Design optimization procedure for an orthopedic insole having a continuously variable stiffness/shape to reduce the plantar pressure in the foot of a diabetic patient.

Foot ulcers and lower-limb amputations are among the major problems in diabetic patients. Orthopedic insoles can reduce the risk of diabetic foot ulcers in patients through pressure redistribution on the bottom of the foot. The purpose of this study was to propose an optimization method to design the dedicated insoles for diabetic patients in order to decrease the maximum plantar pressure. At first, a three-dimensional finite element model of bones, ligaments and soft tissue of a diabetic patient's foot was created using CT scan images. Then, the foot plantar pressure was calculated by means of a finite element software. Next, the stiffness and shape of a simple flat insole were separately modified to reduce the maximum foot plantar pressure. The optimization method resulted in a dedicated insole design with a continuously variable stiffness/shape within its area that creates a smooth pressure distribution for the patient comfort. The results showed a 40% reduction in the maximum foot pressure, which we attribute to the modification of insole stiffness. In addition, the optimal shape of the proposed insole decreased the maximum plantar pressure by 25% compared to the flat insole.