Biomedical Engineering Reference
In-Depth Information
invasive biopsies by spectroscopic techniques (FTIR, Raman) or imaging tech-
niques (microCT, high resolution CT).
From the above discussions, data with respect to mineralization and osteopo-
rosis are contradictory (Table
2
). Such disparity suggests that both lower and
higher mineralization may associate with osteoporotic bone loss. A case study
conducted by Ciarelli et al. reported bimodal mineralization distribution in frac-
tured cases (i.e. greater standard deviation than normal cases) such that both the
lower and upper peak regions were associated with fractured cases [
46
]. High and
low mineralization levels each have their own drawbacks in terms of biome-
chanical properties at tissue level. Highly mineralized specimens tend to be brittle
and absorb less amount of energy before fracture, whereas lower mineralized
specimens have lower stiffness. The disparity on the trends of mineralization in
osteoporosis may also be a result of excessive spatial heterogeneity, study design
(age range included, criterion on what constitutes osteoporosis, fractured versus
osteoporotic samples) and simple lack of power due to limited availability of
biopsies of fractured samples. Importantly, most studies do not report BMD and
DOM simultaneously; therefore, the relation of matrix level mineral content to
BMD is unknown.
Irrespective of various observations in average mineralization levels (Table
2
),
most investigators agreed that the statistical spread of mineral content within the
field of interest either narrowed, indicating a more homogeneous distribution
(similar aged minerals) [
23
], or found no change especially in trabecular bone [
24
].
With advanced technology and more research on distribution parameters, heter-
ogeneity of mineralization could provide an interesting complementary parameter
to distinguish osteoporotic from normal individuals.
Mineral crystal status (size, crystallinity and substitutions) has also been
investigated in osteoporotic individuals. There is a lack of consensus in the
literature regarding the state of mineral crystals. A group of studies reported that
the osteoporotic bones have longer and/or more perfect mineral crystals compared
to normal individuals, using techniques like spectroscopy and X-ray diffraction
[
22
,
23
,
29
,
48
,
70
,
118
,
148
]. Others reported no change in crystal size [
77
,
97
],
while some found decreased crystal size in individuals with osteoporosis [
11
,
80
].
As individual mineral crystals grow in size, the mineral content is expected to
increase, therefore, changes in mineral crystal's size to some extent reflect degree
of mineralization [
21
]. However, in some cases average crystallinity observed over
an area in osteoporotic and fractured individuals was found to be greater than
normal, despite average mineralization being lower [
22
,
23
]. It is speculated that if
resorption were to act more efficiently and rapidly on smaller crystals, then the
larger ones would be left behind. Because of statistical averaging, mineralization
on the whole may seem less, but large crystals left behind may increase average
crystallinity. Similarly a low formation and/or higher maturation rates can lead to
higher crystallinity. For above reasons, a change in statistical spread was also
noticed in such a way that mineral crystal's size distribution in both cortical and
cancellous bone narrowed and shifted to higher levels in osteoporotic patients
[
21
,
23
]. Similar to BMD and mineralization, crystallinity was also suggested [
41
]
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