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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Most acute low back pain is nonspecific mechanical pain and improves within weeks
- No routine imaging without red flags or progressive neurologic deficit
- Red flags include cancer, infection, trauma, osteoporosis/steroids, saddle anesthesia, urinary retention
- Cauda equina requires urgent MRI and decompression
- First-line: remain active, heat, NSAIDs or muscle relaxant if needed, PT if persistent
Overview
Low back pain is usually mechanical and self-limited. The key task is identifying serious causes: malignancy, infection, fracture, cauda equina, inflammatory spondyloarthritis, or progressive neurologic deficit.
Epidemiology
Very common. Risk factors include lifting, vibration, poor conditioning, obesity, smoking, psychosocial stress, depression, and prior episodes.
Clinical Features
Symptoms
Mechanical pain worse with movement/lifting
Radicular pain below knee in dermatomal pattern
Neurogenic claudication relieved by sitting/flexion
Saddle anesthesia, urinary retention, or fecal incontinence
Fever, IVDU, immunosuppression, or bacteremia risk
Cancer history, weight loss, or night pain
Signs
Paraspinal tenderness or spasm
Positive straight-leg raise
Focal weakness, sensory loss, or reduced reflex
Reduced anal tone or perineal sensory loss
Midline vertebral tenderness after trauma/osteoporosis
Investigations
First-line
Focused clinical assessmentPattern recognition, red flags, functional impact, and targeted examination
Basic labs when indicatedCBC, CMP, ESR/CRP, CK, urinalysis, or disease-specific testing depending on suspected condition
Initial imaging when indicatedPlain radiographs or MRI/ultrasound based on suspected structural, inflammatory, infectious, or neurologic disease
Second-line
Disease-specific confirmatory testingAutoantibodies, HLA-B27, synovial fluid, nerve conduction studies, DEXA, or cultures as appropriate
MRI/ultrasound/CTUsed for early inflammatory disease, occult fracture, tendon tear, infection, or surgical planning
Screening before immunosuppressionTB, hepatitis, vaccination review, and baseline labs when biologic or high-risk therapy is planned
Specialist
Specialist referralRheumatology, orthopedics, infectious disease, ophthalmology, neurology, or spine surgery depending on red flags and disease severity
1
Initial management
- Address red flags and emergencies first
- Use guideline-directed first-line therapy matched to disease severity
- Educate the patient and set functional goals
- Use analgesia and rehabilitation when appropriate
2
Escalation
- Escalate to specialist-directed therapy if severe, refractory, progressive, or organ-threatening disease
- Use imaging, procedures, immunosuppression, antibiotics, or surgery according to diagnosis
- Monitor response objectively and revise diagnosis if response is atypical
3
Prevention and follow-up
- Manage comorbidities and medication toxicity
- Vaccinate and screen when immunosuppression is used
- Prevent disability, falls, fracture, infection, and functional decline
Complications
- Functional impairment: Pain, weakness, stiffness, deformity, or disability depending on disease
- Diagnostic delay: Missed infection, fracture, inflammatory disease, neurologic compromise, or organ-threatening complication
- Medication toxicity: NSAID, steroid, antibiotic, anticoagulation, opioid, or immunosuppressive adverse effects
- Chronic disease burden: Reduced quality of life, work impairment, deconditioning, and mental health impact
USMLE Step 2 CK Exam Tips
- 1Acute low back pain without red flags = no imaging
- 2Saddle anesthesia + urinary retention = cauda equina; urgent MRI/decompression
- 3Radicular pain with positive straight-leg raise = disc herniation
- 4Back pain + fever + IVDU = epidural abscess/osteomyelitis
- 5Do not prescribe bed rest
- 6MRI only for red flags/progressive deficits or intervention planning
practicetest your knowledge on low back painApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — musculoskeletal and beyond.
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