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Torsion-induced pressure distribution changes in human intervertebral discs

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Title:
Torsion-induced pressure distribution changes in human intervertebral discs an In Vitro study
Physical Description:
Book
Language:
English
Creator:
Yantzer, Brenda Kay
Publisher:
University of South Florida
Place of Publication:
Tampa, Fla
Publication Date:

Subjects

Subjects / Keywords:
Intradiscal pressure
Pressure transducer
Nucleus pulposus
Lumbar spine
Biomechanics
Spinal load
Dissertations, Academic -- Biomedical Engineering -- Masters -- USF
Genre:
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Abstract:
ABSTRACT: Introduction. To test the effects of torsion torques on intradiscal pressure and disc height in human lumbar specimens. Methods. Six human lumbar cadaveric functional spine units (FSU) were loaded in the neutral position with 600 N compression. Nucleus pressure measurements were obtained at 0 Nm, 0.5 Nm, 1.0 Nm and 2 Nm torsion torque. Posterior elements were removed and pressure measurements were repeated at the same torsion torques for the disc body unit (DBU). The pressure in the nucleus was measured by pulling a pressure probe through the disc along a straight path in the midsagittal plane.Results. There was no statistically significant difference of nucleus pressure or intervertebral disc height with different torsion torques among or between the FSU's and DBU's. However, a disc height increase ranging from 0.13 mm to 0.16 mm occurred with the insertion of a 1.85 mm diameter cannula. Conclusions. Small torsion torques showed no significant difference in intradiscal pressures or disc heights. Disc height increases were seen with the insertion of the cannula that could lead to methods of disc height restoration.
Thesis:
Thesis (M.S.)--University of South Florida, 2005.
Bibliography:
Includes bibliographical references.
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System requirements: World Wide Web browser and PDF reader.
System Details:
Mode of access: World Wide Web.
Statement of Responsibility:
by Brenda Kay Yantzer.
General Note:
Title from PDF of title page.
General Note:
Document formatted into pages; contains 90 pages.

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aleph - 001913698
oclc - 174145626
usfldc doi - E14-SFE0001397
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ABSTRACT: Introduction. To test the effects of torsion torques on intradiscal pressure and disc height in human lumbar specimens. Methods. Six human lumbar cadaveric functional spine units (FSU) were loaded in the neutral position with 600 N compression. Nucleus pressure measurements were obtained at 0 Nm, 0.5 Nm, 1.0 Nm and 2 Nm torsion torque. Posterior elements were removed and pressure measurements were repeated at the same torsion torques for the disc body unit (DBU). The pressure in the nucleus was measured by pulling a pressure probe through the disc along a straight path in the midsagittal plane.Results. There was no statistically significant difference of nucleus pressure or intervertebral disc height with different torsion torques among or between the FSU's and DBU's. However, a disc height increase ranging from 0.13 mm to 0.16 mm occurred with the insertion of a 1.85 mm diameter cannula. Conclusions. Small torsion torques showed no significant difference in intradiscal pressures or disc heights. Disc height increases were seen with the insertion of the cannula that could lead to methods of disc height restoration.
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Spinal load.
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Torsion-Induced Pressure Distribution Chang es in Human Intervertebral Discs: an In Vitro Study by Brenda Kay Yantzer A thesis submitted in partial fulfillment of the requirement s for the degree of Master of Science in Biomedical Engineering Department of Chemical Engineering College of Engineering University of South Florida Major Professor: Wesley M. Johnson, Ph.D. Thomas B. Freeman, M.D. William E. Lee III, Ph.D. Date of Approval: October 19, 2005 Keywords: Intradiscal pressure, pressure transducer, nucleus pulposus, lumbar spine, biomechanics, spinal load Copyright 2005, Brenda Kay Yantzer

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i Table of Contents List of Tables iii List of Figures iv Abstract ix Chapter One: Introduction 1 1. 1 Significance 1 1.2 Background 2 1.2.a Anatomy of the Human Spine 2 1.2. b Comparative Porci ne and Human Anatomy 4 1.2.c T he Degenerative Process 4 1.2.d Research Objective 6 1.3 Curr ent Intervertebral Disc Model 7 1.4 Intradiscal Pressure History 8 1.5 Pressure Measurements 8 1. 6 Apparatus 9 Chapter Two: Materials and Methods 10 2.1 Cadaveric Material 10 2.2 Experimental Technique 11 2.3 Validation 13 2.4 The Effect of Different To rsion Torques on Pressure and Disc Height 14 2.5 Statistical Analysis 14 Chapter Three: Results 15 3.1 Tissue Degradation During Testing 15 3. 2 The Effect of Pressure Probe Orientation 15 3. 3 The Effect of Disc Degeneration on Pressure 16 3.4 The Effect of Pressure with Applied Torsion 16 3.5 The Effect of Disc Height with Applied Torsion 17 3.6 The Correlation of Pressure and Disc Height with Torsion 19 Chapter Four: Discussion 20 4.1 Discussion of Results 20 4.2 Limitations 21

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ii 4.2. a Sample Size and Variability 21 4.2.b Testing 22 Chapter Five: Future Work 23 5.1 Research 23 5.1.a Sample Size and Variability 23 5.1.b Testing 23 5. 2 Applications 25 References 26 Appendices 31 Appendix A Tables 32 Appendix B Figures 40

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iii List of Tables Table 1 Cadaveric Specimen Record 32 Table 2 Mean Pressures of 6 FSU and 6 DBU Specimens (n=6) 33 Table 3 Compiled Pressure Versus Torque ANOVAS for 6 FSU and 6 DBU Specimens (n=6) 34 Table 4 Mean Pressures of 4 FSU and 4 DBU Specimens (n=4) 35 Table 5 Compiled Pressure Versus Torque ANOVAS for 4 FSU and 4 DBU Specimens (n=4) 36 Table 6 Mean Height Differences of all 6 FSU and 6 DBU Specimens 37 Table 7 Compiled Height Versus Torque ANOVAS for 6 FSU and 6 DBU Specimens 38 Table 8 Linear Regression Analysis 39

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iv List of Figures Figure 1 A. Cannula, B. N eedle and C. Pressure Probe 40 Figure 2 X-ray of FSU UF05H007 41 Figure 3 MRI of Lum bar Spine UT04K009 42 Figure 4 MRI of Lum bar Spine UF05B003 43 Figure 5 Disarticulation of a Spine into an FSU (Functional Spine Unit) 44 Figure 6 Potted L2 Vertebral Body 45 Figure 7 Potted L1 Vertebral Body 46 Figure 8 X-ray of FSU UF05H007 with Screws 47 Figure 9 Axial Compression of an FSU in the MTS Machine 48 Figure 10 Insertion of the A. Cannula and B. Needle into an FSU 49 Figure 11 A. Pressure Gauge and B. Pressure Probe 50 Figure 12 Pressure of FSU UT04K009. Taken at 0 Nm Torque at the Start and End of t he Testing Protocol 51 Figure 13 Pressure of DBU UT04K009. Taken at 0 Nm Torque at the Start and End of t he Testing Protocol 51 Figure 14 Probe Orientati ons of DBU UJ04L015 at 0 Nm Torsion Torque 52 Figure 15 Probe Orientati ons of DBU UJ04L015 at 0. 5 Nm Torsion Torque 52 Figure 16 Probe Orientati ons of DBU UJ04L015 at 1. 0 Nm Torsion Torque 52 Figure 17 Probe Orientati ons of DBU UJ04L015 at 2. 0 Nm Torsion Torque 52 Figure 18 Pressure of FSU UT04K009 at Different Torques 53

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v Figure 19 Pressure of DBU UT04K009 at Different Torques 53 Figure 20 Pressure of FSU UJ 04L015 at Different Torques 54 Figure 21 Pressure of DBU UJ 04L015 at Different Torques 54 Figure 22 Pressure of FSU UJ 04J002 at Different Torques 55 Figure 23 Pressure of DBU UJ 04J002 at Different Torques 55 Figure 24 Pressure of FSU UF05H007 at Different Torques 56 Figure 25 Pressure of DBU UF05H007 at Different Torques 56 Figure 26 Pressure of FSU UM05H007 at Different Torques 57 Figure 27 Pressure of DBU UM05H007 at Different Torques 57 Figure 28 Pressure of FSU UF05B003 at Different Torques 58 Figure 29 Pressure of DBU UF05B003 at Different Torques 58 Figure 30 Pressure Versus Torque of 6 FSU’s and 6 DBU’s (n=6). Results Shown in M ean Standard Deviation 59 Figure 31 Pressure Versus Torque of 4 FSU’s and 4 DBU’s (n=4). Results Shown in M ean Standard Deviation 60 Figure 32 FSU Two Hour Creep Curves 61 Figure 33 DBU Two Hour Creep Curves 62 Figure 34 Combined FSU and DBU Two Hour Creep Curves 63 Figure 35 Continuous FSU Creep Cu rves with Two Hour Creep and Testing 64 Figure 36 Continuous DBU Creep Cu rves with Two Hour Creep and Testing 65 Figure 37 Axial Displacement of FSU UT04K009 66 Figure 38 Axial Displacement of FSU UT04K009 with Logarithmic Trendline 66

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vi Figure 39 Axial Displacement of FSU UT04K009 with Creep Only 66 Figure 40 Magnitude of the Height Differences of FSU UT04K009 66 Figure 41 Axial Displacement of DBU UT04K009 67 Figure 42 Axial Displacement of DBU UT04K009 with Logarithmic Trendline 67 Figure 43 Axial Displacement of DBU UT04K009 with Creep Only 67 Figure 44 Magnitude of the Height Differences of DBU UT04K009 67 Figure 45 Axial Displacement of FSU UM05H007 68 Figure 46 Axial Displacement of FSU UM05H007 with Logarithmic Trendline 68 Figure 47 Axial Displacement of FSU UM05H007 with Creep Only 68 Figure 48 Magnitude of the Height Differences of FSU UM05H007 68 Figure 49 Axial Displacement of DBU UM05H007 69 Figure 50 Axial Displacement of DBU UM05H007 with Logarithmic Trendline 69 Figure 51 Axial Displacement of DBU UM05H007 with Creep Only 69 Figure 52 Magnitude of the Height Differences of DBU UM05H007 69 Figure 53 Axial Displacement of FSU UJ04L015 70 Figure 54 Axial Displacement of FS U UJ04L015 with Logarit hmic Trendline 70 Figure 55 Axial Displacement of FSU UJ04L015 with Creep Only 70 Figure 56 Magnitude of the Height Differences of FSU UJ04L015 70 Figure 57 Axial Displacement of DBU UJ04L015 71 Figure 58 Axial Displacement of DB U UJ04L015 with Logarit hmic Trendline71 Figure 59 Axial Displacement of DBU UJ04L015 with Creep Only 71

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vii Figure 60 Magnitude of the Height Differences of DBU UJ04L015 71 Figure 61 Axial Displacement of FSU UJ04J002 72 Figure 62 Axial Displacement of FS U UJ04J002 with Logar ithmic Trendline 72 Figure 63 Axial Displacement of FSU UJ04J002 with Creep Only 72 Figure 64 Magnitude of the Height Differences of FSU UJ04J002 72 Figure 65 Axial Displacement of DBU UJ04J002 73 Figure 66 Axial Displacement of DB U UJ04J002 with Logar ithmic Trendline 73 Figure 67 Axial Displacement of DBU UJ04J002 with Creep Only 73 Figure 68 Magnitude of the Height Differences of DBU UJ04J002 73 Figure 69 Axial Displacement of FSU UF05H007 74 Figure 70 Axial Displacement of FSU UF05H007 with Logarithmic Trendline 74 Figure 71 Axial Displacement of FSU UF05H007 with Creep Only 74 Figure 72 Magnitude of the Height Differences of FSU UF05H007 74 Figure 73 Axial Displacement of DBU UF05H007 75 Figure 74 Axial Displacement of DBU UF05H007 with Logarithmic Trendline 75 Figure 75 Axial Displacement of DBU UF05H007 with Creep Only 75 Figure 76 Magnitude of the Height Differences of DBU UF05H007 75 Figure 77 Axial Displacement of FSU UF05B003 76 Figure 78 Axial Displacement of FSU UF05B003 with Logarithmic Trendline 76 Figure 79 Axial Displacement of FSU UF05B003 with Creep Only 76 Figure 80 Magnitude of the Height Differences of FSU UF05B003 76

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viii Figure 81 Axial Displacement of DBU UF05B003 77 Figure 82 Axial Displacement of DBU UF05B003 with Logarithmic Trendline 77 Figure 83 Axial Displacement of DBU UF05B003 with Creep Only 77 Figure 84 Magnitude of the Height Differences of DBU UF05B003 77 Figure 85 Normalized Data Versus Time of FSU UT04K009 78 Figure 86 Normalized Data Vers us Time of DBU UT04K009 79 Figure 87 Normalized Data Vers us Time of FSU UM05H007 80 Figure 88 Normalized Data Vers us Time of DBU UM05H007 81 Figure 89 Normalized Data Versus Time of FSU UJ04L015 82 Figure 90 Normalized Data Versus Time of DBU UJ04L015 83 Figure 91 Normalized Data Versus Time of FSU UJ04J002 84 Figure 92 Normalized Data Versus Time of DBU UJ04J002 85 Figure 93 Normalized Data Versus Time of FSU UF05H007 86 Figure 94 Normalized Data Vers us Time of DBU UF05H007 87 Figure 95 Normalized Data Versus Time of FSU UF05B003 88 Figure 96 Normalized Data Vers us Time of DBU UF05B003 89 Figure 97 Differential Height Versus Torque of 6 FSU’s and 6 DBU’s (n=6). Results Shown in Mean Standard Deviation 90

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ix Torsion-Induced Pressure Distribution Changes in Human Intervertebral Discs: an In Vitro Study Brenda Kay Yantzer ABSTRACT Introduction. To test the effects of torsi on torques on intradiscal pressure and disc height in human lumbar specimens. Methods. Six human lumbar cadav eric functional spine units (FSU) were loaded in the neutral position with 600 N compressi on. Nucleus pressure measurements were obtained at 0 Nm, 0.5 Nm, 1.0 Nm and 2 Nm torsion torque. Posterior elements were removed and pressure meas urements were repeated at the same torsion torques for the disc body unit (DBU). The pressure in the nucleus was measured by pulling a pressure probe thr ough the disc along a straight path in the midsagittal plane. Results. There was no statistically significant difference of nucleus pressure or intervertebral disc height with different torsion torques among or between the FSU’s and DBU’s. However, a disc hei ght increase ranging from 0.13 mm to 0.16 mm occurred with the insertion of a 1.85 mm diameter cannula. Conclusions. Small torsion torques show ed no significant difference in intradiscal pressures or disc heights. Disc height increases were seen with the insertion of the cannula that could lead to methods of disc height restoration.

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1 Chapter One: Introduction 1.1 Significance Low back pain (LBP) is a widespread problem in society, both in occurrence and economics.28,41 Chronic LBP affects more than five million Americans each year and is the second most common reason for lost workdays in adults under the age of 45.1,41 Studies have indicate d that long periods of awkward postures and highly repetitiv e activities have been associated with LBP.10,28 The pain is often severe and debilita ting and it is estimated that more than $50 billion is spent annually on the lower back.1 The causes for back pain include disease, trauma and degenerati on due to age. These causes can be related to the spine (intervertebral di sc and facet joints) or can be myofascial (muscles and fasciae). Specifically, degenerat ion of the intervertebral disc (IVD) is a major cause of pain, where the spine suffers diminished mechanical functionality due to dehydration of t he nucleus pulposus within the disc.5,21,29 The pain caused by the IVD, called discogenic pain, is the number one disease contributing to lost workdays and is an indication for fusion surgery.41 While only 5 percent of all LBP is discogenic, it a ccounts for 95 percent of surgeries for back pain. Small intervertebral movements such as during walking appear to reduce low back pain and have been hypothesiz ed to prevent degenerative changes in the intervertebral disc.37 These various intervertebral movements include flexion, extension, lateral bending and torsion. Previous studies on porcine specimens have suggested that small torsion ro tations have an effect on disc height.37 In a previous research study, it was proposed that torsion torque could affect the pattern of fluid loss and depressurization of the intervertebral disc that occurs in daily loading, and therefore have an instantaneous effect on disc height and

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2 intradiscal pressure.17,37 The previous research by van Deursen tested only porcine disc body units (DBU’s: moti on segments with posterior elements removed), to determine if torsion torque had an affect on intradiscal pressure and disc height. Only DBU’s were used because it allowed fixation of the specimens into the testing apparatus. The motivati on behind the current research was to extend and expand the previous research to include testing not only DBU’s in human specimens, but testing functional spine units (FSU’s: motion segments with posterior elements intact) as well The reason behind testing FSU’s was because those results would have more clinical relevance since people have posterior elements (at least prior to a surg ical operation). The objective of this research was to biomechanically test t he hypothesis that small torsion torques cause decreased pressure in the nucleus pulposus while increasing disc height in the human lumbar spine. 1.2 Background 1.2.a Anatomy of the Human Spine The spine performs 3 significant roles including: strength for the skeleton (load-bearing); provision of movement; and protection of t he neural elements (spinal cord, nerve roots) from trauma.21,28,29 The adult spinal column consists of 7 cervical vertebrae, 12 thoracic vertebr ae, 5 lumbar vertebrae, 5 fused sacral vertebrae and 3 to 4 fused coccygeal segments.21 Motion occurs in 6 degrees of freedom: rotational and translational motion in 3 different planes. By the right hand Cartesian coordinate system and by a se mi-arbitrary convention, motion is allowed by rotation about the x-axis (flexion-extension or lateral bending), rotation about the z-axis (torsion), translation about the z-axis (axial compression), and translation about the x and y axes (shear motion in the x and y axes, respectively). The vertebrae provide anterior support and structure of t he spine (bearing about 80% of the spinal load), while the facet joints afford posterior stability

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3 (bearing about 20% of the spinal load).21,29,39 Intervertebral discs lie in between the vertebrae and are responsible for tr ansmitting loads (compressive, tensile and shear, in short duration loading and low magnitude loadi ng) and providing shock absorbance (dissipating energy by c onverting kinetic energy into heat over a longer period of time and over more components to dampen loading affects).28,39 In addition, the discs allow flexibility and motion of the spinal column.28,29,39 Intervertebral discs are made up of two parts including a gelatinous nucleus pulposus surrounded by a str ong fibrous and cartilaginous annulus fibrosus.1,4,15,29 The primary structural com ponents that make up both the nucleus and the annulus in clude collagens and proteoglycans. Each component is very important because each offers uni que structural integrity and stability to the disc.4,6,12 Specifically, proteoglycans intera ct with water to provide stiffness and compressive resilience to the tissue, while collagens provide tensile strength to the tissue.4,6,12 The nucleus is composed of hydrophilic proteins called proteoglycans and collagen protein fibers that are arranged in an irregular manner, forming a gel matrix.4,6,12,29 The nucleus is located in the c enter of the disc and is almost 90% water in young individuals.12,29 The water content is highest at birth but decreases to 70% with degeneration due to age. The annulus is the outer por tion of the disc. It is comprised of multiple layers of collagen fibers that are arranged in alternating directions (30 to the disc plane and 120 to each other), which are placed under tension when the nucleus absorbs water and swells.6,18,21,25,29 The annulus has a higher water content in younger people, about 78%, but decreases to about 70% with degeneration due to age.29,39 There are two layers of vertebral cartilage endplates, located above and below the disc, that allow for the exch ange of nutrients and water. Since IVD’s are not vascularized, except at birt h, this exchange mechanism is very important.7,28

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4 The amount of water in the nucl eus is dependent on its chemical composition in addition to the external load on the disc.2,3,9,24 When there is a high load on a disc, the pre ssure inside the nucleus increases, forcing water out of the disc and into the endplate. There, the capillaries can remove the water. When lying down, the nucleus pressure dec reases and the water returns. In effect, a pump is created resulting in circul ation that brings nutrition into the disc while removing the products of metabolism out of the disc.7,28,34 The size of the spinal canal has been found to correlate with the occurrence of back pain.21 Nerve roots exit at each vertebral level. They pass laterally through openings ca lled neuroforamina, travel under the facet joints and superior to the disc.21 As the disc height dec reases, the neuroforamina decreases as well causing the two vertebr al bodies to come closer together. Branches of the sinuvertebral nerve inner vate the outer layers of the annulus, and as the vertebral bodies come toget her, the nerve begins to be pinched.21 Back pain is thought to originate from the stimulation of this nerve. 1.2.b Comparative Porcine and Human Anatomy Animal model fidelity is an import ant issue concerning disc degeneration and bone morphology when com paring human spines to animal spines. In general, the porcine vertebrae are smalle r than the human vertebrae in all dimensions, and have similar ligam entous structure and facet joint orientation.31,43 In addition, compressive and s hear stiffness values of porcine specimens are comparable to human specimens.43 Therefore, porcine spines may be useful for studying and comparing human spines to an animal model. 1.2.c The Degenerative Process Degeneration of the spine is a preval ent problem that generally advances with age, although its occurrence is not restricted to only the elderly.28 Degenerations of the spi ne are the leading cause of pain, altered function and

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5 deformity.5,28 Degeneration of the IVD is a normal physiologic process associated with age, and usually begins around the age of 30.32 At that age, there are gradual changes in the types of proteoglycans present and therefore the overall water content of t he IVD changes similarly as well.29 In fact, degeneration may be accelerated with excessive loading of the disc.32,39 The change in water content on the disc decre ases the load experienced by the nucleus, while increasing the load experienced by the annulus.39 As the nucleus shrinks, the changes in load distribution have occurred and can result in tears, cracks, or fissures in the annulus.16,19 The defects usually occur in the posterior and posterolateral regions of the annulus, which can prolifer ate and cause the nuclear material to migrate from t he center to the per iphery of the disc.16,19 The expansion of the nucleus through the annular layers causes stretching and delamination of these layers and causes back pain due to stimulation of the sinuvertebral nerve.19 A complete extrusion of the nucleus through all of the layers of the annulus can result, causing a disc herniation.19 The nucleus that was protected from the va scular system and immune system, is now exposed to it and it causes an inflammatory response to occur.21 In addition, the herniated disc may compress a nerve root causi ng severe pain. The biomechanical properties of the disc including the abili ty to transmit load, absorb shock and allow motion, change significant ly with degeneration due to age.39 Because of aging, the disc desiccates and becomes less compressible. Additionally, the vertebral endplates become sclerotic, less porous, and less able to transport nutrients to the disc.34 Since diffusion is the main mechanism of transport through the disc, when the disc is unable to obtain as many nutrients or remove waste products efficiently, the pump action is largely lost.34 Also, an acidic environment is created when t he metabolic end-products accumulate.34 There may be an inflammatory response to the site as we ll. Both the acidity and inflammatory response cause pain. As a result of the desiccation of the disc, there is a reduction in the height of the disc. The annular fibers bow out, and this leads to thecal sac and nerve

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6 root compression. Furthermo re, spinal stability is alte red. Stability is changed when the discs are no longer capable of s upporting the weight of the spine, and facets and ligaments are forced to support more weight. The facets and ligamentum flavum can become hypertrophi ed, leading to less space for the thecal sac and nerve roots, causing neural compression and pain.21 With the degenerating facets, the discs experience additional shear stress, and become further degraded. This causes increased pain, spinal instability and spinal misalignment.26 Since a reduction in disc height is a major source of pain for millions of people, treatments or surgical operations should focus on restoration of disc height. In order to restore disc height, it is critical to understand what motions could contribute to a disc height change. 1.2.d Research Objective The hydrostatic pressure within the nuc leus pulposus is a key component for the ability of the IVD to support physiologic loads.36 Horst and Brinkmann studied the distribution of axial stress on the vertebral body end plate by using pressure transducers in IVD’s of cadaveric lumbar spine segments.13,28 McNally and Adams used intradiscal stress profilo metry to determine the pressure distributions within the human IVD.3,24 Van Deursen found a decrease in intradiscal pressure and an increase in disc height with increased torsion in the porcine DBU.37 Although intradiscal pressure s and the affects of aging, degeneration and loading have been studi ed and modeled, there is little information on disc heights and intradiscal pre ssures related to torsional torques applied to the human lumbar spine.20,24,27,35 The purpose of the present research was to gain a more detailed understanding of height and intradiscal pressure changes that may accompany torsiona l torques, by measuring pressure distributions within loaded human cadav eric lumbar intervertebral discs.

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7 1.3 Current Intervertebral Disc Model The IVD is subjected to many differ ent loads in everyday life. It is a complex mechanical system that is assu med to distribute compressive stresses evenly between adjacent vertebrae because the nucleus pulposus and inner annulus act as a pressurized fluid t hat does not vary with location or direction.2,3,37 According to Adams et al,3 the nucleus acts as a sealed hydraulic system, where the fluid pressure rises s ubstantially when volume is increased (by fluid injection) and falls when volume is decreased (by surgical excision or endplate fracture).2,3,37 The IVD, therefore, is able to withstand compression because of the swelling pressure exert ed by the nucleus pulposus which is constrained radially by the annulus fibrosus.14,28 Previous loading and disc degeneration can cause peaks in the recorded pressure. Previous authors have reported that small axial torsion rotations of the porcine disc caused a decrease of pressure in the nucleus pulposus.37 Furthermore, the pressure reduction in t he nucleus under torsional rotations was related to an increase of disc height.37 An increase of disc height would explain the pain reduction patients with low back pain can achieve through small rotations.37 The increase in disc height woul d decrease facet joint loading and increase the foraminal space, thus minimizing pain.37 However, the results were obtained from porcine specimens without poste rior elements. Porcine specimens generally show no signs of IVD degener ation and posterior elements are important because of their clinical relevance in the human population. To determine if IVD condition and pos terior elements affected pressures and disc heights with different torsion torques in human specimens, torsion torques were applied to human cadaveric specimens. The pressure profiles were measured through the human IVD in neutral position, 0. 5 Nm, 1.0 Nm and 2.0 Nm of torsion (up to 1.5 right tors ion), as described by McNally and Adams et al.3,24 Both FSU’s and DBU’s were tested in human cadaveric specimens. Those torsion torques were within the ph ysiologic range (5-7 r ange of motion) to prevent damage to the facet joints and remain within the range used in the

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8 previous porcine research.37,39 Disc heights were measured and recorded to determine if there was a significant change with the application of different torsion torques. 1.4 Intradiscal Pressure History Most of the present knowledge related to intradiscal pressures was produced from studies by Nachemson.27 These pressure measurements were performed in the 1960’s and 1970’s in c adaveric IVD’s using a polyethylenecovered disc pressure probe connect ed to an external electromanometer.27,33,36 Nachemson and collaborators went on to measure IVD pressures in vivo for different body postures and while perfo rming a variety of lifting maneuvers.27 Their measurements revealed that the nucleus pulposus behaved as a hydrostatic fluid.2,3,27,36 Although useful data was recorded, the method had many disadvantages including the probe hav ing a very cumbersome assembly and calibration, as well as the probe displaying poor dynamic characteristics.27 Additionally, high pressures could damage the probe.27 A new method of measuring intradiscal pressure was developed that used a more advanced pressure sensor with strain gauges.41 This method minimized those problems. 1.5 Pressure Measurements There are different techniques for m easuring nuclear pressure including simple liquid-coupled systems to stra in-gauge transducers mounted on the ends.24 These techniques have demonstrated that the center of the nucleus behaves as a fluid, except in discs that are severely degenerated.24 There are no measurements, however, that report the stress in FSU’s compared to DBU’s in specimens with and without disc degenerat ion. Pressure measurements could be obtained by inserting a pressure pr obe into the disc and varying its position and orientation in several different specimens, with and without posterior elements, and recording the pressure continuously.24,30

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9 A probe capable of measuring stresses within a disc was developed and tested by McNally and Adams et al.3,24 The probe measured the component of compressive stress perpendicular to its s ensitive surface, the sensing element, and was mounted on the side of the probe so it could be rotated to measure the component of stress in different orientati ons. The gross mechanical properties of the disc were not adversely affected as the diameter (1.27 mm) of the probe was small and could be positioned anywhere wit hin the nucleus or annulus. By moving the probe through the disc, a conti nuous plot of pressure against time could be obtained along any path and a comple te plot of pressure measurements within the disc under different par ameters could be constructed.3,23,24 1.6 Apparatus The pressure probe (OrthoAR Model No: 0571521-57, Medical Measurements Incorporated, Hackensack, NJ ) used in this research consisted of a pressure sensor mounted on a 125 mm long, 1.27 mm diameter stainless steel probe (Figure 1, C.) The finish at the end of the probe was rounded and the sensor was located proximal to the end. The probe was connected to a 50 cm long, 3.17 mm outer diameter cable cons tructed from an ultraflex catheter material that terminated in a lightweight connector. The catheter material was flexible to reduce tension wh ile making measurements. The operating principle of t he pressure probe was based on the piezoresistance of semiconductor strain gauges.24 It was a microelectromechanical system (MEMS) dev ice using a full bridge gauge to form a Wheatstone bridge. The piezor esistors generated an output voltage proportional to the applied pressure. The pressure transducer had a full scale range of 0-2 MP a with a burst pressure of 3.5 MPa and could withst and temperatures of 25C to 37C.

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10 Chapter Two: Materials and Methods 2.1 Cadaveric Material Ten human lumbar cadaveric sp ines were obtained at routine postmortems from individuals who had been mobile prior to death and had no history of disease known to affect t he biomechanical properties of the spine.24 The ages of the individuals ranged from 38 to 65 years (mean, 50 years; Table 1). The ten specimens were radiogr aphed using magnetic resonance imaging (MRI; GE LX, High Field 1.5 Tesla Scanner) and X-rayed using the digital Faxitron (Model No: MX-20, Wheeling, Illi nois) to determine if any bone, disc, or facet joint abnormalities were present. Figure 2 was an example of an X-ray taken of specimen UF05H007. Figures 3 and 4 demonstrated examples of MRI’s taken of spines UT04K009 and UF05B003, re spectively, before disarticulation. Four specimens revealed either bridgi ng osteophytes across the disc space of interest, a collapsed disc space or vertebral compression fractures, causing them to be excluded from testing. The remaining 6 specimens were stored in a freezer at -17 C for up to 6 months before disartic ulation. Previous research by Dhillon, Bass and Lotz reported that freezing specim ens for a reasonable amount of time using a typical method of freezing and thawing did not significantly effect the properties of human lumbar discs.8 Each specimen was then thawed at 7 C and disarticulated into an L1-L2 FSU (functional spine unit) consisting of two adjacent vertebral bodies and the IVD (intervertebr al disc) between them (Figure 5). Excess musculature was removed from eac h FSU but caution was taken to keep the disc, ligaments and facet joint capsules intact. After disarticulation, each specimen was potted with a mildly exothe rmic polyester resin using 4 X 4 inch potting frames on either end (Figures 6 and 7). Screws were used to secure the vertebral bodies into the resin and additi onal x-rays were taken with a digital X-

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11 ray unit (Faxitron, Model No: MX-20, Wheel ing, Illinois) to c onfirm that no screws had penetrated the disc-space (Figure 8) The specimens were routinely sprayed with saline during tissue preparatio n and potting to prevent desiccation. One specimen at a time was disartic ulated, prepared and potted, while the remaining specimens were kept in the freezer. After each specimen was prepared and was ready to be used, it wa s thawed and tested immediately. Each specimen was tested during a two day period. 2.2 Experimental Technique The experiment was performed under the University of South Florida, Institutional Review Boar d requirements. Six L1L2 human cadaveric lumbar motion segments were tested with and witho ut posterior elements using a servo hydraulic materials testing system (MT S Systems Incorporated, 858 Bionix II, Eden Prairie, MN). The upper framed vertebral body was tightened into a stationary fixture attached to an anti-ro tation device and a load cell, while the bottom framed vertebral body was tightened in to a fixture attached to the torsion motor (Figure 9). The fixture system allowed axial compression to be continuously applied with and without comb ined torsional loading. The testing sequence included each FSU being axially compressed for 2 hours, immediately followed by combined axial compressi on and torsion torque (while taking pressure measurements) for less t han 16 minutes (Figures 9 and 10). Subsequent to testing, the posterior elements of each FSU were removed to convert the FSU into a DBU. The same testing protocol was repeated for each of the 6 DBU’s. The water content of an IVD may c hange postmortem as a result of an extended period of unloading. Therefore, a preliminary creep test was performed on each specimen to normalize the water distribution of the disc.2,23 Fluid was squeezed out of the disc by compressing each FSU or DBU for 120 minutes at 600 N, to simulate relaxed standing (Figure 9).23,36,38,40,42 It was found in previous studies that simulating muscle forces substantially affects intradiscal

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12 pressure, so 600 N was applied to all specimens for both the creep and torsional tests.38,40,42 Following the creep test, all 6 FSU’s and all 6 DBU’s were compressed continuously at 600 N, to simulate physi ologic loading, while torsion torque was applied at 0 Nm, +0.5 Nm, +1.0 Nm and +2.0 Nm. Du ring each different torsion torque application, pressure measurem ents were obtained with the pressure probe. Only positive torsional torques were applied because initial testing revealed no significant difference betw een positive and negative torsion torques. The various positions were achieved by the MTS using MPT software and a custom computer-controlled torsion motor that rotat ed the lower vertebral body over a specified torque. The durati on of each test lasted 15 minutes and 45 seconds. Time, axial force, axial displacement, torsi on torque, torsion angle, and intradiscal pressures were recorded by MPT during each test. Creep was a factor that affected each specimen, however, the co ntribution due to creep was taken into account using a logarithmic function during data analysis.11 The pressure measurements were collected using a pressure probe (Figure 1 C). The pressure probe was in troduced into the disc by the following method. A 1.25-mm diameter hypodermi c needle (Figure 1 B), surrounded by a 1.85-mm stainless steel cannula (Figur e 1 A), was pushed into the anterior annulus in the midsagittal plane of the IVD until it pushed through the posterior annulus (Figure 10). Care was taken to ensure the cannula was parallel to and equidistant from the two ve rtebral end plates. The needl e was removed from the cannula and the pressure probe was inse rted. The cannula was pulled back so the transducer tip was exposed to the posterior annulus, and the pressure probe was manually pulled through the disc at a speed of about 2 mm/sec until it emerged from the anterior annulus comp letely. The pressure-sensitive membrane of the pressure probe was oriented either horizontally or vertically in order to measure the pressures in t he horizontal or vertical directions, respectively. The cannula was inserted into the same needle track to reduce alterations of the IVD that could aris e from multiple needle sticks. The

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13 measurements were reproducible and did not perturb the tissue to any significant extent. The pressure probe was calibrated bef ore the start of the experiment and at the end of the testing using a National Institute of Standards and Technology (NIST) certified pressure gauge (Figure 11 A). There was no change in the probe, so any pressure changes that we re seen during data collection were due only to pressure changes of the specim en itself and the torsion torque applied, not from changes in the pressure probe. 2.3 Validation Degradation could be a limit ing factor when testing cadaveric specimens. To determine if degradation occurred, a pr essure measurement at 0 Nm torsion torque was taken after the other four to rsions torques (0 Nm, 0.5 Nm, 1.0 Nm and 2.0 Nm) were applied. The initial pressure m easurements taken at 0 Nm and the repeat measurement take n at 0 Nm at the end of the test were compared to determine if there was a significant difference between them If there was no significant difference between the two 0 Nm measurements, then the testing did not significantly degrade the cadaveric tissues under investigation. The likelihood of specimen degradation occurring under r epeated loading prevented the testing of all combinat ions on each motion segment. Another problem that could occur dur ing testing is equipment failure. In order to test that the probe did not m easure pressure inaccurately, it was calibrated at the beginning an d calibrated at the end of testing, and the results were compared. The pressure probe wa s calibrated using an NIST certified pressure gauge (Figure 11 A). The NIST certified pressure gauge used was a bubble-free, glycerin-filled, nylon-case gauge with a 1% full-scale accuracy. The glycerin gauge was mounted on pipe fittings t hat were connected to the pressure probe (Figure 11 B). Both the gauge and the probe were connected up to a nitrogen tank pressure source (Figure 11).

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14 2.4 The Effect of Different Torsion Torques on Pressure and Disc Height Pressure profiles were obtained fo r all 6 FSU and all 6 DBU specimens while torsion toque was varied independe ntly. Intradiscal pressure and disc height were dependent variables that were recorded and analyzed. Up to 5 pairs of horizontal and vertical pressure pr ofiles were obtained from each motion segment (including FSU’s and DBU’s). T he compressive force applied was 600 N in order to simulate relaxed standing in vivo .40,42 2.5 Statistical Analysis The results from the torsion torques applied to all 6 specimens (FSU’s or DBU’s) were averaged, including pre ssures and differential disc heights. Descriptive statistics and single factor analysis of variances (ANOVAS) were performed with pressure (among and bet ween 6 FSU’s and 6 DBU’s), torsion torque (0 Nm, 0.5 Nm, 1.0 Nm and 2.0 N m), and differential disc heights (among and between 6 FSU’s and 6 DBU’s). The nu ll hypothesis was Ho: 1=2, while the alternative hypothesis was Ha: 1 2. The alpha value of =0.05, beta value of =0.35, and power of 65% used during da ta analysis were determined a priori. Results with a p-value of 0.05 or less were considered significant. As detailed in results section 3.4, 2 specimens were removed from the data analysis because of disc degeneration. The statistical analysis performed on the remaining 4 specimens included descr iptive statistics and single factor analysis of variances (ANOVAS) of pr essure (among and between 4 FSU’s and 4 DBU’s), torsion torque (0 Nm, 0.5 Nm, 1.0 Nm and 2.0 Nm), and differential disc heights (among and between 4 FSU’s and 4 DBU’s). The null hypothesis was Ho: 1=2, while the alternative hypothesis was Ha: 1 2. An alpha value of =0.05, beta value of =0.5, and power of 50% were used for the analysis. Results with a p-value of 0.05 or le ss were considered significant. Linear regression analysis was performed for pressure versus torsion on n=6, for pressure versus torsion on n= 4 and for height versus torsion on n=6.

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15 Chapter Three: Results 3.1 Tissue Degradation During Testing The mean pressure measurements taken at the beginning and completion of the test protocol at 0 Nm were compared between all functional spine units (FSU’s) and all disc body units (DBU’s ). The results revealed a mean FSU pressure of 0.65 MPa, and no signific ant difference between the two 0 Nm measurements of the FSU’s (p=0.67). Similarly, there was no significant difference between the 0 Nm measurements of the DBU’s (p=0.54), with a mean DBU pressure of 0.57 MPa. An example of the pressu res at 0 Nm taken at the beginning and end of the test could be se en in the FSU specimen UT04K009 (Figure 12) and DBU specimen UT04K00 9 (Figure 13). Since it was demonstrated that there was no signific ant difference between the pressure measurements taken at 0 Nm before t he test started and at 0 Nm at the completion of the test pr otocol, it is clear that no apparent degradation occurred and testing did not significantly disturb the cadaveric tissues. 3.2 The Effect of Pressure Probe Orientation The results of intradiscal pressure s taken with the pressure probe in horizontal and vertical orientations re vealed that there was no significant difference of pressures in the lumbar L1-L2 FSU or DBU. This finding was independent of the torsion torque applied and presence or absence of posterior elements (FSU: 0 Nm p=0.91, 0.5 Nm p= 0.95, 1.0 Nm p=0.83, 2.0 Nm p=0.95; DBU: 0 Nm p=0.97, 0.5 Nm p=0.84, 1.0 Nm p=0.90, 2.0 Nm p=0.30) (Table 2). Figures 14, 15, 16 and 17 demonstrated an example of horizontal and vertical pressures recorded for DBU UJ04L015, at 0 Nm, 0.5 Nm, 1. 0 Nm and 2.0 Nm,

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16 respectively. This result confirmed the work done by McNally and Adams, who found that pressure was not affected by pressure probe orientation in healthy specimens without disc degeneration. 3.3 The Effect of Disc Degeneration on Pressure Intervertebral discs (IVD’s) with littl e or no degeneration revealed pressure graphs very different from those discs with increased degeneratio n. The graphs of normal IVD’s in the FSU’s and DBU’s revealed a pressure plateau corresponding to the functi onal nucleus and inner annulus. 24 The central region of the nucleus exhibited a hydrostatic pr essure, however the ‘stepped’ portion of the graph correlated to the functional annu lus. Graphs from normal discs looked like those in Figures 18-19 (49 year old) Figures 20-21 (38 year old), Figures 2223 (43 year old) and Figures 24-25 (65 year old) (Table 1). The spikes that could be seen in a few graphs were due to artifa cts caused by movement of the probe during its insertion or removal. Gr aphs from degenerated discs were generally similar to those shown in Figures 26-27 (56 year old) and Figures 28-29 (52 year old) (Table 1). Those graphs were irr egular with numerous spikes, and showed no clear-cut region of hydrostatic pressure It could therefore be said that degeneration of the disc had an apparent effe ct on intradiscal pressure, which confirmed the research done by McNally and Adams. 3.4 The Effect of Pressu re with Applied Torsion To make quantitative comparisons between pressures recorded from different specimens, mean pressures of the 6 specimens were determined for each torsion torque of the 6 FSU specim ens and of the 6 DBU specimens (Figure 30). Descriptive statistics and ANOVAS were performed among and between all 6 FSU’s and DBU’s and each torsion tor que applied (Table 3). Results showed that there was no significant differ ence (p>0.05) between pressure and the torsion torque applied between 6 FSU’s and torsion, 6 DBU’s and torsion, and

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17 the FSU’s compared with the DBU’s and torsion. The mean pressures of the 6 specimens tested ranged from 0.62 MPa to 0.68 MPa for FSU’s and 0.52 MPa to 0.61 MPa for DBU’s (Table 2). A trend in the 6 FSU’s and 6 DBU’s towards a decrease in intradiscal pressure with an in crease in torsion torque was observed (Figure 30). However, the results revealed no significant differences in pressure when torsion torque was increased among and between FSU’s and DBU’s. Additionally, the standard deviations were large, due to high va riability of the human specimens (Figure 30). Upon in spection of Table 2, specimens UM05H007 and UJ04J002 revealed a decrease in their confirmation pressures at 0 Nm after the test was completed, w hen compared to their pressures at 0 Nm before the test started. This was probabl y due to an artifact during testing. When analyzing data, it was observed that 2 specimens had much lower average pressures for any given torsion torque. The lower average pressures were most likely due to disc degenerat ion, based on results of research performed by McNally and Adams (Figures 26-29). Those 2 specimens were removed from the analysis to determine if there any significant changes of pressure with an increase in torsion to rque could be observed with a sample of normal discs n=4 (Table 4). The pre ssures increased slightly and showed a trend towards a pressure decrease with an increase in torsion torque. However, there was still no significant differenc e in pressure among and between the 4 FSU’s and DBU’s (p>0.05) (Table 5). The standard deviations decreased, however, revealing less variability of the human specimens with an n=4 (Figure 31). 3.5 The Effect of Disc He ight with Applied Torsion One of the goals of the re search preformed was to determine if disc height changes, specifically an increase, could be correlated with applied torsion torque under a predetermined loading protocol. To determine any difference in disc height, the amount of axial displacem ent had to be calculated. However,

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18 although the rate of creep decreased duri ng the testing, it did not reach equilibrium. This was concluded by ex amining creep curves of the FSU and DBU during initial loading (Figures 32, 33 and 34) and examining creep curves of the FSU and DBU during in itial loading and testing (Figures 35 and 36). Because of this, the contribution due to creep had to be removed to obtain the possible disc height change due to torsion torque only, and not due to creep and torsion torque. To determine the contribution due to creep, the following steps were taken. Axial displacement versus time was graphed showing creep and any height differences that occurred (Figure 37). Then, any height differences were removed and a logarithmic trendline added (Figure 38) to predict the axial displacement due to creep only (Figure 39). The axial displacement with height changes and creep was subtracted from the axial displacement due to creep alone. Finally, axial displacement s howing any occurring height differences without creep were exposed (Figure 40). This procedure was repeated for all 6 FSU and all 6 DBU specimens (Figures 41-84). To determine if disc height changed with applied torsion torque, graphs of axial displacement, torsion torque, and pr essure were created (Figures 85-96). There was no change in disc height observed wit h an increase in torsion torque. There was an observed difference in disc height some time after each torsional change that could be directly expl ained by the insertion of the cannula. For example, the torsion torque changed and held its position while disc height remained constant. When the cannula wa s inserted with the needle, however, a disc height difference could be observed (F igures 85-96). In fact, a disc height increase occurred during each cannula insertion into each specimen. The mean height difference ranged from 0.13 mm to 0.16 mm for all specimens (FSU and DBU) when any torsion torques were applied (Figure 97, Table 6). This led to the question of whether the height increase changed as torsion was increased or with the removal of posterior elements. There was no significant difference between differential disc height due to specific torsion

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19 torques applied (p>0.05) (Tables 6 and 7). Additionally, there was no significant difference between differential disc height and torsion torques among and between the FSU’s and the DBU’s (p>0.05) (Tables 6 and 7). 3.6 The Correlation of Pressure and Disc Height with Torsion The linear regression analysis of pressure versus torsion for the 6 FSU’s and 6 DBU’s revealed no correlation (Table 8). Those slopes were negative and very close to zero. The anal ysis of pressure versus torsion for the 4 FSU’s and 4 DBU’s also revealed no correlation (Tabl e 8). Those slopes were negative and very close to zero. Finally, the analysis of height versus torsion for the 6 FSU’s and 6 DBU’s revealed no correlation (Table 8). Those slopes were negative and very close to zero. Therefore, it c an be said that there is no correlation of pressure or disc height with different torsion torques.

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20 Chapter Four: Discussion 4.1 Discussion of Results To our knowledge, the effects of va rying torsion torques on disc height and intradiscal pressure in human L1-L2 s pecimens with and without posterior elements under 600 N have not been previo usly studied. It was found that torsion torques of 2 Nm and less had no in stantaneous effects on the disc, either in disc height increase or intradiscal pressu re decrease. However, a disc height increase occurred with the insertion of a cannula. Such an increase has valuable implications because it demonstrated how to gain disc height in an intervertebral disc (IVD). A method to increase disc hei ght could lead to a low cost, minimally invasive technique to minimize chroni c low back pain for millions of people. The current research did not find a si gnificant increase in disc height or decrease in intradiscal pressure of t he human L1-L2 disc space. However, if other human functional spine units (FS U’s) demonstrate a disc height increase under different parameters, then clinical relevance could be applied in approaches such as therapies, treatments, or surgeries t hat reflect the results. Other human FSU specimens could reveal different results because the facet joints of the human lumbar spine ar e oriented differently as one proceeds caudally down the spine. For example, t he L1-L2 facets joints are oriented closer to the mid-sagittal plane at about 26-34, wh ile the L5-S1 facet joints are oriented farther from the mid-sagi ttal plane at about 40-56.22 The facet joints in between those act as transitions, and are therefore oriented accordingly. The facet joints of the lower vertebral bodies may ‘ri de up’ on each other during torsional rotations and it may be possible to obtain a decrease in intradiscal pressure and an increase in disc height in those moti on segments. Since low back pain (LBP)

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21 is prevalent in the lower motion segment s (ie: L3-L4, L4-L5 and L5-S1), it could be very important to determine the validity of this hypothesis. There was no disc height increase due to torsion observed in this study, however, there was a disc height increas e seen due to the insertion of the cannula. The implications are important regarding future work because more research could lead to the development of a biocompatible material of a specific size to be inserted into a degenerated di sc to regain disc height. The height gain would have an immediate, pain-reducing e ffect through the decrease of contact forces on facet joints, the increase in foraminal space, and the normalization of pressure distribution in the disc.37 In addition, it can be inferred that the height gain would enhance avascular nutrit ion and thus counteract degenerative changes.37 In order for the pressure probe to record compressive pressure consistently, the pressure must act ev enly on the probe membrane, requiring the surrounding medium to be capable of conforming to its surface.24 Because plateaus or peaks can be seen in all graphs, it can be inferred that the pressure probe accurately recorded the pressures taken and that there was enough mobile proteoglycans-water gel combinat ion in the IVD’s to be accurately measured. The tests revealed that the pressure measurements were reproducible and did not significantly alter the tissues being studied. 4.2 Limitations 4.2.a Sample Size and Variability The small sample size (n=6) and vari ability were limitations of this research. The small sample size l ed to an underpowered study both with the analysis using 6 specimens (Power=65%) and with the analysis using 4 specimens (Power=50%). The high vari ability of the spec imens including age range and disc condition, led to high standard deviations.

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22 4.2.b Testing Torsion torques of less than 2 Nm were used in order to keep the forces within physiologic loading ranges. However, the range of motion was up to 3, which is less than the maximum ranges of motion reported in Panjabi and White. Loading should not damage t he motion segment, but could incorporate the higher end of the range (ie: 6).39 It could be possible that higher torsion torques could reveal a decrease in intradiscal pressure and an increase in disc height. Only two degrees of freedom were used in the current research, because of the degradation and dehydrat ion issues associated with the lengthening of the testing time. However, other degrees of freedom including flexion-extension and lateral bending could demonstrate a change in intradiscal pressure and disc height. One lumbar motion segment (L1-L2) wa s used to perform these tests. This was due specifically to specimen availability. Although the L1-L2 motion segment generated useful resu lts, the motion segments in the lower lumbar spine (ie: L4-L5 and L5-S1) are highly a ssociated with low back pain (LBP). Therefore, determining the results of increased torsion torques on intradiscal pressure and disc height in other motion segments would be important.

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23 Chapter Five: Future Work 5.1 Research 5.1.a Sample Size and Variability Although there was some variety of the degree of degeneration in the discs used in this research, a future study could include a much larger sample size of nondegenerated discs and severely degenerated discs to compare age to degeneration. Although the te sting preformed revealed important results regarding disc height and intradiscal pre ssure changes with different applied torsion torques, it is hard to make generalizations with only 6 specimens. Additionally, the dynamic properties of the spine may be lost with age and degeneration. Therefore, futu re work would include test ing a larger sample size of nondegenerated and degenerated FSU’s and DBU’s using the same testing parameters. 5.1.b Testing The current research also revealed that different applied torsion torques less than 2 Nm do not significantly increas e disc heights nor decrease intradiscal pressures. Although the pressures t end to decrease with increased applied torsion torques, there was no significant change in pressure. Even though this finding is very important, a question arises as to whether applied torsion torques greater than 2 Nm would have similar or opposite affects under the same loading conditions. Since 2 Nm is a very sma ll applied torque, it would be useful to determine what result higher torsion to rques yield, under the same loading conditions. Future steps would include te sting the specimens up to a specimenspecific physiologic applied torsion torque, under the same loadin g conditions. In

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24 addition to testing specimens under lar ger applied torsion torques as described above, it would be beneficial to test the same torsion to rques at different loading rates. Different loading rates of torsion torque could show a different outcome because loading rates would change the stiff ness of the disc. As a result, this may have a significant effect on disc height and intradiscal pressure. The current research focused on determining disc height and intradiscal pressure changes in only the torsion degr ee of freedom with axial compression. Important future work woul d expand the testing of tors ion torques on disc heights and intradiscal pressures to include other degrees of freedom such as flexion, extension, left bending and right bending und er similar loading conditions. The effects of different torques and angles in other degrees of freedom could reveal important effects that various to rques have on disc height and intradiscal pressures. The likelihood of spec imen degradation occurring under repeated loading prevented the testing of all combi nations on each motion segment in this research. Although testing in all 6 degrees of freedom would present a considerable problem with regard to degr adation, an improvement in the testing environment could help alleviate this problem. Designing and building a tank capable of testing specimens in a simula ted ideal physiologic testing environment (37C saline water) could help to minimize the occurrence of degradation, while being able to determine disc height and intradiscal pressure changes in specimens in all ranges of motion. This would necessitate the design of a new fixture system, but could be worth the investment. Another area of significant future wo rk includes studying disc height and intradiscal pressure changes among other f unctional spine units in the lumbar spine. Although the availability of specim ens limited this research to testing only the L1-L2 motion segments, it would be va luable to study other segments for a significant reason. Since the facet joints of the human lumbar spine are oriented differently as you proceed caudally down the spine, it could be useful to determine if the orientation of the facet joints play a role in any disc height or intradiscal pressure changes with increased torsion torques. It is hypothesized

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25 that while there would be no change seen in the rostral motion segments with transitional facet joint orientations (ie: L2-L3 and L3-L4), the lower motion segments (ie: L4-L5 and L5-S1) may reveal a disc height gain or an intradiscal pressure decrease. If there was an observed height change of the lower segments and not the upper segments, it could be explained by a phenomenon of the facet joints riding up on each other that facilitates the changes. This has clinical significance because pain reduci ng therapies, including torsion torque, could be incorporated into treatment for people with low back pain. 5.2 Applications The current research demonstrated that while disc height increases were not observed with changes in torsion to rque, disc height increases were seen with the insertion of the cannula. This is a very important finding as this shows how to gain disc height in a degenerated IVD. In fact, if a cannula of a specific size can increase disc height, then it c an be hypothesized that the addition of specific materials of a certain size will c ause in increase in disc height as well. For example, material of a specific diam eter and length could be inserted to gain disc height. The advantages surrounding this idea include an appealing minimally invasive technique as well as a lower cost product and surgical procedure. Obviously a great deal of future work surrounds this idea on the order of determining types, shapes and size s of materials, interactions with biological tissue, migration, and patient candidacy, to name a few, but it opens the doors for new research.

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26 References 1. Adams, M., Bogduk, N., Burton, K., Dolan, P. Biomechanics of back pain. Churchill Livingstone. 2002. 2. Adams, M.A., McMillan, D.W., Gr een, T.P., Dolan, P. Sustained loading generates stress concentrations in lumbar intervertebral discs. Spine 1996; 21: 434-438. 3. Adams, M.A., McNally, D.S., Dolan, P. “Stress” distribution inside intervertebral discs. J Bone Joint Surg 1996; 78: 965-972. 4. Ashman, R.B. Disc anatomy and biomechanics. Spine 1989; 3: 13-26. 5. Buckwalter, J.A. Spine Update: Aging and Degeneration of the Human Intervertebral Disc. Spine 1995; 20: 1307-1314. 6. Bushell, G.R., Ghosh, P., Tayl or, T.F., Akeson, W.H. Proteoglycan chemistry of the intervertebral discs. Clin Orthop 1977; 115-123. 7. Crock, H.V., Yoshizawa, H. The blood supply of the lumbar vertebral column. Clin Orthop 1976; 6-21. 8. Dhillon, Nripendra, Bass, Elisa, Lotz, Jeffrey. Effect of frozen storage on the creep behavior of human intervertebral discs. Spine 2000.; 26: 883888. 9. Ekstrom, L., Holm, S., Holm, A.K., Hansson, T. In vivo porcine intradiscal pressure as a function of external loading. J Spinal Disord Tech 2004; 17: 312-316.

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27 10. Evans, W., Jobe, W., Se ibert, C. A cross-secti onal prevalence study of lumbar disc degeneration in a working population. Spine. 1989; 14: 60-64. 11. Fung, Y.C. Biomechanics: Mechanica l Properties of Living Tissues. New York, Springer-Verlag. 1993. 12. Hayes, A.J., Benjamin, M., Ral phs, J.R. Intracellular matrix in development of the in tervertebral disc. Matrix Biology 2001; 20: 107-121. 13. Horst, M., Brinckmann, P. Measurement of the distribution of axial stress on the end-plate of the vertebral body. Spine. 1981; 6: 217-232. 14. Hukins, D.W.L., Meakin, J.R. Relationship between structure and mechanical function of the tissues of the intervertebral joint. Amer Zool 2000; 40: 42-52. 15. Humzah, M.D., Soames, R.W. Human intervertebral disc: structure and function. Anat Rec 1988; 220: 337-356. 16. Iatridis, J.C., MacLean, J.J., Ry an, D.A. Mechanica l damage to the intervertebral disc annulus fibros us subjected to tensile loading. J Biomech 2004; 38: 557-565. 17. Janevie, J., Ashton-Miller, J., Schultz, A. Large compressive preloads decrease lumbar motion flexibility. J Orthop Res 1991; 9: 228-236. 18. Johnstone, B. Urban, J. P.G., Roberts, S., Menage, J. The fluid content of the human intervertebral disc: com parison between fluid content and swelling pressure profiles of discs removed at surgery and those taken postmortem. Spine 1992; 17: 412-416. 19. Lee, S.H., Derby, R., C hen, Y., Seo, K.S., Kim, M. J. In vitro measurement of pressure in intervertebral di scs and annulus fibrosus with and without annular tears during discography. Spine J 2004; 4: 614-618.

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28 20. Lu, Y.M., Hutton, W.C., Gharpuray, V. M. Can variations in intervertebral disc height affect the mechani cal function of the disc? Spine 1996; 21: 2208-2216. 21. Marieb, E.N., Mallatt, J. Human Anatomy Third Edition. Benjamin Cummings. 2001. 160-184. 22. Masharawi, Y., Rothschild, B., Dar, G., Peleg, S., Robinson, D., Been, E., Hershkovitz, I. Facet orientati on in the thoracolumbar spine. Spine 2004; 29: 1755-1763. 23. McMillan, D., McNally, D.S., Gar butt, G. Stress distributions inside intervertebral discs: the validity of experimental “str ess profilometry”. Proc Mech Inst Eng 1996; 210: 81-87. 24. McNally, D.S., Adams, M.A. Inter nal intervertebral disc mechanics as revealed by stress profilometry. Spine 1992; 17: 66-73. 25. Mercer, S., Bogduk, N. The ligam ents and annulus fibrosus of human adult cervical intervertebral discs. Spine 1999; 24: 619-628. 26. Mimura, M., Panjabi, M.M., Oxland, T.R., Crisco, J.J., Yamamoto, I., Vasavada, A. Disc degeneration affects t he multidirectional fl exibility of the lumbar spine. Spine 1994; 19: 1371-1380. 27. Nachemson, A. Disc pressure measurements. Spine. 1981; 6:93-97. 28. Niosi, C.A., Oxland, T.R. Degenerativ e mechanics of the lumbar spine. Spine J. 2004; 4: 202S-208S. 29. Nordin, M., Frankel, V.H. Basic Biomechanics of the Musculoskeletal System Third Edition. Philadelphia, PA, Lippincott Williams and Wilkins. 2001. 10-14, 257-260, 293-295.

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29 30. Park, C., Kim, Y.J., Lee, C.S., An, K., Shin, H.J., Chang, H., Kim, C.H., Shin, J.W. An in vitro animal study of the bi omechanical responses of annulus fibrosus with aging. Spine 2005; 30: E259-E265. 31. Panjabi, M.M., Goel, V ., Oxland, T., Takata, K., Duranceau, J., Krag, M., Price, M. Human lumbar vertebr ae: quantitative three-dimensional anatomy. Spine 1992; 17: 299-306. 32. Polga, D.J., Beaubien, B.P., Kalleme ier, P.M., Schellhas, K.P., Lew, W.D., Buttermann, G.R., Wood, K.B. Measurement of in vivo intradiscal pressure in healthy thoracic intervertebral discs. Spine 2004; 29: 1320-1324. 33. Sato, K., Kikuchi, S., Yonezawa, T. In vivo intradiscal pressure measurements in healthy individuals and in patients with ongoing back problems. Spine 1999; 24: 2468-2474. 34. Selard, E., Shirazi-Adl, A., Urban, J. P.G. Finite element study of nutrient diffusion in the human intervertebral disc. Spine 2003; 28: 1945-1953. 35. Shirazi-Adl, S.A., Shrivastava, S.C ., Ahmed, A.M. Stress analysis of the lumbar disc-body unit in compression: a three-dimensional nonlinear finite element study. Spine 1984; 9: 120-133. 36. Steffen, T., Baramki, H.G., Rubin, R., Antoniou, J., Aebi, M. Lumbar intradiscal pressure measured in t he anterior and posterolateral annular regions during asymmetrical loadi ng. Clin Biomech. 1998; 13: 495-505. 37. van Deursen, D.L., Snijders, C.J., Kingma, I., van Dieen, J.H. In vitro torsion-induced stress distribution c hanges in porcine intervertebral discs. Spine 2001; 26: 282-286. 38. Wang, J.L., Parnianpour M., Shirazi-Adl, A., E ngin, A.E. The dynamic response of L2/L3 motion segment in cyclic ax ial compressive loading. Clin Biomech 1998; 13: S16-S25.

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30 39. White, A.A., Panjabi, M.M. Clinical Biomechanics of the Spine Second Edition. Philadelphia, PA, Lippi ncott Williams and Wilkins. 1990. 40. Wilke, H., Claes, L., Schmitt, H. A universal spine tester for in vitro experiments with muscle force simulation. Eur Spine J 1994; 3: 91-97. 41. Wilke, H.J., Neef, P., Caimi, M., Hoogland, T., Claes, L.E. New in vivo measurements of pressures in the interv ertebral disc in daily life. Spine. 1999; 24: 755-762. 42. Wilke, H.J., Wolf, S., Claes, L.E ., Arand, M., Wiesend, A. Influence of varying muscle forces on lum bar intradiscal pressure: an in vitro study. J. Biomechanics 1996; 29: 549-555. 43. Yingling, V.R., Callaghan, J.P., McGill, S.M. The por cine cervical spine as a model of the human lumbar spi ne: an anatomical, geometric, and functional comparison. J Spinal Disord 1999; 12: 415-423.

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31 Appendices

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32 Appendix A – Tables Table 1 Cadaveric Specimen Record Gender Age (yr) Level F 38 L1-L2 F 49 L1-L2 M 43 L1-L2 M 52 L1-L2 F 65 L1-L2 M 56 L1-L2 Avg age: 50.5 yrs

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33 Appendix A – (Continued) Table 2 Mean Pressures of 6 FSU and 6 DBU Specimens (n=6) Avg Pressure (MPa) FSU n=6 0 Torque (Nm) 0.5 Torque (Nm) 1.0 Torque (Nm) 2.0 Torque (Nm) 0 conf Torque (Nm) Pressure MPa MPa MPa MPa MPa UT04K009 FSU Test 1 0. 77 0.78 0.77 0.77 0.77 UM05H007 FSU Test 1 0.44 0.36 0.38 0.32 0.36 UJ04L015 FSU Test 1 0.90 0.85 0.86 0.86 0.84 UJ04J002 FSU Test 1 0. 91 0.74 0.73 0.72 0.72 UF05H007 FSU Test 1 0. 75 0.74 0.73 0.72 0.72 UF05B003 FSU Test 1 0.32 0.33 0.27 0.35 0.31 Mean FSU 0.68 0. 63 0.62 0.62 0.62 SD FSU 0.24 0.23 0.24 0.23 0.23 Avg Pressure (MPa) DBU n=6 0 Torque (Nm) 0.5 Torque (Nm) 1.0 Torque (Nm) 2.0 Torque (Nm) 0 conf Torque (Nm) Pressure MPa MPa MPa MPa MPa UT04K009 DBU Test 2 0. 71 0.71 0.71 0.70 0.69 UM05H007 DBU Test 2 0.46 0.33 0.24 0.44 0.33 UJ04L015 DBU Test 2 0.84 0.82 0.79 0.76 0.61 UJ04J002 DBU Test 2 0. 73 0.72 0.70 0.69 0.68 UF05H007 DBU Test 2 0. 72 0.71 0.70 0.70 0.70 UF05B003 DBU Test 2 0.19 0.29 0.11 0.25 0.12 Mean DBU 0.61 0. 60 0.54 0.59 0.52 SD DBU 0.24 0. 23 0.29 0.20 0.24

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34 Appendix A – (Continued) Table 3 Compiled Pressure Versus Torque ANOVAS for 6 FSU and 6 DBU Specimens (n=6) FSU Pressure vs. Torque ANOVAS P-value 0 Nm FSU 0.5 Nm FSU 0.73 >0.05 0 Nm FSU 1.0 Nm FSU 0.70 >0.05 0 Nm FSU 2.0 Nm FSU 0.67 >0.05 0.5 Nm FSU 1.0 Nm FSU 0.95 >0.05 0.5 Nm FSU 2.0 Nm FSU 0.93 >0.05 1.0 Nm FSU 2.0 Nm FSU 0.98 >0.05 DBU Pressure vs. Torque ANOVAS P-value 0 Nm DBU 0.5 Nm DBU 0.92 >0.05 0 Nm DBU 1.0 Nm DBU 0.66 >0.05 0 Nm DBU 2.0 Nm DBU 0.89 >0.05 0.5 Nm DBU 1.0 Nm DBU 0.72 >0.05 0.5 Nm DBU 2.0 Nm DBU 0.97 >0.05 1.0 Nm DBU 2.0 Nm DBU 0.73 >0.05 FSU and DBU Pressure vs. Torque ANOVAS P-value 0 Nm FSU 0 Nm DBU 0.62 >0.05 0.5 Nm FSU 0.5 Nm DBU 0.78 >0.05 1.0 Nm FSU 1.0 Nm DBU 0.59 >0.05 2.0 Nm FSU 2.0 Nm DBU 0.82 >0.05

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35 Appendix A – (Continued) Table 4 Mean Pressures of 4 FSU and 4 DBU Specimens (n=4) Avg Pressure (MPa) FSU n=4 0 Torque (Nm) 0.5 Torque (Nm) 1.0 Torque (Nm) 2.0 Torque (Nm) Pressure MPa MPa MPa MPa UT04K009 FSU Test 1 0.77 0.78 0.77 0.77 UJ04L015 FSU Test 1 0.90 0.85 0.86 0.86 UJ04J002 FSU Test 1 0.91 0.74 0.73 0.72 UF05H007 FSU Test 1 0.75 0.74 0.73 0.72 Mean FSU 0.83 0.78 0.77 0.76 SD FSU 0.08 0.05 0.06 0.06 Avg Pressure (MPa) DBU n=4 0 Torque (Nm) 0.5 Torque (Nm) 1.0 Torque (Nm) 2.0 Torque (Nm) Pressures MPa MPa MPa MPa UT04K009 DBU Test 2 0.71 0.71 0.71 0.70 UJ04L015 DBU Test 2 0.84 0.82 0.79 0.76 UJ04J002 DBU Test 2 0.73 0.72 0.70 0.69 UF05H007 DBU Test 2 0.72 0.71 0.70 0.70 Mean DBU 0.75 0.74 0.72 0.72 SD DBU 0.06 0.05 0.04 0.03

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36 Appendix A – (Continued) Table 5 Compiled Pressure Versus Torque ANOVAS for 4 FSU and 4 DBU Specimens (n=4) FSU Pressure vs. Torque ANOVAS P-value 0 Nm FSU 0.5 Nm FSU 0.31 >0.05 0 Nm FSU 1.0 Nm FSU 0.32 >0.05 0 Nm FSU 2.0 Nm FSU 0.25 >0.05 0.5 Nm FSU 1.0 Nm FSU 0.97 >0.05 0.5 Nm FSU 2.0 Nm FSU 0.78 >0.05 1.0 Nm FSU 2.0 Nm FSU 0.83 >0.05 DBU Pressure vs. Torque ANOVAS P-value 0 Nm DBU 0.5 Nm DBU 0.78 >0.05 0 Nm DBU 1.0 Nm DBU 0.50 >0.05 0 Nm DBU 2.0 Nm DBU 0.35 >0.05 0.5 Nm DBU 1.0 Nm DBU 0.68 >0.05 0.5 Nm DBU 2.0 Nm DBU 0.49 >0.05 1.0 Nm DBU 2.0 Nm DBU 0.77 >0.05 FSU and DBU Pressure vs. Torque ANOVAS P-value 0 Nm FSU 0 Nm DBU 0.17 >0.05 0.5 Nm FSU 0.5 Nm DBU 0.35 >0.05 1.0 Nm FSU 1.0 Nm DBU 0.23 >0.05 2.0 Nm FSU 2.0 Nm DBU 0.23 >0.05

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37 Appendix A – (Continued) Table 6 Mean Height Differences of all 6 FSU and 6 DBU Specimens Avg Height Difference (mm) FSU 0 Torque (Nm) 0.5 Torque (Nm) 1.0 Torque (Nm) 2.0 Torque (Nm) Height Differences mm mm mm mm UT04K009 FSU Test 1 0.18 0.14 0.14 0.14 UM05H007 FSU Test 1 0.12 0.09 0.12 0.11 UJ04L015 FSU Test 1 0.15 0.14 0.11 0.12 UJ04J002 FSU Test 1 0.21 0.15 0.15 0.17 UF05H007 FSU Test 1 0.18 0.16 0.20 0.14 UF05B003 FSU Test 1 0.10 0.09 0.05 0.11 Mean FSU 0.16 0.13 0.13 0.13 SD FSU 0.04 0.03 0.05 0.02 Avg Height Difference (mm) DBU 0 Torque (Nm) 0.5 Torque (Nm) 1.0 Torque (Nm) 2.0 Torque (Nm) Height Differences mm mm mm mm UT04K009 DBU Test 2 0.17 0.14 0.12 0.12 UM05H007 DBU Test 2 0.14 0.13 0.13 0.17 UJ04L015 DBU Test 2 0.16 0.13 0.13 0.12 UJ04J002 DBU Test 2 0.13 0.17 0.16 0.15 UF05H007 DBU Test 2 0.18 0.16 0.12 0.14 UF05B003 DBU Test 2 0.12 0.12 0.06 0.07 Mean DBU 0.15 0.14 0.12 0.13 SD DBU 0.02 0.02 0.03 0.03

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38 Appendix A – (Continued) Table 7 Compiled Height Versus Torque ANOVAS for 6 FSU and 6 DBU Specimens FSU Heights vs. Torque ANOVAS P-value 0 Nm FSU 0.5 Nm FSU 0.18 >0.05 0 Nm FSU 1.0 Nm FSU 0.28 >0.05 0 Nm FSU 2.0 Nm FSU 0.21 >0.05 0.5 Nm FSU 1.0 Nm FSU 0.97 >0.05 0.5 Nm FSU 2.0 Nm FSU 0.82 >0.05 1.0 Nm FSU 2.0 Nm FSU 0.84 >0.05 DBU Heights vs. Torque ANOVAS P-value 0 Nm DBU 0.5 Nm DBU 0.77 >0.05 0 Nm DBU 1.0 Nm DBU 0.14 >0.05 0 Nm DBU 2.0 Nm DBU 0.32 >0.05 0.5 Nm DBU 1.0 Nm DBU 0.18 >0.05 0.5 Nm DBU 2.0 Nm DBU 0.42 >0.05 1.0 Nm DBU 2.0 Nm DBU 0.65 >0.05 FSU and DBU Heights vs. Torque ANOVAS P-value 0 Nm FSU 0 Nm DBU 0.63 >0.05 0.5 Nm FSU 0.5 Nm DBU 0.32 >0.05 1.0 Nm FSU 1.0 Nm DBU 0.83 >0.05 2.0 Nm FSU 2.0 Nm DBU 0.93 >0.05

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39 Appendix A – (Continued) Table 8 Linear Regression Analysis Linear Regression Analysis Pressure vs. Torque n=6 Slope FSU -0.03 DBU -0.01 Pressure vs. Torque n=4 Slope FSU -0.03 DBU -0.02 Height vs. Torque n=6 Slope FSU -0.01 DBU -0.01

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40 Appendix B – Figures Figure 1 A. Cannula, B. Needle and C. Pressure Probe A. Cannula B. Needle C. Pressure Probe

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41 Appendix B – (Continued) Figure 2 X-ray of FSU UF05H007 L1 Vertebral Body L2 Vertebral Body L1-L2 Disc Space

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42 Appendix B – (Continued) Figure 3 MRI of Lu mbar Spine UT04K009 L1 Vertebral Body L2 Vertebral Body L1-L2 Disc Space

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43 Appendix B – (Continued) Figure 4 MRI of Lu mbar Spine UF05B003 L1 Vertebral Body L2 Vertebral Body L1-L2 Disc Space

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44 Appendix B – (Continued) Figure 5 Disarticulation of a Spine into an FSU (Functional Spine Unit) L1 Vertebral Body L2 Vertebral Body L1-L2 Disc Space

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45 Appendix B – (Continued) Figure 6 Potted L2 Vertebral Body

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46 Appendix B – (Continued) Figure 7 Potted L1 Vertebral Body

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47 Appendix B – (Continued) Figure 8 X-ray of FS U UF05H007 with Screws L1 Vertebral Body L2 Vertebral Body L1-L2 Disc Space

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48 Appendix B – (Continued) Figure 9 Axial Compression of an FSU in the MTS Machine L1 Vertebral Body L2 Vertebral Body L1-L2 Disc Space

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49 Appendix B – (Continued) Figure 10 Insertion of the A. Cannula and B. Needle into an FSU A. Cannula B. Needle

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50 Appendix B – (Continued) Figure 11 A. Pressure Gauge and B. Pressure Probe A. Pressure Gauge B. Pressure Probe

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51 Appendix B – (Continued) 0.00 0.50 1.00 024681012 Time (sec)Pressure (MPa) 0 Nm Start 0 Nm End Figure 12 Pressure of FSU UT04K009. Take n at 0 Nm Torque at the Start and End of the Testing Protocol 0.00 0.50 1.00 024681012 Time (sec)Pressure (MPa) 0 Nm Start 0 Nm End Figure 13 Pressure of DBU UT04K009. Ta ken at 0 Nm Torque at the Start and End of the Testing Protocol

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52 Appendix B – (Continued) 0.00 0.50 1.00 0246810 Time (sec)Pressure (MPa) Horizontal Vertical Figure 14 Probe Orientations of DB U UJ04L015 at 0 Nm Torsion Torque 0.00 0.50 1.00 0246810 Time (sec)Pressure (MPa) Horizontal Vertical Figure 15 Probe Orientations of DB U UJ04L015 at 0.5 Nm Torsion Torque 0.00 0.50 1.00 0246810 Time (sec)Pressure (MPa) Horizontal Vertical Figure 16 Probe Orientations of DB U UJ04L015 at 1.0 Nm Torsion Torque 0.00 0.50 1.00 0246810 Time (sec)Pressure (MPa) Horizontal Vertical Figure 17 Probe Orientations of DB U UJ04L015 at 2.0 Nm Torsion Torque

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53 Appendix B – (Continued) 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 18 Pressure of FSU UT04K009 at Different Torques 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 19 Pressure of DBU UT04K009 at Different Torques

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54 Appendix B – (Continued) 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 20 Pressure of FSU UJ04L015 at Different Torques 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 21 Pressure of DBU UJ04L015 at Different Torques

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55 Appendix B – (Continued) 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 22 Pressure of FSU UJ 04J002 at Different Torques 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 23 Pressure of DBU UJ 04J002 at Different Torques

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56 Appendix B – (Continued) 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 24 Pressure of FSU UF05H007 at Different Torques 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 25 Pressure of DBU UF05H007 at Different Torques

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57 Appendix B – (Continued) 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 26 Pressure of FSU UM05H007 at Different Torques 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 27 Pressure of DBU UM05H007 at Different Torques

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58 Appendix B – (Continued) 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 28 Pressure of FSU UF05B003 at Different Torques 0.00 0.50 1.00 1.50 2.00 0246810121416 Time (sec)Pressure (MPa) 0 Nm 0.5 Nm 1.0 Nm 2.0 Nm Figure 29 Pressure of DBU UF05B003 at Different Torques

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59 Appendix B – (Continued) 0.00 0.20 0.40 0.60 0.80 1.00 0.000.501.002.00Torque (Nm)Pressure (MPa) FSU DBU Figure 30 Pressure Versus Torque of 6 FSU’s and 6 DBU’s (n=6). Results Shown in M ean Standard Deviation

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60 Appendix B – (Continued) 0.00 0.20 0.40 0.60 0.80 1.00 0.000.501.002.00 Torque (Nm)Pressure (MPa) FSU DBU Figure 31 Pressure Versus Torque of 4 FSU’s and 4 DBU’s (n=4). Results Shown in M ean Standard Deviation

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61 Appendix B – (Continued) 0.00 2.00 4.00 6.00 8.00 10.00 02000400060008000 Time (sec)Displacement (mm) UT04K009 FSU UM05H007 FSU UJ04L015 FSU UJ04J002 FSU UF05H007 FSU UF05B003 FSU Figure 32 FSU Two Hour Creep Curves

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62 Appendix B – (Continued) 0.00 2.00 4.00 6.00 8.00 10.00 02000400060008000 Time (sec)Displacement (mm) UT04K009 DBU UM05H007 DBU UJ04L015 DBU UJ04J002 DBU UF05H007 DBU UF05B003 DBU Figure 33 DBU Two Hour Creep Curves

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63 Appendix B – (Continued) 0.00 2.00 4.00 6.00 8.00 10.00 02000400060008000 Time (sec)Displacement (mm) UT04K009 FSU UM05H007 FSU UJ04L015 FSU UJ04J002 FSU UF05H007 FSU UF05B003 FSU UT04K009 DBU UM05H007 DBU UJ04L015 DBU UJ04J002 DBU UF05H007 DBU UF05B003 DBU Figure 34 Combined FSU and DBU Two Hour Creep Curves

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64 Appendix B – (Continued) 0.00 2.00 4.00 6.00 8.00 10.00 0200040006000800010000 Time (sec)Displacement (mm) UT04K009 FSU UM05H007 FSU UJ04L015 FSU UJ04J002 FSU UF05H007 FSU UF05B003 FSU Figure 35 Continuous FSU Creep Cu rves with Two Hour Creep and Testing

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65 Appendix B – (Continued) 0.00 2.00 4.00 6.00 8.00 10.00 0200040006000800010000 Time (sec)Displacement (mm) UT04K009 DBU UM05H007 DBU UJ04L015 DBU UJ04J002 DBU UF05H007 DBU UF05B003 DBU Figure 36 Continuous DBU Creep Cu rves with Two Hour Creep and Testing

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66 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 37 Axial Displacement of FSU UT04K009 y = 0.1626Ln(x) + 0.5702 R2 = 0.9043 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 38 Axial Displacement of FSU UT04K009 with Logar ithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 39 Axial Displacement of FSU UT04K009 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 40 Magnitude of the Height Differences of FSU UT04K009

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67 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 41 Axial Displacement of DBU UT04K009 y = 0.2858Ln(x) + 1.0828 R2 = 0.8444 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 42 Axial Displacement of DBU UT04K009 with Logar ithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 43 Axial Displacement of DBU UT04K009 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 44 Magnitude of the Height Differences of DBU UT04K009

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68 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 45 Axial Displacement of FSU UM05H007 y = 0.2022Ln(x) + 0.9863 R2 = 0.7561 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 46 Axial Displacement of FSU UM05H007 with Logarithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 47 Axial Displacement of FSU UM05H007 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 48 Magnitude of the Height Differences of FSU UM05H007

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69 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 49 Axial Displacement of DBU UM05H007 y = 0.2681Ln(x) + 0.6631 R2 = 0.9024 -1.00 0.00 1.00 2.00 3.00 4.00 05001000 Time (sec)Displacement (mm) Figure 50 Axial Displacement of DB U UM05H007 with Logarithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 51 Axial Displacement of DBU UM05H007 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 52 Magnitude of the Height Differences of DBU UM05H007

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70 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 53 Axial Displacement of FSU UJ04L015 y = 0.181Ln(x) + 0.2074 R2 = 0.9718 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 54 Axial Displacement of FSU UJ04L015 with Logar ithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 55 Axial Displacement of FSU UJ04L015 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 56 Magnitude of the Hei ght Differences of FSU UJ04L015

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71 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 05001000 Time (sec)Displacement (mm) Figure 57 Axial Displacement of DBU UJ04L015 y = 0.2732Ln(x) + 0.7938 R2 = 0.8465 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 58 Axial Displacement of DBU UJ04L015 with Logar ithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 59 Axial Displacement of DBU UJ04L015 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 60 Magnitude of the Hei ght Differences of DBU UJ04L015

PAGE 82

72 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 61 Axial Displacement of FSU UJ04J002 y = 0.1556Ln(x) + 0.4698 R2 = 0.9288 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 62 Axial Displacement of FS U UJ04J002 with Logar ithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 63 Axial Displacement of FSU UJ04J002 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 64 Magnitude of the Height Differences of FSU UJ04J002

PAGE 83

73 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 65 Axial Displacement of DBU UJ04J002 y = 0.3641Ln(x) + 0.7095 R2 = 0.9434 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 66 Axial Displacement of DB U UJ04J002 with L ogarithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 67 Axial Displacement of DBU UJ04J002 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 68 Magnitude of the Height Differences of DBU UJ04J002

PAGE 84

74 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 69 Axial Displacement of FSU UF05H007 y = 0.298Ln(x) + 0.7509 R2 = 0.9319 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 70 Axial Displacement of FS U UF05H007 with Logarithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 71 Axial Displacement of FSU UF05H007 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 72 Magnitude of the Height Differences of FSU UF05H007

PAGE 85

75 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 73 Axial Displacement of DBU UF05H007 y = 0.0408Ln(x) 0.1381 R2 = 0.7132 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 74 Axial Displacement of DB U UF05H007 with Logarithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 75 Axial Displacement of DBU UF05H007 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 76 Magnitude of the Height Differences of DBU UF05H007

PAGE 86

76 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 77 Axial Displacement of FSU UF05B003 y = 0.3647Ln(x) + 1.0265 R2 = 0.9094 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 78 Axial Displacement of FSU UF05B003 with Logar ithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 79 Axial Displacement of FSU UF05B003 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 80 Magnitude of the Height Differences of FSU UF05B003

PAGE 87

77 Appendix B – (Continued) -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 81 Axial Displacement of DBU UF05B003 y = 0.4774Ln(x) + 0.934 R2 = 0.9454 -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 82 Axial Displacement of DBU UF05B003 with Logar ithmic Trendline -1.00 0.00 1.00 2.00 3.00 4.00 02004006008001000 Time (sec)Displacement (mm) Figure 83 Axial Displacement of DBU UF05B003 with Creep Only -1.00 -0.50 0.00 0.50 02004006008001000 Time (sec)Displacement (mm) Figure 84 Magnitude of the Height Differences of DBU UF05B003

PAGE 88

78 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 85 Normalized Data Versus Time of FSU UT04K009

PAGE 89

79 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 86 Normalized Data Versus Time of DBU UT04K009

PAGE 90

80 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 87 Normalized Data Ve rsus Time of FSU UM05H007

PAGE 91

81 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 88 Normalized Data Ve rsus Time of DBU UM05H007

PAGE 92

82 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 89 Normalized Data Versus Time of FSU UJ04L015

PAGE 93

83 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 90 Normalized Data Versus Time of DBU UJ04L015

PAGE 94

84 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 91 Normalized Data Versus Time of FSU UJ04J002

PAGE 95

85 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 92 Normalized Data Versus Time of DBU UJ04J002

PAGE 96

86 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 93 Normalized Data Versus Time of FSU UF05H007

PAGE 97

87 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 94 Normalized Data Versus Time of DBU UF05H007

PAGE 98

88 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 95 Normalized Data Versus Time of FSU UF05B003

PAGE 99

89 Appendix B – (Continued) -0.5 0 0.5 1 1.5 02004006008001000 Time (sec) Norm Pressure Norm Axial Disp Norm Torsion Torque Figure 96 Normalized Data Versus Time of DBU UF05B003

PAGE 100

90 Appendix B – (Continued) 0.00 0.05 0.10 0.15 0.20 0.000.501.002.00 Torque (Nm)Differential Height (mm) FSU DBU Figure 97 Differential Height Versus To rque of 6 FSU’s and 6 DBU’s (n=6). Results Shown in Mean Standard Deviation