Slipped disc

Reviewed by Mr Dai Rees, consultant and orthopaedic surgeon and Dr John Pillinger, GP

What is a disc?

The spine is made up of the vertebrae (the bones making up the spine), which have cartilage discs between them.

The discs consist of a circle of connective tissue with a central gel-like core. This makes the spine flexible and at the same time acts as a protective buffer.

In the centre of this column of vertebrae and discs is the spinal canal, which contains the spinal cord stretching from the brain-stem down to the first or second lumbar vertebra. It continues as a bundle of nerve fibres called the cauda equina stretching down towards the sacrum, which is the extension of the spine. Between each vertebra, the spinal cord has nerve root connections to other parts of the body.

The spine is divided into three parts:

neck (cervical vertebrae)

chest (thoracic vertebrae)

the lower back (lumbar vertebrae).

The spine is connected to the ribs at the chest.

What is a slipped disc?

A slipped disc is when the soft part of the disc bulges through the circle of connective tissue. This prolapse may push on the spinal cord or on the nerve roots. However, it is worth noting that 20 per cent of the population have slipped discs without experiencing any noticeable symptoms.

The term 'slipped disc' does not really describe the process properly - the disc does not actually slip out of place, but bulges out towards the spinal cord.

What is the cause of a slipped disc?

A slipped disc occurs due to the breaking down of the circle of connective tissue with advancing age. This causes a weakness allowing the soft part to swell.

Slipped discs most often affect the lower back and are relatively rare in the chest part of the spine.

It is possible that hard physical labour can increase the likelihood of a slipped disc. They are also occasionally seen following trauma such as an injury from a fall or a road traffic accident.

At what age can a slipped disc occur?

A slipped disc in the lower back is most often seen between the ages of 30 and 50. In the cervical vertebrae around the neck, slipped discs are most often seen between the ages of 40 and 60.

What are the symptoms of a slipped disc?

A slipped disc can be symptom free. If it causes pain, it is primarily due to the pressure on the nerve roots, the spinal cord or the cauda equina.

Symptoms of nerve root pressure Paralysis of single muscles, possibly with pain radiating to the arms or legs. There may also be a disturbance of feeling in the limbs.

Symptoms of pressure on the spinal cord

Disturbance of feeling, muscle spasms or paralysis in the part of the body below the spinal cord pressure. For example, pressure on the spinal cord in the chest area will cause spasms in the legs but not in the arms.

Pressure on the spinal cord may cause problems with control of the bladder.

Symptoms of pressure on the cauda equina

The symptoms can include loss of control of the bladder function, disturbance of feeling in the rectum and the inside of the thighs and paralysis of both legs. These are serious symptoms and anyone developing them should contact a doctor immediately. (They are so-called 'red flag' symptoms.)

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