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Designing for Lower Torso and Leg Anatomy
Published in Karen L. LaBat, Karen S. Ryan, Human Body, 2019
The femoralartery is the primary arterial blood supply for the leg. It crosses from the pelvis to the leg at the groin. It travels along the medial thigh, sending branches to the tissues throughout the thigh, and then wraps around the medial femur to the back of the knee where it is renamed the popliteal artery. Below the knee, on the posterior side of the tibia, it branches into the posterior tibial and fibular arteries—two vessels which supply blood to the anatomical leg, ankle, and foot. Arterial pulses can be found in the groin (near the iliopsoas muscle) and at the back of the knee between the medial and lateral hamstring tendons (refer to Figure 2.17). Problems with low blood pressure or with peripheral arterial disease (PAD) may make it difficult to feel pulses at these points. PAD is caused by fatty deposits in the arteries which can restrict blood flow. Restricted arterial blood flow in the lower torso and legs causes leg pain, and, in the extreme, tissue death, which can lead to amputation of the foot and/or leg. A prosthetic limb, a custom-fit wearable product to substitute for the amputated limb, may be worn to help maintain independence, mobility, and quality of life.
Determination effect of two different NiTi stents on the vessel wall and studying their flexibility using finite element method
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Fatemeh Salemizadehparizi, Reza Mehrabi
The popliteal artery is located behind the knee joint and different forces apply to it during the leg flexion (Conti et al. 2017; Noble et al. 2021). As a result, the implanted stent is subjected to significant mechanical loads and contacts slightly with the arterial wall. Cambiaghi et al. reported a clinical case of a 60-year-old man with in-stent occlusion 8 months following angioplasty/stenting of a popliteal artery lesion. The report's findings revealed that after treating popliteal artery stenosis, a supera interwoven nitinol stent fractured. Despite having a stronger radial force and easy implementation than traditional tube stents, supera interwoven nitinol stents are susceptible to breakage (Cambiaghi et al. 2017). This kind of clinical reports showed the importance of studying the flexibility of different stents under different loadings before the implantation. In our previous work, we studied the mechanical behavior of two different stents under tensile loading and bending loading (Mehrabi and Parizi 2018). In order to predict the performance of the implanted stent, it is necessary to simulate the effects of the exerted forces on the stent and blood vessel artery. To this purpose, two self-expanding Nitinol stents as named Zilver stent and Navalis stent are subjected to the torsional loading. Navalis and Zilver are peripheral vascular self-expanding stents that are currently available in the market. We choose these two stents with two different structures to study the effect of their geometry on their flexibility ability. Chen et al. showed the shape of the struts and links affects the flexibility of biodegradable stents (Chen et al. 2020). Here we study the flexibility of Zilver and Navalis stents made of NiTi. These stents are compared with each other under the same loading conditions and the same material property that is used for this simulation. Two main properties of SMAs, shape memory effect as well as superelasticity behavior have been simulated for two designed stents. For this aim, a phenomenal constitutive model based on microplane theory is implemented in UMAT subroutine to use in ABAQUS package (Mehrabi et al. 2014). Hence arteries are subjected to significant mechanical stresses generated by the stent implantation. In this study, both stents were deployed into a stenosed artery, then the distribution of the stress on three layers of the vessel and plaque was evaluated.