Impact of leg bending in the patient-specific computational fluid dynamics of popliteal stenting

Endovascular treatment of the femoro-popliteal artery has recently become a valuable therapeutic option for popliteal arterial aneurysms.However,its efficacy remains controversial due to the relatively high rate of complications,such as stent occlusion as result of intra-stent thrombosis.The elucidation of the interplay among vessel geometrical features,local hemodynamics,and leg bending seems crucial to understand onset and progression of popliteal intra-stent thrombosis.To this aim,patient-specific computational fluid dynamic simulations were performed in order to assess the intra-stent hemodynamics of two patients endovascularly treated for popliteal arterial aneurysm by stent-grafts and experiencing intra-stent thrombosis.Both Newtonian and non-Newtonian blood rheological models were considered.Results were presented in terms of tortuosity,luminal area exposed to low(<0.4 Pa)and high(>1.5 Pa)time-averaged wall shear stress(TAWSS),area exposed to high(>0.3)oscillatory shear index(OSI),and flow helicity.Study outcomes demonstrated that leg bending induced significant hemodynamic differences(>50%increase)in both patients for all the considered variables,except for OSI in one of the two considered patients.In both leg configurations,stent-graft overlapping induced a severe discontinuity of the lumen diameter where the proximal stented zone is characterized by low tortuosity,low velocity,low helicity,low TAWSS,and high OSI;while the distal part has higher tortuosity,velocity,helicity,TAWSS,and lower OSI.Sensitivity study on applied boundary conditions showed that the different inlet velocity profiles for a given inlet waveform affect slightly the numerical solution;conversely,the shape and magnitude of the prescribed inlet waveform is determinant.Focusing on the comparison between the Newtonian and non-Newtonian blood models,the area with low TAWSS is greater in the Newtonian model for both patients,while no significant difference occurs between the surfaces with high TAWSS.