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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- Raised pressure within closed fascial compartment → ischaemia → necrosis if untreated. Most common: anterior compartment of lower leg
- Causes: tibial fracture (most common), crush injury, burns (circumferential), tight cast/dressing, reperfusion injury, bleeding into compartment
- Earliest signs: pain OUT OF PROPORTION to injury and pain on PASSIVE STRETCH of muscles in the compartment
- The 6 Ps (late signs): Pain, Pressure, Paraesthesiae, Paralysis, Pallor, Pulselessness — by the time pulses are absent, damage is irreversible
- Clinical diagnosis — do NOT delay for pressure measurement. If suspected → emergency FASCIOTOMY within 6 hours
- Compartment pressure >30 mmHg or within 30 mmHg of diastolic (delta pressure <30) = fasciotomy indicated
Overview
Compartment syndrome is a surgical emergency in which raised pressure within a closed osteofascial compartment compromises the perfusion of muscles and nerves within that compartment. If not treated promptly with fasciotomy, irreversible ischaemic necrosis occurs within 6–8 hours, leading to muscle death (Volkmann's contracture in the forearm), rhabdomyolysis, renal failure, and potentially limb loss or death. The most common site is the anterior compartment of the lower leg, typically following tibial shaft fracture. It can also occur in the forearm (supracondylar fracture in children), thigh, foot, hand, and abdomen. The pathophysiology involves increased compartment contents (haemorrhage, oedema) or decreased compartment volume (tight cast, eschar), leading to tissue pressure exceeding capillary perfusion pressure.
Epidemiology
Compartment syndrome occurs in approximately 1–10% of tibial shaft fractures. It is most common in young males (larger muscle bulk = less compliance in compartments). Other at-risk groups: patients with crush injuries, circumferential burns, prolonged immobilisation (e.g. found on floor), post-revascularisation (reperfusion oedema), and patients on anticoagulants (increased bleeding risk). Bilateral compartment syndrome should raise suspicion of crush injury or prolonged recumbency. Abdominal compartment syndrome occurs in critically ill patients (massive fluid resuscitation, intra-abdominal pathology).
Clinical Features
Symptoms
Pain: SEVERE, out of proportion to the injury. Increasing despite adequate analgesia (including opioids)
Pain on passive stretch of muscles in the affected compartment (e.g. passive dorsiflexion of toes/ankle for anterior compartment) — earliest reliable sign
Paraesthesiae (numbness/tingling in distribution of nerves traversing the compartment)
Tightness and swelling over the affected limb segment
Signs
Tense, swollen compartment on palpation ("woody hard")
Pain on passive stretch of muscles within the compartment (most sensitive early sign)
Sensory deficit in the distribution of nerves within the compartment
Weakness or paralysis of muscles in the compartment (LATE sign — indicates necrosis has begun)
Pallor and pulselessness are VERY LATE signs — pulses may be present even with established compartment syndrome
Increasing analgesic requirement in a patient with a limb fracture or cast
Investigations
First-line
Clinical diagnosisCompartment syndrome is primarily a CLINICAL diagnosis. Pain out of proportion + pain on passive stretch + tense compartment = act immediately
Compartment pressure measurementUsing Stryker device or arterial line transducer. Absolute pressure >30 mmHg or delta pressure <30 mmHg (diastolic BP minus compartment pressure) = diagnostic. Use if clinical picture is equivocal or patient is unconscious/sedated
Second-line
Serum CKMarkedly elevated (often >10,000 IU/L) from muscle necrosis → rhabdomyolysis
U&EsHyperkalaemia from rhabdomyolysis. AKI from myoglobinuria
Urine myoglobinDark/cola-coloured urine. Myoglobinuria causes AKI via tubular obstruction
Specialist
Intra-abdominal pressure (via bladder catheter)For abdominal compartment syndrome — IAP >20 mmHg with organ dysfunction
1
Immediate
- Remove ALL constricting dressings, casts, splints immediately — split cast to skin and spread
- Keep limb at heart level (do NOT elevate above heart — reduces arterial perfusion pressure)
- High-flow analgesia — but escalating pain despite analgesia is a key warning sign
- Urgent senior orthopaedic/surgical review
2
Fasciotomy (EMERGENCY)
- DEFINITIVE treatment — must be performed within 6 hours of symptom onset to prevent irreversible damage
- Open all compartments in the affected limb segment through adequate skin incisions
- Lower leg: four compartments (anterior, lateral, superficial posterior, deep posterior) — typically via two-incision technique
- Forearm: volar (Henry approach) ± dorsal incision
- Leave wounds OPEN — delayed primary closure or skin grafting at 48–72 h once swelling settles
- Fasciotomy after 6+ hours: risk of reperfusion injury, but may still be indicated
3
Post-fasciotomy management
- IV fluids: aggressive hydration to prevent AKI from myoglobinuria (target urine output >1 mL/kg/h)
- Monitor: U&Es, CK (serial), renal function, potassium
- Hyperkalaemia management if develops (see hyperkalaemia entry)
- Wound management: staged closure or split-thickness skin grafting at 48–72 h
- Rehabilitation: physiotherapy for recovery of function
Complications
- Volkmann's ischaemic contracture: Irreversible fibrosis and shortening of forearm muscles from untreated compartment syndrome — clawed hand deformity
- Rhabdomyolysis and AKI: Muscle necrosis → myoglobin release → myoglobinuria → acute tubular necrosis
- Amputation: If diagnosis delayed and limb is non-viable
- Permanent nerve damage: Sensory and motor deficits in affected compartment
- Hyperkalaemia: From massive muscle cell death — can cause cardiac arrest
- Infection: Open fasciotomy wounds — risk of surgical site infection
UKMLA Exam Tips
- 1Pain out of proportion + pain on passive stretch = compartment syndrome until proven otherwise. ACT IMMEDIATELY
- 2Pulses may be NORMAL even with established compartment syndrome — pulselessness is a VERY LATE sign. Do not be falsely reassured by palpable pulses
- 3The 6 Ps: Pain, Pressure, Paraesthesiae, Paralysis, Pallor, Pulselessness — but by the time you have all 6, irreversible damage has occurred
- 4First action: remove all casts and dressings to skin. Do NOT elevate above heart level (reduces perfusion)
- 5Fasciotomy within 6 hours to prevent irreversible damage. This is TIME-CRITICAL — do not delay for investigations
- 6Post-tibial fracture: patient in cast with increasing pain despite morphine → THINK compartment syndrome → split cast IMMEDIATELY
- 7Volkmann's contracture (forearm) = the devastating consequence of missed compartment syndrome in a supracondylar fracture in a child
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