An Evaluation of Lower Limb Mechanical Characteristics in People with Patellofemoral

Home , Joint stiffness

An evaluation of lower limb mechanical characteristics in people with Patellofemoral

Pain Syndrome during repeated loading.

by Elise Desira

16956940

Primary Supervisor: Dr Amitabh Gupta

Co-supervisor: Dr Peter Clothier

Thesis submitted for the degree of Master of Research.

December 2019

Dedications

I dedicate this thesis to my fiancé, Zion and my family; Michelle, Mark, Emma and Luke.

Zion; It is safe to say that this whirlwind of a year would not have been possible without you.

You have supported me in all my endeavours and have always encouraged me to embrace new opportunities. Thank you for all your support, reassurance, boring weekends in, excel expertise, laughs, lunch deliveries and love. Without you this thesis and my sanity would not be possible. I can’t wait discover what the future has in store for us and to begin our lives as husband and wife. Only eight weeks to go! I love you!

To my family. Your patience, understanding, love and support has been invaluable throughout this process. You have always been there for me when life got overwhelming, offering a laugh, advice and listening ear. Thank you for teaching me the value of hard work and for being excellent role models in my life. I can’t thank you enough for all opportunities you have provided for us. I love you all!

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Acknowledgements

Research is a difficult art (Smith, 2013). As such there are several people who need acknowledgement, whose efforts were fundamental in the completion of this project.

I thank Dr Amitabh Gupta for his expertise and guidance throughout this research project.

Your patience and persistence have been greatly appreciated. Thank you for the countless emails, phone calls and demonstrations. Your efforts have helped me grow as a clinician and budding researcher.

I thank Dr Peter Clothier and Mr Daniel Thompson for their assistance throughout this research project. Your contributions have provided me with the skills and knowledge to learn and develop in the area of laboratory research and human movement. Dan, I also thank you for your friendship throughout the last few years. Your personal experience having been through this journey has been invaluable.

I thank Mr Brendan Howe for his technical assistance throughout this project. I appreciate all the time you have dedicated to this project and for your unrelenting patience.

I thank all the participants who volunteered their time to this project. Your willingness to participate and learn has been greatly appreciated. Without you this project would not be possible.

Lastly, I thank Dani Hutchinson for her patience and understanding over the last two years.

Thank you for being so flexible and allowing me to embrace new opportunities and grow as a practitioner. iv

Statement of Authentication

The work presented in this thesis is, to the best of my knowledge and belief, original except as

acknowledged in the text. I hereby declare that I have not submitted this material, either in

full or in part, for a degree at this or any other institution.

…………… …………………….. (Signature)

Contents Dedications ...... ii Acknowledgements ...... iii Statement of Authentication ...... iv List of Tables ...... vii List of Figures ...... xii Abbreviations ...... xiv Appendices ...... xvii Abstract ...... xviii CHAPTER ONE ...... 1 Introduction ...... 1 1.1 Summary of the problem ...... 1 1.2 Significance of the study ...... 3 1.3 Research objectives ...... 4 1.4 Research hypotheses ...... 4 CHAPTER TWO ...... 5 Literature Review ...... 5 2.1. The incidence and pathogenesis of PFPS ...... 6 2.2 The etiological factors of PFPS ...... 7 2.3 Intrinsic risk factors associated with the development of PFPS ...... 8 2.3.1 Non-modifiable risk factors associated with PFPS ...... 8 2.3.2 Modifiable risk factors associated with PFPS ...... 10 2.4 Extrinsic risk factors associated with the development of PFPS ...... 14 2.4.1 Modifiable extrinsic risk factors associated with PFPS ...... 15 2.5 Summary of PFPS etiology and risk factors...... 17 2.6 Force attenuation in the lower limb ...... 18 2.7 The knee and ankle joint interaction ...... 21 2.8 Repeated single-leg hopping ...... 23 CHAPTER THREE ...... 25 Methods ...... 25 3.1 Study design ...... 25 3.2 Ethical considerations ...... 25 3.3 Participant recruitment ...... 26 3.4 Inclusion and exclusion criteria ...... 26 3.5 Laboratory set up and instrumentation ...... 28 vi

3.6 Testing Procedure ...... 33 3.7 Data Processing ...... 34 3.8 Dependent Variables ...... 37 3.9 Statistical Analyses ...... 39 CHAPTER FOUR ...... 41 Results ...... 41 4.1 Participant profile ...... 41 4.2 Spatiotemporal characteristics of the hop cycle ...... 42 4.3 Kinematic variables during the loading period...... 44 4.4 Kinetic variables during the loading period ...... 46 4.4.1 Knee flexion and ankle dorsiflexion moment ...... 46 4.4.2 Vertical stiffness ...... 48 4.4.3 Knee and ankle joint stiffness ...... 49 4.4.4 Knee and ankle mechanical work ...... 52 4.4.5 Knee and ankle joint power ...... 54 CHAPTER FIVE ...... 57 5.1 Discussion ...... 57 5.2 Conclusion ...... 67 References ...... 68 Appendices ...... 83

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List of Tables

Table 1: Anthropomorphic characteristics (mean (SD)) for people with patellofemoral pain syndrome (PFPS) and the matched, healthy control participants...... 41 Table 2: Pain during rest, functional tasks and scores of the Anterior Knee pain Scale (AKPS) (mean (SD)) for participants with patellofemoral pain syndrome (PFPS) and the healthy, matched participants...... 42 Table 3: Duration (ms) (mean (SD)) of hopping cycle, flight and contact phases, loading and propulsive periods for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 43 Table 4: Knee and ankle joint excursion (degrees) (mean (SD)) for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 45 Table 5: Coefficient of variation (CV) (%) (mean (SD)) for ankle and knee joint excursion during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 46 Table 6: Ankle and knee joint moment (N·m.kg-1) (mean (SD)) during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 47 Table 7: Coefficient of variation (CV) (%) (mean (SD)) of ankle and knee joint moment during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 47 Table 8: Vertical stiffness (N∙kg-1∙m-1) during the loading period (mean (SD)) for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 48 Table 9: Coefficient of variation (CV) (%) (mean (SD)) of vertical stiffness during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) viii

and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 49 Table 10: Ankle and knee joint stiffness (Nm.kg-1.rad-1) (mean (SD)) during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 49 Table 11: Coefficient of variation (CV) (%) of knee and ankle joint stiffness during loading (mean (SD)) for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 51 Table 12: Ankle and knee mechanical work done (J.kg-1.rad) (mean (SD)) during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 53 Table 13: Coefficient of variation (CV) (%) (mean (SD)) of knee and ankle mechanical work during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 54 Table 14: Ankle and knee joint power (J.kg-1.s-1) (mean (SD)) during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1...... 55 Table 15: Coefficient of variation (CV) (%) (mean (SD)) of knee and ankle joint power during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1)...... 56

Tables in Appendices

Appendix H Table 16: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of the duration of the hop cycle for participants with and without PFPS...... 95 Table 17: Pairwise comparison results (mean difference, standard error, significance and 95% confidence intervals) of the duration of the hop cycle for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1...... 96 Table 18: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of the duration of the contact phase for participants with and without PFPS...... 97 Table 19: Pairwise comparison results (mean difference, standard error, significance and 95% confidence intervals) of contact duration for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1...... 97 Table 20: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of the duration of the loading period for participants with and without PFPS...... 98 Table 21: Pairwise comparison results (mean difference, standard error, significance and 95% confidence intervals) of the duration of the loading period for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1...... 99 Table 22: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of propulsive duration for participants with and without PFPS...... 100 Table 23: Pairwise comparison (mean difference, standard error, significance and 95% confidence intervals) of propulsive duration for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1...... 100 Table 24: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of flight duration for participants with and without PFPS...... 101 x

Table 25: Pairwise comparison results (mean difference, standard error, significance and 95% confidence intervals) of flight duration for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1. .... 102 Appendix I Table 26: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of knee excursion for participants with and without PFPS...... 103 Table 27: Pairwise comparisons (standard error, significance and 95% confidence intervals) of knee excursion for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1...... 104 Table 28: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of ankle excursion for participants with and without PFPS...... 105 Table 29: Pairwise comparison (mean difference, standard error, significance and 95% confidence intervals) of ankle excursion for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1. .... 105 Appendix J Table 30: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of vertical stiffness for participants with and without PFPS...... 107 Table 31: Pairwise comparison (mean difference, standard error, significance and 95% confidence intervals) for vertical stiffness for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1. .... 108 Table 32: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of knee mechanical work for participants with and without PFPS...... 110 Table 33: Pairwise comparison (mean difference, standard error, significance and 95% confidence intervals) of knee mechanical work for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1...... 110 Table 34: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of ankle mechanical work for participants with and without PFPS...... 111 xi

Table 35: One-way ANOVA results (standard error, significance and 95% confidence intervals for the comparison of ankle mechanical work for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1...... 112 Table 36: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of knee power for participants with and without PFPS...... 113 Table 37: Pairwise comparison (mean difference, standard error, significance and 95% confidence intervals) of knee power for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1. .... 113 Table 38: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of ankle power for participants with and without PFPS...... 114 Table 39: One-way ANOVA results (mean difference, standard error, significance and 95% confidence intervals) of ankle power for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1. .... 115 Table 40: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β) for the comparison of knee excursion for participants with and without PFPS...... 116 Appendix K Table 41: Coefficient of variation pairwise comparison (mean difference, standard error, significance and 95% confidence intervals) for knee excursion for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1...... 117 Table 42: One-way ANOVA results (degrees of freedom (df), f value, p value and observed power (1-β)) for the comparison of vertical stiffness for participants with and without PFPS...... 119 Table 43: Coefficient of variation pairwise comparison (mean difference, standard error, significance and 95% confidence intervals) of vertical stiffness for participants with and without PFPS. Comparisons were made against the reference frequency of 132 hops.min-1...... 120

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List of Figures

Figure 1: Aerial view of the experimental set up in the Human Movement Laboratory (HML)...... 30 Figure 2: Participant set up with rigid bodies and foot markers secured over the five segments...... 31 Figure 3: Rigid body markers were represented by clusters of markers over each of the five segments during the static calibration trial and all other markers represented the anatomical landmarks used for digitisation...... 33 Figure 4: A visual representation of a complete hop cycle including gait events: toe-off (TO),

peak of vertical displacement during flight phase (Zpeakf) initial contact (IC), peak

vertical ground reaction force (vGRFpeakc). Each gait cycle was divided into the flight phase and contact phase. Each contact phase was divided into the loading period and propulsive period...... 36 Figure 5: Ankle dorsiflexion and knee flexion excursion (degrees) (mean) during the loading period for people with patellofemoral pain syndrome (PFPS) and healthy matched control participants, with statistically significantly greater ankle excursion at maximal effort in the healthy participants and greater knee excursion at 108 hops.min-1 in participants with PFPS, compared to hopping at 132 hops.min-1 during the loading period (* p < 0.01 for within group comparisons)...... 44 Figure 6: Ankle and knee joint stiffness (Nm.kg) (mean) during the loading period for people with patellofemoral pain syndrome and the matched, healthy participants. Greater knee joint stiffness was observed at 132 hops.min-1 in participants with PFPS, however, there were no statistically significant between and within group differences (p > 0.01)...... 50 Figure 7: Coefficient of variation (CV) (%) of knee and ankle joint stiffness during the loading period for participants with patellofemoral pain syndrome and matched, healthy participants...... 52 Figure 8: Coefficient of variation (%) of knee and ankle joint power during the loading period for participants with patellofemoral pain syndrome and the matched, healthy participants...... 56

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Figures in Appendices

Appendix H Figure 9: Duration of the hop cycle...... 95 Figure 10: Duration of the contact phase...... 96 Figure 11: Duration of the loading period...... 98 Figure 12: Duration of the propulsion period...... 99 Figure 13: Duration of the flight phase...... 101 Appendix I Figure 14: Knee excursion...... 103 Figure 15: Ankle excursion...... 104 Appendix J Figure 16: Knee moment...... 106 Figure 17: Ankle Moment...... 106 Figure 18: Vertical stiffness...... 107 Figure 19: Knee Stiffness...... 108 Figure 20: Ankle stiffness...... 109 Figure 21: Knee Mechanical Work...... 109 Figure 22: Ankle Mechanical Work ...... 111 Figure 23: Knee power...... 112 Figure 24: Ankle Power ...... 114 Appendix K Figure 25: Coefficient of variation of knee excursion...... 116 Figure 26: Coefficient of variation of ankle excursion...... 117 Figure 27: Coefficient of variation of knee moment...... 118 Appendix L Figure 28: Coefficient of variation of ankle moment...... 118 Figure 29: Coefficient of variation of vertical stiffness...... 119 Figure 30: Coefficient of variation of knee stiffness...... 120 Figure 31: Coefficient of variation of ankle stiffness...... 121 Figure 32: Coefficient of variation of knee mechanical work...... 121 Figure 33: Coefficient of variation of ankle mechanical work...... 121 Figure 34: Coefficient of variation of knee power...... 122 Figure 35: Coefficient of variation of ankle power...... 122

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Abbreviations

ACLR Anterior Cruciate Ligament Reconstruction

AKP Anterior Knee Pain

AKPS Anterior Knee Pain Scale

AMTI Advanced Mechanical Technology, Inc.

ANOVA Analysis of Variance

ASIS Anterior Superior Iliac Spine

BMI Body Mass Index

CI Confidence Interval cm Centimetre

COM Centre of Mass

COML Centre of Mass during Loading

CV Coefficient of Variation deg Degree f Effect size fMRI Functional Magnetic Resonance Imaging

HREC Human Research Ethics Committee

HML Human Movement Laboratory

Hz Hertz

IC Initial Contact

ITB Iliotibial Band

J.kg-1.sec-1 Joules per kilogram per second

J.kg-1.rad-1 Joules per kilogram per radian kg Kilogram k Vertical stiffness xv

Kankle Ankle joint stiffness

Kknee Knee joint stiffness

M Moment m.s-1 Metres per second ms Millisecond

MRI Magnetic Resonance Imaging

N Newtons

NDI Northern Digital Inc.

N.kg.m-1 Newtons per kilogram per metre

N.m.kg-1 Newton metre per kilogram

OA Osteoarthritis

ODAU Optotrak Data Acquisition Unit II

P Power

PFPS Patellofemoral Pain Syndrome

PFJ Patellofemoral joint

PSIS Posterior Superior Iliac Spine

Q-angle Quadriceps Angle

ROM Range of motion s Second

SCU Systems Control Unit

SD Standard deviation

SLTHT Single-leg, triple hop test

TO Toe Off

VAS Visual Analogue Scale vGRF Vertical ground reaction force xvi

W Work

WSU Western Sydney University

1β Power

ɵ Angular displacement

Δ Vertical displacement

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Appendices

Appendix A: Letter of Ethical Approval from WSU Ethics Committee ...... 84 Appendix B: Participant Consent Form ...... 85 Appendix C: Participant Flyer ...... 86 Appendix D: Participant Information Sheet ...... 87 Appendix E: Anterior Knee Pain Scale (AKPS) ...... 90 Appendix F: Visual Analogue Scale (VAS) ...... 91 Appendix G: Exercise Pre-screening Questionnaire ...... 92 Appendix H: Statistical results of spatiotemporal characteristics during the loading period. 95 Appendix I: Statistical results of kinematics during the loading period...... 103 Appendix J: Statistical results of kinetics during the loading period...... 106 Appendix K: Statistical results of the coefficient of variation of kinematics during the loading period...... 116 Appendix L: Statistical results of the coefficient of variation of kinetics during the loading period...... 118

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Abstract

Introduction: Patellofemoral Pain Syndrome (PFPS) is characterised by pain in the region of the patellofemoral joint during functional tasks, sporting activities or following prolonged sitting. Strength deficits are commonly reported, however, there is no empirical evidence to support alterations in lower limb control. The knee and ankle joints of the lower limb interact to allow force absorption during loading activities. It is plausible that this interaction is altered in people with PFPS. Aim: The purpose of this study was to evaluate the knee and ankle joint interaction in people with PFPS compared to healthy counterparts, during on-the-spot, repetitive, single-leg, hopping tasks. Participants: Ten participants with PFPS (symptom duration of 30.44 (28.56) months and VAS pain score of 2.6 (1.5) prior to testing) and ten healthy participants volunteered for the study. Participants were aged between 18 and 40 years and were matched for sex, age, height, body mass and limb dominance.

Procedures: Each participant performed four trials of single-leg, on-the-spot hopping. These four trials were performed in a random order and at different cadences (132, 120, 108, 96 hops.min-1). A fifth trial was performed at the participant’s maximal height of hopping. Spatiotemporal characteristics, joint kinematics and kinetics were recorded using synchronous collection of force plate (AMTI, Multicomponent force plate, Gen 5 BP400600-1000, Watertown, MA) and motion data (Optotrak Certus System, NDI, Waterloo, Canada). Variability was calculated as the coefficient of variation (CV). Repeated measures analysis of variation (ANOVA) were performed, followed by post hoc tests to determine differences between groups during the different efforts of hopping. Results: There were no statistically significant differences between groups for all spatiotemporal, kinematic, kinetic and CV scores for all dependant variables at the knee and ankle joints (p > 0.05). There was statistically significantly greater knee excursion during loading for participants with PFPS at 108 hops.min-1 and ankle excursion during loading for healthy participants at maximal efforts, compared to the reference cadence of 132 hops.min-1. Vertical stiffness was significantly lower in the healthy participants at 96 hops.min-1 and maximal efforts when compared to 132 hops.min-1. Compared to hopping at 132 hops.min-1, the lower cadences demonstrated xix

statistically significant differences in spatiotemporal characteristics of hopping, including a greater duration of contact and flight phases and propulsive period in both the PFPS and healthy participant groups. Conclusion: Participants with PFPS had similar movement patterns and mechanical characteristics at the knee and ankle joints compared to matched, healthy, participants. Pain was not provoked in participants with PFPS who had longstanding symptoms, even during repetitive loading at maximal efforts. It is possible that the knee did not flex through enough range during the trials and was not reflective of positions in which knee pain is experienced during functional activities in people with PFPS. The lack of differences between groups may also be reflective of the lack of pain experienced by participants with longstanding PFPS during testing, therefore, not leading to any motor compensations. These findings may guide future studies to examine activities that provoke pain symptoms and mimic the positions in which anterior knee pain is experienced. However, the current study demonstrated that even when there are relatively large forces transmitted though the knee and PFJ during single-leg hopping, which varied from submaximal to maximal efforts, the task may not be sensitive to detect compensatory strategies in people with longstanding PFPS.

CHAPTER ONE Introduction

1.1 Summary of the problem

Patellofemoral pain syndrome (PFPS) is one of the most common knee pathologies treated by physiotherapists in clinical practice (Van Cant, Pitance & Feipel, 2017). It is characterised by anterior knee pain during weight bearing activities, such as running, jumping, squatting and ascending or descending stairs (Van Cant et al., 2017). A diagnosis of PFPS is often a diagnosis of exclusion whereby no other pathoanatomical cause of pain has been determined

(Thomeé, Augustsson & Karlsson, 1999; Van Cant et al., 2017).

Three factors have been suggested to contribute to the pathogenesis of PFPS, which include tissue overload, lower limb malalignment and muscular imbalances (Thomeé et al., 1999).

Lower limb malalignment and muscular imbalances may affect movement of the trunk and lower limb, with the potential to disrupt tissue homeostasis and result in pain. However, there is little empirical evidence to support this hypothesis and there are a multitude of intrinsic and extrinsic factors that may contribute to the onset of PFPS. Consequently, many clinical trials have been performed in an attempt to demonstrate efficacious treatments such as short term use of nonsteroidal anti-inflammatory drugs, medially directed patella taping, in-foot orthoses and a variety of lower limb strengthening and exercise programs (Rixe, Glick, Brady &

Olympia, 2013; Sanchis-Alfonso, McConnell, Monllau & Fulkerson, 2016; Vora, Curry,

Chipman, Matzkin & Li, 2017). However, the incidence of PFPS remains high and the available evidence on the etiological factors that contribute to PFPS remains conflicted.

In healthy individuals, the function of the knee and ankle joints are inherently synergistic to allow the transfer of force along the kinetic chain of the lower limb (João, Veloso, Cabral,

Moniz-Pereira & Kepple, 2014). It has been demonstrated that the knee and ankle joints adapted concomitantly with drop landings from different heights in healthy cohorts (Zang,

Bates & Dufek, 2000). It is plausible that after a knee injury the synergistic relationship between the knee and ankle is affected. However, to date, there are no studies which have accurately examined the knee and ankle interaction in people with PFPS.

The knee and ankle interaction have been investigated in people recovering from Achilles tendon repair (Willy, Brorsson, Powell, Willson, Tranberg & Grävare Silbernagel, 2017) and anterior cruciate ligament (ACL) reconstruction (Wikstrom, Tillman, Chmielewski & Borsa,

2006), with findings that loading was shifted to the non-injured joint in an attempt to protect the injured site. In people with knee pain, tasks which have been used to examine the knee- ankle interaction have involved propulsion and forward translation. An example of this is the single-leg triple-hop test (SLTHT) which has been used to examine people with PFPS (Bley,

Correa, Dos Reis, Rabelo, Marchetti & Lucareli, 2014; Dos Reis, Correa, Bley, Rabelo,

Fukuda & Lucareli, 2015). This task attempts to mimic the type of lower limb loading experienced during sports and found decreased ankle dorsiflexion range and power with concomitant increases in knee power and decreases in knee flexion during the period of loading between the first and second hops (Dos Reis et al., 2015). However, there are some limitations to the SLTHT with the movement patterns being variable between efforts and the task not able to examine the effect of repetitive loading or load, that can vary between submaximal and maximal efforts. Therefore, examining the knee and ankle interaction during activities which relatively increase the effort of the task, increase the contribution of the knee and ankle joints to the performance of the activity and allow for repetitive loading are 3 required. These changes to the same task have the potential to be sensitive to any changes in mechanical characteristics in people who have had PFPS which may only become apparent at different levels of effort.

An evaluation of on-the-spot, single-leg hopping allows an examination of the knee and ankle joint interaction during repeated and rapid loading, with minimal compensation at other segments during loading when there is an attenuation of forces. Compared to previous studies that have examined jumping and hopping tasks, repeated, single-leg hopping minimises the involvement of the trunk and forward translation of the centre of mass (Lamontagne &

Kennedy, 2013). As well as being easy to perform, hopping has clinical utility to be used when assessing patients with lower limb pathology by replicating the forces and muscle actions used during sporting activity (Wikstrom et al., 2006).

1.2 Significance of the study

The purpose of this study was to evaluate the interaction of the knee and ankle joints in individuals with PFPS compared to healthy, matched control participants during a repetitive, on-the-spot, single-leg hopping task. The knee and ankle joints are synergistic in their action during lower limb loading and may be impacted by lower limb pathologies such as PFPS.

Determining whether there is a change in the function of the knee and ankle during loading provides greater understanding of the intrinsic changes that may occur in people with PFPS, which is a recalcitrant problem and remains difficult to manage.

Knowledge obtained from this project has the potential to influence the assessment and management of individuals with PFPS by determining the alterations to movement patterns and how force is attenuated in the lower limb. Results of this study may direct future research 4 to determine if muscular deficits and changes in loading pattern of the knee and ankle are a cause and/or effect of PFPS. Results of this research also have the potential to influence clinical practice through the development of a clinical tool to assist in the assessment and rehabilitation of individuals with PFPS.

1.3 Research objectives

The primary objective of this study was to evaluate whether there were mechanical differences between people with and without PFPS during the loading phase of a repetitive loading task that varied in effort. This would determine if differences in movement strategies were associated with a history of anterior knee pain. The second objective of this study was to determine if there was greater variability in either performance or movement patterns between groups with and without PFPS.

1.4 Research hypotheses

Primary null hypotheses

(i) There would be no differences in spatiotemporal performance of the task and mechanical characteristics of the knee and ankle joints between people with and without PFPS during on- the-spot, single-leg hopping.

(iii) There would be no differences in the mechanical characteristics of the knee and ankle joints between the trials of on-the-spot, single-leg hopping at different cadences.

(ii) There would be no difference in variability of the performance of the task and mechanical characteristics of the knee and ankle joints between people with and without PFPS during on- the-spot, single-leg hopping. 5

CHAPTER TWO Literature Review

Physical activity is an important facet for the maintenance of a healthy wellbeing.

Recreational or organised sport encourages participation in physical activity, enabling people to prevent disease, manage lifestyle comorbidities and develop social skills (Yu, Green &

Walker, 2018). Approximately 13.1 million Australians participate in at least one physical activity for the purpose of exercise, recreation or sport and represents 83% of the Australian population (Yu et al., 2018).

Participation in sport is also associated with injury and the most common lower limb joint injured amongst young people aged from 18 to 24 years, is the knee joint (Australian Institute of Health and Welfare, 2017). Knee injuries may be due to a single incident, such as excessively twisting the joint, as well as injuries that develop over time and have an insidious onset. Sedentary individuals and novice athletes who are not exposed to intense and repetitive exercise, may also experience knee pain from a sudden change in activity or prolonged periods of sitting (Willy et al., 2019). Although knee injuries are common amongst younger individuals, they can be chronic, persist across the lifespan and have a high correlation with early knee osteoarthritis (OA) (Favero, Ramonda, Goldring, Goldring & Punzi, 2015; Heidari,

2011). The risk of early OA has been reported to be 3 to 6 times higher amongst individuals who have previously sustained a knee injury (Driban, Eaton, Lo, Ward, Lu & Mcalindon,

2014).

Patellofemoral pain syndrome (PFPS) is one of the most common knee pathologies treated by physiotherapists in clinical practice (Van Cant et al., 2017). PFPS is characterised by the gradual onset of anterior knee pain during weight bearing activities, such as running, jumping, squatting and stair use (Van Cant et al., 2017) and is a diagnosis of exclusion whereby there is no discernible pathoanatomical cause of pain (Thomeé et al., 1999; Van Cant et al., 2017).

The amount and type of activity performed by an individual are associated with PFPS

(Thomeé et al., 1999). Management of PFPS includes limiting the amount and altering the type of activities to avoid aggravating pain (Willy et al., 2019). However, PFPS remains a recalcitrant condition and is often experienced during periods of greater activity or change in the type of activity. It has been estimated that 70 to 90% of individuals diagnosed with PFPS will have recurrent episodes or chronic pain (Powers, Bolgla, Callaghan, Collins & Sheenan,

2012) and that symptoms can persist for up to 20 years (Crossley, Callaghan & van

Linschoten, 2016). Furthermore, PFPS has been associated with the development of patellofemoral joint (PFJ) degeneration which has been confirmed by osteoarthritic changes observed on magnetic resonance imaging (MRI) and radiographs (Collins, Oei, de Kanter,

Vicenzino & Crossley, 2018; Crossley, 2014; Wyndow, Collins, Vincenzino, Tucker &

Crossley, 2016). The likelihood of developing chronicity and greater risk of developing OA provides impetus to develop greater understanding of the changes associated with PFPS and how it may be better managed.

2.1. The incidence and pathogenesis of PFPS

The incidence of PFPS is reported to range from 8 to 44% of all knee conditions being treated in sport clinics (Bley et al., 2014; Crossley, Van Middelkoop, Callaghan, Collins, Rathleff &

Barton, 2016; Van Cant et al., 2017). The relatively high incidence and poor patient outcomes 7 instigates the need to better understand the factors that may contribute to the onset of PFPS

(Dutton, Khadavi & Fredericson, 2016).

Three factors have been suggested to contribute to the pathogenesis of PFPS and include overload, lower limb malalignment and muscular imbalances (Thomeé et al., 1999).

Malalignment of the lower limb primarily describes suboptimal static or dynamic postures adopted during activity (Daneshmandi, Saki & Sahheidari, 2011). Dynamic knee valgus, internal rotation of the femur, lateral tracking of the patella and foot pronation are commonly cited as deviations observed in people with PFPS (Dos Reis et al., 2015; Waryasz &

McDermott, 2008). Muscular imbalances, including weakness of the hip extensors, abductors, external rotators and quadriceps, along with tightness of the iliotibial band, are all theorised to contribute to PFPS (Dutton et al., 2016; Willy et al., 2019). Malalignment and muscular imbalances, combined with an increase in activity, potentially cause a relative overload of the

PFJ. As the PFJ and surrounding tissues are not adapted to withstand this increase in stress, it is plausible that there may be a generation of pain (Powers et al., 2012; Willy et al., 2019).

However, there is little empirical evidence to support the impairments described in the suggested tissue-based model. It is probable that several factors lead to pain in the anterior region of the knee, which is syndromic rather than a tissue-based pathology.

2.2 The etiological factors of PFPS

There is consensus that PFPS manifests as a multifactorial problem, however, the underlying etiology remains poorly understood (Crossley, 2014; Halabchi, Mazaheri, Seif-Barghi, 2013;

Petersen, Ellermann, Gösele-Hoppenburg, Best, Rembitzki, Brüggemann & Liebau, 2014).

The development and persistent nature of PFPS has been said to be attributed to proximal, distal and local factors which contribute to the excessive loading experienced at the PFJ 8

(Willy et al., 2019). These features are both intrinsic and extrinsic in nature and often increase an individual’s risk of developing PFPS. Further, numerous clinical trials have tested treatments ranging from strengthening and stretching protocols, orthotic prescription, patella taping and patella mobilisation with variable results (Rixe et al., 2013; Sanchis-Alfonso et al.,

2016; Willy et al., 2019). It is possible that PFPS is a broad classification for a number of different pathologies and as such without a detailed knowledge of the multiple contributing factors, no single treatment or approach will effectively treat all people with PFPS (Saltychev,

Dutton, Laimi, Beaupré, Virolainen & Fredericson, 2018). A recently published clinical practice guideline (Willy et al., 2019) has suggested four sub-classifications for PFPS including overuse/overload without other impairments, muscle performance deficits, movement coordination deficits and mobility impairments. Given the currency of the guideline, these suggestions have not yet translated to clinical practice. Additionally, the empirical evidence to support suggested etiological factors or current treatment approaches highlights why the incidence of PFPS remains recalcitrant and difficult to manage.

2.3 Intrinsic risk factors associated with the development of PFPS

Intrinsic risk factors refer to personal factors of an individual such anthropomorphic characteristics, muscle strength and foot position (Halabchi et al., 2013). Numerous intrinsic factors, both modifiable and non-modifiable have been suggested to be associated with the development of PFPS. The following section will describe the modifiable and non-modifiable intrinsic risk factors suggested to contribute to the pathogenesis of PFPS.

2.3.1 Non-modifiable risk factors associated with PFPS

Women are 2.23 times more likely to experience PFPS compared to their male counterparts

(Boiling, Padua, Marshall, Guskiewicz, Pyne & Beutler, 2010; Smith et al., 2018). The 9 discrepancy in the incidence of PFPS between women and men was previously attributed to several anthropomorphic differences between the two sexes (Vora et al., 2017). These included differences in pelvic width, femoral anteversion, tibial torsion, cartilage thickness, ligament laxity and hormones all of which were suggested to increase a woman’s risk of developing PFPS (Dutton et al., 2016; Willy et al., 2019). However, there are now a number of high and moderate quality studies that suggest that sex is not a risk factor for the development of PFPS (Boiling, Padua, Marshall, Guskiewicz, Pyne & Beutler, 2009; Neal,

Lack, Lankhorst, Raye, Morrissey & van Middelkoop, 2018).

Oestrogen in women has been suggested to increase ligament laxity and the onset of PFPS

(Tumia & Maffulli, 2002). General joint laxity and hypermobility of the patella which has been positively correlated with PFPS due to decreased stability from passive structures, has been suggested to lead to tissue overload at the PFJ (Al-Rawi & Nessan, 1997; Witvrouw,

Lysens & Bellemans, 2000). Greater increases in tissue laxity, as a result of hormonal changes, have the potential to change patella tracking in hypermobile individuals (Dutton et al., 2016). Combined with greater ligament laxity, alteration in the recruitment of quadriceps has been observed during menstruation, potentially influencing load transfer at the PFJ

(Tenan, Peng, Hackney & Griffin, 2013) and potentially limiting the effect of strengthening exercise in women. However, the impact of a woman’s menstrual cycle on PFP requires further investigation as findings are inconclusive (Casey, Rho & Press, 2016) and have not been specifically investigated in women with PFPS.

The quadriceps angle (Q-angle) is a measure to quantify the pull of the quadriceps femoris muscle on the patella (Loudon, 2016) and is measured by drawing a line from the anterior superior iliac spine (ASIS), passing through the patella and intersecting the line from the tibial 10 tubercle to the patella (Almeida, Silva, Magalhaes, Burke & Marques, 2016). A larger Q angle has previously been suggested to contribute to greater patellofemoral stresses, as greater load would be placed on the lateral facet of the patella and lateral femoral condyle (Dutton et al., 2016). However, recent findings have contradicted previous literature concluding that the

Q angle is not a risk factor for the development of PFPS when assessed in both weight bearing and non-weight bearing positions (Willy et al., 2019). The evidence remains conflicted with a suggestion that an increased Q angle may still be a potential contributing factor towards an individual’s symptoms once PFPS has developed (Vora et al., 2017).

2.3.2 Modifiable risk factors associated with PFPS

It had been previously suggested that weight and body mass index (BMI) were strongly correlated with the onset of PFPS as a result of increased PFJ loading through a higher body composition (Crossley, 2014). Higher weight and BMI were also thought to be a sequalae of

PFPS as individuals would often have to cease physical activity due to pain. Periods of inactivity and further weight gain potentially lead to additional patellofemoral stress and difficulty when returning to physical activity (Crossley, 2014). A number of studies have now refuted these suggestions and concluded that patient characteristics such as age, height, weight and BMI are not associated with the development of PFPS (Lankhorst, Bierma-

Zeinstra & van Middelkoop, 2013; Neal et al., 2018). However, it is possible that greater body mass and BMI contribute to the development of patellofemoral OA, as higher body weight and BMI are associated with greater loss of patella cartilage (Crossley, 2014).

Women with PFPS have been shown to have weakness of the hip external rotators, abductors and extensors during isometric strength testing (Prins & van der Wurff, 2009; Willy et al.,

2019). It had been anticipated that hip weakness was a predisposing factor to the development 11 of PFPS, however, recent evidence has concluded that weakness of the hip extensors, abductors and external rotators are in fact a result of PFPS (Rathleff, Rathleff, Crossley &

Barton, 2014; Willy et al., 2019). These findings support physiotherapy management focused towards hip strengthening exercises to improve pain and function of individuals with PFPS

(Nascimento, Tiexeira-Salmela, Souza & Resende, 2018; Rathleff et al., 2014). However, there remains no evidence to confirm if PFPS persists when hip weakness is not treated.

The iliotibial band (ITB) acts as a stabiliser of the patella, acting to resist excessive medial gliding of the patella. However, when shortened, the ITB has been suggested to pull the patella laterally given its attachment to the patella via the lateral retinaculum (Dutton et al.,

2016; Hudson & Darthuy, 2009). Weakness of the vastus medialis and hip abductors have also been suggested to contribute to greater lateral patella displacement (Powers, Witvrouw,

Davis & Crossley, 2017). Greater relative lateral tracking of the patella has been shown to increase contact forces at the PFJ and lateral cartilage pressure, thus contributing to the development of PFPS (Scotti, 2017). Although a relationship between the ITB and PFPS has been reported in observational studies (Hudson et al., 2009), it could be suggested that assessment of the ITB using the Obers test may not be reflective of the arthrokinematics of the PFJ during functional activities, because the Obers test is performed in a non- weightbearing position (Hudson et al., 2009). The study by Hudson et al. (2009) also failed to report if participants experienced weakness of the hip abductors or vastus medialis which may confound their findings, as hip abductor weakness may cause a compensation leading to dynamic valgus of the knee which results in shortening of the ITB (Arab & Nourbakhsh,

2010; Powers, 2010). Interventions that incorporate hip abductor strengthening have been established to be of benefit for PFPS cohorts (Dutton et al., 2016).

Quadriceps weakness and atrophy are reported in only some of the studies examining strength in people with PFPS. Quadriceps atrophy has been suggested to be a sequalae of quadriceps inhibition, where the central nervous system does not fully activate the quadriceps as a result of pain (Giles, Webster, McClelland & Cook, 2013). It has been demonstrated that there is atrophy of the vastus medialis (Giles et al., 2013; Pattyn, Verdonk, Steyaert, Vanden Bossche,

Van Den Broecke, Thijs & Witvrouw, 2011; Willy et al., 2019) and lateralis of people with

PFPS when assessed using MRI (Giles et al., 2013). Quadricep weakness has also been reported as a sequalae of PFPS in the general population, however, is a risk factor for the onset of PFPS in military recruits (Van Tiggelen, Witvrouw, Coorevits, Croisier & Roget,

2004; Willy et al., 2019). It has been demonstrated that military recruits who had weakness during isometric quadricep strength during screening, went on to developed PFPS after a six- week training protocol (Van Tiggelen et al., 2004). Therefore, as quadriceps weakness has been shown to have some association with PFPS, strengthening this muscle is a common management strategy (Giles et al., 2013; Güney, Yuksel, Kaya & Doral, 2014; Willy et al.,

2019). The challenge remains to be able to provide strengthening programs that do not provoke anterior knee pain which are often aggravated by functions that require quadriceps muscle activity.

Despite research findings in support of quadricep weakness, it has suggested that quadriceps activation and the contribution of the quadriceps to functional activities was no different in people with PFPS compared to control participants when performing a squatting task evaluated using functional MRI (fMRI) (Pattyn, Verdonk, Steyaert, Van Tiggelen &

Witvrouk, 2013). These findings challenge the importance of strengthening exercise in the treatment of people with PFPS, especially as participants were observed to have similar patterns of movement and functional capacity compared to healthy participants (Pattyn et al., 13

2013), therefore, rejecting hypotheses of quadriceps dysfunction in individuals with PFPS.

These findings conflict the current practice guidelines (Willy et al., 2019) which do not provide a clear or strong rationale for the inclusion or exclusion of strengthening exercise programs for people with PFPS.

Altered foot and ankle biomechanics have been reported in people with PFPS (Boling et al.,

2009; Barton, Levinger, Crossley, Webster & Menz, 2011; Willy et al., 2019). It has been suggested that pronounced subtalar foot pronation (ples planus) would induce femoral internal rotation and relative tibial external rotation (Barton et al., 2011; Boling et al., 2009), subsequently leading to alterations to the line of pull of the quadriceps muscle. This can possibly increase stress at the lateral compartment of the PFJ, leading to pain (Barton et al.,

2011). The assessment of foot posture has traditionally been performed in a static position, such as the use of the foot posture index and may not be a valid assessment of dynamic foot position or force (Barton et al., 2011). Further, previous studies have determined foot kinematics with different methods, making it difficult to conclude whether there are in fact alterations to foot motion in people with PFPS (Powers et al., 2017). For example, greater navicular drop, which has been proposed to reflect greater foot pronation, was found to be associated with the development of PFPS within a sample of military personnel (Boling et al.,

2009). These findings conflict with other studies that measured greater plantar pressure under the lateral boarder of the foot in people with PFPS, which was suggested to be due to a more supinated foot (Thijs, Van Tiggelen, Roosen, De Clercq, Witvrouw, 2007; Willy et al., 2019).

Clinical practice guidelines are not consistent in the report of their recommendations.

However, it has been concluded that excessive foot pronation is not a feature of people with

PFPS and conflicts with the strong recommendation for the use of in-shoe, foot orthoses

(Willy et al., 2019). 14

Poor endurance of the ankle plantarflexors (Van Cant et al., 2017) and reduced range of ankle dorsiflexion (Schacht, 2014) have been associated with PFPS. It was suggested that these impairments would impact knee flexion, either by requiring further flexion range to absorb force at landing (Schacht, 2014) or limiting knee flexion range as the tibia is unable to achieve adequate forward translation on the talus (Rabin, Portnoy & Kozol, 2016). It has been demonstrated that reduced dorsiflexion range of motion as a result of ankle plantarflexor tightness, caused greater knee flexion angles during running to facilitate shock absorption

(Schacht, 2014). Additionally, reduced dorsiflexion range of motion was observed to lead to deficits in knee flexion angles during functional tasks, such as lateral step downs (Rabin et al.,

2016). Plantarflexor endurance, determined by the number of repetitions of a heel raise able to be performed, was lower in participants with PFPS compared to healthy control participants

(Van Cant et al., 2017). The findings of impairments at the ankle and knee joints in previous studies supports the need for future studies to examine the kinetic chain along the lower limb, which may have demonstrable alterations in movement patterns and capacity to withstand load.

2.4 Extrinsic risk factors associated with the development of PFPS

Extrinsic risk factors describe factors outside of the human body such as those in the environment (Halabchi et al., 2013). For people with PFPS, these most commonly include the surface, footwear and the type, frequency and intensity of the activity (Dutton et al., 2016).

The following section describes the common extrinsic risk factors that have been studied as being associated with PFPS.

2.4.1 Modifiable extrinsic risk factors associated with PFPS

High impact and repetitive loading activities have been associated with PFPS and recent evidence has suggested that higher rates of PFJ loading is a greater risk to developing PFPS rather than the magnitude of load (Atkins, James, Yang, Sizer, Brismée, Sawyer & Powers,

2018). This suggests that activities of either high or low load may contribute to PFPS, and that the type of activity, especially those with a relatively high rate of loading, may be more likely to lead to the development of PFPS (Akins et al., 2018). Running and marching, are activities with relative greater loading than activities of daily living such as walking and are sustained for longer periods (Dorotka, Jimenez-Boj, Kypta, & Kollar, 2003; Kunene, Ramklass &

Taukobong, 2019). Individuals that participate in these activities have a relatively high incidence of PFPS and it is plausible that both the rate of loading and repetition contribute to its development.

Individuals who specialised in one sport were reported to be at greater risk of developing

PFPS, compared to those who participated in a range of different sports (Dutton et al., 2016;

Hall, Barber Foss, Hewett & Myer, 2015). Aspects of sports specialisation which may contribute to PFPS could include participation in training for extended periods and participation in competition with similar loads, compared to people who vary their exposure to the same magnitude and type of load, by performing a variety of sports which may be reflective of a variety of different postures and positions (Dutton et al., 2016; Hall et al.,

2015). These findings may suggest that broadening exposure to different types of activities, in addition to avoiding excessive periods of participation in a single type of activity, may be protective of PFPS.

A key component of exposure to load which may contribute to the pathogenesis of PFPS is the frequency of training. It was observed in a group of runners that those who trained twice a week for a running event were less likely to develop PFPS compared to those who did not train (Kunene et al., 2019; Nielson, Nohr, Rasmussen & Sørensen, 2013). This principal may apply to the change in exercise habits of relatively sedentary people who commence a new sport or exercise program, without being exposed to an appropriate period of tissue adaptation and consequently risking the development of PFPS. Similarly, military recruits may also not be accustomed to intense periods of training which reflect higher incidences of PFPS development (Dorotka et al., 2003; Lankhorst et al., 2013). Therefore, exposure to a certain amount of load that is not excessive and performed in preparation for increases in load are possibly protective strategies for the development of PFPS. Elite runners, who participated in regular competition, may have had relatively greater tissue adaptation due to their regular and high training loads and were more resilient and less at risk of PFPS (Dutton et al., 2016;

Kunene et al., 2019). It may be suggested that it is not the participation in an activity of high intensity or for prolonged duration that increases the risk of PFPS, but a sudden increase or change in the type and intensity of the activity for which the body is not accustomed to (Vora et al., 2017).

Running downhill, on hard surfaces and on stairs have been suggested to be training errors that contribute to the development of PFPS (Dutton et al., 2016; Kunene et al., 2019).

Although, varying an individual’s training environment may be a feasible modification to minimise PFPS, some sports such as basketball and netball are played on surfaces which cannot be modified. Another feasible method to reduce the development of PFPS is to change footwear because the use of older or worn footwear has been suggested to increase the risk of developing PFPS in runners (Kunene et al., 2019). The science and merit underpinning 17 footwear selection continue to evolve (Cheung, Ng & Chen, 2006). In the context of PFPS, there are inconsistencies in the reporting and impact of the intrinsic foot position and subsequent development of PFPS (Willy et al., 2019). It is recognised that the choice of footwear may influence foot position, however, it is not known whether the type of footwear does in fact increase the risk of developing PFPS (Cheung et al., 2006). During running, footwear has been suggested to influence peak forces generated at the PFJ (Esculier, Dubois,

Bouyer, McFadyen & Roy, 2017). Gait retraining for runners using lighter shoes or minimalist shoes could lead to lower peak PFJ forces during running (Bonacci, Hall, Fox,

Saunders, Shipsides & Vicenzino, 2018; Esculier et al., 2017; Sinclair, Richards, Selfe, Fau-

Goodwin & Shore, 2016). However, whether this reduction in PFJ load does in fact alter the risk of developing PFPS, changing running technique and altering the force across the knee complex remains unclear.

2.5 Summary of PFPS etiology and risk factors.

A multitude of intrinsic and extrinsic factors may contribute to the development of PFPS.

Common terms such as ‘overuse’ and ‘overload’ are associated with PFPS (Al-Rawi et al.,

1997; Thomeé et al., 1999; Witvrouw et al., 2000), however, there is little empirical evidence to support one or more of these factors as being associated or causative of PFPS. The weighting of single factors and the influence of their interaction with other factors on the pathogenesis of PFPS remain a clinical challenge. Further research is required to develop a greater understanding of the etiological factors in the development of PFPS and to influence clinical practice guidelines.

2.6 Force attenuation in the lower limb

During activity, bone, cartilage, muscles, tendons, ligaments, nerves and vessels all act to accommodate internal and external forces placed on the body (Coventry, O’Connor, Hart,

Earl & Ebersole, 2006). The ability to absorb, transmit and dissipate force is dependent on the ability to coordinate a multi-segmented system such as the human body, in such a way that allows performance to be effortless and pain free (Lu & Chang, 2012).

Stiffness is defined as the ability of an object to resist deformation in response to a force

(Brughelli & Cronin, 2008; Butler, Crowell & Davis, 2003). Stiffness changes as a result of neuromuscular adaptations whereby the muscle tendon unit, composed of both the contractile and non-contractile components, resist the change in joint angle during movement (Misgeld,

Zhang, Lüken & Vittorio, 2017). Commonly, the leg has been modelled as a massless spring and describes the shortening of the leg during loading which is due to flexion of the hip, knee and ankle (Blickhan, 1989; Lamontagne et al., 2013). Stiffness has also been used to describe the relative change in force acting about a joint due to a change in geometry during human movement (Lamontagne et al., 2013). Stiffness of a joint can describe the mechanical component and contribution of a joint to a multi-segmented system to allow force attenuation and is modulated by either a change in the moment acting about the joint or the joint excursion (Butler et al., 2003). Stiffness changes with respect to the activity being performed, which may vary from walking, running and landing from a jump, as well as the effort of the task such as running at faster speeds and landing from greater heights (Kuitunen, Ogiso &

Komi, 2011). Additionally, stiffness may change due to other intrinsic and extrinsic factors including strength (Watsford, Murphy, Mclachlan, Bryant, Cameron, Crossley & Makdissi,

2010), fatigue (Dutto & Smith, 2002), pain and neuromuscular control (Sutherlin, Mangum, 19

Russell, Saliba, Hertel & Hart, 2018), surface stiffness (Ferris & Farley, 1985) and footwear

(Bishop, Fiolkowski, Conrad, Brunt & Horodyski, 2006).

Biomechanical research has suggested that stiffness may be optimised to enhance athletic performance and reduce the risk of lower limb injury (Butler et al., 2003; Waxman, Ford,

Nguyen & Taylor, 2018). A causative link between greater leg stiffness and pathology has been suggested in runners with tibial stress fracture (Grimston, Ensberg, Kloiber & Hanley,

1991) and early knee osteoarthritis (Waxman et al., 2018). In contrast, reduced lower limb stiffness due to excessive joint range of motion has been suggested to increase the risk of sustaining soft tissue injury during athletic activity (Granata, Padua & Wilson, 2001;

Williams, McClay & Hamill, 2001). However, the link between pathology such as PFPS and changes in stiffness at a joint or the entire leg remain unclear.

The report of how lower limb joints control and optimise force dissipation is inconsistent in the literature. Specifically, the examination of different activities such as, jump-and-land, drop jumps, counter-movement jumps and running, make comparisons between studies problematic. During drop landings, the ankle was observed to significantly contribute to force absorption during stiff landings while the hip and knee joints contributed to a relatively greater proportion of force absorption during soft style landings (DeVita & Skelly, 1992).

Similarly, it has been demonstrated in running and hopping that the knee was relatively stiffer than the ankle when using a forefoot landing pattern compared to a rearfoot landing pattern

(Butler et al., 2003). This has also been shown to impact other segments in the kinetic chain confirming that landing on the rearfoot had a concomitant finding of relatively higher ankle stiffness when compared to forefoot landings (Laughton, McClay Davis & Hamill, 2003).

Both the ankle and knee joint have been shown to vary their contribution to force dissipation 20 with findings that the ankle had a significant contribution during single-leg, drop landings from a 35 cm step (Coventry et al., 2006; Yeow, Lee & Goh, 2011). In contrast, landing from a 60 cm step resulted in the knee joint being a greater contributor to force dissipation (Yeow et al., 2011). Consistent results have also been reported in studies investigating double leg drop landings, concluding the knee goes through greater range of motion to contribute to force attenuation at landing, compared to the ankle (DeVita et al., 1992; Zhang et al., 2000).

The knee and ankle joints interact during force absorption, however, the contribution to force attenuation at each joint is dependent on a number of factors including the type and effort of the task which both reflect the force or energy that needs to be absorbed. The change in knee and ankle interaction is demonstrated by the changes in movement patterns observe during different gait velocities (de David, Carpes & Stefanyshyn, 2015), cadences of hopping

(Hobara, Inoue, Muraoka, Omuro, Sakamoto & Kanosue, 2010), foot strike patterns

(Arampatzis, Bruggemann & Metzler, 1999) and landings from jumping from different heights (Butler et al., 2003). Comparing the change in knee and ankle kinematics and kinetics is problematic when studies have investigated distinctly different tasks, varying in the translational and rotational forces about the axes of rotation. Further, each of these tasks has differences in how the centre of mass is displaced, including the direction and force by which it is displaced. To more accurately describe the changes at the knee and ankle joints in response to different amounts of force absorption, it would be necessary to constrain the type of activity to ensure that comparisons can be made between groups, as well as between different efforts of a similar activity. 21

2.7 The knee and ankle joint interaction

Knee and ankle function are inherently synergistic to allow the transfer of force along the kinetic chain of the lower limb (João et al., 2014). This synergistic interaction allows energy produced by the knee musculature to accommodate the ground reaction force transmitted through the joints (João et al., 2014). It has been demonstrated that the knee and ankle joints adapt concomitantly with changes in task demand (Zang et al., 2000) and in response to deficits at one joint (Farrokhi, O’Connell, Gil, Sparto & Fitzgerald, 2015; Mikkelsen, Jarvis &

Kulig, 2018; Wikstrom et al., 2006; Willy et al., 2017). The use of a stiff heeled shoe during sauté jumps performed by elite dancers led to the foot being placed in greater plantarflexion and decreased the ankle moment, thereby reducing the ability of the ankle joint to contribute to the jumping task (Mikkelsen et al., 2018). Concomitantly, there was a finding of greater work done at the knee joint (Mikkelsen et al., 2018). Similarly, a compensatory increase in knee joint loading and mechanical work done was observed during running and hopping after

Achilles tendon repair compared to the contralateral and uninjured limb, highlighting the potential for an increase in peak patellofemoral stress (Willy et al., 2017). An inverse relationship has been reported in people with knee pathology when people with an ACL reconstruction were observed to land with greater knee extension and plantarflexion (Farrokhi et al., 2015; Wikstrom et al., 2006). It is evident that pathology can influence the knee and ankle interaction, however, this has not been examined in people with PFPS.

It is possible that altering the interaction between the knee and ankle joints may be a protective strategy to avoid loads and positions that may aggravate or mimic a position of injury or reflect the incomplete recovery of strength and control (Wikstrom et al., 2006). In a recalcitrant condition such as a PFPS, which is not commonly due to a single or serious 22 trauma, a compensatory strategy may evolve due to habituation to a combination of both pain avoidance and/or the development of physical impairments with longstanding symptoms. This was exemplified by the finding of a reduced contribution of the ankle plantarflexors to the moment around the ankle during stance phase in people with knee OA with self-reported instability (Farrokhi et al., 2015). This caused individuals to adopt a more flexed position during the stance phase of gait as part of the lower limb compensation (Farrokhi et al., 2015) and demonstrates that adaptations in the knee and ankle joints may not always lead to an optimal movement strategy and in fact be an example of a functional impairment.

The interaction of the knee and ankle joints may change with the presence of pain or disease.

Although it has been demonstrated that there are changes in the joint function in people with

PFPS (Collins, Hart, Garrick, Schache, Vicenzino & Crossley, 2014), it has not been determined whether there is a change in the ability of the lower limb to absorb force at loading during a repetitive task at different forces. It is possible that there is a relative overload or underload at the knee joint with a relative inverse change at the ankle joint.

Step downs, lateral hops, forward hops, drop jump and land, running and cutting have been investigated in people with PFPS (Ferreira, Barton, Delgado, Rabelo, Politti & Lucareli,

2018; Harrison, Ford, Myer & Hewett, 2011; Silva, Politti, Novello, Ferreira, Rabelo, Akalan

& Lucareli, 2017) in attempts to demonstrate functional impairments and compensatory movement strategies that exist within this cohort. The findings of these activities are inconclusive because of the differences between tasks and the relatively high level of variability within the performance of each task. Changes within the performance of each task, even with repeated efforts makes it difficult to identify whether changes were due to the 23 presence of pathology or the natural variability between efforts, especially in single efforts such as landing from a jump (Stergiou, 2016).

The single-leg, triple-leg hop test (SLTLHT) has been reported to be a valid tool to assess the dynamic stability of the knee and quantify the progress of individuals with PFPS during their rehabilitation (Bley et al., 2014; Dos Reis et al., 2015). There were differences in trunk and lower limb kinematics between women with and without PFPS during the SLTHLT (Dos Reis et al., 2015). Findings included decreased ankle dorsiflexion range and power and concomitant increases in knee power and decreases in knee flexion during the period of loading between the first and second hops, compared to the healthy cohort (Dos Reis et al.,

2015). These findings are important to consider in people with PFPS, however, the SLTHT is a full body motion with motion along all three axes. Therefore, it is difficult to attribute any of the observed differences between groups to changes at specific lower limb joints as these may be due to differences at any or multiple segments along the kinetic chain. Further, an individual’s performance during this task may be highly variable as it is not a continuous or rhythmic activity. Further research is required to better identify the underlying alterations in the ankle and knee joint interaction in people with PFPS which reflect the change in effort and allow comparison between people with and without PFPS.

2.8 Repeated single-leg hopping

Single leg hopping is a movement characterised by repeated vertical bounding on a single-leg

(Beerse & Wu, 2017) and limits the movement primarily to the ankle, knee and hip because the translation of the centre of mass is primarily along the vertical axis (Lamontagne et al.,

2013). Therefore, most of the force absorbed is modulated by lower limb joints and muscles

(Lamontagne et al., 2013). Single-leg hopping is also a skill which can be manipulated using a 24 change in cadence to examine modifications in movement strategies. The preferred or self- selected cadence for hopping in humans approximates to 132 hops.min-1 (2.2 Hertz) (Waxman et al., 2018). Hopping at a cadence higher or lower than this preferred frequency will force the joints to modulate their function as they need to adapt to the demand of having to translate the centre of mass either higher or lower (Lamontagne et al., 2013; Waxman et al., 2018). As well as being easy to perform, hopping can be used as a clinical test, replicating the forces and muscle actions used during sporting activity (Wikstrom et al., 2006). An evaluation of on-the- spot, single-leg hopping offers an opportunity to examine the knee and ankle joint interaction during repeated and rapid loading, with minimal compensation at other segments.

Single-leg hopping has been used as a methodology to identify kinematic differences in healthy adults and children (Beerse et al., 2017; Padua, Arnold, Perrin, Gansneder, Carcia &

Granata, 2006), however, single-leg hopping has not yet been used to examine changes in movement strategy in people with PFPS. The purpose of this study was to evaluate the interaction of the knee and ankle joints in individuals with PFPS compared to healthy individuals during a repeated, single leg hopping task.

CHAPTER THREE Methods

3.1 Study design

This was an observational, cross-sectional study which included participants with and without

PFPS. Sample size calculations were performed and determined that a total sample of 12 participants were required. To determine this sample size, power was calculated a priori

(G*Power) (Faul, Erdfelder, Buchner & Lang, 2009; Mudie, Gupta, Green & Clothier, 2016).

A partial eta square of 0.168 determined an effect size (f) of 0.45. The effect size was an input parameter in the model for power calculation, along with an alpha of 0.05, power (1-β) of

0.95 and a 0.5 measurement correlation amongst groups, with an epsilon non-sphericity correction of 1 (Mudie et al., 2016).

3.2 Ethical considerations

Ethical approval was granted by the Western Sydney University Human Research Ethics

Committee (Human Research Ethics Committee (HREC) Number: H12994) (Appendix A).

The ethical principles of integrity, justice, respect and beneficence were acknowledged

(National Health and Medical Research Council, 2007). Each participant provided written and informed consent prior to participating in the experimental protocol (Appendix B).

Participants were free to cease participation in the study at their discretion and without reason or consequence.

3.3 Participant recruitment

The primary researcher conducted site visits and liaised with managerial staff to generate involvement of local physiotherapy clinics, medical centres and sporting clubs in study advertising. A total of seven physiotherapy clinics, one medical centre and two sporting clubs agreed to advertise the study’s recruitment poster (Appendix C) at their premise or on their online domains. Physiotherapists were provided with an information session by the primary researcher to discuss the study aims and answer any potential questions about the study.

Participating physiotherapists were also able to refer potential recruits to the study.

The study’s recruitment poster and supporting information were also advertised at the

Campbelltown Campus of Western Sydney University (WSU). Physical posters were placed at various sites on campus and online announcements via the university e-platform were circulated to students.

Interested volunteer participants were able to contact the primary investigator via telephone or email. Once contacted by a volunteer participant, the primary investigator provided the participant with an information sheet, which further explained the aims and methods of the study (Appendix D). The primary researcher also conducted initial screening of the recruit based on the inclusion and exclusion criteria and answered any questions from potential recruits.

3.4 Inclusion and exclusion criteria

A matching, sampling strategy was used to compare participants with PFPS to a healthy control participant. Participants were matched based on their sex, age, height, body mass and 27 limb dominance. Limb dominance was self-reported by participants as the side on which they would prefer to kick a ball with (Waxman et al., 2018).

A total of 20 participants were included in the study, including 16 female and 4 male participants. All included participants were between 18 and 40 years of age. These age parameters were guided by the need to reduce the likelihood of participants having comorbidities such as osteoarthritis of their knee (Wallace et al., 2017).

Volunteer recruits with PFPS were included if they reported two or more aggravating activities such as ascending or descending stairs, rising from a chair, squatting, kneeling, walking, running and/or jumping, consistent with current guidelines and previous research conducted on PFPS (Crossley et al., 2016; Dos Reis et al., 2015; Thomeé et al., 1999; Willy et al., 2019). A participants report of pain had to have started insidiously with no known traumatic incident, be experienced at the anterior aspect of the knee and present for at least three months prior to testing (Bley et al., 2014; Thomeé et al, 1999; Wilson et al., 2007).

The report of the presenting history and score on the Anterior Knee Pain Scale (AKPS)

(Appendix E) confirmed an individual’s diagnosis of PFPS. The AKPS is a multiple-choice questionnaire which evaluates both the functional limitations and severity of symptoms of individuals (Kujala, Jaakkola, Koskinen, Taimela, Hurme & Nelimarkka, 1993). The questionnaire is scored out of 100 with lower scores indicating severe pain and impairments, while normal knee function was reflective of a score of 100 (Santos et al., 2019). The AKPS has been identified as a valid and reliable assessment tool for individuals with PFPS

(Ittenbach, Huang, Barber Foss, Hewett & Myer, 2016; Myer, Barber Foss, Gupta, Hewett &

Ittenbach, 2016; Papadopoulos, Thom, Noyes, Jones & Stasinopoulos, 2013). 28

The Visual Analogue Scale (VAS) (Appendix F) was a tool used to determine the likelihood of exacerbating a participant’s symptoms during testing. The VAS was a 100 mm horizontal line, with word anchors at each end including ‘no pain’ on the left and ‘worst pain imaginable’ on the right. The scale was also numbered from 0 to 10, with pictorial descriptors placed at each end reflective of pain expression (Coté, Lerman & Todres, 2009). All participants rated their resting pain and their pain experienced during a series of functional tests, including squats and step ups, using the VAS. Following instruction by the primary researcher, participants performed three squats to 90 degrees of knee flexion and three step ups on a 12 cm high step, leading with the limb for which the participant reported PFPS symptoms. The performance of functional tests was included in this protocol to further enhance the diagnostic accuracy. As there is no definitive clinical test to diagnose PFPS, a squatting manoeuvre has been proposed as the best available test to reproduce anterior knee pain, with positive results elicited in 80% of people (Crossley et al., 2016).

Volunteer recruits without PFPS did not report a history of anterior knee pain nor pain during functional testing. All potential volunteer recruits were excluded if they reported having sustained a previous injury to the knee or other musculoskeletal injury to the lower limb, including ankle injuries and lower limb fractures. Potential recruits were also excluded if they were systemically unwell, reported pregnancy, were not proficient in English or had contraindications identified on pre-screening health questionnaires (Appendix G).

3.5 Laboratory set up and instrumentation

Experimental testing was conducted in the Human Movement Laboratory (HML) at

Campbelltown Campus of Western Sydney University (WSU). Each participant completed one testing session of approximately two hours duration. 29

Kinetic (Advanced Mechanical Technology, Inc. (AMTI) Multicomponent force plate, Gen 5

BP400600-1000, Watertown, MA) and kinematic (Optotrak Certus System, Northern Digital

Inc. (NDI), Waterloo, Canada) data were collected synchronously at a frequency of 1500 Hz and 150 Hz, respectively using First Principles software (Version 1.2.4).

Kinetic data from an embedded 600 x 400 mm multicomponent force plate, were collected via a multiplexor board. The multiplexor board then transported analogue signals to the Optotrak

Data Acquisition Unit (ODAU II). Three motion capture sensor banks (Optotrak Certus

System, Northern Digital Inc. (NDI), Waterloo, Canada) were placed equidistant around the force plate, at a distance of four meters (Figure 1), and recorded the signal emitted from active markers which represented lower limb segments and allowed the calculation of kinematic data. The motion capture sensor banks were cabled to the Optotrak system control unit (SCU).

Both kinematic and kinetic data were collected (First Principles, Version 1.2.4) on a desktop computer (Dell Desktop Computer, Dell Precision Tower 3620, Dell Australia). All data were saved and stored for processing (Visual 3D software, C-Motion, Version 4, Germantown,

MD).

Figure 1: Aerial view of the experimental set up in the Human Movement Laboratory (HML).

The capture volume of the testing space was calibrated using a sixteen-marker cubic reference emitter and a four-marker digitising probe (NDI, Optotrak, Canada) which was used to record the origin of the capture volume. A five-segment model was created to resemble the trunk and the lower limb being tested using rigid body markers and single active markers (NDI,

Optotrak, Canada). A 4-marker rigid body was used to represent the pelvis, a 3-marker rigid bodies to represent the trunk, thigh and shank (Figure 2). Single active markers were taped over the calcaneus, and head of the 1st and 5th metatarsals to represent the foot (Figure 2)

(Mudie et al., 2016).

Figure 2: Participant set up with rigid bodies and foot markers secured over the five segments.

Rigid bodies and smart markers were placed away from areas of large muscle bulk (Farris &

Sawicki, 2012) and secured using double sided tape (Stylus Double Sided Cloth Tape 48 mm x 25 m and Scotch Permanent double-sided Tape 19 mm x 7.6 mm) and Velcro strapping, to minimise movement artefact over the skin (Mudie et al., 2016). The primary researcher positioned and secured all rigid bodies and smart markers to ensure reliability and consistency of participant set-up between participants. Excess wires and cables were taped (BSN Medical

Fixomull Stretch Non-Woven Tape 5 cm x 10 m) onto the participant’s skin to reduce movement and ensure good visibility of the markers to the motion sensor banks. Participant’s comfort was checked during functional tasks and familiarisation periods, with tape and markers adjusted as needed. All rigid bodies and markers were connected to a Strober unit that was cabled to the Optotrak Systems Control Unit (SCU).

Participants stood stationary in anatomical position on the embedded force plate during digitisation. A four-point digitising probe was used to create imaginary markers over anatomical landmarks (left and right anterior superior iliac spine (ASIS), posterior superior iliac spine (PSIS) and acromioclavicular joints, medial and lateral femoral condyles, malleoli, spinous process of the C7 and T8 vertebrae, suprasternal notch and xiphoid process) to create a digital skeleton of the participant (First Principles, Version 1.2.4) (Figure 3). A five second static trial in anatomical position was recorded for each participant to allow calibration of the skeletal model (Wu et al., 2002).

Figure 3: Rigid body markers were represented by clusters of markers over each of the five segments during the static calibration trial and all other markers represented the anatomical landmarks used for digitisation.

3.6 Testing Procedure

Each participant completed five trials of repeated, on-the-spot single-leg hopping. Four efforts were completed with a digital, audible metronome (https://www.google.com/search?q

=metronome) at 132, 120, 108 and 96 hops per minute representing frequencies of 2.2, 2.0,

1.8 and 1.6 Hz, respectively. During trials with the participant hopping in synchrony with the metronome, participants were instructed to land on the audible tone which was set at the specific frequency of hopping. A range of frequencies were included for analysis to demonstrate changes in performance when an individual’s system is challenged by modulation of speed and hopping height, including 2.2 Hz which has been identified as the preferred frequency of hopping in humans (Waxman et al., 2018). The fifth trial was a maximal effort and completed without the audible metronome. During the maximal effort, participants were instructed to repeatedly hop in succession as high as possible. 34

During all trials, participants were instructed to hop with their hands folded across their chest to reduce the contribution of arm movement during the single-leg hopping efforts (Bley et al.,

2014; Lamontagne et al., 2013) and to land on the ball of their foot, avoiding heel contact on the force plate. The contralateral limb was flexed to avoid contact with the force plate. All trials were performed barefoot to reduce the effect of force attenuation due to footwear (Dos

Reis et al., 2015).

Prior to the performance of each trial, familiarisation efforts were performed. This ensured the participant was able to hop in synchrony with the metronome and subsequently able to hop as high as possible during the maximal effort without any risk of fatigue. The primary investigator provided feedback to ensure the participant maintained their position the middle of the force plate and landed in time with the tone of the metronome. The order of trials with a metronome was randomised by the primary researcher and the maximal effort was always performed as the last trial. Each trial was performed to a maximum of 20 hops and a two- minute rest period was provided between trials to reduce the effects of fatigue (Dos Reis et al., 2015; Mudie et al., 2016).

3.7 Data Processing

Each recorded trial was converted to C3D file format (First Principles, version 1.2.4) and exported for processing (Visual 3D, C-Motion, Version 4, Germantown, MD).

Force plate data were filtered using a fourth order zero-lag bidirectional low-pass Butterworth filter with a 50 Hz cut off frequency (Bobbert & Richard Casius, 2011; Mudie et al., 2016).

Interpolation for missing marker signals was performed using a spline filter with a fourth order, bidirectional, low-pass Butterworth filter with an 8 Hz cut-off frequency (Bobbert et al., 2011; Hobara, Inoue, Omura, Muraoka & Kanouse, 2011; Hobara, Kimura, Omuro, Gomi, 35

Muraoka, Iso & Kanosuei, 2008). If a gap of more than 100 missing data points was identified during interpolation, the hop cycle was discarded and not used for analysis. Kinetic and kinematic data were then exported as a MATfile format (Matlab Version 2017a, Mathworks,

Massachusetts) to calculate dependent variables.

Dependent variables were calculated (Microsoft Office Excel, 2007 and MATLAB, 2012B

32-bit) as the mean of five consecutive hop cycles completed at each hopping frequency and maximal effort. A hopping cycle included the complete flight and contact phases of a hop

(Figure 4) and was defined as the duration from successive toe-off events.

ΔCOM during fight

ΔCOM during loading

Contact Flight Phase Phase

Hop Cycle Duration 100%

0% TO ZpeakF IC vGRFpeakC TO

vGRF

Loading Propulsive Period Period

Time (ms)

Figure 4: A visual representation of a complete hop cycle including gait events: toe-off (TO), peak of vertical displacement during flight phase (Zpeakf) initial contact (IC), peak vertical ground reaction force (vGRFpeakc). Each gait cycle was divided into the flight phase and contact phase. Each contact phase was divided into the loading period and propulsive period. 37

3.8 Dependent Variables

Gait events including toe-off (TO) and initial contact (IC) were determined from the vGRF of the force plate signal when it was ≥ 10 N for a hop cycle and peak vGRF was determined as the greatest value between IC and the subsequent TO (Visual 3D, C-Motion, Version 4,

Germantown, MD) (Mudie et al., 2016). Spatiotemporal characteristics included durations of: the hop cycle, flight phase, contact phase, loading period and propulsive period (Figure 4)

(Matlab Version 2017a, Mathworks, Massachusetts). Spatiotemporal characteristics were expressed in milliseconds (ms).

Kinematic variables included angular displacement (ɵ) of the knee and ankle joints during the loading period. Angular displacement (degrees) was the difference in angle at peak vGRF and angle at IC (Equation 1).

ɵ = 푗표푖푛푡 푎푛푔푙푒 푎푡 푝푒푎푘 푣퐺푅퐹 − 푗표푖푛푡 푎푛푔푙푒 푎푡 푖푛푖푡푖푎푙 푐표푛푡푎푐푡 (퐼퐶) (Equation 1)

Inverse dynamics were performed using kinematic and ground reaction force data to determine joint moment (Visual 3D, C-Motion, Version 4, Germantown, MD) (Winter, 2009).

Joint moments were normalised to body mass for each participant (Waxman et al., 2018) and subsequently, kinetic data including moment, power and work at the knee and ankle joints were calculated for the loading period (Visual 3D, C-Motion, Version 4, Germantown, MD).

Vertical stiffness (k) refers to the body being modelled on a massless spring and the associated deformation of the spring when reacting to the vGRF during loading (Beerse et al.,

2017; Brughelli et al., 2008). Vertical stiffness was defined as the ratio of the change in vGRF during the loading period (from IC to peak vGRF) to the displacement of the centre of mass 38 during (COM) during loading period (Equation 2) (Hobara, Hashizume, Funken, Willwacher,

Müller, Grabowski & Potthast, 2019). Vertical stiffness was normalised to body weight by dividing the change in vGRF (N) over the loading period by each participant’s body mass

(kg) during calculations and expressed in newtons per kilogram per meter (N∙kg-1∙m-1).

푃푒푎푘 푣퐺푅퐹 푘 = (Equation 2) ΔCOML

The change in knee flexion and ankle dorsiflexion moments (M) during the loading period, were normalised to body mass and calculated as the difference in moment at peak vGRF and

IC. Moment was expressed in newton meters per kg (N·m.kg-1) (Equation 3).

푀 = 푗표푖푛푡 푚표푚푒푛푡 푎푡 푝푒푎푘 푣퐺푅퐹 − 푗표푖푛푡 푚표푚푒푛푡 푎푡 퐼퐶 (Equation 3)

Normalised knee (kknee) and ankle (kankle) joint stiffness (k) was expressed in Newton meters per kilogram per radian (Nm.kg-1.rad-1) and calculated by dividing the normalised joint moment (M) by the joint angular displacement (ɵ) in radians (Equation 4).

푀 푘 = (Equation 4) ɵ

Normalised Angular Power (P) of the knee and ankle joints were expressed as Joules per kg per second (J.kg-1.s-1) and was calculated by multiplying the normalised joint moment (M) by the joint angular displacement in radians and divided by the loading duration (s) (Equation 5).

푀 푥 ɵ 푃 = (Equation 5) 푙표푎푑푖푛푔 푑푢푟푎푡푖표푛 39

Normalised Angular Work (W) of the knee and ankle joints was expressed in Joules per kg radians (J.kg-1.rad) and calculated by multiplying the normalised joint moment (M) by the joint angular displacement (ɵ) in radians (Equation 6).

푊 = 푀 푥 ɵ (Equation 6)

The coefficient of variation (CV) was determined for each kinematic and kinetic variable and calculated as the quotient of the standard deviation and mean, multiplied by 100 to yield a percentage score (Equation 7).

푠푡푎푛푑푎푟푑 푑푒푣푖푎푡푖표푛 퐶푉 = ( ) 푥 100 (Equation 7) 푚푒푎푛

3.9 Statistical Analyses

Independent T-tests were performed to determine baseline differences in age (years), height

(cm), body mass (kg) and BMI between participants with PFPS and matched, healthy participants. Statistical significance was accepted at p < 0.05.

A 2-factor repeated measures Analysis of Variance (ANOVA) with between (2 levels –with and without PFPS) and within (5 levels – 132, 120, 108, 96 hops per minute and maximal effort) group factors were performed to determine differences in the dependent variables.

Statistical significance was accepted at p < 0.05 and Bonferroni correction was performed to reduce the risk of type 1 error. Mauchly’s test of sphericity was performed and if significant, a

Greenhouse-Geisser correction procedure was implemented (Mudie, 2017).

If there was a statistically significant difference for a main effect, post hoc independent t-tests were performed to determine the differences at each level for each main effect, with statistical significance accepted at p < 0.01 with Bonferroni adjustment for multiple analyses.

If statistically significant within group differences were observed, post hoc 1-way ANOVA were performed for both the PFPS and healthy participant groups to determine at which cadence within each group there were statistically significant differences for dependant variables when compared to the reference standard of 132 hops.min-1. Statistical significance was accepted at p < 0.01 and with Bonferroni adjustment for multiple analyses.

CHAPTER FOUR Results

4.1 Participant profile

Six participants with PFPS reported symptoms on their dominant limb (right leg) and four participants reported symptoms on their non-dominant limb (left leg). Six pairs of participants therefore had testing performed on their dominant limb and four pairs had testing on their non-dominant limb. Participants with PFPS reported symptoms for (mean (SD)) 30.44 (28.56) months prior to testing. There were no statistically significant differences between groups for age, height, body mass or BMI (Table 1), reflecting the matched sampling of recruits.

Participants with PFPS had a lower score on the AKPS and a report of pain during physical tests (Table 2).

Table 1: Anthropomorphic characteristics (mean (SD)) for people with patellofemoral pain syndrome (PFPS) and the matched, healthy control participants.

PFPS Healthy t-value p-value Age (years) 25.3 (6.1) 25.1 (5.3) 0.08 0.94 Height (cm) 167.2 (9.1) 167.1 (9.8) 0.02 0.98 Body Mass (kgs) 69.7 (13.5) 64.3 (10.0) 1.02 0.32 BMI 25.2 (6.3) 23.1 (2.7) 1.00 0.34

Table 2: Pain during rest, functional tasks and scores of the Anterior Knee pain Scale (AKPS) (mean (SD)) for participants with patellofemoral pain syndrome (PFPS) and the healthy, matched participants.

PFPS Healthy VAS at present (/10) 2.6 (1.5) 0 (0) VAS during squats (/10) 2.4 (1.5) 0 (0) VAS during step ups (/10) 1.8 (1.4) 0 (0) AKPS (/100) 78 (8.5) 100 (0)

4.2 Spatiotemporal characteristics of the hop cycle

There were no statistically significant between group differences for the duration of the cycle

(F (1, 18) = 1.03, p = 0.32, 1-β = 0.16), contact phase (F (1,18) = 0.05, p = 0.83, 1-β = 0.06), loading period (F (1,18) = 1.91, p = 0.18, 1-β = 0.26), propulsive period (F (1,18) = 1.10, p =

0.31, 1-β = 0.17) or flight phase (F (1,18) = 1.78, p = 0.20, 1-β = 0.24) (Appendix H: Figures 9-

13 and tables 16 - 25).

There was statistically significantly greater cycle duration time (ms), compared to 132 hops.min-1, for participants with PFPS at 120 hops.min-1 (mean difference = - 50, standard error = 10, p = < 0.01, CI - 90 to - 20) and maximal efforts (mean difference = - 16, standard error = 30, p = < 0.01, CI - 25 to - 7) and for healthy participants at 108 hops.min-1 (mean difference = - 80, standard error = 10, p = < 0.01, CI - 13 to - 3), 96 hops.min-1 (mean difference = - 14, standard error = 20, p = < 0.01, CI - 22 to - 6) and maximal efforts (mean difference = - 19, standard error = 20, p = < 0.01, CI - 25 to - 13) (Table 3).

There was statistically significant greater duration (ms) for the contact phase for participants with PFPS at 120 hops.min-1 (mean difference = 40, standard error = 20, p = < 0.01, CI - 60 to

- 10) and 96 hops.min-1 (mean difference = -100, standard error = 20, p = < 0.01, CI - 170 to - 43

10) and for healthy participants at 96 hops.min-1 (mean difference = 100, standard error = 20,

p = < 0.01, CI – 160 to - 50) (Table 3).

There was statistically significant greater propulsion duration (ms) for healthy participants at

96 hops.min-1 (mean difference = - 90, standard error = 20, p = < 0.01, CI - 150 to - 30)

compared to the reference standard of 132 hops.min-1 (Table 3). There was statistically

significant greater duration of the flight phase during maximal efforts for both participants

with PFPS (mean difference = - 90, standard error = 10, p = < 0.01, CI - 130 to - 50) and

healthy participants (mean difference = - 120, standard error = 10, p = < 0.01, CI - 150 to -

80) (Table 3). There were no statistically significant differences during pairwise comparisons

for either cohort during the loading period (Table 3).

Table 3: Duration (ms) (mean (SD)) of hopping cycle, flight and contact phases, loading and propulsive periods for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1. Hopping Cadence (hops.min-1) Duration Group 132 120 108 96 Max Hop cycle PFPS 454 (44) 505 (38) * 528 (48) 581 (66) 615 (79) * Healthy 461 (31) 497 (15) 541 (17) * 600 (56) * 648 (52) Contact Phase PFPS 311 (56) 347 (59) * 352 (44) 413 (70) * 384 (66) Healthy 311 (27) 335 (21) 350 (68) 413 (41) * 383 (50) Loading Period PFPS 140 (28) 148 (23) 158 (34) 154 (43) 120 (38) Healthy 145 (21) 154 (14) 180 (24) 158 (34) 144 (28) Propulsive Period PFPS 171 (32) 200 (44) 201 (22) 261 (66) 265 (66) Healthy 166 (9) 181 (11) 189 (18) 255 (52) * 239 (60) Flight Phase PFPS 158 (29) 158 (35) 168 (41) 168 (41) 234 (46) * Healthy 150 (22) 162 (26) 173 (33) 204 (35) 266 (26) * 44

4.3 Kinematic variables during the loading period.

There were no statistically significant differences between groups for knee flexion (F (1,18) =

2.94, p = 0.10, 1-β = 0.37) or ankle dorsiflexion excursion (F (1,18) = 2.96, p = 0.10, 1-β =

0.37) during the loading period (Figure 5).

55 PFPS - Ankle Dorsiflexion Healthy - Ankle Dorsiflexion * 50 PFPS - Knee Flexion 45 Healthy - Knee Flexion 40

30 * 25

Joint Excursion during Loading Phase (degrees) Phase Loading during Excursion Joint 0 132 120 108 96 Max

-1 Cadence (Hops.min )

Figure 5: Ankle dorsiflexion and knee flexion excursion (degrees) (mean) during the loading period for people with patellofemoral pain syndrome (PFPS) and healthy matched control participants, with statistically significantly greater ankle excursion at maximal effort in the healthy participants and greater knee excursion at 108 hops.min-1 in participants with PFPS, compared to hopping at 132 hops.min-1 during the loading period (* p < 0.01 for within group comparisons). 45

There were statistically significant within group differences for knee flexion (F (2.64, 47.51) =

14.74, p= < 0.001, 1-β = 1.00) and ankle dorsiflexion (F (2.87, 51.67) = 28.92, p= < 0.001, 1-β =

1.00) excursion during cadence comparisons (Appendix I). Pairwise comparisons determined that knee flexion excursion was greater when hopping at 108 hops.min-1 (mean difference = -

8.70, standard error = 1.39, p = < 0.001, CI = - 13.85 to - 3.56) compared to 132 hops.min-1 for participants with PFPS (Table 4 and Appendix I: Figure 14 and tables 26 and 27).

Pairwise comparisons determined there was greater ankle dorsiflexion excursion when hopping at maximal efforts (mean difference = - 16.06, standard error = 2.15, p = < 0.01, CI =

- 23.99 to - 8.13) compared to 132 hops.min-1 for healthy participants (Table 4 and Appendix

I: Figure 15 and tables 28 and 29).

Table 4: Knee and ankle joint excursion (degrees) (mean (SD)) for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Hopping Cadence (hops.min-1) Joint excursion Group 132 120 108 96 Max Ankle Dorsiflexion PFPS 30 (6) 34 (7) 36 (8) 38 (10) 42 (13) Healthy 34 (5) 37 (5) 41 (7) 45 (7) 50 (6) * Knee Flexion PFPS 17 (6) 22 (7) 25 (8) * 24 (9) 22 (9) Healthy 20 (6) 24 (4) 30 (6) 30 (8) 29 (8)

There were no statistically significant between group differences for the CV of knee (F (1,17) =

2.70, p = 0.12, 1-β = 0.34) and ankle excursion (F (1,17) = 0.15, p = 0.71, 1-β = 0.07) during the loading period (Table 5 and Appendix K: Figures 25 and 26). There were statistically significant within group differences for the CV for knee flexion during the loading period (F

(4, 68) = 2.75, p = 0.04, 1-β = 0.73) (Appendix K: Figure 25 and tables 40 and 41), however, no within group differences were observed for the CV for ankle excursion during the loading 46

period (F (4, 68) = 0.41, p = 0.80, 1-β = 0.14) (Appendix K: Figure 26). There was a trend for greater CV for knee flexion for participants with PFPS at 108 hops.min-1 compared to 132 hops.min-1, however, this did not reach statistical significance (mean difference = 10.59, standard error = 3.90, p = 0.03, CI = 1.59 to 19.59).

Table 5: Coefficient of variation (CV) (%) (mean (SD)) for ankle and knee joint excursion during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Hopping Cadence (hops.min-1) CV Group 132 120 108 96 Max Ankle dorsiflexion PFPS 13 (12) 8 (4) 9 (6) 8 (6) 10 (9) Healthy 8 (3) 9 (3) 10 (4) 11 (8) 7 (5) Knee flexion PFPS 26 (14) 18 (8) 15 (5) 22 (17) 24 (12) Healthy 17 (7) 16 (10) 12 (5) 17 (11) 22 (10)

4.4 Kinetic variables during the loading period

4.4.1 Knee flexion and ankle dorsiflexion moment

There were no statistically significant between group differences for knee flexion moment (F

(1,18) = 0.01, p = 0.91, 1-β = 0.05) and ankle dorsiflexion moment (F (1,18) = 0.01, p = 0.93, 1-β

= 0.05) during the loading period (Table 12). There were no statistically significant within group differences for knee moment (F (4, 72) = 1.54, p = 0.20, 1-β = 0.45) or ankle moment (F

(2.86, 51.51) = 1.22, p = 0.31, 1-β = 0.30) (Appendix J: figures 16 and 17).

Table 6: Ankle and knee joint moment (N·m.kg-1) (mean (SD)) during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Joint Hopping Cadence (hops.min-1) moment Group 132 120 108 96 Max Ankle PFPS 4.5 (2.1) 6.7 (3.0) 5.2 (2.6) 4.8 (2.4) 5.9 (3.1) Healthy 5.7 (2.2) 5.4 (2.5) 4.8 (1.9) 5.2 (2.1) 5.7 (1.8) Knee PFPS 5.6 (3.6) 3.6 (1.1) 3.8 (2.1) 4.9 (2.5) 5.2 (2.3) Healthy 3.9 (1.9) 4.3 (1.9) 4.9 (2.7) 4.8 (2.7) 5.6 (2.9)

There were no statistically significant between group differences for the CV of knee joint moment (F (1, 17) = 2.16, p = 0.16, 1-β = 0.28) or ankle joint moment (F (1,17) = 0.28, p = 0.60,

1-β = 0.08) (Appendix L: Figures 27 and 28). There were no statistically significant within group differences for the CV of knee joint moment (F (2.23-37.98) = 0.24, p = 0.81, 1-β = 0.09) or ankle joint moment (F (2.36, 40.07) = 0.34, p = 0.75, 1-β = 0.11) (Table 7 and Appendix L: figures 27 and 28).

Table 7: Coefficient of variation (CV) (%) (mean (SD)) of ankle and knee joint moment during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Hopping Cadence (hops.min-1) CV Group 132 120 108 96 Max Ankle PFPS 42.1 (13.0) 57.4 (39.8) 50.2 (19.6) 51.8 (25.3) 47.4 (22.2) moment Healthy 46.2 (23.7) 47.1 (24.1) 46.1 (20.6) 48.7 (24.0) 46.3 (16.6) Knee PFPS 60.4 (59.3) 55.4 (23.4) 72.8 (67.1) 59.0 (37.4) 49.9 (23.9) moment Healthy 47.3 (15.1) 51.8 (12.2) 48.2 (13.2) 40.4 (21.6) 59.9 (25.6)

4.4.2 Vertical stiffness

There were no statistically significant between groups differences for vertical stiffness (F (1, 18)

= 1.25, p = 0.28, 1-β = 0.19) during the loading period (Table 6). There were statistically significant within group differences for vertical stiffness (F (2.40, 43.11) = 17.25, p = < 0.01, 1-β

= 1.00) (Appendix J: Figure 18). Pairwise comparisons determined that there was lower vertical stiffness in the healthy participants when hopping at 108 (mean difference = 0.06, standard error = 0.01, p = < 0.01, CI = 0.03 to 0.10) and 96 hops.min-1 (mean difference =

0.07, standard error = 0.01, p = < 0.01, CI = 0.03 to 0.11) compared to 132 hops.min-1

(Appendix J: Tables 30 and 31).

Table 8: Vertical stiffness (N∙kg-1∙m-1) during the loading period (mean (SD)) for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Hopping Cadence (hops.min-1) Group 132 120 108 96 Max PFPS 0.22 (0.07) 0.18 (0.04) 0.17 (0.05) 0.15 (0.03) 0.18 (0.04) Healthy 0.21 (0.03) 0.18 (0.02) 0.14 (0.01) * 0.14 (0.01) * 0.14 (0.03)

There were no statistically significant between groups differences for the CV of vertical stiffness (F (1, 18) = 0.70, p = 0.41, 1-β = 0.13) during the loading period (Table 7). There were statistically significant within group differences for the CV of vertical stiffness (F (2.37, 42.61) =

9.73, p = < 0.01, 1-β = 0.99) (Appendix L: Figure 29). There was a trend for greater variability in vertical stiffness during loading amongst the healthy cohort at 96 hops.min-1 during pairwise comparisons, however, the differences were not statistically significant (mean difference = - 5.16, standard error = 1.16, p = 0.02, CI = - 9.45 to - 0.87) (Appendix L: Tables

42 and 43). 49

Table 9: Coefficient of variation (CV) (%) (mean (SD)) of vertical stiffness during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Hopping Cadence (hops.min-1) Group 132 120 108 96 Max PFPS 8.71 (5.48) 7.63 (3.41) 9.78 (4.65) 11.76 (7.13) 17.10 (12.41) Healthy 6.52 (2.75) 6.22 (2.45) 8.57 (3.70) 11.68 (4.46) 15.05 (6.95)

4.4.3 Knee and ankle joint stiffness

There were no statistically significant between groups differences for knee joint stiffness (F

(1,18) = 2.83, p = 0.11, 1-β = 0.36) or ankle joint stiffness (F (1,18) = 1.17, p = 0.29, 1-β = 0.18) during the loading period (Figure 7 and Appendix J: Figure 19 and 20). There were no statistically significant within group differences for knee joint stiffness (F (1.40, 25.20) = 2.94, p =

0.09, 1-β = 0.44) or ankle joint stiffness (F (2.17, 39.06) = 1.74, p = 0.19, 1-β = 0.36) (Table 8 and

Appendix J: Figure 19 and 20).

Table 10: Ankle and knee joint stiffness (Nm.kg-1.rad-1) (mean (SD)) during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Joint Hopping Cadence (hops.min-1) stiffness Group 132 120 108 96 Max Ankle PFPS 8.7 (3.5) 11.8 (5.9) 8.6 (4.4) 8.0 (4.5) 10.3 (9.9) Healthy 10.3 (4.5) 8.6 (3.9) 6.9 (3.1) 6.6 (3.2) 6.7 (2.7) Knee PFPS 27.4 (31.9) 10.1 (4.3) 9.5 (6.9) 12.8 (6.0) 15.2 (6.2) Healthy 11.4 (2.7) 10.1 (3.9) 9.4 (5.1) 9.5 (4.8) 11.6 (6.0)

) 30

- .rad

1 PFPS - Ankle Dorsiflexion - 25 Healthy - Ankle Dorsiflexion

Nm.kg PFPS - Knee Flexion

20 Healthy - Knee Flexion

Joint Stiffness during the Loading Phase ( PhaseLoadingthe during StiffnessJoint 0 132 120 108 96 Max Cadence (Hops.min-1)

Figure 6: Ankle and knee joint stiffness (Nm.kg) (mean) during the loading period for people with patellofemoral pain syndrome and the matched, healthy participants. Greater knee joint stiffness was observed at 132 hops.min-1 in participants with PFPS, however, there were no statistically significant between and within group differences (p > 0.01).

There were no statistically significant between groups differences for the CV of knee joint stiffness (F (1, 17) = 1.67, p = 0.21, 1-β = 0.23) or ankle joint stiffness (F (1,17) = 0.01, p = 0.92,

1-β = 0.05) (Table 9). There was a trend for greater CV of knee joint stiffness in participants with PFPS at 108 hops.min-1 when compared to matched, healthy participants (Figure 8).

There were no within group differences for the CV of knee joint stiffness (F (1.53, 26.05) = 0.42, 51

p = 0.61, 1-β = 0.10) and ankle joint stiffness (F (2.53, 42.96) = 0.63, p = 0.57, 1-β = 0.16) during the loading period (Appendix L: Figures 30 and 31).

Table 11: Coefficient of variation (CV) (%) of knee and ankle joint stiffness during loading (mean (SD)) for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Hopping Cadence (hops.min-1) CV Group 132 120 108 96 Max Ankle PFPS 46.1 (13.3) 57.7 (40.7) 55.4 (21.3) 52.1 (23.6) 45.9 (21.0) Stiffness Healthy 48.6 (25.9) 48.1 (23.7) 45.1 (24.2) 66.6 (60.0) 45.1 (16.7) Knee PFPS 76.9 (108.0) 57.8 (30.9) 110.7 (193.2) 57.6 (50.6) 55.4 (21.9) Stiffness Healthy 50.5 (11.6) 50.7 (10.4) 46.6 (12.2) 47.5 (28.2) 60.6 (28.3)

120 -

100 Nm.kg

)

- .rad

1 40

PFPS - Ankle Dorsiflexion 20 Healthy - Ankle Dorsiflexion PFPS - Knee Flexion Healthy - Knee Flexion 0 132 120 108 96 Max -1 Joint Stiffness during the Loading Phase ( PhaseLoadingthe during StiffnessJoint Cadence (Hops.min )

Figure 7: Coefficient of variation (CV) (%) of knee and ankle joint stiffness during the loading period for participants with patellofemoral pain syndrome and matched, healthy participants.

4.4.4 Knee and ankle mechanical work

There were no statistically significant between group differences for knee (F (1,18) = 0.98, p =

0.34, 1-β = 0.16) or ankle mechanical work (F (1,18) = 0.85, p = 0.37, 1-β = 0.14) during the loading period (Table 14). There were statistically significant within group differences for knee mechanical work (F (4, 72) = 3.34, p = < 0.01, 1-β = 0.82) and ankle mechanical work (F

(4, 72) = 4.06, p = < 0.01, 1-β = 0.90), however, pairwise comparisons did not detect any statistically significant differences (p > 0.01) in participants with PFPS or matched, healthy participants (Appendix J: Figures 21 and 22 and tables 32 - 35).

Table 12: Ankle and knee mechanical work done (J.kg-1.rad) (mean (SD)) during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Mechanical Group Hopping Cadence (hops.min-1) Work 132 120 108 96 Max Ankle PFPS 2.47 (1.30) 4.11 (1.96) 3.31 (1.69) 3.10 (1.60) 4.01 (1.70)

Healthy 3.21 (1.13) 3.51 (1.57) 3.45 (1.28) 4.11 (1.60) 4.83 (1.37)

Knee PFPS 1.61 (1.09) 1.53 (0.90) 1.85 (1.21) 2.24 (1.60) 2.18 (1.54)

Healthy 1.54 (1.23) 1.90 (1.08) 2.66 (1.65) 2.69 (1.97) 3.11 (2.36)

There were no statistically significant between group differences for the CV of knee mechanical work (F (1,18) = 0.42, p = 0.53, 1-β = 0.09) and ankle mechanical work (F (1,18) =

0.01, p = 0.94, 1-β = 0.05) (Appendix L: Figures 32 and 33). There were no statistically significant within group differences detected, using pairwise comparisons for the CV of knee mechanical work (F (4, 72) = 0.73, p = 0.57, 1-β = 0.23) or CV for ankle mechanical work (F

(2.62, 47.15) = 0.23, p = 0.85, 1-β = 0.09) during the loading period (Table 15 and Appendix L: figures 32 and 33).

Table 13: Coefficient of variation (CV) (%) (mean (SD)) of knee and ankle mechanical work during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Hopping Cadence (hop.min-1) CV Group 132 120 108 96 Max Ankle PFPS 44.98 50.44 46.13 50.40 47.78 mechanical (18.75) (23.94) (17.61) (27.63) (26.42) work Healthy 44.77 47.40 49.29 52.16 48.37 (21.34) (23.52) (17.00) (32.95) (17.31) Knee PFPS 61.40 58.30 49.57 58.29 51.04 mechanical (21.70) (15.77) (21.92) (25.94) (21.41) work Healthy 48.37 55.67 51.94 41.69 67.14 (18.48) (21.70) (14.68) (17.36) (29.41)

4.4.5 Knee and ankle joint power

There were no statistically significant between group differences for knee joint power (F (1,18)

= 0.20, p = 0.66, 1-β = 0.07) or ankle joint power (F (1,18) = 0.08, p = 0.79, 1-β = 0.06) during the loading period (Table 10). There were statistically significant within group differences for knee power (F (4, 72) = 4.55, p = < 0.001, 1-β = 0.93) and ankle power (F (2.30, 41.47) = 5.43, p =

0.01, 1-β = 0.86), however, pairwise comparisons did not detect any statistically significant differences (p > 0.01) in participants with PFPS or matched, healthy participants (Appendix J:

Figure 23 and 24 and tables 36 - 39).

Table 14: Ankle and knee joint power (J.kg-1.s-1) (mean (SD)) during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1.

Joint Hopping Cadence (hops.min-1) Power Group 132 120 108 96 Max Ankle PFPS 17.87 30.61 23.59 23.65 38.19 (9.00) (20.69) (16.36) (18.46) (26.65) Healthy 22.82 22.95 19.71 27.34 34.00 (9.76) (9.43) (8.29) (13.00) (15.27) Knee PFPS 12.24 10.88 11.76 14.60 18.09 (8.40) (6.91) (6.70) (8.71) (9.64) Healthy 10.52 12.48 15.13 15.87 20.39 (8.40) (7.15) (10.13) (8.82) (13.96)

There were no statistically significant between group findings for CV of knee power (F (1,18) =

0.49, p = 0.50, (1-β = 0.10) or ankle power (F (1,18) = 0.33, p = 0.57, 1-β = 0.08) during the loading period (Table 11). There was a trend for a difference in the CV of knee joint power in participants with PFPS compared to healthy participants at 132 hops.min-1 and at maximal efforts (Figure 9). There were no significant within group differences for CV of power at the knee (F (4,72) = 0.94, p = 0.45, 1-β = 0.28) or ankle (F (4, 72) = 0.51, p = 0.73, 1-β = 0.16) joints during the loading period (Table 11 and Appendix L: Figures 34 and 35). 56

70 65 60 55 50 45 40 35 30 25 PFPS - Ankle Dorsiflexion Loading Phase (%) PhaseLoading 20 Healthy - Ankle Dorsiflexion 15 PFPS - Knee Flexion 10 Healthy - Knee Flexion 5 Coefficient of variation of Joint Power during during ofPower ofJoint variation Coefficient 0 132 120 108 96 Max -1 Cadence (Hops.min )

Figure 8: Coefficient of variation (%) of knee and ankle joint power during the loading period for participants with patellofemoral pain syndrome and the matched, healthy participants.

Table 15: Coefficient of variation (CV) (%) (mean (SD)) of knee and ankle joint power during the loading period for participants with patellofemoral pain syndrome (PFPS) (n = 10) and the matched, healthy participants (n =10), with statistical differences (* p = < 0.01) compared to hopping at 132 hops.min-1).

Hopping Cadence (hops.min-1) CV Group 132 120 108 96 Max Ankle PFPS 44.77 (20.79) 53.82 (21.74) 51.35 (17.27) 57.92 (20.71) 47.13 (31.54) power Healthy 46.41 (22.40) 48.48 (23.29) 48.92 (19.83) 49.87 (22.73) 46.49 (17.92) Knee PFPS 62.19 (22.57) 56.62 (19.16) 48.06 (21.95) 49.35 (17.86) 53.00 (26.72) power Healthy 48.57 (17.71) 54.72 (14.49) 50.74 (14.94) 42.67 (20.88) 60.05 (27.34)

CHAPTER FIVE

5.1 Discussion

The main finding of this study was that there were no significant differences in the motor performance and mechanical characteristics during repeated on-the-spot, single-leg hopping, between people with and without PFPS. Further, the variability of the mechanical characteristics during each of the efforts was consistent between people with and without

PFPS. Variability of knee power and knee joint stiffness during loading demonstrated a trend to be greater in participants with PFPS, however, post hoc testing did not detect a statistical difference. These findings support the null hypothesis that there were no changes in movement patterns in people who were classified as having PFPS, even with a change in effort which induced a greater demand for load attenuation in the lower limb joints.

Similarities in the duration of loading, vertical stiffness and knee flexion excursion were also observed between the current study and previously published results (Waxman et al., 2018) which examined single-leg hopping at 132 hops.min-1 only, in healthy participants.

A trend observed in the current study was that participants with PFPS demonstrated greater variability of knee power and knee mechanical work compared to the matched, healthy participants when hopping at 132 hops.min-1. In comparison, the greatest variability in knee power variability and knee mechanical work for matched, healthy participants was observed at maximal efforts. It was anticipated that greater variability in kinematic and kinetic variables would be observed in both groups at maximal efforts due to the marked increase in difficulty to complete the hopping task and relative difficulty in maintaining a consistent performance when hopping in synchrony with an audible cue. However, given that this was not observed in participants with PFPS, it could be concluded that participants with PFPS had greater 58 inconsistencies in measures of power and work during the loading period when performing submaximal efforts at 132 hops.min-1, even though this cadence is the preferred hopping frequency in humans (Farley, Blickhan, Saito & Taylor, 1991; Farley & Morgenroth, 1999;

Waxman et al., 2018).

Ankle dorsiflexion excursion and the variability of vertical stiffness was greater for both

PFPS and healthy groups as the height of hopping increased from 132 hops.min-1 to maximal efforts. This finding is consistent with previous studies (Kim, João, Tan, Mota, Vleck, Aguiar

& Veloso, 2013; Waxman et al., 2018) who examined hopping in healthy participants only.

The requirement to attenuate force during loading is likely achieved via greater ankle dorsiflexion and a trend towards greater knee flexion and decreased vertical stiffness. Thus, increasing hopping height and the need to attenuate the forces during loading becomes greater and explains the findings of greater ankle dorsiflexion and variability in vertical stiffness.

The finding of statistically significantly lower vertical stiffness at 108 and 96 hops.min-1 compared to 132 hops.min-1 for healthy participants, could highlight a reduced ability to modulate vertical stiffness in people with longstanding PFPS. In contrast, healthy participants may be able to utilise multiple strategies in response to a change in the demand of the task. A similar finding was reported for people with PFPS who did not modify their movement coordination during stair descent compared to healthy individuals (Aminaka, 2010), reflected by a finding of consistently smaller knee joint excursions. Despite similar conclusions, the stair descent task may have differed to the single-leg hopping task used in the current study, because of alterations in velocity of movement, joint excursion and magnitude of force being attenuated at each of the lower limb joints, making comparison of results problematic.

Participants with PFPS have been observed to have lower knee flexion and ankle dorsiflexion excursions during loading when completing the single-leg triple hop test (SLTHT) compared to healthy participants (Dos Reis et al., 2015). It has been suggested that the lower angular excursions may be a protective strategy to avoid pain, as greater knee flexion increases patellofemoral joint loading (Dos Reis et al., 2015). However, it is also plausible that participants with PFPS have deficits of quadricep muscle strength at greater knee flexion angles, with the observation of lower knee flexion excursion potentially being an avoidance strategy during rapid loading (Powers et al., 2017). In the current study it was hypothesised that there would be no persistent changes in how the lower limb was able to absorb the vGRF during single-leg hopping, even when required to accommodate the increase in the vGRF when the height of hopping was greater. Although there was tendency for participants with

PFPS in this study to have similar movement patterns to previously published findings (Dos

Reis et al., 2015), the magnitude of change in the current study was not significant. It is plausible that the difference between the previous study (Dos Reis et al., 2015) and the current study was due to differences in the type of task performed, the sample population and the experience of pain.

This is the first study that has examined mechanical characteristics of people with PFPS during repeated single-leg hopping. On-the-spot, single leg hopping, although not a movement typically used in sporting activities, does allow mechanical characteristics to be examined under similar loads experienced during running (Kluitenberg, Bredeweg, Zijlstra,

Zijlstra & Buist, 2012) and jumping (Mcnair & Prapavessis, 1999), while being able to control vertical displacement. Further, the repetitive task was primarily dependent on motion at lower limb joints in a multi-segmented limb, allowing the examination of knee and ankle interaction. Symptom reproduction in people with PFPS have typically been reported during 60 loading of the patellofemoral joint in a flexed position (Willy et al., 2019), therefore supporting the use of the hopping as a task in the current study. The similar mechanical findings between groups in the current study, however, may be due to the lack of report of pain during testing with all participants able to complete all trials without pain reproduction.

It is possible, that even hopping to maximal heights, was not enough to induce symptoms and differences in mechanical characteristics between groups. It has been suggested that a VAS score of 6 out of 10 or more needs to be experienced by participants for there to be changes in knee and ankle joint kinetics when tested using saline injections to induce acute pain

(Schache, Crossley & Wrigley, 2005). In addition, it has been reported that a higher intensity of pain results in changes to knee and ankle joint kinetics, with no changes to kinematics

(Schache et al., 2005) when assessed during walking.

The findings of the current and previous studies may suggest that pain experienced by people classified as having PFPS needs a greater focus on treating the neurophysiological processes associated with pain such as central sensitisation and hypersensitivity (Noehren, Shuping,

Jones, Akers, Bush & Sluka, 2016; Pelletier, Higgins & Bourbonnais, 2015) and psychosocial factors (Smith, Hendrick, Bateman, Holden, Littlewood, O Smith & Logan, 2019), rather than managing risk factors and movement deficits. It has been identified that people with PFPS have greater localized and centralized pain sensitivity, when assessed during stair ascent compared to healthy participants (Noehren et al., 2016). A recent systematic review and meta- analysis provided moderate evidence in support of pain sensitisation in individuals with PFPS

(De Oliveira Silva, Rathleff, Petersen, Azevedo & Barton, 2019). It is possible that after initial aggravation of the PFJ, people with PFPS develop maladaptive pain responses towards the activities that aggravates their pain (Smith et al., 2019), such as stair use, running and squatting. As hopping is not an activity of daily living or a movement utilised during sport, it 61 is possible that participants had a low perception of pain during hopping, possibly explaining the absence of mechanical differences between groups during testing. Further, single-leg hopping does not replicate the horizontal translation forces such as experienced during sport, therefore, not mimicking the pain response reported during running, cutting or stair ascent. It must be acknowledged that pain does not always reflect the state of tissue pathology (Smith et al., 2019) which requires further research and a shift in the ‘tissue based paradigm’ towards

‘pain management’ for people with PFPS similar to that which has been encouraged in management of lower back pain (Oliveira et al., 2018).

Comparisons of results of the current study to previous research remains problematic. Direct comparison of findings to the loading period during SLTHT is impractical as participants in the current study were shorter, heavier and older than those tested by Dos Reis et al. (2015).

Additionally, there was variability in the performance of the SLTHT between groups, with the healthy participants hopping 0.09 m further than participants with PFPS (Dos Reis et al.,

2015). The variation in distance could implicate there being a difference in kinematics and kinetics between groups, contributing to observed differences in force attenuation and loading, rather than being due to the pathology. In the current study there were no differences between participants with and without PFPS for all spatiotemporal characteristics, demonstrating that the tasks were comparable between groups. Hopping in synchrony with a metronome allowed the vertical displacement of the centre of mass and the direction of motion to be constrained allowing the tasks to be able to be compared between groups.

The current study supports the notion that there is no underlying strength deficit in people with PFPS by the observation that reactive strength and power (Greuel, Herrington, Liu &

Jones, 2019) were similar between people with and without PFPS. This is supported by a 62 recent study which observed that there was no change in movement patterns during running, single-leg squats and step downs, even when there was demonstrable pain induced by either running, lunging or squats in a sample of people with PFPS (Greuel et al., 2019). Further, there were no strength deficits or pain assessed during dynamometric strength testing, supporting the premise that pain which may inhibit muscle activity during function, does not always lead to a gross strength deficit or change in movement patterns. This is supported by a finding that the contribution of the quadriceps was no different between people with and without PFPS when investigated using functional magnetic resonance imaging (fMRI) (Pattyn et al., 2013). However, these results contrast the current clinical practice guidelines for managing PFPS which include strengthening exercise as a component of management

(Powers et al., 2017; Vora et al., 2017; Willy et al., 2019).

It is plausible that there are changes to intrinsic control parameters in people with PFPS, however, the evidence remains conflicting. The findings from the current study do not demonstrate that a change in movement pattern is observed in people with longstanding

PFPS. A large proportion of interventions surrounding PFPS have focused on addressing intrinsic risk factors such as strength deficits, muscle activation patterns, gait kinematics and adaptive position of the foot and patella (Neal, Barton, Gallie, O’Halloran & Morrissey,

2016). However, treating these impairments may not lead to improvements in people with

PFPS based on the current study. Recent research (Hott, Brox, Pripp, Gunnar, Juel, Paulsen &

Liavaag, 2019) demonstrated that there were no differences between three exercise regimes which included hip-focused, knee-focused and free training. This finding suggests that there may not be isolated strength deficits in people with PFPS, as participants still improved on pain and function outcomes when completing general physical activity. Further, gait retraining was not found to influence lower limb kinematics or muscle activity for runners 63 with PFPS (Santos et al., 2019). Currently, there remains insufficient evidence to support the management of intrinsic risk factors in treating people with PFPS and with the current study determining no underlying alteration in movement pattern or reactive strength, there may be other more imperative factors that contribute to PFPS. Current guidelines on managing PFPS provided level A recommendations supporting the use of patella taping or bracing, short term use of in-shoe foot orthoses, patella mobilisations and exercise therapy (Willy et al., 2019).

Education and strategies to allow people with PFPS to better manage their activity and load may have greater effect on pain and function (Esculier, Bouyer, Dubois, Fremont, Moore,

Mcfayden & Jean-Sébastien, 2018). Future prospective studies are needed to investigate the effect of extrinsic risk factor management such as advice and education about training errors

(Drew & Purdam, 2016), cross training (O’Toole, 1992), footwear (Bonacci et al., 2018), rest and recovery (Dutton et al., 2016) to determine if they can add to the traditional types of treatments which are offered.

A key strength of the current study was that healthy participants were matched to those with

PFPS. Matching was based on age, sex, height, weight, limb dominance. The use of a thorough matching strategy reduced anthropometric variations between groups and the effect of confounding variables at baseline. Previous studies investigating PFPS did not use a matched group for comparison, increasing the likelihood of variability between groups (Gruel et al., 2019; Rees, Younis, MacRaeb, 2019). Further, other studies only matched a single variable such as age (Dos Reis et al., 2015). Therefore, careful consideration of a range of baseline variables in this study has reduced the potential for variability between groups and enhanced the strength of results, with conclusions more likely to be attributable to the pathology.

A further strength of this study was the use of inclusion and exclusion criteria that were consistent with the available body of literature on PFPS. Given that there are no standardised diagnostic tools or protocols, diagnosis of PFPS is largely based on a patient’s history and the report of aggravating activities such a pain with stair use, running, jumping, squatting and kneeling (Thomeé et al., 1999). The exclusion of traumatic mechanism of injury and the report of two or more aggravating activities for inclusion into the PFPS cohort is consistent with the available literature on PFPS (Bley et al., 2014; Dos Reis et al., 2015; Hott et al.,

2019). The use of consistent criteria between studies enhances comparability with other studies and the diagnostic accuracy of determining PFPS. The use of reliable outcome measures to assess pain and function was another strength of the conducted study, confirming the diagnosis of PFPS and establishing each participant’s level of irritability.

Exploration of a large variety of spatiotemporal characteristics that represented the performance of the task, ensured that the tasks being performed by each group were in fact similar and allowed comparison of the kinematics and kinetics. A range of tasks of different effort, ranging from comfortable when hopping at a higher cadence, through to maximal efforts were examined. This ensured that the neuromusculoskeletal system was able to be examined at different levels of physical demand with the possibility that differences may only be evident at different levels of effort. The possible influence of fatigue was controlled by limiting each trial to a short duration and providing adequate rest breaks between trials to ensure that any observed changes were not likely to be due to fatigue, which has been shown to increase the variability of knee and ankle coupling in order to maintain performance

(Mudie et al., 2016).

A limitation of this study was that participants included in the PFPS cohort had symptoms for an average of 30 months prior to testing, ranging from 3 months to 8 years. It is possible that the chronicity of symptoms amongst this group may not represent all people with PFPS and that there is a change in pain tolerance and compensatory strategies over the course of longstanding PFPS. This may limit the ecological validity of the current findings. Further, the participants included in this study reported a history of pain during aggravating functional activities such as stair use, squats and kneeling, rather than during hopping. Therefore, the use of hopping may have a limited capacity to identify a change in the knee and ankle interaction even when the task was performed to greater efforts and increased the functional demand of the knee. Future studies may limit the inclusion of participants who have symptoms for a similar duration and assess the performance of tasks including stair use and running.

Examination of tasks that provoke PFPS have the potential to identify movement impairments and have greater utility in clinical practice. However, participants included in this study were included based on the criteria for classification of PFPS as guided by the literature (Thomeé et al., 1999; Van Cant et al., 2017; Willy et al., 2019) and it remains problematic to completely exclude other diagnoses which may only be evident with radiological imaging or arthroscopic investigation.

It has been acknowledged that symptoms related to PFPS are generally reproduced during loading of the patellofemoral joint proportionate to body weight and with the knee being flexed (Thomeé et al., 1999). Hence, the current study targeted greater loading of the PFJ by including hopping to greater heights and loading that exceeded double the body weight. The loading phase of hopping had a trend towards inducing greater knee flexion excursion with a maximum of 30 degrees observed during testing when hopping at 96 hops.min-1 and at maximal effort. This amount of knee flexion may not have been enough to increase retro- 66 patella force or induce pain and change the performance of hopping in people with PFPS compared to the control group. It has been previously demonstrated that during a step-down task, knee flexion angles ranging from 38 to 48 degrees may be pain free in people with PFPS

(Mason, Keays & Newcombe, 2011; Ophey, Bosch, Khalfallah, van den Berg, Bernards,

Kerkhoffs & Tak, 2019). Future studies investigating tasks such as squat jumps or single-leg drops may be more appropriate to examine in people with PFPS as they require deeper knee flexion and be pain provocative.

Single-leg hopping is not a functional activity as it does not involve horizontal translation.

However, it is an activity that has similar motion and loading capacity as experienced during the stance phase of running or single leg landings (Lamontagne et al., 2013). Despite the limitations, the aim of using single leg hopping was to examine differences in people with and without PFPS during a task which allowed repetition and enabled the participant to maintain relatively stereotypical movement patterns at different levels of effort. The task of single-leg hopping is a task that can be performed in laboratory-controlled conditions and has clinical utility in clinical practice, with the benefits of being easy to perform and replicable over time.

The current study was powered with an adequate sample size, which was calculated a priori.

However, although statistically significant within group interactions were identified, post-hoc analyses were sometimes borderline non-significant. Thus, a larger sample size may have been needed to demonstrate a stronger main effect. Further studies attempting to examine the knee and ankle interaction with alternate protocols should aim to include larger sample sizes to determine whether there are differences in dependant variables between people with and without PFPS. 67

5.2 Conclusion

This thesis demonstrated that despite a significant amount of research having been conducted to determine the factors that describe PFPS, its pathogenesis and risk factors remain poorly understood. To our knowledge, this study was the first to examine the loading phase of a repetitive single-leg, hopping protocol for individuals with PFPS. The current study found no mechanical differences between people with and without PFPS during a repeated, single-leg hopping task at both submaximal and maximal efforts. There were no significant differences in kinematics or kinetics between groups, indicative of similar loading strategies of participants with and without PFPS. This finding supports the few published studies that have examined loading in other weight bearing tasks in people with PFPS. Although the current study did have a number of benefits with its methodological rigour, there needs to be greater understanding of the factors that may be associated with the development of PFPS. This should include a greater understanding of the intrinsic and extrinsic factors as well as an in depth understanding of the pain mechanisms that may contribute to symptoms. A more thorough understanding of the disease process will allow the development of new and innovative perspectives for the management of PFPS.

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Appendices

Appendix A: Letter of Ethical Approval from WSU Ethics Committee

REDI Reference: H12994

Risk Rating: Low 2

HREC HUMAN RESEARCH ETHICS COMMITTEE

4 December 2018

Mr Amitabh Gupta

School of Science and Health

Dear Amitabh,

I wish to formally advise you that the Human Research Ethics Committee (HREC) has approved your research proposal report on completion. In providing this approval the HREC determined that the proposal meets the requirements of the National

Statement on Ethical Conduct in Human Research.

This protocol covers the following researchers:

Amitabh Gupta, Peter Clothier, Daniel Thomson, Elise Desira, Cassandra Thompson

Conditions of Approval

1. A progress report will be due annually on the anniversary of the approval date.

2. A final report will be due at the expiration of the approval period.

3. Any amendments to the project must be approved by the Human Research Ethics Committee prior to being implemented.

Amendments must be requested using the HREC Amendment Request Form

4. Any serious or unexpected adverse events on participants must be reported to the Human Research Ethics Committee via the Human Ethics Officer as a matter of priority.

5. Any unforeseen events that might affect continued ethical acceptability of the project should also be reported to the

Committee as a matter of priority

6. Consent forms are to be retained within the archives of the School or Research Institute and made available to the

Committee upon request.

7. Project specific conditions: There are no specific conditions applicable.

Please quote the registration number and title as indicated above in the subject line on all future correspondence related to this project. All correspondence should be sent to [email protected] as this email address is closely monitored.

Yours sincerely

Professor Elizabeth Deane

Presiding Member, Western Sydney University Human Research Ethics Committee 85

Appendix B: Participant Consent Form

Consent Form

Project Title: "An evaluation of lower limb neuromechanical characteristics of people with knee pain and disease during repeated loading.”

I hereby consent to participate in the above named research project.

I acknowledge that:

• I have read the participant information sheet (or where appropriate, have had it read to me) and have been given the opportunity to discuss the information and my involvement in the project with the researcher/s

• The procedures required for the project and the time involved have been explained to me, and any questions I have about the project have been answered to my satisfaction.

I consent to:

☐ My weight and height being measured.

☐ My skin to be cleaned and prepared for placement of markers on my skin.

☐ Adjustment/removal of t-shirt if interfering with marker placement.

☐ Participation in a warm up and performance of repeated hopping trials.

I consent for my data and information provided to be used in this project.

I understand that my involvement is confidential and that the information gained during the study may be published but no information about me will be used in any way that reveals my identity.

I understand that I can withdraw from the study at any time without affecting my relationship with the researcher/s, and any organisations involved, now or in the future.

Signed:______

Name:______

Date:______

This study has been approved by the Human Research Ethics Committee at Western Sydney University. The ethics reference number is: H12994

What if I have a complaint?

If you have any complaints or reservations about the ethical conduct of this research, you may contact the Ethics Committee through Research Engagement, Development and Innovation (REDI) on Tel +61 2 4736 0229 or email [email protected]. Any issues you raise will be treated in confidence and investigated fully, and you will be informed of the outcome. 86

Appendix C: Participant Flyer DO YOU HAVE KNEE PAIN?

VOLUNTEERS ARE NEEDED FOR A RESEARCH STUDY investigating how people with knee pain move compared to healthy individuals

Are you aged between 18 and 40 years? Have you been diagnosed with Patellofemoral Pain Syndrome? Have you had an Anterior Cruciate Ligament Reconstruction? Are your knees and ankles injury free?

If you answered YES to any of these questions, you may be eligible to participate in our study. Please contact Elise Desira to discuss your potential involvement: Email: [email protected] This project has been approved by the Human Research Ethics Committee at Western Sydney (H12994) 87

Appendix D: Participant Information Sheet

Participant Information Sheet

Project Title: An evaluation of lower limb neuromechanical characteristics in people with knee pain and disease during repeated loading.

Project Summary: You are invited to participate in a research study being conducted by Elise Desira (Physiotherapist and Master of Research student with the School of Science and Health). She is being supervised by Dr Amitabh Gupta (Lecturer in Physiotherapy with the School of Science and Health).

This research project aims to investigate the movement patterns and possible compensations that occur during hopping tasks after sustaining a knee injury. This study aims to compare those with a history of knee pain against healthy individuals, to determine how movement after knee injury deviates from normal.

How is the study being paid for? This research project is funded by the Western Sydney University’s School of Science and Health. Your involvement in this project will be on the basis of an unpaid volunteer.

Is there a criteria I have to meet to be eligible participate in this study? To be eligible to participate in this study you must be between the ages of 18 and 40. Additionally you must not be pregnant and be free from systemic illness, previous ankle injury or lower limb fractures.

To be assigned to the knee pain cohort, you will need to report a history of anterior knee pain or anterior cruciate ligament reconstruction. To be assigned to the healthy cohort, you must not report a history of knee pain. The researchers will discuss your eligibility and conduct further screening if you are interested in participating in the study.

What will I be asked to do? After completing pre-screening questionnaires and providing consent, you will be asked to participate in experimental testing at the Human Movement Laboratory (Building 24, Western Sydney University – Campbelltown Campus). Before testing, you will have your skin prepared and small electrode markers placed on your skin to record muscle activity. You will be taken through a warm up and given opportunity to practice and familiarise yourself with the testing procedure.

For this study you will be asked to complete five trials of on-the-spot hopping, at different hopping cadences/speeds. Here you will land on a force platform which will provide the researchers information on force production and absorption. The hopping task will be performed at a specified frequency set by a visual cue (blue flashing light) on an LCD screen. When the flashing light changes colour (red flashing light) you will be required to stop hopping and maintain single leg balance.

How much of my time will I need to give? As a participant you will be required for approximately 2 hours. This includes the time 88 required to complete the required documentation, preparation, familiarisation and the experimental trials.

What benefits will I, and/or the broader community, receive for participating? The study aims to enhance biomechanical knowledge of human performance with results potentially influencing the management of knee pain and future research. No direct benefits to you are expected from participation (i.e. academic credit). If you are studying an Exercise and Sport Science degree or a unit in biomechanics, you may receive an educational benefit from being exposed to scientific experimental research processes.

Will the study involve any risk or discomfort for me? If so, what will be done to rectify it? There is some risk associated with participating in this experimental protocol. For those with knee pain, repeated hopping may have the potential to increase your pain levels. Participants are free to cease the trials at their discretion should they experience an increase in knee pain. Participants may also have a risk of sustaining a new lower limb injury should they land incorrectly during testing.

Additionally, participants may experience a degree of muscular fatigue, perspiration, increased heart rate and increase blood pressure which are normal responses to exercise. Mild discomfort may be experienced when removing the electrodes and markers (similar to removal of a band-aid).

Every effort will be made to minimise any associated participant risk by: * Evaluating preliminary information relating to health & fitness; * Conducting all trials indoors to minimise environmental effects (heat/cold); * Providing an appropriate warm-up prior to testing and adequate rest breaks to minimise risk of injury; * Observing your technique and providing appropriate feedback during the warm-up and experimental trials as required. In the unlikely event that injury does occur during the testing, the attending researchers will initiate an appropriate first aid treatment and action plan.

How do you intend to publish or disseminate the results? It is anticipated that the results of this research project will be published and/or presented in a variety of forums. Only de-identified and aggregated results from this investigation will be used for publication and presentation purposes, to ensure your privacy and confidentiality is maintained.

Will the data and information that I have provided be disposed of? Please be assured that only the researchers will have access to the information you provide. Please note that minimum retention period for data collection is five years post publication. After this time the data and information you have provided will be securely disposed of.

Can I withdraw from the study? Participation is entirely voluntary and you are not obliged to be involved. If you do participate you can withdraw at any time without giving reason. If you do choose to withdraw, any information that you have supplied will be de-identified and stored for the five-year retention period. After this time your information will be appropriately disposed of.

Can I tell other people about the study? Yes, you can tell other people about the study by providing them with the Primary Investigator’s contact details. They are then welcome to discuss their potential involvement in the project and obtain information sheets. 89

What if I require further information? Please contact Elise Desira should you wish to discuss the research further before deciding whether or not to participate.

Primary Investigator Ms Elise Desira (Email: [email protected]) Supervisor and Investigator Dr Amitabh Gupta, (Ph: 02 4620 3757; Email: [email protected]) Assisting Researchers Dr Peter Clothier, (Ph: 02 4620 3743; Email: [email protected] ) Mr Daniel Thomson, (Ph: 02 4620 3838; Email: [email protected]) Ms Cassandra Thompson email: [email protected] What if I have a complaint? If you have any complaints or reservations about the ethical conduct of this research, you may contact the Ethics Committee through Research Engagement, Development and Innovation (REDI) on Tel +61 2 4736 0229 or email [email protected].

Any issues you raise will be treated in confidence and investigated fully, and you will be informed of the outcome.

This study has been approved by the Western Sydney University Human Research Ethics Committee. The Approval number is H12994.

Appendix E: Anterior Knee Pain Scale (AKPS)

Anterior Knee Pain Scale

Name: ______Date: ______Age: ______Knee: Left OR Right (please circle) Duration of symptoms: ______years ______months

For each question, circle the answer which best corresponds to your knee symptoms.

Appendix F: Visual Analogue Scale (VAS)

Visual Analogue Scale

Choose a number from 0 to 10 which best describes your current level of pain

0 1 2 3 4 5 6 7 8 9 10

No pain Worst pain imaginable ☺ 

Appendix G: Exercise Pre-screening Questionnaire

Pre-Exercise Health Screening

The information provided in the answers of this health screen is required by the researchers to assess your suitability for participation in the research project titled "An evaluation of lower limb neuromechanical characteristics of people with knee pain during repeated loading.” If you do not understand a question please do not hesitate to seek clarification from the researchers.

PLEASE ANSWER ALL QUESTIONS HONESTLY

Name: Date of Birth: / /

Section 1 – Signs and Symptoms 1. Has your doctor ever told you that you have a heart condition or have you ever suffered a stroke? (Please Circle) No Yes

2. Do you ever experience unexplained pains in your chest at rest or during physical activity/exercise? No Yes

3. Do you ever feel faint or have spells of dizziness during physical activity/exercise that causes you to lose balance? No Yes

4. Have you had an asthma attack requiring immediate medical attention at any time over the last 12 months? No Yes

5. If you have diabetes (type I or type II) have you had trouble controlling your blood glucose in the last 3 months? No Yes

6. Do you have any diagnosed muscle, bone or joint problems that you have been told could be made worse by participating in physical activity/exercise? No Yes If yes, provide details: ______

7. Do you have any other medical condition(s) that may make it dangerous for you to participate in physical activity/exercise? No Yes If yes, provide details: ______

Section 2 – Risk Factors 1. Do you have a family history of heart disease (e.g.: stroke, heart attack)? That is has your father, mother, brother, sister had a stroke/heart attack? No Yes

If you answered YES to the previous question, what is/are the gender(s) and age(s) of the relative(s) with heart disease? Male > 55 Male < 55 Female > 65 Female < 65

2. Do you smoke cigarettes on a daily or weekly basis or have you quit smoking in the last 6 months? No Yes

If YES, how many cigarettes do you currently or did smoke per day / week? Please provide details: ______

3. Which statement best describes your current physical activity / exercise level? Sedentary Light Moderate Vigorous

4. How many exercise sessions do you usually do each week?______

5. How many minutes of exercise do you usually do each week? ______

6. How long have you been continuously participating in the above activity? Years______Months______Days ______

7. Have you been told that you have high blood pressure? No Yes

8. Have you been told that you have high cholesterol? No Yes

9. Have you been told that you have high blood sugar? No Yes

10. Have you spent time in hospital (including day admission) for any medical condition/illness/injury during the last 12 months? No Yes