Characterisation of Trabecular Bone Structure - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 37

requests for material [ 5 ]. These restrictions have had the consequence of generally
limiting the age range of study cohorts to the older end of the human age-range,
which while still clinically relevant it does not encompass all clinical groups.
Surgically-sourced bone samples for ex vivo studies can be obtained through direct
patient consenting protocols but rely upon motivated surgical, nursing and medical
liaison staff. For in vivo studies, and where humans ethics approval for human
experimentation is permitted, biopsies are most useful for monitoring changes in
cellular dynamics and bone material properties in response to therapeutic inter-
ventions. In longitudinal studies, serial biopsies are obtained over an appropriate
timescale [ 10 ]. In the past, iliac crest biopsies in particular, were useful in the
diagnosis and characterisation of metabolic disorders affecting bone, including
osteoporosis [ 21 , 70 ]. However, advances in interpretation of bone serology and
imaging have reduced the clinical imperative for in vivo bone biopsy [ 43 , 103 ].
3 Histomorphometry of Trabecular Bone Structure
From the 1960s until the mid 1990s, histological sections were the most widely
used tool for the study of trabecular bone structure. Pioneers in this field, such as
Harold Frost and Michael Parfitt, developed histomorphometric techniques to
enable the characterisation of trabecular bone micro-architecture as well as the
cellular dynamics of bone [ 39 , 85 ].
Protocols have been developed for resin embedding of undecalcified bone
samples to enable thin sections (less than 10 micron thick when cut in the
longitudinal direction) to be cut thus preserving the bone mineral phase. Such
undecalcified sectioning allows bone components to be visualized by utilizing the
physical chemistry of bone mineral, where a modified von Kossa technique [ 15 ]
localizes the mineralized bone phase and haematoxylin and eosin (H&E) is used to
stain the unmineralized or osteoid bone phase (Fig. 4 ). The H&E stain also enables
visualization of bone cells, such as osteoclasts and osteoblasts at the bone surfaces
in the same sections. Surfaces at which active mineralisation is occurring are
localized by sequential administration of fluorescing compounds, which are
incorporated, in vivo, at sites of mineralizing bone [ 39 ]. Together these techniques
have provided a platform on which to conduct cross-sectional biopsy-based clin-
ical studies or ex vivo laboratory-based studies.
In addition to observational descriptions of bone, quantitative protocols were
developed through the adaptation of stereological techniques [ 40 , 56 , 86 ] specif-
ically for the complex architecture of trabecular bone. Bone histomorphometry
uses a suite of structural descriptors, which were developed based on idealized
models of trabecular bone structure as plates, rods or mixed plates and rods [ 85 ].
Independent bone tissue measures such as bone mineral area, bone tissue area
and bone mineral perimeter are applied to stylized models of trabecular bone
structure and indices describing the average architectural properties are derived.
These indices include independent measures of bone volume per tissue volume