Age-Related Changes in Whole-Bone Structure and Strength - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 25

strength between women and men are the result of differences in size, and that
women and men lose vertebral strength at the same rate with aging.
Bouxsein et al. [ 65 ] estimated vertebral compressive strength from QCT
parameters of *700 subjects from a Rochester, Minn. study group (21-97 yrs).
The age-related changes in area and density from this population were described
by Riggs et al. [ 50 ] and are summarized in Table 5 . Using empirical relations
relating density and cross-sectional area to whole-bone vertebral strength, esti-
mated strength was observed to be significantly less in women than men, con-
sistent with differences in bone size. In slight contrast to the study of Ebbesen
et al., the rate of decline in strength was greater in women than men. Failure force
was 20 % less in young women than young men, and this difference increased to
30 % by age *85 years. Women lost strength at a rate of approx. -7 %/decade
compared to -4.5 %/decade for men. The difference in rates was attributed to the
significantly greater rate of decline of vBMD in women.
A recent study by Christiansen et al. [ 66 ] used QCT-based FEA to estimate
strength of T10 and L3 vertebral bodies in 120 subjects, equally divided between
young (35-42 yrs) women and men, and old (73-83 yrs) women and men. The
findings are consistent with those cited above in two regards: 1) young women and
men have differences in bone strength (approx. 15 % lower in women) that are
explained by differences in bone size rather than density; 2) age-related loss of
bone strength is entirely attributed to loss of bone density. However, the findings
differ notably from Ebbesen et al. in that the rate of trabecular bone loss with aging
was significantly greater in women than men, and consequently the rate of decline
in bone strength was significantly greater in women than men. Women lost bone
strength at an estimated -16 %/decade whereas men lost strength at -6.5 %/
decade (L3 and T10 averaged; values based on estimated mean strength).
In summary, there is consensus that at young ages vertebral strength is 15-20 %
lower in women than men, as a result of differences in bone size not bone density.
With aging, changes in strength parallel the loss of vertebral bone density; there is
little to no compensatory increase in vertebral cross-sectional area. The available
literature differ on the relative rates of decline in bone density between women and
men and thus in the rates of decline in bone strength. One study reported similar rates
of decline [ 53 ], whereas two others reported greater rates of decline in women than
men [ 60 ]. The lack of agreement likely reflects differences in donors/study popu-
lation, and highlights the variability that exists in patterns of age-related bone loss.

4 Conclusions

There is a wealth of data on changes in bone structure and BMD with age. Results
often differ between skeletal sites and between sexes. In addition, differences
between sample populations likely contribute to the variability in results between
studies. Nonetheless, there are some patterns that are seen in most studies.
Diaphyseal periosteal expansion occurs at all sites studied and is typically