A 35-year-old woman is admitted 4 hours after a tibia fracture sustained in a fall from height. She complains of severe calf pain and tightness. On examination, she has marked swelling of the calf, pain with passive dorsiflexion of the foot, and intact pedal pulses. Her serum creatinine is 1.0 mg/dL and urine myoglobin is positive. Which of the following is the most likely complication if fasciotomy is not performed urgently?

Explanation

## Pathophysiology of Untreated Compartment Syndrome **Key Point:** Untreated compartment syndrome leads to muscle necrosis (rhabdomyolysis), which releases myoglobin and potassium into the circulation, causing acute kidney injury (AKI) and life-threatening hyperkalemia. ### Cascade of Complications ```mermaid flowchart TD A[Crush injury + elevated compartment pressure]:::outcome --> B[Muscle ischemia]:::outcome B --> C[Muscle necrosis & rhabdomyolysis]:::outcome C --> D[Release of myoglobin & K+]:::outcome D --> E{Systemic effects}:::decision E -->|Myoglobinuria| F[Acute tubular necrosis]:::urgent E -->|Hyperkalemia| G[Cardiac dysrhythmias]:::urgent F --> H[Acute kidney injury]:::urgent G --> I[Cardiac arrest]:::urgent J[Fasciotomy within 6-8 hrs]:::action --> K[Pressure relief]:::action K --> L[Salvage muscle & prevent AKI]:::outcome ``` ### Why AKI Occurs 1. **Myoglobinuria:** Muscle necrosis releases myoglobin (a large heme protein). Myoglobin is filtered by the glomerulus but precipitates in the renal tubules, especially in acidic urine, causing acute tubular necrosis (ATN). 2. **Hyperkalemia:** Damaged muscle releases intracellular potassium. Serum K+ can exceed 6–7 mEq/L, causing life-threatening cardiac dysrhythmias. 3. **Hypovolemia:** Fluid sequestration in the injured compartment worsens renal perfusion. **High-Yield:** Positive urine myoglobin in this patient is an early warning sign of rhabdomyolysis and impending AKI. ### Clinical Management to Prevent AKI | Intervention | Rationale | | --- | --- | | **Urgent fasciotomy** | Relieves compartment pressure, restores perfusion, halts muscle necrosis | | **Aggressive IV hydration** | Maintains urine output >200 mL/hr, dilutes myoglobin, prevents tubular precipitation | | **Alkalinize urine (NaHCO₃)** | Myoglobin is less soluble in acidic urine; alkaline urine reduces precipitation | | **Monitor K+, ECG** | Detect hyperkalemia early; treat with calcium gluconate, insulin + glucose, or dialysis | **Clinical Pearl:** The combination of crush injury, positive urine myoglobin, and compartment syndrome is a medical emergency requiring fasciotomy + aggressive renal protection to prevent AKI and death. ### Why Other Options Are Wrong | Option | Why Wrong | | --- | --- | | Posterior tibial compartment only | Compartment syndrome can affect multiple compartments (anterior, lateral, deep posterior, superficial posterior). The calf swelling and dorsiflexion pain suggest anterior/lateral compartment involvement. | | Chronic venous insufficiency | Acute compartment syndrome causes acute ischemia, not chronic venous obstruction. Chronic sequelae are contracture and functional loss, not CVI. | | Permanent peroneal nerve palsy | While peroneal nerve ischemia can occur, the most life-threatening systemic complication is AKI from rhabdomyolysis, which can cause death. | **Warning:** Do not underestimate the systemic toxicity of rhabdomyolysis. Myoglobinuria is a sign of ongoing muscle necrosis and requires aggressive intervention.