Back pain

Definition

Back pain may occur in the upper, middle, or lower back; it is most often experienced in the lower back. It may originate from the bones and ligaments forming the spine, the muscles and tendons supporting the back, the nerves that exit the spinal column, or even the internal organs.

Description

Back pain can range from mild, annoying discomfort to excruciating agony. Depending on how long it lasts, it can be described as acute or chronic. Acute back pain comes on suddenly but lasts only briefly, and is often intense. While chronic back pain is typically not as severe as acute back pain, it persists for a longer period and may recur frequently. The duration of acute back pain is a few days to a few weeks, with improvement during that time, whereas chronic back pain lasts for more than three months and often gets progressively worse.

The back is composed of bones, muscles, ligaments, tendons, and other tissues that make up the posterior, or back half, of the trunk extending from the neck to the pelvis. Running through and supporting the back is the spinal column, which forms a cage-like structure enclosing the spinal cord. Nerve signals directing movement travel from the brain to the limbs, while nerve signals transmitting pain and other sensations travel from the limbs to the brain. All nerve signals pass through the spinal cord. If the individual vertebrae stacked together to form the spinal column slide out of place, which is referred to as spondylolisthesis, pain may result as the bones rub against each other or as nerves entering the spinal cord are compressed.

Demographics

Lower back pain affects approximately four out of five adults at least once during their lifetime, often inter-fering with work, recreation, or household chores and

other routine activities. It is one of the most common conditions for which Americans seek medical attention, and it is second only to headache as the most common neurological condition in the United States. According to the National Institute for Occupational Safety and Health, back pain related to work is one of the most-often diagnosed occupational disorders.

Health care dollars spent on the diagnosis and treatment of low back pain are estimated to be at least $50 billion annually, with additional costs related to disability and delay in return to work.

Back pain strikes equal numbers of men and women, and it typically begins between the fourth and sixth decades. The likelihood of disc disease and spinal degeneration, both prominent causes of back pain, increases with age. A sedentary lifestyle increases vulnerability to back pain, especially when coupled with obesity or sporadic bursts of overexertion.

Because of their greater flexibility and lack of agerelated degeneration, children and teenagers are much less prone than adults to develop medically significant back pain.

Causes and symptoms

The spinal column is composed of 24–25 movable bones, or vertebrae, held together by ligaments and separated by intervertebral discs that act as shock absorbers. Although this structure allows great flexibility and range of movement, it also affords many opportunities for injury. Compounding the potential for injury is that the human spine bears weight in the upright position and must therefore counteract gravity. Stresses on the muscles and ligaments that support the spine can cause acute pain or chronic injury.

With normal aging, the fluid cushioning the intervertebral discs tends to dry up, making them more brittle and less protective of the vertebrae. The normal wear and tear of daily activities can eventually erode the vertebral edges, undermining stability and putting pressure on nerves that enter and exit the spinal column to control movement and sensation of the arms and legs.

Heavy physical labor accelerates these processes, but lack of physical activity allows the muscles to lose tone, offering less protection to the spine as it twists and turns. Consequently, regardless of activity levels, back pain becomes more common with increasing age. Bone density and muscle flexibility and strength also tend to decrease with age, further increasing the chance of painful injury.

Obesity increases both the weight that the spine must support and the pressure on the discs, thereby elevating the risk of back pain and injury. Physically demanding sports can also damage the back, especially in the case of "weekend warriors" who overexert themselves on occasion while generally maintaining a low level of physical fitness. Even simple movements like bending over may trigger muscle spasms in individuals with chronic pain.

Injuries unrelated to activity may include motor vehicle accidents or falls that subject the spine and its supporting structures to direct impact or unusual torque. These injuries and those related to overexertion may result in painful sprain, strain, or spasm in the back muscles or ligaments.

Excessive strain or compression of the spine may cause disc herniation , in which the disc bulges or even ruptures. The bulging disc or its fragments may be displaced outward, putting pressure on nerve roots entering or exiting the spine and thereby causing pain. Most disc herniations occur in the lumbar or lower part of the spinal column, especially between the fourth and fifth lumbar vertebrae (L4 and L5, respectively) and between the fifth lumbar and first sacral vertebrae (L5 and S1, respectively).

Activities involving hyperextension of the back, such as gymnastics, may result in spondylosis, or disruption of the joint between adjacent vertebrae. A more extreme form of spondylosis is spondylolisthesis, or slippage of one vertebra relative to its neighbor. Impact or excessive mechanical force to the spine may cause spinal fracture. After repeated back injuries, buildup of scar tissue eventually weakens the back and can increase the risk of more serious injury.

Diseases of the bone, such as endocrine conditions or metastatic cancer spreading from the lung, breast, prostate, or other primary site, may cause fractures or other painful conditions in the spinal column. Fractures occurring without apparent traumatic injury, especially in a debilitated or chronically ill person, may be a warning of cancer or other underlying bone disease such as osteoporosis. Osteoporosis is a metabolic bone disease in which progressive decreases in bone strength and density makes the bones brittle, porous, and easily broken.

Other diseases causing back pain include arthritis, which erodes the joints, myopathies and inflammatory conditions, which involve the muscles, and neuropathy, which affects the nerves. Back pain is common in diabetes because this disease may be complicated by myopathy (though this is rare) or neuropathy, both of which create gait disturbances that, in turn, cause back pain. In women, fibromyalgia is a fairly common chronic condition associated with musculoskeletal pain, fatigue , morning stiffness, and other nonspecific symptoms.

Conditions affecting the spine include spinal degeneration from disc wear and tear, which can narrow the spinal canal and cause back stiffness and pain, especially upon awakening or after prolonged walking or standing. Spinal stenosis is a narrowing of the spinal canal, a condition that is present from birth. Both conditions increase the likelihood of back pain from disc disease. Spondylitis, or inflammation of the spinal joints, is characterized by chronic back pain and stiffness.

Anatomical abnormalities of the skeleton subject the vertebrae and supporting structures to increased strain, and often manifest as back pain. Scoliosis is an asymmetric curvature of the spine to one side. Kyphosis, or dowager's hump, refers to a pronounced rounding of the normal forward curve of the upper back, whereas lordosis (swayback) is an exaggeration of the normal backward arch in the lower back.

Lifestyle and general medical factors contributing to back pain include smoking, pregnancy, inherited disorders affecting the spine or limbs, poor posture, inappropriate posture for the activity being performed, and poor sleeping position. Psychological stress is a common but often unrecognized source of back pain. Injuries, arthritis, or other conditions affecting the feet, ankles, knees, or hips may result in abnormal walking patterns that exacerbate or cause back pain.

Apart from all the musculoskeletal structures and nerves, the internal organs can also be a source of pain felt in the back. Kidney stones, urinary tract infections, blood clots, stomach ulcers, and diseases of the pancreas can all be experienced as back pain. Fever or other bodily symptoms suggesting infection or involvement of internal organs should prompt a medical evaluation.

The discomfort of back pain may range from the dull ache of muscle soreness, to shooting or stabbing pain if a muscle acutely goes into spasm, to a toothache-like sensation along the course of a spinal nerve. Surprisingly, the severity of the pain may not be correlated with the severity of injury. In uncomplicated back strain, acute muscle spasm can cause agonizing back pain that prevents the person from standing up straight. On the other hand, a massive disc herniation may not produce pain or any other symptoms.

Depending on its source, back pain is usually aggravated by certain movements, although prolonged sitting or standing may also make it worse. Associated symptoms may include limited flexibility and range of motion, difficulty straightening up, or weakness in the arms or legs.

When back pain is caused by nerve compression , pain may travel, or radiate, from the back to peripheral areas, usually following the course of the nerve as it supplies the arm or leg. There may be numbness, sensitivity to touch, or "pins and needles" (tingling sensations) along the same distribution. Pain originating from an internal organ may also radiate to an area of the back supplied by the same nerve root as that organ.

Sciatica is a common form of nerve pain related to compression of fibers from one or more of the lower spinal nerve roots, characterized by burning low back pain radiating to the buttock and back of the leg to below the knee or even to the foot. In more severe cases, there may be numbness or tingling in the same regions, as well as weakness. Typically, sciatic pain is caused by a herniated or ruptured disc, but it may also rarely be caused by a tumor or cyst.

Worrisome symptoms associated with back pain that warrant immediate medical attention include loss of control of bowel or bladder, change in bowel and bladder habits, or profound or progressive weakness or sensory loss. Any of these may signal compression of one or more nerve roots, or even of the spinal cord itself, which may result in irreversible paralysis if not treated promptly.

Low back pain is unusual in children, unless caused by motor vehicle accidents and other traumatic injuries. One notable exception is back strain and muscle fatigue caused by carrying an overloaded backpack. According to the U.S. Consumer Product Safety Commission, more than 13,260 injuries caused by backpacks were treated at medical offices, clinics, and emergency rooms in 2000.

Persistent back pain in a young child should raise suspicions of a serious problem such as a tumor or infection of the spine, meriting further evaluation and treatment. Teenagers indulging in extreme sports may subject themselves to compression fractures, stress injuries, spondylosis, and rarely, disc herniation.

Diagnosis

According to the Clinical Practice Guideline for Understanding Acute Low Back Problems, published in 1994 by the Department of Health and Human Services Agency for Health Care Policy and Research, the precise cause of back pain is seldom determined, despite the advent of sophisticated diagnostic techniques. Although x rays and other imaging tests typically fail to disclose the reason for back pain, they may be important in ruling out serious conditions demanding specific treatment.

As with most other neurologic conditions, the cornerstone of diagnosis is the history, or analysis, of the patient's complaints, and the physical and neurologic examination. Additional diagnostic testing is needed in only about 1% of individuals with acute back pain. If symptoms do not improve in four to six weeks, further testing may be indicated.

The history focuses on a description of the pain and other symptoms, the circumstances in which the pain first occurred, and conditions that tend to make it better or worse, as well as any injuries and a general medical history. The physical examination should begin with a general medical examination and should include finding areas of back tenderness, testing spinal range of motion and flexibility, and measuring strength, sensation, and reflexes in the legs.

Specialized maneuvers include the straight leg-raising test. While the patient is lying flat on the back, pain in the low back or leg caused by raising a straight leg off the examining table suggests sciatica.

If there is suspicion of a serious cause for back pain, imaging or other tests may be done right away. Reasons for immediate testing include sudden back pain after a fall, suggesting fracture; back pain at night, suggesting a tumor, fever, or other signs of back infection; or loss of bowel or bladder control or progressive leg weakness, suggesting compression of the spinal cord or nerve roots. Cancer patients who develop back pain should have testing to determine if cancer has spread to the spine, which can lead to spinal cord compression and permanent paralysis if not treated promptly. Children with back pain unrelated to backpacks or sports injuries should also be tested sooner rather than later.

X rays are typically performed first as they are readily available and do a good job of visualizing bony structures, fractures, and deformities. However, they do not usually detect injuries of the muscles or other soft tissues. If x rays are negative and the doctor suspects a tumor, infection, or fracture not easily seen on x ray, bone scans may be helpful. In this test, injecting a low-dose radioactive medication into a vein allows the doctor to study bone structure and function using a special scanning camera.

Because magnetic resonance imaging (MRI) provides sharp, clear images of bones, discs, nerves, and soft tissues, it is the best test to show disc herniation and nerve compression. This test uses magnetic signals in water rather than x rays, and therefore poses no risk to the patient other than that associated with a contrast dye, which is not needed in most cases. Although the MRI may show disc bulging, this does not necessarily mean that the disc bulge is causing the back pain or that it needs to be treated. In about half of people without back pain, the MRI shows disc bulges. On the other hand, a bulging disc directly compressing a spinal nerve is more significant and may be causing pain and associated symptoms.

Computed tomography (CT) scan of the spine uses a computer to reconstruct cross-sectional x-ray images. A CT scan is good at visualizing bone problems like spinal stenosis, but it is not as sensitive as the MRI in diagnosing soft tissue injuries, and it has the added disadvantage of considerable x-ray exposure.

Because they are painful and carry a small risk of injury to the patient, certain tests are only done in patients who are about to have surgery so that the surgeon can plan the operation better. In myelography, dye is injected into the spinal canal and the patient is then tilted in different directions on a special table, allowing dye to outline the spinal cord and nerve roots and to show areas of compression. In discography, dye is injected into a disc space thought to be causing the pain, allowing the surgeon to confirm that an operation on that disc will likely relieve pain.

If there is evidence of nerve root compression on CT, MRI, history, or physical examination, electromyography (EMG), nerve conduction velocity (NCV), and evoked potential (EP) studies help determine the motor and sensory function of the involved nerve(s). These tests are also useful in diagnosing myopathy or neuropathy. During the EMG, fine needles inserted into the muscle determine how rapidly and forcefully the muscle contracts when stimulated. By applying a series of weak electrical shocks over areas supplied by a particular nerve, the NCV helps determine sensory function. Both tests are helpful in pinpointing specific patterns of nerve involvement.

In special cases, thermography and ultrasound imaging may provide additional information. Thermography uses infrared sensing devices to measure differences in temperature in body regions thought to be the source of pain. Ultrasound uses high-frequency sound waves to show tears in ligaments, muscles, tendons, and other soft tissues.

Treatment team

Internists and general practitioners are often the first to see patients with back pain. Depending on the cause and severity of pain, neurologists, orthopedists, physical medicine specialists, pain management specialists, psychologists, psychiatrists, and other medical specialists may offer evaluation and treatment. Physical therapists, chiropractors, acupuncturists, vocational rehabilitation counselors, and radiology technicians may all become involved in management.

Treatment

Most cases of acute musculoskeletal back pain respond in a few days or weeks to limited rest, combined with appropriate exercise and education on correct movement patterns to avoid further injury. However, many cases resolve on their own without any treatment during a similar time period.

Although acute back pain was previously treated with complete, prolonged bed rest, this is no longer recommended because it leads to muscular deconditioning and loss of bone calcium, which can make the situation worse. Other complications of bed rest may include depression and blood clots in the legs. In 1996, a Finnish study showed that an exercise program to improve back mobility, coupled with resumption of normal activities and avoidance of rest during the day, allowed better back range of motion by the seventh day than did a program of strict bed rest.

Current wisdom is to limit bed rest for low back pain to one day, beginning immediately after injury or acute onset of pain, followed by resuming activities as soon as possible. While resting or sleeping, the best positions are on one side with a pillow between the knees, or on the back with a pillow under the knees.

Exercise speeds up recovery, reduces the risk of future back injuries, and releases the body's natural pain relievers known as endorphins. Doctors may suggest specific back exercises; aerobic exercises that improve conditioning without undue stress on the back include walking, stationary bicycle, and swimming or water aerobics. Any exercise program should be started slowly and built up gradually. Discomfort during exercise is not unusual, especially when starting out. However, patients experiencing pain of moderate or greater severity or lasting more than 15 minutes during exercise should stop exercising and inform their physician.

Local application of an ice pack or heat to the painful area, or use of muscle balms containing menthol, eucalyptus, or camphor may reduce inflammation, feel soothing, and facilitate exercise. Cold packs are recommended within the first 48 hours after back pain begins, with use of hot packs subsequently.

For back pain following an injury, physical therapy may offer strengthening programs and education in posture, movement patterns, and lifting techniques that protect the back to avoid further injury. Exercises designed to increase flexibility, tone, and strength help to replace fluid into dehydrated discs. Ultrasound, moist heat application, hydrotherapy involving pools or spas, or massage of painful areas may relieve pain and spasm, increase local circulation, and improve mobility.

Transcutaneous electrical nerve stimulation (TENS) uses a battery-powered device generating weak electrical impulses applied along the course of affected nerves to block pain signals traveling to the brain. This technique may also stimulate production of endorphins, or naturally occurring pain relievers, by the brain.

Although traction, or spinal stretching using weights applied to the spine, was once thought to decrease pressure on the nerve roots, this treatment has not been proven to be effective and is now seldom used.

Nonsteroidal anti-inflammatory drugs (NSAIDs) may relieve pain by reducing inflammation. These include naproxen (Aleve) and ibuprofen (Nuprin, Motrin IB, and Advil). Because these drugs may cause gastrointestinal bleeding, patients with ulcers, bleeding disorders, or other gastrointestinal conditions should avoid them. Other side effects may include kidney damage, and salt and fluid retention leading to high blood pressure.

COX-2 inhibitors are a more recently developed class of prescription drugs that reduce pain and inflammation with fewer gastrointestinal effects than the NSAIDs. These include celecoxib (Celebrex) and rofecoxib (Vioxx).

For severe back pain caused by inflammation of nerve roots or other structures, steroids may be injected directly into the inflamed area, often combined with local anesthetic. These can be epidural injections targeting the nerve roots, or trigger point injections into tender areas of muscle.

Other medications that may be indicated include analgesics or pain relievers such as aspirin or acetaminophen (Tylenol), muscle relaxants, antidepressants, or antiepileptic drugs . Muscle relaxants such as cyclobenzaprine (Flexeril), carisoprodol (Soma), and methocarbamol (Robaxin) may relieve painful spasms, but may also cause drowsiness and should not be used when working, driving, or operating heavy equipment.

Some antidepressants, especially when given in low doses, act as pain relievers in addition to reducing symptoms of depression and insomnia. Among these medications are tricyclic antidepressants such as amitriptyline and desipramine; and newer antidepressants such as the selective serotonin reuptake inhibitors (SSRI)s are being tested for their ability to relieve pain. However, a review of studies published in November 2003 suggests that the tricyclic antidepressants, but not the SSRIs, reduce pain symptoms. Although antiepileptic drugs are primarily used to treat seizures , they have a stabilizing effect on nerve cells that makes them effective for certain types of nerve pain.

For severe pain, opioids and narcotics such as oxycodone-release (Oxycontin), acetaminophen with codeine (Tylenol with codeine), and meperidine (Demerol) may be prescribed. However, they may be addicting and associated with troublesome side effects including constipation, impaired judgment and reaction time, and sleepiness. Therefore, these drugs should only be used under a doctor's supervision, only when other medications are ineffective, and only for limited periods. Some pain management specialists believe that habitual use of these drugs may worsen depression and even increase pain.

In some patients, spinal manipulation, also known as osteopathic manipulative therapy or chiropractic, may correct patterns of spinal imbalance that impedes recovery. It may be helpful during the first month of low back pain, but it should be avoided in patients with previous back surgery, back injury related to underlying disease, and back malformations. Before proceeding with chiropractic, it may be wise to get clearance from a medical doctor.

Acupuncture is an alternative medicine technique in which trained practitioners place very-fine needles at precisely specified body locations to relieve pain. Insertion of these needles is thought to unblock the body's normal flow of energy and to release peptides, which are naturally occurring pain relievers. Clinical studies are underway to compare how effective acupuncture is relative to standard treatments for low back pain.

Biofeedback is a treatment recommended by some pain specialists, in conjunction with other treatments. By placing electrodes on the skin and connecting them to a biofeedback machine, the patient learns to modify the response to pain by controlling muscle tension, heart rate, and skin temperature. Meditation or other relaxation techniques may enhance the response to biofeedback training.

Patients who do not respond to the above treatments may be candidates for back surgery if there is a clear abnormality in structure that could be corrected surgically. Although surgery is typically a last resort, it may be done on an urgent basis if the spinal cord or nerve roots are being compromised.

Discectomy is a surgical procedure to relieve pressure on a nerve root caused by a bulging disc or bone spur, whereas foraminotomy enlarges the bony hole, or foramen, where a nerve root enters or exits the spinal canal. In spinal laminectomy , or spinal decompression, a piece of the bony roof of the spinal canal known as the lamina is removed on one or both sides to increase the size of the spinal canal and reduce pressure on the spinal cord and nerve roots.

Spinal fusion stabilizes the spine and prevents painful movements, but with resulting loss of flexibility. The spinal discs between two or more vertebrae are removed, and the neighboring vertebrae are joined together with bone grafts and/or metal devices attached by screws. To allow the bone grafts to grow and fuse the vertebrae together, a long recovery period is needed. The Food and Drug Administration (FDA) has approved the intervertebral body fusion device, the anterior spinal implant, and the posterior spinal implant for use in this type of procedure.

To relieve severe chronic pain, spinal cord stimulation devices may be surgically implanted. These devices discharge electrical impulses to stimulate the spinal cord and to block the perception of pain. Other procedures used as a last resort cut nerve fibers to relieve pain, but patients may find the resultant altered sensations more troubling than the pain itself. Rhizotomy involves cutting the nerve root near its point of entry to the spinal cord. Cordotomy destroys bundles of nerve fibers on one or both sides of the spinal cord, and dorsal root entry zone (DREZ) operation severs spinal neurons.

Clinical trials

The National Institute of Neurological Disorders and Stroke (NINDS) and other institutes at the National Institutes of Health (NIH) fund, support, and conduct general pain research, as well as studies of new treatments for pain and nerve damage associated with back pain and other conditions.

Ongoing studies are comparing the effects of different drugs; different treatment approaches such as standard care, chiropractic, or acupuncture; and surgery versus non-surgical treatments. Treatments under investigation include acupuncture and yoga in chronic low back pain, low-dose radiation to decrease postsurgical scarring around the spinal cord, and artificial spinal disc replacement surgery.

Studies that are currently recruiting patients include magnets in the treatment of sciatica and a comparison of nortriptyline and MS Contin in sciatica. Contact information for both trials is (800) 411-1222, or [email protected].

Prognosis

In about 90% of people, back pain resolves within one month without treatment. Although most people with acute low back pain improve within a few days, others take much longer to recover or develop more serious conditions, especially if left untreated. Fractures, tumors, severe disc herniations, or other spinal conditions compromising nerve roots, spinal cord, or spinal stability may lead to progressive neurologic deterioration if not treated promptly.

Special concerns

Although back pain is usually not a cause for serious concern, it can interfere with work and activities and may even be disabling. Adopting lifestyle habits to prevent back pain and injury are therefore worthwhile, beginning at an early age. These include weight control and nutritionally sound diet, regular exercise, stretching before strenuous exercise, stopping smoking, good posture, and reducing emotional stress contributing to muscle tension.

In the workplace, at home, and while driving, supportive seats can reduce stress and fatigue. Other ergonomically designed furniture, tools, workstations, and living space help protect the body from injury.

Sleeping on the side with knees bent and cradling a pillow, or on the back with a pillow under bent knees, reduces back strain. Proper lifting techniques include bending at the knees rather than the waist, holding the weight close to the body rather than at arm's length, exhaling while lifting a heavy load, not twisting while lifting, and not attempting to lift a load that is too heavy. Frequent stretch breaks while sitting, standing, or working in one position for long periods will reduce muscle fatigue and back discomfort. Wearing comfortable, supportive, lowheeled shoes helps prevent falls and cushions the weight load on the spine during standing and walking.

Children using backpacks should be taught proper lifting techniques, should reduce the amount of books or supplies carried, or should switch to a wheeled carrier.

Resources

PERIODICALS

Birbara, C. A., et al. "Treatment of Chronic Low Back Pain with Etoricoxib, A New Cyclo-Oxygenase-2 Selective Inhibitor: Improvement in Pain and Disability—A Randomized, Placebo-Controlled, 3-Month Trial." Journal of Pain 2003 Aug 4(6): 307–15.

Breckenridge, J., and J. D. Clark. "Patient Characteristics Associated with Opioid Versus Nonsteroidal Anti-Inflammatory Drug Management of Chronic Low Back Pain." Journal of Pain 2003 Aug 4(6): 344–50.

Lewis, Carol. "What to Do When Your Back Is in Pain." U.S. Food And Drug Administration. FDA Consumer Magazine (March-April 1998).

Ohnmeiss, D. D., and R. F. Rashbaum. "Patient Satisfaction with Spinal Cord Stimulation for Predominant Complaints of Chronic, Intractable Low Back Pain." Spine Journal 2001 Sep-Oct 1(5): 358–63.

Staiger, T. O., B. Gaster, M. D. Sullivan, and R. A. Deyo. "Systematic Review of Antidepressants in the Treatment of Chronic Low Back Pain." Spine 2003 Nov 15 28(22): 2540–5C.

WEBSITES

Clinical Trials. (March 18, 2004.) <http://www.clinicaltrials.gov/ct/action/GetStudy>.

National Institute Of Neurological Disorders and Stroke. NIH Neurological Institute. PO Box 5801, Bethesda, MD 20824. (800) 352-9424. (March 18, 2004.) <http://www.ninds.nih.gov/health_and_medical/disorders/backpain_doc.htm>.

Spine-health.com. 1840 Oak Avenue, Suite 112, Evanston, IL 60201. (March 18, 2004.) <http://www.spinehealth.com/topics/cd/kids/kids1.html>.

Spine-health.com. 1840 Oak Avenue, Suite 112, Evanston, IL 60201. (March 18, 2004.) <http://www.spine-health.com/topics/cd/tlbp/type01.html>.

U.S. Food And Drug Administration. 5600 Fishers Lane, Rockville, MD 20857-0001. (888) 463-6332. (March 18, 2004.) <http://www.fda.gov/fdac/features/1998/298_back.html>.

Your Medical Source. (March 18, 2004.) <http://www.yourmedicalsource.com/library/backpain/BAK_types.html>.

Laurie Barclay