Summary
Objectives: The purpose of this study was to quantify the tissue level mechanical properties of
cortical bone of skeletally immature (~five-month-old) Beagle dogs and compare them
to data from mature dogs measured in a previous study.
Methods: Eight femoral cross sectional specimens (two bone sections / dog) were obtained from
four skeletally immature dogs. A pair of calcein bone labels were administered intravenously
to the dogs to mark sites of active mineralization prior to euthanasia. Prepared bone
specimens were placed in a nanoindenter specimen holder and the previously identified
calcein labelled osteons were located. Labelled (n = 128) and neighbouring unlabelled
(n = 127) osteons in skeletally immature femurs were examined by instrumented indentation
testing. Indents were made to a depth of 500 nm at a loading rate of 10 nm/s. Indentation
modulus (IM) and hardness (H) were obtained.
Results: The overall IM of the cortical bone in the skeletally mature groups was significantly
greater than in the immature group (p = 0.0011), however overall H was not significantly
different. The differences between the groups in IM were significant for the unlabelled
osteons (p = 0.001), but not for the labelled osteons (p = 0.56).
Conclusion: There are differences in the IM of unlabelled osteons in skeletally immature and
mature groups of Beagle dogs. In contrast to whole bone mechanical tests, where there
are obvious differences between growing and mature bones, there are only small differences
in the micro-mechanical properties.
Keywords
Bone remodelling - Osteon - Nanoindentation - Age - Dog