Biomedical Engineering Reference
In-Depth Information
resorption [3,4]. Retraction exposes the underlining osteoid to proteolytic
enzymes of osteoblasts [5] and, further, to osteoclastic resorption. The fully
mineralized bone matrix is exposed only after retraction of bone lining
cells and removal of organic osteoid. Therefore, it can be assumed that bone
lining cells are remarkable in vivo regulators of osteoclastic bone resorption.
The exact mechanisms of this cascade are not yet known, but it seems that
soluble factors as well as cell-cell contacts have a role in the activation of
osteoclasts [6,7].
1.5 Osteoporosis
According to Osteoporosis Australia (http://www.osteoporosis.org.au),
osteoporosis is a condition in which the bones become fragile and brittle,
characterized by a decrease in the density of bone and leading to a higher
risk of fractures than in normal bones. Osteoporosis leads to an abnormally
porous bone that is compressible, like a sponge. It occurs when bones lose
minerals, such as calcium, more quickly than the body can replace them,
leading to a loss of bone mass or density. As a result, bones become thinner
and less dense (see Figure 1.6), so even a minor bump or accident can cause
serious fractures.
Osteoporosis is in fact a bone disease where bone mass decreases over time. Its
manifestations are subdivided into postmenopausal and senile forms [8,9]. The
disease process results from a net increase of bone resorption over deposition.
Normal bone matrix
Osteoporosis
FIGURE 1.6
Comparison between normal bone matrix and osteoporosis in the human hip. (Picture from
http://www.halanmediacorp.com/wp-content/uploads/2009/11/osteoporosis.jpg; accessed
Ma rc h 2011.)
