UMEM Educational Pearls


36 year-old female presents with left knee-pain following a motor vehicle crash (XRs are shown). What's the diagnosis AND what is the first test that should be performed to assess for vascular injury?


Answer: Anterior knee-dislocation and Ankle-Brachial Index (ABI) 

Both anterior and posterior knee-dislocations have the potential for popliteal arterial injury. 

ABI compares Doppler pressures of arms to legs to screen for lower limb ischemia (click here to learn more ABIs). ABIs can be used to accurately predict whether patients with knee dislocations have sustained vascular injury. 

A prospective study by Mills et al. demonstrated the sensitivity, specificity, and positive predictive values of an ABI lower than 0.90 were 100% for arterial injury, requiring surgical treatment.

Conversely, the negative predictive value of an ABI that was 0.90 or higher was 100%, suggesting no further workup is required.


Mills W, Barei D, McNair P. The Value of the Ankle-Brachial Index for Diagnosing Arterial Injury After Knee Dislocation: A Prospective Study.  Journal of Trauma-Injury Infection & Critical Care: June 2004 - Volume 56 - Issue 6 - pp 1261-1265.


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