Biomedical Engineering Reference
In-Depth Information
Tri-Lock
Length comparison
Mayo
Figure 10.2
Finite element model of Tri-Lock and Mayo
prostheses. (Adapted from Ruben
et al
.[3].)
In addition to the optimization models described above, some comparative
analysis has also been reported in recent years. This type of work is useful in
analyzing some particular shape characteristics. For instance, Mandell
et al
. [10]
compared the influence of the collar size on the stability and on the stress shielding.
In Sakai
et al
. [25] a new type of fixation was compared with the traditional ones.
Goetzen
et al
. [26] presented computational results for a new distal design. The
stem has a biodegradable pin to increase the distal diameter and thus to improve
distal fixation. When the pin is completely biodegraded a gap is formed between
femur and the distal part of the stem. The load-shift design tries to improve initial
stability in proximal part and consequently, the osseointegration. Ruben
et al
.[3]
compared the Tri-Lock stem from DePuy with the minimally invasive stem Mayo
from Zimmer (see Figure 10.2).
This brief bibliographic review illustrates the relevance of the use of structural
optimization methods to obtain new implant designs with better performance.
In fact, these methodologies used in high-tech industries such as automotive
and aerospace can also be a contribution for Biomedical Engineering, leading
to innovative products made of new materials and using new manufacturing
techniques in order to satisfy the tight design requirements. Moreover, shape
optimization can be very useful to design new custom-made hip implants. In fact,
each patient has his own characteristics and, in some cases, customized prosthesis
is a better choice to improve the quality of life.
10.3
Design Requirements for a Cementless Hip Stem
As mentioned above, aseptic loosening is the main cause of THA failure, and,
for cementless stems, it is essentially due to an inefficient primary stability and
excessive bone loss. Thus, an uncemented hip prosthesis with a good initial stability
