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The equivalence of multi-axis spine systems: Recommended stiffness limits using a standardized testing protocol
Timothy P Holsgrove1, Dhara B Amin2, Sonia Ramos Pascual3
1Department of Engineering, College of Engineering, Mathematics & Physical Sciences, University of Exeter, Exeter, UK; Centre for Orthopaedic Biomechanics, Department of Mechanical Engineering, University of Bath, Bath, UK.
Journal of Biomechanics
|September 28, 2017
Summary
Standardizing multi-axis spine testing protocols ensures comparable results. This study developed a protocol and identified stiffness and phase angle limits for comparing spine testing systems.
Area of Science:
- Biomechanics
- Spine Engineering
- Orthopedic Research
Background:
- Multi-axis spine testing complexity hinders result comparison across studies.
- Lack of standardized protocols limits the reliability of in vitro spine research.
Purpose of the Study:
- Develop and implement a standardized testing protocol for six-axis spine systems.
- Compare the performance of three different spine testing systems.
- Establish stiffness and phase angle limits for inter-system comparison.
Main Methods:
- Utilized standardized synthetic lumbar specimens (n=5) with embedded springs.
- Applied pure moments (flexion-extension, lateral bending, axial rotation) using sine and triangle waves (8Nm, 0.1Hz).
- Measured stiffness, phase angle, and R²; calculated tracking error to minimize non-principal loads.
Main Results:
- All three systems showed similar stiffness, with minor (<14%) significant differences in 4 of 12 tests.
- Greater variability in phase angle was observed, with significant differences in 10 of 12 tests.
- Stiffness and phase angle limits were derived from 95% confidence intervals across all systems.
Conclusions:
- The developed protocol and specimen enable standardized in vitro spine testing.
- Recommendations for stiffness and phase angle limits facilitate comparison between different spine testing systems.
- Enhances the comparability and reliability of multi-axis spine testing research.
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