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Causes/Symptoms
In about 85% of back pain cases, the origin of the pain is unknown, and imaging studies usually fail to determine the cause. Disk herniation and disk degeneration due to aging are the most common
causes of low back pain. Other problems can also cause this pain, however.
Over the years, the disk can wear away (degenerate), causing inflammation and irritation. This age-related condition is a major source of chronic low back pain.
A herniated disk, sometimes, but incorrectly, called a slipped disk, is widely held to be the most common cause of severe back pain and sciatica. A disk in the lumbar area becomes herniated when
it ruptures or thins out and degenerates to the point that the gel within the disk (nucleus pulposus) pushes outward. The damaged disk can take many forms.
A bulge -- The gel has been pushed out slightly from the disk and is evenly distributed around the circumference.
Protrusion -- The gel has pushed out slightly and asymmetrically in different places.
Extrusion -- The gel balloons extensively into the area outside the vertebrae or breaks off from the disk.
There is some debate, however, about how pain develops from a herniated disk and how frequently it causes low back pain. Many people have disks that bulge or protrude and do not suffer back pain.
Extrusion (which is less common than the other two conditions) is highly associated with back pain, since the gel is likely to extend out far enough to press against the nerve root, most often
the sciatic nerve. Extrusion is very uncommon, however, while sciatic and low-back pain are very common. But there may be other causes of low back pain
Ordinarily, at the time of any injury, the immune system triggers key factors that are designed to promote healing. Evidence is now pointing to an abnormal and persistent immune response in the
cells of the nucleus pulposus that may be responsible for nerve injury and pain in the lower back. In such cases, the nucleus pulposus in the herniated disk overproduces certain factors known as
cytokines -- notably tumor necrosis factor (TNF) -- that, in high levels, cause inflammation and cell damage. Evidence now suggests that such cytokines cause a biochemical reaction in the regions
surrounding the bulging or protruded nucleus pulposus, which results in pain.
Abnormalities in the Annular Ring. Research has also focused on tears in the annular ring -- the fibrous band that surrounds and protects the disk. The annular ring contains a dense nerve network
and high levels of peptides that heighten perception of pain. Tears in the annular ring are a frequent finding in patients with degenerative disk disease. Some cases of chronic low back pain may
be caused by inward growth of nerve fibers into the annular ring, which triggers pain within the intervertebral disk.
At some time, up to 40% of people have pain called sciatica. This condition occurs when the sciatic nerve is trapped or inflamed.
The Sciatic Nerve. The sciatic nerve has an extensive pathway.
It first branches from the nerve roots that descend off the lowest part of the spinal cord (in the lumbar and sacral areas). Each of the two branches of the sciatic nerve is about as wide as a
thumb.
Each branch of the nerve threads through the pelvis and deep into either side of the buttocks.
The nerve branches then pass down each hip and along the back of each thigh to the foot.
Causes of Sciatica. A herniated disk pressing on the sciatic nerve is the most common cause of sciatica, although spinal stenosis or other vertebral abnormalities that press on the sciatic nerve
can also cause pain.
Symptoms of Sciatica Pain due to sciatica can vary widely. It may feel like a mild tingling, dull ache, or a burning sensation. In some cases, the pain is severe enough to cause immobility.
The pain most often occurs on one side. Some people have sharp pain in one part of the leg or hip and numbness in other parts. The affected leg may feel weak.
The pain often starts slowly. Sciatica pain may get worse:
• At night
• After standing or sitting for long periods of time
• When sneezing, coughing, or laughing
After bending backwards or walking more than 50 - 100 yards (particularly if it is caused by spinal stenosis).
Sciatica pain usually goes away within 6 weeks, unless there are serious underlying conditions. Pain that lasts longer than 30 days, or gets worse with sitting, coughing, sneezing, or straining
may indicated a longer recovery.
Other than age-related degenerative disk disorders, injuries in the muscles and ligaments supporting the back are the major causes of low back pain. Of note, is the iliac crest pain syndrome (iliolumbar
syndrome), in which there are tears in the ligaments that help support the pelvic bone.
Spinal stenosis is the narrowing of the spinal canal. This typically develops as a person ages and the disks become drier and start to shrink. At some point in this process, any disruption, such
as a minor injury that results in disk inflammation, can cause impingement on the nerve root and trigger pain. Pain from spinal stenosis can occur in both legs, or it can be felt as sciatica. Spinal
stenosis occurs mostly in the elderly with degenerative osteoarthritis, but it can sometimes be caused by other problems, including infection and birth defects.
Spondylolysis is a condition in which the fourth or fifth lumbar vertebrae degenerate or develop small fractures. This condition affects 4 - 6% of the general population, and the rates may be higher
in certain populations. As it progresses, the spine can become unstable and lead to spondylolisthesis, in which one vertebra slips forward over the other and causes sciatica. The condition most
often occurs in older individuals with women having a higher risk than men. It is also a common cause of back pain from stress fractures in young athletes and can also be due to inherited problems,
injury, or bone disease.
Some cases of sciatica pain may occur when a muscle located deep in the buttocks pinches the sciatic nerve. This muscle is called the piriformis. The resulting condition is called piriformis syndrome.
Piriformis syndrome usually develops after an injury. In rare cases leg swelling, deep-vein blood clots, or both may occur. Piriformis syndrome is sometimes difficult to diagnose.
Ankylosing spondylitis is a chronic inflammation of the spine that may gradually result in a fusion of vertebrae. Symptoms include a slow development of back discomfort, with pain lasting for more
than 3 months. The back is usually stiff in the morning; pain improves with exercise. In severe cases, the patient must continually stoop over. It can be quite mild, however, and it rarely affects
a person's ability to work. It occurs mostly in young Caucasians in their mid-20s. The disease is more common in men, but about 30% of the cases are in women. Researchers believe that in most cases
it is hereditary. About 20% of people with inflammatory bowel disease and about 20% of people with psoriasis develop a form of ankylosing spondylitis. There are few effective treatments for this
potentially disabling disease, although etanercept (Enbrel) and infliximab (Remicade), anti-inflammatory agents known as TNF-blockers, are proving to be beneficial.
Any abnormality in joints, vertebrae, or nerve roots can cause back pain:
The facet (z-joints) joints can wear down. In such cases, pain occurs on arching the back or when walking.
In some cases a segment (consisting of two vertebrae and their common joint and disk) becomes unstable when its parts wear down.
In addition to causing sciatica, direct injury to the ganglion (a portion of the nerve just outside the canal which acts as a control center for nerve conduction) can result in back pain as well.
Risk Factors
In most known cases, pain begins with an injury, after lifting a heavy object, or after making a sudden movement. Not all people have back pain after such events, however. In the majority of back
pain cases, the causes are unknown.
Some evidence suggests that after episodes of back pain, some people may experience changes in brain structure and chemicals that produce an exaggerated response in nerve cells. In fact, a 2005
study suggested that chronic back pain actually shrinks the brain by as much as 11%. Such brain changes may cause a persistent perception of pain even though the actual injury has healed.
German researchers have found that chronic back pain appears to be linked to tiny structural changes in the brain. Using a specialized imaging method, they learned that persons with chronic back
pain seemed to have a different, more complex structure to their brain and more activity in the areas involved in pain processing and emotional responses. It is unclear if the brain changes occurred
before the pain or in response to the pain.
A number of conditions may make people more or less susceptible to low back pain.
Intervertebral disks begin deteriorating and growing thinner by age 30. One-third of adults over 20 show signs of herniated disks (although only 3% of these disks cause symptoms). As people continue
to age and the disks lose moisture and shrink, the risk for spinal stenosis increases. The incidence of low back pain and sciatica increases in women at the time of menopause as they lose bone
density. In older adults, osteoporosis and osteoarthritis are also common. However, the risk for low back pain does not mount steadily with ever-increasing age, which suggests that at a certain
point, the conditions causing low back pain plateau.
Inherited Spinal Structure Abnormalities. Many people have a genetic susceptibility to low back pain, usually from inheriting spinal structural abnormalities.
Inherited Weakened Disks. Studies are finding that specific mutations of the COL9A gene may play a role in about 10% of sciatica cases. The gene is normally involved in producing collagen, the
protein building block in all structural tissue in the body. When defective, it may cause the disk to be less able to resist compressive forces. One 2001 study found the defective gene was present
in twice as many patients with disk problems as in patients without back pain.
The likelihood of experiencing back pain increases as children age. Some studies suggest that pain is more common among girls than boys. A common cause of temporary back pain is carrying backpacks
that are too heavy for children. Backpacks should not weigh more than 20% of the child's body weight. They should weigh even less for very young children. Emotional or behavioral problems may also
contribute to back pain in children.
Jobs that involve lifting, bending, and twisting into awkward positions, as well as those that cause whole-body vibration (usually due to long-distance truck driving), place workers at particular
risk for low back pain. The longer a person continues such a job, the higher the risk. Some workers wear back support belts, but evidence strongly suggests that they are useful only for people
who are currently have low back pain. The belts offer little added support for the back and do not prevent back injuries. In one study, workers who wore the belt for prevention reported more back
pain than the workers who did not wear them.
A number of companies are developing programs to protect against back injuries. Although studies are mixed on the outcome of company interventions, one analysis suggested that they do have a positive
effect. Employers and workers should make every effort to create a safe working environment. Office workers should have chairs, desks, and equipment that support the back or help maintain good
posture.
Infections. A number of common and uncommon infections are a cause of back pain. Chronic uterine or pelvic infections can cause low back pain in women. Osteomyelitis is infection in the spine,
a rare cause of back pain. Other infections that cause back pain include Lyme disease, septic arthritis, bacterial endocarditis, Reiter syndrome, mycobacterial, fungal arthritis, and viral arthritis.
Chlamydia pneumonia, an atypical organism that is a common cause of mild pneumonia in young adults, is now believed to cause widespread inflammation in the body's tissue, including blood vessels,
and may be responsible for a number of chronic conditions, including heart disease. Some evidence further suggests it may cause inflammation in arteries of the lower spine and contribute to spinal
stenosis.
Many medical conditions are associated with back pain.
• Osteoporosis is a disease of the skeleton in which the amount of calcium present in the bones slowly decreases to the point where the bones become fragile and prone to fracture. It usually does
not cause pain unless the vertebrae collapse suddenly, in which case the pain is often severe. Studies indicate, however, that the incidence of low back pain and sciatica increase around the time
of menopause, and very tiny fractures in the vertebrae caused by osteoporosis may be an undetected cause of back pain in many elderly women.
• Osteoarthritis occurs in joints where cartilage is damaged and then destroyed, usually as a result of aging. In reaction to this destruction, the bones associated with the joints develop abnormalities.
When osteoarthritis affects the spine, it may damage the cartilage in the disks, the moving joints of the spine, or both. The nerves may become pinched, causing pain and in advanced cases, numbness
and muscle weakness. The patient may also experience muscle spasms and diminished mobility.
• Inflammatory disorders, such as Crohn's disease and rheumatoid arthritis, can produce inflammation in the spine (sacroiliitis), although the spine is less commonly affected than other locations.
• Other conditions that can directly cause pain include fibromyalgia, Paget's disease, Parkinson's disease, abscesses, blood clots, and cancer.
• Other medical conditions cause referred back pain, which occurs in conjunction with problems in organs unrelated to the spine (although usually located near it). Such conditions include ulcers,
kidney disease (including kidney stones), ovarian cysts, and pancreatitis.
It should be noted, however, that a number of medical conditions, such as lung and heart problems and chronic headaches, commonly occur with low back pain. A causal relationship among them, however,
is uncertain.
Persistent low back pain in children is more likely to have a serious cause that requires treatment than back pain in adults. According to one small study, one third of children being treated at
a hospital for back pain were found to have serious underlying problems.
Stress fractures (spondylolysis) in the spine are a common cause of back pain in young athletes. It is unlikely that stress fractures are related to injury. It is more likely an overstressing of
a bony part of the vertebrae in a not yet fully mature skeleton which is prone to developing a fracture. Spondylolisthesis (slips) can occur after one develops a spondylolysis, but they are uncommon.
And when a spondylolisthesis does occur, it is still usually asymptomatic.
Hyperlordosis is an inborn exaggerated inward curve in the lumbar area. Scoliosis, an abnormal curvature of the spine in children, does not usually cause back pain.
Juvenile chronic arthropathy is an inherited form of arthritis. It can cause pain in the sacrum and hip joints of children and young people. It used to be grouped under juvenile rheumatoid arthritis,
but is now defined as a separate problem.
Injuries, benign tumors such as osteoblastoma or neurofibroma and cancers, including leukemia, can also cause back pain in children.
Medications may trigger back pain. For example, anticoagulants can cause bleeding or an internal bruise. Long-term steroid use can cause infection or compression fractures.
Some research is suggesting that some people have motor control abnormalities in the deep muscles near the spine. Such lack of control causes instability in the spine that can lead to pain.
Pregnant women are prone to back pain due to a shifting of abdominal organs, the forward redistribution of body weight, and the loosening of ligaments in the pelvic area as the body prepares for
delivery. Tall women are at higher risk than short women. Although some earlier research had suggested that the use of epidurals for pain relief during labor could lead to chronic back pain, studies
in 2002 reported no increased risk.
Psychological factors are known to play a strong influential role in three phases of low back pain:
• Some evidence suggests preexisting depression and the inability to cope may be more likely to predict the onset of pain than physical problems. For example, a British study reported that people
who showed emotional distress at age 23 were nearly twice as likely to suffer from back pain 10 years later. A 2005 study found that a “passive” coping style (not wanting to confront problems)
was strongly associated with the risk of developing disabling neck or low back pain.
• The perception of pain. Social and psychological factors play a role in the severity of a person's perception of back pain. For example, one study compared truck drivers and bus drivers. Nearly
all the truck drivers liked their work. Half of them reported low back pain but only 24% lost time at work. Bus drivers, on the other hand, reported much lower job satisfaction than truck drivers,
and these workers with back pain had a significantly higher absentee rate than truck drivers in spite of less stress on their backs. Similarly, another study found that pilots, who generally reported "loving
their jobs," reported far fewer back problems than their flight crews. And yet another study reported that low rank, low social support, and high stress in soldiers was associated with a higher
risk for disabling back pain.
• Chronic pain. Depression and a tendency to develop physical complaints in response to stress also increase the likelihood that acute back pain will become a chronic condition. The way a patient
perceives and copes with pain at the beginning of an acute attack may actually condition the patient to either recover or develop a chronic condition. Those who over-respond to pain and fear for
their long-term outlook tend to feel out of control and become discouraged, increasing their risk for long-term problems.
Studies also suggest that patients who reported prolonged emotional distress have less favorable outcomes after back surgeries. It should be strongly noted that the presence of psychological factors
in no way diminishes the reality of the pain and its disabling effects. Recognizing it as a strong player in many cases of low back pain, however, can help determine the full range of treatment
options.
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.
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