Authored by MCN Neurologists
Low back pain is the evolutionary price that we humans have paid for going from a four-legged creature to an up-right, two legged one. And, it is an expensive price. A recent study places the costs – medical, surgical and lost income - generated by low back pain in excess of $90 billion a year. Low back pain is the most common reason for disability in individuals under the age of 45 years old. At some point during our lifetime, 80% of us will have had an episode of significant low back pain and, for 25% of us, the pain recurs within the year.
Sources of Low Back Pain/Lumbar Spine Disorders
An injury is the most common cause for low back pain. The injury may be significant, such as a fall, or trivial, such as turning or bending wrong. Sometimes no specific event triggers the low back pain. In this case, other causes, such as an infection or cancer, should be ruled out.
We have many structures in our low back, also known as the lumbosacral region, which can generate pain. Because most of these structures can produce similar types of pain, it is sometimes difficult to determine the exact painful source. Also, there may be multiple sources for the pain.
So what causes pain in the low back? While the pain generators are many, we can break them down into a few categories – bone, joints, disks, muscle and nerves.
Bones – Two bony structures of the lumbosacral region of the spine are the lumbar vertebrae and the sacrum. To be accurate, the bones themselves are pain insensitive; it is the periosteum, a thin membrane covering every bone of the body, richly supplied by pain sensitive nerves, that is the culprit. We have five lumbar vertebrae that are stacked on top of each other like napkin rings. You can feel the point of each vertebrae, called the spinous process, as a series of hard bumps lined up the middle of the back. The first vertebra (called L1) is located at a level just above the belly button. The fifth vertebra (L5) is located deep within the low back and rests on top of the second major bone of the back, the sacrum. The sacrum is actually a stack of fused vertebrae that roughly looks like an upside down triangle. The sacrum’s role is to attach the spine to the pelvis.
Joints – We need joints in the back to allow us to bend and twist, otherwise we would be ramrod straight and unable to turn or bend. Each vertebra is connected to the vertebrae above and below it by a set of paired joints, called facets. Like your knuckle joints, the facet joints are quite pain sensitive. Another joint in the low back, the sacroiliac joint (or SI joint) connects the sacrum to the pelvis. This joint does not have the mobility of the facets, but it is also supplied by nerves that produce pain.
Disks – An intervertebral disk is a, roughly, hockey puck-shaped cushion that sits between each vertebrae. A disk is constructed of an inner gelatinous core, surrounded by a tough fibrous shell with intersecting bands like a steel-belted radial tire. In a herniated disk, this inner gelatinous core extrudes through a tear in the outer fibrous shell and can press on the nearby spinal nerve root. Only the outer fibrous shell is pain sensitive. The purpose of the disks is to provide some movement to the back as well as provide a cushion for the spine. We name disks by the vertebrae above and below them. Thus, the L4-L5 disk sits between the fourth and fifth lumbar vertebrae.
Muscles – Muscles are a common, often overlooked source of pain, particularly with an acute back sprain injury. A muscle is a definite pain generator – think of a “charley horse” causing calf pain. Likewise, we have multiple layers of muscles in the back, any one of which can produce pain.
Nerves - The spinal nerve roots heading down to the legs to provide sensation and control of movement come from the spinal cord. When they start out, the spinal nerve roots initially run through the central opening of each vertebra, termed the spinal canal. The spinal canal is similar to the tunnel that you create when you stack several napkin rings on top of each other. At regular intervals, the paired spinal nerve roots leave the spinal canal through an opening created by stacking the vertebrae on top of each other, called the intervertebral foramina. The spinal nerve root can get pinched at this point by a herniated disk or bone spur, resulting in pain shooting down the leg (“sciatica”) and weakness in the leg.
How We Diagnose the Cause of Low Back Pain/Lumbar Spine Disorders
To determine what is causing the low back pain, the doctor needs information, such as the history (what you can tell the doctor about the pain), the examination (examining the back as well as how the nerves to the legs are working) and imaging (radiologic procedures – x-rays and scans), which allows us to look into the interior of the body. These imaging procedures have significantly improved our diagnostic accuracy, but each one has its own limitations. The most common procedures are plain x-ray, CT scans and MRI scans. Less common imaging procedures are myelogram and discogram.
Plain x-ray – An x-ray uses electromagnetic radiation focused on a specific body part, in this case the low back. As the x-ray beam passes through the body, more dense tissues such as bone, casts a shadow on an x-ray film or detector. Less dense tissues such as disks and nerves cannot be seen by x-ray. Consequently, only the bony structures in the low back – vertebrae and sacrum - appear on an x-ray of the back.
CT scan – The CT scan is an amazing advancement in x-ray technology developed during the 1970’s that combines multiple x-ray slices (tomography) with a computer (CT = computerized tomography) to allow us a detailed evaluation of, not only bone, but also soft tissues, such as disks and nerves.
MRI scan - Developed in the early 1980’s, the MRI scan is a quantum leap beyond CT scans to provide us with detailed images of the soft tissues of the body, such as disks and nerves. Unlike CT scans, the MRI does not use x-ray technology, but rather complex physics, by which the atoms of the body are aligned by a powerful magnet then subjected to radio waves which produce a change in their direction (resonance). Thus, MRI stands for magnetic resonance imaging. This information is fed into a computer, producing detailed images of the body.
Myelogram – Before the advent of CT scans, myelograms were the best way to look at the contents of the spine. In this method, x-ray dye is injected into the fluid filled space around the spinal cord and nerve roots in the spinal canal. Imaging of a disk or tumor can only be inferred by distortion of the contrast dye. These days, a myelogram is only occasionally done in combination with a CT scan, if the results by CT or MRI scan alone are not clear or equivocal.
Discogram - The discogram is a controversial procedure in which the suspected disks are injected with x-ray dye and x-ray or CT scans are taken. Proponents of this procedure feel that it provides unique views of the disk itself, as well as allows the patient to describe if injection of the disk reproduces their pain. Usually this procedure is done in anticipation of surgery to make sure the correct disk is treated.
Despite these wonderful technological advances that allow us to look into the interior of the body, abnormalities seen in the back are not always the cause of the pain. The problem is that as we age, certain changes normally occur in our spine that do not cause any pain. These changes include loss of water content of the disks, bulging of the disks, tears in disks, bone spurs – the list goes on. A radiologist seeing these changes will report them as being “degenerative” or showing “spine degeneration.” The unfortunate part of this terminology is that, patients told this by their doctor picture their back as disintegrating and falling apart. These changes are part of the natural aging process, just like wrinkles and gray hair. Multiple studies of normal, pain-free subjects have shown that with any imaging procedure used – x-rays, CT scans, MRI scans or myelograms – 25-80% of those individuals (the numbers increase with age) have degenerative changes in the spine, and even herniated disks. This means that just because an abnormality is present on a scan, it does not necessarily mean that it is the cause for the pain. Conversely, there are some causes of low back pain, such as muscle strain and facets, in which the images of the back are normal. Thus, the x-ray or scan is only one piece of information that the doctor uses to diagnose the cause of low back pain.
Treatment of Low Back Pain/Lumbar Spine Disorders
Low back pain treatment success lands squarely on having the correct diagnosis. Appropriate treatment depends upon what the doctor concludes is the cause for the low back pain.
Basically there are only two ways to treat lumbosacral pain – surgery or no surgery. Non-surgical treatment, termed conservative treatment, can be as simple as physical therapy to the back. In fact, studies have shown that up to 80-90% of individuals experiencing an episode of acute low back pain become pain-free by twelve weeks after onset of their symptoms. Medicines are another conservative way to treat back pain. Useful medications include muscle relaxants, anti-inflammatory agents and narcotic analgesics (pain-killers). Narcotic pain-killers, such as Vicodin, can be a slippery slope if the patient relies more and more on the pain-killer, especially if there are other extenuating circumstances such as depression, secondary gain issues and/or pending litigation.
Other non-surgical ways to treat low back pain include agents applied directly to the back, either in the form of a medicated patch containing an anesthetic agent or an anti-inflammatory agent. Another approach is to use an electronic device to deliver measured electrical impulses to the back, termed a TENS (transcutaneous electrical nerve stimulator) unit. This method blocks pain messages, but does not provide a “cure” for the problem.
A more aggressive non-surgical approach is to use injection therapy of cortisone and/or an anesthetic agent into various parts of the back, again depending upon the diagnosis. The injections can be within the muscles, into the joints (facets and sacroiliac) or around the spinal canal (epidural). Often these injections can be diagnostic – that is, if the pain goes away, even for a short time, after a facet injection, then that is the source of the pain.
Physicians commonly use more than one of these non-surgical approaches to treat low back pain. If these conservative measures fail, then the next step is to consider surgery.
The surgical treatment for low back pain depends upon whether or not there is something to operate on. For example, a patient with disabling back pain with severe pain down the leg and leg weakness who is found to have a herniated disk at the L4-5 level would benefit by surgical removal of the offending herniated disk. Sometimes patients who fail all conservative treatment will respond to fusion of two or more vertebrae. However, this approach takes a knowledgeable, skilled spine surgeon to sort out who would benefit from this type of surgery.
As a last resort, there are devices that may be implanted to provide pain control. Such devices include a pump that delivers narcotic analgesic, such as morphine, directly to the spine. Another device, the dorsal column stimulator, is an electronic stimulator, similar to the TENS unit, which is implanted directly onto the surface of the spinal cord to block pain messages.
Low back (lumbosacral) pain is a very common problem; most patients with low back pain will fully recover within three months after an acute onset. Successful treatment – surgical or non-surgical - of the offending pain generator such as bone, disk, muscle, joints or nerves, depends upon correctly identifying the cause of the pain. While imaging procedures such as x-rays and scans can be helpful, ultimately it is the doctor who identifies the cause of a patient’s back pain in the context of the clinical history, physical findings on the examination and imaging studies.
January 1, 2010
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