If you have lower back pain, you are not alone. Nearly everyone at some point has back pain that interferes with work, routine daily activities, or recreation. Americans spend at least $50 billion each year on low back pain, the most common cause of job-related disability and a leading contributor to missed work. Back pain is the second most common neurological ailment in the United States - only headache is more common. Fortunately, most occurrences of low back pain go away within a few days. Others take much longer to resolve or lead to more serious conditions.
Acute or short-term low back pain generally lasts from a few days to a few weeks. Most acute back pain is mechanical in nature - the result of trauma to the lower back or a disorder such as arthritis. Pain from trauma may be caused by a sports injury, work around the house or in the garden, or a sudden jolt such as a car accident or other stress on spinal bones and tissues. Symptoms may range from muscle ache to shooting or stabbing pain, limited flexibility and/or range of motion, or an inability to stand straight. Occasionally, pain felt in one part of the body may "radiate" from a disorder or injury elsewhere in the body. Some acute pain syndromes can become more serious if left untreated.
Chronic back pain is measured by duration - pain that persists for more than 3 months is considered chronic. It is often progressive and the cause can be difficult to determine.
Anatomy of the Back
The back is an intricate structure of bones, muscles, and other tissues that form the posterior part of the body's trunk, from the neck to the pelvis. The centerpiece is the spinal column, which not only supports the upper body's weight but houses and protects the spinal cord - the delicate nervous system structure that carries signals that control the body's movements and convey its sensations. Stacked on top of one another are more than 30 bones - the vertebrae - that form the spinal column, also known as the spine.
Each of these bones contains a roundish hole that, when stacked in register with all the others, creates a channel that surrounds the spinal cord. The spinal cord descends from the base of the brain and extends in the adult to just below the rib cage. Small nerves ("roots") enter and emerge from the spinal cord through spaces between the vertebrae.
Because the bones of the spinal column continue growing long after the spinal cord reaches its full length in early childhood, the nerve roots to the lower back and legs extend many inches down the spinal column before exiting. This large bundle of nerve roots was dubbed by early anatomists as the cauda equina, or horse's tail.
The spaces between the vertebrae are maintained by round, spongy pads of cartilage called intervertebral discs that allow for flexibility in the lower back and act much like shock absorbers throughout the spinal column to cushion the bones as the body moves. Bands of tissue known as ligaments and tendons hold the vertebrae in place and attach the muscles to the spinal column.
Starting at the top, the spine has four regions:
- the seven cervical or neck vertebrae (labeled C1-C7),
- the 12 thoracic or upper back vertebrae (labeled T1-T12),
- the five lumbar vertebrae (labeled L1-L5), which we know as the lower back, and
- the sacrum and coccyx, a group of bones fused together at the base of the spine.
The lumbar region of the back, where most back pain is felt, supports the weight of the upper body.
As people age, bone strength and muscle elasticity and tone tend to decrease. The discs begin to lose fluid and flexibility, which decreases their ability to cushion the vertebrae.
Pain can occur when, for example, someone lifts something too heavy or overstretches, causing a sprain, strain, or spasm in one of the muscles or ligaments in the back. If the spine becomes overly strained or compressed, a disc may rupture or bulge outward. This rupture may put pressure on one of the more than 50 nerves rooted to the spinal cord that control body movements and transmit signals from the body to the brain. When these nerve roots become compressed or irritated, back pain results.
Low back pain may reflect nerve or muscle irritation or bone lesions. Most low back pain follows injury or trauma to the back, but pain may also be caused by degenerative conditions such as arthritis or disc disease, osteoporosis or other bone diseases, viral infections, irritation to joints and discs, or congenital abnormalities in the spine. Obesity, smoking, weight gain during pregnancy, stress, poor physical condition, posture inappropriate for the activity being performed, and poor sleeping position also may contribute to low back pain. Additionally, scar tissue created when the injured back heals itself does not have the strength or flexibility of normal tissue. Buildup of scar tissue from repeated injuries eventually weakens the back and can lead to more serious injury.
Occasionally, low back pain may indicate a more serious medical problem. Pain accompanied by fever or loss of bowel or bladder control, pain when coughing, and progressive weakness in the legs may indicate a pinched nerve or other serious condition. People with diabetes may have severe back pain or pain radiating down the leg related to neuropathy. People with these symptoms should contact a doctor immediately to help prevent permanent damage.
Who is most likely to develop low back pain?
Nearly everyone has low back pain sometime. Men and women are equally affected. It occurs most often between ages 30 and 50, due in part to the aging process but also as a result of sedentary life styles with too little (sometimes punctuated by too much) exercise. The risk of experiencing low back pain from disc disease or spinal degeneration increases with age.
Low back pain unrelated to injury or other known cause is unusual in pre-teen children. However, a backpack overloaded with schoolbooks and supplies can quickly strain the back and cause muscle fatigue. The U.S. Consumer Product Safety Commission estimates that more than 13,260 injuries related to backpacks were treated at doctor's offices, clinics, and emergency rooms in the year 2000. To avoid back strain, children carrying backpacks should bend both knees when lifting heavy packs, visit their locker or desk between classes to lighten loads or replace books, or purchase a backpack or airline tote on wheels.
What conditions are associated with low back pain?
Conditions that may cause low back pain and require treatment by a physician or other health specialist include:
Bulging disc (also called protruding, herniated, or ruptured disc). The intervertebral discs are under constant pressure. As discs degenerate and weaken, cartilage can bulge or be pushed into the space containing the spinal cord or a nerve root, causing pain. Studies have shown that most herniated discs occur in the lower, lumbar portion of the spinal column.
Sciatica is a condition in which a herniated or ruptured disc presses on the sciatic nerve, the large nerve that extends down the spinal column to its exit point in the pelvis and carries nerve fibers to the leg. This compression causes shock-like or burning low back pain combined with pain through the buttocks and down one leg to below the knee, occasionally reaching the foot. In the most extreme cases, when the nerve is pinched between the disc and an adjacent bone, the symptoms involve not pain but numbness and some loss of motor control over the leg due to interruption of nerve signaling. The condition may also be caused by a tumor, cyst, metastatic disease, or degeneration of the sciatic nerve root.
A much more serious complication of a ruptured disc is cauda equina syndrome, which occurs when disc material is pushed into the spinal canal and compresses the bundle of lumbar and sacral nerve roots. Permanent neurological damage may result if this syndrome is left untreated.
Spinal degeneration from disc wear and tear can lead to a narrowing of the spinal canal. A person with spinal degeneration may experience stiffness in the back upon awakening or may feel pain after walking or standing for a long time.
Spinal stenosis related to congenital narrowing of the bony canal predisposes some people to pain related to disc disease.
Osteoporosis is a metabolic bone disease marked by progressive decrease in bone density and strength. Fracture of brittle, porous bones in the spine and hips results when the body fails to produce new bone and/or absorbs too much existing bone. Women are four times more likely than men to develop osteoporosis. Caucasian women of northern European heritage are at the highest risk of developing the condition.
Skeletal irregularities produce strain on the vertebrae and supporting muscles, tendons, ligaments, and tissues supported by spinal column. These irregularities include scoliosis, a curving of the spine to the side; kyphosis, in which the normal curve of the upper back is severely rounded; lordosis, an abnormally accentuated arch in the lower back; back extension, a bending backward of the spine; and back flexion, in which the spine bends forward.
Fibromyalgia is a chronic disorder characterized by widespread musculoskeletal pain, fatigue, and multiple "tender points," particularly in the neck, spine, shoulders, and hips. Additional symptoms may include sleep disturbances, morning stiffness, and anxiety.
Spondylitis refers to chronic back pain and stiffness caused by a severe infection to or inflammation of the spinal joints. Other painful inflammations in the lower back include osteomyelitis (infection in the bones of the spine) and sacroiliitis (inflammation in the sacroiliac joints).
Source: The National Institute of Neurological Disorders and Stroke
Last Reviewed: July 2003
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