Finite element analysis of the foot: Stress and displacement shielding

Abstract

The foot is at the base of the antigravity control system (postural or equilibrium system) that allows the man to assume the upright posture and to move in the space. This podalic cohesion is achieved by the capsulo-ligamentous and aponeurotic formations to which are added the muscular formations with functions of "active ligaments" and postural. A three-dimensional (3D) finite element model of human foot was developed using the real foot skeleton and soft tissue geometry, obtained from the 3D reconstruction of MR images. The plantar fascia and the other main ligaments were simulated using truss elements connected with the bony surfaces. Bony parts and ligaments were encapsulated into a skin of soft tissues, imposing a linear elastic behavior of material in the first case and the hyperelastic law in the second. The model was tested by applying a load of 350 N on the top of the talus and the reaction force applied on the Achilles tendon equal to 175 N acting, and putting it in contact with a rigid wall. The results evidence that the most stressed areas, localized around the calcaneus following a trajectory that includes the cuboid and spreading into metatarsals and first phalanges. The foot is a "spatial" structure perfectly designed to absorb and displace the forces, brought back to the infinite planes of the space.

Keywords: CAD; FE analysis; Foot model.

Fig. 1

Foot anatomy illustration.

Fig. 2

Stress strain data on the plantar heel pad.

Fig. 3

Loading conditions of the FE model.

Fig. 4

Contour maps of the pressure aging on the top of the foot's skin a) and on the bottom b).

Fig. 5

Eq. Von Mises stress of the bony parts of the foot calculated on the bottom a) and on the top of the foot b).

Fig. 6

Contour maps of displacements calculated on the bony parts of the foot a) and Eq. Elastic strain b).