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

A SENSITIVITY ANALYSIS OF ADAPTIVE BONE REMODELING
SIMULTATION IN THE PROXIMAL FEMUR USING 3D MODELS
S. Walscharts 1 , J.M. Garcia-Aznar 2 , G.H. van Lenthe 1 and J. Vander Sloten 1
1. ABSTRACT
The typical bone density patterns in the proximal femur can be explained using bone
remodeling simulations [1]. Yet, density variations have been measured between
individuals. The aim of this study was to use patient specific loading characteristics to
estimate the bone density distribution in the proximal femur and to determine the
importance of different modeling parameters in doing so. We combined a generic
anisotropic bone remodeling scheme [2] with a patient specific musculoskeletal model
of the lower limb. The model includes patient specific muscle attachments of the
relevant muscles of the lower limb. Gait analysis data was used to quantify the loads
that occur during daily life. We varied the initial homogeneous density of the bone, the
load intensity, the number of load cases, their relative importance, as well as the number
of muscles taken into account. We evaluated our findings against the results of
simulations using generic loading. We found that the number of load cases had little
effect on the estimated density, as long as they are distributed over the entire gait cycle.
A high initial density resulted in too high density values in the medullary cavity,
whereas low initial values all led to very similar outcome. The action of the muscle
forces was most pronounced near the attachment regions. The direction of the head
contact force greatly influenced the estimated density pattern. Since this direction is
known to be strongly determined by the gait, data from an entire gait cycle representing
all loads acting on the bone are necessary for predicting physiological density
distributions.
2. INTRODUCTION
The relationship between bone structure and applied loads was first observed and
described by Wolff in 1892 [3]. Since then a lot of models have been proposed that
model bone adaptation in response to mechanical stimuli. Depending on the model,
these stimuli differ from functions of stress or strain to strain energy.
Not only the mechanical stimulus but also the kind of load that is applied varies
between models. Earlier models only considered 2D geometry and thus the load cases
differed mainly in abduction angles [4], with forces acting on the major trochanter.
Although these loads are still being used for 3D simulations [5], a gait based approach
gives a more realistic representation of the mechanical environment [6]. Also extreme
loads like stair walking are sometimes considered [7]. The bones used, as well as the
loads considered, are mostly generic and patient-specific differences are generally
ignored. Valuable information could be lost by omitting the subject-specificity and
simplifying the loads.
1 Biomechanics section, KU Leuven, Leuven, Belgium
2 Multiscale in Mechanical and Biological Engineering Group, Aragón Institute of Engineering Research
(I3A), University of Zaragoza, Zaragoza, Spain