Biomedical Engineering Reference
In-Depth Information
0.08
0.07
P
= 0.15 kN
P
= 0.2 kN
P
= 1.2 kN
0.06
0.05
0.04
0.03
-100
0
100
200
300
400
500
600
700
800
t
(day)
FIGURE 5.9
Variation of porosity
p
for bone material subjected to several multifield loads.
when the loading is relatively small, the variation in porosity is similar
to that in disuse mode. On the other hand, if the loading is large
enough, the porosity will remain unchanged. The first result is due to
an insufficiency of environmental stimuli. After the electromagnetic
field is removed, there is no other loading to stimulate bone model-
ing except the initial mechanical loading. Thus, bone tissue reverts to
disuse-mode remodeling and bone mass loss is triggered again. This
leads to the conclusion that, although electromagnetic treatment is
effective, active exercise is necessary to maintain the curative effect.
The second result can be explained as follows. The electromagnetic
load makes the bone structure more rigid. The initial mechanical
loading cannot stimulate bone remodeling sufficiently after the elec-
tromagnetic field is unloaded. The bone tissue begins to remodel
itself in disuse mode, which causes bone loss and increased porosity.
This indicates that although an electromagnetic field can induce bone
hypertrophy, it can be automatically cured after the field is removed.
But this occurs only in some cases. In other cases, as shown in the
third case (
p
= 1.2 kN), the bone mass gain is permanent.
5.5 Bone Surface Modeling Model Considering Growth Factors
Section 5.4 described a model dealing with internal bone remodeling due
to electromagnetic loading. Extension to the case of surface modeling was
reported in He et al. [3] and is reviewed in this section.
