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Research Papers

Validation of a Novel Spine Test Machine

[+] Author and Article Information
Erin M. Mannen

Mechanical Engineering,
The University of Kansas,
1530 W. 15th Street,
Learned Hall, Room 3138,
Lawrence, KS 66045
e-mail: erinmannen@gmail.com

Sahibjit S. Ranu

The University of Kansas,
Bioengineering Graduate Program,
1530 W 15th Street,
Learned Hall Room 3135A,
Lawrence, KS 66045
e-mail: s794r616@ku.edu

Ana M. Villanueva

Mechanical Engineering,
The University of Kansas,
1530 W 15th Street,
Learned Hall Room 3138,
Lawrence, KS 66045
e-mail: amvillanuevap@ku.edu

Elizabeth A. Friis

Mechanical Engineering,
The University of Kansas,
1530 W 15th Street,
Learned Hall Room 3138,
Lawrence, KS 66045
e-mail: lfriis@ku.edu

Manuscript received February 27, 2014; final manuscript received August 7, 2014; published online November 14, 2014. Assoc. Editor: Rita M. Patterson.

J. Med. Devices 9(1), 011002 (Mar 01, 2015) (8 pages) Paper No: MED-14-1137; doi: 10.1115/1.4028759 History: Received February 27, 2014; Revised August 07, 2014; Online November 14, 2014

A novel spine test machine was developed for physiological loading of spinal segments. It can be used in conjunction with external motion-capture systems (EMCS) to measure angular displacement, but can also measure in-plane rotations directly, though the inherent error is unknown. This study quantified error inherent in the displacement measurement of the machine. Synthetic specimens representative of cadaveric spinal specimens were tested. Machine displacement was compared to EMCS displacement. The maximum machine displacement error was <2 deg for lumbar and thoracic specimens. The authors suggest that researchers use EMCS in conjunction with the test machine when high accuracy measurements are required.

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Figures

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Fig. 2

Stiff (lumbar) synthetic specimen in bending mode with an optical motion tracking pin inserted to measure actual displacement of the specimen

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Fig. 4

Typical one-cycle load versus displacement graphs are shown for a moderate (thoracic) synthetic specimen in bending (a) and a flexible (cervical) synthetic specimen in axial rotation (b). The solid lines represent the actual displacements as measured by the optical motion tracking pin, and the dashed lines represent the displacements as measured by the spine test machine.

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Fig. 5

Mean ± standard deviation of the maximum displacement errors at each target loading range between −15 and 15 Nm in the spine test machine for each stiffness range: flexible (cervical), moderate (thoracic), and stiff (lumbar) in both bending (a) and axial rotation (b). The error is defined as the difference between the actual displacement measured by the optical motion tracking pin and the displacement measured by the spine test machine. Note the different y-axis scales for bending and axial rotation.

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Fig. 3

Ranges of both bending and axial rotation stiffness values found in cadaveric studies in the literature [6,11-20]. The means ± standard deviation of the bending and axial rotation stiffness values measured in the synthetic specimens fall within these ranges for each specimen type.

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Fig. 6

Bending test setup of a full thoracic cadaveric specimen with attached ribcage test loaded in the spine test machine

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Fig. 1

The spine test machine includes the frame with two drive assemblies, a control box, and a computer with software (a). It is depicted here with a synthetic spine. The upper arm is the axial rotation drive (b), and the lower arm is the bending drive (c).

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