Ankle Brachial Index in Lower Extremity Trauma

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February 14, 2019 by dailybolusoflr

By: Julian Botta MD

What anatomy is relevant?

Where do we feel for pulses in the lower extremity? Posterior tibialis and dorsalis pedis.

The popliteal artery supplies most of the blood to the distal lower extremity, but its collaterals might still allow for a palpable pulse, causing an injury to it to be missed!

Obtained from:

Who’s at risk for vascular injury?

  • Penetrating injury
  • Crush injury
  • Bony injury
    • Dislocation
    • Fracture

Note: Knee dislocation may be subtle, particularly in obese patients! Obese patients are more at risk for knee dislocation with low-energy injuries, and their dislocations or their resulting knee effusion may be masked by thicker subcutaneous tissue. Be aware that the knee may spontaneously reduce, but the vascular damage is already done, so maintain a high index of suspicion.

Most of them are relatively intuitive, but  board exams like us to know the hard and soft signs of extremity vascular injury:

Hard signs

  • Absent pulses
  • Bruit or thrill
  • Active or pulsatile hemorrhage
  • Signs of limb ischemia/ compartment syndrome (the 6 Ps)
  • Pulsatile or expanding hematoma

Soft signs

  • Proximity of injury to vascular structures
  • Major single nerve deficit (arteries tend to be near nerves)
  • Non-expanding hematoma
  • Reduced pulses
  • Knee or elbow dislocation
  • Hypotension or moderate blood loss at the scene

Obtained from:

When concerned for lower extremity vascular injury, measure an ABI!


If > 0.9, normal. If 0.9 or less, the next step is CT angiography.

Can also use the Arterial Pressure Index: API = (Affected leg SBP) / (Unaffected leg SBP) – this has the same cut off as the ABI

The combination of the hard and soft signs and ABI detects vascular injury in penetrating extremity trauma with 100% sensitivity!

References and further reading

Annals of EM:

What Is the Utility of Physical Examination, Ankle-Brachial Index, and Ultrasonography for the Diagnosis of Arterial Injury in Patients With Penetrating Extremity Trauma? Long, Brit et al. Annals of Emergency Medicine , Volume 71 , Issue 4 , 525 – 528

EAST Guidelines:

Evaluation and management of penetrating lower extremity arterial trauma: An Eastern Association for the Surgery of Trauma practice management guideline. Fox, Nicole et. al. Journal of Trauma and Acute Care Surgery: November 2012 – Volume 73 – Issue 5 – p S315–S320

LitFL – Extremity Arterial Injury:

emDocs – Knee Dislocation:

March 2018 EMRAP – Knee Dislocation:

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