Machine vision photogrammetry: a technique for measurement of microstructural strain in cortical bone

Area of Science:

• Biomechanics
• Materials Science
• Orthopedics

Background:

• Cortical bone damage, fracture, and remodeling are critical areas in bone research.
• Traditional methods lack the resolution to measure microstructural deformations and strains in cortical bone.
• Understanding these micro-level changes is key to comprehending bone's mechanical behavior.

Purpose of the Study:

• To develop and validate a novel technique for measuring microstructural strain fields in cortical bone.
• To assess the accuracy and limitations of the developed digital stereoimaging method.
• To investigate localized strains around microstructural features like cracks and osteocyte lacunae.

Main Methods:

• Digital stereoimaging technique applied to cortical bone specimens.
• Comparison of images acquired at two distinct stress states to measure surface displacements and strains.
• System accuracy evaluated using an undeformed image set with known pixel translation.
• Analysis of strain errors based on sub-image parameters and applied displacement.

Main Results:

• The digital stereoimaging technique accurately measures microstructural displacements and strains.
• Increased correlation sub-image parameter improved displacement measurement accuracy.
• Strain calculation errors ranged from 39 to 564 microstrain.
• Significant localized strains (up to 30,000 microstrain) observed at microcrack tips and near osteocyte lacunae.

Conclusions:

• The digital stereoimaging technique provides a viable method for characterizing microstructural strain in cortical bone.
• This technique offers a new tool for investigating bone strength, fracture mechanisms, and mechanotransduction.
• Further application of this method is expected to deepen the understanding of bone's response to mechanical stimuli.