Lumbar epidural

Behind the body of each vertebra is an arch of bone called the lamina. The arches form a channel called the vertebral canal. The spinal cord runs down the vertebral canal from the brain, protected by the bony arches.

Spinal nerves run out from the spinal cord through gaps between the arches. These are the nerve roots. They run to different levels in the trunk, arms and legs. The lowest spinal nerves run to the buttocks and bladder.

The spinal cord only runs part way down the spine. It stops at the level of the lowest ribs. Below this spinal nerves run down the vertebral canal to the correct gaps between the arches. These nerves packed in the canal look like the tail of a horse and are called the cauda equina in Latin.

The spinal nerves and cord carry feeling impulses from the body up to the brain and impulses from the brain down to the muscles.

What is a lumbar epidural?

The lower back is called the lumbar spine. Epidural injections into the lower back are used to treat a number of different painful conditions. The condition most often treated is pain in the leg, called sciatica. Sciatica is caused when problems in the spine cause pain to radiate down the leg.

The injections are usually given into the back. The needle is inserted between the gaps of the vertebrae, into an area known as the epidural space. This is a space that surrounds the spinal cord. The nerves that carry painful sensations pass through this space. The injection is just outside the covering of the spinal cord, which is called the dura; hence the name epidural.

An epidural injection can target the painful area. The injection bathes the nerves and intervertebral discs in local anaesthetic and steroid solution. Only a small amount of steroid is needed and it will not cause any of the side effects sometimes associated with taking steroid tablets. They are not the same kind of steroids that athletes may take. This steroid injection relieves pain and inflammation. Leg pain (sciatica), caused by inflamed nerves in the lower spine, can be treated in this way. Bathing inflamed discs in this way may also reduce some low back pain.

What has gone wrong?

You have suffered general wear and tear or damage from an injury, to the intervertebral discs in your spine. When the disc is inflamed, the nearby nerves can become irritated. These nerves supply sensation to the leg and hence the brain is fooled into believing that the leg is injured. This is not the case; although you may feel leg pain the problem is in the spine.

The aims

The aim of the procedure is to reduce the inflammation of the disc. This in turn reduces the leg pain and some of the lower back pain.

The benefits

Your pain should be reduced and you should be able to move around more easily. You can then exercise to prevent the problem happening again. If successful, this treatment can avoid the need for surgery.

Are there any alternatives?

By the time you consider a lumbar epidural you should have already tried other more simple treatments. These include rest, painkilling and anti-inflammatory tablets, and physiotherapy with exercise.

You may also have tried a transcutaneous electrical nerve stimulation (TENS) machine for your pain. This works by sending soothing pulses across the surface of the skin and along the nerve fibres. These pulses prevent pain signals from reaching the brain. They also stimulate your body to produce higher levels of its own natural painkillers, called endorphins.

What if you do nothing?

If you do nothing there are several things that may happen:

• With time and rest the inflammation and pain may settle on its own

• The pain and difficulty in moving around may remain the same

• The pain may get worse

• The disc may become further damaged and injure the nerves that control movement. You may then develop weakness and difficulty in moving your legs. Some of this may become permanent

• In rare, but severe cases, you may lose control of your bladder and bowels. The nerves that control these are in the same area of the spine and can be damaged by an inflamed disc

Who should have it done?

The following groups of patients should have the procedure done:

• Patients with leg pain caused by inflamed intervertebral discs

• Patients with low back pain that has not settled by other means

Who should not have it done?

Each patient has the final decision as to whether to proceed or not. If you are unhappy about the procedure for any reason you should not continue.

There are specific medical situations when an epidural should not be done and they are as follows:

• When a patient is on medication that prevents blood from clotting, such as warfarin. This would lead to more bleeding than normal. It may be possible to stop the medication a few days before the procedure. This will need to be discussed with your doctor

• When a patient is suffering from an illness that prevents blood from clotting, such as haemophilia. This would also lead to more bleeding than normal

• When there is infection of the skin over the site where the needle needs to be put in

• When the patient has a bloodstream infection

• When a patient has noticed a recent worsening of their symptoms, especially weakness and loss of bladder or bowel control

Author: Dr Sean White FRCA. Consultant in pain and anaesthesia.

© Dumas Ltd 2006