Development of an in vitro three dimensional loading-measurement system for long bone fixation under multiple loading...

Area of Science:

• Biomechanics
• Orthopedic Surgery
• Biomedical Engineering

Background:

• Accurate measurement of bone stiffness is critical for evaluating fracture healing and implant performance.
• Existing methods often introduce errors due to fixture stiffness, limiting in vivo motion simulation.
• Understanding unconstrained three-dimensional (3D) motion is essential for realistic biomechanical testing.

Purpose of the Study:

• To design and validate an in vitro loading-measurement system for equine radii.
• To mimic in vivo unconstrained 3D relative motion between long bone ends.
• To directly determine bone construct stiffness, free from fixture-related errors.

Main Methods:

• Utilized intact and instrumented equine cadaveric radii (osteotomized/ostectomized).
• Applied axial, torsion, and 4-point bending loads with fixtures allowing unconstrained 3D motion.
• Measured 3D relative motion using an infrared optical tracking system to determine stiffness.

Main Results:

• Measured intact bone stiffness closely matched theoretically predicted values.
• Observed 3D motion components were consistent with unconstrained loading of oblique fractures.
• Bone failure patterns were reproducible and aligned with theoretical predictions.

Conclusions:

• The developed 3D loading-measurement system effectively mimics clinical unconstrained motion.
• The system accurately applies uniform loads and measures interfragmentary motion for direct stiffness determination.
• It possesses the resolution to differentiate stiffness in intact versus instrumented equine radii.