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

PATIENT-SPECIFIC MODELLING OF VERTEBROPLASTY: HOW
CAN WE OPTIMIZE THE OUTCOME OF THE TREATMENT?
1. ABSTRACT
R.P. Widmer 1 , B. Helgason 2 and S.J. Ferguson 3
Vertebral fragility fractures are often treated by injecting bone cement, typically
polymethylmethacrylate (PMMA), into the collapsed vertebral bodies (vertebroplasty).
Until now, the extent to which cement type, cement volume, cannula placement and
other augmentation parameters affect the outcome of the treatment has not been studied
in a systematic fashion. The aim of this study is to investigate and introduce methods
that allow pre-computing realistic cement distributions with a high accuracy, even in a
clinical setting, where only limited computational power is available and no significant
delay in the treatment pathway can be accepted. We also aim to introduce a framework
that serves, in combination with an adequate mechanical FE model of the bone-cement
composite, as an assessment tool for scientists and clinicians to determine the patientspecific
procedure parameters that optimize the treatment outcome. The flow of a non-
Newtonian fluid in trabecular bone is governed by a modified version of Darcy’s law.
This formulation implies several flow parameters to be calculated, e.g. the bone
permeability, fluid interface positions and non-linear rheology properties. We generally
approach this issue by mapping pre-computed micro-scale values to the macroscopic
length scale. We successfully established a framework that allows investigating the
procedure parameters that minimize the local risk of fracture and maximizes patient
safety. Ongoing work focuses on accuracy improvement with statistical error
quantification and the completion of a thorough sensitivity analysis to identify
parameters (cement viscosity, needle position, etc.) with the most significant effect on
the post-operative risk of fracture.
2. INTRODUCTION
Osteoporosis is a common disease that manifests itself in fractures occurring at different
anatomical sites, e.g. at the spine, the hip, or the wrist, with consequent morbidity and
mortality. Augmentation of weak cancellous bone, through the injection of a reinforcing
biomaterial, is a popular, minimally invasive intervention for the stabilization of
fractured osteoporotic bone. However, subsequent fractures of the augmented, adjacent
or remote levels immediately following the augmentation have been reported and
altered load patterns are considered as one of the main causes [1]. Moreover, two
studies published in 2009 cast doubts over the efficacy of vertebroplasty. In both
studies, patients with osteoporotic vertebral fractures were randomized to undergo either
a vertebroplasty or a sham procedure. Buchbinder et al. [2] concluded that “similar
1
Doctoral Student, ETH Zurich, Institute for Biomechanics, HPP O 14, Schafmattstrasse 30, CH-8093
Zurich, Zurich, Switzerland
2
Senior Research Associate, ETH Zurich, Institute for Biomechanics, HPP O 12, Schafmattstrasse 30,
CH-8093 Zurich, Zurich, Switzerland
3
Professor, ETH Zurich, Institute for Biomechanics, HCI E355.2, Wolfgang-Pauli-Strasse 10, CH-8093
Zurich, Zurich, Switzerland