Biomechanical behavior of plantar fat pad in healthy and degenerative foot conditions.

The plantar fat pad of the human foot is a specific tissue made up of adipose chambers enveloped by fibrous septa. Aging, pathology or trauma may affect its histo-morphological configuration and mechanical response. The correlation between histo-morphological configuration and mechanical properties is analyzed by a computational approach, aiming to identify the influence of degenerative phenomena on plantar fat pad mechanics. Finite element meso-models, as numerical model of an intermediate-length scale, are developed for healthy and degenerative conditions, considering the different properties that degenerative phenomena may affect, such as the adipose chambers dimension, the fibrous septa thickness, the fibers orientation and the sub-components mechanical behavior. Histo-morphometric data are analyzed to identify average configurations of the fat chambers and fibrous septa, while specific constitutive formulations are provided to define their mechanical response. Numerical analyses are performed to identify the stress-strain behavior of the plantar fat pad considering healthy and degenerative configurations. The results from meso-models are applied to identify the parameters of a phenomenological constitutive formulation that interprets the overall human fat pad tissue mechanics. The constitutive formulation is implemented within a 3D finite element model of the heel region that is applied to evaluate the influence of degenerative phenomena on the overall mechanical functionality of the foot.