Changes in Cortical Bone Mineral and Microstructure with Aging and Osteoporosis - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 111

Fig. 5 Data from a 71 year
old male. The line shows an
inversely related linear
relationship between
carbonation and crystallinity,
R 2

0.27

0.24

= 50.2%, P \ 0.05 [ 160 ]

0.21

0.18

0.15

0.05 0.055 0.06 0.065

Crystallinity

and found increase in carbonate content with age similar to others, who also found
that mineral crystallinity, obtained from X-ray diffraction, decreased with age.
Raman spectroscopic analysis on a sample set consisting of human femoral cor-
tical bone from individuals of different ages led to a conclusion that there is an
inverse relationship between carbonation and crystallinity (Fig. 5 )[ 160 ].
Crystallinity parameter is a composite indicator of crystal size and/or lattice
perfection and it reflects the overall maturity of the crystal [ 4 , 5 , 10 , 67 , 81 , 105 ,
108 , 128 , 129 ]. On the other hand, this parameter cannot resolve between the
constituent effectors. Smaller crystals with fewer imperfections may technically
have similar crystallinity as larger crystals with more imperfections. Since it is
believed that onset of crystal nucleation occurs in an amourphous state, it is
expected that crystal size and lattice perfection are positively associated. X-ray
diffraction and spectroscopic techniques have been widely used to characterize
crystallinity. In a systematic approach on a large sample set, Handschin et al.,
assessed association between age and crystallinity, which is generally affected by
molecular order (perfection), domain size and lattice strains [ 81 ]. Table 1 lists
some of the studies on humans that had reported age related trends. Simmons
et al.'s conclusion based on no change in crystallite size with degree of miner-
alization, which normally should increase contradicts the general theory of growth
of mineral crystals as reported by other researchers.
Akkus et al.'s observation supported their hypothesis that crystals mature
during the secondary mineralization process to a saturation level and then maintain
a constant crystallinity for the rest of the crystal's life [ 5 ]. They further added that
when bone is homogenized, mature mineral crystals get mixed with smaller
crystallites, which are mostly found in new secondary osteons formed due to bone
turnover, resulting in a constant crystallinity in homogenized bone as observed
in the study [ 5 ]. Similar to Akkus et al.'s study (after 40 years of age), no change
was observed with age in crystallinity in femoral cortex of elderly individuals
(52-85 years) despite an increase in carbonation [ 160 ]. Stagnant crystallinity in
the face of increased carbonation was explained by a scenario where increase in
crystal sizes (increase crystallinity) offset the effect of increased carbonation
(decrease crystallinity).