Sciatica occurs when there is pressure or damage to the sciatic nerve. This nerve starts in the spine and runs down the back of each leg. This nerve controls the muscles of the back of the knee and lower leg and provides sensation to the back of the thigh, part of the lower leg, and the sole of the foot.
What causes sciatica?
In many cases of sciatica there is no single obvious cause. It is thought that general 'wear and tear' on the body may lead to episodes of sciatica. This is why the condition is more common in people who are over 40 years of age or those who have occupations that involve a lot of physical activity.
Common causes of sciatica include:
• Piriformis syndrome (a pain disorder involving the narrow piriformis muscle in the buttocks)
• Slipped disk
• Degenerative disk disease
• Spinal stenosis
• Pelvic injury or fracture
• Tumors
Herniated disc
A herniated (or slipped) disc is the most common identified cause of sciatica.
Your spine is made up of vertebrae, discs, and nerves. The vertebrae are supported and cushioned by discs of cartilage. As a person gets older the discs start to become harder, tougher and more brittle. Repeated strain on the back means that there is a chance that the hardened discs may split or rupture. If a rupture occurs some of the soft core of tissue inside the disc can press against the sciatic nerve, causing 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 (the nucleus pulposus) pushes outward. The damaged disk can take on 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.
Pain in the leg may be worse than the back pain in cases of herniated disks. There is also some debate 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.
Degeneration
Degeneration is the term often given to the various processes which are normally experienced due to age and use. The spinal structures degenerate just like every other part of our physical bodies. The vast majority of spinal degeneration is completely normal, expected and asymptomatic. Degenerative disc disease is the most common diagnosis, with spinal osteoarthritis not far behind. Specific diagnoses related to osteoarthritis include bone spur formation often blamed for foraminal stenosis and facet joint syndrome. Spinal stenosis is another common process which occurs naturally, mostly due to advanced age. Most of these conditions are not inherently painful and are rarely the source of any significant discomfort.
Spinal stenosis
Spinal stenosis is the narrowing of the spinal canal, or narrowing of the openings (called neural foramina) where spinal nerves leave the spinal column. This condition typically develops as a person ages and the disks become drier and start to shrink. At the same time, the bones and ligaments of the spine swell or grow larger due to arthritis and chronic inflammation. However, other problems, including infection and birth defects, can sometimes cause spinal stenosis. If the narrowing occurs in your lower back, the sciatic nerve may be compressed, leading to sciatica.
Lumbar Degenerative Disk Disease/Spondylosis
Osteoarthritis occurs in joints of the spine, usually as a result of aging, but also in response to previous back injuries, excessive wear and tear, previously herniated discs, prior surgeries, and fractures. Cartilage between the joints of the spine is destroyed and extra bone growth or bone spurs develop. The rate at which these changes develop varies between people..The end result of these changes is a gradual loss of mobility of the spine, narrowing of the spaces for spinal nerves and spinal cord, and drying out or degeneration of the spinal discs. Depending on which part and how much of the spine is involved, symptoms may be similar to that of a herniated disc, lumbar strain, or spinal stenosis (narrowing of the spinal canal).
Most patients will report the presence of gradually worsening history of back pain over time. For others, there may be minimal history of back pain, but 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.
Patients may experience pain or numbness, which can occur in both legs, or on just one side. Other symptoms include a feeling of weakness or heaviness in the buttocks or legs. Symptoms are usually present or will worsen only when the person is standing or walking upright. Often the symptoms will ease or disappear when sitting down or leaning forward. These positions may create more space in the spinal canal, thus relieving pressure on the spinal cord or the spinal nerves. Patients with spinal stenosis are not usually able to walk for long periods of time. They may be able to ride an exercise bike.
Spondylolisthesis
Spondylolisthesis is a condition where the discs degenerate to such an extent that they are no longer able to properly support the vertebrae. This may lead to a vertebra slipping forward over the one below it. Spondylolisthesis occurs when one of the lumbar vertebrae slips over another, or over the sacrum. If this occurs in the lower back, the slipped vertebra can compress the sciatic nerve, causing sciatic pain.
In children, spondylolisthesis usually occurs between the fifth bone in the lower back (lumbar vertebra) and the first bone in the sacrum area. It is often due to a birth defect in that area of the spine. In adults, the most common cause is degenerative disease (such as arthritis). The slip usually occurs between the fourth and fifth lumbar vertebrae. It is more common in adults over 65 and women.
Other causes of spondylolisthesis include stress fractures (commonly seen in gymnasts) and traumatic fractures. Spondylolisthesis may occasionally be associated with bone diseases.
Spondylolisthesis may vary from mild to severe. It can produce increased lordosis (swayback), but in later stages may result in kyphosis (roundback) as the upper spine falls off the lower spine.
Symptoms may include:
• Lower back pain
• Pain in the thighs and buttocks
• Stiffness
• Muscle tightness
• Tenderness in the slipped area
Pain generally occurs with activity and is better with rest. Neurological damage (leg weakness or changes in sensation) may result from pressure on nerve roots, and may cause pain radiating down the legs.
Osteoporosis and Compression Fractures
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 fractures. It usually does not cause pain unless the vertebrae collapse suddenly, in which case the pain is often severe. More than one vertebra may be affected.
In a compression fracture of the vertebrae, the bone tissue of the vertebra collapses. More than one vertebra may collapse as a result. When the fracture is the result of osteoporosis, the vertebrae in the thoracic (chest) and lower spine are usually affected, and symptoms may be worse with walking.
With multiple fractures, kyphosis (a forward hump-like curvature of the spine) may result. In addition, compression fractures are often responsible for loss of height. Pressure on the spinal cord may also occur, producing symptoms of numbness, tingling, or weakness. Symptoms depend upon the area of the back that is affected; however, most fractures are stable and do not produce neurological symptoms.
Piriformis syndrome
-pressure on the sciatic nerve from the piriformis muscle in the buttocks
The pressure on the sciatic nerve can tighten and irritate the sciatic nerve. Symptoms of piriformis syndrome may include: a sciatica-like pain and/or numbness in the leg that is usually more intense above the knee, usually starts in the rear rather than the low back, and often spares the low back of symptoms or signs.
Piriformis syndrome can mimic the signs and symptoms of sciatica pain from a disc herniation and is part of the different diagnosis of possible causes of sciatica.
Injury
Any significant trauma to the back might damage some of the spinal structures, causing a variety of painful conditions, including sciatica. Vertebral fractures might also influence proper nerve function. While these conditions exist in some patients, they typically either resolve without treatment or will heal with proper medical attention. Injury is seldom a cause of ongoing chronic sciatica.
Ischemia
The most common, yet least diagnosed cause of chronic nerve pain is certainly ischemic sciatica. The harmless, but incredibly painful, oxygen deprivation sciatica process can occur due to disease or injury. However, the majority of patients demonstrate psychosomatic ischemia which is enacted by the subconscious mind. This is the reason why so many sciatic nerve pain syndromes do not respond well to medical or complementary treatment.
Inflammatory Conditions and Arthritis
Inflammatory disorders and arthritis syndromes can produce inflammation in the spine.
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 movement or exercise. In severe cases, the patient stands or sits stooped 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 the cause is hereditary.
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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 injuries, however. In the majority of back pain cases, the causes are unknown.
Aging
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 increasing age, which suggests that at a certain point, the conditions causing low back pain plateau.
High-Risk Occupations
Jobs that involve lifting, bending, and twisting into awkward positions, as well as those that cause whole-body vibration (such as long-distance truck driving), place workers at particular risk for low back pain. The longer a person continues such work, the higher their risk. Some workers wear back support belts, but evidence strongly suggests that they are useful only for people who currently have low back pain. The belts offer little added support for the back and do not prevent back injuries.
A number of companies are developing programs to protect against back injuries. However, studies have been mixed on the outcome of company interventions. 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.
Low back pain accounts for significant losses in workdays and dollars. According to the Bureau of Labor Statistics, back pain was responsible for around 60% of cases of people missing work due to pain involving the upper body. A 2004 study analyzed health care expenses in the United States. The analysis found back pain cost over $90billion, of which $26 billion was spent directly on treating the back pain.
Osteoporosis is a condition characterized by progressive loss of bone density, thinning of bone tissue, and increased vulnerability to fractures. Osteoporosis may result from disease, dietary or hormonal deficiency, or advanced age. Regular exercise and vitamin and mineral supplements can reduce and even reverse loss of bone density.
Medical Conditions in Children
Persistent low back pain in children is more likely to have a serious cause that requires treatment than back pain in adults.
Stress fractures (spondylolysis) in the spine are a common cause of back pain in young athletes. Sometimes a fracture may not show up for a week or two after an injury. Spondylolysis can cause spondylolisthesis, a condition in which the spine becomes unstable and the vertebrae slip over each other.
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 can also cause back pain in children.
Pregnancy
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.
Psychological and Social Factors
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. A "passive" coping style (not wanting to confront problems) was strongly associated with the risk of developing disabling neck or low back pain.
•Social and psychological factors, as well as job satisfaction, all 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.
•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 this presence as a strong player in many cases of low back pain, however, can help determine the full range of treatment options.
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