, remember your discs can't slip anywhere, although they can bulge or herniate and can cause a lot of pain.
The spinal cord runs down through the centre of the back and branches out at each vertebra. These branches are called nerve roots. They leave the spine and bundle together to make larger nerves in your arms and legs.
The biggest nerves in your legs are the sciatic nerve a the back and the femoral nerve at the front.
Lumbar disc bulges and herniation's really only cause pain if they irritate one of these nerve roots, usually the roots that bundle together to make the sciatic nerve. This is what people commonly call a pinched nerve in the lower back. The medical term is radiculopathy.
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When the disc bulge is irritating a nerve root that forms part of the sciatic nerve it can be very painful and distressing. These are the most common symptoms:
Sciatic Nerve Pain is often felt in the leg
Many of us have bulging discs and we don't know it, this tells us that some changes to the disc are normal.
It is unclear why some people are unlucky enough to have a disc bulge that irritates a nerve and causes pain - while the rest of us are happily walking about with bulges and completely unaware of it.
As we age the disc becomes flatter and thinner as the discs ability to hold water gets less and less. In younger people the disc tends to be fatter and taller as it contains more water and so is a little more common to get sciatica from a disc bulge if you are younger (<50).
How it starts varies enormously.
I saw someone recently who had sciatica immediately after lifting golf clubs out of the boot of his car (bending and twisting).
Usually a nerve root irritation from a bulging disc starts with pain, often building in intensity over 24-48 hours. The pain can be very severe and distressing.
Disc problems causing sciatic nerve pain or sciatica are much less common than non specific or simple cause of lower back pain. In fact less than 5% of people with back pain have this as a problem.
I have put together some useful tips and suggestions in this sciatica home treatment section that you may find helpful.