Four-Compartment Fasciotomy
What the Examiner Expects
Emergency decompression of all four compartments of the lower leg to treat or prevent compartment syndrome. The examiner expects you to diagnose compartment syndrome clinically (the 6 P's — pain, pressure, paresthesias, paralysis, pallor, pulselessness, though loss of pulses is a LATE finding) and know that this is a clinical diagnosis that should not be delayed by pressure measurements. The two-incision technique is standard: an anterolateral incision decompresses the anterior and lateral compartments, and a posteromedial incision (2 cm posterior to the tibia) decompresses the superficial and deep posterior compartments. All fascial envelopes must be released fully from knee to ankle.
Key Examiner Focus Points
- Indicated for compartment syndrome: pressure > 30 mmHg or within 30 mmHg of diastolic (delta pressure)
- Lower leg has 4 compartments: anterior, lateral, superficial posterior, deep posterior
- Two-incision technique: anterolateral (releases anterior + lateral) and posteromedial (releases both posterior)
- Clinical signs: pain out of proportion, pain with passive stretch, tense compartments
- Delayed fasciotomy > 6 hours leads to irreversible muscle necrosis and potential amputation
Common Curveballs
Compartment pressures are 25 mmHg and the diastolic BP is 50 mmHg
Delta pressure = diastolic - compartment pressure = 50 - 25 = 25 mmHg. A delta pressure < 30 mmHg is an indication for fasciotomy. Even though the absolute pressure is not > 30, the perfusion pressure is inadequate. Proceed with fasciotomy.
Fasciotomy is performed 12 hours after injury — the muscle is dark and non-contractile
Necrotic muscle. Non-viable muscle must be debrided. If the necrosis is extensive, the limb may not be salvageable — amputation may be necessary. Additionally, watch for reperfusion injury: hyperkalemia, myoglobinuria, acute kidney injury. Aggressively hydrate with crystalloid and monitor potassium.
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