Review articleThe structural and biomechanical basis of the gain and loss of bone strength in women and men
Section snippets
Matching materials and structures for functions
One of the purposes of bone is survival of the host. Bone is a lever. Nature selects materials and structures with properties that meet the contradictory needs of strength for load bearing and movement, yet lightness for speed. Bulk is one means of achieving strength but bulk takes time to grow, is costly to maintain and difficult to move. Stiffness is needed for movement against gravity and static loading while flexibility is needed for energy absorption [2]. If bones were flaccid rather than
Growth—fashioning a bigger, not denser, skeleton
As long bones grow in length and diameter, the mass of bone inside the periosteum increases in proportion to the enlarging volume of the whole bone. This mass of bone is fashioned into a cortex of a given thickness. Volumetric apparent BMD of long bones like the radius or femur is independent of age and no different in boys and girls ages 7 to 9 years. In young adulthood, men and women have the same volumetric apparent BMD but men have bigger bones than women do. Thus, the strength of the
Aging and fragility—the failure of bone remodeling and perhaps modeling
During aging, periosteal apposition continues as it did during growth but more slowly. Bone remodeling occurs at discrete sites or BMUs on the trabecular, endocortical and intracortical components of the endosteal surface of the skeleton. Remodeling during growth deposits a small positive BMU balance increasing trabecular thickness. The reason remodeling is so rapid is to facilitate bone growth as each remodeling event deposits only a small amount of bone. Although the data are limited, it is
Summary
Structural failure (fracture) is a problem in biomechanics. Its solution resides, in part, in identifying the material and structural properties of bone that determine its mechanical resistance to structural failure. Bones must be stiff so that they do not bend when loaded, otherwise movement against gravity would not be possible. However, bones must also be flexible, otherwise their ability to absorb energy by elastic and plastic deformation will decrease and the energy imparted will be
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