COMPUTATIONAL MODELING OF HIP JOINT MECHANICS by Andrew Edward Anderson A ...

222 Pages·2007·2.57 MB·English

COMPUTATIONAL MODELING OF HIP JOINT MECHANICS

by

Andrew Edward Anderson

A dissertation submitted to the faculty of
The University of Utah
in partial fulfillment of the requirements for the degree of

Doctor of Philosophy

Department of Bioengineering

The University of Utah

April 2007
Copyright © Andrew Edward Anderson 2007

All Rights Reserved

ABSTRACT

The hip joint is one of the largest weight bearing structures in the human body.
While its efficient structure may lend to a lifetime of mobility, abnormal, repetitive
loading of the hip is thought to result in osteoarthritis (OA). The etiology of hip OA is
unknown however, due to the high loads this joint supports, mechanics have been
implicated as the primary factor. Quantifying the relevant mechanical parameters in the
joint (i.e. cartilage and bone stresses) appears to be central to an enhanced understanding
of this disease. Experimental studies have provided valuable insight into baseline hip
joint biomechanics but they require a protocol that is inherently invasive. Numerical
modeling techniques, such as the finite element method, open the possibility of predicting
hip joint biomechanics noninvasively and could revolutionize the way pathological hips
are diagnosed and treated. Unfortunately, hip finite element models to date have used
simplified geometry and have not been validated. It can be credibly argued that prior
computational models of the hip joint do not have the ability to predict cartilage and bone
mechanics with sufficient accuracy for clinical application.
The aim of this dissertation is to develop and validate methods that will facilitate
patient-specific modeling of hip joint biomechanics. Toward this objective, subject-
specific FE models of the pelvis and entire hip joint were developed. The accuracy of
model geometry, i.e. cortical bone and cartilage thickness, was assessed using phantom
based imaging studies. FE predictions were compared directly with experimental data for
purposes of validation. The sensitivity of the models to errors in assumed and measured
model inputs was quantified. Finally, recognizing that acetabular dysplasia may be the
single most important contributor of hip joint OA, the validated modeling protocols were
extended to analyze patient-specific models to demonstrate the general feasibility of the
approach and to quantify differences in hip joint biomechanics between a normal and
dysplastic hip joint. The developed modeling methodologies have a number of potential
longer-term uses and benefits, including improved diagnosis of pathology, patient-
specific approaches to treatment, and prediction of the success rate of corrective surgeries
based on pre- and post-operative mechanics.
v
To my father: Richard E. Anderson

“It matters not how long we live but how”
Philip James Bailey
TABLE OF CONTENTS
ABSTRACT.......................................................................................................................iv

LIST OF TABLES.............................................................................................................ix

LIST OF FIGURES.............................................................................................................x

ACKNOWLEDGEMENTS.............................................................................................xiii

CHAPTER

1. INTRODUCTION...................................................................................................1

Motivation................................................................................................................1
Research Goals.........................................................................................................4
Summary of Chapters..............................................................................................5
References................................................................................................................8

2. BACKGROUND...................................................................................................10

Forward..................................................................................................................10
Hip Joint Structure and Function...........................................................................11
Pelvic and Femoral Bone...........................................................................11
Cartilage.....................................................................................................13
Labrum, Capsule, Ligaments, Muscles......................................................15
Hip Joint Pathology................................................................................................20
Osteoarthritis..............................................................................................20
Hip Dysplasia.............................................................................................22
Experimental Hip Joint Biomechanics...................................................................25
Bone Material Properties...........................................................................25
Cartilage Material Properties.....................................................................27
In-Vitro Studies of Hip Joints....................................................................29
In-Vivo Studies of Hip Joints....................................................................32
Numerical Modeling of Hip Joint Biomechanics..................................................35
Analytical Modeling of the Hip Joint........................................................35
Computational Modeling of the Hip Joint.................................................36
References..............................................................................................................43
3. A SUBJECT-SPECIFIC FINITE ELEMENT MODEL OF THE
PELVIS: DEVELOPMENT, VALIDATION AND
SENSITIVITY STUDIES......................................................................................58

Abstract..................................................................................................................58
Introduction............................................................................................................60
Materials and Methods...........................................................................................63
Experimental Study....................................................................................63
Geometry Extraction and Mesh Generation..............................................66
Position-Dependent Cortical Thickness.....................................................69
Assessment of Cortical Bone Thickness....................................................71
Material Properties and Boundary Conditions...........................................72
Sensitivity Studies......................................................................................73
Data Analysis.............................................................................................75
Results ....................................................................................................................76
Reconstructions of Pelvic Geometry.........................................................76
Cortical Bone Thickness............................................................................77
Trabecular Bone Elastic Modulus..............................................................80
FE Model Predictions................................................................................80
Discussion..............................................................................................................85
References..............................................................................................................92

4. FACTORS INFLUENCING CARTILAGE THICKNESS
MEASUREMENTS WITH MULTI-DETECTOR CT
A PHANTOM STUDY..........................................................................................97

Abstract..................................................................................................................97
Introduction............................................................................................................99
Materials and Methods.........................................................................................102
Phantom Description................................................................................102
CT Imaging Protocol................................................................................105
Image Segmentation, Surface Reconstruction, and
Measurement of Thickness......................................................................106
Error Analysis..........................................................................................109
Results ..................................................................................................................110
Contrast Enhanced Scans.........................................................................110
Non-Enhanced Scans...............................................................................115
Discussion............................................................................................................117
Study Limitations.....................................................................................119
Practical Applications..............................................................................120
References............................................................................................................122
5. VALIDATION OF FINITE ELEMENT PREDICTIONS OF
CARTILAGE CONTACT PRESSURE IN THE
HUMAN HIP JOINT...........................................................................................126

Abstract................................................................................................................126
Introduction..........................................................................................................128
Methods................................................................................................................130
Experimental Protocol.............................................................................130
Computational Protocol...........................................................................133
Sensitivity Studies....................................................................................136
Data Analysis...........................................................................................137
Results ..................................................................................................................140
FE Mesh Characteristics..........................................................................140
Peak Pressure, Average Pressure, Contact Area......................................141
Contact Patterns.......................................................................................142
Misalignment and Magnitude Errors.......................................................145
Sensitivity Studies- Cartilage Material Properties and Thickness...........147
Sensitivity Studies- FE Boundary Conditions.........................................149
Discussion............................................................................................................152
References............................................................................................................159

6. PATIENT-SPECIFIC FINITE ELEMENT MODELING
PROOF OF CONCEPT.......................................................................................165

Abstract................................................................................................................165
Introduction..........................................................................................................167
Methods................................................................................................................170
Subject-Selection.....................................................................................170
CT Arthrography......................................................................................170
Image Data Analysis and Segmentation..................................................171
FE Mesh Generation, Cartilage Thickness, Material Properties..............172
FE Boundary and Loading Conditions....................................................174
Sensitivity Studies....................................................................................175
Data Analysis...........................................................................................175
Results ..................................................................................................................177
Discussion............................................................................................................182
References............................................................................................................189

7. DISCUSSION......................................................................................................195

Summary..............................................................................................................195
Limitations and Future Work...............................................................................200
References............................................................................................................205