Understanding Low Back Pain

By David Borenstein, MD

About 80 percent of the world’s population has had a back problem; looking at back pain over a lifespan, women are affected a bit more than men. This means that, more likely than not, you are going to experi­ence this problem in your lifetime.

In most circumstances back pain resolves gradually over time. In fact, about half of back pain episodes are resolved in about a week, and 90 percent are resolved in two months’ time. In the remainder of instances, pain continues for weeks or months after the initial onset of backache.

Is there a way to prevent an episode of back pain? If you do develop low back pain, is there a way to relieve it and get better? This article will help you understand the common causes of back pain, what you need to do to resolve the problem, and what you can do to prevent an episode.

Common causes of back pain affect parts of the spine in dif­ferent ways. Specific complaints (symptoms), physical limitations (signs), and treatments correspond to the structures of the spine that are damaged.

Mechanical Back Pain

Mechanical disorders of the lumbar spine are the most common causes of low back pain. These problems are related to an injury, overuse, or a deformity of an anatomic structure in the lumbar spine of the lower back. Mechanical problems occur in the mus­cles, discs, vertebral joints, or spinal nerves.

These structures are damaged at different times in your life as you age. For instance, muscle problems may be more likely at 20 to 40 years of age, whereas you can have difficulties with spinal nerves after age 60.

The process that results in mechanical problems starts during adolescence. Decreased blood flow to intervertebral discs starts when you are in your twenties. Envi­ronmental factors such as obesity, smoking, and heavy physical activ­ity all increase the potential of developing mechanical low back pain.

Muscle Strain

Back strain is injury to muscles or fascia in the lumbar spine. You can sneeze or cough and develop a mus­cle strain. Lifting an object heavier than your muscles can support can also cause this problem. Damage to back tissues results in a reflex signal being sent through the nervous sys­tem to the spinal cord. The signal tells the damaged muscle to con­tract to try to heal. Signals are also sent to surrounding muscles to pro­tect the injured muscle. Although the severity of the spasm can vary, the pain can be overwhelming, causing immobilization because of this spontaneous recruitment of a number of muscles surrounding the spine. You can have difficulty get­ting out of bed or putting on your clothes because the pain is so severe and the muscles are stiff, not allow­ing movement.

Diagnosis of a muscle spasm is based on the history of an injury and the presence of decreased motion of the spine on physical examination in association with muscle contrac­tion. You may feel that the muscle is “swollen,” but it is actually severely contracted. X-rays and laboratory tests are not useful in making the diagnosis of a muscle strain.

The best way to relieve muscle spasms is to keep moving. Grad­ual motions and stretching relieve spasm and allow muscles to contin­ually test how far they can stretch. In addition to gradual motion, drugs (aspirin-like agents), cold packs initially (pain relief), heating pad subsequently (increase blood flow), and gradual stretching exer­cises—all are appropriate as part of a self-management program to relieve the pain of a muscle strain. Realize that as you improve and the area of involvement gets smaller, the last place to become pain-free is the first to become reinjured.

Intervertebral Disc Herniation

A herniated intervertebral disc occurs in individuals between 30 and 40 years of age. This is a time when discs contain a normal amount of gel in the nucleus pulpo­sus but the outer layer, or annulus, starts to wear out. The crisscross of the fibers is broken, and the con­tained gel escapes. A disc protru­sion, or bulging disc, occurs when the escaped gel remains within the annulus. A disc extrusion, or herni­ation, occurs when the gel escapes outside the outer portions of the annulus. The gel fragment can move side to side or up or down the spinal canal. Of note: discs herniate, they do not “slip.”

Herniated discs may be painless, unless they contact or compress spinal nerves. The gel is considered “foreign” tissue, so the body tries to remove the tissue with an inflam­matory response. The inflammatory response includes cells and enzymes that will dissolve the gel. The problem becomes severe when the inflammatory response attacks the neighboring spinal nerve. Sciatica, or leg pain, occurs when the spinal nerve is inflamed.

Any disc in the lumbar spine can herniate, but the lower discs at the third, fourth, and fifth vertebrae are more susceptible. These discs carry a greater proportion of the weight of the body. Each spinal nerve that is damaged by a neighboring disc trav­els to a different portion of the leg or foot. Here are a couple examples:

  • A damaged lumbar 5 spinal nerve causes numbness in the front of the lower leg and the big toe, weakness in the big toe, and an inability to raise your foot on your heel (foot drop), but no loss of reflex.
  • A damaged sacral 1 spinal nerve causes numbness in the calf and outer two toes, weakness when standing on your toes, and loss of the ankle reflex.

People with a disc problem may have mild back pain on the side of the herniation but a greater degree of leg pain. The pain is deep and sharp and may be accompanied by the tingling sensation known as pins and needles. The pain may vary in intensity but can be severe enough to cause immobility. The affected leg may feel weak. You may have increased pain with sitting, driving, coughing, or having a bowel move­ment, as these activities increase pressure in the herniated disc.

A plain X-ray will not identify the location of a herniated disc. A magnetic resonance imaging (MRI) scan is able to pinpoint the area of disc extrusion that corroborates the findings of physical examination.

Once you have identified a disc herniation, do you need an operation (discectomy) to be cured? Fortunately, the answer is no. More than 80 percent of individuals with a herniated disc have resolution of their predicament without surgery. The gel can be resorbed and nerve returned to normal function, but it could take months to accomplish.

Successful treatment for a herniated disc and sciatica includes some or all of the following components: gradual motion, nonsteroidal anti-inflammatory drugs (NSAIDs), muscle relaxants, pain relievers (analgesics), epidural corticosteroid injections, and physical therapy.

Gradual movement (staying out of bed as much as tolerated) has been shown to be associated with a more rapid improvement in symptoms. Moving allows the structures to heal while avoiding the muscle deconditioning that occurs with prolonged bed rest.

Drug therapy in the form of NSAIDs, muscle relaxants, and analgesics can be helpful in controlling the intensity of inflammation surrounding the disc and nerve, thereby reducing pain. Muscle relaxants are able to diminish the degree of spinal muscle contraction that occurs in the setting of nerve injury. Analgesics (opioid or non-opioid) are used to decrease pain to allow movement that helps heal the disc.

Epidural injections are the kind of therapy given to women during childbirth. The difference with the injections used for sciatica is that the medicine injected is a cortico­steroid (anti-inflammatory drug) versus an anesthetic that numbs the lower half of the body. The epidural injection allows the corticosteroid to be placed specifically over the area of nerve inflammation. A series of three epidural corticosteroid injections may be given over a six-week period of time to resolve sciatic symptoms.

Who needs surgery? In very rare circumstances, a very large disc herniation affects a great number of spinal nerves, including those that supply the bladder and rectum. These individuals, who are at risk of incontinence, require emergency surgery to relieve pressure on the spinal nerves and restore function. The other indication for early disc removal is progressive muscle weakness of the leg or foot.

An important point to remember: disc surgery is performed for leg pain, not back pain. A successful disc operation is associated with rapid improvement of leg pain with a slower resolution of leg numbness.

Disc Degeneration and Osteoarthritis

Intervertebral discs start to lose water when you are in your thirties. When discs lose water, they lose their ability to be cushions between the vertebrae. Losing space between the vertebrae causes more pressure on the facet joints in the posterior part of the spinal arch. Facet joints normally guide motion and are not weight bearing. When increased abnormal pressure is placed on joints, the cartilage between the bones starts to degenerate, or wear out. These degenerative changes occur in all of us as we age. Osteoarthritis is the term used to describe this process. You are at a higher risk of osteoarthritis of the lumbar spine starting in your fifties.

Flattening of discs and narrowing of facet joints may be a painless process but can also cause severe localized back pain. Exactly why certain joints are more painful than others is not known. The pain that people describe is worse when standing and bending backward; discomfort is relieved when they are in bed with the knees bent, rather than flat. Pain may go across the back and down into the buttocks, but it does not radiate into the legs. X-rays and MRIs can detect changes in the discs and joints but are unable to detect the presence of pain.

Self-management is an important part of therapy for osteoarthritis of the lumbar spine. Obesity has a detrimental effect on the functioning of the spine. Questions remain as to the association of low back pain and obesity; however, once you have back pain, being overweight does not help. An essential part of rehabilitation is physical therapy and a regular exercise program to strengthen the muscles in front of the spine, including the abdominals. Losing weight allows less forward pressure on the spine, relieving strain on the pain-generating facet joints.

NSAIDs, analgesics, and muscle relaxants can be effective therapy for this category of back pain, as well. An increasing concern, however, is the potential side effects of the medicines, which limits their utility as you grow older. Of particular concern is the risk of gastrointestinal bleeding and high blood pressure with the prolonged use of NSAIDs.

For those who have contraindica­tions to the use of drug therapy, facet joint blocks may be an option. Physical examination can identify the pain-generating facet joint. Bending the lumbar spine backward and to the symptomatic side frequently identifies a location that is painful. The area is also tender to the touch. In this circumstance a physician can identify the painful facet joint with X-ray techniques and can inject the joint with long-acting anesthetics. These facet joint blocks decrease pain so that you are able to exercise, lose weight, and be at less risk of persistent back discomfort.

Lumbar Spinal Stenosis

The last form of mechanical back and leg pain to be described is lum­bar spinal stenosis. This back problem occurs in individuals 60 years or older. This disorder is almost epidemic in its frequency.

Lumbar spinal stenosis is defined as the condition associated with too little room in the spinal canal for the nerves. When the spinal nerves are compressed, the blood supply to the nerve is cut off. The nerve loses its ability to function due to the lack of oxygen supplied by blood flow. This loss of nerve function can be associated with any combination of pain, numbness, or weakness in the distribution of that particular nerve.

Function can be rapidly restored with the reestablishment of blood flow to the nerve and is the goal of therapy for lumbar spinal stenosis. MRI scans can identify areas of nerve compression in the central or lateral portion of the spinal canal, as well as the neural foramen. For patients with pacemakers, for whom MRI scanning is contraindicated, a CT (computed tomography) scan is able to identify the bony anatomy that may cause compression.

Treatment options range from education and weight loss, to exercises and medications, to spinal injections and surgery. No one therapy works for everyone. Some therapies are not worth the risks. With others the presence of bladder or rectal incontinence related to nerve dysfunction requires surgical decompression.

This overview of low back pain should provide you with information about the factors that promote back health. Remember, stressing over a back attack that you know will resolve only makes it last longer. Instead, learn more about common back issues and effective management—and make the knowledge work for you. Your spine will be better off for it.


Resources

American Academy of Orthopedic Surgeons (AAOS), aaos.org; the national professional organization of orthopedic surgeons

American Association of Neurological Surgeons (AANS), aans.org; the national professional organization of neurosurgeons

American College of Rheumatology (ACR), rheumatology.org; the national professional organization of rheumatologists

American Physical Therapy Association (APTA), apta.org; the national professional organization of physical therapists

The Spine Community, thespinecommunity.com; an online community providing educational content for patients with back pain, arthritis, and spine conditions


Glossary

Annulus Fibrosus The circular, outer portion of the intervertebral disc consisting of strong, interwoven fibers.

Discectomy The surgical removal of a portion or all of an intervertebral disc.

Facet Joint Blocks The therapeutic injection of pain-relieving drugs to an area in or around facet joints.

Facet Joints The paired joints located in the back of the vertebral bodies connecting the spine.

Gel The thick, viscous fluid in the center of an intervertebral disc that is responsible for its shock absorbance.

Intervertebral Disc The cylinder-like structure composed of a gel center (nucleus pulposus) and a fibrous outer covering (annulus fibrosus) that acts as a shock absorber and a universal joint in the spine.

Lumbar Spine The portion of the back between the chest and pelvis consisting of five vertebrae.

Nucleus Pulposus The gel center of the intervertebral disc. This is the portion of the disc that herniates.

Sciatica A pain that follows the sciatic nerve down the leg to the calf or foot.

Spinal Canal The semicircular space formed by the back of a vertebral body and the spinal arch that protects the spinal cord.

Spinal Arch The posterior portion of the spinal canal. The spinal canal protects the spinal cord that runs through its center.


 

Preventing Low Back Pain

The concept of prevention sounds like a worthy enterprise, but it has a poor track record. Most healthy individuals do not want to take time to prevent a problem they are not currently experiencing. Because back pain is so common, however, you will probably have an episode. Some simple changes in behavior can be helpful.

If You Do Not Smoke, Don’t Start. If you are a smoker, stop. Getting oxygen to your tissues is a good idea.

Stop Sitting. Proper body mechanics are essential to a healthy spine. Get out of your chair every hour. Do a gentle stretch and a pelvic tilt; this allows oxygen to get to the tissues of the spine. They will be appreciative.

Eat Smart. Fruits and vegetables should not be strangers to your diet. Too many carbohydrates in the form of refined sugars and high-fat foods tend to have inflammatory effects in the body. Think of fat cells as factories of inflammatory chemicals. The fewer you have, the less inflamed you will be.