Sciatica is a medical condition characterized by
pain going down the leg from the lower back. This pain may go down the back,
outside, or front of the leg. Onset is often sudden following activities like
heavy lifting, though gradual onset may also occur. Typically, symptoms are
only on one side of the body. Certain causes, however, may result in pain on
both sides. Lower back pain is sometimes but not always present. Weakness or
numbness may occur in various parts of the affected leg and foot.
About 90% of the time sciatica is due to a spinal
disc herniation pressing on one of the lumbar or sacral nerve roots. Other
problems that may result in sciatica include spondylolisthesis, spinal
stenosis, piriformis syndrome, pelvic tumors, and compression by a baby's head
during pregnancy. The straight-leg-raising test is often helpful in diagnosis.
The test is positive if, when the leg is raised while a person is lying on
their back, pain shoots below the knee. In most cases medical imaging is not
needed. Exceptions to this are when bowel or bladder function is affected,
there is significant loss of feeling or weakness, symptoms are long standing,
or there is a concern of a tumor or infection. Conditions that may present
similarly are diseases of the hip and early herpes zoster before the rash
appears.
Treatment initially is typically with pain
medications. It is generally recommended that people continue with activities
to the best of their abilities. Often all that is required is time: in about
90% of people the problem goes away in less than six weeks. If the pain is
severe and lasts for more than six weeks then surgery may be an option. While
surgery often speeds pain improvement, long term benefits are unclear. Surgery
may be required if complications occur such as bowel or bladder problems. Many
treatments, including steroids, gabapentin, acupuncture, heat or ice, and
spinal manipulation, have poor evidence for their use.
Depending on how it is defined, 2% to 40% of people
have sciatica at some point in time. It is most common during people's 40s and
50s, and men are more frequently affected than women. The condition has been
known since ancient times. The first known use of the word sciatica dates from
1451.
Definition
The term "sciatica" describes a symptom—pain
along the sciatic nerve pathway—rather than a specific condition, illness, or
disease. Some use it to mean any pain starting in the lower back and going down
the leg. Others use the term more specifically to mean a nerve dysfunction
caused by compression of one or more lumbar or sacral nerve roots from a spinal
disc herniation. Though in this second use it is a diagnosis (i.e., it
indicates a cause and effect). Pain typically occurs in the distribution of a
dermatome and goes below the knee to the foot. It may be associated with
neurological dysfunction, such as weakness. The pain is characteristically of a
shooting type, quickly traveling along the course of the nerve.
Causes
Spinal disc herniation
Main article: Spinal disc herniation
Spinal disc herniation pressing on one of the lumbar
or sacral nerve roots is the most frequent cause of sciatica, being present in
about 90% of cases.
Sciatica caused by pressure from a disc herniation
and swelling of surrounding tissue can spontaneously subside if the tear in the
disc heals and the pulposus extrusion and inflammation cease.
Spinal stenosis
Main article: Lumbar spinal stenosis
Other compressive spinal causes include lumbar
spinal stenosis, a condition in which the spinal canal (the spaces the spinal
cord runs through) narrows and compresses the spinal cord, cauda equina, or
sciatic nerve roots. This narrowing can be caused by bone spurs,
spondylolisthesis, inflammation, or a 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
Main article: Piriformis syndrome
Piriformis syndrome is a controversial condition
that, depending on the analysis, varies from a "very rare" cause to
contributing to up to 8% of low back or buttock pain. In 17% 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 is posited that
this causes compression of the sciatic nerve. It has colloquially been referred
to as "wallet sciatica" since a wallet carried in a rear hip pocket
compresses the buttock muscles and sciatic nerve when the bearer sits down.
Piriformis syndrome causes sciatica when the nerve root itself remains normal
and no herniation of a spinal disc is apparent.
Pregnancy
Sciatica may also occur during pregnancy as a result
of the weight of the fetus pressing on the sciatic nerve during sitting or
during leg spasms. While most cases do not directly harm the fetus or the
mother, indirect harm may come from the numbing effect on the legs, which can
cause loss of balance and falls. There is no standard treatment for
pregnancy-induced sciatica.
Other
Sciatica can also be caused by tumors 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 tumors or cauda equina syndrome. Trauma to the spine, such as from a car
accident, may also lead to sciatica. A relationship has been proposed with a
latent Propionibacterium acnes infection in the intervertebral discs, but the
role it plays is not yet clear.
Pathophysiology
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 (natural hole) through which nerve roots exit the spine.
The intervertebral discs consist of an anulus fibrosus, which forms a ring
surrounding the inner nucleus pulposus. When there is a tear in the anulus
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. Inflammation of
the spinal canal can also spread to adjacent facet joints and cause lower back
pain and/or referred pain in the posterior thigh(s). 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.
The spinal discs are composed of a tough spongiform
ring of cartilage ("anulus fibrosus") with a more malleable center
("nucleus pulposus"). The discs separate the vertebrae, thereby
allowing room for the nerve roots to properly exit through the spaces between
the 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 their
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. Many herniated discs themselves, however, cause no pain or
discomfort: only occasionally does a disc herniation cause sciatica.
Diagnosis
Sciatica is typically diagnosed by physical
examination, and the history of the symptoms. Generally if a person 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.
The most applied diagnostic test is the straight leg
raise to produce Lasègue's sign, which is considered positive if pain in the
distribution of the sciatic nerve is reproduced with passive flexion of the
straight leg between 30 and 70 degrees. While this test is positive in about 90%
of people with sciatica, approximately 75% of people with a positive test do
not have sciatica.
Imaging tests such as computerised tomography or
magnetic resonance imaging can help with the diagnosis of lumbar disc
herniation.[17]The utility of MR neurography in the diagnoses of piriformis
syndrome is controversial.
Management
When the cause of sciatica is lumbar disc
herniation, most cases resolve spontaneously over weeks to months. Initially
treatment in the first 6–8 weeks should be conservative. There does not appear
to be a significant difference in outcomes between advice to stay active and
recommendations of bed rest. Similarly, physical therapy (directed exercise)
has not been found better than bed rest.
Medication
Medicines are commonly prescribed for the treatment
of sciatica, but evidence for pain medication is poor. Specifically,
low-quality evidence indicates that NSAIDs do not appear to improve immediate
pain and all NSAIDs appear about equivalent. Evidence is also lacking in use of
opioids and muscle relaxants by usual means. In those with sciatica due to
piriformis syndrome, botulinum toxin injections may improve pain and or
function. There is little evidence for steroids, either epidural or by pill.
Low-quality evidence supports the use of gabapentin for acute pain relief in
those with chronic sciatica.
Surgery
Surgery for unilateral sciatica involves the removal
of part of the disc, which is known as a discectomy. While it results in
short-term benefits, the long-term benefits appear to be equivalent to
conservative care. Treatment of the underlying cause of the compression is
needed in cases of epidural abscess, epidural tumors, and cauda equina
syndrome.
Alternative medicine
Low to moderate-quality evidence suggests that
spinal manipulation is an effective treatment for acute sciatica. For chronic
sciatica, the evidence is poor. Spinal manipulation has been found generally
safe for the treatment of disc-related pain; however, case reports have found
an association with cauda equina syndrome, and it is contraindicated when there
are progressive neurological deficits.
Epidemiology
Depending on how it is defined, 2% to 40% of people
have sciatica at some point in time. It is most common during people's 40s and
50s and men are more frequently affected than women.
