2006/2007 WELS KONKRET - FH Oberösterreich

Fatigue Analysis of a Reconstructed
Femur – Effects of Prosthetic Materials
Autor: Stefan Reichl
FH-Betreuer: FH-Prof. DI Dr. Wolfgang Steiner
Stefan Reichl
Studiengang:
Automatisierungstechnik
Vorbildung:
HTL für Elektrotechnik in Linz
Bioengineering Research Group
Anglia Ruskin University
Bishop Hall Lane
Chelmsford
Essex CM1 1SQ
U.K.
FH-Studiengang:
Automatisierungstechnik
Studiengangsleiter:
FH-Prof. Univ.-Doz. Mag. Dr.
Günther Hendorfer
Tel.: 07242/72811-3010
E-Mail: sekr.at@fh-wels.at
www.fh-ooe.at/at
Introduction
The Bioengineering Research Group consists of research
engineers working in collaboration with medical
industries and hospitals. Engineering principles are applied
to medicine to bridge the gap between these two
fi elds for improved medical practice and quality of life.
Project Description
Total hip replacement has been the most successful
orthopaedic operation in the previous century.
Nevertheless long-term studies have shown that failure
often occur ten years post operatively, mostly at the
bone-cement interface.
In this context the aim of the study was to investigate
the stress distribution in the bone and the cement
mantle to predict the effect of the stiffness of the stem
on long term stability of a reconstructed femur during a
total hip replacement.
Methods
An accurate 3D model of a human’s leg and a hemi
pelvis was created with modern techniques and special
software from CT-scan data. Different ways of creating
the model were evaluated to fi nd a new solution,
which achieves more accurate results than previous
methods. The model was modifi ed in CAD software to
represent a reconstructed femur with prosthesis and
cement mantle. A fi nite element model was generated
with correct boundary conditions, the hip contact force
and muscle forces to represent the real conditions of a
human’s hip joint. A static fi nite element analysis was
carried out in the FE-package I-DEAS and the effect of
different material properties of the stem was investigated.
In this context a sensitivity analysis of a new method
of assigning heterogeneous anisotropic material
properties to the bones was carried out. To simulate
the loads during a normal gait cycle and during stair
climbing dynamic analyses were performed in ANSYS
and LS-DYNA. Based on
the FE-results, a fatigue analysis was performed in
FEMFAT.
Results
The new method of creating an anatomically accurate
3D model is more effi cient and more accurate. Especially
in an application like fi nite element analysis this
technique has lots of advantages. The results of the
simulation show the stress shielding effect clearly. Furthermore
the effect of different material properties of
the stem on the stress distribution in the cement mantle
and the bone could be shown. As a consequence a
material could be found, which would improve the long
term stability.
Conclusion, Recommendation
The new methods will be used by the Bioengineering
Research Group for further work. The whole project
was quite challenging, but it was a great experience.
It was very interesting to combine the fi eld of medicine
with state-of-the-art techniques from mechanical engineering.
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WELS KONKRET