Age-related influence of bone remodeling on local tissue properties of human cortical bone
With aging, cortical bone experiences deterioration in its mechanical competence, thus resulting in increased bone fragility. Studies have shown that the mechanical properties of cortical bone are significantly dependent on the quality and spatial arrangement of its constituents. Age-related changes have been observed in the mineral and collagen as well as the local microstructural properties of bone. Further, age-related changes in the material components and tissue architecture correlate significantly with decreases in bulk bone post-yield properties. Evidence indicates that these changes may be due in part to the bone remodeling process, which may alter material composition and spatial arrangement in a manner detrimental to the mechanical properties of the tissue.
This study was performed to determine if the bone remodeling process has an age-related effect on the micromechanical and compositional properties of cortical bone, and whether or not such changes are correlated with decreased post-yield properties in newly remodeled tissue. To investigate this issue, the micromechanical properties of secondary osteons (newly remodeled tissue) and interstitial tissue (biologically older tissue) were assessed using a microcompression test protocol. The compositional properties of the mineral and collagen components of osteonal and interstitial tissues were assessed using High Performance Liquid Chromatography, X-ray Diffraction analysis, and Fourier Transform Infrared Microscopy. Additionally, morphometric analysis was performed to assess age-related changes in the proportion of newly remodeled tissue comprising cortical bone.
The results of the micromechanical tests revealed secondary osteons to have significantly higher post-yield properties compared to interstitial tissues, with no age-related changes observed in the mechanical properties of either tissue. Additionally, compositional analyses showed that the bone remodeling process did not result in changes to the composition of the mineral and collagen that were correlated with reduced post-yield properties. However, differences were observed in the composition of the mineral and collagen that reflect tissue aging processes as secondary osteons age into interstitial tissues. Additionally, age-related decreases in the proportion of newly remodeled tissue comprising cortical bone were observed. The bone remodeling process does not appear to result in age-related changes in the composition and post-yield properties of newly remodeled tissue. Rather, it appears that processes associated with tissue aging contribute to the decline in post-yield properties of bone as secondary osteons age to eventually become interstitial tissues.