Age-Related Changes in Whole-Bone Structure and Strength - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 17

-17 %/decade in women and -11 %/decade in men [ 8 , 50 ]. The rate of decline
in total vBMD is intermediate to the rates of decline of cortical and trabecular
bone, and is significantly greater in women (-9 %/decade) than men (-5%/
decade in men).
The distal tibia is accessible to peripheral QCT scanning, and several recent
studies report modest age-related periosteal and endosteal expansion, with cortical
thinning and net loss of cortical area in both women and men (Table 3 ). Overall,
the distal tibia in women is smaller and has lower BMD than in men, differences
that are present at young adulthood and persist with aging [ 3 , 6 , 9 , 50 , 51 ]. In both
sexes, the increase in total area is only about 1 %/decade, with similar increases in
medullary area. The average cortical bone loss is slightly greater in women
(-3 %/decade) than men (-1 %/decade). Trabecular bone density declines in
women and men by -3 %/decade. The combined effect of cortical and trabecular
loss results in declines in total vBMD averaging -5 %/decade in women and
-2.5 %/decade in men, much slower than at the proximal femur.
The longitudinal study by Riggs et al. [ 49 ] gives insight into the rates of change
of bone density at the distal tibia, early and later in life. Somewhat surprisingly, the
rate of trabecular bone loss is identical in pre- and post-menopausal women
(-2.4 %/decade). In men, the rate of trabecular bone loss is actually greater before
age 50 (-4 %/decade) than after age 50 (-1.7 %/decade). Cortical bone exhibits a
different pattern. There is no decline in cortical vBMD in pre-menopausal women,
but a -3.6 %/decade decline in post-menopausal women. In men the rates of
change are not significantly different before and after age 50 (approx.
-1 %/decade), although the rate increases sharply after age 80 (-3.9 %/decade).
3.1.2 Upper Extremity: Distal Radius
The distal radius is of clinical relevance as a common site of osteoporotic frac-
tures, and is accessible by peripheral QCT. The age-related changes at this site are
similar to changes at the distal tibia, albeit a bit more pronounced, especially at
later ages (Table 4 ). In brief, average bone size (i.e., total area) at the distal radius
is 25-30 % smaller in women than men [ 9 , 50 - 52 ]. Most studies indicate modest
periosteal and endosteal expansion in both sexes, with net cortical bone loss
marginally greater in women (-2 %/decade) than men (-1 %/decade). Several
studies indicate loss of trabecular and total vBMD that is comparable in women
and men (approx. -5 %/decade) [ 9 , 50 , 51 ]. One study that examined an older age
range (60-90 years) reported much greater rates of decline in cortical thickness
(-11 %/decade women; -4 %/decade men) and trabecular BV/TV (-11 %/
decade women; -5 %/decade men) [ 52 ].
Similar to the distal tibia, the rate of trabecular bone loss at the distal radius is
not different between pre- and post-menopausal women (approx. -5 %/decade), or
between men before and after age 50 (-4 %/decade). The rate of cortical bone loss
is negligible in pre-menopausal women and younger men, but is significant in
older women (-5 %/decade) and men (-3 %/decade) [ 49 ].