Abstract CMBBE .pdf


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Patient-specific 3D Finite Element model of the human ankle-foot complex
L. Robichon, T. Le Calvez, A. Perrier, V Rampal, P-Y Rohan, P. Wicart, W. Skalli
LBM/Institut de Biomécanique Humaine Georges Charpark, Arts et Metiers ParisTech, 151 bvd de l'Hôpital, 75013, Paris, France

Introduction
Several Finite Element (FE) foot models have
been developed to comprehensively assess the
biomechanical role of the human ankle-foot
complex and to investigate various aspects of
foot mechanics. However, all existing models rely
on the data of one given individual while
personalization is paramount in clinical routine for
diagnosis, patient follow-up and surgical
planning. Recently, approaches have been
proposed for fast 3D reconstruction based on Xray imaging and associated subject-specific FE
models for the lower limb [1] and for the spine [2].
The aim of this study is to adapt such approach
for fast generation of subject-specific FE models
of the human foot-ankle complex.
Materials and Methods
Geometry
Based on bi-planar X-ray radiography, anatomic
landmarks were pinpointed which allowed
parameter assessment yielding deformation of a
morpho-realistic generic foot model. The resulting
model was back-projected on the image and
adjusted using the kriging method. The geometric
model was validated against CT scan
reconstruction of 6 cadaveric feet.
FE mesh
To get a subject-specific mesh, an existing
generic FE mesh was used. 4-node shell
elements were used to discretize the bone
surfaces and 8-node brick elements were used
for the plantar tissue. Control points were defined
with a particular attention to contact zones and
functional areas. Mesh was deformed using the
kriging algorithm.
Method evaluation
Fifteen lower limbs were imaged using bi-planar
X-rays and reconstructed using the method
described above. The subject-specific geometries
were then meshed. The mesh quality was
checked using standard element quality criteria
(aspect ratio, parallel deviation, maximum corner
angle, Jacobian ratio and warping factor) [3]
Results
Geometry
The mean difference between CT-Scans and 3D
reconstructions from biplanar X-ray images was 1
mm.

Method evaluation
A subject-specific mesh was successfully
generated for each subject. All elements fulfilled
the quality criteria. No element was beyond the
error limit and less than 1% of them was beyond
the warning limit.
Conclusions
The approach allowed generating subject specific
FE model of the foot with positive results in terms
of shape accuracy and meshing quality. Such
approach appears promising for subject-specific
FE modelling.
References
[1]

[2]

[3]

Y. Chaibi et al, « Fast 3D reconstruction of the lower
limb using a parametric model and statistical
inferences and clinical measurements calculation from
biplanar X-rays », Comput. Methods Biomech.
Biomed. Engin., vol. 15, no 5, p. 457‑466, mai 2012.
A. Laville et al, « Parametric and subject-specific finite
element modelling of the lower cervical spine.
Influence of geometrical parameters on the motion
patterns », J. Biomech., vol. 42, no 10, p. 1409‑1415,
juill. 2009.
P. M. Knupp, « Algebraic mesh quality metrics for
unstructured initial meshes », Finite Elem. Anal. Des.,
vol. 39, no 3, p. 217‑241, janv. 2003.

Figures

Figure 1: (a) Example of bi-planar X-ray images. (b) and
(c) examples of subject specific FE model of the foot


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