Design and Stress Analysis of Dynamic Spinal Stabilizers

Author

Kohki Ishii, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2010

Degree Name

Master of Science

Department

Mechanical Engineering

First Advisor

Chu, Tsuchin

Abstract

A dynamic lumbar spinal stabilizer with a helical machined spring element was created in the first stage. The stabilizer was built with 30 N/mm of axial stiffness because if the human body is moved to flexion and extension, this amount of a compressive and tensile load would be applied to the intervertebral disc. The stabilizer supports the loads instead of the disc. The stiffness was influenced by the number of coils, the thickness of coils, and length of the coil element. The stiffness can be determined by analytical equations or by finite element analysis (FE), such as ANSYS Workbench. In the second stage, the lumbar spine FE model was successfully constructed by using Autodesk Inventor 2010. There were three different analyzed models; (1) intact model, (2) fused model, and (3) dynamically stabilized model. This intact model is a simplified and basic model used for fused model and dynamically stabilized model. The range of motion (ROM) was the key term in this study. In other words, examination of each model was based on how much ROM was shown when the flexion, extension, and bending moments have been applied on the spine. The ROM of each model with three moments produced appropriate values compared to the references. The stress analysis is also important to optimize the design of the dynamic stabilizer. The maximum stress was 472 MPa on the stabilizer that is less than yield strength of Titanium alloy.