Epidural Injections and Back Pain

An epidural injection involves inserting a needle into the back between 2 vertebrae. The needle can be advanced to the space between a long spinal ligament (the Ligamentum Flavum) and the tough material that lines the spinal canal (called the Dura). As you can imagine, a certain amount of technical skill is required to place the needle just right, missing bone, blood vessels and not going into the spinal canal. That could cause problems. A caudal injection is exactly the same thing except the needle is inserted through a small space in the sacrum not far above the tailbone.

The space that is aimed for is called the epidural space. Only the layer of tissue called the Dura separates the space from the spinal canal that contains the spinal cord and a watery liquid, cerebrospinal fluid (CSF). The most commonly injected substance into the epidural space is local anesthetic, the same kind of drug your dentist uses to freeze your teeth. Epidural injections of local are a kind of nerve block that freezes more than one nerve.

We have learned how to fine tune injections of local into the epidural space. Inject a little and there may be relief from labor pains. Inject enough and everything below and a bit above the site of injection is frozen to the point a patient can’t move her legs or feel any pain during a C-section. While there are serious potential risks, epidural injections are routinely used for labor analgesia and treating chronic pain. I recall from my training days that the rate of death or permanent nerve damage from epidurals was a lot less than the risk of dying from pregnancy.

In back pain, cortisone, with or without local has been used on the assumption that certain kinds of back and leg pain were the result of some kind of inflammatory process. It was thought that when herniated discs were in contact with nerve roots (as in true sciatica), there was local inflammation that cortisone would reduce. This would then lead to a prolonged decrease in pain.

The problem is that there has not been much research on the effectiveness of epidural and caudal injections for pain and what research there is has not been all that positive. For what it’s worth, my clinical experience of administering epidurals for chronic pain for the past 20 years has not been very impressive either. Most people get some immediate pain relief but for the majority it does not last long enough to make this kind of treatment practical or worth the risk.

Some studies have shown that epidural cortisone with local anesthetic may lead to relief for pain related to herniated discs but 3 months after the injection there are no differences between patients who get the injection and those who do not. Spinal stenosis is a condition where narrowing of the spinal canal causes leg pains while walking. As a trainee anesthesiologist I was taught that it might respond to epidural cortisone. However a recent review of the research literature showed that it makes no difference in outcome if cortisone is added to the local anesthetic or not. For other kinds of back pain there is no good evidence or even a good theory to support the use of epidurals. I personally would not use these injections for mechanical back pain no matter what the MRI showed.

As is the case with other nerve blocks for chronic pain, there are too many unanswered questions about epidurals (and caudals) for us to predict with confidence how they might affect someone’s pain. While some people may experience good relief for a while, many if not most do not get the kind of relief that would justify long term repeated use. We still do not know why there are such varying responses.

So, my advice is that patients should know exactly what kind of pain an epidural is supposed to treat and ensure that the doctor performing the injection is adequately trained (and has emergency equipment immediately available). Anesthesiologists are generally the best trained for this procedure. If pain is restricted to the back only, there is little reason to consider an epidural in my opinion. Although lack of evidence is not the same as evidence against, I believe we should be conservative and cautious when contemplating epidurals for back conditions.