Although the mechanical properties of human bone and many of the tissue characteristics upon which they depend have been investigated in detail, the relationship of ageing to these variables is not clear. In this study, an ageing population of human femoral tissue was examined <i>in vitro</i> in order to characterize the mechanical changes and determine the relative significance of the many tissue variables. Cortical and cancellous bone specimens were machined from 47 human femora ranging in age from 20 to 102 years. The cortical specimens underwent uni-axial tensile testing to failure after which the porosity (volume fraction), mineralization and microstructure were determined. Linear regression analysis demonstrated a decrease in ultimate stress (strength), ultimate strain and fracture energy absorption by respectively 5, 9 and 12% per decade while elastic modulus was unaffected. Bone porosity and microstructure changed significantly with age while mineralization was not affected. Both bivariate and multivariate analyses demonstrated the significance of age-related changes in porosity (volume fraction) to the decline in mechanical competence with porosity accounting for 76% of the reduction in tensile strength. Microstructural changes were highly correlated to porosity and had little independent effect. The cancellous specimens were tested in compression to failure in the weight-bearing axis. After determination of apparent density, standard histomorphometric techniques were used to characterize the trabecular architecture. Compressive strength decreased by 8.5% per decade. Apparent density (similarly volume fraction) accounted for 92% of the variance in strength seen with ageing. Architectural changes were highly correlated to apparent density and provided little additional explanatory power to the models. In conclusion, in cortical and cancellous bone, the quantitative changes occurring in ageing bone tissue, rather than the qualitative changes, have the greatest influence on the mechanical competence of bone. Other tissue variables not examined, perhaps collagen structure, are necessary to explain the remaining changes in cortical bone strength. The results indicate that the mechanical properties of cortical and cancellous bone can be estimated <i>in vivo</i> by non-invasive bone density determinations, thereby allowing the prediction of fracture risks and a further understanding of fracture mechanics in the elderly. The data also provide information relevant to the design of fracture and endoprosthetic implants whose clinical success is dependent on the implant-bone interface.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:666097 |
| Date | January 1993 |
| Creators | McCalden, R. W. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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