Taylor Spatial Frame and Ilizarov Apparatus

117 Pages·2011·4.97 MB·English

UNIVERSITY OF THESSALY
Taylor Spatial Frame and Ilizarov Apparatus:
A Biomechanical Analysis using the Finite Element Method (FEM)
by
Themis P. Toumanidou
Submitted to the Department of Mechanical Engineering
in Partial Fulfillment of the Requirements for the Degree of
Master of Science
March 2011
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© Copyright 2011
by Themis P. Toumanidou
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To my beloved sister
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Thesis Committee
Professor Nikolaos Aravas (adviser)
Department of Mechanical Engineering, University of Thessaly
Professor Antonios Giannakopoulos (examiner)
Department of Civil Engineering, University of Thessaly
Lecturer Alexios Kermanidis (examiner)
Department of Mechanical Engineering, University of Thessaly
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Acknowledgments
First of all, I would like to express my gratitude to my thesis adviser, Professor Nikos
Aravas, for his guidance and support throughout my studies. I would have never been in
this position, if he had not believed in our good cooperation and in my willingness to meet
his expectations.
I would like to express my special thanks to Dr. Leonidas Spyrou, whose contribution
to this thesis is invaluable. His research work, together with Professor Aravas, inspired me
to follow the extremely interesting field of biomechanics. I would like to thank him for his
unconditioned help during the difficult moments of this research and for his patience to reach
to the end.
IwouldalsoliketothankthesurgeonsfromtheOrthopaedicDepartmentoftheUniversity
Hospital of Larisa, and especially Professor Konstantinos Malizos and Dr. Nikos Karamanis,
for providing us with prototype models of the fixators and for their clinical experience that
contributed a lot to this work.
At the end of a wonderful era, I would like to thank Kiki, Leonis and Alkmini, for their
optimism, their remarkable patience and support to my choices and to every difficulty that
occurred in this way. Special thanks to Dimitris and Marina, for making the last two years
of my life unique.
Last but not least, I would like to express my deepest gratitude to my family, for unspar-
ingly supporting my studies and encouraging me over all these years.
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ABSTRACT
Taylor Spatial Frame and Ilizarov Apparatus :
A Biomechanical Analysis using the Finite Element Method (FEM)
Themis P. Toumanidou
Advisor : Professor Nikolaos Aravas
External fixation devices are widely used for treating unstable bone fractures. The
Taylor Spatial Frame (TSF) and the Ilizarov apparatus are typical examples of circular
external fixators used to stabilize reconstruction of large segmental tibia defects. These
externalfixationdeviceshavesuccessfulclinicalusebecauseoftheirminimalinvasivenessand
extremeversatility. Thewiderangeoffracturetypestreatedledtoavarietyofconfigurations
of the Ilizarov and TSF frames which have substantial differences in stiffness and stability
of fixation.
The stiffness of the fixation systems under axial compression loading is an important
factor of their mechanical behavior and is influenced by the individual components involved,
such as the wires, half-pins, connecting rods, telescopic struts and the fracture zone itself.
The main objective of this work is the study of the mechanical characteristics of the
TSF and Ilizarov fixators. Detailed three-dimensional finite element calculations are carried
out and the axial stiffness of the systems is studied for various load cycles. The effects of
wire-diameter, wire-crossing angles, and pretension level on the stiffness of the systems are
studied in detail. Different stages of callus consolidation in the tibia bones are simulated
and the system behavior is studied in terms of load transmission and frame rigidity.
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