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Research Papers

The Impact of Posture on the Mechanical Properties of a Functional Spinal Unit During Cyclic Compressive Loading

[+] Author and Article Information
Jeff M. Barrett

Department of Kinesiology,
University of Waterloo,
200 University Avenue West,
Waterloo, ON N2L 6P2, Canada
e-mail: jeffery.barrett@uwaterloo.ca

Chad E. Gooyers

Giffin Koerth Forensic Engineering and Science,
40 University Avenue,
Toronto, ON M5J 1T1, Canada
e-mail: cgooyers@giffinkoerth.com

Thomas Karakolis

Defence Research and Development Canada,
1133 Sheppard Avenue West,
Toronto, ON M3K 2C9, Canada
e-mail: thomas.karakolis@drdc-rddc.gc.ca

Jack P. Callaghan

Mem. ASME,
Department of Kinesiology,
University of Waterloo,
Burt Matthews Hall, Room 3122,
200 University Avenue West,
Waterloo, ON N2L 6P2, Canada
e-mail: jack.callaghan@uwaterloo.ca

1Corresponding author.

Manuscript received October 15, 2015; final manuscript received June 10, 2016; published online July 8, 2016. Assoc. Editor: Brian D. Stemper.

J Biomech Eng 138(8), 081007 (Jul 08, 2016) (7 pages) Paper No: BIO-15-1516; doi: 10.1115/1.4033916 History: Received October 15, 2015; Revised June 10, 2016

To assess how posture affects the transmission of mechanical energy up the spinal column during vibration, 18 porcine functional spinal units (FSUs) were exposed to a sinusoidal force (1500 ± 1200 N) at 5 Hz for 120 min in either a flexed, extended, or neutral posture. Force and FSU height were measured continuously throughout the collection. From these data, specimen height loss, dynamic stiffness, hysteresis, and parameters from a standard linear solid (SLS) model were determined and analyzed for differences between postures. Posture had an influence on all of these parameters. In extension, the FSU had higher dynamic stiffness values than when neutral or flexed (p < 0.0001). In flexion, the FSU had higher hysteresis than both an extended or neutral posture (p < 0.0001). Height loss was greatest in a flexed posture and smallest in an extended posture (p < 0.0001). In extension, the series spring element in the SLS model had a stiffness value higher than both flexed and neutral posture conditions, whereas the stiffness in the parallel spring was the same between extension and neutral (p < 0.01), both higher than in flexion. Viscosity coefficients were highest in extension compared to both flexed and neutral (p < 0.01). Based on these results, it was determined that posture had a significant influence in determining the mechanical properties of the spine when exposed to cyclic compressive loading.

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Figures

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Fig. 1

The standard linear viscoelastic model

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Fig. 2

Fit of the SLS model to experiment for one specimen in extension

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Fig. 3

Summary of SLS parameter values found for each posture

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Fig. 4

Relaxation times for each posture

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Fig. 5

Height loss versus time for each posture

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Fig. 6

Dynamic stiffness as a function of time and posture. The flexed spine had notably less dynamic stiffness than the other two postures, with no changes with time.

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Fig. 7

Hysteresis across time and posture. The flexed posture showcases significantly more hysteresis than an extended or neutral posture.

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