Biomedical Engineering Reference
In-Depth Information
fracture incidence in women most likely results mainly from quantitative differ-
ences in bone structure, rather than from difference in tissue properties or other
risk factors [
132
,
133
]. Nonetheless, additional work is needed to improve our
understanding of gender differences in bone, to aid development of clinical and
pharmacological strategies to address the gender disparity.
5.1 Gender Difference in Cortical Bone Structural
and Composition
5.1.1 Bone Mass and Size
Peak cortical bone mass and areal BMD are higher in most men than women due to
bigger bones in men throughout life [
134
-
136
]. (This topic is reviewed in more detail
in Whole-Bone Structure and Strength and Factor of Risk for Fracture). Men
experience less age-related cortical bone loss due mostly to a slower rate of endosteal
resorption. For example, medullary expansion and thinning of the proximal femur
occurs faster in women than in men, thus leading to lower section modulus (related to
whole-bone strength) in women with increasing age [
137
]. Consistent with these
gender differences in structure, a cross-sectional dual-energy x-ray absorptiometry
(DEXA) study of 1,087 healthy adults (273 men and 814 women) aged 65-87 years
indicates that women experience age-related declines in BMD at all non-spine
skeletal sites, with the largest decline at the femoral neck (-0.0038 g/cm
2
/year) and
the smallest at the trochanter of the hip (-0.0023 g/cm
2
/year), whereas men do not
show significant changes at non-spine sites [
138
]. Even though there are gender
differences in bone geometry and thus areal BMD, the incidence of fracture seems to
be similar in men and women that have a similar absolute areal BMD [
139
].
Both men and women show evidence of periosteal expansion with age. For
example, a single-photon absorptiometry study of the distal radius of 108 women
followed over a mean period of 15 years after menopause indicates that the mean
(±SD) annual decrease in areal BMD is 1.9 ± 0.7%, while medullary bone
diameter increases 1.1 ± 0.9%, and periosteal diameter increases 0.7 ± 0.3% per
year. These results suggest that the increased bone loss after menopause is asso-
ciated with increased periosteal apposition, which may partially preserve whole-
bone strength in the setting of endosteal bone loss [
140
].
5.1.2 Porosity
The most significant age-related change in cortical bone microstructure is the
increased porosity, which affects both women and men. In some (but not all) studies,
bones from women tend to have larger Haversian canal diameter and greater overall
porosity relative to men [
110
]. Dramatic increases of porosity with aging have been
observed in various anatomical locations of the female skeleton, e.g. at the femoral
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