Cross-sectional pinching in human femoropopliteal arteries due to limb flexion, and stent design optimization for maximum cross-sectional opening and minimum intramural stresses

Abstract

High failure rates of femoropopliteal artery (FPA) interventions are often attributed to severe mechanical deformations that occur with limb flexion. One of these deformations, cross-sectional pinching, has a direct effect on blood flow, but is poorly characterized. Intra-arterial markers were deployed into = 50 cadaveric FPAs (80 ± 12 years old, 14F/11M), and limbs were imaged in standing, walking, sitting and gardening postures. Image analysis was used to measure marker openings and calculate FPA pinching. Parametric finite element analysis on a stent section was used to determine the optimal combination of stent strut amplitude, thickness and the number of struts per section to maximize cross-sectional opening and minimize intramural mechanical stress and low wall shear stress. Pinching was higher distally and increased with increasing limb flexion. In the walking, sitting and gardening postures, it was 1.16-1.24, 1.17-1.26 and 1.19-1.35, respectively. Stent strut amplitude and thickness had strong effects on both intramural stresses and pinching. Stents with a strut amplitude of 3 mm, thickness of 175 µm and 20 struts per section produced pinching and intramural stresses typical for a non-stented FPA, while also minimizing low wall shear stress areas, and ensuring a stent lifespan of at least 10 cycles. These results can help guide the development of improved devices and materials to treat peripheral arterial disease.

In Vivo Morphological Changes of the Femoropopliteal Arteries due to Knee Flexion After Endovascular Treatment of Popliteal Aneurysm

“…In some patients, however, localized areas of eccentricity reduction were detected in this zone, which shows the tendency of the stent-graft to pinch in the flexed limb posture, as also reported previously. 12,27 The stent-grafted zone foreshortened on average 4% during limb flexion, which is in line with previously reported data for the non-stented arteries reported by Ansari et al 24 Using a heterogeneous group of patients with and without PAD, as well as human cadavers, this group reported an axial shortening of 4% to 13.9% in the FP segment depending on the axial position along the vessel. Comparison of our data to these results suggests that the implanted stent-grafts were able to maintain these baseline values of physiological foreshortening.…”

“…In some patients, however, localized areas of eccentricity reduction were detected in this zone, which shows the tendency of the stent-graft to pinch in the flexed limb posture, as also reported previously. 12,27…”

Mechanical stresses associated with flattening of human femoropopliteal artery specimens during planar biaxial testing and their effects on the calculated physiologic stress–stretch state

“…The high cost is primarily attributed to the large number of peripheral operations and interventions that fail and require reintervention (Adam et al 2005;Schillinger et al 2006;Conte et al 2006;Schillinger et al 2007). High failure rates of PAD interventions and reconstructions are often attributed to the severe mechanical environment of the flexing limb resulting in adverse interactions between the repair device and the artery (MacTaggart et al 2014;Desyatova et al 2017b;Maleckis et al 2018;Desyatova et al 2018). Computational modeling can be used to simulate these interactions and design devices with optimized performance, but it requires accurate input data on arterial mechanical properties.…”