Biomedical Engineering Reference
In-Depth Information
A
B
caudal
-3000
-2000
-1000
0
1000
2000
Compressive
surface
Neutral axis
Tensile surface
C
caudal
Bone geometry
at baseline
Loading-induced
adaptation
2.11
The adaptive response of bone to mechanical loading is site-
specific such that only those regions within a bone that experience
sufficient microstrain will adapt. (A) Schematic diagram of the rodent
ulna axial compression model. The distal forelimb is fixed between
upper and lower cups. When force is applied to one of the cups, the
ulna is caused to bow laterally. (B) The bending of the ulna under
axial compression generates medial surface compression and lateral
surface tension at the midshaft. There is no strain along the axis
through which the bone is bending (neutral axis). (C) Loading of rat
ulnas for 16 weeks using the axial compression model causes new
bone to be formed on surfaces of high strain (medial and lateral
surfaces). There is minimal new bone formation near the neutral axis
(caudal and cranial surfaces) where there is the least microstrain
during loading.
needed most, in the direction of loading, while not overtly increasing the
overall weight of the bone. This means for a small increase in bone mineral,
much larger increases in bone strength can be generated. The implication of
the site-specific response of bone to mechanical stimuli is that loading needs
to be directed toward the bones and sites where promotion of osteogenesis
is desired. To achieve this and induce the most functional adaptation, the
loading should be in the same direction as the bone is loaded in function.
2.5.4 Bone response to disuse
skeletal disuse results in profound bone loss. In growing bones the effect
of disuse is most apparent at the periosteal surfaces of long bones, where
normal appositional growth is suppressed. This results in bones of smaller
cross-section. after skeletal maturity is achieved, disuse causes frank bone
loss involving accelerated remodeling and bone resorption, with loss occurring
mainly at endosteal and trabecular surfaces of long bones. skeletal disuse
results from a number of conditions, including prolonged bed rest,
164
space
