Abstract
We define acute low back pain (ALBP) as less than 6 weeks of pain between the costal angles and gluteal folds. This may be accompanied by radicular pain, which radiates down one or both legs and may indicate irritation of a nerve root. Low back pain (LBP) is the fifth most common reason for medical office visits in the United States and a leading cause of work-related disability. Only about 1% of patients with ALBP in the primary care setting have a serious underlying cause.
Keywords
cauda equina syndrome, crossed straight leg raise, imaging, low back pain, straight leg raise, slump test, spondylolysis
Introduction
Acute low back pain (ALBP) is defined as less than 6 weeks of pain between the costal angles and gluteal folds. This may be accompanied by radicular pain, which radiates down one or both legs and may indicate irritation of a nerve root.
Low back pain (LBP) is the fifth most common reason for medical office visits in the United States and a leading cause of work-related disability. Only about 1% of patients with ALBP in the primary care setting have a serious underlying cause.
1
What is the differential diagnosis of ALBP?
The differential diagnosis of ALBP is broad and may be categorized into mechanical, nonmechanical, and visceral ( Table 31.1 ). Most patients who present with ALBP are diagnosed with nonspecific, mechanical-type pain.
| Mechanical | Nonmechanical | Visceral |
|---|---|---|
|
|
|
2
What are emergent causes of ALBP that should prompt referral to the emergency department (ED)?
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Cauda equina syndrome (CES); occurs when there is compression on the lower spinal nerve roots that results in urinary retention or incontinence, bilateral lower extremity weakness, and/or saddle anesthesia
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Spinal fracture
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Infection (e.g., epidural abscess, vertebral osteomyelitis)
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Cancer (CA)
3
What symptoms/historical details are red flags that should prompt referral to the ED?
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Severe or progressive neurologic deficits (e.g., those seen in CES).
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Trauma. Suspect fracture when there has been a significant mechanism of injury, including motor vehicle collision >35 mph, fall >15 feet, or automobile versus pedestrian.
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Patient has a history of or risk factors for CA or osteoporosis and presents with sudden onset of LBP after a minor fall or heavy lifting. Suspect pathologic or compression fracture.
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Fever, constitutional symptoms, or risk factors for infection. Risk factors for infection include immune compromise or immunosuppression (human immunodeficiency virus [HIV]/acquired immunodeficiency syndrome [AIDS], alcoholism, diabetes, chronic steroid use), intravenous drug use, recent spinal surgery or injection, or recent bacterial infection.
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Known CA history or worsening LBP >4 weeks that is worse at night, not responsive to analgesics, and associated with unintentional weight loss and/or night sweats.
4
What additional historical features, symptoms, or signs that may not be as concerning in adults are unique red flags for children? (Note: The above red flags are ALSO red flags for children.)
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Age <4 years
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Pain that interferes with daily activity
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Limp or altered gait
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Back pain despite no clear mechanism of injury
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Acute or repetitive trauma
5
List key exam findings that are red flags and might suggest a concerning etiology
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Fever.
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Midline tenderness: Sensitive but not specific for spinal infection, cancer, and compression fracture.
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Sensory or motor deficit: Abnormal neurologic exam of the lower extremities (strength, sensation, reflexes, gait) or loss of anal sphincter tone.
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Straight leg raise (SLR): With the patient supine, knee extended, and ankle dorsiflexed, passive hip flexion of the affected leg to 30–60 degrees reproduces radicular pain. Suggests nerve root irritation, most commonly at L5 or S1 and often caused by a herniated disc.
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Crossed SLR: SLR of the unaffected leg reproduces radicular pain in the affected leg and suggests nerve root irritation.
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Slump test: While seated, the patient slumps forward, flexing the cervical, thoracic, and lumbar spine. The patient then extends the knee and dorsiflexes the ankle on the affected side. This reproduces radicular pain in the affected leg. Pain should then decrease with cervical spine extension. May better detect irritation to upper lumber nerve roots.
6
When is imaging indicated in the evaluation of ALBP?
For both adults and children, consider imaging when patients present with red flags on history or exam that raise suspicion for a serious underlying condition (cauda equina syndrome, fracture, infection, or CA).
7
Which imaging modality is appropriate? Which views? ( Fig. 31.1 )
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X-ray lumbar spine to assess for lytic lesions or fracture in patients with ALBP and red flags for CA or fracture. Standing anteroposterior (AP) and lateral views are typically sufficient. Obtain additional bilateral oblique views if there is concern for a pars interarticularis fracture (spondylolysis). Lateral flexion and extension views may be helpful if there is concern for instability (e.g., spondylolisthesis).
