TY - JOUR
T1 - The equivalence of multi-axis spine systems: Recommended stiffness limits using a standardized testing protocol
AU - Holsgrove, Timothy
AU - Amin, Dhara
AU - Ramos Pascual, Sonia
AU - Ding, Boyin
AU - Welch, William
AU - Gheduzzi, Sabrina
AU - Miles, Anthony
AU - Winkelstein, Beth
AU - Costi, John
PY - 2018/3/21
Y1 - 2018/3/21
N2 - The complexity of multi-axis spine testing often makes it challenging to compare results from different studies. The aim of this work was to develop and implement a standardized testing protocol across three six-axis spine systems, compare them, and provide stiffness and phase angle limits against which other test systems can be compared. Standardized synthetic lumbar specimens (n = 5), comprising three springs embedded in polymer at each end, were tested on each system using pure moments in flexion–extension, lateral bending, and axial rotation. Tests were performed using sine and triangle waves with an amplitude of 8 Nm, a frequency of 0.1 Hz, and with axial preloads of 0 and 500 N. The stiffness, phase angle, and R 2 value of the moment against rotation in the principal axis were calculated at the center of each specimen. The tracking error was adopted as a measure of each test system to minimize non-principal loads, defined as the root mean squared difference between actual and target loads. All three test systems demonstrated similar stiffnesses, with small (<14%) but significant differences in 4 of 12 tests. More variability was observed in the phase angle between the principal axis moment and rotation, with significant differences in 10 of 12 tests. Stiffness and phase angle limits were calculated based on the 95% confidence intervals from all three systems. These recommendations can be used with the standard specimen and testing protocol by other research institutions to ensure equivalence of different spine systems, increasing the ability to compare in vitro spine studies.
AB - The complexity of multi-axis spine testing often makes it challenging to compare results from different studies. The aim of this work was to develop and implement a standardized testing protocol across three six-axis spine systems, compare them, and provide stiffness and phase angle limits against which other test systems can be compared. Standardized synthetic lumbar specimens (n = 5), comprising three springs embedded in polymer at each end, were tested on each system using pure moments in flexion–extension, lateral bending, and axial rotation. Tests were performed using sine and triangle waves with an amplitude of 8 Nm, a frequency of 0.1 Hz, and with axial preloads of 0 and 500 N. The stiffness, phase angle, and R 2 value of the moment against rotation in the principal axis were calculated at the center of each specimen. The tracking error was adopted as a measure of each test system to minimize non-principal loads, defined as the root mean squared difference between actual and target loads. All three test systems demonstrated similar stiffnesses, with small (<14%) but significant differences in 4 of 12 tests. More variability was observed in the phase angle between the principal axis moment and rotation, with significant differences in 10 of 12 tests. Stiffness and phase angle limits were calculated based on the 95% confidence intervals from all three systems. These recommendations can be used with the standard specimen and testing protocol by other research institutions to ensure equivalence of different spine systems, increasing the ability to compare in vitro spine studies.
KW - Multi-axis
KW - Six-axis
KW - Spine simulator
KW - Spine testing
KW - Test machines
KW - Test systems
UR - http://www.scopus.com/inward/record.url?scp=85029760242&partnerID=8YFLogxK
U2 - 10.1016/j.jbiomech.2017.09.010
DO - 10.1016/j.jbiomech.2017.09.010
M3 - Article
SN - 0021-9290
VL - 70
SP - 59
EP - 66
JO - Journal of Biomechanics
JF - Journal of Biomechanics
ER -