Biomedical Engineering Reference
In-Depth Information
effects of mechanical loading on tissue differentiation, growth, adaptation and
maintenance. In any case, it must be kept in mind that a computational model is a
simplified and mathematical representation of a system to analyze its behavior under
different conditions. Therefore, a model always requires experimental validation.
Model validation is an essential part in modeling. In order to validate a model
it is necessary to compare predictions given by the model with results from in-
vitro and in-vivo experiments. In fact, if a model is unable to reproduce some
specific experiments, then the original hypotheses in which the model is based
should be revised and updated. The experiments have to be designed in a way that
the measured data contain information about the different parameters predicted by
the model. Moreover, in-silico models can also improve experimental design by
highlighting which measurements are needed to test a particular theory and whether
additional information can be gained by collecting supplementary data.
3
Biological Background
During the last decades intense research has been performed in orthopaedic
biomechanics. Bone healing and distraction osteogenesis in particular have been
focus of numerous experimental studies [
19
,
32
,
34
,
35
] since there are many cues
not well understood yet. Next are described these processes briefly from a biological
perspective.
3.1
Bone Healing
In the process of fracture healing, bone recovers its original shape and mass
after fracture. It is a very complex process which involves intense cell migration,
differentiation and proliferation within the fracture gap. A fracture callus is created
and the bony union takes place by means of intramembranous and endochondral
ossification. This is the most commonly way fractures heal and involve four
overlapping phases (Fig.
1
): inflammatory, soft callus, hard callus and remodeling
to original bone contour [
4
]:
•
Inflammatory phase
. This phase starts immediately after the fracture occurs and
as a result of vascular disruption an hematoma is formed and is converted into
a clot. It lasts from 1 to 3 days at which the clot is replaced with granulation
tissue [
63
].
•
Soft callus stage
: its starts once the pain has disappeared and ends with the bone
fragments union by tissues with relative stability. It usually lasts approximately
2 weeks during which granulation tissue is converted to fibrous tissue by fibrob-
lasts. Cartilage tissue also replaces the granulation tissue but in the periphery of
the gap rather than in the central part [
63
].
