Acute Compartment Syndrome of the Leg

Acute compartment syndrome (ACS) is a surgical emergency: elevated pressure within a closed fascial compartment compromises tissue perfusion. In the leg, untreated ACS leads to irreversible muscle necrosis within 6-8 hours and potential limb loss. The diagnosis is primarily clinical, pressure measurement confirms the equivocal case, and the treatment is an emergent two-incision, four-compartment fasciotomy.

Who. Men outnumber women 10:1 and the peak age is 20-35 years; the annual incidence is about 7.3 per 100,000. ACS complicates 2-9% of tibial fractures, and tibial shaft fractures are the most common cause. In polytrauma patients 36% of cases are missed.

The tibial diaphysis is the high-risk subgroup. In a series of 1388 tibial diaphyseal fractures, 160 (11.5%) developed ACS, higher than the general tibial-fracture range because the diaphyseal subgroup is the high-risk one. Age was the strongest predictor, with the highest prevalence in the 12-19 and 20-29 year age groups. Male sex, blue-collar occupation, sporting injury and intramedullary nailing were associated on univariate analysis; age and occupation remained significant after adjustment.

Why youth. The clinical translation is uncomfortable: the young patient with a tibial shaft fracture and good pulses is the highest-risk presentation, not the reassuring one. Youth means more muscle bulk within tighter fascia and better physiological compensation, so vital signs and peripheral perfusion stay normal while compartment pressure climbs. Keep the threshold for monitoring and fasciotomy lowest in exactly the patient who looks best.

Causes. Tibial shaft fractures head the list, and high-energy trauma is a high-risk injury in its own right. Anticoagulation lowers the threshold.

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Four compartments. The leg has four fascial compartments, each with its own contents, a nerve with a sensory territory, and a motor function that can be tested at the bedside. The anterior compartment is most commonly affected (75%), but all four must be assessed, and all four released if the syndrome is present.

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The cycle. Pressure rises in a closed fascial space and the arteriovenous gradient falls, so perfusion falls with it. Capillary leak and venous congestion worsen the oedema, the cells are starved of blood, and more oedema means more pressure: the process feeds itself. Necrosis follows at 6-8 hours; rhabdomyolysis and its systemic effects follow, and renal and cardiac failure if untreated.

Tissue tolerance. Nerve suffers first, muscle next, and skin and bone tolerate far longer.

The pressure-perfusion relationship. Tissue perfusion depends on the arteriovenous pressure gradient, not on the absolute arterial pressure. That gradient is what Delta P measures: Delta P = diastolic BP minus compartment pressure. A Delta P above 30 mmHg means adequate perfusion; a Delta P under 30 mmHg sustained for more than 2 hours means inadequate perfusion, and fasciotomy is indicated.

Why an absolute number fails. An absolute threshold of 30-45 mmHg is less reliable, especially in hypotensive patients. A hypotensive trauma patient with a diastolic of 50 mmHg and a compartment pressure of only 25 mmHg has a Delta P of 25, which is inadequate despite a seemingly low absolute pressure.

History. The mechanism is a tibial fracture, a crush, or prolonged compression of the limb, and the time since injury is critical for prognosis. The pain is constant, severe and not relieved by analgesia; on the ward it announces itself as an escalating opioid requirement after a nailing. Ask about numbness, tingling and weakness, anticoagulation, and whether polytrauma or altered consciousness could be masking the symptoms.

Examination. Pain on passive stretch is the most sensitive early sign, and pain out of proportion to the injury is the cardinal symptom. The compartments are tense and woody on palpation. Test sensation in the first web space (deep peroneal) and motor power in the anterior compartment, where weakness shows as a foot drop. Pulses are typically present: do not be reassured by them.

How unreliable, exactly. The sensitivity of clinical findings is only 13-19% and the positive predictive value 11-15%, so any single sign, taken alone, is close to useless for ruling the diagnosis in or out. Two consequences follow. The probability rises with the number of signs present, so signs are cumulative evidence rather than individual tests: one finding is weak, three together are meaningful. And a negative examination does not exclude ACS, which is precisely why continuous Delta P monitoring exists for the at-risk or unassessable patient. Pain on passive stretch remains the most sensitive of a poor set.

Passive stretch, compartment by compartment. Each compartment is stretched by moving the foot against its muscles:

When to measure. Pressure measurement is for the patient the examination cannot answer. The technique is under Investigations. Measure when:

1. The clinical findings are equivocal
2. The patient is unconscious or sedated
3. The patient cannot be assessed clinically (intubated, regional block)
4. Symptoms are borderline and documentation is needed

Differential diagnosis. Two of the mimics share "pain out of proportion" and are the ones not to miss.

Bloods. Pre-operatively send FBC, UEC, coagulation, CK, lactate and a group and screen, and obtain an ECG for the hyperkalaemia risk. After fasciotomy, serial CK and urine output (for myoglobinuria) are the markers that matter.

What rhabdomyolysis looks like on paper.

• CK: often greater than 10,000 U/L, and can exceed 100,000
• Myoglobin: myoglobinuria, with cola-coloured urine
• Potassium: hyperkalaemia, with its cardiac risk
• Creatinine: a rise indicates acute kidney injury
• Lactate: elevated with tissue ischaemia
• Phosphate: elevated from muscle breakdown

Its management is under Postoperative Care.

Compartment pressure measurement. Use a Stryker intracompartmental monitor, or an arterial line transducer with a needle. Measure within 5cm of the fracture site, the zone of highest pressure, and measure all four compartments rather than assuming which is affected.

• Insert the needle perpendicular to the compartment
• Zero at the level of the compartment
• Calculate Delta P = diastolic BP minus compartment pressure

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Algorithm

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The first minutes. Remove all circumferential dressings and split any cast down to skin; this alone can reduce the pressure by 30-65%. Keep the limb at heart level, since elevation may reduce perfusion, and call for senior help immediately.

The next thirty minutes. Assess rapidly: pain, passive stretch, sensation. If the clinical diagnosis is clear, proceed directly to theatre; if it is equivocal, measure the compartment pressures. Consent for fasciotomy and organise theatre urgently.

When observation is legitimate. Conservative management truly only applies to impending compartment syndrome with a borderline Delta P (25-35 mmHg). Even then it means close monitoring every 1-2 hours with a clear escalation plan.

Indications for fasciotomy. Any of the clinical or pressure findings is enough:

• Pain out of proportion to the injury
• Pain on passive muscle stretch
• Tense, woody compartments
• Neurological deficit, sensory or motor
• High clinical suspicion in an obtunded patient
• Delta P less than 30 mmHg
• Absolute pressure over 45 mmHg
• Borderline Delta P (25-35) with a concerning clinical picture
• Any pressure elevation in a symptomatic patient

Relative indications.

• Prophylactic fasciotomy after prolonged ischaemia and revascularisation
• High-risk fractures with swelling in the polytrauma patient
• Combined arterial injury with a tibial fracture

When not to operate. Established irreversible ischaemia beyond 24 hours carries the risk of reperfusion syndrome, and here amputation may be life-saving.

The principle. All four compartments are released through two full-length incisions, a lateral one for the anterior and lateral compartments and a medial one for the two posterior compartments. A local or partial release is negligence. The skin must be released as well as the fascia.

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Lateral IncisionMedial IncisionCompletion

Releases the anterior and lateral compartments. Position the patient supine with a bump under the ipsilateral hip. The incision runs 2cm anterior to the fibula (also described as 2cm lateral to the tibial crest), full length from the fibular head to the lateral malleolus; do not be conservative with it.

Find the septum, then the nerve. Identify the intermuscular septum between the anterior and lateral compartments, and identify and protect the superficial peroneal nerve, which crosses in the distal third.

Release both compartments through the one incision.

1. Incise the fascia longitudinally posterior to the septum: the peroneal muscles should bulge
2. Pass anterior to the septum and incise the anterior compartment fascia longitudinally: tibialis anterior and EDL should bulge

The muscles should bulge and appear pink.

Releases the superficial and deep posterior compartments. Position the patient supine with the leg externally rotated. The incision runs 2cm posterior to the medial tibial border, full length from the tibial tuberosity to the medial malleolus.

Protect the saphenous structures. Identify and preserve the great saphenous vein; the saphenous nerve stays with it, and both stay posterior to the tibial border.

The superficial compartment first, then the key step.

1. Incise the investing fascia over gastrocnemius: the gastrocsoleus complex should bulge
2. Detach the soleus origin from the posterior tibial border, which exposes the deep posterior compartment fascia
3. Incise the deep fascia, protecting the posterior tibial neurovascular bundle, which lies between FDL and tibialis posterior
4. FDL, FHL and tibialis posterior should now be visible

The deep posterior release is mandatory, and detaching soleus is the step that makes it possible. It is the compartment most commonly missed.

Judge the muscle. Viable muscle is pink, contracts when stimulated and bleeds when cut; keep all of it. Necrotic muscle is grey or purple, non-contractile and does not bleed; debride all of it.

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Leave the wounds open. After a thorough saline washout the wounds are not closed. Temporary coverage is with a VAC (negative pressure wound therapy), which is preferred, a vessel loop or shoelace technique for gradual closure, or moist gauze dressings. The second look, and the timing of closure or grafting, are under Postoperative Care.

Never Close Primarily

Primary closure of fasciotomy wounds risks re-establishing compartment syndrome. Wounds must remain open and be closed in delayed fashion.

The shape of the harm. The immediate complications are systemic and come from muscle breakdown; the late ones are what a late or incomplete release leaves behind.

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Volkmann's ischaemic contracture. A fixed flexion contracture of the forearm or leg muscles from ischaemic fibrosis: the muscle is replaced by fibrous tissue, shortened and contracted. It is less common in the leg than the forearm. In the leg it affects the deep posterior compartment (FDL, FHL, tibialis posterior) and presents as claw toes and an equinovarus foot. Prevention, by early recognition and fasciotomy, is the key message; once established, treatment is graded by severity:

1. Mild: stretching, splinting, physiotherapy
2. Moderate: muscle slide procedures
3. Severe: tendon lengthening, releases
4. Very severe: may require amputation

Time decides. Outcome follows the interval from onset to release.

Favourable factors.

• Early diagnosis (less than 6 hours)
• Prompt complete fasciotomy
• Single compartment involvement
• Young, healthy patient
• Isolated injury
• Good systemic perfusion

Poor prognostic factors.

• Delayed diagnosis (greater than 12 hours)
• Incomplete fasciotomy
• Multiple compartment involvement
• Associated vascular injury
• Polytrauma or hypotension
• Significant rhabdomyolysis
• Deep posterior compartment involvement

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What patients are left with. After a timely fasciotomy most do well; after a delayed one, half or more do not.

After timely fasciotomy:

• 80-90% achieve a satisfactory functional outcome
• Chronic pain in 10-15%
• Sensory disturbance in 15-20%
• Motor weakness in 10-15%
• Cosmetic concerns from scars in 20-30%

After delayed fasciotomy (greater than 12 hours):

• 50% or more have significant functional limitation
• High rate of chronic pain
• Volkmann's contracture in 10-30%
• Amputation rate increases significantly

Global Epidemiology

Guidelines Compared Side by Side

There is broad international convergence: diagnosis is clinical, Delta P less than 30mmHg is the favoured objective threshold, and the decisive variable is time to decompression. No major society endorses an absolute-pressure-only rule.

Registry and System-Level Notes

• ACS is a recognised never-event / serious-incident trigger in many national systems; missed or delayed cases are commonly audited.
• Unlike arthroplasty, there is no dedicated international ACS registry; outcome data come from trauma databases (e.g. large single-unit cohorts such as Edinburgh) rather than implant registries.
• Health systems increasingly mandate structured neurovascular observation charts with explicit escalation triggers for at-risk limbs.

Antibiotic and Supportive Care (Principles, not Brands)

• Open fasciotomy / open fracture wounds: first-generation cephalosporin (e.g. cefazolin) as per local antimicrobial guidance; add gram-negative/anaerobic cover for heavily contaminated wounds; clindamycin if penicillin-allergic.
• Rhabdomyolysis: aggressive crystalloid resuscitation, monitor potassium and creatine kinase, treat hyperkalaemia (calcium, insulin-dextrose, salbutamol).
• Always follow local/national antimicrobial stewardship guidelines - agents and durations vary by region and resistance patterns.

Absolute pressure versus Delta P. Delta P (less than 30 mmHg) is the most widely endorsed threshold, but the supporting evidence (McQueen 1996) is observational with very few true ACS cases. Some still use absolute thresholds (over 30 or over 45 mmHg), and no randomised trial defines the optimal cut-off.

Continuous monitoring: benefit or overtreatment? Continuous Delta P monitoring shortens the delay to fasciotomy but may also drive unnecessary fasciotomies in patients whose pressures would have settled. Whether to monitor all high-risk tibial fractures or only the unassessable is debated.

The single reading. A single pressure measurement can be falsely low or high, through the wrong compartment, distance from the fracture, or technique. Many advocate trend-based or continuous data rather than acting on one number.

Adjuncts. Near-infrared spectroscopy and serum biomarkers (CK trends, for example) are investigational. None has replaced clinical assessment plus Delta P, and they are not standard of care globally.