December 18, 2018
What Causes Back Pain?

What Causes Back Pain?

by Wellness Letter

People under age 60 who experience back pain typically have acute backaches—that is, backaches that are sudden and last less than several weeks. These most often occur as pain limited to the back itself and result from a sprain or strain. In older people, chronic conditions such as degenerative changes of the spinal bones and discs, vertebral compression fractures, spinal stenosis (narrowing of the spinal canal, see next page), and spinal deformities are the most common sources of back pain, and the pain tends to be chronic, though older people can also experience acute back pain.

Other back-related disorders may cause symptoms that are not limited to back pain. For example, sciatica—pain that radiates into the buttocks, down the thighs to below the knees and into the calves, and often even to the feet—is caused by irritation of a nerve or nerves leaving the spinal canal in the lumbar region of the back. Stiffness in the back, numbness and tingling, or loss of muscle strength in the legs may accompany back pain.

Although back pain may occur suddenly (such as when bending down to pick something up), underlying problems—including degenerative changes associated with normal aging, weak back and abdominal muscles, obesity, and postural imbalances—set the stage for such “back attacks.” In addition, the discs between the vertebrae become less pliable in older adults, making them more likely to herniate and possibly leading to degeneration of the various spinal bones.

Sprains, strains, and spasms

The frequency of sprains and strains tends to decline after age 60, in part because older adults are less likely to participate in the kinds of vigorous activities that lead to these problems. These sudden causes of back pain usually result from activity or injury. The term “sprain” is used when a ligament (which connects bones) is overstretched or torn, while “strain” is used when a muscle or tendon is overstretched or some of its fibers are torn.

A muscle “spasm” refers to an involuntary, intense, sustained contraction of muscles, often in response to injury of a ligament, muscle, disc, or joint. Though the pain may be intense, muscle spasms ultimately protect you. They are a way your body tries to immobilize the injured area, thus preventing further damage.

Degenerative changes

Degenerative changes to and around the discs and facet joints in the spine, often referred to as degenerative osteoarthritis or spondylosis, are a consequence of aging. As we age, lumbar discs wear out because they are subjected to large loads. Depending on what types of activities you engage in, pressure on the lumbar spine may be as great as 11 times your body weight. Bending, twisting, and lifting increase the load, depending upon the activity and the amount of weight lifted. Age-related loss of strength in the back muscles—which normally bear about one-third of the load on the spine—also increases the stress on the discs and facet joints. Excess body weight may further contribute to disc degeneration.

Over the years, the center of each disc slowly loses its water content and shrinks. This flattening of the discs leads to a narrowing of the space between the vertebrae. In addition, as a result of chronic wear and tear, the vertebrae may develop bone spurs (osteophytes) that can press on a spinal nerve and cause pain.

Another possible cause of pain is deterioration of the facet joints due to loss of disc height and vertebral degenerative changes. Pain also can occur if the nerves in the outer portion of the discs are irritated.

Disc herniation

About 10 percent of people experience symptoms from a herniated disc at some point in their lives. Autopsy studies reveal, however, that most people actually have at least one herniated disc but never experienced any symptoms.

Over the years, the demand of supporting the body’s weight causes the outer layer of each disc to weaken, become thinner, and develop microscopic tears. At the same time, the center of the disc slowly loses its water content and becomes progressively drier. These changes make the disc susceptible to herniation, in which mild trauma from lifting an object or even sneezing causes the center of the disc to bulge through the weakened outer layer.

Any disc can herniate, but about 90 to 95 percent of cases occur in the two lowest discs, which bear the greatest load.

If a disc presses on one or more nerves emerging from the spinal column, symptoms usually occur. In some people, the disc presses on the spinal cord itself or on the cauda equina. This causes pain not only in the back, but also in the part of the body served by the compressed and inflamed nerve. Disc fragments can also break free, a condition known as sequestration.

Disc herniation symptoms can also result from chemical irritation of the nerve rather than direct compression.

When a disc herniates, both the site and extent of the rupture determine the location and severity of the symptoms. For example, a herniated lumbar disc may cause pain, numbness, or weakness in one leg (sciatica). A herniated cervical disc may produce similar symptoms in one arm or hand (less commonly on both sides).

Pain due to a herniated disc usually strikes suddenly. The person may “feel something snap” before the pain begins. Pain may start as a mild tingling or a “pins and needles” sensation before increasing in severity.

Vertebral compression fractures

A healthy vertebra will not break unless it is subjected to very large forces, such as those occurring in a car accident. By comparison, even minor trauma—such as a sneeze—can cause a compression fracture of a vertebra that has been weakened by other conditions, such as:

  • Osteoporosis (reduced bone mass, usually age-related), the most common cause of vertebral compression fractures.
  • Hyperparathyroidism, which can cause osteoporosis and other bone conditions that result in a weak bone structure.
  • Cancer. Vertebral compression fractures, although rarely a first sign of cancer, can occur in people with cancer that has spread to the spine.

Spinal stenosis

This narrowing of the spinal canal typically affects people in their 50s and 60s, usually as the result of degenerative changes in the spine. It may also develop as a complication of surgery, trauma to the spine or, in rare instances, Paget’s disease, a bone disorder that can involve the spine.

As the body ages, gradual deterioration of the discs and facet joints in the spine causes the bones to rub together. This may eventually lead to the formation of overgrowths or bone spurs (osteophytes) at the facet joints as well as around the rims of the vertebrae. Spinal stenosis occurs when these overgrowths narrow the spinal canal. Ligaments may thicken and also contribute to the narrowing of the spinal canal, exerting pressure on spinal nerve roots.

Symptoms of spinal stenosis vary, ranging from vague numbness and weakness in the legs while standing and walking to severe pain and difficulties with bowel and bladder control. Symptoms usually start slowly and are mild at first. The pain does not follow the distribution of specific nerves but rather seems to involve the buttocks, thighs, calves, and, occasionally, the full length of both legs.

The pain feels achy or like cramping and may be associated with weakness, numbness and tingling, a sensation of loss of power in the legs, and a “rubbery” feeling caused by a decreased ability to directly sense the position of the leg. Not surprisingly, this makes people with these symptoms more prone to falls. All the symptoms typically improve with sitting down or bending forward.

This constellation of symptoms is called “neurogenic claudication” and is sometimes confused with another condition, “vascular claudication,” because the symptoms are similar. Vascular claudication is caused by impaired blood flow to the legs due to atherosclerosis (hardening of the arteries), and, like neurogenic claudication, often results in the need to stop walking temporarily. The two conditions can be distinguished from each other, however, by the pattern of the pain and what relieves the symptoms.

People with vascular claudication have pain that starts in their feet or calves and radiates up toward their back and buttocks, whereas people with neurogenic claudication have pain that starts in their lower back and buttocks and radiates down toward their feet.

Vascular claudication is relieved by resting, regardless of body position. By comparison, neurogenic claudication is related to body position and may continue for as long as you remain standing. Bending forward or sitting down usually relieves neurogenic claudication.

Bed rest may increase spinal stenosis pain by exaggerating the natural curve of the lower back, which puts more pressure on the spinal nerves. A person with spinal stenosis may feel more comfortable when sitting in a forward-leaning position, which flexes the lower spine and relieves some of the pressure on the nerves. Likewise, when people with spinal stenosis stand, they may be more comfortable leaning slightly forward. For example, many people with spinal stenosis lean forward on a shopping cart while buying groceries. As the condition worsens, pain may occur while sitting, or it may awaken the person at night.

Sciatica and cauda equina syndrome

Sciatica (which is fairly common) and cauda equina syndrome (which is rare) are usually due to one of the major disorders of the spine, such as disc herniation, degenerative changes of the intervertebral discs, spinal stenosis, or vertebral fracture.

Sciatica—known clinically as lumbosacral radicular pain—affects 40 percent of adults during their lifetime. It occurs when something—commonly spinal stenosis or a herniated disc—irritates some part of the sciatic nerve. The sciatic nerve is formed by nerve roots that emerge from the lower spine, join together in the hip region, and run down the back of each thigh. Near the knee, the sciatic nerves branch into smaller nerves that extend into the calves, ankles, feet, and toes.

Sciatica results from irritation of one of the nerve roots in the lower back. Pain or numbness develops along the sciatic nerve and its branches; the location of symptoms de­­pends on which spinal nerve root is affected.

After age 50, sciatica is more commonly caused by spinal stenosis than disc herniation. Most of the time, sciatica from a herniated disc resolves within six weeks with little or no treatment. In up to 50 percent of cases, sciatica from spinal stenosis resolves by itself within a month, but 25 percent of sufferers have pain for as long as four months.

Compression of the cauda equina may result in sudden onset of impaired bowel and bladder function; loss of sensation in the groin, buttocks, and legs; and severe weakness or paralysis in the legs. These symptoms—known as cauda equina syndrome—indicate an emergency situation that requires immediate surgical attention. Anyone who develops symptoms of cauda equina syndrome should call 911 and be taken to the emergency room of a nearby hospital for immediate evaluation and treatment.

This article first appeared in the UC Berkeley Wellness Letter.

Also see Back Pain: An Ounce of Prevention.

Updated November 2018.