Scientific Publications by FDA Staff

J Vasc Surg 2013 Sep;58(3):804-13

Design considerations for studies of the biomechanical environment of the femoropopliteal arteries.

Ansari F, Pack LK, Brooks SS, Morrison TM

OBJECTIVE: The purpose of this study was to review the available literature regarding the biomechanics of the superficial femoral artery (SFA) and popliteal artery (PA) in patients with peripheral arterial disease (PAD). Stents are one of many available therapies used to treat patients with PAD. Because stents are permanent implants, they undergo a variety of deformations as patients go about their daily activities such as walking, sitting in a chair, or climbing stairs. As a part of the marketing application for United States Food and Drug Administration approval, stents need to be evaluated for long-term durability under a variety of loading modes. The information available in the literature provides direction for such evaluation. METHODS: We performed a literature search of the PubMed database looking for "key vessel" and "mechanics" (all fields) or "deformation" (all fields) or "flexion" (all fields) or "mechanical environment" (all fields) or "tortuosity" (all fields) or "dynamics" (all fields) or "forces" (all fields), where the "key vessel" was "Femoral Artery," "Superficial Femoral Artery," "Popliteal Artery," and "Femoropopliteal." RESULTS: Using a decision tree, we found 12 relevant articles that focused solely on the nonradial cyclic deformations associated with musculoskeletal motion. Despite the many limitations associated with combining these studies, we learned that under walking conditions, the proximal and mid-SFA deforms, on average, by shortening in the axial direction 4.0%, by twisting 2.1 degrees /cm, and by bending 72.1 mm; the distal SFA and proximal PA deform by shortening in the axial direction 13.9%, by twisting 3.5 degrees /cm, and by being pinched such that the aspect ratio of the lumen changes 4.6%. The distal PA deforms by shortening in the axial direction 12.3%, by twisting 3.5 degrees /cm, by bending 22.1 mm, and by being pinched such that the aspect ratio of the lumen changes 12.5%. CONCLUSIONS: A review of the current literature reveals heterogeneous study designs that confound interpretation. Studies included different physiologic settings from young to mature participants, participants with and without disease, and cadavers. Investigators used a range of imaging modalities and definitions of arterial segments, which affected our ability to compile the data as we learned that deformations vary according to the specific anatomic location within the SFA/PA. As a result of this analysis, we identified design considerations for future studies, because although this work has been valuable and significant, there are many limitations with the currently available data such that all we know about the SFA/PA environment is that we don't know.