Re-evaluating the safety and effectiveness of the 0.9 ankle-brachial index threshold in penetrating lower extremity trauma

Abstract

Objective: Current guidelines recommend additional imaging when the ankle-brachial index (ABI) is ≤0.9 after extremity trauma; however, the accuracy of this 0.9 threshold compared with other values has not been evaluated. The primary aim of this study was to compare the safety and effectiveness of various ABI thresholds in predicting lower extremity vascular injuries after penetrating trauma. We hypothesized that a lower ABI threshold can be used safely to avoid unnecessary imaging.

Methods: A retrospective cohort study was performed at a single level I trauma center from January 2015 to December 2017. All patients who presented with penetrating lower extremity trauma and who underwent computed tomography angiography (CTA) were reviewed. Patients taken directly to the operating room without first undergoing CTA or those without documented ABIs were excluded. Demographic information, clinical features of presentation, interventions performed, and outcomes were recorded. P values were obtained using the Kolmogorov-Smirnov test, and a receiver operating characteristic curve was created to compare various ABI thresholds.

Results: A total of 47 patients (81% male), with a mean age of 29 years (range, 14-59 years), met inclusion criteria. Of the 17 limbs (36%) with a vascular abnormality seen on CTA, 6 (35%) required an intervention. The distribution of ABIs in injured limbs requiring revascularization was significantly lower (P = .006) than in those that did not require intervention. An ABI threshold of 0.7 is most accurate, with the highest combined sensitivity (83%) and specificity (91%) for detecting vascular injuries requiring revascularization. In addition, the negative predictive value was no different between a threshold of 0.7 (98%) and a threshold of 0.9 (97%), with both thresholds missing one vascular injury (pseudoaneurysm) requiring repair.

Conclusions: The ABI remains reliable in distinguishing between limbs with and limbs without vascular injury requiring revascularization after penetrating lower extremity trauma. A lower threshold can safely be used without compromising the negative predictive value of a screening ABI. Applying a threshold of 0.7 to our cohort would have avoided 51% (24) of the CTA studies performed without missing additional vascular injuries requiring repair.

Keywords: ABI; Extremity; Injury; Penetrating; Trauma.