Biomedical Engineering Reference
In-Depth Information
Fig. 13 Hysteresis energy
dissipation of bone as a
function of applied strain in
both tension and compression
The KWW relaxation process is believed to relate to the ultrastructural disorder
of collagen fibrils, whereas the Debye process is more associated with the
microstructural and inelastic (creep) behavior of bone [
97
,
98
].
4 Effects of Aging on Mechanical Properties
of Human Cortical Bone
4.1 Age-Related Microstructural and Compositional Changes
It is well documented that aging causes deleterious changes in cortical bone, which
may consequently contribute to fragility fractures. The most prominent age-related
change in cortical bone at the microstructural level is the increased porosity, which
has been noted in numerous studies. Increased porosity contributes to decreased
bone density and is directly correlated to the decreased strength. In addition,
age-related alterations in the nanoscale and chemical properties of the solid bone
tissue (''tissue quality'') are another significant factor that directly affects bone
strength [
32
,
99
-
101
]. One example is age-related accumulation of advanced
glycation end products (AGEs) that may alter the functionality of the collagen
network in bone, thus resulting in a decrease of bone toughness [
71
,
102
-
104
].
4.1.1 Porosity
Loss of bone mass is a major age-related change in cortical bone, resulting mainly
from thinning of the cortex (reviewed in Whole-Bone Structure and Strength) and
increasing intracortical porosity [
105
-
107
]. For example, a study of human
cadaveric humeral cortex reported that mean cortical porosity increases with age,
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