Densitometry and imaging techniques are currently used in clinical settings to measure bone quantity and spatial
structure. Bone tissue mechanical properties are deemed a key component of bone strength, but their assessment
requires invasive procedures. Recently, Reference Point Indentation (RPI) has opened the possibility
of directly assessing the mechanical characteristics of cortical bone in living individuals, adding a new dimension
to the assessment of bone strength.
Two different approaches have been developed for measuring RPI parameters. Both are based on the principle
that the deeper a test probe penetrates into a cortical bone’s outer surface (at the anterior midtibia), the less resistant
is the bone tissue to a mechanical challenge. Impact microindentation (measured by Osteoprobe) results
are expressed as Bone Material Strength index (BMSi) units representing the ratio between the penetration of
the probe into the bone and its penetration in a methyl methacrylate reference phantom.
Impact microindentation was specifically developed for clinical studies and has been tested in several populations
where there are discrepancies between bone density and fracture propensity, such as type 2 diabetes, atypical
femoral fracture, stress fractures, glucocorticoid treatment, patients with osteopenia and fragility fractures,
and individuals infected with HIV, among others. Microindentation will complement, not replace, existing
bone analysis methods, particularly where bone mineral density does not fully explain fracture propensity. The
available evidence provides solid proof of concept; future studies will fully define the role of microindentation
for the assessment of bone health both in clinics and in research.


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