In knee dislocation, which noninvasive test is best for initial vascular screening?

• A. U/S + ABI
• B. Angiography
• C. XRAY
• D. MRI

Answer: (A)

Knee dislocations carry a real risk of popliteal artery injury, so the first step in vascular assessment is a rapid, noninvasive screen of limb perfusion. Combining duplex ultrasonography with the ankle-brachial index provides that quick check: duplex looks for real-time arterial flow and can identify occlusion or abnormal flow patterns, while the ABI compares blood pressure in the ankle to the arm to detect ischemia. This pair is ideal as an initial screen because it is bedside, noninvasive, doesn't require contrast or radiation, and it directly informs whether the limb is perfused well enough or if further imaging is needed.

If these tests suggest compromised blood flow or if there are hard signs of vascular injury, more definitive imaging such as CT angiography or conventional angiography is pursued to map the injury for possible surgical repair. In contrast, plain X-ray assesses bone alignment only, and MRI, while useful for soft tissue, is not the best initial vascular screen.