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PATIENT-SPECIFIC SPINE MODELS – DEVELOPMENT OF A LABORATORY TEST SPINE FOR MODEL VALIDATION



Abstract

Objective: A patient-specific finite element model of the spine is being developed to aid the surgeon in the diagnosis and clinical management of spinal conditions1. To validate the application of the computer model, a laboratory validation spine is being developed. This study is concerned with the development and basic characteristics of the intervertebral disc component of the laboratory spine.

Method: The external profile of the laboratory disc was determined from CT images of a cadaveric spine. A two-part silicon rubber was used to form the annulus part of the disc. Prior to sealing it was possible to fill the cavity with an appropriate medium (such as grease or oil) to represent the nucleus pulposus with the further option of applying external pressurisation through a small pressure inlet in the wall of the disc. The laboratory disc was then tested in denucleated form, and grease-filled with initial intradiscal pressures of 0, 0.1, 0.2 and 0.3 MPa. A finite element model of the disc was also developed and used to investigate the characteristics of the laboratory disc.

Results: The agreement between the finite element results and experimental test results was excellent and the compressive and flexural load-deflection characteristics of both intact and denucleated laboratory discs were found to lie within the range of values reported in the literature for cadaveric discs. Disc bulge characteristics of the intact and denucleated silicon discs were also similar to that observed with natural discs in vitro.

Conclusions: An artificial disc for a laboratory validation spine has been developed and shown to have representative characteristic properties in compression loading. The disc is now being modelled and tested in torsion.

Abstracts prepared by Mr. A. J. Stirling, FRCS, and Miss A. Weaver. Correspondence should be addressed to Miss A. Weaver at the Research and Teaching Centre, Royal Orthopaedic Hospital, Northfield, Birmingham, B31 2AP, UK

BritSpine 2002, the second combined meeting of the British Association of Spinal Surgeons, the British Cervical Spine Society, The British Scoliosis Society and the Society for Back Pain Research, took place at the International Convention Centre in Birmingham UK between 27th February and 1st March 2002. The following presentations and posters were given and displayed.

Reference:

1 Fagan MJ, Julian S and Mohsen A. Medical and Biological Engineering and Computing, 37: 2, 1178–1179, 1999 Google Scholar