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Am Fam Physician. 2001;64(6):1077-1081

There is wide variation in the treatment of acute low back pain. Such pain is rarely due to a serious etiology and, although the differential diagnosis is extensive, low back pain is most often caused by musculoligamentous strain. Atlas and Deyo review the evaluation and management of a patient presenting with acute low back pain.

DisorderHistoryPhysical examination
AllDuration of pain >1 month Bed rest with no relief
CancerAge ≥ 50 years
Previous cancer history
Unexplained weight loss†
Neurologic findings*
Compression fractureAge ≥ 50 years (≥ 70 years more specific)
Significant trauma‡
History of osteoporosis
Corticosteroid use
Substance abuse§
InfectionFever or chills
Recent skin or urinary infection
Injection drug use
Fever (>38°C [100°F])
Tenderness over spinous processes

Acute low back pain can more specifically be defined as pain in the lumbosacral region lasting up to four weeks. Subacute low back pain lasts up to 12 weeks, and chronic low back pain lasts more than 12 weeks. One of the most important initial findings in evaluating acute low back pain is the presence or absence of radiculopathy. Almost all cases of low back pain involve the L5 or S1 nerve root (L4-5 or L5-S1 interspaces). Spinal stenosis may also cause radiculopathy, especially in elderly patients. A thorough history and physical examination can improve the physician's ability to detect serious conditions that may be causing low back pain (see Table 1).

Nerve rootStrengthSensationReflex
L2IliopsoasAnterior thigh, groinNone
L3QuadricepsAnterior/lateral thighPatellar
L4Quadriceps, ankle dorsiflexion (heel walking)Medial ankle/footPatellar
L5*First toe dorsiflexionDorsum of footNone
S1*Ankle plantarflexion (toe walking)Lateral plantar footAchilles

The physical examination should include evaluation of spinal symmetry, flexibility and the patient's posture. The presence of soft tissue tenderness is poorly reproducible between physicians. Assessment of the abdomen and pelvic areas and of hip range of motion may also be useful. If the patient has leg symptoms, a straight leg raise test can screen for nerve root irritation. With the patient seated or supine, the leg is straightened (with ankle dorsiflexed and knee extended). Reproduction of the radiating leg pain with the leg raised to less than 60 degrees is considered a positive test. The crossed straight leg raise test is positive if the test causes contralateral buttock or leg symptoms, and it indicates nerve root irritation. This test is specific but not sensitive. If the straight leg test is positive or if the patient has symptoms consistent with sciatica (pain radiating down the posterior or lateral aspect of the leg), motor, sensory and reflex examinations of the lower extremity should be done. The physical examination can help the physician identify the specific location of the impingement (see Table 2).

Imaging studies may not be helpful because the results are not specific (that is, they do not correlate well with the patient's symptoms) or sensitive (that is, serious causes are not often identified on images). Many patients, especially those older than 60 years, have radiographic evidence of disk degeneration, vertebral osteophytes and facet joint arthritis, but these findings are not necessarily related to symptoms and have been found in many patients who have no symptoms at all. However, obtaining plain radiographs is reasonable if the patient has risk factors for vertebral fracture (see Table 1) or if there is no improvement after conservative treatment.

Computed tomographic (CT) scans or magnetic resonance images (MRI) should be obtained if there is good reason to suspect a serious cause for the acute low back pain. If the patient is a surgical candidate, referral to an orthopedist or neurosurgeon may be appropriate because the surgeon may want to obtain a specific study or view that will help determine the surgery that is required. A CT scan without contrast will be useful if the bony structures need to be evaluated, if the patient has a metallic foreign body in place or if the patient is claustrophobic. An MRI may provide more information in a patient thought to have spinal stenosis, osteomyelitis, an epidural abscess, tumor or a recent fracture that is nondisplaced. Bone scans are not likely to be more accurate than MRIs. Occasionally, the patient will expect an advanced imaging study; in this case, careful attention should be paid to documenting such testing when the clinical evaluation does not warrant the test. Careful patient education is necessary in any case.

Laboratory testing may be useful, but it is not routine. Determination of the erythrocyte sedimentation rate can screen for malignancy or infection, but it remains a nonspecific test. If a genitourinary tract infection is suspected, a urinalysis is reasonable.

The mainstay of treatment is conservative care, reassurance and education. Bed rest has not been shown to improve outcomes in patients with acute low back pain and should, in general, be discouraged. Bed rest may be recommended during periods of severe pain, but early ambulation and continuation of nonstrenuous activities are helpful. The patient with acute low back pain should avoid prolonged sitting or standing; he or she should be told to walk and move his or her back at regular intervals (every 30 minutes). Slow movement will help minimize the chance of back spasm.

Acetaminophen and nonsteroidal anti-inflammatory drugs are useful in many patients with acute low back pain. There is no evidence that muscle relaxants or opioids are more effective than these medications, although they may be useful in certain cases. Physical therapy may also be useful, although the optimal timing of such treatment is not clear. Early referral is not associated with better outcomes than later referral, so a conservative attitude may be reasonable, with referral occurring after the two- to four-week recovery period that is typical in persons with acute low back pain. A variety of treatments has not been shown to be useful, including facet joint injections, oral steroids, transcutaneous electrical nerve stimulation, biofeedback and traction.

Emergency referral should be made in patients with cauda equina syndrome. Non-emergency referral should be made for the patient with progressive neurologic deficits, if a serious condition is suspected or when the patient has each of the following features: leg pain greater than or equal to back pain, a positive straight leg raise test, lack of response to conservative treatment for four to 12 weeks and an image result that correlates with the patient's symptoms.

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