Biomedical Engineering Reference
In-Depth Information
The overall aim of this project is the development of an innovative and economic
concept for the design and production of patient-individual hip cups for primary
surgery by means of sheet metal forming. Specific limitations (e.g. rigid tools) of
conventional forming processes normally prevent a time-saving and economically
reasonable patient-individual production. Nevertheless, the use of metal forming
for the manufacturing of customized products is necessary because of excellent
mechanical component properties, extensive shaping formabilities as well as optimal
material utilization. Currently potential approaches to an individual production are
unitized tools, CNC-controlled incremental forming methods or multi-point forming
[
8
-
10
].
The manufacturing concept developed in this project consists of an innovative
two-stage sheet metal forming process. The development is accompanied by a FE
simulation-based planning as well as a and a new design method adjusted to the
process. The following sections of this paper give the results of a numerical inves-
tigation of the bone remodelling process with a conventional prosthesis via finite
element method (FEM) coupled with multi-body simulation (MBS) as well as the
idea of the concept for the manufacturing of the individual hip-cup. Based on already
executed comparative simulations, the high pressure sheet metal forming (HPF) is
introduced for the manufacturing of the standardized components. Afterwards the
first part of the design method is demonstrated, which contains the deduction of
a universal acetabular geometry, necessary for the production of the standardized
component.
2 Bone Remodelling
As already stated, the migration of hip-cup prostheses due to bone remodelling is
still a problem. A numerical method for the prediction of the bone remodelling
after implantation of a artificial hip-cup is utilized below to emphasize the need of
customized prostheses.
By using a THA the physiological load distribution in the femur and the acetab-
ulum is modified. This modification is due to the fact that the bone stiffness is con-
siderably lower than the stiffness of the implant material. Thus, a large proportion
of the load is not directed over the bone but preferably over the prosthesis. In accor-
dance with Wollfs law, which says that changes in form and function of a bone lead
to changes in internal structure and external form [
11
], the so-called strain-adaptive
bone remodelling occurs, which can lead to a migration or loosening of the prosthesis
[
12
,
13
].
Due to the mentioned problems a qualitative and quantitative prediction of the
bone remodelling is important for implant design. At the Institute of Forming
Technology andMachines a simulationmethod was developed to calculate the strain-
adaptive bone remodelling in the periprosthetic femur via FEM [
14
,
15
]. Further-
more, the bone remodelling in the pelvis after total hip replacement was numerically
