Abstract
Background Context
Complex testing protocols are required to fully understand the biomechanics of the spine. There remains limited data concerning the mechanical properties of spinal specimens under dynamic loading conditions in six axes.
Purpose
To provide new data on the mechanical properties of functional spinal unit (FSU), and isolated disc (ISD) spinal specimens in six degrees of freedom.
Study Design/Setting
Dynamic, six-axis stiffness matrix testing of porcine lumbar spinal specimens.
Methods
The stiffness matrix testing of lumbar porcine FSU (n=6) and ISD (n=6) specimens was completed in a custom six-axis spine simulator using triangle wave cycles at a frequency of 0.1 Hz. Specimens were first tested without an axial preload, and with an axial preload of 500 N with equilibration times of both 30 and 60 minutes. The study was supported through an institutional grant, and the authors are not aware of any conflicts of interest related to this research.
Results
The stiffness matrices were not symmetrical about the principal stiffness terms. The facets increased all the principal stiffness terms with the exception of axial compression-extension. Significant differences were detected in 15 stiffness terms due to the application of an axial preload in the ISD specimens, including an increase in all principal stiffness terms. There were limited differences in stiffness due to an equilibration time of 30 and 60 minutes.
Conclusions
The assumption of stiffness matrix symmetry used in many previous studies is not valid. The biomechanical testing of spinal specimens should be completed in 6 degrees of freedom, at physiological loading rates, and incorporate the application of an axial preload. The present study has provided new data on the mechanical properties of spinal specimens, and demonstrates that the dynamic stiffness matrix method provides a means to more fully understand the natural spine, and quantitatively assess spinal instrumentation.
Complex testing protocols are required to fully understand the biomechanics of the spine. There remains limited data concerning the mechanical properties of spinal specimens under dynamic loading conditions in six axes.
Purpose
To provide new data on the mechanical properties of functional spinal unit (FSU), and isolated disc (ISD) spinal specimens in six degrees of freedom.
Study Design/Setting
Dynamic, six-axis stiffness matrix testing of porcine lumbar spinal specimens.
Methods
The stiffness matrix testing of lumbar porcine FSU (n=6) and ISD (n=6) specimens was completed in a custom six-axis spine simulator using triangle wave cycles at a frequency of 0.1 Hz. Specimens were first tested without an axial preload, and with an axial preload of 500 N with equilibration times of both 30 and 60 minutes. The study was supported through an institutional grant, and the authors are not aware of any conflicts of interest related to this research.
Results
The stiffness matrices were not symmetrical about the principal stiffness terms. The facets increased all the principal stiffness terms with the exception of axial compression-extension. Significant differences were detected in 15 stiffness terms due to the application of an axial preload in the ISD specimens, including an increase in all principal stiffness terms. There were limited differences in stiffness due to an equilibration time of 30 and 60 minutes.
Conclusions
The assumption of stiffness matrix symmetry used in many previous studies is not valid. The biomechanical testing of spinal specimens should be completed in 6 degrees of freedom, at physiological loading rates, and incorporate the application of an axial preload. The present study has provided new data on the mechanical properties of spinal specimens, and demonstrates that the dynamic stiffness matrix method provides a means to more fully understand the natural spine, and quantitatively assess spinal instrumentation.
Original language | English |
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Pages (from-to) | 176-184 |
Number of pages | 9 |
Journal | The Spine Journal |
Volume | 15 |
Issue number | 1 |
Early online date | 16 Sept 2014 |
DOIs | |
Publication status | Published - 1 Jan 2015 |
Keywords
- spine biomechanics
- dynamic
- stiffness matrix
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Sabina Gheduzzi
- Department of Mechanical Engineering - Senior Lecturer
- Centre for Bioengineering & Biomedical Technologies (CBio)
- Centre for Integrated Materials, Processes & Structures (IMPS)
Person: Research & Teaching, Core staff, Affiliate staff
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Richie Gill
- Department of Mechanical Engineering - Professor
- Centre for Therapeutic Innovation
- Centre for Bioengineering & Biomedical Technologies (CBio)
- Bath Institute for the Augmented Human
Person: Research & Teaching, Core staff
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Tony Miles
- Department of Mechanical Engineering - Professor Emeritus
Person: Honorary / Visiting Staff