Knee Dislocation Workup

Updated: Dec 10, 2019
  • Author: H Brendan Kelleher, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Imaging Studies

Plain radiographs are recommended post reduction and prior to any provocative ligamentous stressing. [7]

Briefly, the ankle-brachial index compares the Doppler pressure of an arm to a leg to screen for lower limb ischemia. This straightforward measurement is performed by recording the highest Doppler sound of the brachial pulse and comparing it to the highest Doppler sound of the posterior tibial or dorsalis pedis artery. The ankle Doppler pressure is then divided by the brachial Doppler pressure to calculate the index. Indexes less than 0.9 indicate an abnormal result and should prompt further vascular imaging/assessment.

Duplex ultrasonography is a reliable, noninvasive, low-risk, low-cost option. Duplex ultrasonography appears to be an excellent modality for vascular injury assessment. [27, 30, 31]  Fry et al reported 100% sensitivity and 97% specificity for clinically significant arterial injury. [27] This modality only incurs about 10% of the cost of arteriography with little to no risk profile. [32]

CT angiography is another reliable alternative to arteriography without the risk of direct arterial injury. It does require additional contrast beyond that used for chest/abdomen/pelvis body CTs that are often also indicated in these types of trauma cases; thus, it may have added risk of nephropathy or contrast reactions over arteriography, which uses less contrast. Inaba et al reported 100% sensitivity and 100% specificity for lower extremity arterial injury of significance. [28] Soto et al reported 95% sensitivity and 98.7% specificity. [7, 29]

Direct arteriography is the criterion standard but carries risk of arterial injury from direct catheterization of the artery while also requiring specialist involvement to perform (ie, interventional radiologist or vascular surgeon).