Modeling and Numerical Analysis of a Cervical Spine Unit - Biologically Responsive Biomaterials for Tissue Engineering - page 139

In the last few years some commercial programs were developed as solutions to
modeling, simulation, and analysis of human body or human body parts. For exam-
ple, the AnyBody Modeling System™, by AnyBody Technology A/S Denmark, is
a software solution for simulating the biomechanics of a living structure working in
concert with its environment which is defined in terms of external forces and bound-
ary conditions. AnyBody performs a simulation and calculates the mechanical
properties for the body-environment system. AnyBody can also scale the models to
fit to any population from anthropometric data or to any individual ( http://www.
anybodytech.com/ fi leadmin/user_upload/anybody_lowres__2_.pdf ). The biome-
chanical behavior of advanced anatomical models can be determined by numerical
analysis. The Finite Element Analysis (FEA) of the anatomical systems, normal or
implanted, is a current concern in medical engineering field. Most works are focused
in a global evaluation of the anatomical systems under the loads [ 18, 61 ] .
A comprehensive state-of-the-art and critical review of the Finite Element
Applications in human cervical spine modeling is presented by N. Yognandan et al.
in Finite Element Applications in Human Cervical Spine Modeling [ 67 ] . The authors
are focused on the developments in model construction, constitutive law,
identification, loading and boundary conditions, and model validation.
The Finite Element Method (FEM) is successfully applied to simulations of bio-
mechanical systems. FEM is a method which allows advanced computations taking
into account the essential features of the structure such as complex geometry, mate-
rial inhomogeneity, and anisotropic mechanical properties of the bone and adjacent
tissues. Using FEM, the stress and strain fields in the tissue may be estimated to
predict the biomechanical behavior of the spinal segment. The scientific literature
on the assessment of the bone physical parameters appears to be extensive; however,
it is difficult to use basic information on physical parameters, because the mechani-
cal data referring to the tissues are sometimes grossly inconsistent [ 37 ] . The hetero-
geneity of the tissue structure results from the people's age and gender, anthropometric
data, and normal or pathological state, varying between individuals. Thus, the full
potential of FEM is still not explored due to the absence of precise, high-resolution
medical data [ 8 ]. However, the Finite Element Modeling used in the last 20 years
became a standard tool for biomedical applications [ 25 ] .
The FEM is generally used to understand and predict the biomechanical behav-
iors of vertebrae (taking into account trabecular bone and cortical bone of the verte-
brae), intervertebral discs, ligaments, facet joints, and muscles of the spinal
segments, to analyze quasi-static and dynamic applications. The FEM also includes
complicated porous tissue structures, nucleus pulpous, annulus fibrosus, nonlinear
ligaments, and non-thickness contact elements [ 36, 60, 65 ]. In FEA the tissue's
biomechanical properties are adopted from literature or from experimental studies.
When the biomechanical structure studied by numerical analyses is a certain spinal
unit implanted or not, the internal balance of various components should be deter-
mined [ 66 ] .
Validation of the Finite Element model is an important and challenging process.
The results given by the Finite Element model must be compared with the results