Session VIII - Femur/Knee

The Value of the Ankle-Brachial Pressure Index in the Diagnosis of Arterial Injury after Knee Dislocation

William J. Mills, MD; Patrick McNair, MD; Harborview Medical Center, University of Washington, Seattle, Washington, USA

Purpose: We assessed the efficacy of the Ankle-Brachial Index (ABI) in identifying those patients with clinically significant arterial injury after knee dislocation.

Methods: Thirty-eight consecutive patients with knee dislocation seen within 24 hours of injury at our institution were treated with a standard algorithm for evaluation of potential vascular injury. Ankle-brachial indices were obtained in the emergency department by resident physicians as part of the emergent evaluation of these patients. Those patients with an ABI 0.90 were immobilized and admitted for serial examinations, delayed arterial duplex examination, and eventual ligament reconstruction. Those patients with an ABI <0.90 underwent emergent arteriography or surgical exploration or both. Study exclusion criteria included those patients with a vascular injury recognized and treated at another institution (N = 5), those patients referred to our institution more than 24 hours after injury (N = 7), and patients with bilateral upper extremity injuries precluding adequate brachial pressure measurements (N = 1). Three patients had non-dopplerable pedal pulses in the injured limb, and were considered to have an ABI of 0.

Results: Eleven patients had an ABI of <0.90 (range, 0.0 to 0.74). Of these, 10 underwent emergent arteriography with findings of arterial injury requiring surgical intervention. One patient with an expansile knee hematoma underwent emergent exploration and revascularization for a transected popliteal artery without preoperative arteriography. Twenty-seven patients had an ABI of 0.90 (range, 0.90 to 1.16). None had evidence of vascular injury by daily serial clinical examination or delayed arterial duplex ultrasonography or both within 3 days of admission. Clinical follow-up in this group averaged 19 months (range, 4 to 36). For the diagnosis of arterial injury among this group of patients with knee dislocation, the sensitivity and specificity of an ABI <0.90 was 100%. Similarly, the positive predictive value of an ABI <0.90 was 100%.

Discussion: Arterial injury is frequently associated with knee dislocation and can lead to devastating results when unrecognized and untreated. The appropriate method for diagnosing clinically significant arterial injury after knee dislocation is debated in the literature, but arteriography remains the standard. The ABI has proven to be an effective, noninvasive, and rapid tool for screening arterial injuries in both blunt and penetrating lower-extremity trauma.

Conclusions: These data suggest that noninvasive, readily obtainable ABI can reliably be used to diagnose clinically significant arterial injury in those patients with acute knee dislocation. A level of 0.90 appears to be a useful value below which significant arterial injury is extremely likely and above which observation is indicated. Use of routine arteriography for all patients with knee dislocation is not supported.