A 28-year-old man presents to the emergency department 6 hours after a crush injury to the left leg from a fallen beam at a construction site. Clinical examination reveals severe pain out of proportion to physical findings, pain on passive stretch of the foot, and tense swelling of the anterior compartment. Which of the following is NOT a characteristic feature or consequence of acute compartment syndrome?

Explanation

## Understanding Compartment Syndrome Pathophysiology ### Key Pathophysiologic Features **Key Point:** Compartment syndrome is a surgical emergency characterized by increased pressure within a closed fascial space that compromises tissue perfusion and function. The pathophysiology involves a cascade of events: 1. **Pressure dynamics** — When intracompartmental pressure (ICP) approaches or exceeds the diastolic blood pressure, microvascular perfusion fails, leading to ischemia [cite:Rockwood & Green's Fractures in Adults Ch 1]. 2. **Timeline of tissue damage** — Muscle begins to undergo irreversible necrosis within 4–6 hours of complete ischemia if untreated. 3. **Neurologic progression** — Nerves are more ischemia-resistant than muscle; however, sensory symptoms (paresthesias) typically precede motor loss in the early stages due to preferential involvement of sensory fibers. ### Why Elevated Enzymes Are NOT Diagnostic **High-Yield:** Elevated serum myoglobin and creatine kinase (CK) are **markers of muscle injury**, not diagnostic of compartment syndrome itself. - These enzymes reflect **rhabdomyolysis** and muscle breakdown, which occur in many conditions: crush injury, exertion, statins, sepsis, burns. - Compartment syndrome is a **clinical diagnosis** based on: - Pain out of proportion to findings - Pain on passive stretch (most sensitive sign) - Tense compartment on palpation - Paresthesias and motor changes - Elevated compartment pressure (>30 mmHg or within 30 mmHg of diastolic BP) - Elevated enzymes **support** the diagnosis of rhabdomyolysis but are **not specific** for compartment syndrome and are **not required** for diagnosis. ### Clinical Pearl **Clinical Pearl:** The "5 P's" of compartment syndrome (Pain, Pressure, Paresthesias, Pallor, Pulselessness) are late findings; pulselessness indicates irreversible tissue damage. Early diagnosis relies on clinical suspicion and compartment pressure measurement. ### Correct Answer Rationale Option 4 is the **only statement that is NOT true** because elevated serum myoglobin and CK are neither specific nor required for the diagnosis of compartment syndrome — they are markers of muscle injury that may accompany it but do not define it.