Factor of Risk for Fracture - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 138

(The product of elastic modulus and area is sometimes referred to as 'axial
rigidity'.) Unlike other studies to date, Melton and coworkers have determined
vertebral body strength using QCT-based finite element models [ 44 , 47 ].
Using a modeling approach, Myers and Wilson [ 49 ] examined the how factor of
risk for fracture for a variety of activities of daily living in the L2 vertebra varied
with vertebral aBMD. Their analyses predicted that individuals with extremely low
BMD (e.g. 0.3 g/cm 2 ) may be at risk for vertebral fracture during simple activities
such as tying one's shoes or opening a window. Individuals with low BMD (e.g. up
to 0.6 g/cm 2 ) may be at risk for vertebral fracture during bending and lifting tasks
such as picking up a toddler. This shows that for osteoporotic individuals, vertebral
fractures may occur in non-traumatic controlled activities.
2.2.1 Age-, Sex- and Ethnicity-Related Differences in the Factor
of Risk for Vertebral Fracture
Application of the factor-of-risk for vertebral fracture in a population-based
sample of 697 women and men aged 20-97 years found interactions between age
and sex [ 5 ]. Factor of risk during forward bending was 0.42 ± 0.08 in young men,
0.36 ± 0.08 in young women, 0.50 ± 0.14 in older men and 0.59 ± 0.15 in older
women. Thus, while the factor of risk increased with age in both men and women
(p \ 0.01), the increase was more than three times larger in women than men
(p \ 0.01). A similar interaction was seen for factor of risk in a lifting task. This
was in part due to the fact that while both sexes exhibited a marked decline in
lumbar vertebral compressive strength with age (p \ 0.001), the decline was
greater in women than men (-49 vs.-31%, p \ 0.001). For bending forwards and
lifting, the factor of risk in individuals age 50 and over exceeded one (U [ 1) in
30% of women and 12% of men, similar to reported prevalence of vertebral
fracture. Similarly, an examination of 1,013 healthy volunteers [ 17 ] found the
factor of risk for vertebral fracture when bending forward 90 to increase signif-
icantly with age in both men and women (p B 0.01), but more so in women. In
individuals age 60 and over, the factor of risk exceeded one in 26% of women and
9% of men.
In a cross-sectional study of 1,868 healthy men and women aged 18-91,
factor of risk was compared between individuals of Chinese and Caucasian race
[ 18 ]. In young adults, Chinese had a lower factor of risk than Caucasians in both
men and women (p \ 0.01); in elderly adults, Chinese men had lower factor of
risk than Caucasian men, but Chinese women had higher factor of risk than
Caucasian women (p \ 0.01). However, only 5% of Chinese and 6% of Cau-
casian elderly men had U [ 1, whereas 25% of Chinese and 29% of Caucasian
elderly women had U [ 1. The similar proportions of elderly Chinese and
Caucasian adults with high factor of risk is consistent with the fact that no
differences in incidence of vertebral fractures have been found between Chinese
and Caucasian populations.