Abstract
Abstract
Acute limb compartment syndrome is a surgical emergency characterized by raised pressure within an unyielding tissue compartment. Although there is commonly a history of trauma there are a number of causes of compartment syndrome, which includes iatrogenic insults. The key clinical feature of a compartment syndrome in the conscious patient is severe pain out of proportion to the injury and aggravated by passive muscle stretch. Intracompartmental pressure measurements remain the only objective method of diagnosing an acute compartment syndrome. Although it is subject to false positives, interpreting the pressures in relation to the systemic blood pressure helps confirm the diagnosis when the clinical findings are equivocal and provides essential information in unconscious or uncooperative patients. Successful treatment of an acute compartment syndrome involves prompt, early diagnosis followed by an adequate surgical decompression of all four compartments of the leg by fasciotomies. Delay in diagnosis is almost invariably associated with a poor outcome and loss of limb function. As acute compartment syndromes typically occur in young patients with an average work–life expectancy of up to 30 years, a poor outcome results in severe loss of productivity.
Definition
Compartment syndrome is a condition in which the pressure within a limited space becomes raised, compromising the blood supply and function of the tissues lying within that space.1 There are well-defined compartments in the leg, foot, thigh, buttock, forearm and hand as well as the abdomen. Each compartment contains muscle, nerves and tendons in different proportions. As the intracompartmental pressure (ICP) rises, the local blood flow cannot meet the metabolic needs of the tissues which become ischaemic (starved of blood). A vicious cycle develops as the venous outflow becomes blocked, leading to further pressure increases and tissue damage. The damaged tissue becomes oedematous (swollen) producing more rises in pressure. The tissues most susceptible to injury are nerve and muscle and irreversible muscle damage (necrosis) may occur within three hours of onset. 2 Serious compromise of the arterial supply of the limb and loss of pulses only occurs in the later stages of the condition.
Outcome
The outcome following an untreated acute compartment syndrome is usually catastrophic. 3 Ischaemic muscle becomes necrotic and is replaced by fibrous tissue (scar) causing weakness and disfiguring joint contractures. Nerve damage leads to lack of sensation, muscle paralysis and neurogenic pain that may be severe. Widespread tissue necrosis may be followed by infection, which often becomes chronic. In addition, delayed healing of associated fractures is common. 4
Serious systemic complications may develop if widespread muscle damage is left unchecked. Myoglobin may be released from damaged muscle causing kidney damage and acute renal failure. 3 Extensive tissue necrosis may require amputation and widespread tissue damage is occasionally associated with loss of life. The incidence of these complications is directly related to the timing of treatment.
Early recognition of a compartment syndrome and treatment by fasciotomy (surgical release of the constricting tissues) is essential to prevent irreversible issue damage. There is a direct relationship between the level and the period of compartment pressure rise and the speed and extent of resultant tissue damage. A study of patients who had sustained soft tissue limb trauma associated with increased ICP measurements of 40 mmHg or more for at least six hours all demonstrated poor final outcomes. 5
A further study suggested that delay in surgical decompression for 12 hours resulted in permanent disability in 80% of cases when compared with no apparent clinical defects in patients treated within 12 hours. 6
Causes
The majority of acute compartment syndromes occur as a result of trauma and most are commonly seen after injuries to the leg and forearm. Approximately 40% develop after fractures of the tibial shaft. However, the compartment syndrome may be caused by a soft tissue injury alone, in the absence of a fracture and this group includes burns and bleeding within the compartment. 1 Inadvertent limb compression (e.g. by a constrictive dressing or a plaster cast) may precipitate a compartment syndrome in an acutely swollen leg. Limb traction, fracture manipulation and surgical stabilization may also contribute to compartment pressure rises and lead to a compartment syndrome. 7,8
Prolonged abnormal limb positioning, typically seen after a drug overdose is a potent cause of compartment syndrome. There are also a number of important iatrogenic causes such as lengthy urological or gynaecological surgery that involve placing a patient in the lithotomy position. The combination of abnormal limb elevation and direct limb pressure from stirrups may cause a compartment syndrome which is frequently missed. 1 Re-perfusion after the prolonged use of a tourniquet during surgery or following a vascular injury is another potential iatrogenic cause. 1
Hidden dangers of regional anaesthesia
Clinicians need to be aware that regional anaesthesia (spinals, epidurals and local nerve blocks) may mask vascular and neurological complications in the early postoperative period. The limbs are insensate to pain and touch and difficult to assess, particularly by a junior doctor who may miss vital clinical signs in a patient who seems comfortable. Furthermore, the lithotomy compartment syndromes seem to have a slow and insidious onset and the diagnosis of a compartment syndrome may be very difficult, especially when the patient's perception of pain is altered by regional anaesthesia. 9
Compartment syndrome and vascular problems are also well-recognized complications of total knee replacement. Unfortunately, an inability to dorsiflex the foot may be wrongly attributed to an epidural. 10 After one or two days, it finally becomes apparent that the foot drop is due to muscle damage secondary to vascular insufficiency and not the effects of the regional anaesthetic. Unfortunately, irreversible muscle damage will have occurred by the time the diagnosis is finally made. The outcome following a missed compartment syndrome or vascular injury is always unsatisfactory.
Clearly, regional anaesthesia should not be used in the trauma situation where there in an increased risk of postoperative compartment syndrome. Patient receiving regional anaesthesia for knee replacement must be warned about the potential complications when consent is obtained.
Clinical features
A compartment syndrome should be actively excluded in any case involving high-energy limb trauma. However, it is important to remember that the syndrome may develop after any injury, regardless of the mechanism. Furthermore, the course of a compartment syndrome can be unpredictable and close observation and repeated examinations are essential until acute swelling begins to subside. A single early examination of a patient may exclude a compartment syndrome at that point in time but it may develop hours or days after the initial injury. 1
Unfortunately, there are no specific symptoms for diagnosing compartment syndrome. However, the symptom which is the most reliable in making an early diagnosis in the conscious patient is pain (Box 1). The pain classically persists despite appropriate analgesia, which includes opiates. In addition, passive stretching of the muscles within the affected compartment by the examiner (e.g. the big toe in compartment syndrome of the leg) causes an acute exacerbation of pain. Other important findings include a sensation of tightness in the leg and sensory changes in the skin beyond the involved compartment. Diminished pulses are a late feature by which stage extensive muscle necrosis has occurred.
Clinical features of a compartment syndrome
History of limb trauma
Pain
– seemingly out of proportion to the injury – persisting despite opiate analgesia – increased by passive stretching of compartment muscles
Limb swelling
Sensory changes
Muscle weakness
Loss of pulses*
*Late clinical finding
Investigations
The measurement of ICP was introduced in the 1970s in order to facilitate diagnosis. 11 Early techniques focused on an absolute ICP at which a compartment syndrome could be diagnosed. However, the role of the systemic blood pressure in maintaining an adequate blood flow within the compartment has recently been shown to be important. Variations in the systemic blood flow will have a profound effect on the perfusion pressure of the compartment.
There is now a substantial body of evidence which supports the concept that the level of ICP at which muscle tissue necrosis occurs is directly related to the perfusion pressure (i.e. the difference between the ICP and the systemic blood pressure). 12 Specifically, the ICP is measured and compared with the patient's diastolic blood pressure. A difference (the so-called ‘delta pressure’) of 30 mmHg or less is commonly accepted as indicating compartment syndrome. 13 Modern devices for monitoring ICP contain a transducer-tipped probe and are easy to use and reasonably accurate. 14
Intracompartmental measurements should be made at a point within a few centimetres of the zone of maximum pressure to prevent an underestimation of the pressure. It is recommended that pressure is monitored within 5 cm from the maximum point of injury although care must be taken to avoid communication with the fracture, thereby turning a closed injury into an open injury. 1
Treatment based on a delta pressure of 30 mmHg or less alone may lead to unnecessary surgery. A clinician must also consider the dynamic relationship between the blood pressure and the compartment pressure. A typical patient may have a swollen, traumatized limb and is obviously at risk for a compartment syndrome. However, he appears to be relatively comfortable and does not complain of severe pain and has little or no pain on passive stretching. If the ICPs are borderline, then the clinician can be reassured that the patient can probably be observed and have repeat measurements. The trend of ICP or the delta pressure over time is the key to the accurate diagnosis of a compartment syndrome. 15
ICP measurements are not necessary if the diagnosis of a compartment syndrome is clinically obvious. In this scenario, ICP measurement may only serve to delay the fasciotomies. ICP measurements are probably best reserved for uncooperative patients or equivocal cases.
Confusion may arise when considering which of the four compartments in the limbs to monitor, particularly in an unconscious or uncooperative patient. However, a number of studies have suggested that the anterior compartment of the leg is most commonly affected and routine monitoring should involve the anterior compartment and include other compartments when clinically indicated. 16
The timing of the fasciotomies is crucial. A number of studies have concluded that a poor outcome is inevitable if fasciotomies are delayed for over 12 hours, whereas a full recovery is associated with decompression within six hours of making the diagnosis. 6
Despite the substantial body of scientific and clinical evidence supporting the use of ICP measurements in suspected compartment syndromes, more than half of the departments contacted in a survey stated that they did not have pressure monitoring available in their hospital. 17 Of some concern was the additional finding that 42% of clinicians who undertook ICP measurements did not know at what level they should perform a fasciotomy.
Treatment
The key to successful treatment of an acute compartment syndrome is prompt, early diagnosis (Box 2). The first step is the immediate removal of any circumferential dressings down to skin. Complete Plaster of Paris casts should have a wide strip removed from the front of the splint to alleviate any pressure and the circumferential padding must be cut. Severely injured patients must have their blood pressure maintained to improve the perfusion pressure within a compartment. If the removal of external compression fails to relieve the pressure, the compartment needs immediate surgical decompression.
Common errors
Delayed clinical diagnosis
Failure to measure compartment pressures
Late fasciotomy
Incomplete fasciotomy
Incomplete debridement of non-viable muscle
Poor control of infection
Failure to surgically stabilize associated fracture
Late decompression compartment syndrome – after 12 hours the muscles are necrotic and decompression increases susceptibility to infection
The aim of the surgery is an adequate decompression of all four compartments of the leg. Failure to decompress all the compartments may precipitate increased pressure in an adjacent compartment during the postoperative period. Although surgical decompression by fasciotomy has been widely accepted, a number of surgical approaches have been described. 1 An early technique involved a single laterally based incision that included removal of a portion of the fibula, thereby allowing access to all four compartments. This approach only provided a limited view through which an adequate fascial release was difficult. 2
More recently, the two-incision technique has been widely accepted and is currently the treatment of choice for the compartment syndrome in the leg. 18 However, performing fasciotomies on a tense, swollen limb can be a daunting and difficult undertaking. 2 Palpation of the subcutaneous borders of the tibia can be difficult in the swollen leg and we recommend marking anatomical landmarks before making the incisions. Placing the incisions too close to the subcutaneous borders of the tibia can result in inadvertent exposure of the bone and any fractures, necessitating flap coverage and significantly increasing morbidity.
An incision of adequate length must be made because the intact skin can cause continuing constriction. Studies have shown that lengthening an incision from 8 to 16 cm significantly reduced the ICPs. 19 Furthermore, longer incisions ease the identification of anatomical structures, such as superficial nerves and also allow an appropriate inspection of the underlying muscles.
After decompression, the muscle is inspected and all necrotic tissues must be excised. Occasionally, an entire muscular compartment may need excision. Failure to adequately debride necrotic tissue places the patient at risk for infection and increases the likelihood of subsequent amputation.
The soft tissues are invariably swollen and the fasciotomy wounds are not usually amenable to immediate closure. Excess tension on the skin due to inappropriate early wound closure must be avoided. 2 Wound complications were recorded in 51% of patients who had primary or delayed primary closure when compared with 5% who had split skin grafts. 20 If all devitalized tissue has been confidently excised, we favour immediate coverage with meshed, split skin grafts secured with a foam vacuum suction dressing. Cosmesis may be improved by subsequent scar revision. An alternative safe technique is to leave the wounds open and apply a vacuum foam or moist sterile dressing. A repeat surgical inspection is undertaken at 24–48 hours by which time the limb swelling has usually subsided. One or both of the wounds may be amenable to formal closure at this stage.
Fasciotomies should not be considered benign procedures and there is some evidence to suggest that fasciotomy may lead to chronic venous insufficiency due to impairment of the calf muscle pump. 2
The role of fasciotomy in late cases of compartment syndrome is questionable and it has been suggested that release of the compartments in this situation should not be performed. In one study, fasciotomies performed after 35 hours from injury were invariably associated with severe infection and even death. 21
Prevention of compartment syndrome
Simple techniques such as moderate elevation of traumatized limbs help to reduce ICP. However, very high-limb elevation may inadvertently reduce the arterial and venous pressure gradient, causing an increase in compartmental pressures. 22 This mechanism may explain the development of a compartment syndrome after prolonged abnormal limb positioning during surgical procedures. Care must be taken when positioning patients for surgery. Direct pressure on the limbs must be prevented and the limbs should be appropriately padded with soft bandages.
The use of tourniquets should be carefully monitored and their use limited in the trauma patient to prevent compartment syndrome caused by the rapid reperfusion of a limb, which has been ischaemic for a prolonged period. 1
Limb compartmental pressures may also be elevated by common therapeutic manoeuvres such as immobilizing a fracture in a plaster cast. Swollen limbs which require cast immobilization are usually either placed into temporary ‘backslabs’ or split casts to accommodate further limb swelling without causing a rise in ICP. Conscious patients are advised to keep the affected limb elevated and avoid dependent positions, which may contribute to swelling.
Fracture patients in prolonged traction (longitudinal pull to control limb alignment) require careful monitoring as each kilogram of traction applied to a fractured limb causes a 5% increase in ICP. 8 The simple technique of manually reducing a fracture also causes an ICP raise. Patients with tibial shaft fractures managed by an intramedullary nail are at particularly high risk for compartment syndrome. 15 ICP rises may be caused by intraoperative traction and fracture manipulation plus the passage of the nail into the bone also causes a rise in ICP. All patients undergoing nailing operations must be carefully observed within the first 24 hours for signs of a compartment syndrome (Box 3).
Case report
A 26-year-old man twisted his left ankle when playing football. Later that night, he was seen by his general practitioner (GP) who referred him to the A&E Department because he was complaining of great pain.
The GP had found tenderness over the neck of the fibula with decreased dorsiflexion of the left foot. The casualty officer suspected a stress fracture of the fibula and admitted the patient for observation having immobilized the limb on a plaster foot and back splint with the ankle at a right angle.
The patient continued to suffer severe pain and required frequent administration of pethidine injections over the next 2.5 days but without relief. The patient was seen by various doctors including a consultant orthopaedic surgeon and a senior registrar. The plaster splint was not removed until the afternoon of the third day after admission by which time the patient was completely unable to dorsiflex the foot. At this stage, a decision was made to transfer the patient to theatre for urgent decompression of the lateral compartment of his shin. At operation, necrotic muscle was found in the lateral compartment and a number of operations were required. The patient was left with a common popliteal nerve palsy with weakness of dorsiflexion and inversion of the left foot.
The nursing records showed the patient had made repeated complaints of severe pain not relieved by pethidine injections. It was felt that had the plaster splint been removed earlier to investigate the cause of the patient's intractable pain, the physical signs of the compartment syndrome would have been recognized earlier and that earlier operation would have been achieved a better end-result.
Settlement was achieved for a large sum, which reflected the repeated surgery the patient had had to undergo, the marked scarring that was adherent to bone and prone to injury and infection along with the permanent impaired function in the left leg. It was recognized in deciding upon the amount of compensation that some impairment of function and some scarring would have resulted in any event.
Poor outcome
In a US study of the malpractice costs associated with a missed diagnosis of compartment syndrome in eight patients, the average settlement was US$280,000. 15 The sequelae included amputation and complete loss of function of the lower extremity. The costs were high because the patients were young (the average age was 16 years) with an average work-life expectancy of 30 years. Two factors were found to contribute to the missed diagnosis. ICP had not been measured in any patient and most patients had been evaluated by more than one physician as the syndrome evolved over a period of time. This demonstrates the need for improved communication between health-care workers.
Summary
Compartment syndrome can be a devastating complication of a leg injury. Careful and repeat clinical examinations are required in at-risk patients to ensure that the diagnosis is not missed. In conscious patients, pain on passive stretching of the muscles within the compartment may be the earliest clinical indicator, often in the presence of sensory changes in the distribution of the nerves passing through the compartment.
In unconscious or anaesthetized patients ICP measurement is the only objective method for diagnosing a compartment syndrome and constitutes an indirect measure of muscle and nerve ischaemia. Most authorities agree that the most reliable measure is the difference between the diastolic blood pressure and the ICP (differential or delta pressure). A differential pressure of 30 mmHg or less is accepted as being indicative of a compartment syndrome.
Once a compartment syndrome has been diagnosed, urgent fasciotomies are required. All four compartments in the leg must be released by two extensive fasciotomy incisions. A delay of six hours or greater in the diagnosis or in the undertaking of a fasciotomy usually leads to permanent morbidity.