What Is An Epidural?

Back pain cause by a bulging disk

An epidural is an injection that delivers steroids directly into the epidural space. Sometimes a flushing solution (either lidocaine or normal saline) is also used to help "flush out" inflammatory proteins from around the area that may be the source of pain.

The epidural space is the space between the dura mater (a membrane) and the vertebral wall and is filled with fat and small blood vessels. It is located just outside the dural sac. The dural sac surrounds the nerve roots and cerebrospinal fluid (the fluid that the nerve roots are bathed in).

There are often inflammatory factors and other substances that generate pain (e.g. substance P) that are associated with lumbar disc herniation, and this inflammation can cause significant nerve root irritation and swelling.

Steroids (corticosteroids) have been shown to reduce inflammation by inhibiting the production of substances that cause inflammation, the epidural injection can be highly effective because it delivers the medication directly to the site of inflammation.

When Is An Epidural Typically Recommended?

In general, epidural injections are used to help provide pain relief to enable patients to progress with their rehabilitation. Individuals who have less pain and feel more comfortable are generally able to work on the active therapies – such as stretching, strengthening/pain relief exercises and low impact aerobic conditioning – that are critical in rehabilitating the lower back.

Several common conditions – including lumbar disc herniation, degenerative disc disease, and lumbar spinal stenosis – can cause severe acute or chronic low back and/or leg pain. For these and other conditions that can cause chronic pain, an epidural steroid injection may be an effective non-surgical treatment option.

How Is The Injection Performed?

An epidural steroid injection usually takes between 15 and 30 minutes. The patient lies flat on an x-ray table on their abdomen. Prior to the injection, the skin is numbed with lidocaine, which is similar to the novocaine that the dentist uses (a "local" anesthetic).

Many types of physicians perform epidural injections, including anesthesiologists, interventional radiologists, neurologists, physiatrists and surgeons. Using fluoroscopy (live x-ray) for guidance, the physician directs a needle toward the epidural space. Fluoroscopy is considered important in guiding the needle into the epidural space, as controlled studies have found that medication is misplaced in 13% to 34% of epidural injections that are done without fluoroscopy.

Once the needle is in the exact position, the steroid solution is injected. Following the injection, the patient is usually monitored for 15 to 20 minutes before being discharged to go home.

Sedation is available for patient anxiety and comfort. However, sedatives are rarely necessary, as the procedure is usually not uncomfortable. If a sedative is used, the patient will need to be monitored for a longer period following the injection.

Patients are usually asked to rest on the day of the epidural steroid injection. Normal activities (those that were done the week prior to the injection) may typically be resumed the following day.

What Are The Benefits?

The benefits of the epidural steroid injections include a reduction in pain, primarily in leg pain. Patients seem to have a better response when the injections are coupled with an organized therapeutic exercise program.

While the effects of an epidural injection tend to be temporary—providing relief from pain for one week up to one year—an epidural can be very beneficial for patients during an episode of severe back pain. Importantly, it can provide sufficient pain relief to allow the patient to progress with their rehabilitation program.

An epidural is generally successful in relieving pain for approximately 50% of patients. If a patient does not experience any pain relief from the first injection, further injections will probably not be beneficial. However, if there is some improvement in pain, one to two additional injections may be recommended.

What Are Potential Risks And Side Effects?

As with all invasive medical procedures, there are potential risks associated with lumbar (lower back) epidural steroid injections. Generally, however, there are few risks associated with epidural injections and they tend to be rare. Risks may include:

• Infection. Minor infections occur in 1% to 2% of all injections. Severe infections are rare, occurring in 0.1% to 0.01% of injections.
• Bleeding. Bleeding is a rare complication and is more common for patients with underlying bleeding disorders.
• Nerve damage. While extremely rare, nerve damage can occur from direct trauma from the needle, or secondarily from infection or bleeding.
• Dural puncture ("wet tap"). A dural puncture occurs in 0.5% of injections. It may cause a post-dural puncture headache (also called a spinal headache) that usually gets better within a few days. Although rare, a blood patch may be necessary to alleviate the headache.

Paralysis is not a risk since there is no spinal cord in the region of the epidural steroid injection.

In addition to risks from the injection, there are also potential risks and side effects from the steroid medication. These side effects from an epidural steroid injection tend to be rare. Side effects from steroids are more common when taken daily for several months. Risks and side effects may include:

• A transient decrease in immunity
• High blood sugar
• Stomach ulcers
• Severe arthritis of the hips (avascular necrosis)
• Cataracts
• Transient flushing 
• Increased appetite.

Lumbar epidural steroid injections should not be performed on patients who have a local or systemic bacterial infection, are pregnant (if fluoroscopy is used) or have bleeding problems. Epidurals should also not be performed on patients whose pain is from a tumor or infection, and if suspected, an MRI scan should be done prior to the injection to rule out these conditions.

Injections may be done, but with extreme caution, for patients with allergies to the injected solution, uncontrolled medical problems (such as congestive heart failure and diabetes), and those who are taking aspirin or other antiplatelet drugs (e.g. Ticlid, Plavix).

How Frequently Can Epidural Steroid Injections Be Performed?

There is no definitive research to dictate the frequency of epidural steroid injections for low back pain and/or leg pain. In general, it is considered reasonable to perform up to three injections per year.

Typically, epidural injections are done in two-week intervals. However, there is no general consensus in the medical community as to whether or not a series of three injections need always be performed. If one or two injections lessen the patient’s low back and/or leg pain, some physicians prefer to save the third injection for any potential recurrences of back pain later in the twelve-month period.