Knoop microhardness anisotropy of the ovine radius

The Knoop indenter has been used to characterise fully the Knoop microhardness (HK) anisotropy of compact bone. 2120 indentations were performed on mature ovine radii and a linear relationship was found between HK and the angle between the major diagonal of the indenter and the lamella boundaries (p 0.001). HK increased significantly with ash fraction (p 0.001), but decreased with atmospheric vapour pressure (p<0.05). A significant interaction was found between ash fraction and atmospheric vapour pressure (p<0.01). HK significantly varied with indentation position along the diaphysis and around the cortex (both p 0.001), however radial variation in HK was not statistically significant. The variation of ash fraction showed similar trends. These data show that HK varies similarly to Vickers microhardness, but in addition, can provide clear information on the anisotropy of Haversian bone without the need for excising many different indentation planes. A large number of indentations are required to obtain low type I and type II errors in the statistical analysis.