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Development of a Physiologic In-Vitro Testing Methodology for Assessment of Cervical Spine Kinematics

Bell, Kevin (2013) Development of a Physiologic In-Vitro Testing Methodology for Assessment of Cervical Spine Kinematics. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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In-vitro biomechanical testing has been critical in the design and evaluation of spinal surgical instrumentation, however determination of realistic physiologic loading levels has proven difficult outside of the in-vivo setting. Unconstrained pure moment testing combined with the hybrid testing method is currently the gold standard test protocol for evaluation of motion preservation technology and adjacent level effects. Pure moment testing is well suited for making relative comparisons between treatments, but is currently not based on or representative of in-vivo spine motion, bringing the clinical relevance into question.
The human cervical spine supports substantial compressive load in-vivo arising from muscle forces and the weight of the head. However, traditional in-vitro testing methods rarely include compressive loads, especially in investigations of multi-segment cervical spine constructs. Therefore, a systematic comparison of standard pure moment testing without compressive loading versus published and novel compressive loading techniques (follower load, axial load, and combined load) was performed. To achieve a pure moment test, a robot/UFS testing system was programmed with hybrid control, which combined load and displacement control to overcome the limitations of either control methodology alone. A follower load system was developed with actively controlled linear actuators and integrated into the robot/UFS testing system’s control algorithm. Thorough investigation of the integrated system ensured that the pure moment assumption was upheld and enabled characterization of the kinetics resulting from the application of follower load. In contrast, axial load was applied perpendicular to superior most vertebral body using the robot end-effector; it did not maintain the pure moment assumption resulting in alterations of the segmental motion patterns.
The pure moment testing protocol without compression or follower load was not able to replicate the typical in-vivo segmental motion patterns throughout the entire motion path. Axial load or a combination of axial and follower load was necessary to mimic the in-vivo segmental contributions at the extremes of the extension-flexion motion path. It is hypothesized that dynamically altering the compressive loading throughout the motion path is necessary to mimic the segmental contribution patterns exhibited in-vivo—a novel concept that will be explored in future investigations.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Bell, Kevinkmb7@pitt.eduKMB7
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairTashman, Scotttashman@pitt.eduTASHMAN
Committee CoChairSowa, Gwendolynsowaga@upmc.eduGAS26
Committee MemberDebski, Richardgenesis1@pitt.eduGENESIS1
Committee MemberKang,
Date: 25 September 2013
Date Type: Publication
Defense Date: 11 June 2013
Approval Date: 25 September 2013
Submission Date: 25 June 2013
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 230
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Bioengineering
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Cervical Spine Kinematics Robot Follower Load Compressive Load Physiologic
Date Deposited: 25 Sep 2013 12:47
Last Modified: 19 Dec 2016 14:40


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