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Orthopaedic Emergency Module

Learning Objectives

What you'll be able to do by the end of this module.

Clinical Scenario

Before you read on — watch what happens when the opportunity for diagnosing or preventing compartment syndrome is missed.

A good plan and a not-so-good plan — the consequences of delayed recognition.

Overview

By the end of this module, you should be able to recognise and assess acute compartment syndrome safely and effectively. These objectives focus on clinical decision-making, early escalation, and understanding the consequences of delayed treatment.

Core Learning Objectives

1. Understand the pathophysiologyExplain how increased intracompartmental pressure leads to reduced perfusion, tissue ischaemia, and irreversible muscle and nerve injury.
2. Recognise early clinical featuresIdentify the key early signs of compartment syndrome, including pain out of proportion, pain on passive stretch, and evolving neurological symptoms.
3. Identify high-risk patientsRecognise common risk factors such as fractures, soft tissue injury, vascular compromise, and iatrogenic causes.
4. Perform a focused assessmentConduct a structured clinical examination, recognising when findings are unreliable or evolving.
5. Recognise compartment syndrome as a surgical emergencyInitiate immediate pressure-reducing measures safely (remove compression, correct limb position).
Orthopaedic Emergency Module

Definition & Relevant Anatomy

The pathology, plus the four leg compartments most often affected.

Definition

Acute compartment syndrome (ACS) is a condition in which there is increased pressure within a closed osteofascial or myofascial compartment, resulting in impaired local circulation and reduced tissue perfusion.

Because the surrounding fascia is inelastic and non-compliant, it cannot expand to accommodate rising pressure. This leads to a cascade of events culminating in myoneural ischaemia.

Pathophysiological cascade: Diagram showing the pathophysiological cascade of compartment syndrome

ACS is considered a surgical emergency because, without prompt intervention, it leads to irreversible muscle and nerve necrosis and permanent functional damage.

While it can occur in various anatomical regions such as the forearm, thigh, or abdomen, it most commonly affects the limbs, particularly the leg.

Leg Compartments

Interactive anatomy — select a compartment to review anatomy and clinical relevance.

Neurovascular anatomy of the leg cross-section
The four fascial compartments of the leg
Muscle anatomy of the leg cross-section

The four fascial compartments of the leg

Anterior compartment

Location: Front of lower leg

Contents: Tibialis anterior, extensor hallucis longus, extensor digitorum longus, fibularis tertius, deep peroneal nerve, anterior tibial artery

Function: Dorsiflexion of the ankle and extension of the toes

Clinical relevance: Pressure here may cause severe pain, weakness of dorsiflexion, foot drop, and numbness in the first web space.

Lateral compartment

Location: Outer side of the leg

Contents: Fibularis longus, fibularis brevis, superficial peroneal nerve

Function: Eversion of the foot

Clinical relevance: Pressure here may cause lateral leg pain, weakness of eversion, and sensory change over the dorsum of the foot.

Deep posterior compartment

Location: Deep posterior calf

Contents: Tibialis posterior, flexor hallucis longus, flexor digitorum longus, tibial nerve, posterior tibial vessels

Function: Plantarflexion, inversion, and toe flexion

Clinical relevance: This compartment can be harder to assess clinically. Pressure may cause deep calf pain and plantar sensory disturbance.

Superficial posterior compartment

Location: Back of the leg

Contents: Gastrocnemius, soleus, plantaris

Function: Powerful plantarflexion

Clinical relevance: Pressure here may produce a tense calf and pain on passive stretch.

Interactive 3D Model

Explore the muscles of the lower leg in 3D — press each numbered marker to identify the individual muscles of each compartment.

Muscles of the Lower Leg by Digital Ecorche Massing Models on Sketchfab

Orthopaedic Emergency Module

Pathophysiology

How rising pressure drives ischaemia and irreversible tissue damage.

Tissue Injury Timeline

These timings are approximate, but they highlight an important principle: the longer compartment pressure remains elevated, the greater the risk of irreversible nerve and muscle injury.

Stage 1 Stage 2 Stage 3 Stage 4
0–2 hours
Early

Perfusion begins to fall. Pain increases and tissues become hypoxic, but injury may still be reversible if treated promptly.

2–4 hours
Nerve dysfunction

Sensory nerves are affected early. Paraesthesia, altered sensation, and increasing pain on passive stretch may develop.

4–6 hours
Muscle injury

Muscle ischaemia becomes more severe and necrosis may begin. Functional recovery becomes less reliable.

6–8+ hours
Irreversible damage

Permanent muscle necrosis and nerve injury become increasingly likely, with risk of contracture, rhabdomyolysis, renal failure, and limb loss.

Pathophysiology Diagram

How rising intracompartmental pressure triggers a self-perpetuating cycle — reducing perfusion, causing oedema, and driving further pressure rise.

The vicious cycle of acute compartment syndrome pathophysiology

The vicious cycle of acute compartment syndrome pathophysiology.

Clinical takeaway

Acute compartment syndrome is not simply a problem of swelling. ACS is a problem of failing tissue perfusion. Once the ischaemia-oedema cycle begins, delay rapidly increases the risk of irreversible muscle and nerve injury.

Orthopaedic Emergency Module

Risk Factors

Who is at risk, and the injuries most likely to precede compartment syndrome.

Overview

Although trauma is the most common trigger, a wide range of injury patterns, patient factors, and iatrogenic causes can increase susceptibility.

High-yield point: Fractures are associated with approximately 75% of acute compartment syndrome cases, with tibial shaft fractures representing the single most common fracture-related trigger.

Clinical appearance of a patient with a right fractured tibia and suspected compartment syndrome Clinical appearance of a patient with a right fractured tibia and suspected compartment syndrome.

1. Traumatic Injuries and Fractures

Trauma is the commonest cause of ACS. Fractures are present in most cases, but risk is also increased by soft tissue injury, vascular compromise, and high-energy mechanisms.

  • Tibial shaft fractures — most common fracture-related cause
  • Distal radius fractures — also recognised
  • In children: supracondylar humerus fractures and radial/ulnar forearm fractures
  • Segmental fractures
  • Comminuted fractures
  • Diaphyseal fractures (located within the shaft)
Segmental fracture
Segmental fracture
Comminuted fracture
Comminuted fracture

Open fractures do not protect against compartment syndrome. It is a common misconception that a skin laceration relieves pressure sufficiently. ACS can still occur, particularly in severe open injuries such as Gustilo type 2 and 3 lesions.

  • Crush injuries
  • Severe contusions
  • Burns
  • Gunshot wounds and other penetrating trauma
  • Vascular injury, arterial injury, or reperfusion injury after ischaemia

2. Patient Demographics & Health Status

Who is most commonly affected?

Acute compartment syndrome occurs most frequently in males younger than 35, with the highest prevalence seen in the 12 to 19 year age group.

Contributing patient factors:

  • Young males: larger relative muscle bulk and greater exposure to high-energy trauma
  • Higher BMI in children: recognised as a paediatric risk factor
  • Bleeding diathesis: patients with haemophilia or other bleeding disorders are at increased risk
  • Thrombotic or vascular compromise states: may increase the chance of ischaemia and swelling
  • Pre-existing haematological disease: compartment syndrome has been reported in children with leukaemia even without major trauma

3. Iatrogenic & External Factors

Restrictive circumferential applications can prevent a swollen compartment from expanding and may precipitate or worsen ACS.

Poor positioning during surgery or prolonged procedures associated with hypoperfusion increase the risk of compartment pressure rise and tissue ischaemia.

Extravasation of intravenous fluids into a closed compartment can increase local fluid volume sufficiently to trigger acute compartment syndrome.

IV extravasation causing compartment syndrome IV extravasation — fluid tracking into a closed compartment can precipitate acute compartment syndrome.

4. Other Important Risk Factors

Intense exercise can lead to compartment syndrome. Athletes with previous compartment syndrome may also be at risk of recurrence due to internal scarring.

Certain infections can cause swelling and increased intracompartmental pressure, creating conditions that predispose to ACS.

Drug overdose is a recognised cause, often related to prolonged immobility, pressure injury, or secondary muscle damage.

Key Takeaways

  • Fractures are associated with most cases of acute compartment syndrome.
  • Tibial shaft fractures are the commonest fracture-related cause.
  • Young males, especially teenagers and adults under 35, are at greatest risk.
  • Open fractures do not exclude compartment syndrome.
  • Tight casts, prolonged surgery, vascular injury, reperfusion, and IV extravasation are important non-fracture risks.
  • Always think about ACS when swelling occurs in a closed compartment with pain out of proportion to the apparent injury.
Orthopaedic Emergency Module

Clinical Presentation

Recognise it early — the symptoms, the signs, and pain out of proportion.

Work through each of the 6 Ps below. As you open each card, think about:

  • Is this an early or late sign?
  • How useful is it at the bedside in a real patient?

The 6 Ps — Challenge

For each sign, decide whether it is an early, concerning, or late feature of compartment syndrome — then see if you're right.

0 / 6 answered
0 correct
😫 Pain
Is this an early, concerning, or late sign?

Pain out of proportion to the injury is one of the most important early symptoms. It may be severe, escalating, and poorly responsive to analgesia.

Early & high-yield
⚪️ Pallor
Is this an early, concerning, or late sign?

The limb may appear pale, but this is generally a late and less reliable sign. Colour change alone is less helpful than worsening pain and neurological symptoms.

Late — supportive only
🤌 Paraesthesia
Is this an early, concerning, or late sign?

Tingling, numbness, or altered sensation may reflect nerve ischaemia. This often develops after pain has already become prominent and should increase your concern significantly.

Important & concerning
♿ Paralysis
Is this an early, concerning, or late sign?

Weakness or paralysis suggests advanced muscle and nerve compromise. By the time paralysis is present, tissue injury may already be severe or irreversible.

Late & ominous
❤️ Pulselessness
Is this an early, concerning, or late sign?

Loss of pulses is a late sign. A patient can have a limb-threatening compartment syndrome while distal pulses are still present — do not wait for this.

Very late — do not wait for this
❄️ Poikilothermia
Is this an early, concerning, or late sign?

The affected limb may feel cooler than the opposite side, reflecting impaired perfusion. Like pallor, it is not usually the earliest or most discriminating sign.

Classic, but not an early discriminator

Important Early Clinical Signs

These are not all part of the classic 6 Ps, but they are often more useful in recognising compartment syndrome early.

  • Pain out of proportion
  • Pain on passive stretch
  • Tense swollen compartment
  • Evolving paraesthesia

Late features

  • Pallor
  • Paralysis
  • Pulselessness

Key message

Do not wait for late features. Pain out of proportion and pain on passive stretch are the most clinically useful early indicators.

Orthopaedic Emergency Module

Management

Urgent fasciotomy, the escalation pathway, and what to do while waiting for theatre.

Initial Management

While preparing for definitive surgery, these actions can reduce intracompartmental pressure and maintain tissue perfusion.

Bivalving a cast to relieve compartment pressure Find the gap between the sides of the plaster and use plaster scissors to cut ALL soft layers of the cast. Pull the cast apart to open it up and relieve pressure.
1 ✂️ Remove All External Compression

Immediately remove or bivalve all circumferential dressings, casts, and bandages. For a back slab, feel for the soft part without any plaster and use strong plaster scissors to cut through all layers of padding. Pull apart each side of the cast so the entire limb is exposed.

This is the single fastest intervention to reduce compartment pressure. If this doesn't improve things within a few minutes, make a senior member of the orthopaedic team aware.

2 🦵 Limb Positioning

Position the limb at heart level.

  • Do not elevate above the heart — this reduces arterial perfusion pressure and worsens ischaemia
  • Do not lower below the heart — this worsens venous congestion
3 💊 Analgesia and IV Access
  • Establish IV access with at least one large-bore cannula
  • Give oral or IV analgesia, e.g. titrated morphine or an alternative opioid
  • Consider an anti-emetic
4 🧪 Urgent Investigations
  • FBC, U&E, coagulation profile — baseline
  • Creatine kinase (CK) — elevated levels, especially >1000 U/L, suggest significant muscle injury
  • Lactate — marker of tissue ischaemia
  • Urinalysis / urine dipstick — assess for myoglobinuria and dark "cola-coloured" urine
  • Group and save — prepare for theatre
  • ECG — assess for hyperkalaemia secondary to rhabdomyolysis

Action Summary Table

ActionMechanismEvidence / Relevance
Split cast openRemoves external compressive force~50% pressure reduction
Heart-level positioningPreserves arterial perfusion gradientStandard of care
Supplemental oxygenOptimises oxygen delivery to ischaemic tissueSupportive
BP maintenanceImproves delta pressure and perfusionCritical in hypotension

Surgical Management: Fasciotomy

The definitive treatment is an emergent fasciotomy to decompress all involved compartments and debride non-viable tissue.

In the leg, a dual medial-lateral incision is commonly used to access all four compartments. A single lateral incision may be used but provides less exposure.

Optimal outcomes occur when performed within 6 hours. After 36 hours, irreversible damage is likely and risks may outweigh benefits.

⏰ 0–6 hoursBest window for decompression. Highest chance of recovery.
⏳ 6–36 hoursOutcomes worsen progressively.
✖️ After 36 hoursIrreversible damage likely.

Postoperative Care

Open woundLeft open initially to allow swelling.
Re-exploration24–72 hours to reassess viability.
Closure3–7 days, often requiring grafting.
RehabilitationMultidisciplinary recovery including physio.

Special Considerations

  • 🧸 Paediatrics — high suspicion required
  • 🩸 Bleeding disorders — optimise clotting before invasive testing
  • ❓ Diagnostic uncertainty — use serial exams or continuous monitoring
Orthopaedic Emergency Module

Intracompartmental Pressure Monitoring

Stryker monitoring, the delta-P threshold, and when to act on a pressure reading.

Intracompartmental Pressure (ICP) Monitoring

Pressure measurements are used when the physical examination is inconclusive or when the patient cannot reliably communicate.

Indications
  • Head injury or reduced consciousness
  • Sedated or intubated patients
  • Young children
  • Unclear or evolving clinical findings

Manometer method

Measures resistance during saline injection into the compartment.

Manometer method for compartment pressure measurement Manometer method for intracompartmental pressure measurement.

Slit catheter method

Connected to an arterial line transducer, allowing continuous monitoring and improved accuracy.

Technique

Measurements should be taken within 5 cm of the fracture site for accuracy.

Interactive: Pressure Progression Model

Use the slider to model how rising intracompartmental pressure compromises perfusion and nerves — and what clinical signs to expect at each stage.

ICP
20 mmHg
Intracompartmental pressure
Stage
Normal perfusion
Risk: Low
ΔP (DBP 80 mmHg)
60 mmHg
Well above threshold
Compartment pressure (mmHg)
20 mmHg
Risk: Low

What rising pressure does

Perfusion is maintained. Discomfort may be from injury/swelling, but microcirculation is typically preserved.

Clinical clues: Reassess frequently; rising pain out of proportion is the key red flag.
Delta pressure (ΔP) = Diastolic BP − ICP. Threshold for concern: ΔP ≤ 30 mmHg. Model uses DBP = 80 mmHg. Current ΔP: 60 mmHg — above threshold.
Learning model only — not diagnostic thresholds. Always apply your institution's protocols and clinical judgement.

Criteria for Surgical Intervention

Acute compartment syndrome is primarily a clinical diagnosis, but pressure measurements may support decision-making when the clinical picture is unclear.

  • Intracompartmental pressure (ICP) ≥ 30 mmHg
  • Delta pressure ≤ 30 mmHg, where Delta P = diastolic blood pressure − intracompartmental pressure
Key point If the clinical signs are strongly suggestive, fasciotomy should not be delayed to obtain pressure measurements.
Orthopaedic Emergency Module

BOAST Guidance

Key recommendations from the BOA Standard for Trauma on compartment syndrome.

The BOAST guideline on Diagnosis and Management of Compartment Syndrome of the Extremities emphasises that acute compartment syndrome is a limb-threatening emergency in which early diagnosis and treatment are critical to reduce tissue ischaemia and long-term morbidity.

Quick-Reference Summary

AreaBOAST Recommendation
Who should be assessed?Any patient with limb injury, after extremity surgery, or after prolonged surgery with risk of hypoperfusion
How often?Hourly for at-risk patients
What to document?Timing, mechanism, consciousness, neurovascular status, pain, analgesia response, interpretation, rationale
Initial interventionRelease circumferential dressings, expose skin, elevate limb, reassess within 30 minutes
If uncertainRepeat exams, pressure monitoring, concurrent BP measurement, senior review
Pressure concernΔP < 30 mmHg; consider urgent decompression if absolute pressure > 40 mmHg
Definitive treatmentImmediate fasciotomy with decompression of all involved compartments
After fasciotomyDiscuss with plastics within 24h; re-explore within 72h or sooner if needed
Orthopaedic Emergency Module

Test Your Understanding

Apply what you've learned to a series of clinical scenarios.

Answer all 10 questions to receive your score. Each question has one correct answer. Think carefully before selecting.

Question 1 of 10
What is the primary pathophysiological mechanism driving irreversible tissue injury in acute compartment syndrome?
✅ Correct. The inelastic fascia cannot expand, so rising pressure reduces capillary perfusion → hypoxia → ischaemia → necrosis. This is the core cascade.
❌ Not quite. The primary mechanism is elevated intracompartmental pressure impairing capillary perfusion, leading to tissue hypoxia. Major arterial occlusion and direct bone compression are not the primary drivers.
Question 2 of 10
Which fracture type is the single most common fracture-related cause of acute compartment syndrome?
✅ Correct. Tibial shaft fractures are the most common fracture-related cause of ACS, accounting for a large proportion of cases.
❌ Tibial shaft fractures are the single most common fracture-related cause of ACS. Distal radius and supracondylar fractures are also recognised risks but less common triggers overall.
Question 3 of 10
A patient with a tibial fracture is complaining of severe pain that is getting worse despite IV morphine. Which is the MOST clinically useful early sign of acute compartment syndrome at the bedside?
✅ Correct. Pain on passive stretch is one of the most clinically useful early signs. Pallor, pulselessness, and paralysis are late features — do not wait for them.
❌ Absent pulses, pallor, and paralysis are late signs of ACS. Pain on passive stretch (along with pain out of proportion) is an important early indicator that should prompt urgent assessment.
Question 4 of 10
What is the FIRST action you should take when you suspect acute compartment syndrome in a patient with a below-knee backslab?
✅ Correct. Bivalving or removing the cast is the single fastest intervention to reduce compartment pressure — do this first, then reassess and escalate if needed.
❌ The first action is to remove or bivalve all external compression — this is the fastest pressure-reducing intervention. Elevating the limb above heart level is actually harmful in ACS as it reduces arterial perfusion pressure.
Question 5 of 10
At what limb position should you place the limb of a patient with suspected ACS after removing external compression?
✅ Correct. Position at heart level. Elevation reduces arterial perfusion pressure (worsening ischaemia), and dependency increases venous congestion.
❌ The limb should be positioned at heart level — not elevated (reduces arterial perfusion) and not lowered (increases venous congestion). Positioning matters and can significantly affect outcome.
Question 6 of 10
Which of the following delta pressure values (ΔP = Diastolic BP − ICP) should prompt urgent consideration of fasciotomy?
✅ Correct. ΔP ≤ 30 mmHg is the threshold of concern. Remember: if clinical signs are strongly suggestive, do not delay fasciotomy to await pressure measurements.
❌ The threshold for concern is ΔP ≤ 30 mmHg (Diastolic BP − ICP). A higher ΔP indicates adequate perfusion pressure. An absolute ICP ≥ 30–40 mmHg is also a concern.
Question 7 of 10
A patient has a Gustilo type 3 open tibial fracture. A colleague tells you "it can't be compartment syndrome — the wound is open." What is the correct response?
✅ Correct. Open fractures do NOT reliably protect against ACS. This is a common and dangerous misconception. ACS can and does occur with open fractures, especially Gustilo type 2 and 3.
❌ This is a dangerous misconception. Open fractures do NOT reliably prevent compartment syndrome. The skin laceration does not adequately decompress the deeper fascial compartments. Maintain high clinical suspicion.
Question 8 of 10
What is the optimal time window for fasciotomy to achieve the best chance of full functional recovery?
✅ Correct. Within 6 hours offers the best outcomes. After 36 hours, irreversible damage is likely and the risks of surgery may outweigh the benefits. Time is tissue.
❌ The optimal window is within 6 hours. Outcomes worsen progressively between 6–36 hours, and after 36 hours irreversible damage is very likely. Urgency cannot be overstated.
Question 9 of 10
According to BOAST guidance, how frequently should at-risk patients be assessed for compartment syndrome?
✅ Correct. BOAST recommends hourly assessment for at-risk patients. Waiting for the patient to report symptoms is insufficient, particularly in those who are sedated, intubated, or have altered consciousness.
❌ BOAST guidance stipulates hourly assessments for at-risk patients. Relying on patient-reported symptoms is inadequate, especially in unconscious or sedated patients where clinical features may be masked.
Question 10 of 10
Which blood test result would be most concerning for significant muscle injury in the context of suspected compartment syndrome?
✅ Correct. CK >1000 U/L suggests significant muscle breakdown (rhabdomyolysis). You should also check lactate (ischaemia marker), urine for myoglobinuria ("cola urine"), and ECG for hyperkalaemia.
❌ An elevated CK >1000 U/L is the most concerning result here, indicating significant muscle injury/rhabdomyolysis. This should prompt further monitoring for renal failure, hyperkalaemia, and myoglobinuria.
Your score
—
Orthopaedic Emergency Module

Completion & References

🎓
Module Complete
Well done — you have worked through all sections of the
Acute Compartment Syndrome learning module.
10
Sections
10
Quiz Questions
This module is approved for Continuing Professional Development

Key Learning Points

✓ ACS is a time-critical limb-threatening emergency — the optimal window for fasciotomy is within 6 hours of symptom onset.
✓ Pain out of proportion and pain on passive stretch are the most clinically useful early signs — do not wait for pulselessness or paralysis.
✓ Open fractures do not reliably protect against ACS — maintain vigilance in all at-risk patients.
✓ ΔP ≤ 30 mmHg (Diastolic BP − ICP) is the pressure monitoring threshold for urgent consideration of fasciotomy.
✓ BOAST recommends hourly assessment of at-risk patients — do not rely on patient-reported symptoms alone.

References & Further Reading

1 British Orthopaedic Association Standards for Trauma and Orthopaedics (BOAST). Diagnosis and Management of Compartment Syndrome of the Extremities. London: BOA; 2023. Available at: www.boa.ac.uk
2 McQueen MM, Gaston P, Court-Brown CM. Acute compartment syndrome — who is at risk? J Bone Joint Surg Br. 2000;82(2):200–203.
3 Ulmer T. The clinical diagnosis of compartment syndrome of the lower leg: are clinical findings predictive of the disorder? J Orthop Trauma. 2002;16(8):572–577.
4 Shadgan B, Menon M, Sanders D, et al. Current thinking about acute compartment syndrome of the lower extremity. Can J Surg. 2010;53(5):329–334.
5 Whitesides TE, Haney TC, Morimoto K, Harada H. Tissue pressure measurements as a determinant for the need of fasciotomy. Clin Orthop Relat Res. 1975;(113):43–51.
6 McQueen MM, Court-Brown CM. Compartment monitoring in tibial fractures: the pressure threshold for decompression. J Bone Joint Surg Br. 1996;78(1):99–104.
7 Finkelstein JA, Hunter GA, Hu RW. Lower limb compartment syndrome: course after delayed fasciotomy. J Trauma. 1996;40(3):342–344.
8 NICE. Major trauma: assessment and initial management. NICE guideline NG39. London: NICE; 2016 (updated 2022). Available at: www.nice.org.uk/guidance/ng39
9 Donaldson J, Haddad B, Khan WS. The pathophysiology, diagnosis and current management of acute compartment syndrome. Open Orthop J. 2014;8:185–193.

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