Age-Related Changes in Whole-Bone Structure and Strength - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 24

volume was 30 % less, cortical bone volume 42 % less, total BV/TV 25 % less, and
trabecular BV/TV 32 % less in women compared to men. Failure force was 38 % less
in women than men. With aging from 60-100 years, there was no evidence of
periosteal expansion, although both sexes lost bone. Both total and trabecular BV/TV
declined by -11 %/decade in women and -6 %/decade in men (Table 4 ). Failure
force declined -13 %/decade in women and -9 %/decade in men. Failure force was
strongly correlated with trabecular BV/TV (r 2 = 0.74) Of note, the absolute rates of
decline were not significantly different in women and men, although the percent-per-
decade magnitudes tend to be greater in women, most likely because they have lower
absolute baseline values. In summary, the distal radii of women are smaller, less
dense and weaker than men; both sexes lose bone density and bone strength with
aging. Bone strength in an axial loading setup that produces a clinically relevant
fracture mode (Colles-type) correlates most strongly with trabecular bone volume
fraction at the distal-most region, indicating that trabecular bone loss is most relevant
to diminished fracture resistance of the distal radius.
MacDonald et al. [ 51 ] used HR-pQCT to generate FE models of the distal
radius in 425 women and 199 men (20-99 years). The median estimated failure
load was 40 % less in women than men, nearly identical to the difference mea-
sured by Mueller et al. [ 52 ]. The strength difference corresponded to 30 % smaller
bone size in women along with 25 % lower trabecular BV/TV. With aging, esti-
mated failure load decreased approx. -8%/decade in women and -5 %/decade in
men. These rates are less than those reported by Mueller et al., which may reflect
the wider age range in the MacDonald study group.
3.2.3 Spine
Mosekilde and Mosekilde [ 55 ] performed compression tests on thoracic and
lumbar vertebral bodies from 44 cadavers (27 female, 17 male; 15-87 years, mean
58 years). Whole-bone failure force was normalized by cross-sectional area, and
this average failure stress demonstrated a highly significant age-related decrease of
-15 %/decade (relative to value at 58 years; female and male pooled). We note
that the rate of decrease in whole-bone failure force would likely be slightly less
than this because of the 3 %/decade increase in cross-sectional area also reported
in this study.
Ebbesen et al. [ 53 ] performed compression tests on L3 vertebral bodies from
101 cadavers (51 female, 50 male; 18-96 yrs, mean 57 yrs). Vertebral whole-bone
strength in females was 20 % less than in males, which corresponded to the 20 %
gender difference in cross-sectional area. Both sexes exhibited age-related declines
in whole-bone strength of approx. -16 %/decade, and the rates of decline
(absolute slope of force vs. age regression) did not differ between the sexes.
Notably, the rates of decrease in force are nearly identical to the rates of decline of
trabecular bone density (Table 5 ). When expressed as failure stress (force divided
by cross-sectional area), there were no gender differences in average values or in
rates of decline with age. Thus, the authors concluded that differences in vertebral