Factor of Risk for Fracture - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 143

more realistic loading condition of axial compression plus forward bending.
In addition, studies of vertebral factor of risk using FEA have applied loads to the
vertebral bodies through PMMA-endplates, simulating cadaveric testing methods
[ 44 , 47 ]. However, in vivo loads are applied through the intervertebral disc, and
recent work has shown that vertebral body endplates may experience high tensile
strains due to the Poisson expansion of the disc, placing them at high risk for
failure [ 21 ], whereas PMMA endplates would produce a very different strain
distribution.
Given accurate estimates of bone loading and strength, factor of risk will
indicate the risk of a fracture under a particular loading condition. However, this
does not account for the likelihood of that loading condition occurring. That is,
factor of risk indicates the risk of a hip fracture occurring in a fall, but not the risk
of falling. With improved loading and strength estimates, factor of risk may
improve identification of at-risk individuals. In addition, studies of factor of risk
may provide a way to identify activities that place individuals at high risk for
fractures. For example, identifying non-traumatic loading scenarios that have
increased factor of risk for vertebral fractures may aid in the prevention of oste-
oporotic fractures.
In conclusion, it is clear that both loading and strength are important in fracture
etiology. Thus, in spite of its limitations and challenges, factor of risk remains a
useful concept for examining osteoporotic fractures. Future work in biomechanics
will continue to improve estimates of loading and strength of bone, and thereby the
utility of the factor of risk for predicting fracture risk.

Acknowledgments We would like to acknowledge funding from the National Institutes of
Health: R01AR053986 and a postdoctoral fellowship from the Harvard Translational Research in
Aging Training Program (T32AG023480).

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