Cortical Bone Mechanics and Composition: Effects of Age and Gender - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 73

Fig. 16 Plastic energy
dissipation of bone as a
function of applied strain for
middle aged (45-55 years
old) and elderly bone
([70 years old)
applied strain [ 84 ]. A study on human cadaveric tibia in tension indicates that the
plastic energy dissipation is linearly related to the applied strain with a similar
slope for both age groups (i.e., middle aged and elderly) except that the elderly
bones break at much smaller strain levels (\2%) compared with the middle aged
ones (3-4%) (Fig. 16 ). Another study reported that more microdamage is formed
in elderly bone compared to its younger counterpart under the same loading
conditions [ 130 ].
Age-related changes in bone toughness may be related to changes in the
collagen matrix. A study on cortical bone of human cadaveric femora confirmed
age-dependent decreases in strength, work to fracture, and fracture toughness of
normal bone samples [ 25 ]. Importantly, elastic modulus, strength, and work to
fracture of the collagen network (demineralized bone samples) all decreased with
age, while the concentration of pentosidine (a marker of non-enzymatic glycation)
and bone porosity increased with age. Regression analyses indicate that the age-
related decrease in the toughness of bone (especially its post-yield portion) is
correlated significantly with deterioration of the mechanical integrity of the col-
lagen network, leading to the conclusion that the strength of the collagen network
decreases with age and correlates with bone toughness [ 25 ]. The results of a
Raman spectroscopy study on human cortical bone from donors over a wide age
range (34-99 years) supports the above conclusion, showing that possible changes
in collagen cross-linking chemistry depend on age, and correlate with the age-
related decrease in the toughness of bone [ 131 ].
5 Gender Differences in Human Cortical Bone
Women are more susceptible than men to age-related fractures. Bone fragility
depends on structural characteristics (e.g., bone size/shape) and tissue properties
(e.g., strength, fracture toughness). Available evidence indicates that the higher