Measurement of cancellous bone strain during mechanical tests using a new extensometer device

Area of Science:

• Biomechanics
• Materials Science
• Biomedical Engineering

Background:

• Accurate measurement of bone strain is crucial for understanding bone mechanics and developing effective finite element (FE) models.
• Traditional strain measurement methods can be affected by boundary conditions and specimen end failures, leading to inaccuracies.

Purpose of the Study:

• To develop and validate a novel device for measuring mid-substance strain in bone during uniaxial compression.
• To assess the device's suitability for subsequent FE modeling by ensuring well-defined boundary conditions.

Main Methods:

• Development of an extensometer device utilizing dual instrumented cantilever arms to measure tip-to-tip deflection.
• Comparison of the extensometer device with two standard platen-based strain measurement methods.
• Testing with rubber specimens and canine cancellous bone cores under uniaxial compression.

Main Results:

• The extensometer device demonstrated high linearity (r(2)>0.99) with tip deflection and high accuracy (4.8 microm) and precision (2-5 microm).
• A trend of decreasing apparent modulus with decreasing strain rate was observed.
• Correlation between the extensometer and standard methods was moderate (r(2)=0.55).

Conclusions:

• The developed extensometer accurately measures mid-substance strain, mitigating issues from end failures and specimen non-linearities.
• The device's output and the resulting uniaxial testing conditions are well-suited for finite element analysis.
• This technique enhances the reliability of biomechanical testing and computational modeling of bone.