Bone Abstracts

A micro-indentation technology potentially allows in vivo investigation of intrinsic bone tissue quality, a determinant of bone fragility. Thus the signification of the parameters investigated is still unclear.

Since protein malnutrition affects bone material level properties – geometry and strength – rats were fed a normal or an isocaloric low-protein diet. Both femurs were collected and measurements of geometry using micro CT, material level properties using nanoindentation, micro indentation and bone mechanical properties using a three points bending test were determined. To better understand the clinical signification of micro-indentation values, parameters of micro-indentation were correlated with parameters of bone strength and bone material level properties. Student’s paired t-test for testing differences and regressions analysis were performed.

Protein malnutrition affects bone strength decreasing significantly maximal load, stiffness, energy, and plastic energy. Determinants of bone strength were also significantly altered: like geometry (decreased cortical thickness) and bone material level properties (decreased modulus, hardness and working energy). Parameters of micro-indentation were significantly affected on the same direction; IDI was significantly increased and unloading stiffness and average energy dissipated were significantly decreased. The values of micro-indentation were systematically correlated with the other measurements. The best significant correlations were observed between indentation distances and hardness (nanoindentation) and between average energy dissipated and plastic energy (biomechanics); for all the significant correlation r² are ranged between 0.5 and 0.327.

These observations indicate that parameters of microindentation predict values of material level properties measured by nano-indentation and biomechanics. These observations open large possibilities to investigate in vivo material level properties.