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Undergraduate Research Project Management System

Microstructural and Biomechanical Property Differences of Spinal Rods from Different Lots

Status Complete
Seeking Researchers No
Start Date 07/01/2009
End Date 06/30/2010
Funding Source Parasca Science Research Award
Funding Amount 5,000
Community Partner
Related Course
Last Updated 09/25/2010 01:49AM
Keywords Spinal rod, biomechanical properties, titanium, stainless steel


  Anthony Paris

Student Researchers
  Cheyenne Alabanzas


The objective of this project is to obtain a qualitative and quantitative comparison of the static biomechanical behavior of stainless steel and titanium spinal rods from different lots. Static testing will be done in a controlled environment, which will then provide data for analysis and conclusion.

The spinal rod is a surgical device used to correct deformities of the spine due to medical conditions such as scoliosis and degenerative disc disease. Commonly, rods are implanted along the spinal column to support the fusion of the vertebrae, as shown in Figure 1. The spine is fixed when the grafted bone fuses into a solid bone mass, immobilizing the vertebrae. Since this takes up to a year to develop, the instrumentation aids in allowing the fusion to occur by making the spine stiff. When the fusion is solid, the instrumentation can be removed, although it is usually left in place. The instrumentation may eventually fatigue and fail if fusion is not achieved. Rigid internal fixation is required to enhance fusion rates and ensure mechanical stability.

Spinal rods are mass produced in lots. It was observed during a previous study by the Faculty Advisor that the behavior of the rods during cutting, bending, and testing varied significantly from one lot number to another. It was concluded that although rods are produced to meet the established ASTM standards, there are significant variations in the biomechanical properties of the rods from different lots.

Due to variations in the manufacturing process—including small variations in chemical composition and variations in heat treatment, cold work, and surface treatment from one lot number to another—there will be variations in the microstructure of the rods. Variations in microstructure result in variations in the biomechanical properties. This project will examine those differences in biomechanical properties and microstructure both qualitatively and quantitatively and discuss their effects on clinical performance.

Samples of the spinal rods will be obtained and subjected to biomechanical and microstructural testing. Each of the rods from different batches will be tested for their yield strength, tensile strength, ductility, metallography and hardness. Tensile tests will be performed using an MTS Universal Test Machine. Metallographic equipment will be used to determine the microstructure of the rods. Hardness tests will be performed using a Rockwell Hardness Tester.

The goal of this study is to determine the difference in microstructural and biomechanical properties of the titanium and stainless steel rods from different lots used for spinal instrumentation. A better understanding of the biomechanical behavior of spinal rods is important to physicians and patients considering rod implants, as well as to the engineers and scientists who are researching and designing spinal rod systems. To better understand spinal instrumentation from the clinical perspective, orthopedic surgeon Dr. Andres Munk, M.D., Macomb Orthopedic Surgeons, will serve as a collaborating researcher.

The results of the study will be published in a formal report and submitted for dissemination through conference and journal publication.

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