Biomedical Engineering Reference
In-Depth Information
2.5
Final Remarks
Few studies have considered the coupling effects of the periprosthetic bone
remodeling process with interfacial tissue evolution. In order to achieve a better
understanding of this subject, a model that simultaneously accounts for both
phenomena is investigated here. With this aim, the interface is characterized by a
thin volumetric region that allows the introduction of constitutive behaviors and
adaptive laws in a similar way as it is done for the periprosthetic region.
A classic homogenized material based on a microstructure model was taken
from literature to account for the bone representation. Its material properties
change continuously with respect to a relative density parameter. Following an
identical concept, an interfacial region is proposed with mechanical properties that
continuously change in time and space according to the relative quantity of bone
and fibrous material and mechanical environment.
An optimization-based remodeling law was chosen to be the driving force for
the bone adaptation in which nonlinear boundary conditions are included. For the
interface adaptation, a model based on a relative displacement is proposed, as the
information most frequently reported in experimental observations.
Periprosthetic and interface evolutions run simultaneously. Besides the natural
coupling of both effects due to global equilibrium, a local dependence of the
interface stiffness on the density of bone configurates a kind of local coupling
between the two models.
The numerical experiments, although strongly dependent on a set parameters
whose values are quite difficult to define precisely, show encouraging results. Both
the interface and periprosthetic results differ from classical results under static
interface conditions, achieving a pattern of ingrowth along the interface surface
that is consistent with clinical observations: low connection in the proximal regions
and a kind of two-point support in the distal and medial regions of the shaft. The
distribution of the bone ingrowth was also shown to be sensitive to changes in the
environment, like the stiffness of the prosthesis.
Different geometries, load conditions, and intensive sensitivity to parameters
should be analyzed in further studies, as well as the incorporation of more
accurate and consistent models for both interfacial and periprosthetic remodeling
phenomena. However, the present results show the relative influence that changing
boundary conditions exert on the final stability of the prosthesis. The inclusion of
a volumetric interfacial region with changing material properties has been found
to provide an adequate and flexible approach.
2.6
Acknowledgments
The authors would like to thank the Brazilian CAPES and
CNPq
who provided
partial financial support for this research. We also thank Prof. Tomasz Lekszycki
