Define Acute Compartment Syndrome. Describe its pathophysiology and management.

Definition

Acute compartment syndrome is a surgical emergency in which raised pressure within a closed osteofascial compartment reduces capillary perfusion below the level needed for tissue viability, causing ischaemic injury to muscle and nerve. Common sites are the leg and forearm; common causes are fractures (tibial shaft, supracondylar humerus), crush injury, tight casts, reperfusion, and burns.

Pathophysiology

Bleeding/oedema in a rigid compartment raises interstitial pressure → venous outflow obstruction → further rise in pressure → arteriolar/capillary collapse → tissue ischaemia. A vicious cycle ensues; irreversible muscle necrosis begins within 4–6 hours, leading eventually to Volkmann's ischaemic contracture.

Clinical Features — the 5 PS (with a Crucial Caveat)

The earliest and most reliable sign is pain out of proportion to the injury, aggravated by passive stretching of the muscles in the compartment. Paraesthesia follows. Pallor, pulselessness and paralysis are late and unreliable — the presence of a distal pulse does not exclude compartment syndrome, because the compartment pressure rarely exceeds systolic arterial pressure.

Sites, Causes & a Note on the Chronic Form

Common compartments affected are the anterior and deep posterior of the leg and the volar forearm. Causes include fractures (tibial shaft, supracondylar humerus), crush and reperfusion injury, tight plaster casts or dressings, prolonged limb compression, burns and bleeding disorders. Note the entirely different chronic exertional compartment syndrome: activity-related pain in athletes that resolves with rest, diagnosed by dynamic pressure testing and treated electively (not an emergency).

Management

This is a time-critical emergency. Remove constricting casts and bandages, keep the limb at heart level (not elevated, which lowers perfusion), give oxygen and analgesia, and correct hypotension. The definitive treatment is immediate open fasciotomy of all compartments (a two-incision, four-compartment release in the leg), left open and closed later (delayed primary closure or skin graft). Necrotic muscle is debrided; watch for rhabdomyolysis and acute kidney injury.

Diagnosis is clinical — do not wait for pressure measurement.

• Emergency: raised compartment pressure → ischaemia of muscle and nerve.
• Pain out of proportion + pain on passive stretch = earliest signs.
• Pulses present until late — never exclude it on the basis of a palpable pulse.
• Treatment = urgent open fasciotomy of all compartments; watch for rhabdomyolysis.