Modeling and Numerical Analysis of a Cervical Spine Unit - Biologically Responsive Biomaterials for Tissue Engineering - page 140

of different experimental studies. Thus, new experimental studies suitable for
comparisons with the model are necessary in order to ensure that the model
behavior is realistic [ 25 ] .
Combining in vitro tests or mathematical modeling with FEA provides a more
complete picture of the biomechanical behavior, both of tissues and implants.
Finite Element models developed for a certain patient could be clinically useful
in the assessment of spine fracture risk, involving parametric investigation of the
factors that contribute to fracture risk. The effect of changes in material properties
or geometry of the intervertebral disc determined by its degeneration could be
quantified using numerical analysis [ 15 ] .
The main objective of this study was to obtain a sufficiently accurate model of a
functional unit of human cervical spine, both implanted and non-implanted, and to
analyze the biomechanical behavior of the implanted model, using FEM.
Based on CT scans and 3D reconstruction techniques a multi-solid model that
accurately reproduces the geometry of the vertebra was developed. In order to
achieve this objective, a cadaveric third cervical vertebra was scanned using
Siemens SOMATOM Plus 4 Power system in Medical Imaging Laboratory of
CMPICSU Research Centre in Politehnica University of Timisoara. The 2D
DICOM images were imported into Mimics software and processed using
Geomagic Studio software to obtain surface patches and SolidWorks CAD soft-
ware to accomplish the solid generation phase. In this way, the vertebral body was
created taking into account the material inhomogeneity and underlying the impor-
tance of the density influence. The main idea was to create two different solid
bodies: one for the spongy core of the vertebra and another one for the cortical
shell. By combining the two solids, a multi-solid body can be obtained. The
advantage of using multi-solid bodies is that for each constitutive element differ-
ent material properties can be set.
Using the reconstruction steps, the obtained solids satisfy all of the basic require-
ments, and they can be assembled into a multi-solid body. The proposed model has
the following advantages:

• Provides accurate information about the vertebra size, both for bone structures

and soft tissues
Allows the determination of sections in different planes •

• Allows determining of joint centers and axes of motion

• May impose motion constraints

• Allows determining of motion laws of joints

• Allows allocation of inertial characteristics (mass, moments of inertia) and mate-

rial characteristics of layers
Allows stress and strain evaluation for different components, based on numerical •

analysis

The evaluation of stress and strain distribution occurring in a real solid object can
prevent the unexpected changes in mechanical behavior or even failure. Because an
experimental analysis of the human spine behavior involves many issues, a virtual