Acute compartment syndrome of the lower extremity is a clinical condition that, although uncommon, is seen fairly regularly in modern orthopedic practice. The pathophysiology of the disorder has been extensively described and is well known to physicians who care for patients with musculoskeletal injuries. The diagnosis, however, is often difficult to make. In this article, we review the clinical risk factors of acute compartment syndrome of the lower extremity, identify the current concepts of diagnosis and discuss appropriate treatment plans. We also describe the Canadian medicolegal environment in regard to compartment syndrome of the lower extremity.
Acute compartment syndrome (ACS) of the lower extremity is a clinical condition that is seen fairly regularly in modern orthopedic practices. Although the pathophysiology of the disorder is well known to physicians who care for patients with musculoskeletal injuries, the diagnosis is often difficult to make. A delay in diagnosis that leads to a delay in treatment can result in permanent disability. Delayed or missed diagnosis can be devastating to both patients and members of the health care team.
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RISK FACTORS
The most frequently quoted data about the predisposing factors for ACS come from the Royal Infirmary of Edinburgh.1 The average annual incidence is 3.1 per 100 000 people (7.3 per 100 000 men and 0.7 per 100 000 women). The most common cause of ACS is fracture of the tibial diaphysis. About 36% of all cases of ACS are associated with tibial fracture. The second most common cause is blunt soft-tissue injury, which was reported in 23.2% of all ACS cases in the Scottish series.1 The reported incidence of ACS following tibial fracture varies from 2.7% to 11%. The Edinburgh group found an incidence of 7%.1
The pathophysiology of ACS involves an insult to normal tissue homeostasis within a compartment, which leads to increased tissue pressure, reduced capillary blood flow, local tissue hypoxia and local tissue necrosis. It can help to think of the possible causes of compartment syndrome as factors that can increase the contents of a compartment, those that can decrease the fascial volume of the compartment and metabolic insults that can disrupt the microvasculature (Box 1).
Box 1
Possible causes of compartment syndrome
Conditions that increase compartment contents
Fracture
Soft-tissue injury
Crush syndrome
Revascularization
Exercise
Fluid infusion
Arterial puncture
Ruptured ganglia/cyst
Osteotomy
Snake bite
Nephrotic syndrome
Leukemia infiltration
Viral myositis
Acute hematogenous osteomyelitis
Conditions that reduce compartment volume
Burns
Repair of muscle hernia
Circumferential dressings
Casts
Medical comorbidities
Diabetes
Hypothyroidism
Bleeding diathesis/anticoagulation
Age
Acute compartment syndrome occurs most frequently among young people. Physicians often believe that younger individuals are more likely than older individuals to have tight, strong fascia, that there is more muscle filling the compartment of younger people and that younger people are more likely to sustain an injury of significant energy and are thus at greater risk of ACS. These are all theories that may be true but have not been proven.
There seems to be a much higher incidence of ACS following tibial fracture in people under 35 years of age than in those aged greater than 35 years (Fig. 1). In the Edinburgh cohort,1 there was a 30-fold increase in the likelihood of compartment syndrome following tibial fracture in patients under 35 compared with those over 35.
Fig. 1
Fig. 1
Age distribution of patients with tibial fracture with and without acute compartment syndrome involvement (P.J. O’Brien, unpublished data, 2009). ACS = acute compartment syndrome.
Open fractures
It was previously believed that an open fracture, by the nature of the disrupted skin and openings in the fascia, would decompress the compartment and prevent compartment syndrome. There is logic to this idea; however, the evidence does not support it. A series published in 1990 by McQueen and colleagues2 prospectively reviewed 67 tibial fractures treated by intramedullary nailing and monitored the compartment pressure. In this and other series, there was no difference in pressure profiles between open and closed injuries.
Traction
Traction has been reliably shown to increase the intracompartmental pressure (ICP) in injured limbs but this has not resulted in a consistent increase in ACS. Many groups have looked at ICP as a surrogate for ACS. However, ACS remains a clinical diagnosis: a conglomerate of signs and symptoms, one of which may be an increase in ICP.3
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Clinical diagnosis of ACS
Acute compartment syndrome can develop in any of the 4 compartments of leg; however, the anterior compartment is the most commonly affected and probably the most easily recognizable one. From an anatomic standpoint, this makes sense because it is the tightest compartment.
Optimum management of ACS following tibial fracture relies on early diagnosis and prompt surgical fasciotomy. Delayed diagnosis even for a couple of hours may result in serious irreversible complications, loss of limb or even death.
The initial diagnosis of ACS is based on the clinical presentation of the syndrome. This is very important but is not always enough or even possible for an early accurate diagnosis.
It is advocated that the main clinical symptom of a developing ACS is pain. Palpable tenseness, paresthesia, paresis and pulselessness may also be associated with compartment syndrome. The pain associated with a developing ACS is described as severe and out of proportion with the apparent injury, increasing with time and often resistant to analgesic medications. Although this distinctive pain can be an important and leading hallmark feature, it may not be useful in children who are unable to provide feedback and in adults who have an altered level of consciousness. Following an injury to the lower leg, pain from a tibial fracture and associated injuries may mask the pain of an impending compartment syndrome. Paresthesia and paresis do not develop until a significant compromise of flow and compartmental ischemia have already developed. Pulselessness and slow capillary refill are late signs of ACS and usually imply vascular injury rather than compartment syndrome.
Several studies have shown that the absence of clinical findings is more useful in excluding ACS than their presence is in confirming the diagnosis.1,3 Following a tibial fracture, evidence of progressive pain, paresthesia and functional losses are particularly important signals of a developing compartmental syndrome because all other symptoms and signs may be altered by direct trauma. Detection of this progression is obviously dependent on careful and sequential clinical examinations, preferably performed by the same clinician.
To confirm the clinical diagnosis of ACS, especially in difficult clinical situations, different diagnostic interventions have been used over the last few decades. In ACS, increased pressure within a compartment causes impairment of local blood flow, intracompartmental ischemia and hypoxia that eventually result in neuromuscular injury and dysfunction. Therefore, for diagnosis of ACS, any finding of increased ICP, intracompartmental ischemia, neuromuscular hypoxia and dysfunction should be taken into consideration. In fact, the diagnosis of ACS following tibial fracture requires a high index of suspicion and careful clinical evaluation as well as the monitoring of intracompartmental conditions by a reliable diagnostic method during the first 48 hours after fracture or surgical fixation.
The cascade of ACS following a tibial fracture starts with abnormal elevation of ICP in 1 or more compartments of the limb, most commonly the anterior compartment. The normal resting ICP is 0–8 mm Hg. A gradual increase of ICP results in a gradual decrease of local blood perfusion within the compartment. At a certain level of ICP, when it rises above the capillary blood pressure, intracompartmental blood circulation ceases. From this point, intracompartmental ischemia and hypoxia rapidly progress and compromise the viability of the muscles within the compartment. The first clinical symptoms of ischemia appear at an ICP of 20–30 mm Hg. At an ICP of 30–33 mm Hg, the fascial membranes reach their maximum tolerance of stretch, which limits the compliance of the compartment. Experts have advocated fasciotomy for absolute compartment pressures from 30 to 45 mm Hg.3 If the clinical observations are inconclusive, ICP measurement can help to confirm or exclude the diagnosis.
Compartment pressure measurement at a single point in time is the most widely used technique to assist in the diagnosis of ACS if the clinical diagnosis is in question. Currently, an ICP that is within 30 mm Hg of the patient’s diastolic blood pressure (Δp ≤ 30) is the most commonly accepted threshold for surgical intervention. There is some evidence that continuous monitoring of ICP is a safe and effective way of assessing patients who are at risk of developing ACS. Again, a Δp ≤ 30 is the surgical threshold in the continuous monitoring protocol.3
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Recent advances in the diagnosis of acute compartment syndrome
A coenzyme or biomarker specific to skeletal muscle ischemia has not yet been identified. Tibial fracture and ACS both result in early inflammation. Therefore, inflammatory biomarkers such as an elevated white blood cell count, erythrocyte sedimentation rate, creatine kinase, myoglobin, troponin I and fatty acid binding protein levels cannot specify the occurrence of compartment syndrome. Detection of a sensitive and specific biomarker for skeletal muscle ischemia would be a major advance in the diagnosis of ACS. Unfortunately, none are currently available.
The diagnostic value of imaging interventions in early detection and monitoring of ACS is limited. Magn