A 28-year-old man sustains a crush injury to the right leg in a motor vehicle accident. On examination 6 hours later, he has severe pain out of proportion to clinical findings, pain on passive stretch of the foot, and tense compartments. His urine is dark brown. Which clinical feature best distinguishes acute compartment syndrome from rhabdomyolysis in this patient?

Explanation

## Distinguishing Compartment Syndrome from Rhabdomyolysis ### Key Clinical Discriminator **Key Point:** Pain with passive stretch of muscles in the affected compartment is the hallmark and most specific finding of acute compartment syndrome and is NOT a feature of isolated rhabdomyolysis. ### Comparative Features | Feature | Acute Compartment Syndrome | Rhabdomyolysis | |---------|---------------------------|----------------| | **Pain with passive stretch** | **Present (pathognomonic)** | **Absent** | | Myoglobinuria | May occur (if muscle necrosis) | Present | | Elevated CK | May occur (if muscle necrosis) | Markedly elevated | | Tense compartments | Present | Absent | | AKI | Secondary (from myoglobin) | Primary (from myoglobin) | | Compartment pressure elevation | Primary pathology | Not primary | ### Pathophysiology **High-Yield:** Compartment syndrome is a surgical emergency caused by elevated pressure within a closed fascial space, leading to: 1. Microvascular compression → tissue ischemia 2. Nerve and muscle dysfunction 3. Pain out of proportion to clinical signs 4. **Exquisite pain on passive muscle stretch** (most sensitive and specific finding) Rhabdomyolysis, by contrast, is muscle breakdown with release of intracellular contents (myoglobin, potassium, phosphate) into the bloodstream. Muscle pain occurs but is NOT elicited by passive stretch in the same manner. ### Clinical Pearl **Clinical Pearl:** The "5 P's" of compartment syndrome (Pain, Pressure, Pallor, Paresthesia, Pulselessness) are late findings. Pain with passive stretch is an EARLY and SPECIFIC sign that should trigger emergency fasciotomy consideration. Waiting for late signs (pulselessness, paralysis) results in irreversible tissue damage. ### Why This Matters Both conditions can coexist after crush injury. However: - **Compartment syndrome** requires urgent surgical decompression (fasciotomy) within 6–8 hours to prevent permanent disability. - **Rhabdomyolysis** requires aggressive IV hydration, monitoring of urine output, and management of hyperkalemia and AKI. The presence of pain with passive stretch should immediately raise suspicion for compartment syndrome and prompt compartment pressure measurement and fasciotomy, even if rhabdomyolysis is also present. **Mnemonic: POPS** — **P**ain with passive stretch, **O**ut of proportion, **P**ressure elevation, **S**urgical emergency. [cite:Rockwood & Green's Fractures in Adults Ch 1]