## Clinical Diagnosis: Anterior Tibial Compartment Syndrome with Nerve Ischemia **Key Point:** Foot drop in the setting of compartment syndrome indicates deep peroneal nerve ischemia from increased compartment pressure, not primary nerve injury. This is a surgical emergency. **High-Yield:** The anterior tibial compartment is the most commonly affected compartment in leg trauma. It contains: - Tibialis anterior muscle - Extensor digitorum longus - Extensor hallucis longus - **Deep peroneal nerve** (motor to dorsiflexors and toe extensors) **Clinical Pearl:** Foot drop + pain on passive toe extension (passive stretch of dorsiflexors) = anterior compartment syndrome with nerve ischemia. The presence of dorsalis pedis pulse does NOT exclude compartment syndrome; pulses are preserved until late stages. **Warning:** Confusing compartment syndrome with primary nerve injury delays fasciotomy. Nerve ischemia from elevated compartment pressure is reversible if decompressed within 6–8 hours; permanent denervation occurs after 12–24 hours. ### Pathophysiology of Compartment Syndrome–Induced Nerve Ischemia ```mermaid flowchart TD A[Trauma/Fracture]:::outcome --> B[Edema + hemorrhage in compartment]:::outcome B --> C[Increased compartment pressure]:::outcome C --> D{Pressure exceeds perfusion pressure?}:::decision D -->|Yes| E[Microvascular occlusion]:::urgent E --> F[Nerve ischemia]:::urgent F --> G[Loss of motor function: foot drop]:::urgent G --> H{Fasciotomy within 6-8 hours?}:::decision H -->|Yes| I[Nerve function may recover]:::action H -->|No| J[Permanent denervation]:::urgent ``` **Mnemonic:** **PERONEAL** — **P**ain out of proportion, **E**dema, **R**educed perfusion, **O**pen fasciotomy, **N**erve ischemia, **E**mergency, **A**nterior compartment, **L**ate findings = foot drop. [cite:Rockwood & Green's Fractures in Adults Ch 1; Campbell's Operative Orthopaedics 13e] 
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