Which finding best discriminates compartment syndrome from crush syndrome in a 35-year-old man with a crush injury to the leg from a collapsed building?

Explanation

## Compartment Syndrome vs. Crush Syndrome **Key Point:** Myoglobinuria with acute kidney injury is the hallmark of crush syndrome and distinguishes it from compartment syndrome. Crush syndrome results from prolonged compression of muscle tissue, leading to rhabdomyolysis and systemic effects; compartment syndrome is a local pressure phenomenon. ### Pathophysiology Comparison | Feature | Compartment Syndrome | Crush Syndrome | | --- | --- | --- | | **Primary pathology** | Increased pressure within closed fascial space | Muscle necrosis from prolonged compression | | **Myoglobinuria** | Absent or minimal | Present (dark cola-colored urine) | | **Acute kidney injury** | Rare | Common (from myoglobin precipitation) | | **Hyperkalemia** | Mild | Severe (from muscle cell lysis) | | **Serum CK** | Moderately elevated | Markedly elevated (>5000 IU/L) | | **Systemic effects** | Localized to limb | Systemic (rhabdomyolysis, DIC, shock) | | **Onset** | Hours (after injury/swelling) | Hours to days (after compression relief) | **High-Yield:** Crush syndrome is a **systemic rhabdomyolysis** syndrome characterized by the **"crush triad"**: myoglobinuria, hyperkalemia, and acute kidney injury. Compartment syndrome is a **local surgical emergency** without systemic rhabdomyolysis. **Mnemonic:** **CRUSH** = **C**rash injury → **R**habdomyolysis → **U**rine dark (myoglobin) → **S**evere hyperkalemia → **H**yperkalemic cardiac arrhythmias. **Clinical Pearl:** Crush syndrome typically develops after the crushing force is released ("reperfusion injury"). The freed myoglobin enters the circulation and precipitates in renal tubules, causing acute tubular necrosis and oliguria. ### Why Other Features Are Non-Discriminatory - **Pain out of proportion** is the classic sign of compartment syndrome, not crush syndrome. - **Swelling and tense compartments** are findings in compartment syndrome; crush syndrome may present with less dramatic local signs initially. - **Elevated CK** occurs in both, but crush syndrome shows much higher levels (>5000 IU/L) due to massive muscle necrosis. [cite:Rockwood & Green's Fractures in Adults Ch 1; Harrison Principles of Internal Medicine 21e Ch 297]