A 35-year-old woman is admitted with acute compartment syndrome of the forearm following a supracondylar fracture of the humerus in her 8-year-old child (she sustained the injury while protecting the child). Clinical examination shows severe pain, swelling, and loss of finger sensation. Compartment pressure measurement is being arranged. Which of the following investigations would be most appropriate to assess the extent of muscle necrosis and guide the need for amputation if fasciotomy is delayed?

Explanation

## Assessment of Muscle Necrosis in Compartment Syndrome ### Markers of Muscle Damage **Key Point:** Serum myoglobin and creatine kinase (CK) levels, along with urinalysis for myoglobinuria, are the most appropriate investigations to assess the extent of muscle necrosis and rhabdomyolysis in compartment syndrome. ### Why These Markers? When compartment pressure compromises microvascular perfusion, muscle ischemia leads to necrosis and release of intracellular contents: - **Myoglobin**: Released from damaged muscle; appears in serum and urine - **CK**: Enzyme released from muscle; markedly elevated in rhabdomyolysis - **Myoglobinuria**: Indicates significant muscle breakdown; associated with acute kidney injury (AKI) risk ### Diagnostic and Prognostic Values | Marker | Significance | |---|---| | Serum myoglobin > 500 ng/mL | Indicates significant muscle necrosis | | Serum CK > 5,000 IU/L | Suggests extensive rhabdomyolysis | | Myoglobinuria (dark urine) | High risk of acute tubular necrosis (ATN) and AKI | | CK > 15,000 IU/L | Associated with poor prognosis; may indicate need for amputation | **High-Yield:** The degree of CK elevation and presence of myoglobinuria correlate with: 1. Extent of muscle necrosis 2. Risk of acute kidney injury 3. Prognosis and need for aggressive fluid resuscitation 4. In delayed cases, likelihood of irreversible damage (amputation) ### Clinical Management Implications **Clinical Pearl:** In this case (delayed fasciotomy scenario), markedly elevated CK (> 15,000–20,000 IU/L) and heavy myoglobinuria suggest extensive irreversible muscle necrosis. This finding would influence the decision between: - Fasciotomy (if some salvageable muscle remains) - Primary amputation (if necrosis is extensive and fasciotomy unlikely to restore function) ### Why These Markers Guide Amputation Decision 1. **Extent of damage**: Very high CK and myoglobinuria indicate widespread muscle necrosis 2. **Salvageability**: Severe rhabdomyolysis suggests limited viable muscle to preserve 3. **Systemic complications**: Heavy myoglobinuria carries high AKI risk, worsening prognosis **Warning:** Do NOT rely solely on clinical appearance to judge muscle viability in compartment syndrome. Histological necrosis may not be clinically obvious. CK and myoglobin levels provide objective evidence of the extent of damage. ### Why Other Options Are Incorrect - **EMG/NCS**: Assess nerve function, not muscle viability or extent of necrosis - **Bone scan**: Assesses bone perfusion and metabolic activity, not muscle damage - **CT angiography**: Evaluates vascular patency but does not quantify muscle necrosis [cite:Campbell's Operative Orthopaedics 13e Ch 56; Harrison 21e Ch 297]