Biomedical Engineering Reference
In-Depth Information
0
µ
m <
25
µ
m <
< 25
µ
m
< 50
µ
m
50
µ
m <
Initial
Optimized
Initial
Optimized
Totally coated
Half coated
Figure 10.11
Relative tangential displacement for the initial
and the optimized shape obtained for the minimization of
displacement function
f
d
(load case 1).
areas. Assuming a bone ingrowth threshold of 25
m, which is a conservative
value, large portions of porous coated regions will be a candidate for efficient
osseointegration. In Figure 10.11 the displacements are shown only for the most
severe load case. For the other two load cases the tangential displacement at
stem-bone interface is lower.
µ
10.6.2
Optimal Geometry for Normal Contact Stress -
f
t
Table 10.3 presents the numerical results for the minimization of normal contact
stress cost function. In this case, it is also possible to verify that objective function
values for totally coated stems are lower than those obtained for partially coated
implants.
In Figure 10.12 it is possible to compare the initial shape with the optimized
ones. Usually, the maximum normal contact stress is observed at the stem tip. To
minimize the stress objective function it is necessary to decrease this peak stress.
Consequently, a small and circular stem tip is the best solution (see Figure 10.12),
Table 10.3
Objective function values. Minimization of stress function
f
t
.
f
−
initial
f
−
final
t
t
Totally coated
24.26
8.31
Half coated
39.03
9.25
