Simulation of Osteoporotic Bone Remodeling - Computational Biomechanics of the Musculoskeletal System - page 332

25.1 introduction
The skeleton is made up of cortical bone and trabecular bone. Bone has a functional adaptation
ability, that is, it can adapt to mechanical load or other biophysical stimuli in terms of its mass and
architecture. There are two fundamental physiological processes of bone functional adaptation:
modeling and remodeling. (Frost, 2001). Modeling results in longitudinal bone growth. In this pro-
cess, continuous bone resorption and formation occur separately at different locations so that the
whole bone morphology changes. Remodeling is an important bone renewal mechanism, which is
performed by groups of osteoclasts and osteoblasts forming BMUs. Remodeling by BMUs com-
prises BMU activation, bone resorption by osteoclasts, and bone formation by osteoblasts.
It is possible to quantitatively simulate bone remodeling process to predict the adaptation of bone
mass and architecture to mechanical load and/or biophysical stimuli. (Slade et al., 2005; Ritzel et al.,
1997). Such simulations can also predict the outcomes of some experimental protocols without the
need to physically carry out the experiments. Computational simulation of bone remodeling is a quick
and convenient way to quantify the osteoporotic process, which can shorten the research period and
significantly reduce costs related to experimental work.
In this chapter, computer simulations of trabecular bone and cortical bone remodeling processes
at the BMU level will be developed, and the related osteoporotic processes will be predicted as
examples.

25.2 develoPment oF bone remodelIng ProCeSS
SImulatIon modelS For oSteoPoroSIS
Computational simulation of bone remodeling includes quantitative descriptions of the BMUs,
taking into account the birthrate of BMUs, the progression of each BMU through the bone, the
resorption and formation of bone performed by each BMU, and variations in the morphological and
material properties of the bone tissue, that is, porosity in trabecular bone and the thickness of corti-
cal bone (Hernandez et al., 2001, 2003; Gong et al., 2010).

25.2.1 m odel d eVelopment

25.2.1.1 Computational Simulation of trabecular bone remodeling
The computational simulation of trabecular bone remodeling at the BMU level comprised 8 state
variables and 12 constants (see Tables 25.1 and 25.2, respectively), taking into consideration a quan-
titative description of the contributions of biological factors and their coupling relationships with
mechanical load (Gong et al., 2006, 2010).

table 25.1
State variables in the Computational Simulation of trabecular
bone remodeling

State variable

E
p
N R
N F
fa
S A
e
Φ

Elastic modulus (MPa)
Porosity
Number of resorbing BMUs (BMUs/mm 2 )
Number of refilling BMUs (BMUs/mm 2 )
BMU activation frequency (BMUs/mm 2 /day)
Normalized specific surface area
Strain ( me )
Mechanical stimulus (Pa)