Background

The spinal cord runs within the bony structure of the vertebral column and is encased by a membranous sac called the dural sac. This sac contains spinal fluid that bathes and nourishes the spinal cord. The epidural space is the space between the outer surface of the dural sac and the bones of the vertebral column.

Nerves from the lower limb (including the sciatic nerve) enter the vertebral column and pierce the dural sac to reach the spinal cord. For various reasons these nerves can become irritated as they enter the vertebral column and cause pain in the lower limbs. This pain is felt as shooting down the lower limb and is referred to as nerve root pain or, technically, radicular pain (from the Latin radix, a root). The common name for this sort of pain is sciatica.

The term 'epidural steroid injection' refers to the injection of the corticosteroids into the epidural space of the vertebral column as a means of treating pain caused by irritation of the spinal nerves.

How does an ESI work?

There are two ways, in which it is thought that epidural steroid injections may work.

The first belief is that some leg pain involves the inflammation of one or more of the nerves, their covering, or their roots, in the back. The injection of steroids directly into the part of the spinal column called the epidural space is thought to aid in reducing this inflammation.

The other belief is that the corticosteroids act like a local anesthetic and block the pain long enough to allow the body to begin the process of repairing itself.

The chief effect of an epidural steroid injection is to reduce pain, but the effect is not long lasting and differs from person to person. Most patients will receive good relief for some weeks or up to three months after injection, but only a small portion obtain longer-lasting relief. Some patients do not experience any pain relief and may in fact suffer an increase in pain and/or other symptoms as detailed later.

How is an ESI administered?

A canula may be inserted into a vein prior to the procedure (see below). You will be asked to position yourself so that the vertebrae in your back are as widely spaced as possible. Local anesthetic will be injected into the skin and underlying tissues to decrease the discomfort of introducing the epidural needle.

Once the local anesthetic is working the epidural needle is advanced into the epidural space using the bones as landmarks and other technical aids to ensure that the needle is positioned correctly.

When the needle is in the epidural space, a syringe containing the corticosteroid solution is connected to the needle. After making sure that the needle is not in the blood vessel or in the spinal fluid, the doctor injects the solution slowly. The doctor will ask you to describe how you are feeling while the solution is being injected.

You may briefly feel pins and needles in the legs. You may get a headache. If the needle touches a bone you will feel a short local pain. You should tell your doctor about these feelings.

The corticosteroid will be injected in a form that may include a saline solution and/or a local anesthetic; however, the dosage and the volume of the steroid and the other components will vary according to the individual doctor's judgement.

What are the risks?

With any operation or injection procedure there are risks. In the case of epidural steroid injections these risks are small.

There are a variety of side effects and complications, most of which relate not to the steroid itself, but to the way the injection is given.

The most common side effect is a temporary increase in pain. It occurs in about one percent of epidural steroid injections and appears to be related to the volume of substance injected into the epidural space.

Headaches, another complication with an incidence of one percent, may be related to the accidental puncture of the innermost membrane, which surrounds the spinal cord. The headache is caused either by a leakage of the fluid surrounding the spine, or as a result of and accidental injection of air into the spinal fluid. In most cases the headache subsides within a few hours but sometimes it can persist for days, rarely for longer. In such rare cases, it may be necessary to repeat the epidural procedure, this time injecting some of the patient's own blood, taken from a vein in the arm, which forms a small clot allowing any punctures of the membrane surrounding the nerve root to heal.

If you are allergic to one of the additives in the steroid solution, you may experience a hot flush or develop a rash. However, this should get better within a few hours or days.

As with any injection through the skin, it is possible for bacteria to gain entry causing an infection. The risk of this with an epidural injection is very small.

It is also theoretically possible that a nerve could be damaged. In the procedure, the needle is inserted very slowly, and if the lining around the nerve was touched there would be pain in the leg. The doctor would then change the position of the needle slightly to avoid any risk of damage to the nerve.

Sometimes a patient's blood pressure falls at the time of the injection. If so, the doctor will insert a venous canula so that intravenous fluids or medication can rapidly control the blood pressure if necessary.

Certain other side effects may occur if the wrong amounts of local anesthetic or corticosteroid are injected into the epidural space or if the drugs are accidentally injected into the spinal fluid. These side effects are extremely rare if the procedure is properly performed.

The side effects include:

• fluid retention
• difficulty breathing
• swelling of the face or other
• parts of the body
• high blood pressure
• irritation or damage to the
• nerves of the pelvis or lower limbs

Repetitions

You are unlikely to benefit from a repeat epidural steroid injection if the first does not offer relief. It is unreasonable ever to undergo more than three injections if none has provided any relief. Even if epidural steroid injections provide relief, only in exceptional cases would more than three injections be justified within a three-month period.

The wisdom of repeating an epidural steroid injection should be seriously questioned if, as a result of any previous injection, your complaint has been made worse.

IF YOU HAVE QUESTIONS ABOUT THE PROCEDURE OR INFORMATION YOU HAVE JUST READ, PLEASE ASK THE NURSING STAFF OR YOUR DOCTOR WHO WILL BE MORE THAN HAPPY TO ANSWER ANY QUESTIONS YOU MAY HAVE.

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