Biomedical Engineering Reference
In-Depth Information
adaptive response of bone to loading should be proportional to the strain
rate. For lower loading frequencies within the physiological range, experi-
mental evidence shows this to be true. The data also suggest that activi-
ties that involve higher loading rates are also effective for increasing bone
formation, even if the duration of the activity is short.
5.2.3 Bone Mechanostat
As described in Wikipedia, the bone Mechanostat is a model describing
bone growth and bone loss. It was promoted by Harold Frost and described
extensively in the
Utah Paradigm of Skeletal Physiology
in the 1960s [37]. The
bone Mechanostat is a refinement of the law described by Julius Wolff [5]. To
explain the strain-dependent behavior of bone tissues, Frost [38] proposed
a “mechanostat” hypothesis describing bone modeling and remodeling,
which was updated twice [37,39]. In his hypothetical model, mechanobiologic
negative feedback mechanisms would work under the control of a subject's
mechanical usage. In doing so they would adjust skeletal architecture in a
way that tended to prevent mechanical usage from causing structural failure
of skeletal tissues and organs.
It was proposed that mechanically dedicated message traffic would domi-
nate the effects of most nonmechanical agents. Most (not all) nonmechanical
agents would have permissive roles in affecting skeletal architecture and
health. They could optimize or impair mechanical usage effects but could
not replace or duplicate them. The mechanism of this process is shown in
Figure 5.1, where
MU
denotes the skeleton's usual mechanical usage. Most
systemic (
S
) agents reach the skeleton from the blood. Local (
L
) agents include
local molecular biological agents, related phenomena, and local innervations.
MFL
indicates a mechanical feedback loop; here, each one is for modeling
(
MFLm
) and remodeling (
MFLr
).
The updated Mechanostat indicated that signals were dependent on strains.
Aided by sense systems that detect and process the signals, threshold ranges
of the strain-dependent signals (the
MESm
for modeling and the
MESr
for disuse-mode remodeling) help to switch the two whole-bone-strength
MFL
{
modeling highway
}
((
Modeling drift
))
MU
bone
signal(s)
[Nonmechanical Agents:L S]
{
remodeling highway
}
((
Remodeling BMU
))
MFLr
FIGURE 5.1
Mechanobiologic negative feedback mechanisms [35].
