A 28-year-old male presents to the emergency department 6 hours after a motor vehicle accident with a closed fracture of the right femur. On examination, the limb is swollen and tense. The patient complains of severe pain out of proportion to the clinical findings and has pain on passive stretching of the foot. Sensation in the foot is intact but diminished. Capillary refill is normal. What is the most likely complication developing in this patient?

Explanation

## Clinical Presentation Analysis The patient presents with the classic triad of compartment syndrome: ### Key Clinical Features **High-Yield:** Pain out of proportion to clinical findings is the most sensitive and earliest sign of compartment syndrome. **Key Point:** The "5 P's" of compartment syndrome are: 1. **Pain** (especially on passive stretch) — earliest and most sensitive 2. **Pressure** (tense compartment on palpation) 3. **Paresthesia** (diminished sensation, late finding) 4. **Pallor** (late finding) 5. **Pulselessness** (very late finding) ### Why This Case Fits Compartment Syndrome | Feature | Present in Case | Significance | |---------|-----------------|---------------| | Closed fracture of long bone | Yes | High-risk mechanism | | Severe swelling (tense) | Yes | Increased compartment pressure | | Pain out of proportion | Yes | **Most sensitive early sign** | | Pain on passive stretch | Yes | Pathognomonic finding | | Diminished sensation | Yes | Indicates nerve ischemia | | Intact capillary refill | Yes | Vascular compromise not yet complete | | Intact motor function | Implied | Not yet lost (late finding) | **Clinical Pearl:** Compartment syndrome is a surgical emergency. Diagnosis is clinical; waiting for sensory loss or motor deficit delays treatment and risks permanent disability. Compartment pressure measurement (>30 mmHg or within 30 mmHg of diastolic BP) confirms diagnosis if clinical suspicion exists. ### Pathophysiology Closed femur fractures cause muscle trauma and bleeding within the fascial compartment. Increased pressure compresses microvascular circulation → tissue ischemia → further edema → vicious cycle. Irreversible muscle necrosis occurs within 6–8 hours of onset. **Warning:** Do NOT wait for all "5 P's" to develop. Paresthesia and motor loss are late findings indicating irreversible damage. Fasciotomy must be performed urgently (ideally within 6–8 hours). ## Why Other Options Are Incorrect **Fat embolism syndrome** typically presents 24–72 hours post-injury with petechial rash, confusion, and respiratory distress — not at 6 hours with localized compartment signs. **Rhabdomyolysis** can coexist but presents with myoglobinuria, dark urine, and elevated CK — not the acute localized pain and passive stretch pain of compartment syndrome. **Pulmonary embolism** is a later complication (days to weeks) and does not present with localized limb pain and compartment signs.