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Aging bone quality found to be a factor of fracture risk
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Bone quality is just as important as bone quantity in regards to fracture vulnerability in aging bones, according to research from the U.S. Department of Energy’s Lawrence Berkeley National Laboratory.
The paper was published in the Proceedings of the National Academy of Science. Senior paper author Robert Ritchie, PhD, ScD, and colleagues found that the ability of an aging bone to endure fracture is lessened over time as the mechanical properties of human cortical bone become compromised.
“We found that these changes degrade both the intrinsic and extrinsic toughness of bone,” Ritchie, a Berkeley Lab materials scientist, stated in a release from the laboratory.
Analyzing bone samples of patients between the ages of 34 years and 99 years, Ritchie and the researchers used in situ small-angle X-ray scattering and wide-angle X-ray diffraction to produce their results. At micrometer levels, X-ray CT and in situ fracture toughness measurements were used.
As a composite of collagen and hydroxyapatite, human cortical bone derives its stiffness, strength and toughness at the molecular level from the characteristic structure at the nanoscale to the osteonal structures at near-millimeter levels.
“Mechanisms that strengthen and toughen bone can be identified at most of these structural length scales and can be usefully classified, as in many materials, in terms of intrinsic toughening mechanisms at small length scales, promoting non-brittle behavior, and extrinsic toughening mechanisms at larger length scales acting to limit the growth of cracks,” Ritchie stated in the release. “However, with biological aging, the ability of these mechanisms to resist fracture deteriorates leading to a reduction in bone strength and fracture toughness.”
“We found that biological aging increases non-enzymatic cross-linking between the collagen molecules, which suppresses plasticity at nanoscale dimensions, meaning that collagen fibrils can no longer slide with respect to one another as a way to absorb energy from an impact,” he added. “We also found that biological aging increases osteonal density, which limits the potency of crack-bridging mechanisms at micrometer scales.”
Reference:
- Zimmerman EA, Schaible E, Bale H, et al. Age-related changes in the plasticity and toughness of human cortical bone at multiple length scales. Proc Natl Acad Sci USA. 2011. doi: 10.1073/pnas.1107966108.
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