Title: Silicone annulus for mechanically testing nucleus replacement implants for the lumbar intervertebral disc

Authors: Dang Lei, David W.L. Hukins, Duncan E.T. Shepherd, Douglas Wardlaw

Addresses: School of Mechanical Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK. ' School of Mechanical Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK. ' School of Mechanical Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK. ' Department of Orthopaedic Surgery, Woodend Hospital, Eday Road, Aberdeen AB15 6ZQ, UK

Abstract: Nucleus replacement implants are designed to replace the nucleus pulposus of the intervertebral disc, while preserving the integrity of the annulus fibrosus. The aim of this study was to design and manufacture a geometrically accurate annulus for use in mechanical testing lumbar nucleus replacement devices. The key dimensions for the annulus were determined from measurements made on magnetic resonance images and from cadaver lumbar discs. Cluster analysis enabled three size ranges to be defined. The smallest of these was chosen for designing the annulus. Solid modelling software was used to design an annulus with the required dimensions and reasonable curvatures. A mould was made using rapid prototyping and used to manufacture a synthetic annulus from silicone rubber. The stiffness of the silicone annulus was found to be in the range 718–907 N/mm and so mimicked the mechanical properties of the natural annulus. The silicone annulus can be used in the pre-clinical testing of nucleus replacement implants.

Keywords: silicone annulus; nucleus replacement implants; lumbar intervertebral disc; mechanical testing; cluster analysis; solid modelling; rapid prototyping; stiffness.

DOI: 10.1504/IJMEI.2010.031520

International Journal of Medical Engineering and Informatics, 2010 Vol.2 No.2, pp.195 - 204

Published online: 08 Feb 2010 *

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