University of Southern California Dissertations and Theses

Hip and pelvis kinematics and kinetics in persons with femoroacetabular impingement

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Hip and pelvis kinematics and kinetics in persons with femoroacetabular impingement

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Copyright!2015! ! Jennifer!Bagwell!

HIP AND PELVIS KINEMATICS AND KINETICS IN PERSONS WITH
FEMOROACETABULAR IMPINGEMENT

By

Jennifer J. Bagwell

A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(BIOKINESIOLOGY)

May 2015

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DEDICATION

To my parents for teaching me how to live

And to Colin and Brannon for making this adventure that is life worthwhile

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ACKNOWLEDGEMENTS
Completing this dissertation has been a challenging, enriching, and rewarding journey. I
feel honored to have had the opportunity to work with such brilliant, dedicated, and innovative
people. I continue to be amazed by the faculty, students, and staff with whom I have the privilege
of working. Even more amazing is that they have so gratuitously given their time and support to
me in my endeavors to become a better scientist, teacher, and physical therapist.
Firstly, I want to recognize Dr. Christopher Powers, my PhD advisor. His work ethic and
commitment have made me a better scientist. His insistence on clear communication has resulted
in improved scholarly writing, presentations, and discussions. I will also be forever grateful for
his continued support throughout the many changes I have encountered while pursuing my PhD.
I am also thankful for the guidance of Dr. Kornelia Kulig who approaches each meeting with
unending energy and scientific curiosity. She has motivated me to explore concepts more deeply
and has been a mentor with regard to my dissertation work and my professional development. I
feel fortunate to have had the support of Dr. Susan Sigward who has provided guidance
regarding biomechanical concepts, the PhD process, and career development. She has been a
supporter, friend, and role model. I will be forever grateful to Dr. Sam Ward who has been
generous with his time and who always encouraged me to view my data with increased scientific
rigor. I would also like to thank Dr. Patrick Colletti who assisted with the development of the
radiographic aspects of this project and who provided an always enthusiastic and insightful
outside perspective.
In addition to my dissertation committee, I am grateful to our program chair, Dr. James
Gordon, for always supporting all of the students in our department. I am also thankful for the
assistance with project development and subject recruitment provided by Dr. Jason Snibbe, Dr.
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Brian Giordano, and Jennifer Cabrera and the subject recruitment from Dr. Michael Gerhardt,
Sabrina Duran, and Edith Rodriguez. I would also like to thank Dr. Steve Reischl for providing
his clinical perspective and support. The former and present MBRL lab members have been
instrumental to my development as a scientist and to my ability to maintain my sanity. I am
particularly indebted to Kaiyu Ho for her assistance with computational modeling and to Joanne
Smith, Hsiang-Ling Teng, and the other members of G12 for their biomechanical insight and,
most importantly, for their friendship. I am also grateful for the volunteer assistance of Haley
Nakata and the data collection assistance from Dr. Thiago Fukuda.
The support of my friends and family has been extraordinary. My parents taught me the
value of education and intellectual curiosity. They have showed unconditional love, have
encouraged all of my endeavors, and they taught me to believe in myself through their unending
belief in me. Colin, my husband, has been my constant source of encouragement, entertainment,
and love. I am forever indebted to him and our amazing son, Brannon, for sharing me with this
endeavor and for making every day a privilege (even when it involved hours of data processing).
They are my everything.
The financial support for my dissertation was provided by the USC Division of
Biokinesiology and Physical Therapy and the endowment from Jacquelin Perry to the
Musculoskeletal Biomechanics Research Laboratory. I am also thankful for the grants I have
received from the USC Department of Radiology, the International Society of Biomechanics, and
the California Physical Therapy Fund. Lastly, I would like to recognize my research participants
for making this research possible.

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TABLE OF CONTENTS
DEDICATION ............................................................................................................................................ II
ACKNOWLEDGEMENTS ..................................................................................................................... III
LIST OF TABLES .................................................................................................................................. VII
LIST OF FIGURES ............................................................................................................................... VIII
ABSTRACT ............................................................................................................................................... IX
CHAPTER I: OVERVIEW ........................................................................................................................ 1
CHAPTER II: BACKGROUND & SIGNIFICANCE ............................................................................. 4
STATEMENT OF THE PROBLEM ................................................................................................................. 4
HIP AND PELVIS KINEMATICS AND KINETICS IN FEMOROACETABULAR IMPINGEMENT ......................... 7
INFLUENCE OF KINEMATICS AND BONY MORPHOLOGY ON JOINT STRESS ........................................... 10
SUMMARY ............................................................................................................................................... 12
CHAPTER III: SAGITTAL PLANE MOTION OF THE PELVIS INFLUENCES TRANSVERSE
PLANE MOTION OF THE FEMUR: KINEMATIC COUPLING AT THE HIP JOINT ............... 13
INTRODUCTION ....................................................................................................................................... 14
METHODS ............................................................................................................................................... 15
Participants ............................................................................................................................................ 15
Procedures .............................................................................................................................................. 16
Data Analysis ......................................................................................................................................... 17
Statistical Analysis ................................................................................................................................. 17
RESULTS ................................................................................................................................................. 18
DISCUSSION ............................................................................................................................................ 21
CCONCLUSION ........................................................................................................................................ 23
CHAPTER IV: A COMPARISON OF HIP KINEMATICS AND KINETICS IN PERSONS WITH
AND WITHOUT CAM FEMOROACETABULAR IMPINGEMENT DURING A DEEP SQUAT
TASK .......................................................................................................................................................... 24
INTRODUCTION ....................................................................................................................................... 25
METHODS ............................................................................................................................................... 27
Participants ............................................................................................................................................ 27
Instrumentation ...................................................................................................................................... 29
Procedures .............................................................................................................................................. 29
Data Analysis ......................................................................................................................................... 30
Statistical Analysis ................................................................................................................................. 31
RESULTS ................................................................................................................................................. 31
DISCUSSION ............................................................................................................................................ 35
CONCLUCION .......................................................................................................................................... 38

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CHAPTER V: ACETABULUAR STRESS IN PERSONS WITH AND WITHOUT CAM
FEMOROACETABULR IMPINGEMENT: FINITE ELEMENT ANALYSIS OF A DEEP SQUAT
TASK .......................................................................................................................................................... 39
INTRODUCTION ....................................................................................................................................... 40
METHODS ............................................................................................................................................... 41
Participant .............................................................................................................................................. 41
MR Assessment ....................................................................................................................................... 41
Finite Element Model Development ....................................................................................................... 42
Data Analysis ......................................................................................................................................... 44
RESULTS ................................................................................................................................................. 44
DISCUSSION ............................................................................................................................................ 46
CONCLUSION .......................................................................................................................................... 48
CHAPTER VI: SUMMARY AND CONCLUSIONS ............................................................................ 49
REFERENCES .......................................................................................................................................... 54

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LIST OF TABLES

Table 3-1

Coupling ratios during maximum pelvis sagittal plane excursion
for periods of anterior and posterior pelvis tilt
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Table 4-1 Demographic and functional outcome data (mean + standard
deviation)
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Table 4-2 Kinematic and kinetic data during the deep squat task (mean +
standard deviation)
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Table 5-1

Hip kinematics used for control and cam finite element models 43

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LIST OF FIGURES

Figure 2-1 Cam deformity prematurely abutting the acetabular rim with
hip internal rotation (B) (Byrd, 2010).
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Figure 3-1 Subject performing maximum posterior pelvis tilt (left) to
maximum anterior pelvis tilt (right) at 60° of hip flexion. This
task was repeated at hip flexion angles of 0°, 30°, and 90°.

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Figure 3-2 Average angle-angle diagram of the femur transverse plane
kinematics versus the pelvis sagittal plane kinematics at hip
flexion angles of 0°, 30°, 60°, and 90° while performing a
maximum anterior pelvis tilt from a maximum posterior pelvis
tilt. Star indicates starting point.
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Figure 3-3 Average angle-angle diagram of the femur transverse plane
kinematics versus the pelvis sagittal plane kinematics at hip
flexion angles of 0°, 30°, 60°, and 90° while performing a
maximum posterior pelvis tilt from a maximum anterior pelvis
tilt. Star indicates starting point.
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Figure 4-1 Example of the deep squat task 30
Figure 4-2 Comparison of hip kinematics between groups A) sagittal plane
B) frontal plane and C) transverse plane
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Figure 4-3 Comparison of sagittal plane kinematics between groups A)
pelvis B) femur and C) hip
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Figure 4-4 Comparison of hip kinetics between groups A) sagittal plane B)
frontal plane and C) transverse plane
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Figure 5-1

Depiction of the force vector used for simulations (derived from
peak hip forces found by Bergmann, et al. (2001) (Bergmann et
al., 2001).
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Figure 5-2
Acetabular stress profiles for the A) control model B) minimum
cam model C) average cam model and D) maximum cam model
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ABSTRACT
Cam femoroacetabular impingement (FAI) is a cause of chondral damage, labral tears,
and hip osteoarthritis. Cam morphology refers to decreased offset at the femoral head-neck
junction which contributes to abutment of the femoral head-neck junction with the acetabular
labrum or cartilage at end range of hip flexion and/or hip internal rotation. Previous literature
suggests that range of motion and kinematic impairments at the hip and pelvis may contribute to
FAI. In addition, previous studies have suggested that these motions of the femur and pelvis may
be coupled. Therefore, it is important to understand the normal kinematic relationship between
the femur and pelvis before understanding the role of altered kinematics in persons with cam
FAI. To date, few studies have reported full kinematic and kinetic profiles in this population.
This is important as it is not known if abnormal kinematics are solely driven by altered bony
morphology or if muscular control plays a role. Use of computational modeling may enhance our
understanding of potential underlying causes of altered kinematics and the influence of altered
kinematics on joint stress. As such, the overall purpose of this dissertation was to examine hip
and pelvis kinematics and kinetics in persons with cam FAI.
Chapters I and II provide an overview and a background of the current literature related
to FAI. The purpose of Chapter III was to determine whether there is a consistent and predictable
kinematic relationship between the pelvis and the femur in healthy individuals. Transverse plane
motion of the femur and sagittal plane motion of the pelvis during maximum anterior and
posterior pelvis tilt were quantified at different hip flexion angles. The observed ratios of
transverse femur motion to sagittal pelvis motion were consistent across all hip flexion angles
during anterior and posterior pelvis tilt. On average, for every 5° of anterior pelvis tilt there was
1.2-1.6° of internal femur rotation and for every 5° of posterior pelvis tilt there was 1.2-1.6° of
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external femur rotation. This finding suggests that altered pelvis movement in the sagittal plane
may influence transverse plane femur motion. These results are relevant to persons with FAI
because pelvis anterior tilt and hip internal rotation are both thought to contribute to
impingement.
The purpose of Chapter IV was to compare hip and pelvis kinematics and kinetics during
a deep squat task between persons with cam FAI and matched controls. Compared to the control
group, persons with cam FAI demonstrated decreased peak hip internal rotation, decreased
posterior pelvis tilt, and decreased mean hip extensor moments. The observed decrease in
posterior pelvis tilt may contribute to impingement by approximating the femoral head-neck
junction with the acetabulum. However, the findings of decreased posterior pelvis tilt and
decreased hip internal rotation in persons with cam FAI is contrary to the coupling behavior
reported in Chapter III. Therefore, it was hypothesized that the decreased hip internal rotation in
the presence of diminished posterior pelvis tilt may be the result of mechanical abutment.
Additionally, decreased hip extensor moments may underlie the observed decrease in pelvis
posterior tilt.
To expand upon the findings of Chapter IV, the purpose of Chapter V was to evaluate the
contact location and magnitude of acetabular cartilage stress during simulated squatting using
finite element modeling. The finite element models utilized the respective group kinematics and
morphological profiles representative of the control and cam groups. Despite decreased hip
internal rotation and flexion in the cam FAI group, the model of average cam morphology and
the model of maximum cam deformity resulted in increased acetabular stress and a shift in
contact location indicative of impingement. This finding suggests that even a moderate cam
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deformity may be important with respect to joint stress and provides evidence that the decreased
hip internal rotation observed in the cam FAI group is likely the result of mechanical abutment.
Taken together, the results of this dissertation suggest that posterior pelvis tilt and hip
external rotation may protect against impingement. Therefore, addressing kinematic impairments
in this population may be an avenue for conservative intervention to decrease impingement or to
allow for increased femur flexion prior to impingement. In particular, emphasizing utilization of
hip extensors to increase pelvis posterior tilt might be beneficial for this population.
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CHAPTER I
OVERVIEW
Cam femoroacetabular impingement (FAI) is a cause of chondral damage (Anderson et
al., 2009; Beck, Kalhor, Leunig, & Ganz, 2005; Johnston, Schenker, Briggs, & Philippon, 2008;
Kaya, Suzuki, Emori, & Yamashita, 2014; Nepple, Carlisle, Nunley, & Clohisy, 2011), labral
damage (Johnston et al., 2008; Meermans, Konan, Haddad, & Witt, 2010; Nepple et al., 2011;
Tamura et al., 2013; Tanzer & Noiseux, 2004), and hip osteoarthritis (Agricola et al., 2013;
Anderson et al., 2009; Beck et al., 2005; Gosvig, Jacobsen, Sonne-Holm, Palm, & Troelsen,
2010). Cam morphology refers to decreased offset at the femoral head-neck junction (Beck et al.,
2005; Ito, Minka, Leunig, Werlen, & Ganz, 2001; Pfirrmann et al., 2006). A proposed
mechanism contributing to pathology in persons with cam FAI is abutment of the femoral head-
neck junction with the acetabular labrum and/or cartilage (Beck et al., 2005).
Impingement has been shown to occur at end range hip flexion and hip internal rotation
(Clohisy et al., 2009; Ito et al., 2001; Myers, Eijer, & Ganz, 1999; Sierra, Trousdale, Ganz, &
Leunig, 2008; Tanzer & Noiseux, 2004). Therefore, it is not surprising that previous literature
suggests that range of motion and kinematic impairments in this population involve sagittal plane
pelvis or hip motion and transverse plane hip motion (Audenaert, Peeters, Vigneron, Baelde, &
Pattyn, 2012; Clohisy et al., 2009; Hunt, Guenther, & Gilbart, 2013; Lamontagne, Kennedy, &
Beaule, 2009; Philippon, Maxwell, Johnston, Schenker, & Briggs, 2007; Rylander, Shu, Favre,
Safran, & Andriacchi, 2013; Wyss, Clark, Weishaupt, & Notzli, 2007). In addition, previous
studies have suggested that these motions may be coupled (Duval, Lam, & Sanderson, 2010;
Khamis & Yizhar, 2007; Pinto et al., 2008; Tateuchi, Wada, & Ichihashi, 2011). Therefore, it is
important to understand the normal kinematic relationship between the femur and the pelvis prior
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to understanding the role of altered motion of the femur or the pelvis in a pathological
population.
After establishing normal kinematic relationships between the pelvis and the femur, a
more informed exploration of hip kinematics and kinetics in persons with cam FAI can be
undertaken. While previous studies indicate that hip and pelvis kinematics may be altered during
functional tasks in persons with FAI (Brisson, Lamontagne, Kennedy, & Beaule, 2013; Hunt et
al., 2013; Kennedy, Lamontagne, & Beaule, 2009; Kumar et al., 2014; Lamontagne et al., 2009;
Rylander et al., 2013), there are few studies reporting full kinematic and kinetic profiles in this
population. This is important as it is not known if bony morphology is the sole factor
contributing to kinematics or if muscular control plays a role. Furthermore, altered kinematics
could represent a strategy to avoid impingement or could be the result of bony abutment. Use of
computational modeling may enhance the understanding of the potential underlying cause of
altered kinematics as well as the effects of kinematic differences on joint stress.
The primary objective of this dissertation was to examine hip and pelvis kinematics and
kinetics in persons with cam FAI. Three studies with the following specific aims were performed
to achieve this goal:

Specific Aim 1: To systematically explore whether there is a consistent and predictable
kinematic relationship between sagittal plane motion of the pelvis and transverse plane motion of
the femur during anterior and posterior pelvis tilt in healthy individuals. It was hypothesized that
the ratio between transverse femur motion and sagittal pelvis motion would be consistent across
hip flexion angles and during periods of anterior and posterior pelvis tilt.

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Specific Aim 2: To compare three-dimensional hip and pelvis kinematics and hip kinetics during
a deep squat task between persons with cam FAI and age and sex matched controls. It was
hypothesized that persons in the cam FAI group would demonstrate decreased peak hip flexion,
decreased peak hip abduction, decreased peak hip internal rotation, and decreased posterior
pelvis tilt at the time of peak hip flexion. It also was hypothesized that persons with cam FAI
would have diminished hip moments in all three planes during this task.

Specific Aim 3: To evaluate the contact location and magnitude of acetabular joint stress in a
finite element model using the respective group kinematics and morphological profiles of
persons with cam FAI and matched controls during a deep squat task. It was hypothesized that
the cam FAI models would demonstrate increased joint stress and a shift in contact location
compared to the control model.

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CHAPTER II
BACKGROUND & SIGNIFICANCE
STATEMENT OF THE PROBLEM
Historically hip osteoarthritis has been classified into two categories: primary and
secondary. Secondary osteoarthritis is due to a known cause, such as dysplasia, Perthes, slipped
capital femoral epiphysis, or known trauma and all other types of hip OA are deemed idiopathic
in nature and termed primary hip osteoarthritis (Goodman et al., 1997; Harris, 1986). Recently,
several authors have speculated that primary hip osteoarthritis is not as common as previously
thought, but rather subtle bony morphological traits may be responsible for abnormal wear of the
acetabulum and the resultant pathology (Goodman et al., 1997; Harris, 1986; Ito et al., 2001;
Tannast, Siebenrock, & Anderson, 2007). Myers and colleagues first coined the term
“femoroacetabular impingement” in 1999 (Myers et al., 1999). Since the development of that
term, research regarding hip bony anatomy and congruency has expanded dramatically and two
primary types of FAI have emerged, cam and pincer.
Of the two types of FAI morphology, cam FAI has consistently been shown to contribute
to hip pathology (Agricola et al., 2013; Anderson et al., 2009; Gosvig et al., 2010; Johnston et
al., 2008; Meermans et al., 2010; Nepple et al., 2011; Tanzer & Noiseux, 2004). Cam FAI is
hypothesized to result from a deformity on the femoral side, usually described as decreased
offset at the head-neck junction (Beck et al., 2005; Ito et al., 2001; Pfirrmann et al., 2006). The
less spherical femoral head is thought to change the contact from between the acetabular cup and
femoral head to between the antero-superior acetabular rim and femoral head-neck junction with
motions such as hip flexion and hip internal rotation (Clohisy et al., 2009; Ito et al., 2001; Myers
et al., 1999; Sierra et al., 2008; Tanzer & Noiseux, 2004) (Figure 2-1).
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Figure 2-1. Cam deformity prematurely abutting the acetabular rim with hip internal rotation (B)
(Byrd, 2010)

Cam morphology has been shown to result in acetabular labral damage (Johnston et al.,
2008; Meermans et al., 2010; Nepple et al., 2011; Tamura et al., 2013; Tanzer & Noiseux, 2004),
hip chondral damage (Anderson et al., 2009; Beck et al., 2005; Johnston et al., 2008; Kaya et al.,
2014; Nepple et al., 2011), and hip osteoarthritis (Agricola et al., 2013; Anderson et al., 2009;
Beck et al., 2005; Gosvig et al., 2010). Furthermore, it is thought that repetitive abutment and the
resultant abnormal forces at the area of bony deformity in cam FAI may result in further bone
formation at that location, creating a detrimental cycle (Tanzer & Noiseux, 2004). Further
support for the concept of altered morphology in response to loading comes from several studies
indicating that those participating in particular types of loading and movements due to sports
participation are more likely to develop FAI morphology (Gerhardt et al., 2012; Kapron et al.,
2011; Ross et al., 2014; Siebenrock, Behning, Mamisch, & Schwab, 2013; Siebenrock et al.,
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2011). Therefore, activities, loading history, and abnormal movement patterns likely play a role
with regard to the etiology of this pathology.
While femoral head-neck sphericity or offset measures have been associated with pain
and pathology, many individuals with an aspherical femoral head do not demonstrate pain or
pathology (Allen, Beaule, Ramadan, & Doucette, 2009; Hack, Di Primio, Rakhra, & Beaule,
2010; Kang et al., 2010). Surgeons often target the bony deformity in individuals with hip
pathology, but bony anatomy alone is insufficient to fully explain FAI and many individuals with
anatomical signs of FAI do not develop symptoms (Allen et al., 2009; Audenaert, Peeters, Van
Onsem, & Pattyn, 2011; Hack et al., 2010; Kang et al., 2010; Laborie et al., 2011). This suggests
that other factors may be contributing to the development of pain in this population. Because
impingement is proposed to occur as a result of abutment at end range of motion (Audenaert et
al., 2012; Chegini, Beck, & Ferguson, 2009; Ganz et al., 2003; Ito et al., 2001), hip and pelvis
kinematics could be important with respect to pathology in this population.
The overall purpose of this dissertation was to examine hip and pelvis kinematics and
kinetics in persons with cam FAI. While several investigations of hip kinematics in persons with
cam FAI have been undertaken (Brisson et al., 2013; Hunt et al., 2013; Kennedy et al., 2009;
Kumar et al., 2014; Lamontagne et al., 2009; Rylander et al., 2013), results are inconsistent and
there are few studies reporting full kinematic and kinetic profiles in this population. These
previous studies suggest that the primary range of motion and kinematic impairments in this
population involve sagittal plane pelvis or hip motion and transverse plane hip motion
(Audenaert et al., 2012; Clohisy et al., 2009; Hunt et al., 2013; Lamontagne et al., 2009;
Philippon et al., 2007; Rylander et al., 2013; Wyss et al., 2007). In addition, previous studies
have suggested that these motions may be coupled in healthy populations (Duval et al., 2010;
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Khamis & Yizhar, 2007; Pinto et al., 2008; Tateuchi et al., 2011). Therefore, it is important to
understand the normal kinematic relationship between these motions prior to understanding these
motions in a pathological population. A systematic evaluation of the coupling relationship
between the femur and the pelvis in healthy individuals would aid in the interpretation of an
exploration of hip kinematics in persons with cam FAI. Lastly, it is not clear if differences in hip
kinematics represent a protective mechanism for persons with cam FAI to avoid impingement or
if altered kinematics are the result of bony abutment. Computational modeling could improve the
understanding of the impact of the observed kinematics and bony morphology on joint stress in
persons with cam FAI.

HIP AND PELVIS KINEMATICS AND KINETICS IN FEMOROACETBULAR
IMPINGEMENT
Due to the movement dependent nature of cam FAI, abnormal hip and pelvis kinematics
and kinetics could be important with respect to this pathology. Several studies have evaluated hip
and pelvis kinematics during gait in persons with cam FAI. The results of these studies are varied
and have reported that persons with cam FAI exhibit small decreases in sagittal plane (Hunt et
al., 2013; Rylander et al., 2013), frontal plane (Brisson et al., 2013; Hunt et al., 2013; Kennedy et
al., 2009), and transverse plane hip kinematics (Hunt et al., 2013; Rylander et al., 2013) and in
frontal plane pelvis kinematics (Kennedy et al., 2009) when compared to healthy controls. A
limitation of studies that have evaluated gait in this population is that maximum hip flexion
during level walking is only 20-30° and does not reflect the hip flexion range thought to be
related to impingement (Chegini et al., 2009).
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In contrast, fewer studies have performed kinematic evaluations in persons with cam FAI
during tasks involving large hip flexion excursions. Rylander, et al. (2013) reported that
individuals with cam FAI demonstrated decreased sagittal plane hip motion and peak hip internal
rotation during stair climbing when compared to controls (Rylander et al., 2013). Kumar, et al.
(2014) reported greater peak hip adduction and a greater internal rotator moment in a preliminary
investigation of persons with FAI and control subjects during a squat task (25% of body height).
These authors did not report pelvis kinematics (Kumar et al., 2014). Lamontagne, et al. (2009)
reported a trend toward decreased total sagittal plane pelvis excursion during a maximum depth
squat task in persons with cam FAI compared to controls. These authors reported no differences
in hip kinematics or in the pelvis angle at peak hip flexion, the time point most important with
respect to impingement (Lamontagne et al., 2009). In a separate study, the same group compared
several radiographic variables as well as hip kinematics during a maximum depth squat between
a symptomatic group with cam morphology, an asymptomatic group with cam morphology, and
an asymptomatic group without cam morphology. These authors report that diminished total
sagittal plane pelvis excursion during squatting significantly distinguished the symptomatic cam
FAI group from the other two (Ng, Lamontagne, Adamczyk, Rahkra, & Beaule, 2014).
Previous studies in this area indicate that hip kinematics may be altered during
performance of end range of motion functional tasks and that deep squatting, in particular, may
be a useful, differentiating task in this population. Although kinematic comparisons have been
made between persons with cam FAI and pain-free control subjects during tasks involving large
hip flexion angles, the kinetics underlying observed differences in hip and pelvis kinematics have
only been described by Kumar, et al. (2014). This study included only seven persons with FAI
(Kumar et al., 2014). It is important to understand the kinetics demonstrated by persons with cam
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FAI as it is not known if abnormal hip and pelvis kinematics are solely driven by abnormal bony
morphology or if altered muscular control contributes to kinematic differences. Previous research
has shown that individuals with FAI have hip muscle weakness (Casartelli, Maffiuletti, et al.,
2011), suggesting that impaired muscular control may be contributing to altered kinematics in
this population.
The most consistent findings of the previous research in persons with cam FAI suggests
that the primary range of motion and kinematic impairments in this population involve sagittal
plane pelvis or hip motion and transverse plane hip motion (Audenaert et al., 2012; Clohisy et
al., 2009; Hunt et al., 2013; Lamontagne et al., 2009; Philippon et al., 2007; Rylander et al.,
2013; Wyss et al., 2007). In addition, previous research has suggested that femur transverse
motion and pelvis sagittal motion may be coupled in healthy persons (Duval et al., 2010; Khamis
& Yizhar, 2007; Pinto et al., 2008; Tateuchi et al., 2011). As a result of the highly congruent
nature of the hip joint and the closely approximated joint surfaces (Llopis, Cerezal, Kassarjian,
Higueras, & Fernandez, 2008; Safran et al., 2013) it is likely that movement of one segment may
influence the other. The inherent stability and high levels of congruency of the hip occur
secondary to the ball and socket bony morphology, the thick capsule and ligaments (Philippon et
al., 2014; Safran et al., 2013), and the strong muscles surrounding the joint (Safran et al., 2013).
Duval, et al. (2010) reported that internal rotation of the lower extremity during standing
resulted in an anterior pelvis tilt and external rotation of the lower extremity resulted in a
posterior pelvis tilt. These authors proposed that this kinematic relationship occurred as a direct
result of bony approximation between the femoral head and the acetabulum (Duval et al., 2010).
Further support for kinematic coupling between the pelvis and the femur comes from studies in
which lateral calcaneal wedging was used to induce foot pronation (Khamis & Yizhar, 2007;
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Pinto et al., 2008; Tateuchi et al., 2011). These studies revealed that calcaneal eversion resulted
in internal tibia rotation, internal femur rotation, and anterior pelvis tilting. This kinematic
relationship between the pelvis and femur has been shown to exist during bilateral (Khamis &
Yizhar, 2007; Pinto et al., 2008) and unilateral standing (Pinto et al., 2008; Tateuchi et al., 2011).
The fact that transverse plane motion of the femur can influence sagittal plane motion of
the pelvis is suggestive of kinematic coupling between these two segments. Coupling arises
when a force or torque in one direction causes motion in another direction (Raynor, Moskovich,
Zidel, & Pugh, 1987). For example, at the foot-ankle complex there is a well-studied relationship
between calcaneal eversion and internal tibia rotation (Hintermann, Nigg, Sommer, & Cole,
1994; Tillman, Hass, Chow, & Brunt, 2005) and in the cervical spine axial rotation has been
demonstrated to be coupled with ipsilateral lateral flexion (Cook, Hegedus, Showalter, & Sizer,
2006; Wachowski et al., 2009). While previous research supports the premise that internal femur
rotation contributes to anterior pelvis tilt, it is not clear if the same coupling relationship occurs
reciprocally (i.e. whether sagittal plane pelvis motion influences transverse plane femur motion).
Additionally, research in this area has focused on upright standing postures, so it is not known if
this relationship exists at greater hip flexion angles similar to what occurs during dynamic
movement.
If kinematic coupling exists between anterior pelvis tilt and internal femur rotation,
motion of one of these segments would result in motion of the other. This potential coupling may
have implications in persons with FAI. If anterior pelvis tilt and hip internal rotation are coupled,
this would be doubly disadvantageous in persons with cam FAI. Conversely, posterior pelvis tilt
may decrease both hip flexion and hip internal rotation, thereby decreasing impingement in this
population.
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INFLUENCE OF KINEMATICS AND BONY MORPHOLOGY ON JOINT STRESS
In addition to a comprehensive kinematic and kinetic exploration of persons with cam
FAI, consideration of the bony morphology is critical to understanding the etiology of cam FAI.
It is also important to understand how much of a cam lesion is necessary for the contact location
to shift or for contact stress to increase in the presence of altered kinematics. Use of
computational modeling may aid in interpreting the effects of both movement patterns and bony
morphology on joint stress and contact location in persons with cam FAI.
Although previous finite element analyses and computational models have examined the
influence of FAI on joint contact mechanics (Arbabi et al., 2010; Chegini et al., 2009; Jorge et
al., 2014; Tannast, Kubiak-Langer, et al., 2007), only one study has directly incorporated
kinematics from persons with cam FAI and control subjects. Ng, et al. (2012) utilized finite
element modeling to simulate a maximum depth squat task using the bony morphology of two
persons with cam FAI and persons without cam FAI. While the bony morphology differed
between the models, it was not clear if the kinematics were different between these participants
(Ng, Rouhi, Lamontagne, & Beaule, 2012). Additionally, the participants in their study
demonstrated alpha angles greater than 70°, so the stress profiles in the presence of more
moderate cam morphology have not been explored.
Given the potential contribution of hip and pelvis kinematics to FAI, it is important to
understand the interaction between altered kinematics and bony morphology in persons with cam
FAI. Therefore, exploring the influence of altered morphology and kinematics displayed by
persons with cam FAI on joint stress would assist in interpreting the potential causes of altered
kinematics in persons with cam FAI. For example, diminished hip motion could be the result of
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bony impingement or could be a protective mechanism for people with cam FAI to avoid
abutment.

SUMMARY
Due to the movement dependent nature of cam FAI, understanding normal and abnormal
hip kinematics and kinetics in this population is important. While studies indicate that there may
be kinematic coupling between the femur and pelvis segments, this relationship has not been
fully explored in an asymptomatic population. In particular, it is not clear if movement of the
pelvis results in coupled movement of the femur. Additionally, this relationship has not been
analyzed at larger hip flexion angles, such as those demonstrated to contribute to impingement in
persons with FAI. An improved understanding of this non-pathological kinematic coupling will
facilitate a more meaningful understanding of the role of kinematics in persons with cam FAI.
Few studies have reported full hip and pelvis kinematic and kinetic profiles in this
population during a task involving large hip flexion angles. Inclusion of kinetics may be
important to understanding if kinematics are solely driven by altered bony morphology or if
muscular control is an important factor. Another method to further assess the effect of bony
morphology and hip kinematics is use of computational modeling. Because altered kinematics in
persons with cam FAI could serve to avoid impingement or could be the result of bony abutment,
use of finite element modeling may enhance understanding of the potential underlying causes of
altered kinematics and the effects of kinematic differences on joint stress.

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CHAPTER III
SAGITTAL PLANE MOTION OF THE PELVIS INFLUENCES TRANSVERSE PLANE
MOTION OF THE FEMUR: KINEMATIC COUPLING AT THE HIP JOINT
Previous studies have suggested that internal femur rotation can influence pelvis motion.
This indicates that there may be kinematic “coupling” of these two segments. The purpose of this
chapter was to determine whether there is a consistent and predictable kinematic relationship
between the pelvis and the femur. Sixteen subjects performed three trials of maximum anterior
and posterior pelvis tilt at four different hip flexion angles (0°, 30°, 60°, and 90°). Ordinary least
squares regressions were used to calculate the ratio of transverse femur motion to sagittal pelvis
motion using the mean kinematic curves during anterior pelvis tilt and during posterior pelvis
tilt. R
2
values were used to assess the strength of the kinematic relationship between the pelvis
and femur at each hip flexion angle.

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INTRODUCTION
The hip joint is a complex, anatomical structure comprised of the pelvis and the femur.
The inherent stability of the hip occurs secondary to the ball and socket bony morphology, the
thick capsule and ligaments (Philippon et al., 2014; Safran et al., 2013), and the strong muscles
surrounding the joint (Safran et al., 2013). As a result of the highly congruent nature of this joint
and the closely approximated joint surfaces (Llopis et al., 2008; Safran et al., 2013) it is likely
that movement of one segment may influence the other.
Previous studies have suggested a potential relationship between transverse plane femur
and sagittal plane pelvis motions. Duval, et al. (Duval et al., 2010) reported that internal rotation
of the lower extremity during standing resulted in an anterior pelvis tilt and external rotation of
the lower extremity resulted in a posterior pelvis tilt. These authors proposed that this kinematic
relationship occurred as a direct result of bony approximation between the femoral head and the
acetabulum. Further support for kinematic coupling between the pelvis and the femur comes
from studies in which calcaneal wedging was used to induce foot pronation (Khamis & Yizhar,
2007; Pinto et al., 2008; Tateuchi et al., 2011). These studies revealed that calcaneal eversion
resulted in internal tibia rotation, internal femur rotation, and anterior pelvis tilting. The
kinematic relationship between the pelvis and femur has been shown to exist during bilateral
(Khamis & Yizhar, 2007; Pinto et al., 2008) and unilateral standing (Pinto et al., 2008; Tateuchi
et al., 2011).
The fact that transverse plane motion of the femur can influence sagittal plane motion of
the pelvis is suggestive of kinematic coupling between these two segments. Coupling arises
when a force or torque in one direction causes motion in another direction (Raynor et al., 1987).
At the foot-ankle complex, for example, there is a well-studied relationship between calcaneal
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eversion and internal tibia rotation (Hintermann et al., 1994; Tillman et al., 2005). In the cervical
spine, axial rotation has been shown to be coupled with ipsilateral lateral flexion (Cook et al.,
2006; Wachowski et al., 2009). While previous research supports the premise that internal femur
rotation contributes to anterior pelvis tilt, it is not clear if the same coupling relationship occurs
reciprocally (i.e. whether sagittal plane pelvis motion influences transverse plane femur motion).
Additionally, research in this area has focused on upright standing postures, so it is not known if
the same coupling behavior exists at greater hip flexion angles similar to those that occur during
functional tasks.
The purpose of the current study was to systematically explore whether there is a
consistent and predictable kinematic relationship between sagittal plane motion of the pelvis and
transverse plane motion of the femur during anterior and posterior pelvis tilting. It was
hypothesized that sagittal plane pelvis motion and transverse plane femur motion would be
significantly correlated at various hip flexion angles. It also was hypothesized that the ratio
between transverse femur motion and sagittal pelvis motion would be similar between anterior
and posterior pelvis tilting. The presence of kinematic coupling at the hip joint may have
implications for clinical conditions where internal femur rotation has been shown to be
contributory to pathology (i.e. femoroacetabular impingement).

METHODS
Participants
Sixteen subjects (nine females and seven males between the ages of 22-43 years)
participated in this study. Participants had no history of hip pain, no previous hip surgery, and no
complaints of lower extremity or low back pain during the preceding 6 months. Data collection
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occurred in the Jacquelin Perry Musculoskeletal Biomechanics Research Laboratory at the
University of Southern California. Prior to participation, all subjects were informed of the
purpose of the study and provided written informed consent.

Procedures
Three-dimensional kinematics were collected at 250 Hz using an 11-camera Qualisys
motion analysis system (Qualisys AB, Göteborg, Sweden). Reflective markers (11 mm diameter)
were placed on the most distal aspect of the second toes, the first and fifth metatarsal heads, the
medial and lateral malleoli, the medial and lateral femoral epicondyles, the greater trochanters,
the iliac crests, the L5-S1 junction, and the lateral aspects of the bilateral acromia. Semi-rigid
plastic plates with mounted tracking markers were secured to the heels, shanks, and thighs. Prior
to data collection, a standing calibration trial was collected to determine the segmental
coordinate systems and the joint centers. All markers were then removed with the exception of
the semi-rigid clusters and the markers on the iliac crests, L5-S1, and the bilateral acromia.
Subjects were instructed to stand upright with the feet shoulder width apart and toes
pointing forward with shoulders flexed to 90°. Participants then performed a maximum anterior
and posterior pelvis tilt without moving at the trunk or flexing the knees. Subjects practiced this
motion at a set pace of 20 beats-per-minute in each direction (maximum anterior pelvis tilt to
maximum posterior pelvis tilt).
Following familiarization with the movement, five continuous repetitions of this task
were performed. Subjects then performed a bilateral squat to 30° of hip flexion as determined
using a goniometer. Starting from this position, subjects again performed five repetitions of
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maximum anterior and posterior tilt of the pelvis at the same pace described above. This task
subsequently was performed at hip flexion angles of 60° and 90° (Figure 3-1).

Figure 3-1. Subject performing maximum posterior pelvis tilt (left) to maximum anterior pelvis
tilt (right) at 60° of hip flexion. This task was repeated at hip flexion angles of 0°, 30°, and 90°.

Data Analysis
Three-dimensional kinematic data were processed with Visual 3D software (C-motion,
Inc., Germantown, MD). Data were low-pass filtered at 6 Hz using a 4th-order Butterworth filter.
The middle three repetitions at each hip flexion angle for each subject were averaged. The femur
and pelvis angles were calculated as the orientation of the femur and pelvis segments relative to
the global coordinate system. The average angle-angle plot was calculated across the 16 subjects
at each hip flexion angle.

Statistical Analysis
The ratio of femur transverse motion to pelvis sagittal motion was calculated at each hip
flexion angle as the slope of the ordinary least squares regression line during the period of
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anterior pelvis tilt and during the period of posterior pelvis tilt using Microsoft Excel 2010
(Microsoft Excel, Redmond, WA). This provided an estimate of the change in femur transverse
rotation per degree of pelvis sagittal tilt.

RESULTS
Mean transverse plane femur excursions during the 0°, 30°, 60°, and 90° hip flexion
angle conditions were 7.4 + 4.3°, 7.0 + 5.5°, 5.6 + 4.2°, and 5.3 + 2.8°, respectively. Mean
sagittal plane pelvis excursions during the 0°, 30°, 60°, and 90° hip flexion angle conditions were
23.4 + 7.5°, 20.8 + 12.2°, 20.3 + 11.9°, and 16.6 + 8.9°, respectively. The average femur
transverse motion to pelvis sagittal motion ratios ranged from 0.23 to 0.32 and from 0.25 to 0.31
for anterior and posterior tilting, respectively (Table 3-1 and Figures 3-2 and 3-3). The R
2
values
between femur transverse and pelvis sagittal motion indicated a strong, linear relationship at each
hip flexion angle tested (R
2
values of 0.97 or greater; Figures 3-2 and 3-3).

Table 3-1. Coupling ratios during maximum pelvis sagittal plane excursion for periods of
anterior and posterior pelvis tilt
0° Hip
Flexion
30° Hip
Flexion
60° Hip
Flexion
90° Hip
Flexion
Internal Femur Rotation: Anterior Pelvis Tilt 0.32 : 1 0.30 : 1 0.23 : 1 0.26 : 1
External Femur Rotation: Posterior Pelvis Tilt 0.31 : 1 0.31 : 1 0.25 : 1 0.29 : 1
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Figure 3-2. Average angle-angle diagram of the femur transverse plane kinematics versus the pelvis sagittal plane kinematics at hip
flexion angles of 0°, 30°, 60°, and 90° while performing a maximum anterior pelvis tilt from a maximum posterior pelvis tilt. Star
indicates starting point.

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0° Hip Flexion
30° Hip Flexion
60° Hip Flexion
90° Hip Flexion
Pelvis Posterior
Tilt
Femur External Rotation
Pelvis Anterior
Tilt
Femur Internal Rotation
R
2
=0.97
R
2
=0.98
R
2
=0.98
R
2
=0.99
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Figure 3-3. Average angle-angle diagram of the femur transverse plane kinematics versus the pelvis sagittal plane kinematics at hip
flexion angles of 0°, 30°, 60°, and 90° while performing a maximum posterior pelvis tilt from a maximum anterior pelvis tilt. Star
indicates starting point.
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0!
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0° Hip Flexion
30° Hip Flexion
60° Hip Flexion
90° Hip Flexion
Pelvis Anterior
Tilt
Pelvis Posterior
Tilt
Femur Internal Rotation
Femur External Rotation
R
2
=0.99
R
2
>0.99
R
2
>0.99
R
2
>0.99
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DISCUSSION
A consistent pattern of kinematic coupling of anterior pelvis tilt and internal femur
rotation (and, conversely, posterior pelvis tilt and external femur rotation) was observed at each
hip flexion angle evaluated. When averaged across all hip flexion angles, for every 5° of anterior
pelvis tilt there was 1.2-1.6° of internal femur rotation. Similarly, for every 5° of posterior pelvis
tilt there was 1.2-1.6° of external femur rotation. This relationship was consistent across hip
flexion angles, suggesting that kinematic coupling between these segments is robust.
Our findings confirm and expand upon previous reports of kinematic coupling between
the femur and the pelvis (Duval et al., 2010; Khamis & Yizhar, 2007; Pinto et al., 2008; Tateuchi
et al., 2011). Consistent with the current study, Duval et al (2010) found a significant
relationship between internal femur rotation and anterior pelvis tilt. Contrary to the findings of
the current study, however, these authors reported that the relationship between external femur
rotation and posterior pelvis tilt was less pronounced than that between internal femur rotation
and anterior pelvis tilt (Duval et al., 2010). The findings of the current study reveal that coupling
was nearly identical during anterior pelvis tilting and posterior pelvis tilting.
To the best of our knowledge, this is the first study to demonstrate that motion of the
pelvis in the sagittal plane can influence motion of the femur in the transverse plane. While it is
beyond the scope of this paper to explain the mechanism underlying the observed coupling,
several possibilities exist. Motion at any joint is heavily influenced by bony anatomy. The hip
joint in particular, is highly congruent with closely approximated joint surfaces (Llopis et al.,
2008; Safran et al., 2013) secondary to its thick capsule (Philippon et al., 2014; Safran et al.,
2013), strong musculature (Safran et al., 2013), and the negative pressure within the joint space
(Nepple et al., 2014). As such, it is logical that motion of one segment would have a predictable
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influence on the other. Many highly congruent joints exhibit kinematic coupling. For example,
the relationship at the foot-ankle complex between calcaneal eversion and tibial internal rotation
has been well documented (Hintermann et al., 1994; Tillman et al., 2005).
Duval, et al. (2010) suggested that internal rotation of the femur causes the femoral head
to rotate posteriorly into the posterior acetabulum which pushes the pelvis into an anterior tilt.
Conversely, it is possible that anterior tilt of the pelvis rotates the acetabulum antero-inferiorly
into the anterior femoral head, which pushes the femur into internal rotation. Other factors, such
as muscle activation, soft tissue length, and bony alignment (i.e. femoral or acetabular version or
inclination) also may influence intersegmental coupling (Duval et al., 2010).
Understanding contributory factors to hip joint motion is important in populations where
abnormal kinematics have been implicated. In persons with femoroacetabular impingement, for
example, anterior pelvis tilt and femur internal rotation increase approximation of the femoral
head-neck junction with the acetabulum (Arbabi et al., 2010; Jorge et al., 2014). Such abutment
is hypothesized to contribute to labral damage (Johnston et al., 2008; Nepple et al., 2011;
Tamura et al., 2013), chondral damage (Johnston et al., 2008; Kaya et al., 2014; Nepple et al.,
2011), and hip osteoarthritis (Agricola et al., 2013; Gosvig et al., 2010). Additionally, kinematic
studies have identified differences in sagittal (Hunt et al., 2013; Lamontagne et al., 2009; Ng et
al., 2014; Rylander et al., 2013) and transverse plane hip and pelvis kinematics (Hunt et al.,
2013; Rylander et al., 2013) between persons with and without femoroacetabular impingement.
Our findings indicate that altered sagittal plane pelvis kinematics may influence hip rotation.
There are certain limitations of this study that should be considered when interpreting the
results. In particular, only isolated motion of the pelvis was examined. The ratio of femur to
pelvis motion may vary during more dynamic tasks that involve greater excursions and muscular
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demands. Additionally, the ratio between femur rotation and pelvis tilt may differ between
weightbearing and non-weightbearing tasks. Furthermore, the coupling behavior only was
evaluated in healthy participants. The reported coupling ratios may differ in persons with hip or
back pain. The ratio also may differ in the presence of abnormal bony morphology of the hip.

CONCLUSIONS
A consistent pattern of kinematic coupling of anterior pelvis tilt and internal femur
rotation and, conversely, posterior pelvis tilt and external femur rotation, was observed at hip
flexion angles ranging from 0°-90°. For every 5° of anterior pelvis tilt there was 1.2-1.6° of
internal femur rotation and for every 5° of posterior pelvis tilt there was a similar 1.2-1.6° of
external femur rotation. Our findings suggest that altered pelvis control or positioning in the
sagittal plane has the potential to influence transverse plane motion of the femur.

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CHAPTER IV
HIP KINEMATICS AND KINETICS IN PERSONS WITH CAM
FEMOROACETABULAR IMPINGEMENT DURING A DEEP SQUAT TASK
Although kinematic comparisons have been made between persons with cam FAI and
pain-free control subjects during tasks involving large hip flexion angles, the kinetics underlying
the observed differences in hip and pelvis kinematics have not been well described. This is
important as it is not known if abnormal hip and pelvis kinematics are driven by abnormal bony
morphology or altered muscular control. The purpose of this study was to compare hip and pelvis
kinematics and kinetics during deep squatting between persons with cam FAI and healthy
controls. Fifteen persons with cam FAI and 15 matched controls performed a deep squatting task.
Peak hip flexion, abduction, and internal rotation, and mean hip extensor, adductor, and external
rotator moments were quantified. Additionally, sagittal femur and sagittal pelvis angles at the
time of peak hip flexion were assessed. Independent t-tests (α < 0.05) were used to evaluate
between group differences.

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INTRODUCTION
Cam femoroacetabular impingement (FAI) is hypothesized to occur secondary to
deformity of the femoral head resulting in a decreased offset at the head-neck junction (Beck et
al., 2005; Ito et al., 2001; Pfirrmann et al., 2006). This impingement results in a less spherical
femoral head and causes a shift in contact location from the acetabular cup and femoral head to
the antero-superior acetabular rim and the femoral head-neck junction (Ganz et al., 2003; Ito et
al., 2001). Research indicates that cam morphology may contribute to the development of labral
pathology (Johnston et al., 2008; Meermans et al., 2010; Nepple et al., 2011; Tamura et al., 2013;
Tanzer & Noiseux, 2004), chondral pathology (Anderson et al., 2009; Beck et al., 2005; Johnston
et al., 2008; Kaya et al., 2014; Nepple et al., 2011), and hip osteoarthritis (Agricola et al., 2013;
Anderson et al., 2009; Beck et al., 2005; Gosvig et al., 2010).
While cam morphology is commonly thought to be an important factor with respect to
hip pathology, many individuals with an aspherical femoral head do not report pain or exhibit
pathology (Allen et al., 2009; Hack et al., 2010; Kang et al., 2010). This suggests that other
factors may be contributing to the development of pain and/or pathology in this population.
Because impingement is proposed to occur as a result of bony abutment at end range of hip
flexion or hip internal rotation (Chegini et al., 2009; Ganz et al., 2003; Ito et al., 2001), abnormal
hip and pelvis kinematics could be a contributing factor.
Several studies have evaluated hip and pelvis kinematics during gait in persons with cam
FAI. The results of these studies are varied and have reported that persons with cam FAI exhibit
small decreases in sagittal (Hunt et al., 2013; Rylander et al., 2013), frontal (Brisson et al., 2013;
Hunt et al., 2013; Kennedy et al., 2009), and transverse plane hip kinematics (Hunt et al., 2013;
Rylander et al., 2013) and diminished frontal plane pelvis motion (Kennedy et al., 2009) when
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compared to healthy controls. A limitation of studies that have evaluated gait in this population is
that maximum hip flexion during level walking is only 20-30° and does not reflect the hip
flexion range thought to be related to impingement (Chegini et al., 2009).
In contrast, fewer studies have performed kinematic evaluations in persons with cam FAI
during tasks involving large hip flexion excursions. Rylander, et al. (2013) reported that
individuals with cam FAI exhibited decreased sagittal plane hip motion and peak hip internal
rotation during stair climbing when compared to healthy controls (Rylander et al., 2013).
Lamontagne, et al. (2009) reported a trend toward decreased total plane sagittal pelvis excursion
during a maximum depth squat task in persons with cam FAI compared to healthy controls.
These authors reported no differences in hip kinematics or in the pelvis angle at peak hip flexion,
the time point most important with respect to impingement (Lamontagne et al., 2009). Ng, et al.
(2014) compared several radiographic variables as well as hip kinematics during a maximum
depth squat between a symptomatic group with cam morphology, an asymptomatic group with
cam morphology, and an asymptomatic group without cam morphology. These authors reported
that diminished total sagittal pelvis excursion during squatting significantly distinguished the
symptomatic cam FAI group from the other two (Ng et al., 2014).
Previous studies in this area indicate that hip kinematics may be altered during
performance of end range of motion functional tasks. Furthermore, deep squatting may be a
differentiating task in this population. Although kinematic comparisons have been made between
persons with cam FAI and pain-free control subjects, only one study to date has evaluated
kinematics and kinetics in persons with cam FAI during a task involving large hip flexion angles.
Kumar, et al. (2014) reported greater peak hip adduction and greater internal rotator moments in
a preliminary investigation of persons with FAI and control subjects during a deep squat task.
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However, this study was limited by the small number of FAI subjects (N=7) and by the fact that
the control group was not age or sex matched to cam FAI group. It is important to further
investigate the kinematic and kinetic profiles of persons with cam FAI and matched controls
during a task involving large hip flexion angles as it is not known if abnormal hip and pelvis
kinematics are solely driven by abnormal bony morphology or altered muscular control. Previous
research has shown that individuals with FAI exhibit hip muscle weakness (Casartelli,
Maffiuletti, et al., 2011), suggesting that impaired muscular control may be contributing to
altered kinematics in this population.
The purpose of the current study was to compare three-dimensional hip kinematics and
kinetics during deep squatting between persons with cam FAI and age and sex matched controls.
I also was interested in comparing the sagittal pelvis and femur angles at the time of peak hip
flexion between groups to determine the kinematic strategy used to achieve hip flexion. Based on
previous research and the potential range of motion limitations due to bony impingement, it was
hypothesized that persons in the cam FAI group would demonstrate decreased peak hip flexion,
decreased peak hip abduction, decreased peak hip internal rotation, and a more anteriorly tilted
pelvis at the time of peak hip flexion. It was also hypothesized that persons with cam FAI would
have diminished hip moments in all three planes during this task.

METHODS
Participants
Thirty participants were recruited for this study: 15 individuals with unilateral
symptomatic cam FAI (nine females, five males) and 15 age and sex matched controls.
Participants in the cam FAI group were recruited from two orthopedic clinics. Persons with cam
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FAI were eligible if they were skeletally mature (Song et al., 2012), 45 years of age or younger,
and had an alpha angle measurement of greater than 50.5° (Beaule, Zaragoza, Motamedi,
Copelan, & Dorey, 2005; Hack et al., 2010; Kennedy et al., 2009; Lamontagne et al., 2009;
Notzli et al., 2002). Persons with cam FAI were excluded if they demonstrated radiographic
signs of hip osteoarthritis (Notzli et al., 2002) or if they had complaints of bilateral hip pain.
Control subjects were recruited from the university community and were age matched
(within 3 years) and sex matched to the subjects with cam FAI. Control subjects were excluded if
there was a history of hip pain, lower extremity or low back surgery, or complaints of lower
extremity or low back pain during the preceding 6 months. A clinical examination was
performed on all control subjects to rule out hip pathology. Specifically, subjects were excluded
if they had a positive log roll test (Martin & Sekiya, 2008), greater than 5 cm asymmetry
between sides with the Flexion ABduction External Rotation test (FABER test) (Philippon et al.,
2007; Vad et al., 2004), or pain with internal rotation of the hip in 90° of hip flexion (Reiman,
Goode, Cook, Holmich, & Thorborg, 2014).
Following the clinical screen, potential control subjects received MRIs to rule out cam
morphology. Subjects were excluded if they demonstrated radiographic evidence of cam FAI
(alpha angle greater than 50.5° measured via axial oblique MRIs), hip dysplasia, or pincer FAI
(lateral center edge angle less than 20° or greater than 40° measured via coronal pelvis MRIs)
(Gold, Burge, & Potter, 2012). Prior to participation, all subjects were informed of the purpose of
the study and provided written informed consent and HIPPA authorization.

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Instrumentation
Three-dimensional kinematics were collected at 250 Hz using an 11-camera Qualisys
motion analysis system (Qualisys AB, Göteborg, Sweden) and ground reaction forces were
collected at 1500 HZ using a force plate (Advanced Medical Technology, Inc., Watertown, MA).
Reflective markers (11mm diameter) were placed on the most distal aspect of the second toes,
the first and fifth metatarsal heads, the medial and lateral malleoli, the medial and lateral femoral
epicondyles, the greater trochanters, the iliac crests, the anterior superior iliac spines, the L5-S1
junction, and the lateral aspects of the bilateral acromia. Semi-rigid plastic plates with tracking
markers mounted to them were secured to the heels, shanks, and thighs. A standing calibration
trial was collected to determine the segmental coordinate systems and the joint axes. All markers
were then removed with the exception of the semi-rigid clusters and the markers on the iliac
crests, L5-S1, and the bilateral acromia.

Procedures
Prior to the biomechanical assessment, all participants completed the hip outcome score
(Martin, Kelly, & Philippon, 2006; Martin & Philippon, 2007, 2008). The hip outcome score
subscales for activities of daily living and sports have been reported to be valid and reliable
measurements for persons with acetabular labral tears and FAI (Lodhia, Slobogean, Noonan, &
Gilbart, 2011; Martin et al., 2006; Martin & Philippon, 2008). Individuals in the cam FAI group
also rated their current and worst pain over the previous week.
For biomechanical testing, subjects were instructed to perform a bilateral squat while
standing with the involved limb on a force plate, feet shoulder width apart, and toes pointing
forward. Shoulders were flexed to 90° and a step was placed behind the subject at one-third the
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height of the subject’s tibial tuberosity (Lamontagne et al., 2009) (Figure 4-1) . Subjects were
asked to “squat as low as possible, coming as close as possible to the step.” Subjects were
instructed to maintain heel contact throughout the task. Five consecutive squats were performed
at a pace of 1.33 seconds descent and 1.33 seconds ascent controlled via a metronome.

Figure 4-1. Example of the deep squat task

Data Analysis
Using Visual 3D software (C-motion, Inc., Germantown, MD), kinematic data were low-
pass filtered at 6 Hz and ground reaction force data was low-pass filtered at 20 Hz using a 4th-
order Butterworth filter. The middle three repetitions of the squat task were averaged for
analysis. Hip kinematics were calculated as the motion of the pelvis relative to the femur. The
femur and pelvis angles were calculated as the orientation of the femur and pelvis segments
relative to the global coordinate system. Inverse dynamics equations were utilized to calculate
the net joint moments. Mean moments were reported as internal moments normalized to body
mass. Moment data were averaged between 20-80% of the squat cycle.

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Statistical Analysis
Variables of interest included peak hip flexion, peak hip abduction, peak hip internal
rotation, mean hip extensor moment, mean hip adductor moment, and mean hip external rotator
moment. Peak femur flexion and pelvis angle at the time of peak hip flexion also were evaluated.
Between group differences in demographic data were evaluated using two-tailed independent t-
tests. The kinematic and kinetic variables of interest were assessed using one-tailed independent
t-tests. Statistical analyses were performed using PASW software (SPSS, Inc., Chicago, IL).

RESULTS
The cam FAI group and the control group were similar with respect to age, height, and
mass (Table 4-1). Participants in the cam FAI group were moderately impaired based on hip
outcome scores of 65.8 + 15.9 on the activities of daily living subscale and 36.5 + 20.8 on the
sports subscale (Table 4-1).

Table 4-1. Demographic and functional outcome data (mean + standard deviation)
Control
Group
Cam FAI
Group
p value
Age (years) 31.9 + 7.6 32.2 + 7.8 0.925
Height (cm) 169.9 + 9.1 171.0 + 9.6 0.761
Mass (kg) 69.6 + 16.0 72.1 + 14.7 0.647
Hip Outcome Score ADL (0-100) 100 + 0 65.8 + 15.9
Hip Outcome Score Sports (0-100) 100 + 0 36.5 + 20.8
VAS Score (pre) (0-10 cm) NA 3.4 + 2.5
VAS Score (worst over last week) (0-10 cm) NA 6.4 + 2.4
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Persons in the cam FAI group exhibited decreased peak hip internal rotation during the
squat task compared to the control group (9.4 + 7.8° vs. 15.2 + 9.5°; p=0.041) (Table 4-2 and
Figure 4-2). At the time of peak hip flexion, persons in the cam FAI group exhibited decreased
posterior pelvis tilt (23.4 + 11.2° vs. 12.5 + 17.1°; p=0.032) and decreased peak femur flexion
compared to the control group (83.2 + 19.0° vs. 100.4 + 13.4°; p=0.004) (Table 4-2 and Figure
4-3). There were no differences in peak hip flexion or peak hip abduction between groups (Table
4-2 and Figure 4-2).
Persons in the cam FAI group demonstrated decreased mean hip extensor moments
compared to the control group (0.45 + 0.15 Nm/kg vs.0.56 + 0.12 Nm/kg; p=0.018). There were
no differences in the mean hip adductor moment or mean hip external rotator moment between
groups (Table 4-2 and Figure 4-4).

Table 4-2. Kinematic and kinetic data during the deep squat task (mean + standard deviation)
Control
Group
Cam FAI
Group
p value
Peak Hip Flexion (°) 113.0 + 6.7 106.6 + 14.0 0.065
Peak Hip Abduction (°) 11.9 + 6.8 11.8 + 6.2 0.961
Peak Hip Internal Rotation (°) 15.2 + 9.5 9.4 + 7.8 0.041
Pelvis Angle at Peak Hip Flexion (°) 12.5 + 17.1 23.4 + 11.2 0.032
Femur Angle at Peak Hip Flexion (°) 100.4 + 13.4 83.2 + 19.0 0.004
Mean Hip Extensor Moment (Nm/kg) 0.56 + 0.12 0.45 + 0.15 0.018
Mean Hip Adductor Moment (Nm/kg) 0.09 + 0.17 0.12 + 0.11 0.633
Mean Hip External Rotator Moment (Nm/kg)
0.05 + 0.10 0.06 + 0.10 0.626
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Figure 4-2. Comparison of hip kinematics between groups A) sagittal plane B) frontal plane and C) transverse plane

Figure 4-3. Comparison of sagittal plane kinematics between groups A) pelvis B) femur and C) hip

0 20 40 60 80 100
0
20
40
60
80
100
120
Sagittal Plane Hip
Percent of Squat
Degrees Hip Flexion

CAM
CON
0 20 40 60 80 100
0
5
10
15
Frontal Plane Hip
Percent of Squat
Degrees Hip Abduction

CAM
CON
0 20 40 60 80 100
-10
-5
0
5
10
15
20
Transverse Plane Hip
Percent of Squat
Degrees Hip Internal Rotation

CAM
CON
0 20 40 60 80 100
0
5
10
15
20
25
30
35
Sagittal Plane Pelvis
Percent of Squat
Degrees Pelvis Anterior Tilt

CAM
CON
0 20 40 60 80 100
0
20
40
60
80
100
Sagittal Plane Femur
Percent of Squat
Degrees Femur Flexion

CAM
CON
0 20 40 60 80 100
0
20
40
60
80
100
120
Sagittal Plane Hip
Percent of Squat
Degrees Hip Flexion

CAM
CON
A) B) C)
A) B) C)
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Figure 4-4. Comparison of hip kinetics between groups A) sagittal plane B) frontal plane and C) transverse plane
0 20 40 60 80 100
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
Sagittal Plane Hip
Percent of Squat
Nm/kg (Extensor (-))

CAM
CON
0 20 40 60 80 100
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
Frontal Plane Hip
Percent of Squat
Nm/kg (Adductor (-))

CAM
CON
0 20 40 60 80 100
-0.2
-0.1
0
0.1
Transverse Plane Hip
Percent of Squat
Nm/kg (External Rotator (-))

CAM
CON
A) B) C)
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DISCUSSION
Persons with cam FAI demonstrated altered kinematics and kinetics during deep
squatting compared to the control group. Specifically, the cam FAI group exhibited decreased
peak hip internal rotation and decreased pelvis posterior tilt at the time of peak hip flexion. The
cam FAI group also exhibited decreased mean hip extensor moments compared to the control
group.
On average, the cam FAI group had approximately 6° less hip internal rotation compared
to the control group. This finding is consistent with Rylander et al (2013) who reported
decreased peak hip internal rotation in persons with cam FAI during stair climbing (Rylander et
al., 2013). Conversely, Lamontagne, et al. (2009) and Kumar, et al. (2014) found no difference in
peak hip internal rotation during deep squatting in persons with cam FAI compared to control
subjects (Kumar et al., 2014; Lamontagne et al., 2009). Lamontagne, et al. (2009) used a similar
study design and patient population as the current study. In the study by Kumar, et al. (2014)
study participants were instructed to squat to a depth of 25% of the participant’s height
(approximately 80° peak hip flexion, compared to greater than 100° in the current study).
Therefore, the conflicting results may be a reflection of the heterogeneity of this population or
may be the result of different squat depths evaluated.
Despite the diminished peak hip internal rotation observed in the cam FAI group, there
was no difference in the mean hip external rotator moment between groups. As such, the
observed decrease in peak hip internal rotation in the cam FAI group cannot be explained by
greater external rotator muscular control. This suggests that bony abutment may have contributed
to the diminished hip internal rotation observed in the cam FAI group. This seems logical given
previous reports of a relationship between cam morphology and diminishing passive hip internal
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rotation range of motion (Audenaert et al., 2012; Notzli et al., 2002; Wyss et al., 2007).
Additionally, a previous finite element modeling study by Jorge, et al. (2014) demonstrated the
extent to which cam morphology can limit hip internal rotation. These authors found that at 90°
of hip flexion, internal rotation was limited to 2.8° in the presence of a large cam deformity
(alpha angle 98°) (Jorge et al., 2014). A post-hoc analysis of the data obtained in the current
study revealed that the degree of cam morphology and peak hip internal rotation during the deep
squat task were inversely correlated (R=0.476; p=0.04).
Persons with cam FAI also exhibited diminished posterior tilt of the pelvis as participants
approached maximum depth compared to the control group. This finding is consistent with
Lamontagne, et al. (2009), who reported a trend toward decreased total sagittal pelvis motion
during a maximum depth squat in persons with cam FAI. These authors suggested that decreased
posterior motion of the pelvis was the primary explanation for this trend (Lamontagne et al.,
2009). Decreased posterior pelvis tilt (or a more relatively anteriorly tilted pelvis) would be
expected to increase impingement between the femur and the acetabulum, particularly during a
task involving deep hip flexion.
The observed decrease in posterior pelvis tilt in persons with cam FAI may be the result
of several factors including decreased lumbopelvic mobility, guarding, or altered hip extensor
muscle activation. With respect to the latter, a significant decrease in the mean hip extensor
moment was found in the cam FAI group. The decreased hip extensor moment implies decreased
utilization of the hip extensors to accomplish the squat task. In particular, decreased activation of
the gluteus maximus and/or hamstring muscles could have contributed to the lack of posterior
pelvis tilt. Hypothetically, more relative posterior tilt of the pelvis during this phase of squatting
would limit the potential for impingement in the presence of cam morphology.
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Despite the decrease in posterior pelvis tilt observed in persons with cam FAI, there was
no difference in peak hip flexion. This finding is consistent with previous investigations of squat
kinematics in this population (Kumar et al., 2014; Lamontagne et al., 2009). In the current study,
the relative contribution of the pelvis and the femur in achieving peak hip flexion differed
between groups. At the time of peak hip flexion persons with cam FAI demonstrated decreased
femur flexion (almost an 18° decrease in femur flexion compared to the control group). This
coupled with greater relative anterior pelvis tilt resulted in the similar hip flexion angle. Reduced
femur flexion in the cam FAI group is meaningful because an inability to flex the femur may
result in difficulty preforming tasks such as sitting down in a low chair.
Despite significant differences in sagittal and transverse plane kinematics and kinetics,
there were no differences in peak hip abduction or mean hip adductor moments between groups.
Similarly, previous kinematic analyses have failed to identify frontal plane differences in this
population during squatting (Lamontagne et al., 2009) or stair climbing (Rylander et al., 2013).
Given the bilateral nature of squatting, this finding is not surprising. It is likely that unilateral
tasks involving greater frontal plane demands would be more informative of frontal plane
control.
Taken together, the results of our study suggest that clinical strategies to improve
posterior tilt of the pelvis and external rotation of the femur may protect against impingement.
Previous studies have reported hip muscle weakness in persons with FAI (Casartelli, Leunig,
Item-Glatthorn, Lepers, & Maffiuletti, 2011; Casartelli, Maffiuletti, et al., 2011). In particular,
the gluteus maximus may be important given its ability to posteriorly tilt the pelvis and
externally rotate the femur. Future research should examine the effect of hip strengthening or
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neuromuscular retraining of hip extensor muscles on hip and pelvis biomechanics, pain, and
function in this population.
The current study has several limitations. All participants in the cam FAI group were
symptomatic prior to testing; therefore, it is not possible to determine if altered kinematics or
kinetics were the cause or effect of pain. In either scenario, however, it could be argued that the
kinematics displayed may be perpetuating pathology in persons with cam FAI. Additionally,
electromyographic and strength data were not collected as a part of this study. Future studies
should obtain such data to allow for a more complete understanding of the underlying differences
in hip and pelvis kinematics and kinetics.

CONCLUSIONS
Persons with cam FAI exhibit altered hip and pelvis kinematics and kinetics during a
deep squat task. Specifically, persons with cam FAI demonstrated decreased hip internal
rotation, decreased posterior pelvis tilt, and diminished hip extensor moments. Our findings
suggest that altered kinematics may contribute to FAI and that the observed kinematic
differences may have neuromuscular influences.

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CHAPTER V
ACETABULAR STRESS IN PERSONS WITH AND WITHOUT CAM
FEMOROACETABULAR IMPINGEMENT: FINITE ELEMENT ANALYSIS OF A
DEEP SQUAT TASK
Cam femoroacetabular impingement (FAI) can cause mechanical impingement during
tasks involving large hip flexion angles (Clohisy et al., 2009; Ito et al., 2001; Myers et al., 1999;
Sierra et al., 2008; Tanzer & Noiseux, 2004). The purpose of this chapter was to evaluate the
contact location and magnitude of acetabular stress in simulated finite element models of cam
FAI using kinematic data from Chapter IV. MRI data was collected from one asymptomatic
person who did not have FAI morphology or hip dysplasia. Models were created to simulate
three different magnitudes of cam morphology reflecting the cam FAI group in Chapter IV.
Mean control group and cam group kinematics at peak hip flexion from Chapter IV were applied
to the control model and cam models, respectively. Simulations used force values from a
previous instrumented hip prosthesis study (Bergmann et al., 2001). The variables of interest
were contact location and the peak acetabular von Misses stress.

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INTRODUCTION
The term femoroacetabular impingement (FAI) refers to hip pain and pathology in the
presence of specific bony morphology. Cam FAI morphology is defined as a decreased offset at
the femoral head-neck junction (Beck et al., 2005; Ito et al., 2001; Pfirrmann et al., 2006). The
less spherical, cam-type femoral head has been reported to cause a shift in contact location from
the acetabular cup and femoral head to the antero-superior acetabular rim and the femoral head-
neck junction (Ganz et al., 2003; Ito et al., 2001). Impingement primarily occurs with actions that
involve large degrees of hip flexion and hip internal rotation (Clohisy et al., 2009; Ito et al.,
2001; Myers et al., 1999; Sierra et al., 2008; Tanzer & Noiseux, 2004). Therefore, knowledge of
the interplay between both bony morphology and joint kinematics in persons with cam FAI is
important to understanding the etiology of this condition.
In Chapter IV it was reported that persons with cam FAI exhibited decreased pelvis
posterior tilt and decreased peak hip internal rotation compared to control subjects during a deep
squat task. However, it could not be definitively determined if this kinematic profile represented
a protective mechanism for persons with cam FAI to avoid impingement or if the observed
kinematic differences were limited as a result of bony abutment. Furthermore, it is not known
how much of a cam lesion is necessary for the contact location to shift or for contact stress to
increase given these altered kinematics.
Although previous finite element analyses and computational models have examined the
influence of FAI on joint contact mechanics (Arbabi et al., 2010; Chegini et al., 2009; Jorge et
al., 2014; Tannast, Kubiak-Langer, et al., 2007), only one study has directly incorporated
kinematics from persons with cam FAI and control subjects. Ng, et al. (2012) utilized finite
element modeling to simulate a maximum depth squat task using the bony morphology of two
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persons with cam FAI and two persons without cam FAI. While the bony morphology differed
between the models, it was not clear if the kinematics were different between these participants.
Additionally, the participants with FAI in the study by Ng, et al. (2012) had extreme cam
morphology (Ng et al., 2014). To date, stress profiles in the presence of more moderate cam
morphology have not been explored.
Given the potential contribution of hip and pelvis kinematics to FAI, the purpose of this
study was to evaluate the contact location and magnitude of acetabular joint stress in a finite
element model using the respective group kinematics and morphological profiles of persons with
cam FAI and matched controls during a deep squat task. It was hypothesized that the cam FAI
models would demonstrate increased joint stress and a shift in contact location compared to the
control model.

METHODS
Participant
One asymptomatic male (age 28, height 177.8 cm, mass 77.1 kg) who did not have FAI
morphology or hip dysplasia (alpha angle 41.9° and 20°< lateral center edge angle < 40°)
participated in this study. Prior to participation, the subject was informed of the purpose of the
study and provided written informed consent and HIPPA authorization.

MR Assessment
Magnetic resonance images of the hip and pelvis were obtained with the participant in
neutral hip alignment using a sagittal 3D high resolution, fat-suppressed, fast spoiled gradient
recall echo sequence with repetition time of 16.3 ms, echo time of 2.1 ms, flip angle of 12°,
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matrix 256 x 256, 1 mm slice thickness, and a 10 cm field of view in a 3 Tesla GE MR scanner
(General Electric Healthcare, Milwaukee, WI).

Finite Element Model Development
MR images of the femur and hemipelvis were manually segmented using a commercial
software package (Sliceomatic, Tomovision, Montreal, Quebec) and the femur and hemipelvis
meshes were created using a finite element pre-processor (Hypermesh, Altair Engineering Inc.,
Troy, MI). The femur was modeled as a rigid body and the acetabulum was modeled using
homogenous, isotropic, tetrahedral continuum elements with an elastic modulus of 17.0 MPa and
a Poisson ratio of 0.30 (Rapperport, Carter, & Schurman, 1985; Wei, Sun, Jao, Yeh, & Cheng,
2005).
Three different cam models were created in Hypermesh by manually adding nodes to the
control model femur at the 1:30 position of the femoral head-neck junction. This location was
chosen as a less spherical femoral head in this area has been most associated with the
development of hip pain (Khanna, Caragianis, Diprimio, Rakhra, & Beaule, 2014). The femoral
head-neck junction morphology was recreated three separate times to correspond to: 1) the
minimum cam bony morphology required to establish the presence of cam FAI (alpha angle
50.5°), 2) the average cam bony morphology for persons with cam FAI in Chapter IV (alpha
angle 54°), and 3) the maximum cam bony morphology for persons with cam FAI in Chapter IV
(alpha angle 66°).
After the femoral head-neck geometry was altered, the respective meshes were recreated
using an element size of 1 mm. Using the kinematic data from Chapter IV, the mean three-
dimensional hip angles at the time of peak hip flexion for the control group were utilized in the
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control model and the mean three-dimensional hip angles for the cam group were utilized in the
cam models (Table 5-1). Detailed procedures utilized to obtain kinematic data from a deep squat
task in persons with and without cam FAI are reported in Chapter IV.

Table 5-1. Hip kinematics used for control and cam finite element models
Control
Group
Cam FAI
Group
Hip Flexion (°) 112.6 106.3
Hip Abduction (°) 10.5 10.5
Hip Internal Rotation (°) 14.8 8.9

Finite element analysis was performed using a nonlinear solver (Abaqus, SIMULIA,
Providence, RI) using a hard contact algorithm with the femur as the master surface and the
acetabulum as the slave surface, with a surface-to-surface, small sliding contact and a surface
coefficient of friction of 0.02 (Besier, Gold, Delp, Fredericson, & Beaupre, 2008). The
acetabulum was constrained in space and the three rotational degrees of freedom of the femur
were constrained, though translation of the femur was allowed in all directions. The forces used
for each of the simulations were derived from peak hip forces during a stand to sit task reported
by Bergmann, et al. (2001) (Bergmann et al., 2001). Using the approximate mean mass of
subjects in our study (70kg), these forces in the local coordinate system of the femur were
calculated to be 361 N in the x direction (medial), 113 N in the y direction (anterior), and 1195 N
in the z direction (superior) (Figure 5-1) (Bergmann et al., 2001). This force was applied in the
femoral coordinate system.

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Figure 5-1. Depiction of the force vector used for simulations (derived from peak hip forces
found by Bergmann, et al. (2001)) (Bergmann et al., 2001).

Data Analysis
Acetabular average von Mises stress was calculated as the mean stress among the top
10% of stress values from all elements in the acetabular surface (out of 13,386 total elements) in
each of the four different models (one control and three levels of cam morphology). Eswaran, et
al. (2007) previously utilized the top 10% of stress values among all elements to evaluate
vertebral bone strain as a method for better identifying tissue more likely to be at risk of injury
(Eswaran, Gupta, & Keaveny, 2007). Similarly, we were most interested in assessing stress in
the tissue more likely to be at risk of injury in the acetabulum. Descriptive statistics were used to
compare stress values between the control and cam FAI models

RESULTS
The average von Mises Stress values for the control, minimum cam, average cam, and
maximum cam models were 9.64 MPa, 9.27 MPa, 11.36 MPa, and 28.43 MPa, respectively. In
the control model, contact occurred between the acetabular cup and the femoral head (Figure 5-
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2A). Similarly, in the minimum cam model, the contact location remained localized to the
acetabular cup and the femoral head (Figure 5-2B). In the average cam model, the contact shifted
antero-superiorly on the acetabulum (Figure 5-2C). In the maximum cam model, there was an
obvious shift in contact location to the antero-superior rim of the acetabulum and toward the
femoral head neck junction of the femur (Figure 5-2D).

A) B)
C)! !!D)
Figure 5-2. Acetabular stress profiles for the A) control model B) minimum cam model C)
average cam model and D) maximum cam model

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DISCUSSION
Despite the diminished amount of hip flexion and hip internal rotation used in the cam
FAI models, increased stress and a shift in contact location indicative of impingement was
observed. In particular, the degree of cam morphology had a large influence on acetabular stress.
Compared to the control model, the stress values obtained in the minimum cam model were
similar. However, the average cam model resulted in an 18% increase in stress compared to the
control model. The maximum cam model resulted in a 195% increase in stress compared to the
control model.
In addition to the observed increases in joint stress, increasing cam morphology also
resulted in a change in contact location. The contact location observed in the minimum cam
model was similar to that of the control model. However, in the average cam model contact
occurred more antero-superiorly within the acetabular cup. In the presence of the maximum cam
morphology, the contact occurred between the antero-superior acetabular rim and the femoral
head-neck junction, suggesting bony impingement.
The location of contact observed in the maximum cam model corresponds to the most
common location of cartilage and labral damage reported in persons with FAI. For example,
Kaya, et al. (2014) reported the location of cartilage damage observed during 100 consecutive
hip arthroscopies. These authors found that persons with FAI most commonly exhibited
acetabular cartilage damage in the antero-superior and the middle-superior zones (Kaya et al.,
2014). Similarly, the antero-superior zone has been reported to be the most common location of
acetabular labral tears in persons with cam FAI (Tamura et al., 2013). The contact location for
our maximum cam model was within the antero-superior zone and our average cam model was
in the middle-superior zone.
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These observed differences in stress magnitudes and contact locations occurred despite
less hip flexion and hip internal rotation in the cam FAI models compared to the control model.
This suggests that a moderate cam deformity can increase stress even in the presence of
diminished hip motion. Previous studies have identified diminished hip internal rotation
kinematics in persons with cam FAI during functional tasks such as stair climbing (Rylander et
al., 2013) and deep squatting (Chapter IV). It has been hypothesized that reduced hip internal
rotation could be a neuromuscular compensation to avoid impingement or that motion could be
limited secondary to mechanical abutment (Rylander et al., 2013).
The findings of the current study suggest that diminished hip internal rotation during
squatting may be the result of mechanical abutment. If motion were limited due to a
neuromuscular compensation to avoid impingement, a change in stress magnitude and location
would not be expected with increasing cam morphology. Our finding of reduced hip internal
rotation secondary to mechanical abutment is consistent with Jorge, et al. (2014) who utilized
finite element modeling to demonstrate that when the hip is in a flexed position, a cam deformity
can significantly limit hip internal rotation. These authors found that at 90° of hip flexion,
internal rotation was limited to 2.8° in the presence of a large cam deformity (alpha angle 98°)
(Jorge et al., 2014).
The results of the current study are consistent with the findings of Chegini, et al. (2009)
and Arbabi, et al. (2010) who reported that during a stand to sit task, greater cam deformity
resulted in increased joint stress (Arbabi et al., 2010; Chegini et al., 2009). Our results are also
consistent with the findings of Ng, et al. (2012) who reported higher stress during a simulated
maximum depth squat task in two subject-specific cam models (severe cam morphology- alpha
angles of 73° and 83°) compared to two control models (alpha angles of 42° and 45°) (Ng et al.,
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2012). These authors did not report the kinematic values, so it was not possible to compare the
combined effect of bony morphology and hip kinematics in their study to the current findings.
However, the results of both studies suggest that stresses may be elevated in persons with cam
FAI during squatting.
Our study has several limitations. Due to the close approximation of the hip joint
surfaces, the thinness of the acetabular and femoral cartilage, and computational demands, the
cartilage surfaces were not included in this model. It is likely that the inclusion of cartilage
would decrease absolute stress values, but the contact location would not be expected to vary
significantly. Additionally, because the focus was on the effects of bony geometry and
kinematics only, the same force vector was utilized in all models. Hip joint forces would likely
differ in magnitude and direction across subjects. Lastly, I chose to focus solely on manipulation
of the alpha angle and kinematics, therefore other subtle anatomical variations, such as
differences in femoral or acetabular version between groups were not considered in this study.
Future research should consider both alterations of the force vector, if realistic values can be
obtained, as well as exploration of other anatomical factors.

CONCLUSION
A simulated model of cam FAI with an alpha angle of 54° resulted in increased stress and
a shift in contact location. This occurred despite less hip flexion and hip internal rotation. This
finding suggests that previous reports of decreased hip internal rotation are the result of bony
abutment. Additionally, a modest cam deformity may have a deleterious effect on contact stress
and location.
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CHAPTER VI
SUMMARY AND CONCLUSIONS
Cam femoroacetabular impingement (FAI) is a cause of chondral damage (Anderson et
al., 2009; Beck et al., 2005; Johnston et al., 2008; Kaya et al., 2014; Nepple et al., 2011), labral
damage (Johnston et al., 2008; Meermans et al., 2010; Nepple et al., 2011; Tamura et al., 2013;
Tanzer & Noiseux, 2004), and hip osteoarthritis (Agricola et al., 2013; Anderson et al., 2009;
Beck et al., 2005; Gosvig et al., 2010). Cam morphology refers to decreased offset at the femoral
head-neck junction (Beck et al., 2005; Ito et al., 2001; Pfirrmann et al., 2006). A proposed
mechanism contributing to pathology in persons with cam FAI is abutment of the femoral head-
neck junction with the acetabular labrum and/or cartilage. Impingement has been shown to occur
at end range hip flexion and hip internal rotation (Clohisy et al., 2009; Ito et al., 2001; Myers et
al., 1999; Sierra et al., 2008; Tanzer & Noiseux, 2004). Due to the movement dependent nature
of this pathology, understanding hip kinematics and kinetics may be important to understanding
this condition. As such, the primary objective of this dissertation was to examine hip and pelvis
kinematics and kinetics in persons with cam FAI.
Previous literature suggests that the range of motion and kinematic impairments in this
population involve sagittal plane pelvis or hip motion and transverse plane hip motion
(Audenaert et al., 2012; Clohisy et al., 2009; Hunt et al., 2013; Lamontagne et al., 2009;
Philippon et al., 2007; Rylander et al., 2013; Wyss et al., 2007). In addition, previous studies
have suggested that these motions may be coupled (Duval et al., 2010; Khamis & Yizhar, 2007;
Pinto et al., 2008; Tateuchi et al., 2011). Therefore, it is important to understand the normal
kinematic relationship between motion of the femur and motion of the pelvis prior to
understanding these movements in a symptomatic population.
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The purpose of Chapter III was to systematically explore whether there is a consistent
and predictable kinematic relationship between sagittal plane motion of the pelvis and transverse
plane motion of the femur during anterior and posterior pelvis tilt in healthy individuals. In
accordance with my hypothesis, a consistent pattern of kinematic coupling of internal femur
rotation and anterior pelvis tilt (and, conversely, external femur rotation and posterior pelvis tilt)
was observed at each hip flexion angle tested. When averaged across all hip flexion angles, for
every 5° of anterior pelvis tilt there was 1.2-1.6° of internal femur rotation and for every 5° of
posterior pelvis tilt there was 1.2-1.6° of external femur rotation. This relationship was consistent
across all hip flexion angles tested, suggesting that kinematic coupling between these segments is
robust. The implication of this finding for persons with FAI is that normal kinematic coupling
dictates that increased anterior pelvis tilt results in femur internal rotation. Thereby, anterior
pelvis tilt has the potential to increase impingement, whereas posterior pelvis tilt may be
protective against impingement.
After establishing these kinematic relationships in healthy persons, hip kinematics and
kinetics were evaluated in persons with cam FAI. Specifically, the purpose of Chapter IV was to
compare three-dimensional hip kinematics and kinetics during a deep squat task between persons
with cam FAI and age and sex matched controls. Compared to the control group, persons with
cam FAI exhibited decreased peak hip internal rotation, decreased posterior pelvis tilt, and
decreased mean hip extensor moments. Despite the diminished hip internal rotation, there were
no differences in hip external rotator moments between groups. This suggests that bony
abutment, rather than hip external rotator control contributed to the diminished hip internal
rotation observed in the cam FAI group. This seems logical given the previous reports of a
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relationship between cam morphology and diminishing passive hip internal rotation range of
motion (Audenaert et al., 2012; Notzli et al., 2002; Wyss et al., 2007).
To further explore the influence of actual kinematics in persons with cam FAI, the
purpose of Chapter V was to evaluate the contact location and magnitude of acetabular joint
stress in a finite element model using the respective group kinematics and morphological profiles
of persons with cam FAI and matched controls from Chapter IV. This study also sought to
clarify how much of a cam lesion was necessary for the contract location to shift or for contact
stress to increase given the kinematics.
Despite attenuated hip flexion and hip internal rotation in persons with cam FAI, the
average and maximum cam models resulted in increased acetabular stress and an antero-superior
shift in contact locations. The contact locations observed in Chapter V corresponded to the
locations of cartilage and labral pathology reported in persons with FAI (Endo et al., 2010;
Tamura et al., 2013). These findings suggest that the reduced hip internal rotation observed in the
cam FAI group in Chapter IV may have been the result of bony impingement. Additionally,
these results demonstrate that a small difference in cam deformity can have a substantial effect
on joint stress, as was observed with the large stress increases between the minimum and the
average cam FAI models. Therefore, while kinematic differences may be important with respect
to pathology in persons with cam FAI, bony anatomy appears to be important as well.
Taken together the three studies that comprise this dissertation suggest that altered hip
and pelvis kinematics may play a role in FAI. The finding of decreased pelvis posterior tilt (or a
more relatively anteriorly tilted pelvis) in persons with cam FAI could result in increased
impingement between the femur and the acetabulum. This indicates that the inability of the
pelvis to posteriorly tilt during a deep squat may be contributing to bony impingement in persons
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with cam FAI. Additionally, the findings of decreased posterior pelvis tilt and decreased hip
internal rotation in persons with cam FAI is contrary to the coupling behavior reported in
Chapter III. This departure from the typical coupling behavior of the pelvis and the hip in
persons with cam FAI further suggests that bony morphology may be limiting hip internal
rotation in persons with cam FAI.
The results of this dissertation suggest a potential avenue for non-surgical interventions in
persons with cam FAI. Addressing sagittal pelvis motion, specifically facilitating increased
posterior pelvis tilt, may be beneficial in persons with cam FAI. Possible explanations for the
observed decrease in posterior pelvis tilt in persons with cam FAI were not explored in this
dissertation; however, possible contributing factors include decreased lumbopelvic mobility,
guarding, or altered hip extensor muscle strength and/or activation.
With respect to the data collected in this dissertation, the decreased hip extensor moment
demonstrated by the cam FAI group in Chapter IV implicates decreased utilization of the hip
extensors during the squat task. Therefore, increased activation of the gluteus maximus and
hamstring muscles could potentially aid in increasing posterior pelvis tilt. Hypothetically, more
relative posterior tilt of the pelvis during this phase of squatting may allow for greater femur
flexion prior to impingement. Given the coupling behavior at the hip demonstrated in Chapter
III, increased posterior tilt of the pelvis may be associated with decreased hip internal rotation.
The gluteus maximus also may help to limit impingement by resisting hip internal rotation
during this task.
Significant changes in stress were observed to be associated with small changes in cam
deformity. From a surgical perspective, this illustrates the potential benefits of reducing the size
of the cam lesion in a person with cam FAI (i.e. the benefits of an osteochondroplasty). When
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!
surgery is deemed necessary and the bony morphology is corrected, it is not clear whether
kinematic and kinetic profiles normalize. The results of this dissertation suggest that even if
kinematics and kinetics remain unchanged, stress would be expected to decrease following a
surgery to decrease cam morphology. It is possible that addressing kinematic alterations may
further decrease stress in persons with cam FAI following surgery, but more research is
necessary to assess this.
Future research should evaluate the effect of surgical intervention on the observed
kinematic and kinetic profiles in persons with cam FAI during functional tasks. Additionally,
future biomechanical studies should incorporate electromyographic and strength data to allow for
a more complete understanding of differences in movement behavior. This could help clarify
whether decreased hip muscle strength or activation is the reason for the observed differences in
pelvis motion. Lastly, optimal treatment of persons with FAI is not well established. There is a
need for studies focused on the efficacy of treatment techniques for this population. In particular,
future research should assess the effects of hip muscle strengthening or motor control training on
movement and functional outcomes in this population.

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10.1097/BLO.0b013e3180399430

Abstract (if available)

Abstract Cam femoroacetabular impingement (FAI) is a cause of chondral damage, labral tears, and hip osteoarthritis. Cam morphology refers to decreased offset at the femoral head-neck junction which contributes to abutment of the femoral head-neck junction with the acetabular labrum or cartilage at end range of hip flexion and/or hip internal rotation. Previous literature suggests that range of motion and kinematic impairments at the hip and pelvis may contribute to FAI. In addition, previous studies have suggested that these motions of the femur and pelvis may be coupled. Therefore, it is important to understand the normal kinematic relationship between the femur and pelvis before understanding the role of altered kinematics in persons with cam FAI. To date, few studies have reported full kinematic and kinetic profiles in this population. This is important as it is not known if abnormal kinematics are solely driven by altered bony morphology or if muscular control plays a role. Use of computational modeling may enhance our understanding of potential underlying causes of altered kinematics and the influence of altered kinematics on joint stress. As such, the overall purpose of this dissertation was to examine hip and pelvis kinematics and kinetics in persons with cam FAI. ❧ Chapters I and II provide an overview and a background of the current literature related to FAI. The purpose of Chapter III was to determine whether there is a consistent and predictable kinematic relationship between the pelvis and the femur in healthy individuals. Transverse plane motion of the femur and sagittal plane motion of the pelvis during maximum anterior and posterior pelvis tilt were quantified at different hip flexion angles. The observed ratios of transverse femur motion to sagittal pelvis motion were consistent across all hip flexion angles during anterior and posterior pelvis tilt. On average, for every 5° of anterior pelvis tilt there was 1.2-1.6° of internal femur rotation and for every 5° of posterior pelvis tilt there was 1.2-1.6° of external femur rotation. This finding suggests that altered pelvis movement in the sagittal plane may influence transverse plane femur motion. These results are relevant to persons with FAI because pelvis anterior tilt and hip internal rotation are both thought to contribute to impingement. ❧ The purpose of Chapter IV was to compare hip and pelvis kinematics and kinetics during a deep squat task between persons with cam FAI and matched controls. Compared to the control group, persons with cam FAI demonstrated decreased peak hip internal rotation, decreased posterior pelvis tilt, and decreased mean hip extensor moments. The observed decrease in posterior pelvis tilt may contribute to impingement by approximating the femoral head-neck junction with the acetabulum. However, the findings of decreased posterior pelvis tilt and decreased hip internal rotation in persons with cam FAI is contrary to the coupling behavior reported in Chapter III. Therefore, it was hypothesized that the decreased hip internal rotation in the presence of diminished posterior pelvis tilt may be the result of mechanical abutment. Additionally, decreased hip extensor moments may underlie the observed decrease in pelvis posterior tilt. ❧ To expand upon the findings of Chapter IV, the purpose of Chapter V was to evaluate the contact location and magnitude of acetabular cartilage stress during simulated squatting using finite element modeling. The finite element models utilized the respective group kinematics and morphological profiles representative of the control and cam groups. Despite decreased hip internal rotation and flexion in the cam FAI group, the model of average cam morphology and the model of maximum cam deformity resulted in increased acetabular stress and a shift in contact location indicative of impingement. This finding suggests that even a moderate cam deformity may be important with respect to joint stress and provides evidence that the decreased hip internal rotation observed in the cam FAI group is likely the result of mechanical abutment. ❧ Taken together, the results of this dissertation suggest that posterior pelvis tilt and hip external rotation may protect against impingement. Therefore, addressing kinematic impairments in this population may be an avenue for conservative intervention to decrease impingement or to allow for increased femur flexion prior to impingement. In particular, emphasizing utilization of hip extensors to increase pelvis posterior tilt might be beneficial for this population.

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University of Southern California Dissertations and Theses

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Asset Metadata

Creator Bagwell, Jennifer J. (author)

Core Title Hip and pelvis kinematics and kinetics in persons with femoroacetabular impingement

School School of Dentistry

Degree Doctor of Philosophy

Degree Program Biokinesiology and Physical Therapy

Publication Date 04/15/2015

Defense Date 03/23/2015

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag biomechanics,femoroacetabular impingement,hip,kinematics,kinetics,OAI-PMH Harvest,pelvis

Format application/pdf (imt)

Language English

Contributor Electronically uploaded by the author (provenance)

Advisor Powers, Christopher M. (committee chair), Colletti, Patrick M. (committee member), Kulig, Kornelia (committee member), Sigward, Susan M. (committee member), Ward, Samuel R. (committee member)

Creator Email jenny.j.bagwell@gmail.com,petersjj@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c3-547914

Unique identifier UC11298538

Identifier etd-BagwellJen-3296.pdf (filename),usctheses-c3-547914 (legacy record id)

Legacy Identifier etd-BagwellJen-3296.pdf

Dmrecord 547914

Document Type Dissertation

Format application/pdf (imt)

Rights Bagwell, Jennifer J.

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the a...

Repository Name University of Southern California Digital Library

Repository Location USC Digital Library, University of Southern California, University Park Campus MC 2810, 3434 South Grand Avenue, 2nd Floor, Los Angeles, California 90089-2810, USA