Characterisation of Trabecular Bone Structure - Skeletal Aging and Osteoporosis: Biomechanics and Mechanobiology - page 35

Fig. 2 X-ray image of sagittal femoral head slice (left) in contrast to a macerated sagittal slice
from a vertebral body (right) showing marked differences in the amount of bone and the
arrangement of trabeculae
Histological studies have shown, as expected, that there is considerable heter-
ogeneity in the trabecular microstructure at clinically relevant sites [ 4 , 46 ]. For
example, bone volume fraction varies from less than 7% in the centrum of ver-
tebral bodies to more than 25% in regions in the femoral head [ 3 , 35 ] (Fig. 2 ).
Consequent to this variability in bone volume fraction, the trabecular architecture
is highly variable, not just in terms of how plate-like or rod-like it is but in the
dimensions of the trabecular elements and how they are arranged in space [ 46 - 48 ].
Eckstein evaluated trabecular microstructure at seven sites (distal radius, L2
vertebra, femoral neck, femoral trochanter, iliac crest, calcaneus) in 79 female and
86 male cadavera, and reported that correlation coefficients between sites were
weak to moderate (0.01-0.56). For example, BV/TV at one site explained only
10-32% of the variance of BV/TV at other sites.
The amount of trabecular bone adjacent to joints through which large forces are
transmitted suggests that it plays an important role in maintaining the mechanical
integrity of the joint complex and in the mechanical dynamics of the body a whole.
Optimization of the micro-architecture of the trabecular network in response to extant
loads imparts optimal strength with minimal mass [ 23 , 41 ], with inbuilt safety margins
[ 8 ]. The large mineral surface area afforded by the complex trabecular network pro-
vides a vast substrate on which directed cellular activity can interact with the bone
mineral material [ 13 ]. This enables bone to be removed or laid down very rapidly in a
coordinated manner in response to biomechanical or physiological signals [ 93 ].
As stated previously, there is considerable heterogeneity in the distribution of
trabecular bone within skeletal sites [ 4 , 98 ] and between skeletal sites [ 4 ].
Therefore, where a sample is taken is extremely important as to its relevance to the
experimental questions that can be answered. In relation to studies of osteoporotic
bone it is necessary that the samples have a structure that is equivalent to the
structure where a fracture may have occurred or is at increased risk of occurring.