Biomedical Engineering Reference
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hallux valgus (Coughlin et al. 2004; Kim et al. 2008). Currently, mobility and stability are assessed
by manual dorsal excursion (Smith and Coughlin 2008), load-bearing radiographs (Coughlin and
Jones 2008), or custom-made mechanical devices (Klaue, Hansen, and Masquelet 1994). Yet the
quantification of hypermobility has been believed to be subjective and confined to static measure-
ment (Martin et al. 2012; Wukich, Donley, and Sferra 2005; Faber et al. 2001).
Plantar pressure distribution is another set of parameters commonly used to classify foot types
and deformities (Hillstrom et al. 2012). Various studies have demonstrated reduced pressure at
the hallux region (Blomgren, Turan, and Agadir 1991; Hutton and Dhanendran 1981; Kernozek,
Elfessi, and Sterriker 2003). Kernozek, Elfessi, and Sterriker (2003) found increased peak pressure
at the central forefoot region peak and heightened pressure time integrals, while Stokes et al. (1979)
discovered a lateral loci of peak pressure in the hallux valgus forefoot. However, converse findings
on the medial shift of pressure were also detailed (Martínez-Nova et al. 2008; Mickle et al. 2011).
Wen et al. (2012) commented that the medial metatarsal region may not be directly related to hallux
valgus, whereas a reduction in hallux loading and increased loading on the central metatarsal would
be more persistent in hallux valgus patients.
Surgical interventions have also been evaluated by means of plantar pressure assessment. Mittal,
Raja, and Geary (2006) indicated that the McBride procedure could improve hallux function by
increasing the contact area under the hallux. Saro et al. (2007) compared plantar pressure results
between the operated and non-operated foot and demonstrated a significant reduction in peak pressure
under the hallux and heel region. Dhukaram, Hullin, and Senthil Kumar (2006) compared the differ-
ences between a Mitchell and Scarf osteotomy by their differences in plantar pressure distribution.
Inasmuch as hallux valgus is not well-understood, numerous studies have examined the
pathomechanism of hallux valgus and the biomechanical outcome of interventions by means of
manual examinations and planar pressure studies to determine the altered load transfer pattern.
Recently, FE analysis or simulations have been used to examine the internal stress/strain and load
transfer behavior of the foot in the clinical field (Cheung and Nigg 2008). Yu et al. (2008) suggested
the contribution of high-heeled shoes to the development of hallux valgus by simulating a foot
shod with varying heel heights. Kai et al. (2006) undertook a primary FE analysis of the first ray
to evaluate the relationship between first ray hypermobility and hallux valgus. In the present study,
first ray models of a normal subject and hallux valgus patient were constructed and simulated at the
initial push-off phase. The stress/strain and joint loading were studied to evaluate the alteration in
kinematics and stability with the structural change of hallux valgus.
4.2
model develoPment
4.2.1 G
eometry
c
onStruction
The models of the normal foot and hallux valgus foot were constructed from radiographic images
of two women. The subject of the normal foot model was aged 28, 165 cm tall, and weighed 54 kg.
The subject of the hallux valgus model had asymptomatic hallux valgus, was aged 28, 165 cm tall,
and weighed 56 kg. Both participants reported no other musculoskeletal pathology, pain, or lower
limb trauma or surgery within the past six months.
An ankle-foot orthosis was fabricated to keep the foot in the neutral position with minimum
compression on the encapsulated soft tissue. The neutral position upon scanning was defined by
the Society of Biomechanics, based on the joint coordinate system (Wu et al. 2002). The alignment
of the participant was considered normal with a 25° calcaneal inclination angle (DiGiovanni and
Smith 1976). A pad was also placed beneath the calcaneal and talus body to maintain foot alignment
with respect to the scanning machine.
The geometry of the normal foot model was constructed via coronal magnetic resonance images
with a 3.0T scanner (Siemens Medical Solutions, Erlangen, Germany), while that of the hallux valgus
foot was constructed via coronal computer tomography (Aquilion, Toshiba Medical System, Japan).
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