Some Steroid Injections Work Better Than Others for Back Pain and Here's WhySteroid injections into the epidural space have been used for pain coming from herniated discs as well as pain from spinal stenosis (narrowing of the spinal canal). This space is the area between the bony ring of the spine and the covering of the spine called the dura. The dura is the sac that encloses the spinal fluid and nerves of the spine.
When doing an epidural steroid injection, the doctor inserts a needle through the skin so that the tip of the needle is in the epidural space. The epidural space is normally filled with fat and blood vessels. Fluid such as the lidocaine and cortisone that is injected during an injection is free to flow up and down the spine and inside the epidural space to coat the nerves that run inside the spinal canal.
The steroid injection is an antiinflammatory combined with a numbing agent. The dual effect is to reduce swelling around the spinal cord or spinal nerves and stop painful messages from being sent to the brain.
Surgeons are fine-tuning the use of steroid injections to get the best results -- quick pain relief that is long-lasting. There are several openings in the bones that surround the epidural space where a needle can be placed. An epidural steroid injection can be performed by placing the needle in one of several openings. In this study, they compared the results of two different techniques used to administer the injection for two different problems.
Although the steroid injection has the same biologic effects on local cells and tissues, where it is injected determines what areas are bathed in the drug. For example, discs tend to push backwards, putting pressure on the spinal cord from the front or anterior epidural space. The logical place to inject the steroid mixture is in the area where the spinal nerves are being compressed irritated.
The best approach to steroid injection for the disc has been transforaminal. The needle is placed at an angle just underneath the pedicle in an area called the safe triangle. The pedicle forms a bridge of bone in the vertebral arch around the spinal cord. The surgeon guides the needle into the epidural space along this pathway using a special type of X-ray called fluoroscopy.
An alternate approach is the interlaminar technique. In this technique, the needle is placed between two spinous processes (the bumps along your back) or laminae (columns of bone that are part of the vertebrae) so that the injection spreads into both sides of the epidural space.
The interlaminar technique works well for spinal stenosis because the fluid goes into both sides of the epidural space. And usually the spinal canal is too small all the way around the spinal cord. The transforaminal technique only injects the steroid into one half of the epidural space. That works fine for herniated discs if the disc is pressing back and off to one side or the other.
In this study, they tried doing a transforaminal injection from both sides at the same time. In this way, it was possible to deliver the steroid into both sides of the epidural space. Patients with spinal stenosis or herniated disc were randomly placed in one of two groups: one group received steroid injection via the interlaminar approach and the other group received a steroid injection via the transforaminal approach. The patients did not know which type of epidural steroid injection they received.
A special dye was also injected into the epidural space to show just exactly where the steroid spread inside the epidural space. If pain was not reduced to a five or less (on a scale from zero to 10), the inection was repeated two weeks later.
The overall results showed that pain was less for those in the transforaminal injection group. And among the transforaminal group, a more significant improvement was seen in the spinal stenosis patients. Patients with herniated discs got the same benefit no matter which approach was used. When injected from both sides at the same time, the transformainal approach was a better choice for patients with spinal stenosis.
It's possible that the reason for this difference has to do with the amount scar tissue and fibrosis that's present in spinal stenosis compared with herniated disc patients. When placed bilaterally, the transforaminal injection allowed a higher concentration of steroid to reach the anterior epidural space.
The interlaminar technique is affected more by the soft tissues along the back side of the epidural space. There's hypertrophy (thickening) of the posterior longitudinal ligament and the bone in this area. The steroid fluid can't always get past these structures when injected from behind. This isn't a problem when the steroid is injected from the side (as with the transforaminal approach).
The authors state that patients with back pain from a disc herniation or spinal stenosis can benefit from steroid injections for short-term pain relief. The technique may not make as much of a difference in cases of disc herniation. But the transforaminal approach definitely works better than the interlaminar technique for patients with spinal stenosis.
Jung Hwan Lee, MD, et al. Comparison of the Effectiveness of Interlaminar and Bilateral Transforaminal Epidural Steroid Injections in Treatment of Patients with Lumbosacral Disc Herniation and Spinal Stenosis. In The Clinical Journal of Pain. March-April 2009.
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