Sciatica: Causes, Diagnosis, And Treatment
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by Sibel Demir-Deviren
Spine Center , University of California San Francisco

What is Sciatica?

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.

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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.

sciatic nerve path illustration

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.

a) disc herniation
b) spinal stenosis
c) degenerative disc disease
d) spondylolysis and spondylolisthesis
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.

path of sciatic nerve through sciatic notch, piriformis muscle, superior gamellus, obdurator internus, inferior gamellus muscle

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?

sciatic nerve path illustration

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 Resourcesbold text

American Academy of Physical Medicine and Rehabilitation

American Academy of Orthopaedic Surgeons

North American Spine Society

Scoliosis Research Society

Key References

1. Peul WC, Van Houwelingen HC, Van Den Hout WB, et al: Surgery versus prolonged conservative treatment for sciatica: N Engl J Med 356: 2245-56, 2007.

2. Weinstein JN, Lurie, JD, Tosteson TD, et al: Surgical vs nonoperative treatment for lumbar disk herniation: SPORT observational cohort: JAMA: 296: 2451-59, 2006.

3. Weinstein JN, Tosteson TD, Lurie, JD, et al: Surgical vs nonoperative treatment for lumbar disk herniation: SPORT randomized trial: JAMA: 296: 2442-50, 2006.

4. Filler AG, Haynes J, Jordan SE, et al: Sciatica of nondisc origin and piriformis syndrome: diagnosis by magnetic resonance neurography and interventional magnetic resonance imaging with outcome study of resulting treatment: J Neurosurg Spine: 2: 99-115, 2005.

5. Stafford MA, Peng P, and Hill DA: Sciatica: a review of history, epidemiology, pathogenesis and the role of epidural steroid injection in management: British J of Anaesthesia: 99 (4): 461-73, 2007.

6. Derby R, Kine G, Saal JA, et al: Response to steroid and duration of radicular pain as predictors of surgical outcome: Spine: 17: S176-83, 1992.

7. Vad VB, Bhat AL, Lutz GE, et al: Transforaminal epidural steroid injections in lumbosacral radiculopathy: a prospective randomized study: Spine: 27:11-6, 2002.

8. Riew KD, Yin Y, Gilula L, et al: The effect of nerve-root injections on the need for operative treatment of lumbar radicular pain: a prospective, randomized, controlled, double-blind study: J Bone Joint Surg Am: 82-A: 1589-93, 2000.

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This page created 28 Apr 2009 20:39
Last updated 10 May 2012 01:51

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