THE EFFECTS OF MENISCAL SIZING ON THE KNEE USING FINITE ELEMENT METHODS A dissertation presented to The faculty of the Fritz J. and Dolores H. Russ College of Engineering and Technology of Ohio University In partial fulfillment of the requirements for the degree Doctor of Philosophy Stephen D. Fening March 2005 © 2005 Stephen D. Fening All Rights Reserved This dissertation entitled THE EFFECTS OF MENISCAL SIZING ON THE KNEE USING FINITE ELEMENT METHODS by STEPHEN D. FENING has been approved for the School of Mechanical Engineering and the Russ College of Engineering and Technology by Bhavin Mehta Associate Professor of Mechanical Engineering Dennis Irwin Dean, Fritz J. and Dolores H. Russ College of Engineering and Technology FENING, STEPHEN D. Ph.D. March 2005. Individual Interdisciplinary Ph.D. – Biomedical Engineering The Effects of Meniscal Sizing on the Knee Using Finite Element Methods (125pp.) Director of Dissertation: Bhavin Mehta The knee, one of the most complex joints in the body, is also one of the most commonly injured joints in humans. Most injuries that occur in the knee either cause meniscal damage or are the function of a previously damaged meniscus, a complex tissue that has been historically underappreciated. Many techniques for the replacement of a damaged meniscus have been surgically explored. The most successful approach thus far has been meniscus allograft, the transplantation of a meniscus from a cadaver to a patient. This procedure has been performed over the last 25 years with inconsistent results. Meniscal sizing appears to be a major source of this inconsistency. The purpose of this dissertation is to study the effects of meniscal sizing on stresses in the knee joint using finite element methods. All research was conducted on the porcine based on its similarity to the human knee. MRI and CT scans recreated the geometry of the knee. CT images were used to construct the shapes of bones and soft tissues were modeled from MRI. The geometric model included the femur, tibia, and both menisci. For simplicity, the material model used was a linear isotropic material even though this model does not adequately model the function of biological tissues. The geometric model was imported as a STL file and meshed with tetrahedral elements. The tibia was fully constrained on its distal surface, the menisci were constrained both at the horn attachments and their periphery, and the femur was constrained by a spring element mimicking the behavior of the entire bone of the femur, muscle, tendon, and ligament attachments. A force of 465 Newtons, half of the body weight of the porcine, was applied to the femur. The meniscus was scaled in three dimensions – medial-lateral, anterior-posterior, and proximal-distal – to examine the effects of differently sized menisci. Results demonstrate that all three dimensions are statistically significant, with the medial-lateral dimension being most significant. Even very small changes in meniscal size demonstrated dramatic changes in stress levels. Approved: Bhavin Mehta Associate Professor of Mechanical Engineering 6 TABLE OF CONTENTS ABSTRACT........................................................................................................................4 LIST OF FIGURES ...........................................................................................................8 LIST OF TABLES ...........................................................................................................11 CHAPTER 1 INTRODUCTION....................................................................................12 1.1 General knee anatomy....................................................................................12 1.2 Anatomy of the menisci.................................................................................15 1.2.1 Gross Anatomy ..............................................................................15 1.2.2 Architecture....................................................................................19 1.2.3 Vascular Pattern.............................................................................22 1.2.4 Neurophysiology............................................................................22 1.2.5 Histology........................................................................................23 1.2.6 Function .........................................................................................23 1.2.7 Development & maturation............................................................25 1.2.8 Healing...........................................................................................26 1.2.9 Anatomical interspecies variation..................................................27 1.3 Meniscal injury ..............................................................................................28 1.3.1 Tearing ...........................................................................................29 1.3.2 Meniscectomy................................................................................31 1.3.3 Effects of Meniscal Injury .............................................................32 1.4 Meniscus allograft & repair ...........................................................................37 1.4.1 Repair.............................................................................................37 1.4.2 Meniscus transplant .......................................................................39 1.4.3 Meniscus allograft..........................................................................41 1.4.4 Pre-operative planning and size matching .....................................42 1.4.5 Surgical technique..........................................................................43 1.4.6 Results of meniscal allograft..........................................................45 1.5 Software used in research ..............................................................................47 1.5.1 Amira® ..........................................................................................47 1.5.2 Algor® ...........................................................................................47 1.5.3 LS-DYNA......................................................................................48 1.5.4 Superforge®...................................................................................48 1.5.5 Dytran® .........................................................................................48 1.5.6 MARC®.........................................................................................49 CHAPTER 2 LITERATURE REVIEW.........................................................................50 7 CHAPTER 3 BIOMATERIAL CHARACTERIZATION.............................................59 3.1 Determining material properties ....................................................................59 3.2 Biomaterial properties of cartilage.................................................................65 3.2.1 Articular cartilage ..........................................................................65 3.2.2 Menisci...........................................................................................66 3.3 Biomaterial properties of cortical bone..........................................................67 CHAPTER 4 DETERMINING GEOMETRY FROM MRI/CT SCANS......................70 4.1 Approaches to finding geometry....................................................................70 4.2 Using CT and MR images .............................................................................71 4.3 Constructing three-dimensional geometries with Amira® ............................72 4.4 Importing models...........................................................................................75 CHAPTER 5 ANALYSIS OF THE KNEE....................................................................79 5.1 Failed approaches...........................................................................................79 5.2 Successful methodology ................................................................................84 5.2.1 Mesh generation.............................................................................84 5.2.2 Material properties.........................................................................86 5.2.3 Boundary conditions ......................................................................88 5.3 Design of Experiment (DOE) Setup ..............................................................92 CHAPTER 6 RESULTS AND CONCLUSIONS..........................................................97 CHAPTER 7 FUTURE RECOMMENDATIONS.......................................................115 REFERENCES...............................................................................................................118 8 LIST OF FIGURES Fig. 1.1: Human knee anatomy of a right knee.............................................................13 Fig. 1.2: Anatomy of the meniscus ...............................................................................16 Fig. 1.3: Attachments of the meniscus to the tibial plateau ..........................................17 Fig. 1.4: Movement (in mm) of the menisci during knee flexion with weight bearing ............................................................................................................18 Fig. 1.5: Collagen microstructure of articular cartilage ................................................20 Fig. 1.6: Collagen microstructure of the meniscus .......................................................20