Biomedical Engineering Reference
In-Depth Information
0.044
0.040
0.036
0.032
0.028
P
= 1.8 kN
P
= 1.9 kN
P
= 2.0 kN
P
= 2.1 kN
0.024
0.020
0.016
0
200
400
600
800
1000
t
(day)
FIGURE 5.4
Variation of porosity
p
for several overloads.
An increase in Φ can result in faster bone remodeling, and vice versa.
Qu et al. [2] investigated only the modeling and disuse-mode remodeling of
bone tissues. They distinguished the following six loading cases:
• Case 1:
P
= 1.8, 1.9, 2.0, 2.1 kN,
E
i
= 0,
H
i
= 0. The results for this load-
ing case are shown in Figure 5.4. It can be seen that overloads can
activate bone modeling. The porosity of bone tissue decreases
when the environmental stimuli exceed the
MESm,
which is
defined as the modeling threshold. Overloads result in a denser
and stronger bone structure. The elastic module
E
increases due
to the decrease in porosity. Then the environmental stimulus
decreases at the same time as the strains become smaller. When
porosity returns to the remodeling threshold it will not change
any further. The result shows that bone tissue can model itself
to force its strains to revert to the remodeling range. It can also
be seen that the greater the pressure is, the less porous the bone
material will be. But it should be mentioned that if the loading is
so great that the strain cannot be reduced to the remodeling range
when the porosity reaches its lower limit, the bone structure will
model itself in another way.
• Case 2:
P
= 0, 0.05, 0.10, 0.15 kN,
E
i
= 0,
H
i
= 0. This case is investigated
to demonstrate the bone disuse-mode remodeling process. The cor-
responding results are presented in Figure 5.5. It can be seen from
the figure that, as the loadings decrease, the bone materials become
more porous to resist the decrease of the environmental stimulus.
But, as already mentioned, the porosity of a bone tissue should be
