Epidurals: Procedure, Benefits, and Risks

Epidural injections are used to treat radicular pain (also known as sciatica) to produce long term pain relief.

The Epidural space
The spinal cord is enclosed within a sac of fluid known as the dural sac. The epidural space is the space between this dural sac and the bony vertebral column. The epidural space is an important space where medicine can be delivered close to the spinal nerves.

When an epidural is used
Doctors will look for disc prolapse or scarred nerve root pain symptoms when deciding to use an epidural. This kind of pain typically presents as a shooting or electric shock-like pain down the leg. Commonly known as sciatica, this is called radicular or nerve root pain by doctors.

Epidurals are also occasionally used for other types of pain in the leg, known as referred pain, which may be of a deep dull aching quality. Occasionally, they are also used for acute attacks of low back pain (lumbago) when conservative therapy is not effective.

Caudal Epidural injections
When a pain relief injection is performed near the tail bone, it is known as a Caudal epidural injection. Caudal epidural injections are given close to the tail bone through the caudal opening and the fluid travels up the spinal canal to the target area.

Transforaminal Epidural injections

In this instance, the needle is aimed under X-ray or CT guidance directly between the nerve root and the corner of the disc. The main advantage of this technique is a greater concentration of therapeutic agent at the site of nerve compression.

What an epidural injection can do for your pain:

1. Making an accurate diagnosis
A transforaminal epidural injection can help to confirm the diagnosis of radicular pain, as well as confirm the level of nerve compression.

2. Anti-inflammatory action
It is widely accepted that a prominent cause of sciatic pain is the inflammation that has arisen from an injured disc. An epidural injection not only flushes the area with local anaesthetic, but also introduces cortisone, which is a steroid based anti-inflammatory agent.

3. Stretching of scar tissue or adhesions
One of the body’s responses to a disc injury is the formation of new tissue. Adhesions are bands of tissue that can form between the disc and normal structures in the back such as the lining of the spinal cord and nerve roots. The injection may act by breaking down these adhesions. The injection acts like a hose of water being squirted into a blocked pipe in an effort to shift the blockage.

4. Breaking the pain cycle
After an injury, changes in the electrical activity of the spinal cord occur. Occasionally this causes normally innocuous messages travelling into the spinal cord to be interpreted as pain. It is thought that local anaesthetics temporarily block these abnormal messages, which in turns helps to break the pain cycle. By blocking the pain the muscles can relax which is an important step to start the healing process.

Method of injection:
The injection is best performed under X-ray or CT guidance to improve accuracy. Additionally, contrast material is injected to enhance the x-ray image, ensuring the injection goes into the epidural space to the desired level and to prevent injection into small blood vessels.

What happens after the injection?

You can return to gentle activities immediately after the injection. The outcome of the intervention is the same regardless of what you do immediately after injection. The next day you can resume light activity including return to light work. It usually takes 7-14 days for the full effects of the injection to work.

Injection Side Effects
During the procedure itself the most common side effect is the temporary increase in pain in the back or leg. Allergy to the local anaesthetic is possible, but rare, and any known allergies should be mentioned to the doctor.

The injection is done slowly because this minimises the chances of side effects. However, it is not uncommon to feel short-term light-headedness, headaches, or nausea. The anaesthetic causes the legs to become tingly and a bit numb for periods of up to 1-2 hours. You may feel weak and unsteady for up to an hour afterwards, and for this reason it is essential to have another person drive you home. (Note that accident insurance would be ruled invalid if the person who had just been injected was the driver in an accident.)

As with any injection through the skin, it is possible for bacteria to gain entry causing an infection, but again this is very rare.

Injection Risks
There are risks with any injection. In this case, the risks fall into two main categories: those associated with the injection itself, and those associated with the use of cortisone or steroid.

The risks with the caudal approach to epidural injections are minor because the needle is not inserted near any of the vital spinal structures. Within the caudal epidural space are several veins, and injection into these veins may produce sudden onset of dizziness or light-headedness. This should be reported immediately to the doctor.

Intra vascular injection via the transforaminal approach has the small risk of blockage of the small blood vessels supplying the spinal cord, which could lead to spinal cord damage. Your doctor will take every possible precaution to prevent intra vascular injection.

There is also a small risk of the needle puncturing the spinal fluid sac. This would cause total temporary numbness in the legs and may produce a headache afterwards.