Biomedical Engineering Reference
In-Depth Information
5
Theoretical Models of Bone
Modeling a
nd Remodeling
5.1 Introduction
In the previous two chapters, internal and surface bone remodeling processes
subjected to multifield loading were discussed. No effects of growth factors
on bone remodeling were included in the models presented in those two
chapters. In this chapter, a hypothetical regulation mechanism for bone
modeling and remodeling under multifield loading presented in references
1-3 is discussed.
In this hypothesis, the bone modeling and remodeling mechanism is
described as follows: The circular loads that we bear during ordinary daily
activities generate microdamage in cortical bones and these microcracks are
removed by osteoclasts. Then, growth factors, which are in a latent form in
osteocytes, are activated by osteoclasts and released into bone fluids. These
growth factors stimulate osteoblasts to refill the cavities. In particular, the
related constitutive model presented in Hazelwood et al. [1] includes a
number of relevant mechanical and biological processes and could be used to
address differences in remodeling behavior as a volume element of bone is in
a condition of disuse or overload. The model is then extended for analyzing
surface bone remodeling under electromagnetic loading [3].
Functional adaptation of a living bone refers to the ability of the tissue to
respond to changes in its environment. For cortical bone tissues, one potential
response is remodeling, which involves a two-stage process carried out by
teams of BMUs. Another response of cortical bone tissue is modeling, which
refers to biological processes that produce functionally purposeful sizes and
shapes of skeletal organs. For the most part, in a bone the processes involve
modeling drifts of independent resorption and formation. Resorption of a
packet of bone by osteoclasts is followed by refilling of the resorption cavity
by osteoblasts. This sequence typically requires 3 to 4 months to complete
at each locus, and the resorption and refilling cavities, while individually
small, may collectively add substantial temporary porosity or “remodeling
space” to the bone. The chief purpose of these processes seems to be to fit
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