sciatica

Sciatica
Classification and external resources
Left gluteal region, showing surface markings for arteries and sciatic nerve
ICD-10	M54.3-M54.4
ICD-9	724.3
eMedicine	emerg/303
MeSH	D012585

Sciatica ( /saɪˈætɪkə/; sciatic neuritis)^[1] is a set of symptoms including pain that may be caused by general compression or irritation of one of five spinal nerve roots that give rise to each sciatic nerve, or by compression or irritation of the left or right or both sciatic nerves. The pain is felt in the lower back, buttock, or various parts of the leg and foot. In addition to pain, which is sometimes severe, there may be numbness, muscular weakness, pins and needles or tingling and difficulty in moving or controlling the leg. Typically, the symptoms are only felt on one side of the body. Pain can be severe in prolonged exposure to cold weather.

Although sciatica is a relatively common form of low back pain and leg pain, the true meaning of the term is often misunderstood. Sciatica is a set of symptoms rather than a diagnosis for what is irritating the root of the nerve, causing the pain. This point is important, because treatment for sciatica or sciatic symptoms often differs, depending upon the underlying cause of the symptoms and pain levels.

The first known use of the word sciatica dates to 1451.^[2]

Cause

Sciatica is generally caused by the compression of lumbar nerves L4 or L5 or sacral nerves S1, S2, or S3, or by compression of the sciatic nerve itself. When sciatica is caused by compression of a dorsal nerve root (radix) it is considered a lumbar radiculopathy (or radiculitis when accompanied with an inflammatory response). This can occur as a result of a spinal disk bulge or spinal disc herniation (a herniated intervertebral disc), or from roughening, enlarging, or misalignment (spondylolisthesis) of the vertebrae, or as a result of degenerated discs that can reduce the diameter of the lateral foramen through which nerve roots exit the spine. The intervertebral discs consist of an annulus fibrosus, which forms a ring surrounding the inner nucleus pulposus. When there is a tear in the annulus fibrosus, the nucleus pulposus (pulp) may extrude through the tear and press against spinal nerves within the spinal cord, cauda equina, or exiting nerve roots, causing inflammation, numbness or excruciating pain. Sciatica due to compression of a nerve root is one of the most common forms of radiculopathy.

Pseudosciatica or non-discogenic sciatica, which causes symptoms similar to spinal nerve root compression, is most often referred pain from damage to facet joints in the lower back and is felt as pain in the lower back and posterior upper legs. Pseudosciatic pain can also be caused by compression of peripheral sections of the nerve, usually from soft tissue tension in the piriformis or related muscles (see piriformis syndrome and see below).

Spinal disc herniation

One of the possible causes of sciatica is a spinal disc herniation pressing on one of the sciatic nerve roots. The spinal discs are composed of a tough spongiform ring of cartilage (annulus fibrosus) with a more malleable center (nucleus pulposis). The discs separate the vertebrae, thereby allowing room for the nerve roots to properly exit through the spaces between the L4, L5, and sacral vertebrae. The discs cushion the spine from compressive forces, but are weak to pressure applied during rotational movements. That is why a person who bends to one side, at a bad angle to pick something up, may more likely herniate a spinal disc than a person jumping from a ladder and landing on his or her feet.

Herniation of a disc occurs when the liquid center of the disc bulges outwards, tearing the external ring of fibers, extrudes into the spinal canal, and compresses a nerve root against the lamina or pedicle of a vertebra, thus causing sciatica. This extruded liquid from the nucleus pulposus may cause inflammation and swelling of surrounding tissue, which may cause further compression of the nerve root in the confined space in the spinal canal.

Sciatica caused by pressure from a disc herniation and swelling of surrounding tissue can spontaneously subside if the tear in the disc heals and pulposis extrusion and inflammation cease.

Sciatica can be caused by tumours impinging on the spinal cord or the nerve roots. Severe back pain extending to the hips and feet, loss of bladder or bowel control, or muscle weakness, may result from spinal tumours. Trauma to the spine, such as from a car accident, may also lead to sciatica.

Spinal stenosis

Other compressive spinal causes include lumbar spinal stenosis, a condition in which the spinal canal (the spaces through which the spinal cord runs) narrows and compresses the spinal cord, cauda equina, or sciatic nerve roots. This narrowing can be caused by bone spurs, spondylolisthesis, inflammation, or herniated disc, which decreases available space for the spinal cord, thus pinching and irritating nerves from the spinal cord that travel to the sciatic nerves.

Piriformis syndrome

In 15% of the population, the sciatic nerve runs through the piriformis muscle rather than beneath it. When the muscle shortens or spasms due to trauma or overuse, it can compress or strangle the sciatic nerve beneath the muscle. Conditions of this type are generally referred to as entrapment neuropathies; in the particular case of sciatica and the piriformis muscle, this condition is known as piriformis syndrome. It has colloquially been referred to as "wallet sciatica" since a wallet carried in a rear hip pocket will compress the muscles of the buttocks and sciatic nerve when the bearer sits down. Piriformis syndrome may be a cause of sciatica when the nerve root is normal.^[3][4]

Diagnosis

Sciatica is diagnosed by physical examination, neurological testing and patient history. Generally if a patient reports the typical radiating pain in one leg as well as one or more neurological indications of nerve root tension or neurological deficit, sciatica can be diagnosed.^[5]

The most applied diagnostic test is the straight leg rising test, or Lasègue's sign, which is considered positive if pain in the sciatic nerve is reproduced with between 30 and 70 degrees passive flexion of the straight leg^[6]

Diagnosis of sciatica through imaging can be achieved either with computerised tomography or with magnetic resonance imaging.^[7] MR neurography has been shown to diagnose 95% of severe sciatica patients, while as few as 15% of sciatica sufferers in the general population are diagnosed with disc-related problems.^[8] MR neurography may help diagnose piriformis syndrome—another cause of sciatica that does not involve disc herniation.^{[citation needed]}

Treatment

When the cause of sciatica is due to a prolapsed or lumbar disc herniation 90% of disc prolapses resolve with no intervention. Treatment of the underlying cause of the compression is needed in cases of epidural abscess, epidural tumors, and cauda equina syndrome.

Although medications are commonly prescribed for the treatment of sciatica, evidence from clinical trials to guide the use of analgesics to relieve pain and disability is lacking.^[9] Research has shown no significant difference between placebos, NSAIDs, analgesics, and muscle relaxants. Evidence is lacking in use of opioids and compound drugs.^[10][11]

Research has failed to show a significant difference in outcomes between advice to stay active and recommendations of bed rest.^[12] Similarly, physical therapy (exercises) has not been found better than bed rest.^[13]

Elective surgery is the main option for unilateral sciatica and focuses on removal of the underlying cause by removing disk herniation and eventually part of the disc. In a controlled study, surgical intervention was found to have better results after one year but after four and ten year follow ups no significant differences were found.^[14]

Moderate quality evidence suggests that spinal manipulation is effective for the treatment of acute sciatica; however, only low level evidence was found to support spinal manipulation for the treatment of chronic sciatica.^[15] Spinal manipulation has been found safe for the treatment of disc-related pain.^[16]

See also

• Laminectomy
• Hemilaminectomy

References