New methods to study lumbar spine biomechanics: Delineation of in vitro load-displacement characteristics by using a robotic/UFS testing system with hybrid control

Delineation of the load-displacement characteristics of osteoligamentous spinal specimens has become fundamental to the investigation of the biomechanics of the spine. In vitro biomechanical testing of the spine requires not only highly specialized testing machines and devices for measuring loads and displacements, but also implementation of a control method to govern the application of loads and displacements to a specimen. Traditionally, in vitro load-displacement characteristics of the spine have been obtained through biomechanical tests that are performed in either a load control or a displacement control mode, with relative advantages and disadvantages. These control methods are in fact complementary, in that one method or the other is viewed as being more applicable in certain regions of the nonlinear load-displacement curve. A combination of load control and displacement control methods, termed hybrid control, offers advantages over either load control or displacement control methods alone for in vitro biomechanical testing of the spine. This article describes the application of a robotic/UFS (universal force-moment sensor) testing system with hybrid control to the delineation of the in vitro load-displacement characteristics of human lumbar functional spinal units (FSUs). Preliminary results obtained using this system demonstrate successful delineation of FSU load-displacement response in quarter-degree increments throughout specimen flexion/extension range of motion, with minimal coupled loads in secondary degrees-of-freedom. Characteristic S-shaped curves of the moment-rotation response were obtained, consistent with previous reports of the FSU having a region of low stiffness (neutral zone) bounded by regions of increasing stiffness (elastic zones). Further developments of hybrid control theory as applied to the spine could help to elucidate the interactions that occur among the passive, active, and neural control subsystems of the spine.

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

[2]  Richard S. C. Cobbold,et al.  Transducers for biomedical measurements: principles and applications , 1974 .

[3]  J E Lemons,et al.  Investigation of video techniques for dynamic measurements of relative vertebral-body motion in vitro. , 1996, Biomedical instrumentation & technology.

[4]  Robert L. Piziali,et al.  A Motion Transducer for Use in the Intact In-Vitro Human Lumbar Spine , 1977 .

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

[6]  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.

[7]  K. Markolf.  Deformation of the thoracolumbar intervertebral joints in response to external loads: a biomechanical study using autopsy material. , 1972, The Journal of bone and joint surgery. American volume.

[8]  A. M. Ahmed,et al.  The role of secondary variables in the measurement of the mechanical properties of the lumbar intervertebral joint. , 1981, Journal of biomechanical engineering.

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

[10]  J N Weinstein,et al.  A Technique to Evaluate an Internal Spinal Device by Use of the Selspot System: An Application to Luque Closed Loop , 1987, Spine.

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

[12]  W C Hayes,et al.  Variations of stiffness and strength along the human cervical spine. , 1991, Journal of biomechanics.

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

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

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

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

[17]  Harry N. Norton,et al.  Handbook of transducers , 1969 .

[18]  N. Langrana,et al.  Lumbosacral spinal fusion. A biomechanical study. , 1984, Spine.

[19]  G A Livesay,et al.  The use of a universal force-moment sensor to determine in-situ forces in ligaments: a new methodology. , 1995, Journal of biomechanical engineering.

[20]  M M Panjabi,et al.  Three-Dimensional Movements of the Whole Lumbar Spine and Lumbosacral Joint , 1989, Spine.

[21]  E. C. Hodgman,et al.  A conceptual framework to guide nursing curriculum. , 1973, Nursing forum.

[22]  M M Panjabi,et al.  A technique for measurement and description of three-dimensional six degree-of-freedom motion of a body joint with an application to the human spine. , 1981, Journal of biomechanics.

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

[24]  T. Brown,et al.  Some mechanical tests on the lumbosacral spine with particular reference to the intervertebral discs; a preliminary report. , 1957, The Journal of bone and joint surgery. American volume.

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

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

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

[28]  E. Koeneman,et al.  An Apparatus for Applying Pure Nonconstraining Moments to Spine Segments In Vitro , 1995, Spine.

[29]  M. Panjabi.  The stabilizing system of the spine. Part I. Function, dysfunction, adaptation, and enhancement. , 1992, Journal of spinal disorders.