A 40-year-old man sustains a knee dislocation (tibiofemoral dislocation) in a motorcycle accident. After closed reduction, serial ABI (ankle-brachial index) shows ABI of 0.72 (normal >0.9) in the right lower limb. The next most appropriate step is:
- A Serial limb checks and repeat ABI at 6 hours
- B Urgent knee MRI to assess ligament injuries
- C CT arteriography to identify popliteal artery injury before vascular surgery consult ✓
- D Fasciotomy for anticipated compartment syndrome
Explanation
Knee dislocation carries a 20–40% incidence of popliteal artery injury. An ABI below 0.9 after reduction is an objective indicator of vascular compromise and mandates urgent CT arteriography (CTA) to identify the site and nature of popliteal artery injury (intimal flap, transection, or thrombosis) before vascular surgery intervention. ABI 0.72 is clearly abnormal and cannot be watched serially — ischemia time determines limb viability; delay beyond 6–8 hours is associated with high amputation rates. MRI is deferred until vascular injury is excluded/addressed. Prophylactic fasciotomy is considered after vascular repair, not as the immediate next step for suspected arterial injury.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.