If there has been damage to the blood supply of a limb or severe damage to the soft tissues (with or without a fracture), then there may be swelling or haemorrhage of the muscles. Some muscles are enclosed in a rigid fascia. If they swell, the pressure inside that compartment may rise and actually cut off the blood supply to the muscle. Over a period of hours the muscle dies, and is then replaced by fibrous tissue that contracts. The end result is a Volkmann’s ischaemic contracture – a useless, withered, clawed limb. Even those muscles that are not in a fixed fascia can behave in the same way if the limb is encased in a tight dressing or a closed plaster. Ischaemia can therefore be iatrogenic (caused by a doctor), and all dressings and casts should be split if there is any possibility that the limb might continue to swell.

Compartment syndrome is diagnosed by having a ‘high index of suspicion’. There are said to be five Ps – pain, paralysis, pallor, paraesthesia and pulseless – but these are also present in the ischaemic limb. Not all of these need to be present for a compartment syndrome to be diagnosed. Only pain and paralysis are reliable features. The pulse can still be present as the artery passing through the compartment has stiff walls that may resist the pressure even when the tissues in the compartment are not being perfused. The cardinal sign of compartment syndrome is the finding of extreme pain when the muscles in the compartment are stretched (passively extending the fingers for the flexor compartment of the forearm, flexion and extension of the toes for the compartments of the lower leg). Compartment syndrome can also develop in the small muscles of the hand and of the foot after a severe crush injury.

Measurement of the pressure within the compartment (using a wick catheter or a transponder) is difficult to perform and appears to be unreliable in deciding whether decompression is indicated, so the diagnosis is a clinical one.

Late or chronic compartment syndrome is rare, so if late pain is a problem, consider deep infection (especially gangrene) and regional pain syndrome (sometimes called Sudek’s atrophy or reflex sympathetic dystrophy).

The commonest presentation is being called to see a patient (especially a child) in whom there has been trauma and who is now complaining of severe and increasing pain just at a time when the pain should be settling down. This could be after an elective operation but is usually after trauma. It can be difficult to distinguish between a patient who is anxious and a developing compartment syndrome. It is best to be on the safe side and act on the assumption that it is a compartment syndrome.

A reliable physical sign is to distract the patient and then flex and extend the digits at the end of the limb in question. If the patient cries out in pain (because the ischaemic muscles are being stretched) then the diagnosis has been made.

The treatment of a compartment syndrome is a surgical emergency.

• The first thing to do is to divide the plaster and dressings in case it is these that are constricting the circulation.
  
• If there is not an immediate improvement, the patient must go to the operating theatre and the compartments in question should be opened up from end to end.

If there is no compartment syndrome found, then no great harm has been done, and the wound can be closed the following day. If there is a compartment syndrome the muscle will pout out and if it has been caught early enough the muscle will reperfuse. If it has been left too late and it is literally a matter of a few hours then the muscle will be dead and will need excising. Either way the wound should be left open initially, then a second look taken a day later when it will be clear what is the likely outcome, and the swelling will have gone down.