Application of the Finite Element Technique in the Design and Evaluation of the Artificial Facets for the Lumbar Spine

[+] Author and Article Information
Miranda N. Shaw, Koichi Sairyo, Jayant Jangra, Ashok Biyani, Nabil Ebraheim

Spine Research Center, Medical University of Ohio, University of Toledo, Toledo, OH 43606

Vijay K. Goel

Spine Research Center, Medical University of Ohio, University of Toledo, Toledo, OH 43606vijay.goel@utoledo.edu

J. Med. Devices 1(2), 176-179 (Dec 12, 2006) (4 pages) doi:10.1115/1.2735974 History: Received March 23, 2006; Revised December 12, 2006

An experimentally validated three-dimensional (3D) finite element (FE) model of the ligamentous L3–S1 segment was used to study the effects of artificial facet designs on the segment biomechanics (motion, facet loads, and stresses). The intact model was modified to simulate several artificial facet designs across the L4–L5 segment including capping with and without screws and pedicle screw based designs with sliding articulating surfaces. For the pedicle screw based design, the effect of increasing the connecting shaft thickness and increasing width surrounding the pedicle screw, butted against the vertebral pedicle for further support, was studied. All of the FE models were evaluated in response to 6 Nm moment in extension, flexion, bending, and rotation. The predicted increases in motion, compared to the intact case, were smaller. The predicted facet loads decreased up to 25.7% in extension and 25.1% in bending at the implanted level as compared to intact spine segment. For all of the loading modes, the stresses in both implant designs were less than the yield stress of titanium. Therefore, the implants are unlikely to fail. Additional cadaver and other experimental protocols are essential for the evaluations of the most appropriate designs identified through the FE investigations.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Three-dimensional finite element model of the ligamentous L3–S1 segment: (a) intact model, and (b) a midsagittal crosssection of the model showing important anatomical features

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Figure 2

Artificial facet caps: (a) caps tied to the bony surface to simulate perfect bone osteointegration; (b) caps secured with screws; (c) superior and inferior facet caps with pedicle screw support from U.S. Published Patent Application No. 2005/0043797 (Lee 2005/0043797)

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Figure 3

The pedicle screw based artificial facet design with a 3-mm-thick shaft connecting the facets to the pedicle screw: (a) and (b) finite element models; and (c) lateral view of the artificial facet proposed in U.S. Patent No. 6579319 (2).

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Figure 4

Percent changes in total facet loads for 6Nm applied moment for the artificial facet FE models in each loading mode. A positive percent change indicates an increase in facet loads, whereas a negative percent change indicates a decrease in facet loads. Flexion mode is not shown since facets do not interact in this mode




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