Acute compartment syndrome
Acute compartment syndrome is rising pressure inside a closed compartment of muscles wrapped in fascia (tough connective tissue), which squeezes blood vessels and nerves.
Remember
Pain out of proportion to the injury and made worse by passive stretch of the muscles, such as when the toes are moved, should make you think of pressure rising inside a closed compartment and starving the muscle and nerve of blood, so urgent treatment should not wait for the pulses to disappear.
Memory aid
a swollen muscle inside a tight, barely stretching sleeve that squeezes its own blood supply
Picture the compartment as a tight sleeve that squeezes the blood supply of the muscle as it swells.
Acute compartment syndrome commonly occurs in the lower leg, where the muscles sit in compartments, each wrapped in fascia, a tough sheet of connective tissue that barely stretches. After an injury such as a fracture or a crush injury, bleeding and swelling fill the compartment. With no room to expand, the swelling raises the pressure in the tissue between the cells.
Capillaries are the tiny vessels that deliver blood to the cells, and the pressure inside them is very low, roughly 8 mm Hg. Once the pressure in the compartment rises above that, capillary perfusion, the flow of blood through the smallest vessels that feed the muscle, slows and may stop. Muscle and nerve then become ischaemic, meaning short of blood, so they swell further and the pressure climbs again, a vicious circle.
The key clue is pain out of proportion to the injury. The pain is deep, poorly localised and not relieved by analgesia (pain relief), and it is made worse by passive stretch of the muscles in the compartment, for example when the toes are moved. The limb is swollen, tense and firm, with shiny skin over the compartment. If the pressure is not released, paraesthesia (pins and needles) and paralysis follow.
Do not wait for the pulses to disappear. Perfusion of muscle can stop long before the pulses go, so a pale, pulseless limb is a late sign.
Treatment is urgent fasciotomy, a surgical cut through the fascia that releases the pressure. Tight casts and bandages can also cause compartment syndrome, so these are removed early, but urgent fasciotomy is still needed unless the pressure falls quickly and the symptoms settle. Muscle and nerve tissue die while treatment is delayed, and untreated disease can end in paralysis, loss of limb and death.
Key facts
- Mechanism
- raised pressure in a closed fascial compartment reduces capillary perfusion and causes ischaemia of muscle and nerve.
- Earliest clue
- pain out of proportion to the injury, worse on passive stretch of the muscles in the compartment.
- Other signs
- a swollen, firm limb with shiny skin over the compartment, and deep, poorly localised pain not relieved by analgesia.
- Late signs
- pallor (a pale limb) and pulselessness (no pulse), so do not wait for them before acting.
- Common causes
- fractures, crush injuries, and tight casts or bandages.
- Treatment
- remove any tight cast or bandage first, then urgent fasciotomy, a surgical cut through the fascia to release the pressure, unless the pressure falls quickly.
- Confirmation
- the diagnosis is clinical (made from the signs and symptoms), and a compartment pressure of more than about 30 mm Hg, or within about 30 mm Hg of the diastolic blood pressure, confirms it.
Exam traps
- A blocked artery also starves a limb of blood, but it typically gives a cold, pale, pulseless limb rather than a tense, swollen compartment, and in compartment syndrome the pulses are often still present early on.
- A clot in a deep vein usually causes pain, swelling and discoloured skin in one leg, but it does not typically cause a tense compartment with severe pain on passive stretch of the toes.
- Rhabdomyolysis (the breakdown of damaged muscle) is a real complication of prolonged muscle ischaemia and can cause hyperkalaemia (a high blood potassium), but it is a later consequence of the pressure problem, not the process that makes a limb tense and painful in the first place.
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