Diagnosing Compartment Syndrome
Compartment syndrome is primarily a clinical diagnosis based on pain out of proportion to injury and pain with passive muscle stretch, with compartment pressure measurement reserved only for cases where clinical diagnosis remains uncertain, particularly in obtunded or uncooperative patients. 1
Clinical Diagnostic Approach
Primary Clinical Signs (The "4 P's")
Pain out of proportion to injury is the earliest and most reliable warning sign, appearing before irreversible tissue damage occurs. 1 This is your most critical diagnostic indicator.
Pain on passive stretch of the affected muscle compartment is considered by many to be the most sensitive early sign of acute compartment syndrome. 1 When both severe pain and pain on passive stretch are present together, the positive predictive value increases to 68%. 2
Paresthesia (sensory changes) results from nerve ischemia and represents an intermediate finding. 1
Paresis (motor deficits) is a late sign indicating significant tissue damage has already occurred. 1 When pain, pain on passive stretch, and paralysis are all present, positive predictive value reaches 93%, but by this stage irreversible muscle ischemia has likely begun. 2
Late Signs (Indicating Irreversible Damage)
Pulselessness, pallor, and decreased temperature are too late for their absence to reassure you—when present, they often reflect irreversible compartment syndrome and indicate arterial occlusion. 2, 1 Never wait for these signs to make your diagnosis.
Understanding the Limitations of Clinical Examination
Clinical signs have low sensitivity (approximately 25% for severe pain alone) and low positive predictive value, but high specificity and negative predictive value. 2, 1 This means:
- The absence of clinical signs is more accurate in excluding compartment syndrome than their presence is in confirming it 2
- Palpation of the suspected compartment is unreliable in isolation (sensitivity 54%, specificity 76% in children) 2, 1
- As the number of clinical signs increases, the likelihood of compartment syndrome increases 2
When to Measure Compartment Pressure
Direct measurement of intracompartmental pressure is indicated only when clinical diagnosis remains uncertain, particularly in obtunded, confused, sedated, or uncooperative patients where clinical signs cannot be elicited. 2, 1
Measurement Techniques
Use traditional needle manometry, multiparameter monitors (typically used for arterial blood pressure), or dedicated transducer-tipped intracompartmental pressure monitors. 2, 1 Note that an 18-gauge needle may overestimate compartment pressure by up to 18 mmHg compared to a slit catheter or side-ported needle. 2
Measure pressure in all relevant compartments of the affected limb. 2
Diagnostic Thresholds
Absolute pressure threshold: Compartment pressure ≥30 mmHg warrants fasciotomy when combined with clinical signs. 2, 1
Differential pressure threshold (preferred): Fasciotomy should be performed when the differential pressure (diastolic blood pressure minus compartment pressure) is ≤30 mmHg in a patient with any other signs or symptoms of compartment syndrome. 2, 1 This is the most recognized cut-off for intervention in current practice because tissue perfusion depends on both diastolic blood pressure and intracompartmental pressure. 2
When combined with continuous pressure monitoring, the differential pressure threshold has demonstrated sensitivity up to 94% with estimated specificity of 98% in patients after tibial shaft fracture. 2
High-Risk Populations Requiring Heightened Surveillance
Monitor the following patients repetitively (every 30-60 minutes) during the first 24 hours:
- Tibial shaft fractures (highest risk, approximately 4-5% develop compartment syndrome) 1
- Young men under 35 years with tibial fractures 1
- Fractures combined with: crush injury, hemorrhagic injury, vascular injury, or reperfusion of ischemic lesions 2, 1
- Hypotensive patients 2
- Patients on anticoagulation 1
Monitoring Strategy
Use scoring charts (such as that provided by the UK's Royal College of Nursing) to maintain heightened awareness among healthcare workers caring for at-risk patients. 2 While clinical signs are not completely reliable, their systematic recording helps prevent missed diagnoses.
Continuous compartment pressure monitoring may be considered in high-risk, obtunded patients, though there is little evidence it reduces missed diagnoses compared with serial examination in alert, cooperative patients. 2, 1
Critical Pitfalls to Avoid
Never wait for late signs (pulselessness, pallor, paralysis) to make your diagnosis—these indicate irreversible damage has already occurred. 2, 1
Never rely solely on palpation for diagnosis, as it has poor sensitivity and specificity. 2, 1
Never elevate the limb excessively when compartment syndrome is suspected—this further decreases perfusion pressure and worsens the condition. Position the limb at heart level instead. 1, 3
Never delay diagnosis in obtunded patients—proceed directly to compartment pressure measurement when clinical signs cannot be elicited. 2, 1
Do not miss compartment syndrome in patients without fractures—it can occur with soft tissue injuries alone. 1
Role of Imaging (Limited)
Plain radiographs should not be used to rule out compartment syndrome and are frequently normal unless infection and necrosis are advanced. 1
CT has higher sensitivity than plain radiography, showing fat stranding, fluid and gas collections along fascial planes, fascial thickening, and non-enhancing fascia, but should never delay surgical intervention. 1
Ultrasound has no established role in acute compartment syndrome diagnosis, though it may identify underlying causes (such as hematomas) that can support clinical suspicion. 1, 4
Immediate Actions Upon Diagnosis
When compartment syndrome is suspected or diagnosed: