In Vivo Patient-specific Material Properties of the Subcalcaneal Fat: an Inverse Finite Element Analysis

Subcalcaneal fat serves as shock absorber and provides cushioning to the underlying foot structures and the body as a whole. Changes in mechanical response of the subcalcaneal fat (i.e., stiffening due to age [1] or diabetes [2]) can compromise the ability to dissipate plantar stress and potentially cause tissue injury. Inverse finite element (FE) analysis has been used to quantify mechanical properties of the soft tissue from in vivo, in vitro or ex vivo compression data [3-5]. However, several of these FE models assume simplified anatomy (i.e., 2D, plane strain or axisymmetric), material representation (i.e., lumped skin, fat and muscle) and/or boundary conditions (i.e., neglect bone movement or adjacent structures). In the current study, patient-specific subcalcaneal fat hyperelastic properties were determined from magnetic resonance imaging (MRI) heel compression data using inverse FE analysis. The FE model incorporates 3D anatomically realistic layers of plantar soft tissue (skin, fat and muscle) and physiologic calcaneus movement.