Biomedical Engineering Reference
In-Depth Information
and subcalcaneal tissue was shown to be different than other plantar soft tissue by compressive
material test in vitro (Ledoux and Blevins, 2007).
Although recent advances in experimental measurement techniques provide data for footwear
evaluation and design improvements, some important information, such as how the internal foot
structures respond to impact loading and where damage may occur, remains difficult to obtain from
experiments alone. Because of the complexity of the structures, limited measurement techniques,
large variation in shoe design, and individual subject differences, consistent results regarding the
biomechanical performance of the foot and footwear cannot be achieved in terms of the perfor-
mance of different therapeutic and functional footwear. Experimental evaluation of individual
shoes and optimal designs cannot be run efficiently and effectively. It has been suggested that a
shift in focus from external to internal loading in the understanding of sporting injuries, and plac-
ing greater emphasis on subject-specific investigations, may be beneficial (Miller and Hamill 2009).
5.1.2 c
omputational
a
pproacH
Researchers have identified that computational modeling, based on FE methods, can allow realistic
simulation of foot structures and the footwear interface and offer in-depth biomechanical informa-
tion on both the foot and footwear. We have comprehensively reviewed the FE models developed for
foot biomechanics and footwear design (Cheung et al. 2009). Both experimentation and modeling
are important in investigating the biomechanics of foot impact. Finite element analysis (FEA) may
be the most effective, combined with experiments.
The early FE models started from simplified two-dimensional or partial foot structures to inves-
tigate the effects of sole materials defined with either linear or hyperelastic or hyperfoam materials
(Nakamura, Crowninshield, and Cooper 1981; Lemmon et al. 1997). Several studies used two-
dimensional heel models to understand the loading response of the plantar heel pad (Verdejo and
Mills 2004; Goske et al. 2006; Spears et al. 2007). Most of those models focused on the effects of
sole design with varying materials or shapes on plantar pressure distribution in static conditions.
Several three-dimensional FE models were developed for footwear sole design and evaluation
(Even-Tzur et al. 2006; Antunes et al. 2008; Cheung and Zhang 2008). FE models were used to
investigate the effects of different sole materials, including silicone gel, plastazote, polyfoam, EVA,
air and water pockets, and reinforcement bars within the sole, on plantar foot pressure and bone
stresses during balanced standing, stance phases, or impact. Most models were analyzed under
static or quasi-static loading, while nonlinear and viscoelastic properties were added to the FE
model to study EVA midsole viscous damping of the shoe-heel interaction to heel pad stress and
strain attenuation during heel strike in running (Even-Tzur et al. 2006).
The viscoelastic effect is often implemented for the footwear sole and soft tissues under dynamic
loading. Recent computational studies on the viscoelastic material behavior of elastomeric mate-
rials and human soft tissue using the FE method were reported (Eskandari et al. 2008; Liu, Van
Landingham, and Ovaert 2009; Fontanella et al. 2012). Such viscoelastic and hyperelastic models
may provide a physically based simulation of tissue deformations for dynamic phenomena. A num-
ber of studies were undertaken to measure the nonlinear elastic or viscoelastic material properties
of foot plantar soft tissues using mechanical or ultrasound indentation techniques (Erdemir et al.
2006; Gefen, Megido-Ravid, and Itzchak 2001; Zheng et al. 2000). The subject-specific plantar
heel pad behavior could be obtained using the indenting test and analyzing by inverse FEA with a
partially three-dimensional computational model. Optimized heel pad material coefficients were
0.001084 MPa (µ), 9.780 (α) (with an effective Poisson's ratio (ν) of 0.475), for a first-order nearly
incompressible Ogden material model (Chokhandre et al. 2012).
During a frontal car crash accident, the driver's foot and ankle may be injured due to the intru-
sion of the brake pedal. In car crash injury simulations, impact FE models of the foot and lower limb
using explicit analysis were often developed to address the impact injury mechanism (Takahashi
et al. 2000; Untaroiu, Darvish, and Crandall 2005; Cardot et al. 2006). A validated FE model of
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