Load-displacement characteristics of the cervical spine during shear loading

Dowling-Medley, J.J.; Doodkorte, R. J.; Melnyk, A. D.; Cripton, P. A.; Oxland, T. R.

Affiliations

¹Department of Mechanical Engineering, University of British Columbia, Vancouver, BC

²Department of Biomedical Sciences, Radboud University Nijmegen, Nijmegen, Netherlands

³ICORD, Faculty of Medicine, University of British Columbia, Vancouver, BC

⁴Department of Orthopaedics, University of British Columbia, Vancouver, BC

Abstract

The biomechanics of the cervical spine during shear loading are not well-established as compared to other loading regimes. The objectives of this study are to determine the load-displacement characteristics of the cervical spine during the application of pure shear loads. Shear loads were applied to fresh-frozen human cadaveric functional spine units (n=5). Loads were applied to each specimen up to 100 N via a materials testing machine and custom-designed apparatus. Three directions (anterior, posterior and right lateral) were tested in each of three specimen conditions (intact, posterior ligament removal, disc-only). Anterior shear stiffness [CI] was found to decrease significantly from 186 N/mm [98, 327] in the intact state to 105 N/mm [78, 142] in the disc-only state (p=0.03) in the 20-100 N load range. Posterior stiffness was found to have a significant decrease from 134 N/mm [92, 182] to 119 N/mm [83, 181] in the 20-100 N load range. No significant differences were found between specimen states in the lateral directions, nor in the initial stiffness between 0-20 N in any direction or any specimen condition. Coupled displacements and rotationstended to be small (less than 2° or 1 mm). Results suggest that the posterior elements provide resistance in the presence of shearing loads in the anterior and posterior direction, but have a lesser effect in other directions. This was expected as the facet joints in the cervical spine are oriented such that they would tend to block anterior-posterior translations. Greater shear stiffness in the lateral direction could be explained by facet-lamina interactions and uncovertebral joint interactions. Results corresponded well with existing studies concerning the biomechanics of the cervical spine in shear. These results may be used to improve the definition of and validation of existing finite element models of the human neck, where such models may eventually be used to inform injury criterion and safety design.

Links

URL: http://ibrc.osu.edu/wp-content/uploads/2017/03/2017-IBS-Paper_2_JDM_revised.pdf

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