Age-Related Changes in Whole-Bone Structure and Strength - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 19

3.1.3 Spine
Similar to other bones, vertebrae of women are smaller than men. Based on QCT
data, the cross-sectional area of the vertebral body is 20-25 % less in women than
men [ 8 , 50 , 53 ].
The phenomenon of age-related periosteal expansion is also observed in the
vertebral bodies of the spine in both sexes (Table 5 ). Ruhli et al. measured linear
dimensions in a sample of spines from 71 ''modern'' donors (30 female, 41 male)
and reported that vertebral diameter increased modestly with age in men (e.g.,
sagittal diameter of C7 increased by approx. 3 %/decade) but not in women [ 54 ].
Mosekilde and Mosekilde reported a 3 % increase per decade in the area of the L2
vertebral body from a pooled sample of cadavers from males and females [ 55 ].
Using QCT, Riggs et al. reported a similar modest increase in area of approx. 2 %/
decade in both sexes [ 50 ]. In another study using QCT, Sigurdsson et al. reported
periosteal expansion of approx. 5 %/decade in both sexes, notably greater than
values from other studies or other sites.
Loss of trabecular bone is pronounced in the vertebral body, with average
declines of -18 %/decade in women and -13 %/decade in men (Table 5 ). The
decline in total vBMD is also significantly greater in women (-12 %/decade)
than men (-6 %/decade). Riggs et al. [ 49 ] reported that trabecular bone loss in
the lumbar spine accelerates with age, which is different than their findings at the
distal tibia and radius (reviewed above). Trabecular vBMD declined at a rate of
-16 %/decade in pre-menopausal women and -26 %/decade in post-meno-
pausal women. The rate of loss was slower in men, but also increased with age
(-8.4 %/decade before age 50; -18.5 %/decade after age 50).
3.2 Metaphyseal and Vertebral Bone Strength
There are surprisingly few studies of metaphyseal and vertebral strength at the
whole-bone level that provide data on age-related changes in mechanical prop-
erties. Mechanical testing of cadaveric specimens is the gold standard for this
information, but such studies are challenging because it is difficult to collect
enough samples across a large age range from young to old (e.g., 20-90 years).
Moreover, many investigators have focused on evaluating how well metrics from
DXA and QCT imaging (e.g., BMD) correlate to bone strength, and may have
included age as a covariate but not reported age-dependence per se. We review the
available data on whole-bone mechanical properties and age in this section.
In the past decade, CT-based finite element analysis (FEA) methods have been
shown to be accurate enough to allow surrogate assessment of bone strength using
virtual analysis. In the ''continuum'' approach developed by several groups (e.g.,
Keyak et al., Keaveny et al.), a QCT image set is used to generate a computer finite
element model that incorporates geometric and densitometric information and can
be used to perform a virtual mechanical test. If properly validated by comparison