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 limbs (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 a corticosteroid into the epidural space of the vertebral column as a means of treating pain caused by irritation of the spinal nerves.
How does an epidural steroid injection work?
There are two ways, in which it is thought that the 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 differs from person to person. Most patients will receive good relief for months after the injection. Some patients do not experience any pain relief and may, in fact, suffer an increase in pain and/or other symptoms as detailed later. The goal of your injection is to provide at least 50-75% relief so you can begin an appropriate exercise program and return to normal activities/work.
How is an epidural steroid injection administered?
You will be helped to position yourself on a special bed designed for these types of procedures. A Hep-Lock IV (intravenous catheter) will be inserted into a vein for the administration of any IV medication, if requested. Your doctor will inject local anesthetic 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 a fluoroscopy unit (a type of x-ray) to ensure that the needle is in the right place.
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 a blood vessel or in the spinal fluid by the use of a contrast agent, your doctor will inject the solution slowly and 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. 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 the form that may include a saline solution and/or a local anesthetic. The dosage and the volume of the steroid and other components will vary according to your doctor’s judgment.
What are the risks of an epidural steroid injection?
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 1% of epidural steroid injections and appears to be related to the volume of fluid injected into the epidural space.
Headache, another complication with an incidence of 1%, may be related to the accidental puncture of the innermost membrane, which surrounds the spinal cord. The headache is caused either by leakage of the fluid surrounding the spine, or as a result of an accidental injection of air into the spinal fluid. In most cases the headache subsides within a few hours but sometimes it can persist for a day, 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 puncture of the membranes surrounding the nerve roots to heal.
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. Bleeding is also a risk of this procedure, which is why you are counseled to stop taking aspirin products, anti-inflammatory products, and blood thinners.
Sometimes the patient’s blood pressure falls at the time of the injection. If so, your doctor will use the IV inserted prior to the beginning of the procedure to stabilize the blood pressure using intravenous (IV) fluids and/or medication if necessary.
You are most likely to experience the best relief with one or two injections. It is unreasonable to undergo more than two 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.
If you have any questions about the procedure or information you have just read, please ask your doctor who will be more than happy to answer any questions you may have. After your injection you should feel the same or better for the first 12 hours. Then the anesthesia will wear off and you may experience a return of your pain. The steroid will start working within three days of the injection with maximal effect by one week. If you are prone to fluid retention or have a history of heart failure, you should monitor your weight each day post procedure and call your doctor for a gain greater than three pounds. If you have glaucoma and experience blurred vision, call your doctor or your ophthalmologist. The steroid may give a flushed/red appearance to your skin and face, but this will subside over 1-3 days.
You should call your doctor if you experience a fever over 101 within 72 hours of the procedure.