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Research Papers

A Comparison of the Human Lumbar Intervertebral Disc Mechanical Response to Normal and Impact Loading Conditions

[+] Author and Article Information
David Jamison, IV

School of Biomedical Engineering,
Science and Health Systems,
Drexel University,
Philadelphia, PA 19104

Marco Cannella

Department of Physical Therapy,
Drexel University,
Philadelphia, PA 19104

Eric C. Pierce

Naval Surface Warfare Center,
Tampa, FL 32407

Michele S. Marcolongo

Department of Materials Science
and Engineering,
Drexel University,
Philadelphia, PA 19104
e-mail: marcolms@drexel.edu

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received January 3, 2013; final manuscript received June 4, 2013; accepted manuscript posted June 17, 2013; published online July 10, 2013. Assoc. Editor: James C Iatridis.

J Biomech Eng 135(9), 091009 (Jul 10, 2013) (5 pages) Paper No: BIO-13-1004; doi: 10.1115/1.4024828 History: Received January 03, 2013; Revised June 04, 2013; Accepted June 17, 2013

Thirty-four percent of U.S. Navy high speed craft (HSC) personnel suffer from lower back injury and low back pain, compared with 15 to 20% of the general population. Many of these injuries are specifically related to the intervertebral disc, including discogenic pain and accelerated disc degeneration. Numerous studies have characterized the mechanical behavior of the disc under normal physiological loads, while several have also analyzed dynamic loading conditions. However, the effect of impact loads on the lumbar disc—and their contribution to the high incidence of low back pain among HSC personnel—is still not well understood. An ex vivo study on human lumbar anterior column units was performed in order to investigate disc biomechanical response to impact loading conditions. Samples were subjected to a sequence of impact events of varying duration (Δt = 80, 160, 320, 400, 600, 800, and 1000 ms) and the level of displacement (0.2, 0.5, and 0.8 mm), stiffness k, and energy dissipation ΔE were measured. Impacts of Δt = 80 ms saw an 18–21% rise in k and a 3–7% drop in ΔE compared to the 1000 ms baseline, signaling an abrupt change in disc mechanics. The altered disc mechanical response during impact likely causes more load to be transferred directly to the endplates, vertebral bodies, and surrounding soft tissues and can help begin to explain the high incidence of low back pain among HSC operators and other individuals who typically experience similar loading environments. The determination of a “safety range” for impacts could result in a refinement of design criteria for shock mitigating systems on high-speed craft, thus addressing the low back injury problem among HSC personnel.

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Figures

Grahic Jump Location
Fig. 1

Representative acceleration waveforms in the x, y, and z directions on a high speed craft. The z-axis accelerations are generally an order of magnitude higher than x and y. Top inset: coordinate axis for this system. Bottom inset: sample impact magnified for clarity.

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Fig. 2

Comparison of the load-displacement curves between 80 ms and 1000 ms (top), along with the results for k (middle), and ΔE (bottom). Values are normalized to the baseline 1000 ms impact (represented by dashed lines). Error bars indicate standard error (** denotes p <0.01. *** denotes p <0.001).

Grahic Jump Location
Fig. 3

A representative impact event (top) and its corresponding frequency spectrum (bottom). The signal consisted of high frequencies at 10–15 Hz and 20–30 Hz, which were below noise frequencies (<50 Hz). The frequency analysis was performed via fast Fourier transform with a custom written code in matlab.

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