Low Back Pain
Low back pain is very common. It affects 4 of 5 people at some time during their lives. It is the leading cause of disability for those aged 19 to 45 and is the second most common cause of missed work days (after the common cold) for adults younger than 45. Low back pain becomes more common as people age. It affects half of the people older than 60 at any given time. Each year, the treatment of low back pain costs more than $80 billion, and insurance claims for disability due to low back pain exceed $8 billion. Thus, although low back pain rarely results from life-threatening disorders, it is a significant health problem. However, the number of back injuries in the workplace is decreasing, perhaps because awareness of the problem has increased and preventive measures have improved.
The spine (spinal column) consists of the back bones (vertebrae), which are separated and cushioned by shock-absorbing disks made of cartilage. The vertebrae are also covered by a thin layer of cartilage. They are held in place by ligaments and muscles, which help stabilize the spine. These muscles include the two iliopsoas muscles (which run along both sides of the spine), the two erector spinae muscles (which run along the length of the spine behind it), and the many short paraspinal muscles (which run between the vertebrae). The abdominal muscles (which run from the bottom of the rib cage to the pelvis) also help stabilize the spine.
Enclosed in the spine is the spinal cord (see Section 6, Chapter 76 and Section 6, Chapter 93). Along the length of the spinal cord, the spinal nerves emerge through spaces between the vertebrae to connect with nerves throughout the body. The part of the spinal nerve nearest the spinal cord is called the spinal nerve root. Because of their position, spinal nerve roots can be compressed when the spine is injured, resulting in pain.
The lower (lumbar) spine consists of five vertebrae. It connects the chest to the pelvis and legs, providing mobility--for turning, twisting, and bending. It also provides strength--for standing, walking, and lifting. Thus, the lower back is involved in almost all activities of daily living. Low back pain can limit many activities and reduce the quality of life.
Causes
Low back pain has many causes, although often no specific cause can be identified.
One of the most common causes is muscle and ligament strains and sprains. Strains and sprains may result from lifting, exercising, or moving in an unexpected way (such as when falling or when in a car accident). When due to exercise, injury to the lower back is sometimes called weight lifter's back (lumbar strain). Weight lifter's back may be caused not only by snatching a heavy weight from the ground in weight lifting but also by pushing against an opposing lineman in football, suddenly turning to dribble after a rebound in basketball, swinging a bat in baseball, or swinging a club in golf. The lower back is more likely to be injured when a person's physical conditioning is poor and the supporting muscles of the back are weak. Having poor posture, lifting improperly, being overweight, and being tired also contribute.
Osteoarthritis (degenerative arthritis) causes the cartilage that covers and protects the vertebrae to deteriorate. This disorder is thought to be due, at least in part, to the wear and tear of years of use. The disks between the vertebrae deteriorate, narrowing the spaces there and compressing spinal nerve roots. Irregular projections of bone (spurs) may develop on the vertebrae and also compress spinal nerve roots. All of these changes can cause low back pain as well as stiffness.
In osteoporosis, bone density decreases, making the bones more likely to fracture. The vertebrae are particularly susceptible to the effects of osteoporosis, often resulting in crush (compression) fractures (which may cause sudden, severe back pain) and compression of spinal nerve roots (which may cause chronic back pain). However, most fractures due to osteoporosis occur in the upper and middle back and cause upper and middle rather than low back pain.
 See the figure A Herniated Disk.
A ruptured or herniated disk can cause low back pain. A disk has a tough covering and a soft, jelly-like interior. If a disk is suddenly squeezed by the vertebrae above and below it (as when lifting a heavy object), the covering may tear (rupture), causing pain. The interior of the disk can squeeze through the tear in the covering, so that part of the interior bulges out (herniates). This bulge can compress, irritate, and even damage the spinal nerve root next to it, causing more pain. A ruptured or herniated disk also commonly causes sciatica.
 See the figure What Is Sciatica?
In older people, a common cause of low back pain is spinal stenosis (narrowing of the spinal canal, the passageway that runs through the center of the spine and contains the spinal cord). Spinal stenosis also develops in middle-aged people who were born with a narrow spinal canal. It is caused by such disorders as osteoarthritis and Paget's disease. Spinal stenosis may cause sciatica as well as low back pain.
In ankylosing spondylitis, the spine and large joints are inflamed, resulting in stiffness and back pain. This disorder is more common among men, usually starting between the ages of 20 and 40.
Sometimes low back pain is referred pain (see Section 6, Chapter 78), which originates in another part of the body, such as the kidneys, bladder, uterus, or prostate, but is felt in the lower back. For example, premenstrual syndrome or a bladder infection can cause low back pain.
Other less common causes of low back pain include shingles; cancer that has spread to the spine from organs such as the breast, lung, prostate, or kidney; bone cancer (multiple myeloma); fibromyalgia; and birth defects such as scoliosis. Stress may contribute to low back pain, but how it does so is unclear. Heavy physical labor, obesity, smoking, and lack of exercise also contribute to low back pain.
Symptoms and Types of Low Back Pain
Low back pain may be intermittent or constant; superficial or deep; or dull and aching, throbbing, or sharp and stabbing, depending on the cause and type of pain. There are several types of low back pain.
Local pain occurs in a specific area of the lower back. It is usually due to sprains and strains. Sudden pain may be felt when the injury occurs. Local pain can often be relieved by changes in position or by light activity followed by stretching. Intense physical activity or inactivity tends to make it worse. Local pain may be constant and aching or, at times, can be intermittent and sharp. The lower back may be sore when touched. Muscle spasms may develop because the body moves in unusual ways as it tries to avoid the movements that trigger pain. Usually, local pain resolves gradually over days to weeks.
Pain due to compression of a spinal nerve root may be due to such disorders as a herniated disk, osteoarthritis, osteoporosis, spinal stenosis, or Paget's disease. The pain often occurs within minutes or hours of lifting a very heavy weight, but it may occur spontaneously. This type of pain tends to be a dull ache with a sharp, intense radiating pain sometimes superimposed on it. The pain can radiate to different parts of the body, depending on which nerve root is affected. Commonly, the pain extends from the lower back into the buttock and down the leg on the affected side, causing sciatica. Coughing, sneezing, straining, or bending over while keeping the legs straight can evoke the sharp, radiating pain. If a herniated disk is the cause, the pain is worsened by walking a distance. If spinal stenosis is the cause, the pain is typically increased by straightening the back (for example, when walking) and is relieved by bending the spine forward (for example, when leaning forward). If a compression fracture is the cause, the pain usually starts suddenly, stays in a particular area of the back, and worsens when a person stands or walks. The area near the fracture may be tender.
Usually, the pain and tenderness disappear gradually after a few weeks or months. If pressure on the nerve root is great, the pain may be accompanied by muscle weakness in the leg, a pins-and-needles sensation, or even loss of sensation and of bladder and bowel control.
Referred pain (which originates in other organs (see Section 6, Chapter 78)) tends to be deep, aching, constant, and relatively widespread (diffuse). Typically, movement does not affect it, and it worsens at night. For example, kidney infections can cause low back pain that is felt to the side rather than the center of the back.
Diagnosis
The symptoms, history, and results of a physical examination may suggest the cause of low back pain. As part of the physical examination, a doctor may ask the person to move in certain ways to determine the type of pain. For example, a doctor may ask the person to lie flat, then lift the leg without bending the knee. Usually, no other procedures are needed if the cause is a strain or sprain. If another cause is suspected, other procedures are often needed.
X-rays of the lower back can help detect a herniated disk, degenerative changes due to osteoarthritis, compression fractures due to osteoporosis, and scoliosis. However, magnetic resonance imaging (MRI) or computed tomography (CT) provides clearer images and can confirm or exclude the diagnosis of a herniated disk, spinal stenosis, or cancer. Rarely, when results of MRI are unclear, myelography (see Section 6, Chapter 77) with CT is required. Occasionally, electromyography (see Section 6, Chapter 77) is performed to confirm the location of nerve damage.
Prevention
The most effective way to prevent low back pain is to exercise regularly (see Section 1, Chapter 6). Two types of exercises--aerobic exercise and specific muscle-strengthening and stretching exercises--are helpful.
Aerobic exercise, such as swimming and walking, improves general fitness, decreases obesity, and generally strengthens muscles. Specific exercises to strengthen and stretch the muscles in the abdomen, buttocks, and back can help stabilize the spine and decrease strain on the disks that cushion the spine and the ligaments that hold it in place.
Muscle-strengthening exercises include pelvic tilts and abdominal curls. Stretching exercises include the sitting leg stretch, knee-to-chest stretch, and hip and quadriceps stretch. Stretching exercises can increase back pain in some people and therefore should be performed carefully. As a general rule, any exercise that causes or increases back pain should be stopped. Exercises should be repeated until the muscles feel mildly but not completely fatigued. Breathing during each exercise is important. When lifting weights, wearing a weight-lifting belt may help prevent back injury. People who have back pain should consult a doctor before beginning to exercise.
 See the figure Exercises to Prevent Low Back Pain.
Exercise can also help people maintain bone density and a desirable weight. Thus, exercise may reduce the risk of developing two conditions that can lead to low back pain--osteoporosis and obesity.
Maintaining good posture when standing and sitting reduces stress on the back; slouching should be avoided. Chair seats can be adjusted to a height that allows the feet to be flat on the floor, with the knees bent up slightly and the lower back flat against the back of the chair. If a chair does not support the lower back, a pillow can be used behind the lower back. Sitting with the feet on the floor rather than with the legs crossed is advised. People should avoid standing or sitting for long periods. If prolonged standing or sitting is unavoidable, changing positions frequently may reduce stress on the back.
Sleeping in a comfortable position on a firm mattress is recommended. Pillows under the waist and head can be used for support by people who sleep on their side, and a pillow under the knees can be used by those who sleep on their back. Pillows under the head should not force the neck to bend too much.
Learning to lift properly helps prevent back injury. The knees should be bent enough that the arms are level with the object to be lifted. The legs, not the back, should be used to lift. Lifting an object over the head increases the risk of back injury. Using a steady footstool makes such lifting unnecessary. Heavy objects should be carried close to the body. Stopping smoking is also recommended.
Treatment
For low back pain that has recently developed, treatment begins with avoiding activities that stress the spine and cause pain--such as lifting heavy objects and bending. Bed rest for a few days may relieve pain. However, it does not hasten the resolution of the pain, and most experts recommend continued activity. Bed rest, if required, should last no more than 1 or 2 days. If a specific disorder is causing low back pain, treating that disorder--for example, giving antibiotics to treat a bladder infection--may relieve the low back pain.
Over-the-counter or prescription nonsteroidal anti-inflammatory drugs (NSAIDs) (see Section 2, Chapter 18 and Section 6, Chapter 78) can be taken to relieve pain and reduce inflammation. Muscle relaxants, such as methocarbamol, carisoprodol, cyclobenzaprine, or diazepam, may be given to relieve muscle spasms, although many experts question their usefulness. These drugs are not recommended for older people, who are more likely to experience side effects.
Application of heat or cold and massage may help (see Section 1, Chapter 7). Usually, traction is not useful. Some reports suggest that acupuncture and chiropractic manipulation hasten the resolution of pain, but others suggest little or no benefit. During recovery, a back brace or corset is sometimes recommended for a short period or for use during back-stressing activities. However, these support garments can be uncomfortable and, if worn for a long time, may weaken the back muscles by doing their work for them.
After the pain has subsided, light activity, as recommended by a doctor or physical therapist, can speed healing and recovery. Specific exercises to strengthen and stretch the back are usually recommended to help prevent low back pain from becoming chronic or recurring. Other preventive measures (maintaining good posture, using a firm mattress with appropriately placed pillows, lifting properly, and stopping smoking) should be continued or started. In response to these measures, most episodes of back pain resolve in 1 to 2 weeks. Regardless of treatment, 80 to 90% of such episodes resolve within 6 weeks.
If low back pain is chronic, additional measures are needed. Aerobic exercise may help, and weight reduction, if necessary, is advised. If the pain is severe, NSAIDs may not provide sufficient pain relief, and opioid analgesics (see Section 6, Chapter 78) may be required. If these analgesics are ineffective, some experts recommend that a corticosteroid, such as dexamethasone or methylprednisolone, plus a local anesthetic, such as lidocaine, be periodically injected around the spinal canal--as an epidural injection. However, these injections are effective usually only for several days to weeks.
Transcutaneous electrical nerve stimulation (TENS) is sometimes recommended (see Section 6, Chapter 78). A device that produces a gentle tingling sensation by generating a low oscillating current is used. A therapist applies the device to the painful area several times a day for 20 minutes to several hours at a time, depending on the severity of the pain. People are sometimes taught to use the device themselves.
If a disorder is causing severe and constant pain or serious symptoms, surgery may be necessary. If spinal nerve root compression due to a herniated disk is causing symptoms such as relentless sciatica, weakness, loss of sensation, or loss of bladder and bowel control, surgical removal of the disk (diskectomy) and part of the vertebra (laminectomy) may be necessary. A general anesthetic is usually required. The hospital stay after surgical removal of a disk is usually 1 or 2 days. Often, microsurgical techniques, with a small incision, can be used. A local anesthetic is used, and hospitalization is not required. However, when the incision is small, the surgeon may not be able to see and therefore may not remove all fragments of the herniated disk. After either procedure, most people can resume all of their activities after a few weeks. More than 90% of people recover fully.
For severe spinal stenosis, surgery to widen the spinal canal by removing a larger part of the vertebra may be performed. A general anesthetic is usually required. The hospital stay is usually 4 or 5 days. People may need 3 to 4 months before they can resume all of their activities. About two thirds of the people have a good or full recovery. For most of the rest, symptoms are prevented from worsening.
When the spine is unstable because of degeneration due to osteoarthritis, vertebrae may be fused together. However, fusion decreases mobility and may put additional stress on the rest of the spine.
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