Experimental testing of cadaver specimens is a useful means to quantify structural and material response of tissue and passive joint properties against applied loading[1,4]. Very often, specific material response (i.e., stress-strain behavior of a ligament or plantar tissue) has been the goal of experimental testing and is accomplished with uniaxial and/or biaxial tests of prepared tissue specimens with uniform geometries[2,5]. Material properties can then be calculated directly and if testing data involves individual sets of multiple loading modes (e.g. compression only, shear only, volumetric) an accurate representation of the global response of the specimen may be possible. In foot biomechanics, however, it is practically impossible to perform isolated mechanical testing in this manner. The structural response, therefore the stiffness characteristics, of the foot have been quantified, usually using a dominant loading mode: e.g., whole foot compression [6], heel pad indentation [3]. This approach ignores the complexity of most in vivo loading conditions, in which whole foot deformation involves interactions between compression, shear (e.g. heel pad) and tension (e.g. ligaments). Therefore, the purpose of this study was to quantify the mechanical response of a cadaver foot specimen subjected to compression and anterior-posterior (AP) shear loading of isolated heel and forefoot regions as well as whole foot compression. Results from the experimental tests represent a novel methodology to quantify a complete structural biomechanical response. Combined with medical imaging, followed by inverse finite element (FE) analysis, the data may also serve for material characterization of foot tissue.
A mathematical method for quantifying in vivo mechanical behaviour of heel pad under dynamic load
