Symptoms and Causes:

In about 85% of back pain cases, the origin of the pain is unknown, and imaging studies usually fail to determine its cause. Disk disease, spinal arthritis, and muscle spasms are the most common diagnoses. Other problems can also cause back pain, however.

Lumbar Degenerative Disk Disease/Spondylosis

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. These changes are age-related to some degree. However, the rate at which these changes develop varies between people, and may be accelerated by trauma or excessive wear and tear. The end result of these changes is a gradual loss of spinal structure and function, as well as chronic pain, muscle spasms, and reduced mobility. 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).

Herniated Disk

A herniated disk, sometimes (incorrectly) called a slipped disk, is a 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 (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.

Leg pain 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. Extrusion is very uncommon, however, while sciatic and low-back pain are very common. But there may be other causes of low back 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.

Cauda equina syndrome. Cauda equina syndrome is the impingement of the cauda equina (the four strands of nerves leading through the lowest part of the spine). The cause is usually massive extrusion of the disk material. Cauda equina syndrome is an emergency condition that can cause severe complications to bowel or bladder function. It can cause permanent incontinence if not promptly treated with surgery. Symptoms of the cauda equina syndrome include:

• Dull back pain
• Weakness or numbness in the buttocks, in the area between the legs, or in the inner thigh, backs of legs, or feet; may cause stumbling or difficulty in standing
• An inability to control urination and defecation
• Pain accompanied by fever (can indicate an infection)

Sciatica

The Sciatic Nerve. The sciatic nerve has an extensive pathway.

• It first branches from the nerve roots that travel down from 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 passes down each hip and along the back of each thigh to the foot.

Sciatica is not a diagnosis but a description of symptoms that include:

• Leg pain
• Possible numbness or tingling in the buttock and down the back of the leg
• Possible weakness of the leg muscles

Causes of Sciatica. A herniated disk pressing on the sciatic nerve is the most common cause of sciatica, although spinal stenosis, degenerative disc disease, spondylolisthesis, or other abnormalities of vertebrae that press on the sciatic nerve can also cause pain.

The main nerve traveling down the leg is the sciatic nerve. Pain associated with the sciatic nerve usually originates when nerve roots in the spinal cord become compressed or damaged. Symptoms can include tingling, numbness, or pain that radiates to the buttocks, legs, and feet.

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.

Muscle and Ligament Injuries/Lumbar Strain

Strain and injury to the muscles and ligaments supporting the back are the major causes of low back pain. The pain is typically more spread out in the muscles next to the spine, and may be associated with spasms in those muscles. The pain may move to the buttocks but rarely any farther down the leg.

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. It is sometimes difficult to diagnose.

Spinal Stenosis

Spinal stenosis is the narrowing of the spinal canal, or narrowing of the nerve root canals 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.

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 occurs when one of the lumbar vertebrae slips over another, or over the sacrum.

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.

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 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 the cause is hereditary.

About 20% of people with inflammatory bowel disease and about 20% of people with psoriasis develop a similar form of arthritis involving the spine. There are multiple treatments for this potentially disabling disease, including various immune suppressant medications. Etanercept (Enbrel) and infliximab (Remicade), anti-inflammatory agents known as TNF-blockers, are proving to be beneficial.

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. [For more information, see In-Depth Report #18: Osteoporosis.]

Emergent Causes of Back Pain

Several serious conditions can also cause back pain. Often, these symptoms develop over a short period of time, become more severe, and may have other findings that go along with them. Some of these conditions include:

• Infection in the bone (osteomyelitis) or the disk (diskitis)
• Cancer that has spread to the spine from another part of the body (most commonly lung cancer, colon cancer, prostate cancer, and breast cancer)
• Cancer that begins in the bones (the most common diagnosis in adults is probably multiple myeloma, seen in middle age or older adults); benign tumors such as osteoblastoma or neurofibroma and cancers, including leukemia, can also cause back pain in children
• Trauma

Miscellaneous Abnormalities and Diagnoses

Any abnormality in joints, vertebrae, or nerve roots can cause back pain, including:

• Fibromyalgia.
• Other medical conditions that cause referred back pain, occuring 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.
• Chronic uterine or pelvic infections can cause low back pain in women.
• The facet joints (z-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.
• Injury to nerve roots, notably deep root ganglia (nerve cells in the spine whose fibers extend from skin to muscle tissue), may be important in some cases; some patients may have scar tissue that traps the nerve roots in the lower spine and causes sciatica.