Variability in reference point microindentation and recommendations for testing cortical bone: maximum load, sample...

Area of Science:

• Biomechanical Engineering
• Materials Science
• Orthopedic Research

Background:

• Reference Point Indentation (RPI) is a promising technique for assessing bone fracture risk and mechanical properties.
• Standardized testing protocols are lacking, hindering consistent application of RPI in clinical and laboratory settings.

Purpose of the Study:

• To investigate the influence of key testing parameters on the Indentation Distance Increase (IDI) measured by RPI.
• To provide evidence-based recommendations for optimizing RPI test protocols for bone analysis.

Main Methods:

• The RPI tool was used to indent bovine and human bone samples (femora, femoral heads, and necks).
• Five parameters were evaluated: maximum load, sample orientation, mode of use (freehand vs. supported), surface preparation, and measurement spacing.
• The Indentation Distance Increase (IDI) was analyzed in relation to each parameter.

Main Results:

• IDI is significantly affected by maximum load, mode of use, and surface preparation, necessitating consistency in these factors.
• Supported device use and bone surface preparation (periosteum removal, machining) reduce the coefficient of variation.
• A sample thickness at least 10 times the indentation depth is recommended for representative measurements.
• Measurement spacing did not significantly influence IDI, with 500 µm being adequate.

Conclusions:

• Optimizing RPI parameters, including consistent load, supported use, and appropriate surface preparation, enhances measurement reliability.
• Adhering to recommended protocols minimizes variability and improves the accuracy of bone mechanical characterization using RPI.
• These findings support the broader clinical and laboratory application of RPI for bone assessment.