Microstructural elasticity and regional heterogeneity in human femoral bone of various ages examined by nano-indentation

The elastic modulus and hardness of secondary osteonal and interstitial bone was examined through the thickness of the cortex of human femora of various ages by nano-indentation. There was a clear difference between the stiffness and hardness of secondary osteonal and interstitial bone, the latter being stiffer (F-1,F-48 = 56.0, P<0.001). There were some differences between the bones of different subjects; however, there were no differences that could be reliably associated with the chronological age of the subject, or with differences in location through the thickness of the cortex (F-2,F-48 = 0.21, P = 0.810). Previous studies have been equivocal in relating changes in the macroscopic 'composite' material stiffness of bone to the age of the individual. By combining the results of the nano-tests with histological measures, we were able to produce a good relationship of the microstructural properties at the matrix level with the bending modulus of whole bone (R-2 := 0.88, P<0.001) and this improved further by taking into account the age of the individual (R-2 = 0.94, P<0.001). Our results suggest that using differences in the volumetric proportions of secondary osteons versus interstitial bone, and the properties of these elements/structures in isolation may be a more accurate method of determining differences in elastic modulus of whole bone between individuals of various ages. (C) 2002 Elsevier Science Ltd. All rights reserved.