The risk of arterial injury with knee dislocation is well known. The most effective method for rapidly and accurately diagnosing arterial injury in this setting remains a topic of debate. Both physical examination and arteriography have been advocated, although each of these methods has its critics. The authors propose that the ankle-brachial index (ABI) can accurately predict whether patients with knee dislocations have sustained vascular injury.

A prospective study enrolled 38 patients with knee dislocation to evaluate for potential arterial injury using clinical pulse examination and ABI. Patients with an ABI lower than 0.90 underwent arteriography. Those with an ABI of 0.90 or higher were immobilized and admitted for serial examination and delayed arterial duplex evaluation.

Of the 38 patients, 11 (29%) had an ABI lower than 0.90. All 11 had arterial injury requiring surgical treatment. The remaining 27 patients had an ABI of 0.90 or higher. None had vascular injury detectable by serial clinical examination or duplex ultrasonography. The sensitivity, specificity, and positive predictive value of an ABI lower than 0.90 were 100%. The negative predictive value of an ABI that reached 0.90 or higher was 100%.

The ABI is a rapid, reliable, noninvasive tool for diagnosing vascular injury associated with knee dislocation. Routine arteriography for all patients with knee dislocation is not supported.