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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
- Acute compartment syndrome is a surgical emergency
- Most common association is tibial shaft and forearm fractures
- Earliest key symptom is pain out of proportion, especially with passive stretch
- Pulses can remain intact until late
- Treatment is removal of constriction and emergent fasciotomy
Overview
Acute compartment syndrome occurs when pressure within a closed fascial compartment compromises perfusion, causing ischemic muscle and nerve injury, rhabdomyolysis, and contracture if not decompressed.
Epidemiology
Associated with tibial shaft fractures, forearm fractures, crush injury, burns, reperfusion, tight casts, anticoagulation, bleeding disorders, and prolonged compression.
Clinical Features
Symptoms
Severe escalating pain out of proportion
Pain with passive stretch
Paresthesias or numbness
Tightness/fullness of limb
Pain not relieved by analgesia
Weakness/paralysis is late
Signs
Tense swollen compartment
Pain on passive stretch
Sensory deficit
Motor weakness in late disease
Pallor/pulselessness are late and may be absent
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
- 1Pain out of proportion after fracture = compartment syndrome
- 2Pain with passive stretch is classic early sign
- 3Normal pulses do not exclude it
- 4Tibial shaft fracture is classic association
- 5First step: split/remove cast and call surgery
- 6Definitive treatment is fasciotomy
- 7Delta pressure <=30 supports fasciotomy
practicetest your knowledge on compartment syndromeApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — musculoskeletal and beyond.
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