Biomedical Engineering Reference
In-Depth Information
process. This figure illustrates that the transverse and axial
loads have the same effect on the bone. The inner radius of the
bone decreases while the outer radius increases as the exter-
nal pressure increases. This results in an increase in the bone's
cross-sectional area and, consequently, a thicker and stronger
bone. When the external pressure decreases, the inner radius
increases and the outer radius decreases; this means that the
bone becomes thinner and weaker. On the other hand, greater
pressure can increase the rate of bone surface remodeling, which
can accelerate the recovery of injured bone.
• Figure 4.2 presents an interesting change of radius against time.
The outer radius of the bone increases at first as the transverse
pressure increases. It begins to decrease after a few days and
finally converges to a stable value that is greater than its ini-
tial value. A similar result was presented by Cowin and Van
Buskirk [4]. The earlier analysis was based on a model of surface
remodeling and was attributed to the surrounding bone mate-
rial becoming more or less stiff rather than being due to surface
movement.
• Case 2:
T
0
(
t
) = 29.5°C, 29.8°C, 30°C, 30.2°C, 30.5°C, φ
b
− φ
a
= 30V,
p
(
t
) = 1
MPa,
P
(
t
) = 1500 N
• Figure 4.3 shows the effects of temperature change on bone
surface remodeling. In general, the radii of the bone decrease
when the temperature increases and they increase when the
temperature decreases. It can also be seen from the figure that ε
and η are almost the same. Since
a
0
<
b
0
, the change of the outer
surface radius is normally greater than that of the inner one.
The area of the bone cross section decreases as the temperature
increases. This also suggests that a lower temperature is likely
to induce thicker bone structures, whereas a warmer environ-
ment may improve the remodeling process with a less thick bone
structure.
• This result seems to coincide with actual fact. Thicker and stron-
ger bones perhaps make a person living in Russia look stronger
than one living in Vietnam. It should be mentioned here that
how this change may affect the bone remodeling process is still
an open question. As an initial investigation, the purpose of this
study is to show how a bone may respond to thermal loads and
to provide information for the possible use of imposed external
temperature fields in medical treatment and in controlling the
healing process of injured bones.
• Case 3: φ
b
− φ
a
= -60, -30, 30, and 60 V,
p
(
t
) = 1 MPa,
P
(
t
) = 1500 N, and
T
0
= 0
