ACUTE COMPARTMENT SYNDROME
Surgical Emergency | Clinical Diagnosis | Fasciotomy Within 6 Hours | Irreversible After 8 Hours
THE 6 P'S (LATE SIGNS)
Critical Must-Knows
- Clinical diagnosis - do not wait for pressure measurement if clinical suspicion high
- Pain on passive stretch is the earliest and most sensitive clinical sign
- Absolute pressure over 30mmHg or delta P under 30mmHg are indications for fasciotomy
- Fasciotomy within 6 hours gives best outcomes - after 8 hours damage is irreversible
- All compartments must be released - leg has 4, forearm has 3, thigh has 3
Examiner's Pearls
- "Tibial fractures are the most common cause (36% of all ACS)
- "Absence of pulse does NOT rule out ACS - ACS occurs at pressures below arterial occlusion
- "Deep posterior compartment (leg) is most commonly missed
- "Volkmann's contracture is the end result of untreated forearm ACS
Clinical Imaging
Imaging Gallery
Critical Compartment Syndrome Exam Points
Clinical Diagnosis
Do not delay fasciotomy waiting for pressure measurements if clinical suspicion is high. Pain out of proportion to injury and pain on passive stretch are the key early signs. A single normal pressure does not exclude ACS.
Pressure Thresholds
Absolute pressure over 30mmHg or Delta P (DBP minus compartment pressure) under 30mmHg indicate fasciotomy. Delta P is more reliable in hypotensive patients. Continuous monitoring more reliable than single measurement.
Time Critical
Fasciotomy within 6 hours gives best outcomes. Irreversible muscle necrosis begins at 8 hours. After 12 hours, 90% of patients have permanent deficits. Delay is the most common cause of litigation.
Complete Release
Release ALL compartments. Leg has 4 compartments (anterior, lateral, superficial posterior, deep posterior). The deep posterior compartment is most commonly missed. Use two-incision technique for complete release.
At a Glance
| Category | Key Information |
|---|---|
| Definition | Increased pressure within closed fascia causing microvascular compromise |
| Most Common Cause | Tibial shaft fractures (36% of all ACS) |
| Time Critical | Fasciotomy within 6 hours for best outcomes; irreversible after 8 hours |
| Earliest Sign | Pain on passive stretch of affected muscles |
| Pressure Thresholds | Absolute over 30mmHg OR Delta P under 30mmHg |
| Leg Compartments | 4 compartments (anterior, lateral, superficial posterior, deep posterior) |
| Missed Compartment | Deep posterior (most commonly incomplete in fasciotomy) |
| Key Principle | Clinical diagnosis - do not delay for pressure if high suspicion |
Quick Decision Guide
| Clinical Finding | Pressure Reading | Action | Timing |
|---|---|---|---|
| High clinical suspicion | Not measured / unavailable | Immediate fasciotomy | Do not delay for measurement |
| Moderate suspicion | Absolute over 30mmHg or ΔP under 30 | Fasciotomy | Within 1 hour |
| Low-moderate suspicion | Borderline (25-30mmHg) | Serial monitoring | Repeat every 1-2 hours |
| Unconscious/obtunded patient | Any elevation | Low threshold for fasciotomy | Cannot rely on clinical exam |
| Established ACS over 8 hours | Elevated | Consider risks of late fasciotomy | Discuss with patient/family |
6 P'sThe 6 P's of Compartment Syndrome
Memory Hook:Pain and Pressure come first - Paralysis and Pulselessness are too late!
ADSLLeg Compartments - ADSL
Memory Hook:ADSL like internet - need ALL 4 for the leg to work!
VDPForearm Compartments
Memory Hook:VDP - Very Dangerous Pressure in the forearm
CASTCauses of ACS - CAST
Memory Hook:Remove the CAST if compartment syndrome suspected!
Overview and Epidemiology
Acute compartment syndrome (ACS) is a surgical emergency where increased pressure within a closed fascial compartment compromises perfusion, leading to muscle and nerve ischemia. Without timely fasciotomy, irreversible necrosis occurs.
Definition:
- Elevated pressure within a closed osseofascial compartment
- Compromises local blood flow (capillary perfusion pressure approximately 25mmHg)
- Leads to ischemia of muscles and nerves
- Irreversible damage after 6-8 hours of ischemia
Why Does ACS Occur?
ACS occurs when compartment pressure exceeds capillary perfusion pressure (approximately 25mmHg). Arteries remain patent as arterial pressure is higher, so pulses are present until very late. The ischemia is at the microvascular level, not arterial occlusion.
Common causes:
- Fractures (75% of cases) - tibial shaft most common
- Soft tissue injury without fracture
- Arterial injury with ischemia-reperfusion
- Burns (especially circumferential)
- Crush injuries
- Tight casts/dressings (external compression)
- Extravasation of IV fluids
- Prolonged limb compression (drug overdose position)
High-risk scenarios:
- Tibial shaft fractures (especially high-energy)
- Forearm fractures in children (supracondylar)
- Vascular injury with delayed reperfusion
- Polytrauma patients (especially obtunded)
- Anticoagulated patients (compartment hematoma)
Anatomy - Compartments by Region
Know Your Compartments
You MUST know the compartments in each region - a missed compartment leads to incomplete decompression and persistent ACS. The deep posterior compartment of the leg is most commonly missed.
The leg has 4 compartments:
Leg Compartments
| Compartment | Contents | At-Risk Nerve | Fasciotomy Access |
|---|---|---|---|
| Anterior | Tibialis anterior, EHL, EDL, peroneus tertius | Deep peroneal nerve | Anterolateral incision |
| Lateral | Peroneus longus, peroneus brevis | Superficial peroneal nerve | Anterolateral incision |
| Superficial posterior | Gastrocnemius, soleus, plantaris | Sural nerve | Posteromedial incision |
| Deep posterior | Tibialis posterior, FHL, FDL, popliteus | Tibial nerve, posterior tibial vessels | Posteromedial incision - MOST MISSED |
Deep Posterior - Most Missed
The deep posterior compartment is separated from superficial posterior by the deep transverse intermuscular septum. It contains tibialis posterior, FHL, FDL. Must be specifically released - most common cause of incomplete fasciotomy.
Pathophysiology
The ischemia cycle:
Fracture, crush, vascular injury, or reperfusion leads to bleeding and edema within closed compartment.
Increased compartment volume within non-compliant fascia causes pressure rise. Capillary perfusion pressure is approximately 25-30mmHg.
Capillaries and venules collapse. Arterial inflow continues briefly, worsening edema. Ischemia begins.
Muscle and nerve ischemia. Reversible if decompressed. Pain on passive stretch occurs.
Muscle necrosis begins. Nerve injury (neuropraxia initially, axonotmesis later). Myoglobin release.
Significant muscle death. Volkmann's contracture develops. Renal failure risk from myoglobinuria.
Why Pulses Are Present
Systolic arterial pressure (typically over 90mmHg) exceeds compartment pressures, so arterial pulses remain until very late. ACS is a microvascular problem, not arterial occlusion. Never rule out ACS because pulses are present.
Pressure thresholds:
- Normal compartment pressure: under 10mmHg
- Capillary perfusion pressure: approximately 25-30mmHg
- Symptomatic ischemia: usually over 30mmHg absolute
- Delta P (diastolic BP minus compartment pressure): under 30mmHg indicates ischemia
Classification Systems
Compartment syndrome can be classified by:
Classification by Timing
| Type | Onset | Features | Management |
|---|---|---|---|
| Acute | Minutes to hours | Surgical emergency, follows trauma or ischemia-reperfusion | Emergent fasciotomy |
| Chronic (exertional) | During exercise | Reversible with rest, typically in athletes | Conservative or elective fasciotomy |
| Crush syndrome | Hours post-release | Systemic effects dominant, reperfusion injury | Fasciotomy plus resuscitation |
Matsen Classification
Matsen's classification divides causes into: Increased content (bleeding, edema, IV extravasation) versus Decreased compartment size (tight casts, closure of fascial defects, MAST trousers). Both mechanisms lead to elevated compartment pressure.
Clinical Presentation and Assessment
Clinical Diagnosis
ACS is a clinical diagnosis. Do not delay fasciotomy waiting for pressure measurements if clinical suspicion is high. Serial reassessment is essential in at-risk patients.
History:
- Mechanism of injury
- Time since injury (critical for prognosis)
- Pain character - out of proportion to injury
- Increasing analgesia requirements
- Numbness or weakness developing
The 6 P's - Clinical Signs:
Clinical Signs in Order of Appearance
| Sign | Timing | Mechanism | Reliability |
|---|---|---|---|
| Pain out of proportion | EARLY | Muscle ischemia | Most sensitive early sign |
| Pain on passive stretch | EARLY | Muscle ischemia | Most specific early sign |
| Pressure (tense compartment) | EARLY | Increased volume | Variable - subjective |
| Paresthesia | INTERMEDIATE | Nerve ischemia | Indicates progression |
| Paralysis | LATE | Muscle necrosis | Poor prognosis if present |
| Pallor/Pulselessness | VERY LATE | Complete vascular compromise | Do not wait for these |
Pain on passive stretch - location specific:
- Anterior leg: Pain on passive plantar flexion of toes/ankle
- Deep posterior leg: Pain on passive dorsiflexion of toes
- Volar forearm: Pain on passive extension of fingers
- Dorsal forearm: Pain on passive flexion of fingers
The Obtunded Patient
In unconscious, intubated, or heavily sedated patients, you cannot rely on pain assessment. Have a very low threshold for pressure measurement and fasciotomy. These patients are at highest risk of missed ACS.
Special populations at risk:
- Polytrauma patients (often sedated/ventilated)
- Regional anesthesia (masks pain)
- Pediatric patients (cannot articulate)
- Drug intoxication
- Neurological injury
Investigations and Pressure Measurement
Pressure measurement techniques:
Most commonly used in clinical practice.
Technique:
- Sterilize skin
- Insert needle into compartment at 90 degrees
- Inject small amount of saline
- Read pressure on digital display
- Measure at multiple points (within 5cm of fracture site)
Tips: Highest pressure is usually within 5cm of fracture. Measure all compartments and consider serial measurements in borderline cases.
Threshold values:
Pressure Thresholds for Fasciotomy
| Measurement | Threshold | Notes |
|---|---|---|
| Absolute pressure | Over 30mmHg | Traditional threshold |
| Delta P (DBP minus compartment) | Under 30mmHg | More reliable in hypotension |
| Mean arterial pressure minus compartment | Under 40mmHg | Alternative measure |
Delta P vs Absolute
Delta P (diastolic pressure minus compartment pressure) under 30mmHg is more reliable than absolute pressure, especially in hypotensive trauma patients. A patient with DBP of 50mmHg and compartment pressure of 25mmHg has delta P of 25 - this indicates ACS even though absolute pressure is under 30.
Other investigations:
- Bloods: CK (elevated with muscle damage), renal function, coagulation
- Urine: Myoglobinuria (dark urine)
- No role for imaging in acute diagnosis - do not delay for CT/MRI
Management
While preparing for fasciotomy:
- Remove all circumferential dressings - split casts to skin
- Position limb at heart level - elevation reduces arterial inflow
- Correct hypotension - improves perfusion pressure
- Supplemental oxygen
- IV access - prepare for surgery
- Analgesia - but don't mask ongoing symptoms
- Document neurovascular status - before and after any intervention
Cast Management
Split cast completely to skin including padding. Studies show splitting cast and padding decreases compartment pressure by 30-65%. Bivalving alone is insufficient.
Surgical Technique - Fasciotomy
Gold standard for leg compartment syndrome.
Anterolateral Incision
Position: Supine, leg slightly externally rotated
Incision:
- Longitudinal incision from fibular head to lateral malleolus
- 2cm anterior to fibula
- Length: essentially entire leg (15-20cm minimum)
Release:
- Incise skin and subcutaneous tissue
- Identify fascia of anterior compartment
- Release anterior compartment - full length
- Identify intermuscular septum
- Release lateral compartment posterior to septum
Superficial Peroneal Nerve
The superficial peroneal nerve pierces the fascia approximately 10-12cm proximal to lateral malleolus. Identify and protect it during lateral compartment release.
Posteromedial Incision
Incision:
- Longitudinal incision 2cm posterior to medial tibial border
- Avoid saphenous vein and nerve anteriorly
- Length: match anterolateral incision
Release sequence: (1) Incise skin and subcutaneous tissue, (2) Release superficial posterior compartment fascia, (3) Identify and divide deep transverse intermuscular septum, (4) Release deep posterior compartment - THIS IS CRITICAL, (5) Detach soleus from tibia if needed for access.
Deep Posterior Access
The deep posterior compartment lies beneath the deep transverse intermuscular septum. It must be specifically identified and released. Failure to release this compartment is the most common cause of incomplete fasciotomy.
Complications
Complications of Compartment Syndrome and Fasciotomy
| Complication | Cause | Prevention/Management |
|---|---|---|
| Missed ACS / incomplete release | Delayed diagnosis, missed compartment | High index of suspicion, release all compartments |
| Volkmann's contracture | Untreated forearm ACS | Timely fasciotomy; reconstruction if established |
| Myoglobinuric renal failure | Rhabdomyolysis | Aggressive IV fluids, monitor CK/urine |
| Nerve injury | Direct injury or ischemic | Careful technique; neuropraxia may recover |
| Chronic pain | Muscle necrosis, scarring | Physiotherapy, pain management |
| Wound complications | Large open wound | VAC therapy, staged closure, skin graft |
| Weakness | Muscle necrosis | Physiotherapy; tendon transfers if needed |
| Amputation | Established necrosis, sepsis | Rare - occurs with massive tissue loss |
Volkmann's ischemic contracture:
- End result of untreated volar forearm ACS
- Flexed wrist, extended MCPs, flexed IPs
- Muscle fibrosis and contracture
- Treatment: reconstruction (muscle slide, tendon lengthening, free muscle transfer)
Myoglobinuria Management
Rhabdomyolysis causes myoglobinuria (dark urine) and can lead to acute kidney injury. Manage with: aggressive IV fluids (target urine output over 1ml/kg/hr), alkalinize urine (sodium bicarbonate), monitor renal function and electrolytes (hyperkalaemia risk).
Postoperative Care
- Moist dressings to fasciotomy wounds
- Splint limb in functional position
- Elevate but not above heart (balance perfusion)
- Monitor neurovascular status
- IV fluids for renal protection
- Monitor CK, renal function, urine output
- Return to OR for wound inspection
- Debride any necrotic tissue
- Assess for delayed primary closure
- VAC/NPWT if wound not ready for closure
- Plan for skin grafting if needed
- Serial debridements if ongoing necrosis
- Staged closure or skin grafting
- Physiotherapy begins when wound stable
- Active and passive ROM
- Strengthening as tolerated
- May need tendon surgery for contractures
- Assess for permanent deficits
Monitoring parameters:
- CK levels (peak at 24-72 hours)
- Urine output and color
- Renal function (creatinine)
- Potassium (hyperkalaemia from cell lysis)
- Wound appearance
Outcomes and Prognosis
Prognostic factors:
- Time to fasciotomy (most important)
- Completeness of fasciotomy
- Underlying injury severity
- Patient factors (age, comorbidities)
Outcomes by timing:
| Timing | Expected Outcome |
|---|---|
| Under 6 hours | Good recovery expected |
| 6-8 hours | Variable - some permanent deficits |
| 8-12 hours | Likely permanent deficits |
| Over 12 hours | 90% have permanent deficits |
Medicolegal Considerations
Missed or delayed compartment syndrome is a common cause of medical litigation in orthopaedics. Documentation of serial clinical assessments, pressure measurements, and timing of intervention is essential. Early involvement of senior colleagues is prudent.
Evidence Base
McQueen and Court-Brown - Timing of Fasciotomy
- Fasciotomy within 6 hours: normal muscle function expected
- Fasciotomy 6-12 hours: variable outcomes
- Fasciotomy over 12 hours: 90% permanent neurological deficit
- Delay most common due to diagnostic difficulty
McQueen - Continuous Pressure Monitoring
- Continuous monitoring more reliable than single measurement
- Delta P (DBP minus compartment) under 30mmHg threshold
- No missed ACS with continuous monitoring protocol
- More sensitive than clinical assessment alone
Mubarak - Diagnosis and Treatment
- Established pathophysiology and diagnostic criteria
- Described pressure measurement techniques
- Defined clinical signs and treatment principles
- Foundation for modern ACS management
Via et al - Forearm Compartment Syndrome
- Supracondylar fractures most common cause in children
- Volar compartment most commonly affected
- Carpal tunnel must be released with volar fasciotomy
- Volkmann's contracture rates reduced with early fasciotomy
Australian Data - Litigation
- Compartment syndrome among top causes of orthopaedic litigation
- Missed or delayed diagnosis most common allegation
- Documentation of serial assessments is protective
- Early senior involvement reduces risk
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Classic Leg ACS Presentation
"A 28-year-old man presents 6 hours after a motorcycle accident with a closed tibial shaft fracture. His leg is in a plaster backslab. He is requiring increasing analgesia and describes severe pain in his leg. On examination, his toes are pink with sensation present, but he has pain on passive dorsiflexion of his great toe. What is your assessment and management?"
Scenario 2: Obtunded Polytrauma Patient
"You are called to ICU about a 45-year-old intubated patient 18 hours post-polytrauma with bilateral femur fractures, now fixed with IM nails. The ICU nurse is concerned the left leg looks swollen and tense. The patient cannot be assessed clinically. How do you approach this?"
Scenario 3: Established Forearm ACS
"A 7-year-old boy presents 24 hours after a supracondylar humerus fracture was pinned at another hospital. He has severe pain, a tense forearm, cannot extend his fingers actively, and has decreased sensation in the median nerve distribution. The referring hospital did not perform fasciotomy. How do you manage this?"
Scenario 4: Post-Vascular Repair
"You are asked to see a patient in recovery who just had a popliteal artery repair after 5 hours of warm ischemia from a knee dislocation. The vascular surgeon asks if you want to do a prophylactic fasciotomy. What is your response?"
MCQ Practice Points
Pathophysiology Question
Q: Why are peripheral pulses typically present in acute compartment syndrome? A: ACS is a microvascular problem. Compartment pressures (over 30mmHg) exceed capillary perfusion pressure (approximately 25mmHg) but remain below systolic arterial pressure (typically over 90mmHg). Arterial inflow continues, actually worsening edema. Pulselessness is a very late sign.
Anatomy Question
Q: Which compartment is most commonly missed during leg fasciotomy? A: The deep posterior compartment, which contains tibialis posterior, FHL, and FDL. It is separated from the superficial posterior by the deep transverse intermuscular septum, which must be specifically divided. Accessed via posteromedial incision.
Pressure Threshold Question
Q: A trauma patient has BP 80/50 and compartment pressure of 28mmHg. Does this require fasciotomy? A: Yes. The delta P (DBP minus compartment pressure) = 50 - 28 = 22mmHg, which is under the 30mmHg threshold. Delta P is more reliable than absolute pressure in hypotensive patients. Absolute pressure may look acceptable but perfusion is inadequate.
Timing Question
Q: What is the expected outcome if fasciotomy is performed at 12 hours? A: Poor outcome expected. Studies show fasciotomy under 6 hours gives normal muscle function. At 6-12 hours outcomes are variable. Beyond 12 hours, 90% have permanent neurological deficits. Time is muscle.
Forearm Question
Q: What additional release must always be performed with forearm fasciotomy? A: The carpal tunnel must always be released. The median nerve passes through this confined space and will be compressed if not released. Failure to release carpal tunnel is a cause of ongoing median nerve symptoms.
Clinical Sign Question
Q: What is the earliest and most reliable clinical sign of compartment syndrome? A: Pain on passive stretch of the muscles in the affected compartment. For anterior leg compartment: pain on passive plantar flexion. For deep posterior: pain on passive toe dorsiflexion. For volar forearm: pain on passive finger extension.
Australian Context
Epidemiology in Australia:
- Common in high-energy trauma (MVA, motorcycle, sport)
- Mining and industrial crush injuries
- Rural settings - delayed presentation possible
- Indigenous populations - may present late
Health system considerations:
Transfer Considerations
- Do NOT delay fasciotomy for transfer
- If ACS diagnosed at peripheral hospital - operate there
- Time to fasciotomy is critical
- Can transfer after decompression
Documentation
- Serial clinical assessments with times
- Pressure measurements (if performed)
- Discussions with patient/family
- Decision-making rationale
- Consent discussions
Medicolegal considerations:
- Compartment syndrome is a common cause of orthopaedic litigation in Australia
- Delayed diagnosis and incomplete fasciotomy are main issues
- Documentation of clinical assessments is protective
- Early senior involvement is advisable
MIPS Data
Medical indemnity data shows compartment syndrome among top causes of orthopaedic claims. Key risk factors: young patients (expect full recovery), tibial fractures, delayed diagnosis. Meticulous documentation and early escalation are protective.
Guidelines:
- AOA does not have specific ACS guidelines
- BOAST guidelines (UK) are commonly referenced
- Local hospital protocols should be followed
- Pressure monitoring equipment should be available
ACUTE COMPARTMENT SYNDROME
High-Yield Exam Summary
PRESSURE THRESHOLDS
- •Absolute pressure over 30mmHg = fasciotomy
- •Delta P (DBP minus compartment) under 30mmHg = fasciotomy
- •Delta P more reliable in hypotensive patients
- •Do NOT wait for pressure if clinical diagnosis clear
TIMING
- •Under 6 hours: best outcomes (normal function)
- •6-8 hours: variable outcomes
- •Over 8 hours: irreversible damage beginning
- •Over 12 hours: 90% permanent deficits
CLINICAL SIGNS
- •EARLY: Pain out of proportion, pain on passive stretch
- •EARLY: Tense compartment on palpation
- •INTERMEDIATE: Paresthesia (nerve ischemia)
- •LATE: Paralysis, pallor, pulselessness - TOO LATE
LEG COMPARTMENTS (4)
- •Anterior: TA, EHL, EDL, deep peroneal nerve
- •Lateral: peroneus longus/brevis, superficial peroneal
- •Superficial posterior: gastroc, soleus
- •Deep posterior: TP, FHL, FDL - MOST MISSED
FASCIOTOMY TECHNIQUE (LEG)
- •Two-incision technique for complete release
- •Anterolateral: anterior + lateral compartments
- •Posteromedial: superficial + deep posterior
- •MUST divide deep transverse septum for deep posterior
MEDICOLEGAL
- •Common cause of orthopaedic litigation
- •Document serial assessments with times
- •Document decision-making rationale
- •Early senior involvement is protective