Sciatica is pain along the sciatic nerve. It usually results from compression of lumbar nerve roots in the lower back. Common causes include intervertebral disk herniation, osteophytes, and narrowing of the spinal canal (spinal stenosis). Symptoms include pain radiating from the buttocks down the leg. Diagnosis sometimes involves MRI or CT. Electromyography and nerve conduction studies can identify the affected level. Treatment includes symptomatic measures and sometimes surgery, particularly if there is a neurologic deficit.
(See also Evaluation of Neck and Back Pain.)
Etiology of Sciatica
Sciatica is typically caused by nerve root compression, usually due to intervertebral disk herniation, bony irregularities (eg, osteoarthritic osteophytes, spondylolisthesis), spinal stenosis, or, much less often, intraspinal tumor or abscess. Compression may occur within the spinal canal or intervertebral foramen. The nerves can also be compressed outside the vertebral column, in the pelvis or buttocks. L5-S1, L4-L5, and L3-L4 nerve roots are most often affected (see table Motor and Reflex Effects of Spinal Cord Dysfunction by Segmental Level).
Symptoms and Signs of Sciatica
In patients with sciatica, pain radiates along the course of the sciatic nerve (symptoms related to nerve roots L4, L5, and S1), most often down the buttocks and posterior aspect of the leg to below the knee. The pain is typically burning, lancinating, or stabbing. It may occur with or without low back pain. The Valsalva maneuver or coughing may worsen pain due to disk herniation. Patients may complain of numbness and sometimes weakness in the affected leg.
Nerve root compression can cause sensory, motor, or, the most objective finding, reflex deficits. L5-S1 disk herniation may affect the ankle jerk reflex; L3-L4 herniation may affect the knee jerk.
Straight leg raising may cause pain that radiates down the leg when the leg is slowly raised above 60° and sometimes less. This finding is sensitive for sciatica; pain radiating down the affected leg when the contralateral leg is lifted (crossed straight leg raising) is more specific for sciatica. The straight leg raise test can be done while patients are seated with the hip joint flexed at 90°; the lower leg is slowly raised until the knee is fully extended. If sciatica is present, the pain in the spine (and often the radicular symptoms) occurs as the leg is extended.
The slump test can also be done, similarly to the straight leg raise test, but with the patient "slumping" (with the thoracic and lumbar spines flexed) and the neck flexed. The slump test is more sensitive, but less specific, for disk herniation than the straight leg raise test.
Diagnosis of Sciatica
Clinical evaluation
Sometimes MRI, electrodiagnostic studies, or both
Sciatica is suspected based on the characteristic pain. If it is suspected, strength, reflexes, and sensation should be tested. If there are neurologic deficits or if symptoms persist for > 6 weeks, imaging and electrodiagnostic studies should be done. Structural abnormalities causing sciatica (including spinal stenosis) are most accurately diagnosed by MRI or CT.
Electrodiagnostic studies can confirm the presence and degree of nerve root compression and can exclude conditions that may mimic sciatica, such as peroneal nerve palsy, multiple mononeuropathy, or polyneuropathy. These studies may help determine whether the lesion involves single or multiple nerve levels and whether the clinical findings correlate with MRI abnormalities (especially valuable before surgery). However, abnormalities may not be evident on electrodiagnostic studies for up to a few weeks after symptoms begin.
Treatment of Sciatica
Activity as tolerated, analgesics, and sometimes drugs that relieve neuropathic pain
Physical therapy
Sometimes oral or epidural corticosteroids
Surgery for severe cases
Muscle spasm may be relieved with therapeutic heat or cold, and physical therapy may be useful. Whether corticosteroids should be used to treat acute radicular pain is controversial. Given epidurally, corticosteroids may accelerate pain relief, but they probably should not be used unless pain is severe or persistent. Some clinicians try oral corticosteroids, but firm evidence of efficacy is lacking.
Surgery is indicated only for cauda equina syndrome or for unequivocal disk herniation plus one of the following:
Muscular weakness that is worsening or not resolving
Other progressive neurologic deficits
Intolerable, intractable pain that interferes with job or personal functions in an emotionally stable patient and that has not lessened after 6 weeks of conservative treatment
Classic diskectomy with limited laminotomy for intervertebral disk herniation is the standard procedure. If herniation is localized, microdiskectomy may be done; with it, the skin incision and laminotomy can be smaller. Chemonucleolysis, using intradiskal injection of chymopapain, is no longer used.
Predictors of poor surgical outcome include
Prominent psychiatric factors
Persistence of symptoms for > 6 months
Heavy manual labor
Prominence of back pain (nonradicular)
Secondary gain (ie, litigation and compensability)
Key Points
Sciatica is typically caused by nerve root compression, usually due to intervertebral disk herniation, osteoarthritic osteophytes, spinal stenosis, or spondylolisthesis.
Classically, burning, lancinating, or stabbing pain radiates along the course of the sciatic nerve, most often down the buttocks and posterior aspect of the leg to below the knee.
Loss of sensation, weakness, and reflex deficits can occur.
Do MRI and electrodiagnostic studies if there are neurologic deficits or symptoms persist for > 6 weeks.
Conservative treatment is usually sufficient, but consider surgery for disk herniation with a progressive neurologic deficit, or persistent, intractable pain.
