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ISSLS Prize Winner: Vibration Really Does Disrupt the Disc: A Microanatomical Investigation

Wade, Kelly R., PhD; Schollum, Meredith L., PhD; Robertson, Peter A., MD; Thambyah, Ashvin, PhD; Broom, Neil D., PhD

doi: 10.1097/BRS.0000000000001594
BASIC SCIENCE

Study Design. Microstructural investigation of vibration-induced disruption of the flexed lumbar disc.

Objective. The aim of the study was to explore micro-level structural damage in motion segments subjected to vibration at subcritical peak loads.

Summary of Background Data. Epidemiological evidence suggests that cumulative whole body vibration may damage the disc and thus play an important role in low back pain. In vitro investigations have produced herniations via cyclic loading (and cyclic with added vibrations as an exacerbating exposure), but offered only limited microstructural analysis.

Methods. Twenty-nine healthy mature ovine lumbar motion segments flexed 7° and subjected to vibration loading (1300 ± 500 N) in a sinusoidal waveform at 5 Hz to simulate moderately severe physiologic exposure. Discs were tested either in the range of 20,000 to 48,000 cycles (medium dose) or 70,000 to 120,000 cycles (high dose). Damaged discs were analyzed microstructurally.

Results. There was no large drop in displacement over the duration of both vibration doses indicating an absence of catastrophic failure in all tests. The tested discs experienced internal damage that included delamination and disruption to the inner and mid-annular layers as well as diffuse tracking of nucleus material, and involved both the posterior and anterior regions. Less frequent tearing between the inner disc and endplate was also observed. Annular distortions also progressed into a more severe form of damage, which included intralamellar tearing and buckling and obvious strain distortion around the bridging elements within the annular wall.

Conclusion. Vibration loading causes delamination and disruption of the inner and mid-annular layers and limited diffuse tracking of nucleus material. These subtle levels of disruption could play a significant role in initiating the degenerative cascade via micro-level disruption leading to cell death and altered nutrient pathways.

Level of Evidence: 5

Experimental Tissue Mechanics Laboratory, Department of Chemical and Materials Engineering, University of Auckland, New Zealand

Department of Orthopaedic Surgery, Auckland City Hospital, Auckland, New Zealand.

Address correspondence and reprint requests to Neil D. Broom, PhD, Department of Chemical and Materials Engineering, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand; E-mail: nd.broom@auckland.ac.nz

Received 20 October, 2015

Revised 8 March, 2016

Accepted 8 March, 2016

The manuscript submitted does not contain information about medical device(s)/drug(s).

Medtronic (Australasia) and NuVasive funds were received in support of this work.

Relevant financial activities outside the submitted work: consultancy, patents, employment, grants, travel/accommodations/meeting expenses.

Copyright © 2016 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.