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The Effect of Axial Torsion on the Mechanical Properties of the Annulus Fibrosus

Harvey-Burgess, Maxine, MKin; Gregory, Diane E., PhD∗,†

doi: 10.1097/BRS.0000000000002803
BIOMECHANICS
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Study Design. In-vitro study of the tissue mechanics of annulus fibrosus.

Objective. To determine the effect of axial torsion on the mechanical properties of the inter- and intralamellar matrices.

Summary of Background Data. Axial torsion, when combined with repetitive flexion, has been associated with an increased risk of intervertebral disc herniation. However, the mechanisms behind this relationship are poorly understood.

Methods. Bovine intervertebral discs (IVDs) from the caudal region were exposed to a combination of either 0° or 12° of static axial torsion and 0 N or 1000 N of compression for 2 hours in an attempt to created micro-damage to the IVD. Following the loading protocol, one multilayered sample and two single layer samples were dissected from the annulus fibrosus to undergo tensile testing of the inter- and intralamellar matrices. Histological staining was also performed.

Results. The strength of the interlamellar matrix was not affected by axial torsion or compression, suggesting that torsion did not damage the interlamellar matrix. However, intralamellar matrix strength of samples exposed to axial torsion, regardless of compressive loading magnitude, was 48% lower than those from samples that were not exposed to torsion (P < 0.001). Similarly, intralamellar matrix stiffness of samples exposed to axial torsion was 42% lower than from samples that were not exposed to torsion (P = 0.010). Additionally, histological analysis demonstrated more disruption within individual lamellae of the samples exposed to axial torsion compared with samples that were not.

Conclusion. This study suggests that axial torsion damages the components of the intralamellar matrix as a result of the strain it puts on the matrix, thus making the intervertebral disc more susceptible to herniation.

Level of Evidence: N/A

This study exposed bovine intervertebral discs to static axial torsion in order to determine its effect on the inter- and intralamellar matrices. Axial torsion resulted in decreased strength and stiffness of the intralamellar matrix, which may make the intervertebral disc more susceptible to herniation.

Department of Kinesiology and Physical Education, Wilfrid Laurier University, Waterloo, Ontario, Canada

Department of Health Sciences, Wilfrid Laurier University, Waterloo, Ontario, Canada.

Address correspondence and reprint requests to Diane E. Gregory, PhD, Department of Kinesiology and Physical Education/Department of Health Sciences, Wilfrid Laurier University, 75 University Ave West, Waterloo, ON N2L 3C5, Canada; E-mail: dgregory@wlu.ca

Received 15 January, 2018

Revised 24 May, 2018

Accepted 9 July, 2018

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

Funding for this work was provided by the Natural Sciences and Engineering Research Council of Canada.

No relevant financial activities outside the submitted work.

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