Study on the effect of porous structure insoles on the redistribution of plantar pressure

The homogenization of plantar pressure distribution is of great significance for the treatment of diabetic foot, lower extremity sports injuries, and abnormal posture. Reasonable insole design is currently the more mainstream method to adjust the plantar pressure distribution. This research designed nine types of porous insoles with different hole types, hole distributions, and hole sizes. The finite element method is used to simulate the equilibrium state of the foot presses on the insole for obtaining the contact stress distribution of the foot sole and the deformation of the insole. The foot sole is abstracted into a rigid block with a relatively small curvature. Porous insoles with straight and larger holes are not conducive to reducing the peak pressure, while spindle-shaped porous insoles can effectively reduce the peak pressure up to 16.2% and reduce the ratio of contact surface area in high stress areas up to 50%. The influence of porosity on the peak plantar pressure is not clear when the hole types are different. When designing the stiffness distribution of an insole, the continuity of stiffness must be considered. Areas with sudden changes in stiffness may result in higher contact stresses. As the plantar pressure distribution tends to become more uniform, the compression of the insole increases, thus requiring a greater initial thickness of the insole to provide sufficient deformation allowance.