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The lower limb is divided into four separate compartments (figure 1), with each compartment containing specific muscles, nerves and blood vessels (table 1). The tissue that encapsulates each compartment (fascia) is inelastic, so any bleeding or swelling that develops within this confined space after injury can cause the pressure inside the compartment to rise.

Once the pressure within a compartment exceeds capillary pressure, the pressure gradient between the capillaries and surrounding tissue that drives blood flow is affected, impeding the delivery of essential nutrients to the tissues supplied by the capillaries (ischaemia). Following an injury, this condition is known as acute extremity compartment syndrome (AECS).

An early sign of AECS is severe pain. This pain may:

• be out of proportion to what would be expected for the injury sustained
• increase when passively stretching the muscles within the affected compartment
• fail to respond to appropriate medication.

Distension of the leg should also raise suspicions of AECS, but may not be obvious if only the deep compartment is affected.

Altered sensation within a specific distribution of skin (paraesthesia) is considered one of the first signs of reduced oxygen supply to a nerve. However, motor nerves can tolerate longer periods of ischaemia so muscle weakness (paresis) may not develop until late stages of AECS, or not at all. If paraesthesia or paresis are present, the distribution of altered sensation and muscle weakness should correspond to the specific nerve affected (table 1).

Diminished or absent pulses (pulseless-ness), a pale appearance (pallor) or coldness of the extremity (poikilothermia) are more suggestive of vascular injury but may be evident in AECS when intra-compartmental pressure exceeds systolic blood pressure (the pressure within the arteries when the heart contracts). By this stage, irreversible tissue damage is likely to have occurred and amputation may be required. If present, pulseless-ness should correspond to the specific artery affected (table 1).

AECS can be suspected from the clinical symptoms described above, but the diagnostic ability of individual symptoms is poor; clinical symptoms are more useful for ruling out AECS when absent than they are at ruling in the condition when present. For details on the diagnostic accuracy of individual symptoms for AECS, please visit the statistics section.

Confirmation of excessive pressures requires intra-compartmental pressure measurement. Normal compartment pressure is different for adults (<8 mmHg) and children (<15mm Hg) and some institutions will consider surgical intervention once this absolute compartment pressure rises above a specific level (e.g. >40mmHg).

Differential pressure takes the individual’s diastolic blood pressure (pressure in the artery when the heart is not contracting) into consideration and has been shown to have greater diagnostic value than absolute compartment pressure.

Differential pressure = diastolic blood pressure – intra-compartmental pressure.
Differential pressure <30 mmHg indicates the need for surgical intervention.

It is important to note that the decision to operate can be made based on the clinical presentation without pressure measurements, to avoid any complications caused by delayed diagnosis and treatment.

Young males with a fracture of the tibial plateau, shaft of the thigh (femur) or shin (tibia) bone (including high tibial osteotomy surgery) are more likely to develop AECS. Young males typically have larger muscles, which reduce the available space within the compartment and therefore decrease the capacity for swelling.

Older patients may have higher blood pressure and reduced muscle size (resulting in reduced intra-compartmental pressure), therefore greater volumes of swelling/bleeding are required before an abnormal differential pressure is reached. AECS in the absence of fracture occurs in significantly older age ranges and may be related to coexisting medical conditions (e.g. cardiac issues requiring anticoagulant therapy).

AECS may be initially managed by removing constrictive dressings, elevating the limb to heart level and continuous monitoring of intra-compartmental pressures. Once the decision to operate has been made, the fascia should be cut (fasciotomy) as soon as possible to relieve pressure within the affected compartment/s, and dead (necrotic) tissue should be removed (debrided).

In late presentations of AECS, amputation of the extremity may be necessary to minimise the risk of developing (or spreading) an infection, which may trigger sepsis and lead to multi-organ failure.