Position-Dependent Hemodynamics of Popliteal Artery Stent Grafts: The POPFLEX Study.

Background: Endovascular exclusion of popliteal artery aneurysms (PAAs) with long covered stent-grafts is valuable for patients unfit for open surgery but is undermined by late stent thrombosis, even in fully scaffolded segments without kinking, a failure best clarified by computational fluid dynamics (CFD), which requires anatomically accurate 3D models-difficult to obtain in the mobile knee. Methods: In this prospective, single-centre study, consecutive patients undergoing endovascular PAA repair over 24 months (≥20 patients) underwent CT angiography in three knee positions (full extension, 45° and 90° flexion). Every treated limb was included, with limb as the unit of analysis. Images undergo a geometric pipeline: segmentation in 3D Slicer, then refinement in MeshLab, Meshmixer and VMTK. Meshes are converted to hexahedral volumes (ANSA Cadense) and simulated under pulsatile flow (ANSYS Fluent). Primary endpoints are time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI) and relative residence time (RRT) over the stented segment, plus the surface proportion meeting thrombogenic criteria; positions are compared via linear mixed-effects models with limb nested within patient. Results: The protocol reproducibly yields watertight, artefact-free models preserving physiological morphology and supporting TAWSS, OSI and RRT quantification across knee positions. Conclusions: This protocol standardizes generation of CFD-ready popliteal geometries, enabling positional analysis of stent thrombosis.