Biomedical Engineering Reference
In-Depth Information
Figure 6.11
Cross-sectional view of the
head of a femur.
CT image) is shown in
Figure 6.12 for a healthy state (a) and osteoporotic
12)
state (b). It can be seen that the
structure is open and made up of a network of beams or rods (so-called trabeculae).
In the case of the diseased structure, a much higher porosity characterized by much
bigger holes and spaces compared to the healthy bone can be observed. This loss
of density or mass may result in the fracture of the bone even for normal, that is,
every day, loads. The density of the trabeculae was investigated by Galante
et al
. [32]
based on 63 specimens, and a mean value of 1820 kgm
−
3
was found. This value
is exactly in the range of compact bone and this is the reason why some authors
[31, 33] assign the physical properties of the compact bone to the beams or rods of
trabecular bone in the scope of modeling approaches.
The structure of trabecular bone and its relation to mechanical properties have
several important applications in biomedical engineering. The loss of the normal
density of bone (osteoporosis) results in a fragile bone. The knowledge about the
fracture strength as a function of the bone density can help predict the risk of
fracture and recommend appropriate treatments and behavioral rules. The actual
density of the bone can be determined by a safe and painless bone mineral density
(BMD) test
13)
.
A typical structure of a vertebral cancellous bone (
µ
12)
Osteoporosis, or porous bone, is a disease
characterized by low bone mass and
structural deterioration of bone tissue,
leading to bone fragility and an increased
susceptibility to fractures, especially of the
hip, spine, and wrist, although any bone
can be affected.
13)
A routine X-ray can reveal osteoporosis of
the bone, which appears much thinner and
lighter than normal bones. Unfortunately,
by the time X-rays can detect osteoporosis,
at least 30% of the bone has already
been lost. Major medical organizations
are recommending a dual energy X-ray
absorptiometry (DXA, formerly known as
DEXA) scan for diagnosing osteoporosis.
