In primary care, what history questions and physical examination should I use to evaluate a patient with lower back pain?

Primary Care Workup for Lower Back Pain

Initial Diagnostic Triage

Conduct a focused history and physical examination to categorize the patient into one of three groups: nonspecific low back pain (approximately 85% of cases), radiculopathy/spinal stenosis, or back pain with serious underlying pathology—this classification drives all subsequent management decisions. 1, 2

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History Questions to Ask

Red Flag Assessment (Serious Pathology)

Ask specifically about these red flags that indicate potentially serious conditions requiring immediate imaging:

Cauda Equina Syndrome (Surgical Emergency):

• Urinary retention (approximately 90% sensitivity for cauda equina) 2
• Fecal incontinence 2
• Saddle anesthesia (numbness in the perineal/buttock region) 2, 3
• Loss of anal sphincter tone 3

Malignancy:

• History of cancer (increases risk from 0.7% to 9%) 2
• Age > 50 years 2, 3
• Unexplained weight loss 2, 4
• Pain that fails to improve after 1 month of conservative treatment 2

Spinal Infection:

• Fever 2, 4
• Recent infection 2, 4
• Intravenous drug use 2
• Immunocompromised status (including corticosteroid use) 2, 4

Fracture:

• Significant trauma relative to age (motor vehicle crash or fall from height in young patients; minor fall or heavy lifting in older patients with osteoporosis) 2, 3
• History of osteoporosis or chronic steroid use 4

Severe Neurologic Deficits:

• Rapidly progressive motor weakness at multiple levels 2
• Major sensory loss 2
• New-onset bowel or bladder dysfunction 4, 3

Pain Characteristics

Duration and Onset:

• Acute (<4 weeks), subacute (4-12 weeks), or chronic (>12 weeks) 1
• Sudden onset versus gradual 5

Quality and Location:

• Constant versus intermittent 4
• Night pain (note: this has high false-positive rates and should not be used in isolation) 4, 6
• Pain radiation pattern—leg pain suggests radiculopathy 1

Aggravating/Relieving Factors:

• Pain with walking that improves with sitting or spinal flexion suggests neurogenic claudication from spinal stenosis 2
• Morning stiffness improving with exercise, alternating buttock pain, and night awakening in younger patients suggests ankylosing spondylitis 2

Yellow Flag Assessment (Psychosocial Risk Factors)

These predict risk for chronic disabling back pain and must be assessed:

• Depression or anxiety 1, 7
• Job dissatisfaction 1
• Belief that pain is harmful or disabling 1
• Fear-avoidance behavior 1
• Expectation of passive rather than active treatment 1

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Physical Examination

Neurologic Testing

Motor Testing (to localize nerve root involvement):

• Knee extension (L4) 2
• Great toe dorsiflexion (L5) 2
• Ankle plantarflexion (S1) 2

Reflex Testing:

• Patellar reflex (L4) 2
• Achilles reflex (S1) 2

Sensory Testing:

• Assess for dermatomal sensory loss 2
• Check for saddle anesthesia 2, 3

Straight-Leg Raise Test:

• Pain reproduced between 30-70° of hip flexion indicates high sensitivity for disc herniation 2
• Note: approximately 90% of symptomatic disc herniations occur at L4/L5 or L5/S1 levels 2

Rectal Examination (When Red Flags Present)

• Assess anal sphincter tone if cauda equina syndrome is suspected 3

Inspection and Palpation

• Observe gait and spinal alignment 5
• Palpate for focal tenderness over spinous processes (may indicate fracture or infection) 5

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Critical Clinical Reasoning Points

Red Flag Interpretation

Important caveats about red flags:

• Single red flags have low diagnostic accuracy and high false-positive rates 4, 6
• The combination of multiple red flags significantly increases probability of serious pathology 4
• Absence of red flags does NOT meaningfully decrease likelihood of serious disease—64% of patients with spinal malignancy had no associated red flags 6
• History of cancer is the only single red flag that substantially increases probability of malignancy 1

Common Pitfalls to Avoid

• Failure to recognize cauda equina syndrome leads to permanent disability—always assess for urinary retention 2
• Do not attribute pain solely to imaging findings without clinical correlation, as many morphological variations are incidental 2, 8
• Night pain alone is a false-positive for infection >96% of the time in patients without fever, chills, or recent infection history 6
• Ignoring psychosocial yellow flag factors overlooks the strongest predictors of chronicity and disability 2

When Imaging Is NOT Indicated

• Acute low back pain (<4 weeks) without red flags requires NO imaging 1
• Nonspecific low back pain without red flags should NOT be routinely imaged 1
• Routine imaging provides no clinical benefit and leads to unnecessary procedures and costs 1

When Imaging IS Indicated

Immediate MRI is required for:

• Any red flag symptom suggesting cauda equina, malignancy, infection, or fracture 2
• Severe or progressive neurologic deficits 1, 2
• Symptoms persisting >4-6 weeks with radiculopathy in a surgical candidate 1, 2

MRI is preferred over CT because it provides superior soft-tissue visualization, no ionizing radiation, and better assessment of nerve roots and spinal canal 2

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Initial Management Approach (Nonspecific Low Back Pain)

For patients without red flags:

• Provide reassurance about favorable prognosis (most resolve within 4-6 weeks) 2
• Advise to remain active and avoid bed rest 1, 2, 3
• First-line medications: NSAIDs or acetaminophen 1, 2, 7
• Consider muscle relaxants for short-term use 2, 3
• Spinal manipulation offers proven benefit for acute pain 1, 2

Reevaluate within 1 month if symptoms persist or worsen, and conduct earlier reassessment for severe symptoms, progressive deficits, or emergence of new red flags 2