Old Dominion University ODU Digital Commons Mechanical & Aerospace Engineering Theses & Mechanical & Aerospace Engineering Dissertations Summer 2007 Shaken Baby Syndrome: Retinal Hemorrhaging. A Biomechanical Approach to Understanding the Mechanism of Causation Steven Alex Hans Old Dominion University Follow this and additional works at: https://digitalcommons.odu.edu/mae_etds Part of the Biomechanical Engineering Commons, and the Biomedical Commons Recommended Citation Hans, Steven A.. "Shaken Baby Syndrome: Retinal Hemorrhaging. A Biomechanical Approach to Understanding the Mechanism of Causation" (2007). Doctor of Philosophy (PhD), dissertation, Mechanical Engineering, Old Dominion University, DOI: 10.25777/ f1jx-5717 https://digitalcommons.odu.edu/mae_etds/134 This Dissertation is brought to you for free and open access by the Mechanical & Aerospace Engineering at ODU Digital Commons. It has been accepted for inclusion in Mechanical & Aerospace Engineering Theses & Dissertations by an authorized administrator of ODU Digital Commons. For more information, please contact [email protected]. Shaken Baby Syndrome: Retinal Hemorrhaging - a Biomechanical Approach to Understanding the Mechanism of Causation By Steven Alex Hans A Dissertation Submitted to the Faculty of Old Dominion University in Partial Fulfillment of the Requirement for the Degree of Doctor of Philosophy Mechanical Engineering OLD DOMINION UNIVERSITY August 2007 Approved by: Sebastian Bawab (Director) Ayodeji Demuren (Member) Gene Hou (Member) Michael WWoodhouseoodhouse (Member) ABSTRACT Shaken Baby Syndrome: Retinal Hemorrhaging - a Biomechanical Approach to Understanding the Mechanism of Causation Steven Alex Hans Old Dominion University, 2007 Director: Sebastian Y. Bawab Shaken Baby Syndrome (SBS) is a form of abuse where typically an infant, age six months or less, is held and shaken. There may or may not be direct impact associated with this action. Further, there is very little agreement on the actual mechanism of SBS. Clinical studies are limited in showing the exact mechanism of injury and only offer postulations and qualitative descriptions. SBS has received much attention in the media, has resulted in a great deal of litigation and can be the source of unfounded accusations. Therefore, it is necessary to try to quantify the forces that may cause injury due to SBS. The physiology of infants makes injury due to SBS more likely. Infants have relatively large heads supported by weak necks that simply act as tethers (Prange et al., 2003). Therefore, there is minimal resistance to shaking. In addition, the cerebrospinal fluid (CSF) layer surrounding the infant’s brain is up to 10 mm thick as opposed to 1 – 2 mm in older children and adults (Morison, 2002). This thick layer reduces the resistance in rotation of the brain and can cause shearing injuries to the brain tissue. In addition, retinal hemorrhaging has been reported in SBS. The infant’s eyes have a vitreous that is typically more gelatinous and with a higher viscosity than in adult eyes. In addition, this vitreous is firmly attached to the retina and is difficult to remove (Levin, 2000). A preliminary parametric model of an infant eye will be presented so that resultant nodal retinal force of the posterior retina can be investigated and compared with a documented shaking frequency and a documented impact pulse. Retinal forces are then compared with various studies that investigate retinal detachment or adhesive strength. This eye model is built using a variety of material properties that have been reported for the sclero-cornea shell, choroids, retina, vitreous, aqueous, lens, ciliary, optic nerve, tendons, extra ocular muscles, optic nerve, and orbital fatty tissue. The geometry of the eye has been carefully optimized for this parametric model based on scaling to an infant from an adult using idealized eye globe geometry and transverse slice tracings of “The Visible Human Project.” This model shows promise in investigating the forces and kinematics of the infant eye exposed to harmonic shaking and further bolsters some of the few biomechanical studies investigating SBS. However, improvements are necessary to complete the eye model presented. Specifically, improvements on the mechanical properties for the components of the eye and especially the infant eye are needed. There is currently a deficit of biomechanical studies of the materials needed for the infant eye that is specifically geared for use in an explicit finite element code package. Conversions and adaptations of available materials are used in this first version of the infant eye model presented here and are in fair agreement with some of the clinical studies concerning SBS. v DEDICATION This dissertation is dedicated to my wife Christina Hans vi ACKNOWLEDGMENTS I am grateful for my wife during my several years as a graduate student. During the course of my study, she has been extremely supportive and nurturing, allowing me to focus on my work. She has sacrificed her needs and wants during this process and I am indebted to her for that. I would also like to express my gratitude to my advisor, Sebastian Bawab. During my time as a graduate student, Dr. Bawab provided a stimulating environment with care and compassion equal to his demand for quality and excellence. During my research process, Dr. Bawab would frequently calm me when something was not going as planned and refocus my efforts. I have gotten to know Dr. Bawab over the course of almost 10 years now and not only is Dr. Bawab my mentor, he is a true friend—family really. I would also like to acknowledge Michael Woodhouse. Dr. Woodhouse actually is responsible for my interest in biomechanics and helped me narrow my topic of study. Dr. Woodhouse is the definition of a true southern gentleman, and I enjoy working with him. I would also like to thank each of the committee members: Dr. Demuren and Dr. Hou. I have gotten to know these professors over the years and enjoy working on projects with them. Lastly, I would like to thank the mechanical engineering department for making my graduate student experience a positive one. vii TABLE OF CONTENTS Page LIST OF TABLES.............................................................................................................. x LIST OF FIGURES .......................................................................................................... xii CHAPTER I. INTRODUCTION............................................................................................... 1 Aims and Objectives................................................................................ 2 Thesis Overview ...................................................................................... 3 Eye and Surrounding Tissue Anatomy.................................................... 5 II. LITERATURE REVIEW................................................................................... 7 Introduction.............................................................................................. 7 Shaken Baby Syndrome......................................................................... 10 Retinal Hemorrhaging............................................................................ 12 Biomechanical Eye Models ................................................................... 16 Optic Nerve and Related Studies in Pia-mater and Axonal Materials... 19 Infant Brain Studies/Infant Skull Studies/Adult Brain Studies ............. 25 Vitreous Body........................................................................................ 35 Retina Properties/ Choroid Properties/ Retinal Adhesion/ Detachment Studies.................................................................................................... 42 Muscle Modeling Studies ...................................................................... 49 Skin and Fatty Tissue Material Studies ................................................. 54 Conclusion ............................................................................................. 60 III. GEOMETRY OF EYE AND OCULAR REGION ........................................ 62 Introduction............................................................................................ 62 Eye Geometry ........................................................................................ 63 Scaling to infant dimensions.................................................................. 72 Conclusion ............................................................................................. 73 IV. MESHING OF THE EYE AND FATTY TISSUE ........................................ 74 Introduction............................................................................................ 74 Eye Meshing .......................................................................................... 75 Fatty Tissue............................................................................................ 92 Conclusion ............................................................................................. 96 V. OCULAR SHELL LAYERS ........................................................................... 98 Introduction............................................................................................ 98 Sclera and Cornea .................................................................................. 99 Choroid ................................................................................................ 119 Retina..................................................................................................