This month's column focuses on the use of what are called "blocks" to diagnose and treat the source of spinal pain, the pain generator.

A "block" is a procedure in which a surgeon positions a needle—most commonly guided by an x-ray fluoroscope—near a structure (e.g., a nerve) that the surgeon believes is the source of or mediating the pain. The surgeon then injects a local anesthetic to numb the nerve or "block" its function. He or she then monitors the effect of the block to determine if a patient achieves pain relief.

Diagnostic Injections
During the past two decades, x-ray guided diagnostic injection techniques have been developed to identify pain generators, especially in cases of chronic lower back pain (LBP). Discovering the site of pain helps physicians understand the reason for a patient's pain and aids his or her ability to treat the pain. At one time or another, every structure in the lower spine area has been known to cause LBP.

Your physician may use certain medical terms related to performing the block that may be confusing. Understanding what terms like radiculopathy, radicular pain and neuropathic pain mean may help you better understand the procedure. Radiculopathy is due to abnormality within a nerve root, and may cause numbness, weakness, and reflex loss; however, radiculopathy does not actually produce pain. Radicular pain, however, arises as the result of irritation of a spinal nerve or its roots. Neuropathic pain is a result of damage to or irritation of neural structures in the central, peripheral, or autonomic nervous system, but not due to damage to nerve endings.

Many structures may be a source of spinal pain including the vertebrae, the intervertebral discs, spinal cord, nerve roots, facet joints, ligaments, muscles, and sacroiliac joints. Using diagnostic blockade, researchers have determined the most common proven sources of LBP are facet joints, the lumbar disc, and the sacroiliac joint. Muscles and ligaments have been the most reported sources of LBP in the literature; however, muscle sprain, spasm, imbalance, trigger points and pain originating from various ligaments are less likely to be proven as sources of pain. Currently, researchers and physicians focus their clinical time and effort on pain related to facet joints, intervertebral discs, dura mater (the covering over the spinal cord and nerve roots), muscles, and ligaments.

Using Diagnostic Blockade to Identify the Source of Pain
Physicians use diagnostic blockade to determine which structures are the source of or contribute to a patient's pain. Determining the source allows doctors to recommend treatments that will address the cause of the pain. Diagnostic blockade often is used to correlate findings on other diagnostic studies such as X-rays, CT scans or MRI scans, with a patient's pain complaints. If your physician can identify the nerve going to the structure involved in the pain, then he or she can temporarily interrupt the nerve with a local anesthetic precisely placed to block neuronal transmission. This then indicates whether that structure or nerve is functioning as the source of pain or involved in the pain-generating pathway. Occasionally, your physician may deliberately provoke the pain using diagnostic block tests (e.g., discography) to determine the role a structure plays in producing symptoms. Common diagnostic block tests are joint injections, nerve root injections, and discograms.

Using Therapeutic Blockade to Treat Pain
In order to successfully treat your lower back pain using therapeutic blocks, your physician first must accurately identify the pain generator using diagnostic blocks. Focused diagnostic blockade may help your physician determine which structures (e.g., nerves, discs) to address with more therapeutic interventions. Therapeutic blockade utilizes larger volumes of anesthetic and possibly anti-inflammatory steroids.

Epidural steroid injection (ESI)
Steroid hormone has been used for therapeutic blockade more than any other substance. Physicians have injected various steroids into the epidural space (the space between the covering over the spinal cord and the overlying bone and ligaments) or along individual nerve roots to treat pain for almost 50 years. The rationale for this treatment is that one of the primary pain generating processes in the low back is inflammation in various structures within the spinal canal. The major benefit of steroids is their powerful anti-inflammatory effect. Additionally, steroids may have an effect on nerves similar to local anesthetics. There is no question that many patients find pain relief from epidural steroid injections (ESI). Epidural steroid injections most commonly are recommended for the relief of acute radicular (nerve root) pain. Such injections are more controversial when used to treat chronic low back pain. The success of the procedure depends on delivery of the medication onto the pain-generating area. The most accurate way of assessing the spread of the medication is by using an X-ray control. This is the recommended standard for this procedure by Medicare.

Therapeutic facet joint injection
Numerous other areas in the back can be treated with therapeutic blockade. One of the most commonly used therapeutic block techniques is facet joint injection. Facet joints are the joints that connect one vertebra to the next. These joints guide and allow for movement. They can become quite painful in certain situations. Researchers estimate that facet joints play a role in chronic back pain 7% to 75% of the time. Long-term benefit of therapeutic facet joint injection (i.e., greater than six months) is debatable, but relief has been reported in up to 63% of cases. For this technique, physicians inject anesthetic and steroid medication into the joint or the ligament capsule around the joint using an X-ray to guide the position of the needle.