A Method to Estimate Cadaveric Femur Cortical Strains During Fracture Testing Using Digital Image Correlation

Area of Science:

• Biomechanics
• Materials Science
• Orthopedic Surgery

Background:

• Mechanical testing of cadaveric femurs is crucial for understanding bone strength.
• Accurate measurement of surface deformation is essential for validating computational models.
• Previous methods may lack the temporal resolution to capture fracture initiation dynamics.

Purpose of the Study:

• To describe a protocol for estimating cortical strain using digital image correlation (DIC).
• To apply DIC to high-speed video of cadaveric femoral surfaces during mechanical testing.
• To enable precise identification of fracture initiation and support validation of Quantitative Computed Tomography-based Finite Element Analysis (QCT/FEA) models.

Main Methods:

• A DIC protocol was developed utilizing high-speed video capture (up to 12,000 frames/s).
• The femoral surface was prepared with a high-contrast fiduciary marker pattern (white primer with speckled black paint).
• Image analysis involved tracking surface deformation in interrogation windows to compute temporal strain.

Main Results:

• The DIC method successfully estimated cortical strain from high-speed video of femoral mechanical testing.
• Surface strain data provided insights into the temporal progression of deformation.
• Key images capturing the fracture event were extracted for detailed analysis.

Conclusions:

• DIC is a viable optical method for measuring cortical strain on bone surfaces.
• This technique facilitates the identification of fracture initiation sites.
• The strain data can be used to validate biomechanical models of proximal femur fracture strength.