Finite element analysis of the deformation of deep veins in the lower limb under external compression

Compression devices applied to the lower limb can help improve venous flow by deforming the muscles and veins. In this study, a two-dimensional finite element model using displacement boundary conditions was employed to simulate the deformations of deep veins in the calf under external compression. Magnetic resonance (MR) scans were performed on four healthy volunteers with and without compression stockings. The displacement boundary condition was extracted from the corresponding deformed (with stocking) and undeformed (without stocking) MR images by using a non-rigid image registration procedure. In the finite element model, soft tissues of the calf were simplified as a homogenous material with hyperelastic properties. The effective bulk modulus of the material was evaluated at a chosen transverse section for each subject, which was also applied to three other locations at 2mm, 6mm and 10mm below the original section. Comparison between the simulation and measurement showed good agreement in area reduction of deep veins (discrepancy=8.7±6.4%), especially for sections close to the chosen location where the effective bulk modulus was evaluated. Beyond a certain distance, the discrepancies increased and became quite variable. The reason for this is that the architecture and stiffness of the calf tissues vary along the leg. The results also showed considerable variation in effective bulk modulus among the four subjects examined.