In vitro spine testing using a robot-based testing system: comparison of displacement control and "hybrid control".

The two leading control algorithms for in-vitro spine biomechanical testing-"load control" and "displacement control"-are limited in their lack of adaptation to changes in the load-displacement response of a spine specimen-pointing to the need for sufficiently sophisticated control algorithms that are able to govern the application of loads/motions to a spine specimen in a more realistic, adaptive manner. A robotics-based spine testing system was programmed with a novel hybrid control algorithm combining "load control" and "displacement control" into a single, robust algorithm. Prior to in-vitro cadaveric testing, preliminary testing of the new algorithm was performed using a rigid-body-spring model with known structural properties. The present study also offers a direct comparison between "hybrid control" and "displacement control". The hybrid control algorithm enabled the robotics-based spine testing system to apply pure moments to an FSU (in flexion/extension, lateral bending, or axial rotation) in an unconstrained manner through active control of secondary translational/rotational degrees-of-freedom-successfully minimizing coupled forces/moments. The characteristic nonlinear S-shaped curves of the primary moment-rotation responses were consistent with previous reports of the FSU having a region of low stiffness (neutral zone) bounded by regions of increasing stiffness (elastic zone). Direct comparison of "displacement control" and "hybrid control" showed that hybrid control was able to actively minimize off-axis forces and resulted in larger neutral zone and range of motion.

[1]  S. Mercer,et al.  Biomechanics of the cervical spine. I: Normal kinematics. , 2000, Clinical biomechanics.

[2]  L. Claes,et al.  Testing criteria for spinal implants: recommendations for the standardization of in vitro stability testing of spinal implants , 1998, European Spine Journal.

[3]  G. Kawchuk,et al.  Identification of Spinal Tissues Loaded by Manual Therapy: A Robot-Based Serial Dissection Technique Applied in Porcine Motion Segments , 2010, Spine.

[4]  Christopher D. Harner,et al.  In-situ forces in the human posterior cruciate ligament in response to posterior tibial loading , 1996, Annals of Biomedical Engineering.

[5]  M M Panjabi,et al.  Biomechanical Evaluation of Spinal Fixation Devices: I. A Conceptual Framework , 1988, Spine.

[6]  A. Patwardhan,et al.  Load-Carrying Capacity of the Human Cervical Spine in Compression Is Increased Under a Follower Load , 2000, Spine.

[7]  I. Kingma,et al.  Quantifying intervertebral disc mechanics: a new definition of the neutral zone , 2011, BMC musculoskeletal disorders.

[8]  John J. Craig,et al.  Hybrid position/force control of manipulators , 1981 .

[9]  Stephen J Ferguson,et al.  Minimizing errors during in vitro testing of multisegmental spine specimens: considerations for component selection and kinematic measurement. , 2007, Journal of biomechanics.

[10]  R Vanderby,et al.  A multi-degree of freedom system for biomechanical testing. , 1994, Journal of biomechanical engineering.

[11]  A. Patwardhan,et al.  A follower load increases the load-carrying capacity of the lumbar spine in compression. , 1999, Spine.

[12]  S Arai,et al.  The use of robotics technology to study human joint kinematics: a new methodology. , 1993, Journal of biomechanical engineering.

[13]  Hiromichi Fujie,et al.  Determination of thein situ forces and force distribution within the human anterior cruciate ligament , 1995, Annals of Biomedical Engineering.

[14]  A. Patwardhan,et al.  Test protocols for evaluation of spinal implants. , 2006, The Journal of bone and joint surgery. American volume.

[15]  Thomas R. Oxland,et al.  Constrained Testing Conditions Affect the Axial Rotation Response of Lumbar Functional Spinal Units , 1998, Spine.

[16]  Adams Ma,et al.  The relevance of torsion to the mechanical derangement of the lumbar spine. , 1981 .

[17]  Manohar M. Panjabi,et al.  A Method to Simulate In Vivo Cervical Spine Kinematics Using In Vitro Compressive Preload , 2002, Spine.

[18]  A. U. Daniels,et al.  Distraction and compression loads enhance spine torsional stiffness. , 1994, Journal of biomechanics.

[19]  G A Livesay,et al.  A combined robotic/universal force sensor approach to determine in situ forces of knee ligaments. , 1996, Journal of biomechanics.

[20]  W C Hayes,et al.  Variation of lumbar spine stiffness with load. , 1987, Journal of biomechanical engineering.

[21]  R. Brand,et al.  Three-dimensional flexibility and stiffness properties of the human thoracic spine. , 1976, Journal of biomechanics.

[22]  Kevin T Foley,et al.  An improved biomechanical testing protocol for evaluating spinal arthroplasty and motion preservation devices in a multilevel human cadaveric cervical model. , 2004, Neurosurgical focus.

[23]  James P Dickey,et al.  Biomechanical Role of Lumbar Spine Ligaments in Flexion and Extension: Determination Using a Parallel Linkage Robot and a Porcine Model , 2004, Spine.

[24]  Justin K Scheer,et al.  Inter-laboratory variability in in vitro spinal segment flexibility testing. , 2011, Journal of biomechanics.

[25]  L. Claes,et al.  The relation between the instantaneous center of rotation and facet joint forces - A finite element analysis. , 2008, Clinical biomechanics.

[26]  D G Wilder,et al.  Biomechanical testing of the spine. Load-controlled versus displacement-controlled analysis. , 1995, Spine.

[27]  Manohar M Panjabi,et al.  Hybrid multidirectional test method to evaluate spinal adjacent-level effects. , 2007, Clinical biomechanics.

[28]  R. Brand,et al.  Mechanical properties of the human thoracic spine as shown by three-dimensional load-displacement curves. , 1976, The Journal of bone and joint surgery. American volume.