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Minimizing errors during in vitro testing of multisegmental spine specimens: considerations for component selection
Philippe Gédet1, Paul A Thistlethwaite, Stephen J Ferguson
1MEM Research Center, Institute for Surgical Technology and Biomechanics, University of Bern Stauffacherstrasse, 78 CH-3014 Bern, Switzerland.
Journal of Biomechanics
|October 28, 2006
Summary
Apparatus design significantly impacts in vitro spine testing. Component friction and motion marker placement affect spinal kinetics and kinematic measurements, necessitating careful configuration for accurate results.
Area of Science:
- Biomechanics
- Spinal Engineering
- Orthopedic Biomechanics
Background:
- Standardized in vitro spine testing is crucial for biomechanical research.
- Apparatus-induced artifacts can compromise the validity of spinal testing protocols.
- Accurate kinematic and kinetic measurements are essential for understanding spinal mechanics.
Purpose of the Study:
- To investigate the influence of machine design, specifically component friction, on in vitro spinal kinetics.
- To evaluate the sensitivity of kinematic measurements to variations in motion capture marker placement.
- To identify methods for minimizing apparatus-induced artifacts in spinal testing.
Main Methods:
- A novel spinal loading simulator was developed to apply pure bending moments and compressive preload.
- Two linear slider types with different friction coefficients (caged ball bearings vs. high-precision roller bearings) were tested.
- Three optoelectronic marker cluster configurations were used to capture motion data simultaneously.
- A polymer tube with consistent bending stiffness simulated polysegmental lumbar spine behavior.
Main Results:
- Slider selection significantly influenced parasitic shear forces, with caged bearings inducing higher forces than roller bearings.
- Higher shear forces necessitated greater applied moments to achieve equivalent spinal rotations.
- Kinematic measurement accuracy varied by marker configuration, with larger marker spacing and parallel motion to the imaging plane yielding higher accuracy.
- Friction-induced shear forces created a linearly increasing moment along the specimen, compromising pure moment application, especially in polysegmental specimens.
Conclusions:
- Mechanical component choices in in vitro spine testing apparatuses markedly affect measured kinetics and kinematics.
- Low-magnitude parasitic shear forces from slider friction can invalidate pure moment application.
- Optimized marker configuration is critical for minimizing kinematic measurement errors due to spatial distribution and system bias.
