DIAGNOSIS

AND

TREATMENT

Herniated Lumbar Intervertebral Disk Richard A. Deyo, MD; John D. Loeser, MD; and Stanley J. Bigos, MD

Low back pain is common, but a herniated intervertebral disk is the cause in only a small percentage of cases. Most symptomatic disk herniations result in clinical manifestations (pain, reflex loss, muscle weakness) that resolve with conservative therapy, and only 5% to 10% of patients require surgery. Sciatica is usually the first clue to disk herniation, but sciatica may be mimicked by other disorders that cause radiating pain. Because more than 95% of lumbar disk herniations occur at the L4-5 or L5-S1 levels, the physical examination should focus on abnormalities of the L5 and SI nerve roots. Plain radiography is not useful in diagnosing disk herniation, but more sophisticated imaging (myelography, computed tomography, or magnetic resonance imaging) should generally be delayed until a patient is clearly a surgical candidate. Conservative therapy includes nonsteroidal anti-inflammatory drugs, brief bed rest (often for less than 1 week), early progressive ambulation, and reassurance about a favorable prognosis. Muscle relaxants and narcotic analgesics have a limited role, and their use should be strictly time-limited. Conventional traction and corsets are probably ineffective. Except for patients with the cauda equina syndrome, surgery is generally appropriate only when there is a combination of definite disk herniation shown by imaging, a corresponding syndrome of sciatic pain, a corresponding neurologic deficit, and a failure to respond to 6 weeks of conservative therapy. Annals of Internal Medicine. 1990;112:598-603. From the University of Washington School of Medicine and the Seattle Veterans Affairs Medical Center, Seattle, Washington. For current author addresses, see end of text.

JLow back pain is a pervasively common problem that affects up to 80% of adults at some time during their lives. A herniated disk is the cause of pain in only a small percentage of patients, and even when a herniated disk is diagnosed, surgery is only rarely necessary. Thus, management of the patient with back pain and sciatica caused by a herniated disk often falls to the primary care physician, who should be familiar with the natural history, consevative therapy, and indications for surgical referral. Disk herniation refers to the protrusion of the gelatinous nucleus pulposus of the disk through a weakened anulus fibrosus. Clinically important herniations most often occur through a posterolateral defect, but midline herniations may occur. Protruding disk material may compress and inflame a spinal nerve root, resulting in pain and paresthesias, usually perceived in the sensory distribution of the nerve. 598

Epidemiology and Natural History The natural history of low back pain (in the absence of underlying neoplastic or infectious causes) is generally characterized by rapid improvement. Only a small portion of all affected persons will have back pain that persists beyond 2 weeks (Table 1). An even smaller proportion will have features suggesting sciatica, which is usually the first clue to a possible herniated disk (1). The incidence of clinically apparent lumbar disk herniation is highest in young adults between the ages of 30 and 40 years. In the typical history, back pain occurs first, followed by recurrences and eventually the development of pain and paresthesias that radiate to the leg, indicating the onset of sciatica. The back pain often becomes less severe when leg pain develops. In one study (2) of patients undergoing surgery for disk herniation, the mean duration of preoperative back symptoms was nearly 3 years. Many risk factors for lumbar disk herniation have been reported in epidemiologic studies. Some of these factors are biomechanical and include twisting and other repetitive motions that occur in the occupational setting. Sedentary occupations are associated with an increased risk for disk herniation, possibly related to muscular deconditioning or the chronic mechanical stress of the sitting position. Occupations involving prolonged driving of motor vehicles may entail a particularly high risk (3). Other apparent risk factors are more closely related to lifestyle, including obesity (a threefold risk in the most obese men compared with the least obese) and cigarette smoking (4, 5). Smoking may increase intradiscal pressure because of chronic coughing, jeopardize disk metabolism because of vascular effects of nicotine, or serve as a marker for psychosocial traits associated with frequent and prolonged pain. Psychosocial factors are clearly associated with back complaints in general. For example, persons with lower educational attainment have a higher risk for back pain and also have worse outcomes (6). Lumbar intervertebral disks may herniate without causing symptoms, creating a pitfall for clinicians who request imaging procedures early in an episode of back pain or in the absence of clinical findings that suggest nerve root compression. A study (7) of myelograms in asymptomatic adults identified 24% with lumbar myelography defects suggesting varying degrees of disk herniation. Similarly, a recent study (8) of lumbar computed tomography found evidence of a herniated disk in 20% of persons who had no history of back pain or sciatica. Because herniations do not necessarily result in nerve root compression or symptoms, the mere anatomic finding does not imply clinical disease. Further, the presence of severe back pain, leg pain, or sciatica does not necessarily imply a herniated disk.

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The diagnosis "herniated disk" has probably been overused, particularly in labeling persons who have severe functional impairments associated with back pain. Waddell (9) has called this the ''nominal'' diagnosis of herniated disk because it is usually made in the absence of confirmatory clinical or imaging evidence. Most symptomatic disk herniations result in clinical manifestations (pain, reflex loss, sensory changes, and muscle weakness) that resolve without surgical intervention. It is estimated that only 5% to 10% of patients with persistent sciatica will require surgery (10). In a randomized trial (11) that compared surgery with conservative treatment for herniated lumbar disks, the recovery of foot weakness was equivalent in the two treatment groups at 4-year follow-up. The major advantage of surgery was more rapid pain relief and a lower rate of relapse. In randomized trials (12, 13) that compared intradiskal chymopapain injection with saline injection for herniated disks, approximately 50% of patients receiving placebo reported an improvement in back pain and sciatica within 6 weeks. Furthermore, 45% of patients showed improvement in reflex abnormalities, and 6 1 % had improvement in muscle weakness (13). Somewhat higher percentages of improvement were seen with active drug injection. Thus, spontaneous recovery is part of the natural history of motor and sensory signs as well as back and leg pain, although invasive treatments may accelerate their resolution in highly selected patients. Unfortunately, recurrence is often part of the natural history of low back problems, even after complete symptom resolution. In a prospective study (14) of occupational back problems (resulting in compensation), approximately one-third of subjects had a recurrence of pain within 3 years. In a clinical trial (11) of therapy for patients with a demonstrated disk herniation, 24% of conservatively treated patients had recurrent pain within 4 years, and 15% of surgically treated patients had relapses. Despite a reasonably favorable prognosis, back pain in general (and herniated disks in particular) have an enormous effect on health care utilization and costs. One estimate placed the annual cost of direct medical care for low back pain at 13 billion dollars and for herniated lumbar disks at 2 billion dollars (15). Back pain is the second leading cause of office visits to primary care physicians (16). Among adults under age 65, medical back problems rank second as a reason for nonsurgical hospital admissions, and back and neck problems rank third among all surgical admissions (17). The indirect costs of disk herniation are also high. In men of working age, the costs of earnings and productivity losses attributable to herniated disks are similar to those of ischemic heart disease (18).

Diagnosis The differential diagnosis of low back pain is broad and includes mechanical lesions (degenerative changes, herniated disks, spinal stenosis, spondylolisthesis); systemic diseases such as metastatic cancer, serious infections, and inflammatory spondyloarthropathies; and vis-

Table 1. Prevalence of Back Pain and Sciatica in the Entire Adult Population* Characteristic Any low back pain Ever had low back pain persisting at least 2 weeks Low back pain persisting at least 2 weeks at a given time (point prevalence) Back pain with features of sciatica lasting at least 2 weeks Lumbar spine surgery

Prevalence, % 60 to 80 14 7 1.6 1 to 2

* Adapted from Deyo and Tsui-Wu (1).

ceral diseases that may present with back pain as a chief symptom but that do not involve the spine (for example, nephrolithiasis, endometriosis, and aortic aneurysm). The differential diagnosis of sciatica includes spinal stenosis (usually in older patients) and less common conditions such as synovial cysts, congenital anomalies of the lumbar nerve roots, primary neural or bone tumors, metastatic cancer, and epidural abscesses. Irritation of the sciatic nerve may also occur simply because of local pressure such as that caused by a wallet in the back pocket. Finally, pain from other sources in the lumbar spine such as the facet joints has been reported to radiate into the upper leg in patterns that mimic sciatica. Nonetheless, a herniated disk is the commonest cause of true sciatica. More than 90% of all episodes of back pain are probably attributable to mechanical causes, but the precise pathoanatomic lesion is rarely identifiable (19). Thus, the early diagnostic evaluation of back pain is devoted to ruling out systemic disease; identifying and monitoring neurologic abnormalities that may eventually require surgery (generally resulting from herniated disks or spinal stenosis); and identifying characteristics of the pain and the patient that may influence conservative therapy (20). For most patients with a herniated disk, back pain precedes the onset of sciatica and the back pain may or may not abate as pain and paresthesias begin to radiate down the leg. The onset of sciatic pain may be gradual or sudden, and frequently there is no specific precipitating event. The patient with a disk herniation often has difficulty inrisingfrom the sitting or supine position and typically experiences at least partial pain relief while supine. This is probably related to the minimization of motion and intradiscal pressure that occurs in the supine position. The sciatica typically radiates down the posterior or lateral aspect of the leg and is aggravated by coughing or sneezing. It often radiates below the knee, and this distal radiation suggests that the pain is probably attributable to a radiculopathy rather than to other causes of radiating pain. Because more than 95% of lumbar disk herniations occur at the L4-5 or L5-S1 levels, the neurologic examination should focus on the L5 and SI nerve roots (2). Dysfunction of the L5 nerve root typically results in no reflex changes, but does result in weakness of the great toe extensor and other dorsiflexors of the foot and in sensory loss along the medial aspect of the foot. Sensation is often reduced in the great toe and in the web

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space between the first and second toes. Compression of the SI nerve root typically results in a diminished ankle reflex, weakness of the plantar flexors of the foot, and sensory deficits of the posterior calf and lateral aspect of the foot. Between 80% and 90% of patients with surgically proven disk herniations will have foot weakness or impaired ankle reflexes. Knee reflexes are diminished in only 5% of patients with proven disk herniations, reflecting the infrequent occurrence of disk herniation above the L4-5 level (2). A positive straight leg raising sign helps to confirm the presence of nerve root irritation. A positive test results when pain occurs in a radicular distribution with a straight leg elevation of 60 deg or less. This test is quite sensitive, and the sign is present in about 95% of patients with a proven herniated disk at surgery. Thus, absence of the sign constitutes a reasonable "rule out" test for lower lumbar disk herniation. However, it is a relatively nonspecific test; the sign is present in 80% to 90% of surgical patients who undergo surgery but are found to have no part of the disk protruding beyond normal anatomic limits (2). The crossed straight leg raising sign is present when elevation of the contralateral leg produces the sciatica. This sign is less sensitive (about 25%) but much more specific (88%) than a positive ipsilateral straight leg raising test (2). Electromyography is sometimes helpful in confirming the radicular origin of physical manifestations or leg pain. It may be particularly useful in discriminating radicular pain from peripheral neuropathy. However, because of its limited specificity, electromyography should not be used as the sole determinant of either the diagnosis or the need for surgery. Plain radiography is rarely useful in diagnosing low back pain and is not helpful in diagnosing a herniated lumbar intervertebral disk. Nonetheless, plain roentgenograms are appropriate in the patient with neurologic deficits to rule out other conditions such as tumor, infection, fracture, and spondylolisthesis. In the absence of neurologic deficits, plain films should probably be reserved for patients with pain that persists beyond 3 to 4 weeks, patients with signs of systemic disease, those with a known history of cancer, and patients with known drug or alcohol abuse (21). A clinical diagnosis of a herniated disk can only be confirmed when appropriate imaging tests such as myelography, computed tomography, or magnetic resonance imaging show an abnormality corresponding to the neurologic deficit. The optimal choice among these three tests, or the most appropriate sequence of tests, remains controversial. The sensitivities of computed tomographic scanning and metrizamide myelography are similar (90% to 95%), as are their specificities (68% to 88%) (22, 23). How magnetic resonance imaging will compare with these other imaging modalities is not yet clear. A common mistake is to request these sophisticated imaging tests early in the course of back pain or in the absence of clinical findings that suggest that the patient is a surgical candidate. Because disk herniation is so common in asymptomatic persons, the isolated finding on an imaging test without corresponding clinical signs may be misleading and may initiate an ill-advised cas600

cade of clinical interventions. These tests, in general, should be limited to the patient who has neurologic abnormalities suggesting a herniated disk and who has not responded to 3 to 4 weeks of conservative therapy. Without such findings, the patient would not be a surgical candidate regardless of the imaging results. The only indication for imaging earlier in the course of back pain would be the presence of the cauda equina syndrome, a progressive neurologic deficit, or the need for a more precise diagnosis in a patient with suspected tumor or infection. Conservative Therapy In the absence of the cauda equina syndrome or a rapidly progressive neurologic deficit, virtually all patients with a suspected disk herniation should be treated conservatively for 4 to 6 weeks. If neurologic deficits still persist at this time, special studies to evaluate any role for surgical intervention are appropriate. Some surgeons believe that delaying surgical treatment in this circumstance beyond 3 months may be associated with worse outcomes, although patients with such prolonged pain may be destined to have a worse prognosis in any event. Bed rest has long been a mainstay of conservative therapy for patients with suspected disk herniation, but recent studies have led to progressively shorter bed-rest recommendations. The rationale for bed rest is based on the clinical observation that many patients with mechanical back pain experience symptomatic relief in the supine position and on the physiologic observation that intradiskal pressure is minimized in the supine position. Nonetheless, in patients with back pain or sciatica in the absence of neurologic deficits, 2 days of bed rest seems to be as effective as 7 days of bed rest with regard to pain resolution and functional recovery (24). In the patient with a neuromotor deficit, bed rest may need to be longer and stricter, but little evidence is available to suggest the optimal duration. Because bed rest promotes muscle weakness, cardiovascular deconditioning, and bone mineral loss, lengthy recommendations for inactivity (more than a week) are to be avoided. Furthermore, the standing posture results in disk pressures that are only slightly higher than those in the side-lying position and that are lower than those in the sitting position. Thus, it is generally safe to recommend standing and brief periods of walking to prevent deconditioning. Patients may often subvert the potential physiologic benefits of bed rest by sitting in bed to watch television or read; such a position raises the intradiscal pressure even above that produced in the standing position. Several well-designed clinical trials suggest that nonsteroidal anti-inflammatory drugs are efficacious in the treatment of back pain in general. In the acute phase, especially with sciatica, narcotic analgesics may be appropriate. Their use should be relatively brief, however, and limited by a specific time prescription rather than contingent on ongoing pain. Evidence supporting the use of "muscle relaxants" such as diazepam, cyclobenzaprine, carisoprodol, and methocarbamol is limited.

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Table 2. Randomized,

Controlled Trials of Conventional

Study (Reference) Lidstrom et al. (28) Weber (29) Mathews and Hickling (30) Coxheadet al. (31) Weber et al. (32)t Pal et al. (33) Mathews et al. (34)

Traction for Sciatica or Proven Lumbar Disk

Herniation

Patients, n

Patient Description

Control Group

Blind Outcome Assessment

Results

62 86 27 292 215 41 143

Sciatica Herniated disk Sciatica Sciatica Herniated disk Sciatica Sciatica

Heat, rest Sham traction* Sham traction* Multiple treatments Sham traction* Sham traction* Heat

Yes No Yes No Yes Yes Yes

Negative Negative Negative Negative Negative Negative Negative (except for women < 45 years old)

* Sham traction consisted of applying the traction apparatus with minimal weight (shown not to produce distraction of the vertebrae in radiographic studies). t Used four different methods of traction.

Nonetheless, some clinical trials do suggest that such agents, especially carisoprodol, are beneficial for treating back pain. All these drugs have sedating effects, and it is unclear how to optimally select patients for their use. It is also unclear whether they offer any advantage over analgesics or nonsteroidal anti-inflammatory drugs alone, although a recent trial (25) suggests a modest benefit for patients receiving combined therapy. Like narcotic analgesics, their use should be strictly timelimited, with 1 week being a general guide. Muscle relaxants and narcotic analgesics should be avoided in patients with chronic pain syndromes (greater than 3 months in duration). Exercise for the treatment of back pain and herniated disks remains controversial; there are various regimens, each of which has its advocates. In the case of acute disk herniation, probably the most important consideration is to avoid prolonged inactivity and debilitation. Even among patients with severe symptoms, most are able to resume some standing and walking activities by the third day of symptoms. It is usually feasible in the first week to have patients work up to a 20-minute walk for every 3 hours spent supine. The ability to sit comfortably is a sign of improvement and suggests that the patient can begin controlled endurance training activities that place a minimal load on the spine and are less stressful than sitting. Endurance activities may be important in promoting recovery and preventing future back problems. Speed walking and stationary bicycling are commonly recommended, but swimming is also appropriate. Jogging is feasible for younger patients with milder symptoms. The traditional isometric flexion exercises (Williams exercises) may be useful for patients with chronic pain but appear to be ineffective in patients with acute back problems (26). Recommendations for rest, medication, and initiating exercise should be given with an explicit time schedule. Having patients continue rest or medication "until the pain is gone" may foster dependence and prolong symptoms and functional limitations. Similarly, patients should be reassured that even if they have mild or moderate symptoms when resuming physical activity, such symptoms are not indicative of permanent harm. A randomized clinical trial (27) for patients with acute back pain compared symptom-limited rest, medication, and activity with strictly time-limited prescriptions. In this small trial, patients receiving the time-limited pre-

scriptions reported less pain and greater functional recovery at follow-up than patients who were told to "let pain be your guide." Although conventional traction is still widely used, there is growing evidence against its efficacy in patients with sciatica or proven disk herniations. Table 2 summarizes seven randomized clinical trials (28-34) of conventional traction using standard weights or motorized traction devices. None of these trials showed a significant benefit for traction compared with the control treatment. Thus, hospital admission for traction is probably inappropriate. Indeed, the early management of patients with herniated disks should generally be at home to avoid reinforcing illness behavior through institutionalization and to maximize patient convenience. There have been no controlled trials of inversion devices or other gravity traction methods, although it is clear that inversion can have important ocular and cardiovascular side effects. As with traction, no studies have convincingly shown the efficacy of corsets or other spinal orthoses. Some observers note that use of rigid orthoses may promote muscle weakness and result in worse long-term outcomes. Furthermore, to truly limit motion in the lumbar spine requires a rigid body cast with extension to the legs. The Quebec Task Force on Spinal Disorders (35) concluded that although both traction and orthoses are commonly used, no scientific evidence exists to support their efficacy. Longer-term intervention to reduce the frequency and severity of expected recurrences of back pain or sciatica should include lifestyle changes such as weight loss, smoking cessation, and regular exercise. Instruction in proper lifting methods, work positions, and rest positions may also be helpful, although such instruction is not sufficient in itself to prevent recurrent back problems. Patient reassurance and education is an important aspect of therapy. The greatest source of patient dissatisfaction with care for back pain appears to be the inadequate explanation of the problems (36). Furthermore, patients need to be reassured that despite recurrences, the natural history of back pain, sciatica, and disk herniation is favorable and that important physical disability is extremely rare. Physicians should also be wary of labeling patients with frightening diagnoses. The term ruptured disk implies a bursting or violent

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Table 3. Indications for Surgical Referral Patient with Sciatica

in the

The cauda equina syndrome (a surgical emergency): characterized by bowel and bladder dysfunction (usually urinary retention), saddle anesthesia, bilateral leg weakness and numbness Progressive or severe neurologic deficit Persistent neuromotor deficit after 4 to 6 weeks of conservative therapy Persistent sciatica, sensory deficit, or reflex loss after 4 to 6 weeks in a patient with positive straight leg raising sign, consistent clinicalfindings,and favorable psychosocial circumstances (for example, realistic expectations and no evidence of depression, substance abuse, or excessive somatization)

dissolution of tissue, but this may be a common radiographic finding in patients who are asymptomatic. Less emotionally laden terms such as extruded disk may be preferable, and physicians should avoid making a nominal diagnosis of disk herniation based simply on the severity of pain or dysfunction. Surgical Intervention The rate of lumbar spine surgery in the United States is three to eight times higher than in most European countries, suggesting that it may be overused. Although it is frequently stated that surgery is becoming more selective and that we have passed out of the era of excessive surgery, the rate of lumbar discectomy actually rose 53% between 1980 and 1985 (National Center for Health Statistics, Unpublished data). Furthermore, wide and unexplained variations in the rate of lumbar spine surgery have been observed among geographic regions of the United States, suggesting that there are widely differing practice styles among physicians. The extensive literature on failed lumbar spine surgery is testimony to the often ineffective use of this procedure. Most neurosurgeons and orthopedists agree that surgery for a herniated disk is only appropriate when there is a combination of definite herniation documented by some imaging procedure, a corresponding pain syndrome, a corresponding neurologic deficit, and failure to respond to 4 to 6 weeks of conservative therapy. In practice, these guidelines are often liberalized (to bulging disks, equivocal neurologic signs, and shorter periods of conservative care), despite evidence that outcomes are worse under these circumstances (37, 38). The presence of a herniated disk on an imaging test alone is not an indication for surgery, nor is persistent pain alone, nor is the observation that nothing else has worked. Several investigators (37, 38) have developed preoperative scoring indexes to quantify the likelihood of a successful surgical outcome. These indexes combine imaging results, physical examination findings, history, and psychosocial features of the patient and have been shown to have substantial predictive value regarding surgical success. The major benefit of surgery for herniated lumbar disks is relief of sciatica. In well-selected patients, approximately 75% will experience complete relief of sciatica and over 90% will have complete or partial relief. 602

The degree of relief declines progressively as the surgical findings change from complete herniation to bulging disk to no herniation. Relief of back pain is less consistent, with approximately 70% of patients experiencing relief of back pain. Complete relief of all pain symptoms occurs in only half the group of patients undergoing lumbar discectomy (2). Patients must have realistic expectations regarding surgery and understand that they are likely to have recurrent back difficulties even after successful surgery. Repeat surgery is much less successful than first-time surgery, unless a new disk herniation is identified with all the other surgical criteria described above. Complications associated with lumbar spine surgery are infrequent, but include death (0.2%), thromboembolism (1.7%), and infections (2.9%) (2). Neurologic complications due to nerve trauma or postoperative epidural hematoma may occur but are very infrequent. A perforation of the dura mater requiring repair occurs in 2% to 5% of operations. Intraoperative complications are commoner in repeat operations. The neurologic deficits resulting from disk herniation are usually relatively minor and tend to resolve slowly with or without surgery. Although surgery may slightly accelerate resolution of neurologic deficits, the major benefit is pain relief. Given the natural history of symptom resolution and the goals of lumbar discectomy, this procedure should always be regarded as elective except in the case of a patient with the cauda equina syndrome. Thus, the patient should always be allowed to make the surgical decision after he or she is given information about the risks and benefits. The choice of surgical procedures is controversial. There are strong advocates for standard laminectomy and discectomy, for microdiscectomy procedures, for percutaneous discectomy, and for discectomy with fusion. The indications for spine fusion are particularly unclear, but it appears to be generally inadvisable for the patient who has a single herniated disk with otherwise uncomplicated surgery (39). Chymopapain injections for herniated disks were introduced in the United States in 1983, following a successful randomized, double-blind, placebo-controlled trial (13). Although chymopapain injection was advocated as a substitute for surgery, in early trials it was compared with placebo injections rather than with standard surgical intervention. Two small subsequent randomized trials (40, 41) both suggested that the outcomes of spine surgery may generally be superior to those of chymopapain injection. Because of such findings and because of the occasional occurrence of anaphylactic reactions and serious neurologic complications, chymopapain has waned in popularity. Primary care physicians should identify a neurosurgeon or an orthopedist who operates in a highly selective manner and who uses criteria such as those described here. Table 3 provides an explicit set of recommendations for surgical referral. Acknowledgments: The authors thank David Buchner and Stephan Fihn for reviewing an earlier draft of this manuscript and Chris Morrison and Kathy Minotto for helping to prepare the manuscript. Grant Support: In part by the Northwest Health Services Research and Development Field Program, Seattle Veterans Affairs Medical Center,

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and by grant HS06344-01 from the National Center for Health Services Research and Technology Assessment. Requests for Reprints: Richard A. Deyo, MD, Seattle Veterans Affairs Medical Center (152), 1660 South Columbian Way, Seattle, WA 98108. Current Author Addresses: Dr. Deyo: Seattle Veterans Affairs Medical Center (152), 1660 South Columbian Way, Seattle, WA 98108. Dr. Loeser: Department of Neurological Surgery, RI-20, University of Washington School of Medicine, Seattle, WA 98195. Dr. Bigos: Department of Orthopaedics, RK-10, University of Washington School of Medicine, Seattle, WA 98195.

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15 April 1990 • Annals

of Internal

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Medicine

• Volume 112 • Number 8

603

Herniated lumbar intervertebral disk.

Low back pain is common, but a herniated intervertebral disk is the cause in only a small percentage of cases. Most symptomatic disk herniations resul...
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