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X-rays No Longer Needed to Guide Nerve Blocks
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Posted on: 12/10/2009
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Improvements in technology continue to change the way medicine is practiced. In this study from Japan, physicians used ultrasound instead of X-rays to guide a needle in performing a nerve block. The procedure was effective for 75 of the 78 patients in the study. And the method proved to be safe as no one felt pain during the procedure or had any negative effects from the treatment.
Switching from using X-rays to ultrasound when doing nerve blocks is possible now that today’s ultrasound machines produce high quality images. And the devices are small enough to be portable making the procedure available in a clinic rather than in the radiology department. Best of all, both patients and medical staff are no longer exposed to so much radiation from the previously used X-ray technique.
Nerve blocks are used for patients with chronic pain. In this study, the patients had a L5 radicular syndrome. L5 is the fifth lumbar segment of the lumbar spine (low back). Radicular tells us that the spinal nerve root that exits from the spinal cord at that level is compressed or irritated. This compromise of the nerve tissue sends pain from the back into the buttock and possibly down the leg.
The cause of the syndrome can be from a herniated disc, spinal stenosis, or spondylolisthesis. Most people know what a herniated disc is but spinal stenosis and spondylolisthesis may not be as familiar. Stenosis refers to a narrowing of the spinal canal where the spinal cord is located. Spondylolisthesis is the slippage of a vertebral body forward over the segment below it. This change in the spinal alignment can put a traction (pulling) or compressive (pinching) force on the spinal cord in the spinal canal and/or spinal nerve roots as they leave the spinal canal.
Pain messages are sent when there is pressure on the nerve tissue from any of these conditions. Applying electrical stimulation to the nerve identifies correct placement of the needle used to inject a numbing agent to stop pain signals from traveling up the spinal cord to the brain. The patient feels a tapping sensation that is not painful when the probe delivers an electrical stimulus around the nerve root. The probe is slowly pushed through the skin and soft tissues entering the spine near the L5 nerve root. At the same time, the multibeam ultrasound unit transmits pictures to a TV or computer monitor to guide the physician's forward advancement of the probe to the correct spot.
By using this ultrasound technique, the patient is spared the intense pain that accompanies the X-ray guided technique. With the X-ray technique, a dye is injected into the nerve (under the outer layer of the nerve) to help identify the exact location of the nerve and placement of the numbing agent. When the nerve is injected with the dye, the nerve endings register pain that is intense. Using an electrical probe eliminates the need to touch the nerve. The researchers also found that placing the injected numbing agent around the nerve root and not directly into it works quite well and is more comfortable for the patient.
The authors provide photos of the ultrasound-guided lumbar nerve block to give the reader an idea of what the patient set up looks like (patient position, location of probe/needle entry into the spine). There are also photos of the ultrasound images with labels to help viewers see what the surgeon sees.
Since L5 nerve root blocks are fairly common, replacing X-ray-guided methods with ultrasound and electrical nerve stimulation is a major breakthrough in pain management. The location of the L5 nerve deep in the spine has made it difficult to reach the nerve root in order to treat this syndrome. Injection without damaging other nearby soft tissues or puncturing the targeted nerve is a positive outcome of the ultrasound-guided technique.
Despite the many advantages of the ultrasound method, the author noted there were three patients who did not respond to the treatment. There was an anatomical reason for these treatment failures. These patients had a larger than average transverse process (a bony protuberance out to the side of the vertebral body). The size of the process made it impossible to get a needle into the proper area to numb the nerve.
Although ultrasound-guided nerve blocks do not utilize X-rays, the use of X-rays is not completely eliminated with nerve block procedures. Fluoroscopy (real-time, 3-D X-rays) is still required as a pre-scan before ultrasound-guided injection. The surgeon uses these X-rays to look for any anatomical variations in form or structure of the spine that could prevent accurate probe/needle placement. And the X-rays help the surgeon find the best spot for probe/needle advancement and placement.
Not everyone will qualify for the ultrasound-guided technique. Besides not finding a clear pathway to the nerve eliminating potential patients, obesity and osteoporosis (brittle bones) may also exclude some patients from benefiting from this treatment approach. But for the majority of patients who need a nerve block for lumbar radiculopathy, ultrasound-guided techniques may very well replace X-ray guided methods that are currently in use.
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References:
Masaki Sato, MD, et al. Ultrasound and Nerve Stimulation-Guided L5 Nerve Root Block. In Spine. November 15, 2009. Vol. 34. No. 24. Pp. 2669-2673.
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