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Evaluation of the threshold of stability for the human spine.

Authors
Tanaka-ML; Nussbaum-MA; Ross-SD
Source
J Biomech 2009 May; 42(8):1017-1022
NIOSHTIC No.
20035846
Abstract
The threshold of stability (ToS) is introduced as a new tool for evaluating spinal stability. Current methods have evaluated the magnitude of spinal kinematic variability, stability diffusion, or Lyapunov exponents. This present method differs by modifying task difficulty to obtain a critical value delineating regions of stability and instability. Conceptually, as task difficulty increases, kinematic variability of the system increases and the basin of stability decreases. When kinematic variability exceeds the basin of stability, stability cannot be maintained over time. This concept is first illustrated using a mathematical model, from which an effective potential function was calculated to show the relationships among kinematic variability, the basin of stability, and task difficulty. In addition, an experiment was performed to evaluate the sensitivity of the ToS to changes in postural control using visual feedback as a control variable. The ToS was found to be more sensitive than the Lyapunov exponent to removal of visual feedback, suggesting it may have use as a diagnostic indicator (e.g. for low back pain). Furthermore, this new method has an additional advantage in which minimal instrumentation is needed. Its simplicity, sensitivity, and low cost suggest that the ToS has potential as a diagnostic or prognostic tool in a clinical setting.
Keywords
Back-injuries; Biodynamics; Biological-effects; Biological-factors; Biological-function; Biological-systems; Biomechanical-modeling; Biomechanics; Clinical-techniques; Environmental-control; Environmental-physiology; Mathematical-models; Muscle-physiology; Muscles; Muscle-contraction; Muscle-tension; Musculoskeletal-system; Physical-reactions; Posture; Spinal-cord; Spinal-cord-disorders; Statistical-analysis; Visual-images; Visual-motor-performance; Author Keywords: Threshold of stability; Lyapunov; Spinal stability; Kinematic variability; Low back pain
Contact
Martin L. Tanaka, Department of Orthopaedic Surgery, Wake Forest University, Winston-Salem, NC 27157
CODEN
JBMCB5
Publication Date
20090529
Document Type
Journal Article
Email Address
mtanaka@wfubmc.edu
Funding Type
Grant
Fiscal Year
2009
NTIS Accession No.
NTIS Price
Identifying No.
Grant-Number-R01-OH-008504
Issue of Publication
8
ISSN
0021-9290
Source Name
Journal of Biomechanics
State
NC; VA
Performing Organization
Virginia Polytechnic Institute and State University
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