Acute Compartment Syndrome: Definition and Pathological Basis
Acute compartment syndrome (ACS) is a time-critical condition in which increased pressure within a closed osteofascial compartment compromises capillary perfusion and subsequently causes ischaemia of muscles and nerves. It is an orthopaedic emergency because irreversible neuromuscular damage may develop before obvious distal arterial occlusion or loss of the peripheral pulse. The diagnosis is primarily clinical; pressure measurement is an adjunct, particularly when the examination is unreliable.
An anatomical compartment is bounded by relatively non-compliant fascia, bone and intermuscular septa. The leg is the commonest site, comprising anterior, lateral, superficial posterior and deep posterior compartments. Other important sites include the forearm and hand, thigh, buttock, foot and the compartments associated with the arm. The osteofascial envelope permits only limited expansion. Therefore, addition of blood, oedema or extravasated fluid raises intracompartmental pressure.
Pathophysiology
The initiating event may be increased compartment volume, reduced compartment size, or both. Haemorrhage and tissue oedema increase the contents. Tight casts, dressings, traction, circumferential burns and prolonged external compression reduce the available volume. As pressure rises, thin-walled veins are compressed first. Venous outflow obstruction increases venous pressure and promotes further interstitial oedema, producing a vicious cycle: