Nitinol Stents in the Femoropopliteal Artery: A Mechanical Perspective on Material, Design, and Performance

Abstract

Endovascular stenting has matured into a commonly used treatment for peripheral arterial disease (PAD) due to its minimally invasive nature and associated reductions in short-termmorbidity and mortality. The mechanical properties of the superelastic Nitinol alloy have played a major role in the explosion of peripheral artery stenting, with modern stents demonstrating reasonable resilience and durability. Yet in the superficial femoral and popliteal arteries, even the newest generation Nitinol stents continue to demonstrate clinical outcomes that leave significant room for improvement. Restenosis and progression of native arterial disease often lead to recurrence of symptoms and reinterventions that increase morbidity and health care expenditures. One of the main factors thought to be associated with stent failure in the femoropopliteal artery (FPA) is the unique and highly dynamic mechanical environment of the lower limb. Clinical and experimental data demonstrate that the FPA undergoes significant deformations with limb flexion. It is hypothesized that the inability of many existing stent designs to conform to these deformations likely plays a role in reconstruction failure, as repetitive movements of the leg and thigh combine with mechanical mismatch between the artery and the stent and result in mechanical damage to both the artery and the stent. In this review we will identify challenges and provide a mechanical perspective of FPA stenting, and then discuss current research directions with promise to provide a better understanding of Nitinol, specific features of stent design, and improved characterization of the biomechanical environment of the FPA to facilitate development of better stents for patients with PAD.

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

“…The FPA is a dynamic artery in the lower limb that experiences complex deformations with limb flexion, which include axial compression, bending, twisting and cross-sectional pinching. The severity of axial compression, bending and twisting has recently been demonstrated using a perfused human cadaver model [7][8][9], and was speculated to contribute to poor clinical outcomes of open and endovascular PAD repairs [6]. The focus of the current study was to characterize cross-sectional pinching of the FPA during limb flexion because it has a direct effect on blood flow, and to determine optimal stent design parameters that maximize stented cross-sectional area while minimizing intramural stresses.…”

“…A significantly higher frequency of FPA reinterventions compared with other arterial beds, such as carotid or iliac arteries, suggests that the local mechanical environment of the FPA plays a significant role in its pathophysiology [6]. Surrounded by powerful muscles, the FPA experiences severe mechanical deformations with limb flexion that include axial compression [7], bending [7,8], twisting [9] and cross-sectional pinching.…”

Modern approaches to femoropopliteal bypass surgery: achievements and future prospects

“…Обусловленная им ишемия нижних конечностей в большинстве случаев имеет прогрессирующее течение и нередко приводит к ампутации [1][2][3][4]. Современные способы консервативного лечения и контролируемой лечебной физической нагрузки могут стабилизировать прогрессирование ишемических проявлений облитерирующего атеросклероза [5][6][7][8]. Однако существенно улучшить качество жизни больных, либо сохранить конечность возможно только при помощи хирургической реваскуляризации [9][10][11][12].…”

Support function of self-expanding nitinol stents – Are radial resistive force and crush resistance comparable?

“…Lumen reduction of the femoropopliteal artery (FPA) due to arteriosclerosis is one cause for peripheral artery disease [1]. Besides surgical methods endovascular therapies, such as balloon angioplasty with or without stent implantation as well as drug coated balloon therapy are widely used for treatment of the affected patients [1,2]. Due to severe mechanical deformations in the FPA during limb movement the implanted stents have to resist high mechanical loading caused by axial tension/compression, bending, torsion as well as radial compression [3].…”