Health Science Campus FINAL APPROVAL OF THESIS Master of Science in Biomedical Sciences Development, validation and clinical application of finite element human pelvis model Submitted by: Alexander A. Ivanov In partial fulfillment of the requirements for the degree of Master of Science in Biomedical Sciences Examination Committee Signature/Date Major Advisor: Nabil Ebraheim, M.D. Academic Vijay Goel, Ph.D. Advisory Committee: Ashok Biyani, M.D. Senior Associate Dean College of Graduate Studies Michael S. Bisesi, Ph.D. Date of Defense: May 15, 2008 A Thesis Entitled Development, Validation and Clinical Application of the Finite Element Model of Human Pelvis. By Alexander A. Ivanov, M.D. Submitted as partial fulfillment of the requirements for the Master of Science in Orthopaedic Science ______________________________ Advisor: Dr. Nabil A. Ebraheim, M.D. ______________________________ Co-Advisor: Dr. Vijay K. Goel, Ph.D. ______________________________ Graduate School The University of Toledo 2008 1 © 2008, Alexander A. Ivanov 2 College of Health Science I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY: Alexander A Ivanov, M.D. ENTITLED: Development, validation and clinical application of finite element human pelvis model BE ACCEPTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF: Master of Science in Orthopaedic Science ______________________________________________________________ Thesis Advisor: Dr. Nabil A. Ebraheim, M.D. _______________________________________________________________ Thesis Co-Advisor: Dr. Vijay K. Goel, Ph.D. Recommendation concurred by: ___________________________________ Committee Dr.Ashok Biyani, M.D. Of Final Examination ________________________________________________________________ Dean, College of Health Science 3 Acknowledgment I would like to extend my gratitude to my advisors Dr. Nabil Ebraheim and Dr. Vijay Goel for their incredible support of this work. I will always consider them as a part of the foundation of my future success. I would also like to thank Dr. Ashok Biyani, my committee member for offering learning and research assistance throughout the process. Special thanks go to Ali Kiapour who has been through it all. Ahmad Faizan and Jayant Jagra who were always available when it was most needed. I thank all my colleagues at the Orthopaedic Surgery and Bioengineering Departments for creating a wonderful learning environment. 4 Abstract Finite element analysis became a very effective and essential tool in the studies of spinal and pelvic biomechanics. Most previous pelvic models included such simplifications as non-complete pelvic structures presentation, non-physiologic properties of ligaments, model validation against just only one mode. Out study is the first attempt, to our knowledge, to generate model with physiologic non-linear characteristic of the ligamentous structures of sacroiliac joint and accurate presentation of entirely pelvic anatomy. The model validation against data in literature showed good prediction of motions in the sacroiliac joint and stress-distribution across pelvic bone. The clinical application showed increased motions and stresses across sacroiliac joint which were not previously confirmed by the clinical and experimental studies due to their low sensitivity and specificity. The developed finite element human pelvis model might be a useful instrument in further clinical and biomechanical studies. 5 Table of Contents Page Acknowledgement..................................................................................................... 4 Abstract..................................................................................................................... 5 Chapter I-Introduction Significance of Low Back Pain Syndrome…………………………………………8 Sacroiliac Joint Syndrome………………………………………………………… 8 Pelvis and Sacroiliac Joint Anatomy…………………………………………….....8 Difficulties in Sacroiliac Joint Biomechanics Studies……………………………..15 Chapter II-Literature Review…………………………………………………...17 Morphometric Studies of Human Pelvis…………………………………………..17 Morphometric Studies of Human Sacroiliac Joint………………………………...21 Biomechanics of Sacroiliac Joint Motions……………………………………….. 23 Previous FE Studies Simulated Human Pelvis…………………………………….30 Previous FE Studies Simulated Human Sacroiliac Joint…………………………..33 Chapter III- Materials and Methods……………………………………………38 Human Pelvis Model………………………………………………………………38 Geometry ……………………………………………………………………..38 Bony Element Modeling ………………………………………………………40 Sacroiliac Joint Modeling …………………………………………………….41 Ligaments Modeling …………………………………………………………..42 Material Property Definitions ………………………………………………...43 Finite Element Model Validation ………………………………………………….45 Chapter IV- Results………………………………………………………………53 Finite Element Model Result……………………………………………………….53 Statistical Analysis of Data…………………………………………………………62 Chapter V-Discussion……………………………………………………………..72 Chapter VI- Clinical Application of Finite Element Human Pelvis Model……80 Introduction………………………………………………………………………….80 Significance of Low Back Pain in Patient after Lumbar Fusion Sacroiliac Joint as a Cause of LBP in Patient after Lumbar Fusion Material and Methods……………………………………………………………….82 Modifications in FE Pelvis Model 6 Boundary and Loading Conditions Results……………………………………………………………………………....86 Discussion…………………………………………………………………………..91 Conclusion…………………………………………………………………………94 Simplifications……………………………………………………………………..95 Future Work……………………………………………………………………......95 References…………………………………………………………………………..96 7 CHAPTER I INTRODUCTION Significance of Low Back Pain Low back pain (LBP) is a very frequent complaint and it’s the second most common cause of people to seek medical attention [1]. It appears that LBP is the most common reason of disability for person after 45 years old [2]. Life time prevalence of this condition ranges from 60 to 90% with annual incidence of 5% [3]. Therefore, it’s easy to understand the importance of studies with objective to elucidate the etiology and pathomechanism of this problem. Sacroiliac Joint Syndrome Among the different sources of LBP, the prevalence of sacroiliac joint syndrome ranges from 13 to 30% of all patients with LBP [4, 5]. The involvement of areas closed to SIJ can simulate SIJ dysfunction; therefore, the diagnosing of syndrome can be very challengeable for a physician [4]. One of the reasons of difficulties in establishing the correct diagnose in SIJ syndrome is a unique anatomy of pelvis, its innervation and specific biomechanics of sacroiliac joint. Anatomy of Pelvis and Sacroiliac Joint From biomechanical perspectives, the pelvis represents the integral complex structure which serves like a link between trunk and lower extremities. The main function of it is to transmit and decrease the force of gravity from lumbar spine to lower extremities and vise versa. The anatomy of pelvis is completely accommodated to its main 8 function. The pelvis consists of three bones (two hip bones and sacrum) and three joints (paired sacroiliac joints and pubic symphysis). Figure 1. The anatomy of pelvis (adopted from Gray H. The anatomy of human body. 1918). Sacrum Sacroiliac Joint Hip Bone Pubic Symphysis Sacrum is a triangular bone situated between two hip bones as a wedge. It connects with lumbar spine by L5/S1 intervertebral disk, and with hip bones by the paired sacroiliac joints. Sacrum is curved upon itself and is titled anteriorly forming a prominent promontorium. The shape of lateral surface of sacrum which corresponds to articular surface of SIJ, “…resembles the shape of the propeller” [6] where 9 posterior aspect in wider than anterior one in the upper part of sacrum, and vise versa at the lower part of sacrum. Pelvis has prominent irregularities with increase contact area in SIJ. The triangular shape with the base in the top and specific lateral surface shape of sacrum makes it highly resistant to movement between hip bones. Figure 2. The anatomy of sacrum (adopted from Gray H. The anatomy of human body. 1918). Hip bone consists of three parts, ilium (Figure 3, 1), ischium (Figure 3, 2) and pubis (Figure 3, 3) which are fused together in the adults. The fusion takes place around acetabulum, articular cavity which connects pelvis to femur. The medial surface of ilium forms the articulate surface of the sacroiliac joint (anterior part of medial surface) and iliac tuberosity (posterior part of medial surface) which serves as a place for attachment massive posterior ligamentous structures of sacroiliac joint. Iliac wing is the thinnest part of the pelvis. It forms iliac crest superiorly which extends from anterior superior iliac spine (ASIS) to posterior superior iliac spine (PSIS). Ilium 10 body is much thicker and extends to acetabulum anteriorly and to the sacroiliac joint posteriorly. Ischium lies below the ilium and serves as place for attachment of massive muscles of lower extremity and ligaments of sacroiliac joint. Pubis is anterior part of pelvis and consists of body, superior and inferior ramus. One third of the pubic bone body contributes to the acetabulum. Superior ramus extends medially from body and connects to the opposite superior ramus by pubic symphysis. The pubis, the ischium and acetabulum enclose the foramen obturator. Figure 3. The anatomy of hip bone (adopted from Gray H. The anatomy of human body. 1918). Iliac Tuberosity PSIS ASIS 1 Articulate Acetabulum Surface 2 of SIJ Ischium 3 ASIS- anterior superior iliac spine PSIS- posterior superior iliac spine SIJ- sacroiliac joint 11 Sacroiliac joint is the joint between