Pain that extends from the buttock down the course of the sciatic nerve is common. Nearly 85% of cases are associated with a disk disorder. The causes, assessment, and management of sciatica are discussed in a new review article.
The mundane malady sciatica has been known to physicians since antiquity. It is defined as pain that radiates from the buttock downward along the course of the sciatic nerve.
- What is the most common cause of sciatica?
Although sciatica has several causes, Mixter and Barr extended previous observations to establish in 1934 that the principal source is compression of a lumbar nerve root by disk material that has ruptured through its surrounding annulus. Neuroradiologic studies affirm that 85% of cases of sciatica are associated with disk disorder. The fourth and fifth lumbar nerve roots and the first two sacral nerve roots join in the lumbosacral plexus to form the peroneal and tibial nerves that leave the pelvis in an ensheathed single trunk as the sciatic nerve, the largest nerve in the body.
Disturbances anywhere along its course can give rise to sciatica, but the most common areas are at the sites of disk rupture and osteoarthritic change — at the L4-L5 and L5-S1 levels and, less frequently, the L3-L4 level — where there is generally compression of the root below the corresponding disk.
Table 1. Causes of Sciatica and of Conditions Simulating Sciatica.
Figure 1. Origin and Course of the Sciatic Nerve and the Main Sites of Damage.
- How do leg-raising tests help establish the cause of sciatica?
Many clinical tests have been devised to determine whether sciatic pain is caused by disk compression of a spinal nerve root; most of the tests are variations of the straight-leg-raising test. In a patient in the supine position, raising the leg with the knee extended stretches the nerve root over the protruded disk and results in a nocifensive response of muscle contraction. A positive sign consists of reproduction or marked worsening of the patient’s initial pain and firm resistance to further elevation of the leg. A diagnosis of disk compression is likely if pain radiates from the buttock to below the knee when the angle of the leg is between 30 and 70 degrees. Sensitivity of the test for disk herniation is approximately 90%, but specificity is low. Many persons without spinal abnormalities have hamstring and gluteal tightness with discomfort elicited by straight-leg raising, but the pain is more diffuse than in sciatica and the leg can be lifted higher if the maneuver is performed slowly. Increased pain on dorsiflexion of the foot or large toe increases sensitivity. The crossed straight-leg-raising test (Fajersztajn’s test) for sciatic pain involves raising the unaffected leg; this test is 90% specific for disk herniation on the contralateral side but is insensitive.
Figure 2. Straight-Leg-Raising Test.
Morning Report Questions
Q: How effective is conservative treatment?
A: The most common initial treatment is pain control by means of medication and physical therapy. Activity is usually self-limited in proportion to the degree of discomfort, and although rest is often recommended, it is not better than movement in patients who are able to remain active. Nonsteroidal antiinflammatory medications may provide short-term relief for low back and sciatic pain; however, it is difficult to determine their effect on sciatica, and many patients report little relief. Orally or systemically administered glucocorticoids have been used to ameliorate sciatica, but it is difficult to interpret their effect. Guidelines recommend restrictions on the use of opioids. Antiepileptic drugs, antidepressant agents (e.g., tricyclic agents), muscle relaxants, and pain medications that enhance the activity of gamma-aminobutyric acid have been used but with little supporting data. The benefits of physical therapy and various exercise regimens are difficult to determine, and the superiority of any one program has not been established, although most appear to be safe. Spinal manipulation for sciatica is widely used and has been studied with an assortment of designs and comparators; therefore, reviews of existing trials, most considered of low or moderate quality, draw limited conclusions.
Epidural injections of glucocorticoids are frequently administered for low back pain and related conditions. Trials have suggested an associated short-term decrease in leg pain but no decrease in the need for subsequent surgery.
Q: How does surgery compare to conservative treatment of sciatica caused by disk disease?
A: Most trials comparing surgical treatment and conservative treatment of sciatica due to lumbar disk disease favor surgery, because it results in earlier relief of pain. A review of major trials with adequate data for analysis concluded that there was conflicting evidence on long-term benefit but that surgery relieved pain more rapidly and to a greater degree than did conservative therapy. North
American Spine Society guidelines state that diskectomy provides more effective and more rapid symptom relief than do other treatments for symptoms that warrant surgery, although less severe symptoms can be managed conservatively. Complications of surgery are infrequent but include dural tears with leakage of cerebrospinal fluid, as well as damage to the root or cauda equina.