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Result(s) for "Spinal rod"

	Project Title	Status	Abstract
1.	Microstructural and Biomechanical Property Differences of Spinal Rods from Different Lots	Current	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.
2.	Spinal Rod Fatigue Testing and Analysis	Current	The objectives of the proposed study are to measure and compare the fatigue behavior of the three available alloys used for surgically implanted spinal rods and to publish the results for possible use by physicians, patients, engineers, and scientists. Orthopedic surgeon Andres Munk, M.D., is a collaborating researcher on the proposed study. Medical patients with spinal injuries or conditions such as scoliosis, degenerative disc disease, spinal trauma or hernia(s) may require surgery to implant spinal rods to give the vertebra and spine needed structural support and to ensure proper bone growth. With movement, these rods are subjected to cyclical loading and fatigue, the primary cause of spinal rod failure. A person with a low intensity level of daily activity can easily walk one million steps and subject a spinal rod to one million loading cycles in six months. Over time, the cyclic loading can lead to fatigue crack initiation and growth and even fracture of the rod. For physicians and patients considering spinal rod implants, there are three different metallic alloy rods available: titanium, stainless steel and vitallium. However, little has been published on the behavior of the alloys or their relative merits. By using fatigue crack growth rate testing, this study will provide a basis for the comparison of the fatigue behavior of the available metallic rods. The fatigue process will be initiated by introducing a circumferential pre-crack to the rod. Rotating bending fatigue will imitate the loading that a spinal rod experiences while implanted. One rotation will be considered to be one cycle and will simulate one walking step of a spinal rod patient. The load and number of cycles will be applied, and the amount of crack growth will be measured. To accurately measure crack growth, a technique called heat tinting will be used—when the alloy is heated to a moderately high temperature, the external surfaces of the alloy oxidize and change color. This will mark the initial crack length. After cycling, the specimen will be broken, and both the initial and final fatigue crack lengths will be measured. The amount of crack growth will be determined from the difference between the initial and final crack lengths. Testing will consist of varying the magnitude of the load and number of cycles. The surgical spinal rods are expensive. To reduce costs, the rotating bending fatigue test protocol will be refined using common round bar stock specimens—the actual surgical spinal rod specimens will not be used until the test method is sufficiently refined to ensure the successful testing of each surgical spinal rod sample. The fatigue crack growth rate will be correlated with the load, number of cycles, and crack length for each material. It is anticipated that the fatigue behavior will depend upon the metallic alloy. The results of the study will be useful to surgeons and patients considering spinal rod implantation and to engineers and scientists working in biomedicine.