Finite Element modeling

External and internal pressures

The difference between the external pressure values - measured at the skin surface by the TexiSense sensor, and the internal pressures that occur within the soft tissues stems from the morphological specificities of the subject.

Indeed, the external pressures are applied on the resting anatomical surface (foot sole, buttocks, etc), propagate through the soft tissues and focus around the bony prominences (talus, ischia) where they reach their maximal value.

Why resort to biomechanical modeling?

Biomechanical modeling makes it possible to:

  1. Take into account the subject's specific morphology: variable soft tissue thickness, shape of the bones, etc.
  2. Consider all mechanical interactions in 3D: foot stances during gait, postural changes of the paraplegic patient, pressure patterns inside a prosthesis socket, etc.
  3. Take into account the mechanical properties of the tissues: muscle, fat, tendons or cartilage behave very distinctly under external load.

The Finite Element Method (FEM) is a popular numerical technique used to solve the equations derived from the Continuum Mechanics theory which, when applied to biological tissues, is referred to as biomechanical modeling.

Introduction to the Finite Element Method

The Finite Element Method (FEM) relies on a discrete representation of the organ under study, called mesh. A mesh is made of elementary building blocks - the elements. Each element has a simple geometric shape: hexahedron, tetrahedron, pyramid or wedge. The 3D points defining the element shape are called nodes. A mesh is thus a set of nodes interconnected by elements.

Usually a FE mesh is built using volumetric images (CT or MRI) of the organ of interest. Anatomical regions such as the skin surface, bones, fat, and muscles are delineated in the image using automatic or semi-automatic image segmentation procedures.

These regions are later subdivided into elements which mechanical behaviour mimics the properties of the corresponding biological tissues. During Finite Element analysis the responses of all mesh elements to the external loads are "assembled" and yield the overall deformation of the organ under the simulated conditions.

The deformations and internal stresses can then be computed in the regions of interest. These values make it possible to assess objectively the level of soreness of the organ.

Simulation of internal pressures due to compression of tissues between bones and external surfaces.

Biomedical model of a feet, heel and lower leg

Biomedical model of a pelvis.