Low Back Pain
DEFINITION
Low back pain can best be described in terms of specific accompanying features. Low back pain is acute if it has a duration of about 1 month or less. Chronic low back pain is usually defined by symptoms of two months or more. Both acute and chronic low back pain can be further defined by the presence or absence of neurologic symptoms and signs. Nonspecific or nonradicular low back pain is not associated with neurologic symptoms or signs. In general, the pain is localized to the spine or paraspinal regions (or both) and does not radiate into the leg. In general, nonspecific low back pain is not associated with spinal nerve root compression. Nonspecific low back pain might or might not be associated with significant pathology on magnetic resonance imaging (MRI) and is often a result of simple soft tissue disorders such as strain, but it can also be caused by serious medical disorders arising in the bony spine, parameningeal, or retroperitoneal regions. See Table 1 for the differential diagnosis for low back pain.
Table 1 Differential Diagnosis of Low Back Pain
| Mechanical Causes | Nonmechanical Causes | Causes of Referred Pain |
|---|---|---|
| Idiopathic (sprain, strain) | Malignancy | Pelvic disease (prostatitis, endometriosis, pelvic inflammatory disease) |
| Spondylosis (disk, annulus, facet) | Infection | Renal disease (kidney stones, pyelonephritis, perinephric abscess) |
| Compression fracture | Inflammatory spondyloarthropathy (ankylosing spondylitis, psoriatic spondylitis, Reiter’s syndrome, inflammatory bowel disease) | Aortic aneurysm |
| Traumatic fracture | Osteochondrosis | Gastrointestinal disease (pancreatitis, cholecystitis, penetrating ulcer) |
| Alignment disorders (kyphosis, scoliosis, spondylolisthesis) | Paget’s disease of bone |
Low back pain accompanied by spinal nerve root damage is usually associated with neurologic signs or symptoms and is described as radiculopathy. There is usually pathologic evidence of spinal nerve root compression by disk or arthritic spur, but other intraspinal pathologies may be present and are often apparent on an MRI scan of the lumbosacral spine.
PREVALENCE
Low back pain is second only to upper respiratory illness as a cause for visiting a physician.1 Up to two thirds of the population has low back symptoms at some time in their lives. In 1995 there were about two worker’s compensation claims for low back pain for every 100 workers. Seventy-five percent of patients with acute low back pain are back to work within 1 month of the onset of symptoms, and only 5% are disabled for more than 6 months.2 However, among those with continuing pain 6 to 10 weeks after onset, most still have some symptoms at 1 year.3
Among persons with chronic low back pain without neurologic deficits, a number of factors play a role in the length of disability. Recurrent low back pain and prolonged disability tend to correlate with prior history of low back pain, advancing age, job dissatisfaction, emotional distress, heavy or repetitive lifting and physical work, prolonged sitting or standing, and the presence of a worker’s compensation claim or pending litigation.4
PATHOPHYSIOLOGY
The pathophysiology of nonradicular low back pain is usually indeterminate. In fact, one of the defining features of this disorder is its nonspecific etiology. Pain can arise from a number of sites, including the vertebral column, surrounding muscles, tendons, ligaments, and fascia. Stretching, tearing, or contusion of these tissues can occur after sudden unexpected force applied to the spine from events such as heavy lifting, torsion of the spine, and whiplash injury. Whether muscle spasm is a significant etiology of lumbar spine pain, either as cause or effect of back injury, has not been proved.
The pathophysiology of radicular spine pain and lumbosacral radiculopathy is usually more obvious. Disk herniation through the annulus fibrosis does not in itself produce pain, but compression by disk of the dural lining around the spinal nerve root sleeve is one likely explanation for the back pain associated with acute disk herniation. This is also likely to contribute to the pain from spinal nerve root compression from arthritic spurs at degenerated facet and uncovertebral joints. Compression can directly stretch nociceptors in dura or nerve root sleeve tissues, but ischemia from compression of vascular structures, inflammation, and secondary edema is also likely to play a role in some cases.
SIGNS AND SYMPTOMS
History and physical examination are critical to the diagnosis and thus to the formulation of a rational approach to management. The following briefly summarizes the major points.
History
The medical history should focus on both triggering and alleviating factors, as well as on the character of the pain. Signs and symptoms such as increased pain with Valsalva maneuvers, straight-leg-raising symptoms, the tendency for the pain to radiate into the buttock or leg, the presence of weakness or sensory deficit, and bowel or bladder urgency or incontinence are associated with neurologic causes of low back pain.
The history should also explore factors that increase the likelihood of an underlying systemic disorder as a cause. These include advanced age, history of cancer, unexplained weight loss, use of injected drugs, chronic infection, prolonged duration of pain, pain that does not respond to rest or recumbency, and failure to respond to previous therapy. Box 1 reviews these factors.
Waddell and colleagues have described a number of historical features that point to nonorganic causes for low back pain, predicting delayed recovery and suggesting the need for a multidisciplinary approach to treatment.5 These are reviewed in Box 2.
Examination
A general examination should be performed to identify potential systemic disorders, such as rheumatologic disease, skin disease, or bone deformities. The spine should be inspected for alignment, curvature, range of motion, focal tenderness, and overlying skin abnormalities such as a tuft of hair or pore. Mechanical maneuvers to elicit radicular and hip-joint symptoms should be considered, including straight-leg raising, reverse straight-leg raising, Patrick’s test, and Lasègue’s sign.
A careful neurologic examination should be undertaken to exclude motor and sensory deficits. Muscle strength in the L2 through S1 myotomes should be examined. The sensory examination should include soft-touch and pain sensation in the same segmental distributions. Muscle stretch reflexes should be elicited at the knee for the L3 to L4 segment and at the ankle for the S1 segment, and they can also be performed in the posterior thigh at the tendinous insertion of internal hamstrings for the L5 segment.
Waddell and colleagues have also described a number of findings on the physical examination that point to nonorganic causes for low back pain, predicting delayed recovery and suggesting the need for a multidisciplinary approach to treatment (Box 3).6
DIAGNOSIS
The appropriate evaluation and management of low back pain rest on a few basic principles. First, it is necessary to determine whether the symptoms are caused by nerve root involvement. Second, it is necessary to determine whether the acute or chronic spine pain is related to a serious underlying medical illness that is manifesting itself as spine pain. After an initial assessment of the likely cause of the symptoms, the spine pain can then be treated.
A number of diagnostic tests can help pinpoint the cause of low back pain. Which test is selected depends on a host of factors uncovered during the history and physical examination. The diagnostic tests are described next.
Routine Radiographs of the Spine
Routine spine radiographs are of limited value because they visualize only bony structures. Guidelines from the U.S. Agency for Health Care Policy and Research (AHCPR) indicated value of routine spine radiographs for acute low back pain in the following settings: acute major trauma, minor trauma associated with risk of osteoporosis, risk of spinal infection, pain that does not respond to rest or recumbency, and history of cancer, fever, or unexplained weight loss.7 They may also be of value in assessing spinal alignment and rheumatologic disorders of bone.
Computed Tomography and Magnetic Resonance Imaging
Computed tomography (CT) and magnetic resonance imaging (MRI) are sensitive tools for evaluating neural structures such as spinal nerve roots and the spinal cord, and they can visualize soft tissue structures within the spinal canal. Of the two modalities, MRI resolution for neural structures is superior to CT. In the absence of motor, sensory, or autonomic deficits, and in the absence of significant trauma, infection, or malignancy, the American Academy of Neurology guideline recommends nonsurgical therapy before these techniques are used in patients with uncomplicated acute low back pain of less than 7 weeks’ duration.8 Patients with acute neurologic deficits associated with low back pain should be considered for MRI or CT of the lumbosacral spine unless surgery and invasive therapeutic options are not indicated.
Computed tomographic Myelography
CT myelography employs traditional myelography (intrathecal instillation of a radiocontrast agent, followed by routine spinal radiographs) followed by CT of the spine. It may be of value when MRI studies are inconclusive, especially in the assessment of the relation between spinal nerve roots and the bony neural foramina. Although this technique involves an invasive procedure, it is the study of choice when there are absolute contraindications to the use of MRI (presence of an implanted electronic device such as cardiac pacemaker or metal object in the inner ear, eye, or brain, such as an aneurysm clip).
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