Age-Related Changes in Whole-Bone Structure and Strength - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 11

Greater rates of change at the distal radius were reported in a longitudinal study
of 108 women tracked from menopause until age 67 years (avg. post-menopausal
follow-up period 15 years) using single photon absorptiometry [ 16 ]. Areal mea-
sures were estimated from diameter measurements assuming a circular cross-
section. Subperiosteal area increased 14 %/decade, while medullary area increased
24 %. Because the absolute increase in subperiosteal area exceeded the absolute
increase in medullary area, there was a net increase in cortical bone of 12 %/
decade. There are several reasons why this study may have found greater rates of
change than other studies of the radius. It may reflect the study population of
Swedish women, as well as the focus on the 15-year interval after menopause,
which may be a period of relatively rapid bone turnover. It is also possible that the
longitudinal study design captured the true rates of change, which may have been
underestimated by cross-sectional studies. However, there are limitations to the
use of a two-dimensional projection method to estimate geometric changes in non-
circular bone cross-sections. Additional longitudinal studies using pQCT are
needed to clarify temporal changes in bone morphology in the upper extremity and
determine if there are indeed such high rates of periosteal and endosteal expansion
and net increases in cortical bone area.

2.2 Structural Mechanical Properties

Data on whole-bone mechanical properties for human long bone diaphyses are
remarkably few. There are some reports on femoral and tibial properties that were
used to provide reference values for the design of synthetic bones used in bio-
mechanical studies of fracture fixation [ 19 ]; however, donor age information is
incomplete and the focus is on elastic not failure properties. Martin and Atkinson
[ 4 ] estimated the bending strength of femoral shafts from 37 donors (22-82 years)
using beam theory along with direct measures of cross-sectional geometry and
indirect measures of material strength (based on bone density). Their results
suggested that female bones had a decline in strength in the second half of life,
attributed to modest declines in both material strength and section modulus (I/c),
while male bones maintained their strength with aging. The sample size in this
study was small, and it is not clear how accurate these estimates of bending
strength are. Notably, Russo et al. [ 6 ] reported similar trends for density-weighted
moment of inertia of the tibial diaphysis, i.e., that it declined slightly with age in
women (-2 %/decade) but not in men.
We identified only two studies that reported mechanical data on long bone
diaphyses across a range of ages, one for femur and one for radius. Martens et al.
[ 20 ] torsionally tested 46 femurs from donors aged 27-80 years (13 female, 33
male). Based on data reported in Table 1 of their paper, torsional rigidity (stiffness
normalized by specimen length) and failure moment did not correlate with age
(rigidity: p = 0.38, r 2 = 0.02; moment: p = 0.095, r 2

= 0.06), whereas fracture