Introduction
Sciatica is a buttock pain radiating down the back of the thigh and leg and possibly into the calf or foot. Other
characteristics of sciatica include varying degrees of weakness in the
leg muscles and numbness and/or tingling that radiates down the leg. These symptoms occur because of compression and/or irritation of the sciatic nerve or nerve roots which are forming the sciatic nerve. The
areas in the buttock and leg affected by this compression are the areas
that the sciatic nerve supplies with messages for normal function. There
are many other names for sciatica including lumbosacral radicular
syndrome, radiating low back pain, nerve root pain, and nerve root
entrapment. 
The
sciatic nerve is formed in the pelvis from nerve roots that begin in
the lower back vertebrae (lumbar 4 [L4], lumbar 5 [L5]) and sacrum
(sacral 1[S1], sacral 2 [S2], sacral 3 [S3]). It is the thickest nerve
in the body and is 2 cm wide at its origin. It enters the
lower limb via the greater sciatic foramen (opening). The nerve passes
along the back of the thigh, supplying the hamstrings (knee flexors) and
all of the muscles below the knee. It also supplies the skin of entire
lower extremity below the knee and foot with the exception of the inside
of the calf and foot. The impingement or irritation of the sciatic
nerve anywhere along its course would cause pain in the area the nerve
supplies.
Who gets sciatica?
Sciatica is a relatively common condition with a lifetime incidence (the number of individuals that have experienced sciatica at some point in their lives)
varying from 13% to 40%. The incidence of sciatica is related to age.
Sciatica is rarely seen before the age of 20 and it most often occurs in
people in their fifties. In addition, there may be a genetic link with
the development of sciatica. It has been shown that the
first-degree relatives of people affected by sciatica have a greater
risk of developing it themselves. Other identified risk factors are
largely work-related and include: awkward working position, working in a
flexed or twisted trunk position, or working with the hand above the
shoulder. Heavy amounts of driving and smoking have also been linked
with sciatica. It has been shown that neither gender nor weight has an
influence on the development of sciatica, although being overweight is
often associated with low back pain in general. For males in the 50-64
year range, body height may be a risk factor for sciatica. It has been
shown that the relative risk increased an average 1.5 fold for every 10
cm increase in body height.
What causes sciatica?
The name sciatica refers to a set of symptoms caused by an underlying problem and is not the name of the problem itself.
Causes of Sciatica
1. Spinal sciatica: compression and/or irritation of a nerve
root or roots (which are forming the sciatic nerve)
inside of the spine
b) spinal stenosis
e) scoliosis
f) trauma
g) spinal tumors and infection
2. Extra-spinal sciatica: compression and/or irritation of the sciatic nerve outside of the spine
a) piriformis syndrome
b) gynecological problems: fibroids and endometriosis
c) bone and soft tissue tumors
d) infection
e) trauma
f) others: vascular and medications
In
about 90% of cases, sciatica is caused by compression and/or irritation
of one or more nerve roots in the lumbar spine, before the sciatic
nerve enters the leg. These nerve roots can become
compressed by a herniated disc, spinal canal stenosis (narrowing of
spinal canal where the nerve roots are passing through) or neural
foraminal narrowing (narrowing of the holes where the nerve roots are
exiting the spine). The relationship between compression of the nerve
root and sciatica is not completely understood. Mechanical compression
of the nerve root may produce neurologic deficits, such as numbness and
tingling in the leg, but the pain associated with sciatica is only
produced if the nerve root is also irritated or inflamed. There is no
definite, known cause of the inflammation of the nerve associated with
sciatica. However, it is thought that the inflammation
could be caused by decreased blood supply to the nerve or associated
nerve roots and/or direct irritation of nerve roots by disc herniation.
Rarely,
the entrapment of the sciatic nerve occurs outside of the spine along
the part of the sciatic nerve that runs through the pelvis or thigh. This is called extra-spinal sciatica. This
type of entrapment is difficult to diagnose because the symptoms are
similar to those of the more frequent causes of sciatica. Extra-spinal
sciatic nerve compression can be caused by tumors, infections,
gynecological problems, and problems associated with muscles, vascular,
and bony structures. Although these are rare causes of sciatica, they are serious and must be thoroughly investigated.
Very
rarely, bone and soft tissue tumors along the course of the sciatic
nerve can cause sciatica. Patients suffering from sciatica with a
history of neurofibromatosis (a genetic disorder of the nervous system)
or malignant tumors that are prone to skeletal metastases (e.g.,
prostate, breast, lung, kidney and thyroid cancers) should be carefully
evaluated for a tumor along the course of the sciatic nerve. The
important risk factors for malignant tumors include age older than 50
years, previous cancer history, unexplained weight loss, pain not
relieved by bed rest, duration of pain more than six to eight weeks and
failure of conservative therapy after six to eight weeks.
Infection
also needs to be excluded in cases of sciatica. The important risk
factors for infection include IV drug use, active or recent infection
elsewhere in the body (e.g., urinary tract, pulmonary, skin, dental),
and immunosuppression (either due to medications or illness affecting
the immune system, like HIV/AIDS). Additional factors to consider
include diabetes and history of tuberculosis.
Piriformis
syndrome is another uncommon cause of sciatica. The sciatic nerve
usually passes underneath the piriformis muscle, but in approximately
15% of the population, it travels through the muscle. In this case, the
symptoms are caused by entrapment of the sciatic nerve in the buttock by
the overlying piriformis muscle. Often, a history of minor trauma may be described, such as falling onto the buttock.
Gynecological causes are fibroids and endometriosis
(cyclic pain). Sciatic endometriosis is uncommon but should be
considered in a woman who presents with sciatica associated with
menstruation. Additional causes include post-traumatic or anticoagulant
induced hematomas (abnormal collection of blood) of the sciatic nerve
and/or muscles.
How is sciatica diagnosed?
Sciatica
is usually diagnosed by taking a history of symptoms and by physical
examination. Patients are usually asked to describe the pattern of the
pain and whether it radiates below the knee; drawings may be used to
evaluate the distribution. Patients may also report sensory symptoms
(numbness, tingling) and weakness in the legs. Physical examination is
largely made up of neurological testing, which includes: sensory and
muscle strength testing, reflex testing, and sciatic tension signs.
Sciatic
tension signs are frequently used to assess patients with sciatica. The
straight leg raise test is performed in the supine position by
elevating the leg with the knee extended and assessing whether this
movement reproduces the sciatic pain in the leg. The test is considered
positive if the pain occurs between 30 and 70 degrees of elevation.
Variations on this test include raising the leg to the point of symptom
reproduction and then lowering the leg slightly and moving the foot
upward passively (dorsiflexion); a positive sign results in reproduction
of radiating pain down the leg. Additional tests include the crossed
straight leg raise test, in which symptoms are reproduced in the
symptomatic leg by performing a straight leg raise test on the opposite
leg. Overall, if a patient reports the typical radiating
pain in one leg combined with a positive result on one or more
neurological tests indicating nerve root tension or neurological
deficit, the diagnosis of sciatica is made.
What is the value of imaging?
Imaging studies can help the doctor to determine the cause of sciatic pain. Diagnostic
imaging includes plain films (x-rays), MRI (magnetic resonance
imaging), MR neurography, computerized tomography (CT)-myelography, and
CT scans. Diagnostic imaging is only useful if the results change the
treatment plan.
In
acute sciatica (during first six to eight weeks), the diagnosis is
based on history taking and physical examination, and treatment is
conservative. Imaging may be indicated at this stage only if there are
indications or “red flags” that the sciatica may be caused by underlying
disease (infections, malignancy) rather than a disc herniation. These
red flags include a history of significant trauma, cancer, unexplained
weight loss, night pain, immunosuppression, recent infection, bladder
and/or bowel dysfunction, bilateral neurologic deficits, saddle
anesthesia (loss of sensation in the buttocks area), progressive
neurologic deficit, and unremitting pain. Diagnostic
imaging is also indicated in patients with severe symptoms who fail to
respond to conservative treatments for six to eight weeks.
Routine
plain films are universally available and inexpensive, but are limited
by an ability to directly visualize nerves and nerve root compression.
They are, however, important in ruling out obvious underlying problems
such as tumors, infections, inflammatory spinal disorder, traumatic bony
injury, or instabilities (e.g., spondylolisthesis, which is forward
slippage of one backbone over another).
MRI
has become the examination of choice for patients with sciatica. It has
the advantage of being non-invasive, and having no known side effects
or radiation exposure. MRI is the most accurate test for
disc herniation detection. Routine protocols for MRI of lumbar spine
provide excellent visualization of the spinal axis including central
canal and foramina, but do not show the sciatic nerve as it runs outside
of the spinal column. Unfortunately, for the patients with extra-spinal
sciatica, routine MRI of lumbar spine will not usually reveal the cause
of the pain. For these patients, high-resolution MR neurography may
identify the anatomic abnormalities causing the problem.
Before
the advent of MRI, CT was the imaging modality of choice for patients
with sciatica. CT can also be performed with intrathecal (space around
the spinal cord) contrast injection (CT-myelography). Currently,
CT-myelography is used for patients who cannot get an MRI.
Natural history of sciatica
Most
patients with acute sciatica respond to conservative (non-surgical)
treatment and their symptoms get better over a period of six to eight
weeks. Approximately 10-30% of people develop chronic sciatica (sciatica
persisting longer than 12 weeks). Unfortunately, it is difficult to
predict at an early stage who is at risk for developing chronic
sciatica.
The
most common cause of sciatica is a disc herniation in the lumbar spine.
Generally, 70% of disc herniations mostly go away in one to two years. In the long term (five years or more), disc herniations decrease in size in 95% of people. Generally,
large, diffuse disc herniations (rupture of the disc) are the most
likely to decrease in size over the first year. In contrast, focal or
localized disc bulges are more likely to be unchanged.
The
mechanism that leads a disc herniation to cause sciatica is not totally
clear. Some disc herniations do not cause any symptoms. In MRI scans of
67 adults with no history of back or leg pain, about one-third had a
substantial abnormality. Disc herniation was seen in the absence of
symptoms in 21%, 22% and 36% of those aged 20-39, 40-60, and more than
60 years of age, respectively, whereas generalized disc bulging was also
seen in 56%, 59% and 79% of asymptomatic individuals, respectively.
These findings emphasize the difficulty involved in defining the complex
interaction between nerve root inflammation and the compression that
seems to be the cause of sciatica.
What is the efficacy of conservative treatments for sciatica?
To
date, conservative treatments for sciatica consist of a wide range of
methods including: treatment with medication (oral analgesics [pain
relievers], muscle relaxants and medications for nerve pain), physical
therapy, bed rest, epidural steroid injections, lumbar supports (lower
back braces), spinal manipulation, complementary alternative medicine,
behavioral treatment, and multidisciplinary rehabilitation. Adequately
informing patients about the causes and expected prognosis is an
important part of the treatment strategy.
Nonsteroidal
anti-inflammatory drugs (NSAIDs) (e.g., ibuprofen, naproxen,
diclofenac) are a large group of drugs commonly used to treat sciatica.
They reduce both pain and inflammation. NSAIDs can have side effects. A
history of gastrointestinal bleeding or peptic ulcers can be a reason
not to use NSAIDs. This risk, however, is reduced with the NSAID
celecoxib (Celebrex). Additionally with NSAIDs, other internal organs,
such as the kidneys and liver, may be detrimentally affected. No
specific NSAID was shown to be superior to another in the treatment of
sciatica.
Because
in the acute setting sciatic pain can be severe, short term narcotic
use can be useful. These should not be prescribed for an extended period
of time, but should be limited to a two to three day course. Other
types of drugs prescribed for sciatic pain include: tricyclic
antidepressants and other antidepressants, gabapentin and other
anticonvulsants, tramadol, topical lidocaine and baclofen.
If
bed rest is prescribed, it should be limited to no more than two to
three days. Greater periods of inactivity can cause prolonged disability
and continued pain. In fact, physical therapy has been shown to not
only reduce pain, but to limit days off from work – and it has been
consistently shown that exercise is the most important component of the
physical therapy. Treatment goals of physical therapy are to restore
strength and function of the core muscles, flexibility of leg and
paraspinal muscles, and also to improve cardiovascular fitness; these
are all things that are often lost due to pain and spasm. However, the
patient should not perform any exercise that provokes their pain. If a
specific exercise provokes the pain, that exercise first should be
modified and/or the number of exercises should be decreased. If it still
aggravates the symptoms, the patient should stop doing that particular
exercise. Postural education to avoid activities that can increase
intradiscal pressure and/or sciatic tension should be provided.
Adjunctive modalities (e.g., cold pack, hot pack, ultrasound, massage)
are usually helpful for short term relief of symptoms.
Epidural
steroid injections to decrease inflammation have been increasingly
utilized with the growing evidence that inflammatory agents are a
significant contributor to the pain and nerve root irritation that
causes sciatica. Injections are offered to patients who have failed
noninvasive conservative treatments, including physical therapy and
medications. It has been shown that selective transforaminal epidural
steroid injections produce symptomatic relief in 70 to 85% of patients.
It also has been reported that 71% of patients with sciatica who receive
transforaminal epidural injections avoid surgery. Transforaminal
epidural injections are also helpful to determine the prognosis of the
surgery if the patient fails conservative treatments. Patients who have
70-80% relief from the epidural steroid injections have greater than 95%
success in achieving an average of 90% leg-pain relief after surgery.
There
are no studies that show lumbar supports are more effective than other
interventions for treatment of sciatica. Most published studies of
spinal manipulation reported mixed efficacy. Acupuncture has become a
popular alternative for the treatment of sciatica, but no definitive
studies have been done that indicate a clear benefit of its use as a
sole treatment or as an adjunct. Traction has no benefit except for
those patients who experience pain relief during the actual traction.
We
know now that psychosocial factors can play an important role in
patients’ symptoms and signs and also in patients’ response to both
nonoperative and operative treatments. For this reason, behavioral
therapies have had a major impact on the treatment and understanding of
long-term effects of sciatic pain on patients with psychosocial
problems. Patients require both physical treatment of their problem as
well as treatment of the psychosocial and behavior aspects of their
condition.
What is the role of surgery in sciatica?
As
mentioned previously, most patients can be treated successfully by
nonoperative treatment if the patient will comply with physical therapy,
medications, and transforaminal epidural steroids. Most
importantly, the patient must allow adequate time to heal. If the
patient does not have a progressive or significant neurologic deficit,
cauda equina syndrome (set of symptoms of saddle anesthesia numbness in
the areas that would touch a saddle if the patient were sitting on one,
bowel or bladder incontinence, new onset sensory deficits in legs, or
new or progressive weakness in legs) or severe pain that will not go
away, a minimum of six to eight weeks should be reserved for
nonoperative treatment.
However,
nonoperative treatment should not extend beyond four to six months if
the patient shows only minimal improvement. The absolute indications for
the surgery are cauda equina syndrome or a progressive neurologic
deficit that includes weakness in the muscles that are supplied by the
impinged nerve root. The relative indications for surgery are: 1)
failure of an adequate trial of nonoperative treatment, and 2)
intractable pain. A prerequisite is radiologic identification of a
compressed nerve that makes sense with the patient’s physical signs and
symptoms. Surgery provides nearly 85% to 95% of patients with good to
excellent results. The type of surgery performed depends on the
diagnosis.
What are the complications of the surgery?
Any
invasive procedure, no matter how carefully it is done has risks. Most
complications can be avoided with proper patient selection, education,
preoperative planning and meticulous attention to anatomy and surgical
techniques. Fortunately, the serious risks associated with surgery are
the exception rather than the rule. The most common
complications include: wrong vertebral level operated on (1.2 – 3.3%),
missed pathology and/or retained disc, dural (the sac of tissue that
covers the spine) tear (0.8-7.2%), epidural (the space outside the dura)
venous bleeding, nerve root lesion (0.2%), residual sciatica, recurrent
disc herniation, cauda equina syndrome, epidural hematoma, infection
(2-3%), iatrogenic vertebral instability, thromboembolism (blood clot
blocking a blood vessel), and postoperative epidural fibrosis (scar
tissue) and/or arachnoiditis (inflammation of the delicate membrane
enclosing the spinal cord and brain). The overall complication rate
ranges from 1% to 3%.
Recurrent
herniations occur with a frequency of 5-15%, with the risk decreasing
over time after surgery. Lack of physical activity is a significant risk
factor for recurrence. Distinguishing between recurrent disc herniation
and epidural fibrosis can be difficult. Contrast enhanced MRI has
become the study of choice to differentiate between disc herniation and
scarring.
Nonoperative versus Operative Treatment
Based
on the studies, operative treatment provides more rapid resolution of
symptoms and a shorter recovery period compared with conservative care,
but no large differences have been found in success rates after one or
two years of follow-up. Patients and doctors weigh the benefits and
harms of both options to make individual choices. This is especially
relevant because the patients’ preference for treatment may have a
direct positive influence on the magnitude of the treatment effect.
Summary
Sciatica
is a fairly common health problem with a lifetime incidence (the number
of individuals that have experienced sciatica at some point in their
lives) varying from 13% to 40%. The most common cause of sciatica is a
herniated disc. The precise mechanism of sciatica is unclear. In
addition to mechanical compression, inflammation may play a role. The
natural history of sciatica is favorable, with resolution of leg pain
within six to eight weeks from onset in the majority of patients.
Consensus is that initial treatment is conservative for about six to
eight weeks. Imaging during this acute phase is indicated only in
patients with “red flag” conditions or who have failed conservative
treatments. If symptoms do not improve after six to eight weeks of
conservative treatments, patients may decide on surgery. Those who are
hesitant about surgery and can cope with their symptoms may choose to
continue conservative care. Patient preference is, therefore, an
important feature in the decision process. Only 2% to 4% of patients
with disc herniations are surgical candidates. The surgery may provide
quicker relief of leg pain than nonoperative treatment, but no clear
differences have been found after one or two years.
More Information
Web Resources
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