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Development of a new method to extract biomechanical characteristics of the in vitro multi-segment thoracic spine

Coombs, Matthew T.
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1455209212

Abstract Details

2016, PhD, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
Spine biomechanical testing has been performed to understand structure-function relationships, injury mechanisms, and support the design and development of orthopaedic instrumentation. Standardized in vitro test protocols recommend pure bending moment loading, which are often applied by cable-pulley systems. However, large hysteresis loops in the measured force-displacement curves due to cable-pulley friction complicates accurate biomechanical study; effects which are compounded with longer multi-segment specimens. A test assembly applying a transverse tip force was devised as an alternative to commonly used pure moment cable-pulley type systems, to investigate the biomechanical response of the multi-segment thoracic spine. The transverse tip force assembly simplified the overall mechanical design, and minimized unmeasured forces and error sources in force measurement. In vitro biomechanical tests were conducted on eight thoracic spines using both the transverse tip load test assembly and the pure moment test assembly. Test results for the transverse tip load assembly resulted in smaller hysteresis loops in the force-displacement curves, indicating removal of friction sources and improved measurement accuracy. However bending stiffness was unexpectedly and sharply smaller for the transverse tip load assembly compared to the pure moment assembly. In order to fully characterize the biomechanical response of the multi-segment thoracic spine, a new method was developed to obtain the bending and shear properties of the intervertebral disc. The spine was modeled as a series of boney vertebrae modeled as rigid bodies, and an elastic intervertebral disc modeled as a Timoshenko beam. Using the Transfer Matrix method, the flexural rigidity and shear stiffness of the intervertebral disc were obtained from the measured in vitro biomechanical study results. It was found that intervertebral flexural rigidity was up to six-times higher for the pure moment test assembly compared to the transverse tip load test assembly. Using the calculated flexural rigidity and an assumption of intervertebral disc geometry, it was possible to determine the Young’s modulus of the intervertebral disc. Using this method, the Young’s modulus for the intervertebral disc was shown to be significantly smaller than rubber, with a maximum modulus of only 2.2x105 Ν/m2 . The very low modulus reported for the intervertebral disc indicated the multi-segment spine is poorly suited for resistance of shear forces. The new transverse tip load test assembly and analysis procedure developed in this study enabled both bending and shear properties to be determined from in vitro biomechanical tests of the multi-segment spine. Further study of the biomechanical response of the multi-segment spine to shear or complex loads is required, given evidence that shear behavior is capable of dominating overall bending response. Updating the methods by which biomechanical outcomes are reported to include shear stiffness is necessary to improve the comparison of bending response between studies. Additionally, reporting changes in shear stiffness may lead to better understanding the biomechanical changes following treatment that result in clinically significant complications.
Jay Kim, Ph.D. (Committee Chair)
Kermit Davis, Ph.D. (Committee Member)
David Thompson, Ph.D. (Committee Member)
Kumar Vemaganti, Ph.D. (Committee Member)
96 p.
Biomechanics
biomechanics; spine; Timoshenko; test method

Recommended Citations

Citations

  • Coombs, M. T. (2016). Development of a new method to extract biomechanical characteristics of the in vitro multi-segment thoracic spine [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1455209212

    APA Style (7th edition)

  • Coombs, Matthew. Development of a new method to extract biomechanical characteristics of the in vitro multi-segment thoracic spine. 2016. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1455209212.

    MLA Style (8th edition)

  • Coombs, Matthew. "Development of a new method to extract biomechanical characteristics of the in vitro multi-segment thoracic spine." Doctoral dissertation, University of Cincinnati, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1455209212

    Chicago Manual of Style (17th edition)

ucin1455209212
263
© 2016, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.