Back Pain

Overview

Four out of five adults experience significant low back pain at some point in their lives. This figure is not surprising, given the amount of stress placed on the back by the upright body position. Not only does the back support the body's weight during standing, walking, and lifting, it must also turn, twist, and bend.

After the common cold, back pain is the most frequent problem that brings people to a doctor's office. It is often difficult to pinpoint the exact cause of back pain because so many different structures can be affected.

In most cases, back pain resolves quickly, regardless of the type of treatment. Fortunately, fewer than 5 percent of people with back pain have a major medical problem that requires either intensive care or surgery.

This section includes information on:

• Causes
• Need-to-know anatomy
• Risk factors

Need-to-know anatomy

The spine is made up of 33 interlocking bones, called vertebrae, that stack upon each other at a slight angle to form the spine's S-shaped curve. This distinctive curvature helps the spine to absorb the shock of movement while still supporting the body's weight. The vertebrae grow progressively larger and stronger from top to bottom. The seven delicate cervical (neck) vertebrae support the head; the larger 12 thoracic (chest) vertebrae bear the weight of the arms and trunk; and the five thickest and sturdiest lumbar (lower back) vertebrae carry the weight of the entire body. Because the lumbar region endures the greatest stress, it is the most vulnerable to strain or other problems. Finally, at the base of the spine are nine fused vertebrae that make up the sacrum (the back wall of the pelvis) and coccyx (tailbone).

Together, the vertebrae, ligaments, and muscles (in the back and abdomen) help to maintain erect posture. Between each vertebra and the next is a flexible pad of cartilagelike tissue, called an intervertebral disk, that cushions the vertebrae as the body moves and prevents them from grinding against each other.

The final important function of the spine is to form a protective shell around the delicate spinal cord. At the rear of each vertebral body is a hole; when the vertebrae are stacked upon each other, these holes create a channel known as the spinal canal, through which the spinal cord runs. Spinal nerves, which branch off from the spinal cord through spaces (foramina) between adjacent vertebrae, extend to all parts of the body. The spinal cord ends at about waist level, dividing into a bundle of nerves that continues downward--the cauda equina (Latin for horse's tail, since its structure resembles the tail of a horse). Because of this intricate interweaving of bone and nerve tissue, problems with the vertebrae can often cause symptoms from pressure on the spinal nerves or the spinal cord.

Causes

Most of the time, the exact cause of back pain is not easily determined. Since about 90 percent of cases remit on their own, it is not always important to find a precise anatomical cause.

People under age 60 tend to have acute backaches, that is, backaches that are sudden and short lived. These most often result from a sprain, strain, spasm, or, less frequently, a degenerated or herniated disk. In older people, chronic conditions such as degenerative changes of the spinal bones and disks, vertebral compression fractures, spinal stenosis, and spinal deformities are the most common sources of back pain.

This section describes the major causes of back pain in adults, including:

• Sprains, strains, and spasms
• Degenerative changes of the spinal bones and disks
• Disk herniation
• Vertebral compression fractures
• Spinal stenosis
• Spinal deformities
• Additional causes of back pain

Sprains, strains, and spasms

Sprains, strains, and spasms usually result from activity or injury. The term sprain is used when a ligament is partly torn, while strain is applied when a muscle is overstretched. A muscle spasm refers to a contraction of muscles in the back in response to injury, which may occur in a ligament, muscle, disk, or joint. Although the pain may be intense, muscle spasm is ultimately a protective measure. The pain ensures that the injured area remains immobile and thus prevents further damage.

Degenerative changes of the spinal bones and disks

Degenerative changes to the disks and facet joints in the lumbar spine, often referred to as degenerative osteoarthritis or spondylosis, are an inevitable consequence of aging. They usually begin at about age 20, but MRI studies have detected changes within the disks in teenagers. Degenerative changes, along with vertebral compression fractures and kyphosis, are responsible for the loss of height experienced by many people over age 50.

As we age, lumbar disks wear out because they are subjected to such large loads. Over the years, the center of the disk slowly loses its water content and shrinks. This flattening of the disks leads to a narrowing of the space between the vertebrae. Also, as a result of supporting heavy loads, 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 disk wear and vertebral changes.

In addition, arthritic changes (caused by a gradual erosion of the cartilage that lines the facet joints of the spine) may lead to pain and loss of the spine's smooth, coordinated motion. Pain can also arise from irritation of nerves present in the outer portion of the disks themselves.

Disk herniation

At some point in their lives, 10 percent of people experience symptoms from a herniated disk. However, autopsy studies show that most people have had a herniated disk but never experienced symptoms.

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

The location and severity of the symptoms caused by a herniated disk depend on the extent and site of the rupture. For example, a herniated lumbar disk may cause pain, numbness, or weakness in one leg (sciatica), while a ruptured cervical disk may produce similar symptoms in one arm or hand (less commonly, both sides can be affected). In general, a spasm of the back muscles plus difficulty walking or standing straight indicates a herniated disk.

Pain due to a herniated disk is usually sudden in onset. The patient may "feel something snap" before the start of pain, which may begin as a mild tingling or a "pins and needles" sensation before increasing in severity.

Vertebral compression fractures

A healthy vertebra will not break unless subjected to a forceful injury, such as in a car accident. By contrast, even minor trauma--such as a sneeze--can cause a compression fracture of a vertebra weakened by osteoporosis, Paget's disease, hyperparathyroidism, or cancer. Osteoporosis (reduced bone mass) is the most common cause of vertebral compression fractures.

Spinal stenosis

Spinal stenosis--a narrowing of the spinal canal--was first recognized in the late 1950s and has received considerable medical attention since then. Degenerative changes in the spine are the most frequent cause of spinal stenosis, which usually affects people in their 50s and 60s and is about twice as common in men as in women. As the body ages, gradual deterioration of the disks and facet joints in the spine causes the bones to rub together. This increased friction may eventually lead to the formation of osteophytes at the facet joints and around the rims of the vertebrae.

Spinal stenosis most often occurs when these overgrowths of bone gradually narrow the central canal of the spine (central stenosis) or the bony canals through which nerves leave the spinal cord (lateral stenosis). Ligaments may thicken and cause narrowing of the spinal canal as well. Central narrowing causes symptoms owing to compression of the spinal cord or the cauda equina. Narrowing of the exit canals causes pain owing to compression of the nerves branching off from the spinal cord or interruption of their blood supply. Spinal stenosis may also result as a complication of surgery, trauma to the spine, or involvement of the spine in Paget's disease.

Symptoms of spinal stenosis usually start slowly and are mild at first.

Central stenosis can cause back pain, but usually the pain radiates into both legs. The pain does not follow the distribution of specific nerves but rather seems to involve the buttocks, thighs, calves, and occasionally, the entire length of both legs. The pain is cramping in nature and may be associated with weakness, a "rubbery" feeling, numbness, and a sensation of loss of power in the legs. As a result of this weakness, people are prone to falls. Because the nerves controlling the bladder emerge from the lower spine, spinal stenosis may also cause urinary incontinence.

Bed rest may increase spinal stenosis pain by exaggerating the natural curve of the lower back, which puts more pressure on the spinal cord. Individuals with spinal stenosis may feel more comfortable when sitting in a forward-leaning position.

Lateral stenosis may develop alone or accompany central stenosis. The characteristic symptom of nerve entrapment due to lateral stenosis is severe pain along the path of the affected nerve. The pain from lateral stenosis is not relieved by bed rest, and the affected individual may pace the floor at night or keep changing positions while sitting.

Spinal deformities

The three basic types of spinal deformities are kyphosis, lordosis, and scoliosis. These conditions usually develop during childhood or adolescence and worsen with age, but they may occur in older individuals solely as the result of degenerative changes.

Kyphosis is characterized by extensive flexion (bending forward) of the spine. It usually affects the thoracic spine but may also occur in the neck or lower back. Thoracic kyphosis is sometimes referred to as dowager's hump, humpback, or hunchback. It is particularly common in older women and can result from disk degeneration (in which the disks lose moisture and shrink), collapse of vertebral bodies due to osteoporosis, or both.

In lordosis, or swayback, the abdomen is thrust too far forward and the buttocks too far to the rear. This condition is common in overweight people with weak abdominal muscles.

Scoliosis is defined as an abnormal sideways bend to the back caused by a twisting of the spine. It can occur at any location in the spine. The amount of pain caused by scoliosis usually depends on the degree of the deformity; more pronounced deformities tend to be more painful. Most scoliosis in our society is inherited and develops in childhood, but it may progress later in life as a result of disk degeneration. Scoliosis that arises during adulthood can be traced to asymmetrical changes in the disks. Scoliosis occurring from degenerative changes alone tends to create fewer problems than childhood scoliosis.

Additional causes of back pain

Ankylosing spondylitis. Ankylosing spondylitis is a chronic inflammation of the facet joints and the joints between the back wall of the pelvis and the hip (the sacroiliac joints). Inflammation may also involve locations where ligaments and tendons attach to bone. In severe cases, the vertebrae may become fused together, resulting in rigidity. Because fusion can be painful, the person tends to lean forward and develop a stooped posture.

Osteomalacia. Bone is mostly made up of collagen but requires the minerals calcium and phosphorus for strength. Osteomalacia is a softening of bone that results from a lack of these minerals. The most common cause of osteomalacia is vitamin D deficiency, which is prevalent in older individuals. Vitamin D is essential for absorption of calcium and phosphorus.

Spondylolysis. Spondylolysis refers to a weak area in the bone that connects the facet joints to the vertebral body.

Spondylolisthesis. Spondylolisthesis, in which one of the vertebrae slips forward, may develop in people with spondylolysis.

Vertebral osteomyelitis. Vertebral osteomyelitis is a serious and increasingly common bacterial infection of the spine. It can cause pain in the neck or back and may be accompanied by fever. It is often associated with autoimmune disorders such as Type I diabetes.

Cancer. In rare instances, back pain is caused by cancer in the spine. Although malignant tumors of the spine account for far less than 1 percent of all cases of back pain, they occur more frequently in older people. Cancer can originate in the vertebrae, as in the case of multiple myeloma (cancer cells that move from the bone marrow to the bones at numerous sites). Alternately, it can spread to the spine from other sites in the body, most often from the breast, prostate, lung, kidney, or thyroid gland.

Other causes. Not all back pain is caused by problems with the spine or muscles involving the back. In some cases, pain originates in the abdominal organs and radiates to the back. Conditions such as pancreatitis (inflammation of the pancreas), peptic ulcers (nonhealing defects in the stomach or small intestine), or an abdominal aortic aneurysm (a ballooning of the wall of the body's largest artery) may also cause back pain.

In addition, back pain may originate from disorders at other body sites. Such disorders include gallstones, kidney stones and infections, and endometriosis (a benign growth of endometrial tissue outside of the uterus).

Risk factors

Not only does the back support the body's weight during standing, walking, and lifting, it must also turn, twist, and bend. Professions such as construction work and nursing, which involve all of these movements, put people at increased risk for back injury.

Although it may seem that back pain occurs suddenly (such as while bending down to pick something up), it is precipitated by a number of factors, including normal aging, weak back and abdominal muscles, obesity, and poor posture. The frequency of sprains and strains tends to decline after age 60, in part because older adults are less likely to participate in the kind of vigorous activities that lead to these problems. Also, the disks between the vertebrae become less pliable in older adults and, as a result, are less likely to herniate. Such rigidity, however, leads to problems of its own, mostly owing to degeneration of the various spinal bones.