ucalgary_2013_sawatsky_andrew.pdf

UNIVERSITY OF CALGARY
The Effect of Vastus Medialis Transection on Patellofemoral Contact Pressure and
Patellar Tracking
by
Andrew James Sawatsky
A THESIS
SUBMITTED TO THE FACULTY OF GRADUATE STUDIES
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE
DEGREE OF MASTER OF SCIENCE
FACULTY OF KINESIOLOGY
CALGARY, ALBERTA
May, 2013
© Andrew James Sawatsky 2013

ii
Abstract
The purpose of this thesis was to examine the effects of imbalance between the forces
exerted by vastus medialis (VM) and vastus lateralis on patellofemoral peak contact
pressures, areas, shapes, and patellar tracking before and after the removal of VM. New
Zealand White rabbits were used and patellofemoral contact mechanics were evaluated at
30°, 60° and 90° and patellar tracking was recorded from 30°-90° before and after VM
transection. Following removal of VM, there were no changes in patellofemoral contact
mechanics and patellar tracking. We conclude that VM weakness does not cause changes
in rabbit patellofemoral contact mechanics. Since muscular alignment and knee joint
geometry are similar in human and rabbits, we question the idea of VM weakness as a
cause for patellar mal-tracking and patellofemoral joint pain.

iii
Preface
Each of the following two chapters is based on scientific manuscripts:
Chapter 3 is based on A. Sawatsky, D. Bourne, M. Horisberger, W. Herzog (2012).
Changes in Patellofemoral Joint Contact Pressures caused by Vastus Medialis Muscle
Weakness. Journal of Clinical Biomechanics. 27,595-601
Used with permission - Elsvier Ltd.
Chapter 4 is based on A. Sawatsky, W. Herzog (2012) Does Knee Extensor Muscle
Imbalance Cause Changes in Patellar Tracking? Submitted to Journal of Clinical
Biomechanics

iv
Acknowledgements
I would like to express my appreciation and sincere thanks to the following:
Dr. Walter Herzog for being my supervisor and providing me with the opportunity to
pursue this degree and for his support.
Dr Janet Ronsky, and Dr. David Longino for serving on my supervisory committee.
Dr. Frances Sheehan, for travelling to Calgary to be my external examiner.
Dr. Tim Leonard for sharing his technical expertise to help me develop my own skills,
and countless hours of discussions, and guidance on my research.
Dr. Christian Egloff for reading my thesis and providing excellent feedback and clinical
insight.
Hoa Nguyen and Azim Jinha for their help with the equipment needed to perform this
work.
My parents, Barry and Kate Sawatsky and sister Krista Sawatsky who were always there
to encouraged me, and provide moral support when things weren't going according to
plan.
And the Herzog group for being willing to help with experiments when I needed a
helping hand.

v
Table of Contents
Approval Page ..................................................................................................................... ii
Abstract ............................................................................................................................... ii
Preface................................................................................................................................ iii
Acknowledgements ............................................................................................................ iv
Table of Contents .................................................................................................................v
List of Tables .................................................................................................................... vii
List of Figures and Illustrations ....................................................................................... viii
List of Symbols, Abbreviations and Nomenclature ........................................................... xi
Epigraph ............................................................................................................................ xii
CHAPTER ONE: INTRODUCTION ..................................................................................1
CHAPTER TWO: LITERATURE REVIEW ......................................................................5
2.1 Introduction ................................................................................................................5
2.2 Muscle Structure of the Knee Extensors ....................................................................5
2.3 Patellofemoral Pain Syndrome ..................................................................................8
2.3.1 Muscle imbalance and PFPS .............................................................................9
2.4 Cadaveric Evidence .................................................................................................11
2.5 Clinical Studies ........................................................................................................15
2.5.1 Electromyography (EMG) ...............................................................................15
2.5.1.1 Limitations of EMG Research ...............................................................16
2.5.2 In vivo Patellar Kinematics .............................................................................17
2.5.2.1 Limitations of In Vivo Patellar Tracking ...............................................19
2.6 Summary ..................................................................................................................20
CHAPTER THREE: CHANGES IN PATELLOFEMORAL JOINT CONTACT
PRESSURES CAUSED BY VASTUS MEDIALIS MUSCLE WEAKNESS ........23
3.1 Introduction ..............................................................................................................23
3.2 Methods ...................................................................................................................27
3.2.1 Animals and surgery ........................................................................................27
3.2.2 Patellofemoral Joint Pressure Measurements ..................................................27
3.2.3 Analysis of pressure sensitive Film .................................................................28
3.2.4 Statistics ...........................................................................................................30
3.3 Results ......................................................................................................................30
3.3.1 Contact Area ....................................................................................................30
3.3.2 Contact Shape ..................................................................................................33
3.3.3 Pressure Distribution .......................................................................................36
3.4 Discussion ................................................................................................................38
3.5 Conclusion ...............................................................................................................42
CHAPTER FOUR: DOES KNEE EXTENSOR MUSCLE IMBALANCE CAUSE
CHANGES IN PATELLAR TRACKING?..............................................................43
4.1 Introduction ..............................................................................................................43
4.2 Methods ...................................................................................................................44
4.2.1 Animal surgery ................................................................................................44