Modeling and Numerical Analysis of a Cervical Spine Unit - Biologically Responsive Biomaterials for Tissue Engineering - page 166

7.5 Conclusions

Classical design and solid reconstruction are two modeling techniques aiming
essentially the same objective: developing of a realistic 3D virtual model which
respects the shape and characteristics of the real object.
The vertebra models obtained by classical design are focused on functional mod-
els, sometimes to the detriment of appearance. On the other hand, 3D reconstruction
models developed for the same structures are focused on virtual multi-solids, func-
tionally and aesthetically identical with the real ones.
Using classical design, solid models like the vertebrae, intervertebral disc, spinal
cord, facet joints, and ligaments were built. The models benefit by several advan-
tages: functionality, small volume of data, facile handling of the model, and shape
and dimensions that are appropriate with the target model.
The 3D reconstruction of the vertebrae led to a systematic processing protocol of
the images scanned by CT into solids, using two environments: one for image pro-
cessing and a CAD one. An important objective achieved by 3D reconstruction is
the developing of multi-solid models of the vertebrae. For inner core and outer shell
structure, different physical and mechanical properties can be assigned.
A synthetic analysis of the differences between the two types of geometric mod-
eling is presented in Table 7.4 . It can be seen that the benefits of solid reconstruction
in terms of accuracy and functionality actually generate two disadvantages: low
changeability and handling. The changeability of the model refers to the object's
property of being modified or transformed while handling quantifies the computa-
tional resources needed for working with the model.
Conclusively, both classical design and solid reconstruction present specific
advantages and disadvantages. It is important to note, however, that choosing one
over the other should be fully in line with the requirements imposed by the model-
ing objective.
In order to achieve a more realistic model, both models will be developed taking
into account additionally the soft tissues such as facet joints, ligaments, muscles,
spinal cord, vertebral artery, and nerves. The 3D reconstruction of these tissues
needs MRI scanning of a cervical spine and the same reconstruction protocol. The
classical CAD model will assume more fidelity of the anatomical geometry.
Based on the designed stabilization system, new models of bone plates and bone
screws will be developed and analyzed.
The results of the simulation highlight two mechanical aspects: the stresses and
strains acting at the bone-screw interface. The behavior of the bone screw-plate

Table 7.4 Comparison of the two types of modeling

Shape
accuracy

Dimensional
accuracy Modeling type Functionality Changeability Handling

Classical CAD modeling + +++ ++ +++ +++

Solid reconstruction +++ +++ +++ + +

+, Acceptable; ++, good; +++, excellent