Compartment Syndrome vs DVT vs Muscle Strain: Calf Pain Red Flags
Vascular Territories · 7 min read · 2025-12-13
Introduction
Calf pain is extremely common. Most cases are benign muscle strains or cramps. But two conditions — acute compartment syndrome and deep vein thrombosis (DVT) — are emergencies that present similarly. The ability to recognize the red flags for each can be limb-saving or life-saving.
Muscle Strain (Gastrocnemius/Soleus Tear)
Mechanism: Sudden push-off, change of direction, or eccentric loading. The patient feels a "pop" or "snap" in the calf.
Presentation: Localized tenderness, swelling, bruising (may appear after 24–48 hours). Pain with plantarflexion against resistance. Positive Thompson's test only if the Achilles is involved.
Key features: Clear mechanism of injury, localized tenderness, reproducible pain with muscle contraction, improving trajectory.
Deep Vein Thrombosis
Risk factors: Immobilization, recent surgery, long flights, oral contraceptives, malignancy, previous DVT, thrombophilia.
Presentation: Diffuse calf swelling, warmth, and tenderness — often without a clear injury mechanism. Pain with walking. The calf may feel "tight" or "heavy."
Key features:
- Unilateral leg swelling (measure circumference — >3cm difference is significant)
- Homans' sign (pain with dorsiflexion) — low sensitivity but classically taught
- Pitting edema
- Dilated superficial veins
- Low-grade fever possible
Red flags: Any combination of calf swelling, risk factors, and no clear injury mechanism should prompt Wells score calculation and D-dimer or ultrasound.
Acute Compartment Syndrome
Cause: Increased pressure within a closed fascial compartment, most commonly after fracture, crush injury, or reperfusion (post-vascular repair). Can also occur with overexertion (chronic exertional compartment syndrome is different).
Presentation: Severe, escalating pain that is out of proportion to the injury. The calf feels tense and "wooden."
The 5 P's (late signs — don't wait for all of them):
- Pain out of proportion — the earliest and most reliable sign
- Pain with passive stretch of the compartment muscles
- Pressure — tense, swollen compartment
- Paresthesia — numbness indicates nerve ischemia
- Pulselessness — very late sign; compartment syndrome can occur with palpable pulses
Key features: Pain with passive stretch is the critical early sign. If extending the toes causes severe calf pain, suspect compartment syndrome.
Red Flag Comparison
Clinical Pearl
Compartment pressure monitoring is definitive, but the clinical decision to perform fasciotomy should not wait for pressure readings if the clinical picture is clear. A tense compartment + pain with passive stretch + escalating symptoms after fracture = fasciotomy, not more monitoring.
Summary
Clear mechanism + localized + improving = strain. Swelling without mechanism + risk factors = DVT (investigate immediately). Escalating pain after fracture + tense compartment + pain with passive stretch = compartment syndrome (surgical emergency).