ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

Thermo-mechanically coupled curing processes of acrylic bone cements used
in vertebroplasty: Material modelling and Finite-Element-Simulation
1. ABSTRACT
R. Landgraf 1,* , J. Ihlemann 1 , S. Kolmeder 2 , A. Lion 2
Vertebroplasty is a widely used surgery process to treat osteoporotic vertebral bodies
that have undergone a compression fracture. During this process a biomaterial gets
injected into the affected vertebral body in liquid state and therein cures to a solid. A
constitutive material model has been developed for the representation of the material
behaviour of acrylic bone cement, which is a class of materials often employed in
vertebroplasty. The material model accounts for the strongly coupled thermal, chemical
and mechanical processes of the exothermal curing process of acrylic bone cements as
well as its behaviour in solid state. By the help of thermo-mechanically coupled finite
element simulations, specific aspects of the clinical vertebroplasty process are
investigated. The application of our approach is demonstrated using a parametric
vertebral body model.
2. INTRODUCTION
Osteoporosis is one of the main diseases of elderly people and is indicated by a loss in
bone density and bone strength. One part of the human body which is mainly affected
by osteoporosis is the spinal column. A loss in bone strength can lead to destabilization
or even to fractures of vertebral bodies. In order to treat destabilized or fractured
vertebral bodies, a minimal invasive surgical procedure called vertebroplasty is often
applied. During this surgery process a biomaterial gets injected into the vertebral body
in liquid state. Afterwards the material cures to a solid which leads to an increasing
strength of the vertebral body, accompanied by an instantaneous decrease of pain and a
stabilization of the vertebrae.
A class of materials commonly used in vertebroplasty are the so-called acrylic bone
cements. These materials are based on Polymethylmethacrylat (PMMA) including
additional ingredients for biomedical issues. They are usually composed by mixing a
polymer powder and a liquid monomer. After a certain setting time this initially liquid
mixture gets injected into the vertebral body by a biopsy needle and cures in vivo during
an exothermal chemical reaction (polymerization) to a viscoelastic solid. Due to the
chemical process, heat gets dissipated and the temperature increases. This in turn affects
both the mechanical behaviour of the material and the polymerization. Furthermore, a
change in volume occurs due to chemical shrinkage and heat expansion.
In order to capture the thermo-mechanical behaviour of acrylic bone cements, a
constitutive material model has been developed [1]. It accounts for the strongly coupled
thermal, chemical and mechanical processes of the exothermal curing process of acrylic
1
Chair of Solid Mechanics, Department of Mechanical Engineering, Chemnitz University of Technology,
Straße der Nationen 62, 09111 Chemnitz, D
2
Institute of Mechanics, Department of Aerospace Engineering, University of the Federal Armed Forces
of Germany, Werner-Heisenberg-Weg 39, 85577 Neubiberg D
* ralf.landgraf@mb.tu-chemnitz.de (corresponding author)