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Factors contributing to patellofemoral joint stress: a comparison of persons with and without patellofemoral pain

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Factors contributing to patellofemoral joint stress: a comparison of persons with and without patellofemoral pain

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Content FACTORS CONTRIBUTING TO PATELLOFEMORAL JOINT
STRESS: A COMPARISON OF PERSONS W ITH AND
WITHOUT PATELLOFEMORAL PAIN.
by
Jacklyn Heino Brechter
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment o f the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(Biokinesiology)
December 2000
Copyright 2000 Jacklyn Heino Brechter
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UNIVERSITY OF SOUTHERN CALIFORNIA
TH E G R A D U A T E SC H O O L
U N ivm sm rP A tt
LOB ANOELBS. CAUPOKNIA M O ST
IT its dissertation, written by
. Jacklyn Heino Brechter ^.. .
under the direction of hax Dissertation
Committee, and appr oved by ail its members,
has been presented to and accepted by The
Graduate School, in partial fulfillment of re
quirements for die degree of
DOCTOR OF PHILOSOPHY
D m of Grmdmt e St ymi es
i ^JjpLuL
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Jacklyn Heino Brechter Christopher M. Powers
ABSTRACT
FACTORS CONTRIBUTING TO PATELLOFEMORAL JOINT
STRESS: A COMPARISON OF PERSONS WITH AND WITHOUT
PATELLOFEMORAL PAIN
Patellofemoral pain (PFP) affects about 25% of the population. PFP has been
associated with elevated patellofemoral joint (PFJ) stress (force per unit area), however
this hypothesis has not been adequately tested. Using a biomechanical model o f the PFJ
(including subject specific contact area obtained through Magnetic Resonance Imaging
(MRI) assessment), the purpose of this study was to determine if individuals with PFP
demonstrate elevated PFJ stress compared to pain-free controls. Methods. 10 subjects
diagnosed with PFP and 10 subjects without pain completed two phases of data
collection, 1) MRI assessment to determine PFJ contact area and 2) comprehensive
motion analysis during self selected free and fast walking velocities, stair ascent and
descent. Data obtained from both MRI and motion analysis were required as input
variables into a biomechanical model to quantify PFJ stress. Results. During level
walking, PFJ stress was significantly greater in subjects with PFP compared to control
subjects. The observed increase in PFJ stress in the PFP group was attributed to a
significant reduction in PFJ contact area, as knee joint kinematics and PFJ reaction force
(PFJRF) were similar between groups. During stair ascent, although peak knee extensor
moment, PFJRF, and cadence were significantly reduced in the PFP group, there was no
significant difference in PFJ stress between groups. Similarly, there were no significant
I
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group differences in PFJ stress during stair descent in spite of a significantly slower
walking cadence. Conclusion. The level walking results are consistent with the
hypothesis that increased PFJ stress may be a predisposing factor with respect to
development of PFP. These findings indicate that treatment designed to increase the
contact area between the patella and the femur may be beneficial in reducing PFJ stress
during functional activities. While results during stair ambulation appear to disagree with
the hypothesis of elevated PFJ stress, subjects with PFP appeared to maintain normal
levels of PFJ stress by slowing their cadence. These findings suggest that persons with
PFP appear to employ compensatory strategies to avoid elevated PFJ stress during stair
ambulation.
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This dissertation is dedicated to the memory of my grandmother and
grandfather who believed in me and inspired me over the years, but
were not here to see the completion of my studies.
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ACKNOWLEDGEMENTS
A project o f this scope and magnitude could not have been completed without the
support and guidance of others. To begin with, I would like to acknowledge the financial
support from the American Physical Therapy Association and the Foundation for
Physical Therapy whose contributions gave life to this project.
Special thanks must go to my dissertation committee. To Dr. Stan Azen for bis
wealth of knowledge in biostatistics and to Dr. Sara Mulroy for her mentoring in
interpretation of biomechanical variables. To Dr. Jacquelin Perry, who is an inspiration
and source of tremendous wisdom, invaluable for understanding relationships between
pieces of information. Special thanks go to Dr. Michael Terk for sharing his considerable
knowledge in the field of Magnetic Resonance Imaging, and for providing the facilities
and expertise to complete this project. Finally, to Dr. Christopher Powers for his
unending support, time, and patience, without whom this project could never have been
completed.
In addition, I would like to thank Dr. Thay Lee for his mentoring, his donation of
specimens, and for the technical support of the Orthopaedic Biomechanics Laboratory,
which were invaluable to this project. Furthermore, the support of the LAC-USC
Imaging Science Center is gratefully acknowledged, as is Dr. Jill McNitt-Gray and my
fellow graduate student Barry Munkasy for their contribution to this project in its early
stages. Also, I would like to acknowledge Dr. Gretchen Salsich for her assistance with
iii
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data collection and her support, and my colleagues at Chapman University for their
patience and understanding during this effort.
Finally, I would like to thank my mother and my family for their love, patience,
and encouragement. Special thanks must go to my husband, Lance Brechter, who placed
his own goals and dreams on hold as I completed this project, and who has shared the
larger half of me with my studies during this time. I thank God for providing this
tremendous support and acknowledge that I could not have accomplished this much on
my own.
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TABLE OF CONTENTS
Dedication....................................................................................................................ii
Acknowledgements................................................................................................... iii
List of Figures......................................................................................................... viii
CHAPTER I: OVERVIEW...................................................................................1
SPECIFIC AIMS AND RESEARCH HYPOTHESES...............................6
Specific Aims......................................................................................6
Research Hypotheses........................................................................ 6
CHAPTER H: LITERATURE REVIEW........................................................... 7
ANATOMY OF THE PATELLOFEMORAL JOINT.................................7
Osseous Structures.......................................................................................7
Patella................................................................................................. 7
Femur.................................................................................................. 9
Soft Tissue Structures................................................................................ 12
Active Stabilizers..............................................................................12
Passive Stabilizers.............................................................................13
BIOMECHANICS OF THE PATELLOFEMORAL JOINT.....................15
Kinematics..................................................................................................15
Flexion...............................................................................................16
Tilt......................................................................................................17
Rotation..............................................................................................17
Medial/Lateral Translation.............................................................. 18
Superior/Inferior Translation........................................................... 19
Kinetics...................................................................................................... 20
Patellofemoral Joint Reaction Force............................................... 22
Mechanical Lever Arm.....................................................................25
Contact Area.....................................................................................28
Patellofemoral Joint Stress..............................................................31
PATHOLOGY OF THE PATELLOFEMORAL JOINT.......................... 32
Incidence and Clinical Presentation..........................................................32
Etiology...................................................................................................... 33
Mechanical Stress Theory................................................................34
Mechanism o f Elevated Patellofemoral Joint Stress.......................... 35
Summary of Patellofemoral Pathology.................................................... 41
CHAPTER HI: QUANTIFICATION OF PATELLOFEMORAL JOINT
CONTACT AREA USING MAGNETIC RESONANCE IMAGING: A
COMPARISON TO THE FUJI FILM TECHNIQUE IN CADAVERIC
SPECIMENS.____________________________________________________ 42
v
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INTRODUCTION........................................................................................43
METHODS...................................................................................................44
Specimen Dissection and Loading............................................................44
Assessment of Contact Area.....................................................................45
Magnetic Resonance Imaging......................................................... 46
Fuji Film...........................................................................................46
Procedure...................................................................................................46
Data Analysis................................................................................... 47
Quantification o f Contact Area Using MRI................................ 47
Quantification of Contact Area using Fuji film..........................49
Statistical Analysis........................................................................ 49
RESULTS.....................................................................................................49
DISCUSSION...............................................................................................50
Conclusion................................................................................................. 52
CHAPTER TV: PA TELLOFEMORAL JOINT STRESS DURING LEVEL
WALKING IN PERSONS WITH AND WITHOUT PATELLOFEMORAL
PAIN.___________________________________________________________ S3
INTRODUCTION........................................................................................54
METHODS...................................................................................................56
Subjects...................................................................................................... 56
Procedure...................................................................................................57
Magnetic Resonance Imaging..........................................................58
Gait Analysis.....................................................................................58
Data Analysis.............................................................................................60
Patellofemoral joint Contact Area.................................................. 60
Knee Joint Kinematics and Kinetics...............................................61
Biomechanical Model......................................................................61
Statistical Analysis.....................................................................................64
RESULTS..................................................................................................... 65
Stride characteristics................................................................................. 65
Knee Kinematics........................................................................................65
Net Knee Joint Moments.......................................................................... 65
Patellofemoral Joint Reaction Force........................................................ 66
Utilized Patellofemoral Joint Contact Area.............................................66
Patellofemoral Joint Stress....................................................................... 66
DISCUSSION...............................................................................................67
Conclusion................................................................................................. 71
CHAPTER V: PATELLOFEMORAL JOINT STRESS DURING STAIR
ASCENT AND DESCENT IN PERSONS WITH AND WITHOUT
PATELLOFEMORAL PAIN._______________________________________ 77
INTRODUCTION........................................................................................78
METHODS................................................................................................... 79
Subjects...................................................................................................... 79
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Procedure....................................................................................................81
Magnetic Resonance Imaging..........................................................81
Motion Analysis................................................................................82
Data Analysis............................................................................................. 84
Patellofemoral joint Contact Area.................................................. 84
Knee Joint Kinematics and Kinetics............................................... 85
Biomechanical Model...................................................................... 85
Statistical Analysis..................................................................................... 87
RESULTS......................................................................................................87
Cadence.......................................................................................................87
Knee Kinematics........................................................................................ 88
Net Knee Joint Moments...........................................................................88
Patellofemoral Joint Reaction Force.........................................................88
Utilized Patellofemoral Joint Contact Area............................................. 88
Patellofemoral Joint Stress....................................................................... 89
DISCUSSION............................................................................................... 89
Conclusion................................................................................................. 93
SUMMARY AND CONCLUSIONS..................................................................99
BIBLIO G RAPH Y................................................................................................103
vii
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LIST OF FIGURES
Figure.1.1. Line drawing demonstrating that the patellofemoral joint reaction force
(PFJRF) is the vector sum o f the quadriceps force (QF) and the patellar
ligament force (PLF).
Figure 2.1. Axial view scematic of Wiberg’s three types of patellae based on the size of
the lateral facet with respect to the medial facet. The Type II patella is most
congruent.
Figure 2.2. Fiber orientation of the quadriceps muscles with respect to the femur. Note
that the vastus intermedius (VI) is aligned along the anatomical axis of the
femur. Reprinted from: Powers, CM. Rehabilitation of Patellofemroal Joint
Disorders: A Critical Review. J Orthop Sports Phys Ther 28(5):345-354,
1998 with permission of the Orthopedic and Sports Sections of the American
Physical Therapy Association.
Figure 2.3. Quadriceps (Q) angle is the angle formed by a line from the anterior superior
iliac spine (ASIS) to the center of the patella and from the center of the
patella to the tibia tubercle. The Q-angle is a clinical measure of the angle of
pull of the quadriceps on the patella.
Figure 2.4. Patellofemoral joint axes for defining patellar mobility.
Figure 2.5. Free body diagram (FBD) of the patella showing the forces acting of the
patella including the quadriceps force (QF), the patellar ligament force
(PLF), the effect of gravity on the mass of the patella (mg), and the reaction
force from the femur (PFJRF).
Figure 2.6. Diagram of the patellofemoral joint reaction force (PFJRF) and its increase
as a result of the increase in compression force from both the quadriceps
force (QF) and the patellar ligament force (PLF) with increased knee flexion.
vm
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Figure 2.7. A) The knee extensor mechanism divided into its two parts, the tibiofemoral
joint and the patellofemoral joint. Each diagram shows three forces, the
fulcrum (indicated by the solid dot), and the moment arms of the levers.
Note that the location of the fulcrum of the patellofemoral joint determines
the lever arms for the quadriceps force (Fq) and the patellar ligament force
(Fp). The joint reaction force (Fp) and (Fr) for the patellofemoral joint and
tibiofemoral joint respectively, and the weight of the limb (W) are also
indicated. From Grood, ES et al Biomechanics of the Knee-Extension
Exercise: Effect of Cutting the Anterior Cruciate Ligament. J Bone Joint
Surg Am 66-A:725-733, 1984. (Reprinted with permission.)
Figure 2.8. Difference between actual (perpendicular) quadriceps lever arm and
effective quadriceps lever arm, which considers the fulcrum action of the
patella.
Figure 2.9. Location of the patellofemoral joint contact area at 0°, 45° and 90° of knee
flexion. The superior (S), medial (M), and lateral (L) borders of the patella
are designated.
Figure 3.1 Custom loading apparatus used to provide patellofemoral joint loading during
assessment of contact area. The compressive force through the
patellofemoral joint was provided by a plastic cap secured to the patella (I)
and rubber tubing anchored to the base of support (2). The slack in the
quadriceps tendon was taken up by suturing rubber tubing to the quadriceps
tendon and securing the tubing to a plastic screw inserted into the proximal
femur (3).
Figure 3.2 A) Representative sagittal plane image of the patellofemoral joint, magnified
2.5 times normal size. B) The blue line indicates contact between the
patella and femur.
Figure 3.3 Comparison of the mean contact area measurements between Fuji film and
MRI for all six specimens.
Figure 4.1. Flow chart of patellofemoral joint model. *Data obtained from van Eijden
and colleagues.7 3 **Data obtained from van Eijden and colleagues.8 1
Figure 4.2. Comparison o f knee joint flexion angle between groups during (A) free
walking and (B) fast walking. No significant differences were found
between the patellofemoral pain (PFP) and the control (CTRL) groups.
ix
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Figure 4.3. Comparison of knee joint moments between groups (A) free walking and (B)
fast walking. Positive values indicate knee extensor moment, negative values
indicate knee flexor moment. *Indicates peak knee extensor moment
significantly smaller in the patellofemoral pain (PFP) group compared to the
control (CTRL) group.
Figure 4.4. Comparison of patellofemoral joint reaction force (PFJRF) between groups
during (A) free walking and (B) fast walking. *Indicates significantly
smaller peak PFJRF in the patellofemoral pain (PFP) group compared with
the control (CTRL) group.
Figure 4.5. Comparison of utilized patellofemoral joint (PFJ) contact area between
groups during (A) free walking and (B) fast walking. *Indicates average
utilized PFJ contact area is significantly less in the patellofemoral pain (PFP)
group compared to the control (CTRL) group during free and fast walking.
Figure 4.6. Comparison of patellofemoral joint (PFJ) stress between groups (A) free
walking and (B) fast walking. *Indicates peak PFJ stress in the
patellofemoral pain (PFP) group is significantly greater than the control
(CTRL) group. **Indicates the PFJ stress time integral (area under the
curve) is significantly greater in the PFP group compared to the control group
during free and fast walking.
Figure 5.1. Force plate and portable staircase set up arrangement This arrangement
permitted the force plate to become one of the steps during stair ascent and
descent.
Figure 5.2. Knee joint angle plotted as a function of the stance phase for both the
patellofemoral pain group (PFP) and the control group (CTRL) during (A)
ascending stairs and (B) descending stairs. There was no significant
difference between groups for peak knee flexion or peak knee extension.
Figure S 3 . Net knee joint moment plotted as a function of the stance phase for both the
patellofemoral pain group (PFP) and the control group (CTRL) during (A)
ascending stairs and (B) descending stairs. ‘ Indicates that peak extension
moment is significantly smaller in the PFP group when compared with the
CTRL group.
x
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Figure 5.4. Patellofemoral joint reaction force (PFJRF) plotted as a function of the
stance phase for both the patellofemoral pain group (PFP) and the control
group (CTRL) during (A) ascending stairs and (B) descending stairs.
*Indicates that peak PFJRF is significantly smaller in the PFP group when
compared with the CTRL group. ’ ’ Indicates that the PFJRF-time integral is
significantly smaller in the PFP group when compared with the CTRL group.
Figure 5.5. Utilized patellofemoral joint (PFJ) contact area plotted as a function of the
stance phase for both the patellofemoral pain group (PFP) and the control
group (CTRL) during (A) ascending stairs and (B) descending stairs. There
was no significant difference between groups.
Figure 5.6. Patellofemoral joint (PFJ) stress plotted as a function of the stance phase for
both the patellofemoral pain group (PFP) and the control group (CTRL)
during (A) ascending stairs and (B) descending stairs. ’ Indicates that the
time to peak PFJ stress was significantly earlier in the PFP group when
compared with the CTRL group.
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CHAPTER I
OVERVIEW
Patellofemoral pain (PFP) is one of the most prevalent disorders of the knee, with
as many as one in four o f the general population reporting symptoms.9 5 PFP also is
commonly associated with active populations. For example, Renstrom described PFP as
the most frequent injury in young tennis players1 2 9 while Jordan reports PFP as the
second highest overuse injury in basic training.8 5 The patellofemoral joint also can
account for as many as 42% of knee injuries to runners.2 7
The most widely accepted hypothesis regarding the etiology of PFP is excessive
mechanical stress causing breakdown of the articular cartilage of the patella.5 5 An
increase in patellofemoral stress can lead to degeneration of the cartilage components and
decrease the ability of cartilage to absorb and transmit forces, leading to subsequent
stiffening of the subchondral bone. Once subchondral bone is involved, pain receptors
are thought to be triggered.5 5 ,5 7 1 2 5
Patellofemoral joint stress is defined as force per unit area, with force being the
patellofemoral joint reaction (PFJRF). Using a simple line drawing (Figure 1.1), Maquet
determined that the PFJRF is the vector resultant of the quadriceps force (QF) and the
patellar ligament force (PLF), and is the force acting to compress the patella onto the
femur.1 0 0 In contrast to earlier investigations which assumed the patella acted as a simple
pulley, Maquet demonstrated that the force in the quadriceps tendon was not equal to the
force in the patellar ligament1 0 0 As the knee joint moves through range of motion, the
1
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PFJRF
Figure.1.1. Line drawing demonstrating that the patellofemoral
joint reaction force (PFJRF) is the vector sum of the quadriceps
force (QF) and the patellar ligament force (PLF).
patella acts as a lever, changing the mechanical advantage of the quadriceps force and the
patellar ligament force. Factors affecting the PFJRF then, include the knee joint angle,
which determines how the mechanical advantage is applied, and the quadriceps force
which is under voluntary control. In general, as the knee joint angle increases, the PFJRF
also increases.
Patellofemoral joint contact area is defined as the area of contact between the
patella and the trochlear groove of the femur.7 7 6 9 Elevation of patellofemoral stress
therefore, could be a result of increasing the PFJRF and/or reducing joint contact area.
As knee flexion increases, the PFJRF tends to increase, however, contact area also
increases.3 0 ,5 8 ’ 7 6 The increase in contact area, though, does not completely offset the
increase in PFJRF, and therefore, as knee flexion increases, stress in the patellofemoral
joint also tends to increase.
2
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Most of the investigations into PFP have focused on abnormal patellar tracking or
malalignment as the cause of the increased stress and mechanical breakdown.5 3 ’ 6 9 ,7 6 ,7 7
With abnormal tracking, the patellofemoral joint contact area is reduced, and may split
into two separate zones.7 6 Increased loading occurs most often in the lateral zone (i.e. the
lateral patellar facet) and is referred to as excessive lateral pressure syndrome.5 4
Despite the common assumption linking abnormal patellar tracking to PFP, recent
findings indicate that as many as 25 to 50% of persons with PFP do not exhibit tracking
abnormalities,1 0 6 ,1 1 0 ,1 1 8 ,1 3 0 suggesting other mechanisms may be involved. This has
significant implications for the treatment of PFP as both conservative and surgical
techniques are aimed at restoring “normal” patellofemoral joint
mechanics.2 5 ,3 0 ,4 4 ,7 8 ,8 2 ,8 3 ,1 1 1 ,1 3 8 The fact that many surgical techniques aimed at restoring
normal patellar tracking (i.e. lateral release) have only a 50% success rate supports this
premise.1 5 9
Another potential cause of PFP, may be related to abnormal gait patterns.1 7 ,1 8 ,1 0 8
Dillon et al reported that persons with PFP demonstrated reduced knee flexion during the
stance phase of gait when compared with pain free subjects.3 3 However, it was not
determined if this was a cause or an effect of PFP. Nadeau et al also reported reduced
loading response knee flexion in persons with PFP.1 0 8 Powers et al did not find a
significant reduction in knee flexion, however, with application of patellofemoral taping,
a common treatment for PFP, these authors noted a reduction in knee pain and
subsequent significant increase in knee flexion.1 2 1
3
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Reduced knee flexion during loading response has been associated with a
reduction in the quadriceps shock absorbing mechanism,1 1 4 and an increase in ground
reaction force.2911 3 In addition, reduced knee flexion results in a reduction in
patellofemoral contact area.5 0 ,3 8 ,1 0 2 Therefore, it is possible that abnormal gait mechanics
may contribute to an elevated patellofemoral joint stress. To date, only one study has
estimated the patellofemoral joint stress during walking.1 0 2 The study was a
mathematical model, however, without in vivo measurement. Furthermore, the patella
was modeled as a simple pulley, contact area was obtained from cadaveric specimens,
and quadriceps forces were extracted from results in published literature
In the presence of normal patellar alignment and gait patterns, PFP may be related
to excessive activity levels. Examples o f normal activities that have been identified as
causing high patellofemoral forces include squatting (up to 8 times body weight),1 0 2 knee
extension (5.1 times body weight),1 0 2 and leg press (14 times body weight). Running has
also been shown to cause forces of 6 to 11 times body weight in the patellofemoral
• • , 4 6 ,1 3 1
joint
Although PFJRF has been quantified in several activities, knowledge of the
PFJRF alone is insufficient to assess the true patellofemoral joint load. Stress is the
variable that likely provides information that is more indicative of patellofemoral joint
pathology. In quantifying patellofemoral joint stress, both the PFJRF and patellofemoral
joint contact area need to be considered. One problem with quantifying contact area is
that it is normally an invasive procedure. Consequently, patellofemoral joint contact has
been obtained from cadaver specimens. Extrapolation of cadaveric data to in-vivo
4
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modeling may be problematic owing to differences between cadaveric specimens and in-
vivo subjects, including age, tissue quality, and methods of loading the extensor
mechanism. Currently, a method for quantifying patellofemoral joint contact area in-vivo
has not been described. By combining individualized patellofemoral joint contact area
with in vivo biomechanical data (i.e. kinematics and kinetics), a complete assessment of
the patellofemoral joint including stress and its contributing factors could be
accomplished.
To date, quantification of patellofemoral joint stress in persons with PFP has not
been reported. Using a biomechanical model o f the patellofemoral joint, the purpose of
this study was to test the hypothesis that individuals with PFP would demonstrate
elevated patellofemoral joint stress compared to pain-firee controls during functional
activities. A secondary purpose o f this study was to identify the biomechanical variables
contributing to elevated patellofemoral joint stress in this population.
The clinical implications of this study include improvement in treatment
selection. By identifying the factors contributing to increased patellofemoral joint stress,
treatment may be directed more efficiently with possible greater long-term success. For
example, if increased patellofemoral joint stress is related to increased force (a result of
an abnormal gait pattern or activity), treatment should be directed toward altering the
force (i.e. changing the gait pattern or activity) for symptom relief, in contrast, if
increased patellofemoral joint stress is related to decreased contact area between the
patella and femur (a result of abnormal patellar kinematics) treatment may focus on
restoring normal tracking (i.e. through either surgical or conservative approaches).
5
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SPECIFIC AIMS AND RESEARCH HYPOTHESES
Specific Aims
1. To compare patellofemoral joint stress (using a biomechanical model) between
persons with and without PFP during level walking.
2. To compare patellofemoral joint stress (using a biomechanical model) between
persons with and without PFP during stair ascent and descent.
3. To identify the biomechanical factors contributing to increased patellofemoral joint
stress in both the PFP and control populations.
Research Hypotheses
1. Persons with PFP will exhibit greater patellofemoral joint stress during level walking
when compared to a pain-free control group.
2. Persons with PFP will exhibit greater patellofemoral joint stress during stair ascent
and descent when compared to a pain-free control group.
3. Persons with PFP will exhibit either smaller patellofemoral joint contact area and/or
elevated PFJRF when compared to a pain-free control group
6
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CHAPTER n
LITERATURE REVIEW
ANATOMY OF THE PATELLOFEMORAL JOINT
The structure of the patellofemoral joint demonstrates its unique role in the
function of the knee joint. The anatomical components of the patellofemoral joint, both
osseous and soft structures, provide the foundation upon which the mechanics of the
patellofemoral joint are derived. To understand the role of the patellofemoral joint in
daily function, and how that function is altered with pathology, an appreciation of the
anatomical structure is necessary.
OSSEOUS COMPONENTS
The two osseous structures comprising the patellofemoral joint are the patella and
the distal femur.
Patella
The patella is the largest sesamoid bone in the body and develops within the
quadriceps tendon.6 0 It is roughly triangular in shape, with the apex directed inferiorly
when viewed from the anterior aspect. The proximal 75% of the posterior (femoral)
surface of the patella is covered with articular cartilage, the thickest in the body.ss A
vertical ridge (median ridge) runs through the center of the patella and separates the
articular surfaces into medial and lateral components or facets,3 4 '1 4 6 with the lateral facet
7
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being deeper and broader than the medial.5 4 ,1 0 4 The medial and lateral facets each may be
further subdivided into inferior, middle, and superior facets,1 0 4 ,1 4 6 with a final component,
the odd facet, located on the medial margin of the patella and situated in a vertical
orientation.2 ’ 3 The distal portion (25%) of the posterior patella, the apex, is non-articular
and is the site of origin of the patellar ligament1 4 6 The patellar ligament is an extension
of the quadriceps tendon and it travels inferiorly to insert into the tibial tubercle.
An axial view of the patella also reveals a somewhat triangular appearance,
although the patellar shape is considerably more variable in this plane. In the axial view,
the medial and lateral articular facets may be visualized on either side of the median
ridge, which forms the apex of the triangle. Wiberg classified the patella into three main
types, depending on the size of the medial patella in the axial plane (Figure 2.1).1 5 3 Type
Figure 2.1. Axial view scematic o f W iberg’s three types of patellae based on
the size of the lateral facet with respect to iuc medial facet The Type n
patella is most congruent
8
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I Wiberg patella have equal sized medial and lateral facets. The lateral facet is twice the
size of the medial facet in a type II Wiberg patella, with a type HI patella having a lateral
facet four times the size of the medial.1 3 3 The patellar shape provides information
regarding conformity with the femoral articulating surfaces. The most common patellar
type, type n, also is the most conforming patellar shape.1 3 3
Femur
The femur is the longest bone of the body and, with its distal end, it articulates
anteriorly with the patella and inferiorly with the tibia. The distal femur is comprised of
two asymmetrical condyles the anterior junction of which forms a shallow depression for
articulation with the patella.6 0 This surface, the trochlear groove or patellar surface of the
femur, is covered with hyaline cartilage and extends more anteriorly on its lateral side. In
contrast, the medial surface is less prominent, providing less bony resistance to motion
yet extends farther distally.6 0 The shape of the femoral trochlea provides bony stability
for the patellofemoral joint and has been reported to be an important factor in
malalignment of the patella.4 2
The anatomical axis of the femur is angled 4-7° laterally from vertical (Figure
2.2).7 3 ,1 2 8 This femoral angulation permits the femoral condyles to lie in a nearly
horizontal plane since the medial condyle extends more inferiorly than the lateral
condyle.3 8 ,4 8 The femoral angulation also results in a lateral component to the direction
of the pull o f the quadriceps muscle group9 6 and therefore on the patella (Figure 2.2).
9
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Variations in this anatomical axis of the femur thus will affect the alignment and mobility
of the patella.2 0 - 8 4 - 9 6
VL 12-1
F 7-10*
VML 15-15*
VMO
60-55*
Figure 2.2. Fiber orientation of the quadriceps muscles with respect to the
femur. Note that the vastus intermedius (VI) is aligned along the anatomical
axis of the femur. Reprinted from: Powers, CM. Rehabilitation of
Patellofemroal Joint Disorders: A Critical Review. J Orthop Sports Phys Ther
28(5):345-354,1998 with permission of the Orthopaedic and Sports Sections of
the American Physical Therapy Association.
The quadriceps (Q) angle is a clinical measurement utilized to understand the
effect of lower extremity alignment on the lateral pull on the patella. The Q-angle is the
angle in the frontal plane made by the intersection of a line drawn from the ASIS to the
center of the patella and a line from the center o f the patella to the tibial tubercle (Figure
2-3).8 4 The average Q-angle8 4 is 10-15° and causes the patella to displace laterally with
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contraction of the quadriceps. With abnormal patellar positioning, the Q angle becomes
*3ss reliable as a source of information, since the abnormal location of the patella is
included in the measurement. However, it has been reported that an altered Q angle,
either higher or lower than average, will affect the alignment and mobility of the
patella.7 6
Figure 2.3. Quadriceps (Q) angle is the angle formed by a line from
the anterior superior iliac spine (ASIS) to the center of the patella and
from the center of the patella to the tibia tubercle. The Q-angle is a
clinical measure of the angle of pull o f the quadriceps on the patella.
In summary, the patellofemoral joint is composed of the patella and the trochlear
surface o f the femur. The shape of the patella in the axial plane conforms to the groove
of the femur in most joints. Variations in the shape of both the patella and trochlea
impact the congruency of the joint surfaces. The femoral alignment and the location of
the tibial tubercle also impact the orientation and thus the congruency of the
ASIS
Tibial
tubercle
;Angle
Center of
Patella (Axis)
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patellofemoral joint and normally create lateral displacement of the patella as the
quadriceps are contracted The increased projection of the lateral trochlear groove
partially counters this lateral mobility, providing bony stability to the patellofemoral
joint Additional stability over the patellofemoral joint is achieved through the soft tissue
structures associated with the patellofemoral joint
SOFT TISSUE STRUCTURES
ACTIVE STABILIZERS
While osseous components provide the basic structure o f the patellofemoral joint
the contractile tissues and ligaments provide the motor and mobility restraints
respectively. The muscles, which control the patellofemoral jo in t are the quadriceps,
which are composed o f the vastus lateralis, vastus medialis, vastus intermedius and the
rectus femoris. Secondary contractile influences on the patellofemoral joint come from
the adductor magnus, tensor fascia lata, and gluteus maximus muscles.1 1 3
The three vasti muscles arise from the femur and insert onto the patella while the
rectus femoris, a two joint muscle, arises on the anterior inferior iliac spine of the pelvis
(with a slip from the lip of the acetabulum) before also inserting with the other
quadriceps onto the patella. The quadriceps tendon remains layered as it inserts onto the
patella5 4 with the rectus femoris inserting most anteriorly onto the patella at its superior
margin. The vastus lateralis and vastus medialis insert onto the patella deep to the rectus
femoris and occupy the superolateral and superomedial margins of the patella
respectively, and superficial to the vastus intermedius,5 4 which inserts on the superior
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border. The convergence of these muscles on the patella serves to redirect the four
separate quadriceps force vectors onto the patellar ligament for a common action on the
tibia.5 4
As a result of their origination on the femur, each individual quadriceps muscle
applies a force to the patella according the muscle fiber orientation in the frontal plane
(Figure 2.2), with a net displacement force causing lateral motion of the patella.
Furthermore, since the attachment of the quadriceps in deep in comparison to the patella,
contraction of the quadriceps causes a compression force between the patella and the
femur.1 1 7
PASSIVE STABILIZERS
Passive support of the patellofemoral joint can be divided into vertical and
horizontal components.1 0 In the vertical direction, the patellar ligament and vertical
components of the patellar retinaculum comprise the main passive support of the
patellofemoral joint.1 0 The patellar ligament is the largest passive stabilizer of the
patellofemoral joint and it plays a large role in the orientation and mobility of the patella.
The length of the patellar ligament is considered normal when it is approximately the
same length as the patella in the superior-inferior direction.8 4 Carson reported that Insall
and Salvati first described this method of assessing patellar ligament length using lateral
view roentgenograms.1 9 These authors reported an average ratio of patellar tendon length
to patella length of about one (1.02 ± .13)1 9 with variations greater than 20% indicating
either a superior displacement (patella alta) or an inferior displacement (patella baja).1 9 ,8 4
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In the horizontal direction, the lateral passive stabilizers are considerably larger and
stronger than the medial stabilizers. Although a vertical structure at its origin, the
iliotibial band descends the length of the thigh then arcs to insert laterally onto the
patella, tibia, fibula, and lateral femoral condyles in several layers.5 2 ,5 3 It is the most
superficial of the lateral stabilizers, and may be referred to as the superficial oblique
retinaculum at its distal portion as it arcs across the inferior pole of the patella.1 0 ,5 3 Deep
to the iliotibial band lies the lateral transverse horizontal retinaculum also called the deep
transverse fibers patella.1 0 ,5 3 In addition, at this depth, a fibrous band, (patellotibial
ligament) arcs infero-laterally from the margin of the patella to insert onto Gerdys
tubercle of the tibia.5 3 At the supero-lateral margin of the patella, a similar fibrous band
(epicondylopatellar ligament) extends from the lateral epicondyle of the femur to the
patella.1 0 ,5 3 Other lateral structures in this deep layer include the patellomeniscal
ligament1 0 and deep fibers connecting some of the lateral stabilizers to the lateral
epicondyle and capsule of the knee providing a bony anchor.1 0 This network of lateral
stabilizers provides extensive passive support of the patella in the lateral direction. In
addition, the relation of the iliotibial band to the gluteus maximus and tensor fascia lata
muscles provides some ability to create tension in the connecting passive structures via
insertion of these muscles onto the iliotibial band.
Medially, the passive stabilizers are considerably less well developed and fewer
than the lateral structures. Superficial is the superficial oblique retinaculum,1 0 which
overlies the arcuate patellotibial ligament and the medial horizontal retinaculum.1 0 The
vastus medialis oblique muscle contributes fibers to the medial horizontal retinaculum at
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the medial margin, providing a dynamic component to this structure.1 0 Additional medial
support is provided by the epicondyopatellar ligament (present about 33% of the time1 0 )
and the medial patellomeniscal ligament.1 0
In summary, there is an extensive network of passive structures supporting the
patellofemoral joint with the primary support arising from the patellar ligament Length
o f the patellar ligament and location of the tibial tubercle are important factors in
patellofemoral joint congruency, alignment and pathology. Laterally, the passive
structures are thicker and more developed than those located medially, a factor thought to
create an imbalance around the patellofemoral joint and cause a tendency of the patella to
displace laterally.1 0 ,5 3
BIOMECHANICS OF THE PATELLOFEMORAL JOINT
Function of the patellofemoral joint depends not only on the anatomical structure,
but also on the relative alignment and function of the lower extremity.2 '5 4 Kinematics of
the patellofemoral joint also are dependent on the motion of the knee joint. Kinetic
analysis of the patellofemoral joint will be presented using inverse dynamics equations.
KINEMATICS
Motion of the patellofemoral joint is tri-planar and is generally described as
flexion, tilt, and rotation about each of the three primary axes respectively (Figure 2.4).
In addition to this angular motion, the patellofemoral joint also translates medially and
laterally (patellar shift) in the frontal plane, and superiorly and inferiorly in response to
quadriceps contraction.
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i / Lateral.
Tilt
Medial/Lateral
translation (shift)
Flexion / Extension
Figure 2.4. PateHofemoral joint axes for defining patellar
mobility.
Flexion
Flexion of the patella occurs as a function of tibiofemoral joint flexion. However,
the magnitude of the flexion motion at the patellofemoral joint is less than that occurring
at the tibiofemoral joint6 8 ,9 1 ,1 2 7 Reports on the magnitude of patellar flexion are quite
consistent, with peak patellar flexion of 80° occurring as the knee joint flexes to
120°
Medial / Lateral
Rotation
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Tilt
Patellar tilt is the rotation of the patella about its longitudinal axis. In general,
various authors use different methodologies to quantify patellar tilt, making comparison
across studies difficult Imaging studies of patellar tilt have reported the lateral
patellofemoral angle9 3 or the patellar tilt angle (PTA)iS , as a measure of the angle o f the
patella in comparison to either the anterior,9 3 or posterior femoral condyles. In addition,
cadaveric studies have assessed patellar tilt about the long axis of the patella.6 6 ,6 7 ,9 8 ,1 4 9
Comparison of these published results reveals approximately a 15° offset between
cadaver and imaging studies, yet relative direction and magnitude of motion is consistent
given this offset A general summary of patellar tilt motion would begin with the patella
in neutral tilt in full knee extension, with some wavering of the patella in early knee
flexion resulting in a medial tilt by 20-30° of knee flexion (5-6°), and a lateral tilt by 30-
45° o f knee flexion. Once the patella is seated in the femoral groove (about 45°), there is
continued lateral tilt of the patella with increased knee flexion, with peak lateral tilt of
about jo0.6 6 ’ 6 7 ’ 98149
Rotation
Patellar rotation is the motion of the inferior pole of the patella toward the fibular
head (lateral rotation) or toward the contralateral limb (medial rotation). This motion
occurs about an antero-posterior axis. Total range o f patellar rotation is minimal (about
6°), beginning in nearly neutral during knee extension and moving medially as the knee is
flexed.6 6 ,7 2 ,9 8 ,1 4 9 Rotation of the patella is strongly influenced by the location of the tibial
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tubercle by virtue of the patellar ligament attachment2 0 ,2 4 For example, rotation of the
patella tends to follow external rotation of the tibia during end range knee extension.
Medial/Lateral Translation
Translation of the patella appears to be consistent across studies. In general, there
is an increase in lateral translation as the tibiofemoral joint flexes from full
extension.1 5 ,6 7 ,9 1 ,1 5 0 In full knee extension, however, some authors describe the patella as
neutral with respect to translation,6 7 ,9 8 ,1 5 0 while others report a laterally translated
patella.1 5 ,7 2 Methodology alone does not explain the variability in patellar translation
although a variety of techniques have been reported, including x-ray photogrammetry
with surgically implanted metal balls,6 7 ,1 4 9 ,1 5 0 MRI (both static and dynamic),1 5 and bone
pins9 1 to name a few. Total patellar translation is quite small and is restricted to less than
15 mm throughout the full range of knee flexion.1 5 ,7 2 ,1 0 9
The magnitude and direction of patellar translation may be influenced by
alignment and structure of the lower extremity,2 4 ,5 0 ,6 8 ,9 4 including size of the lateral
femoral condyle,3 6 hypomobility of lateral soft tissue restraint,3 6 ,6 7 ,9 8 abnormal tibial
tubercle position,3 6 ,6 8 ,9 4 or abnormal Q-angle.1 4 7 -1 5 8 With a larger lateral condyle, more
bony resistance to lateral motion will be present.3 6 Conversely, in the presence of lateral
condyle dysplasia, the normal lateral bowstring effect resulting from an average Q-angle,
could allow lateral translation of the patella at full extension. With abnormal lateral
tension, as with an excessively large Q-angle or hypomobility of the lateral soft tissue
restraints, lateral translation may occur.3 6 ,5 4
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Superior/Inferior Translation
Patellar mobility in the superior and inferior direction results from the contraction
and shortening of the quadriceps muscle group.9 6 Since the patella is within the tendon of
the quadriceps muscle, as the sarcomeres shorten, tension is placed upon the quadriceps
tendon. The tension in the tendon is then transmitted through the patella to the patellar
ligament and to the tibia. Motion of the tibia from full flexion to full extension causes
superior translation of the patella. In contrast, as the knee joint flexes, the patella is
pulled inferiorly and around the distal end of the femur. In full knee flexion the patella
approximates the inferior surface of the femoral condyles.5 0 ,5 1 In contrast, during full
knee extension, the inferior pole of the patella is in contact with the superior portion of
the femoral trochlea.5 0 ,1 2 2 Thus the superior and inferior mobility of the patella causes a
change in the contact area between the patella and the femur, a factor which becomes
important when considering patellofemoral joint kinetics.
Summary of Kinematics
In summary, patellar motion occurs in response to motion of the knee joint and
according to the structure of the patellofemoral joint In general, flexion of the patella is
the movement of the patella about a medial/lateral axis within the sagittal plane, patellar
tilt is the movement of the patella about a longitudinal axis within the transverse plane,
and patella rotation is the movement of the patella about an anterior/posterior axis within
the frontal plane. Finally translation of the patella occurs medially and laterally as well
as superiorly and inferiorly.
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The majority of the patellar motion is flexion (80°), with rotation and tilt limited to
less than 10° total. Translation is also minimal and usually less than 15mm. Structure of
both the bony and the soft tissue of the patellofemoral joint influence the motion and
alignment of the patella. Translation of the patella superiorly and inferiorly changes the
location of the point of contact between the patella and the femur.
KINETICS
Kinetic analysis of the patella involves determination of the forces acting on the
patellofemoral joint. Examination of the tri-axial kinematics o f the patellofemoral joint
indicates that forces must act in all planes to account for this patellar motion. However,
experiments on the development of patellofemoral joint models have determined that the
major forces acting on the patellofemoral joint may be evaluated in a two dimensional
analysis.1 4 8 ,1 5 8 Since the quadriceps muscle is the only contractile tissue acting on the
patella, and the majority of patellar motion occurs in the sagittal plane, such an
PFJRF
PLF
Figure 2.5. Free body diagram (FBD) of the patella showing the forces
acting of the patella including the quadriceps force (QF), the patellar
ligament force (PLF), the effect of gravity on the mass of the patella
(mg), and the reaction force from the femur (PFJRF).
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assumption appears reasonable. A sagittal view free body diagram (FBD) of the patella,
in isolation of the femur, allows depiction of the forces being exerted on the patella
(Figure 2.S). To complete the analysis, it has been assumed that the patella is a rigid
body, and the soft tissue restraints of the patellofemoral joint have been summed together
and will be analyzed for their net effect on the patella.
Utilizing the sagittal view FBD of the patella, the forces acting on it may be
referred to as the quadriceps force (QF), the patellar ligament force (PLF), and the
reaction force resulting from the contact of the patella with the femur, the patellofemoral
joint reaction force (PFJRF). Using Newtons laws of motion, one can write the following
equations for the patella:
Equation 2.1) I F = ma Equation 2.2) I A f = IcM a
Where F - forces, m = mass of the patella, a =linear acceleration of the patella,
and M =moments, /cis=the moment of inertial of the patella about it’s center of mass,
and a = the rotational acceleration o f the patella.
Rewriting these equations using the forces in the FBD, we have:
Equation 2.3) QF + P L F +PFJRF = ma and
Equation 2.4) d q p x QF + dpLf x P L F +d p p ju f x PFJRF ~ I cm&
where d= the distance from the center of mass of the patella to the indicated force. These
equations may be further simplified by considering first that the mass of the patella is
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negligible, and secondly, the PFJRF goes through the center of mass of the patella and so
its distance in the moment equation is zero. Rewriting the equations then:
Equation 2.5) QF + P L F +PFJRF = 0 and
Equation 2.6) J qF x QF +dpL F x PLF = 0
Rearranging the equations we find:
Equation 2.7) QF + P LF = PFJRF
Equation 2.8) J q f x QF - dplf x PLF
Looking at Equation 2.7, we see that the PFJRF is the vector sum of the
quadriceps force and the patellar ligament force. Equation 2.8 reflects the fact that there
is an equilibrium between the moment created by the quadriceps force and the moment
created by the force of the patellar ligament To interpret these equations further, it is
necessary to relate them to patellofemoral joint function.
Patellofemoral Joint Reaction Force
Functionally, the PFJRF can be thought of as that portion of both the quadriceps
muscle pull and the patellar ligament pull that causes compression of the patella onto the
femur. Recall tl^at the angulation of the femur dictates that as the quadriceps muscles
contract (quadriceps force), the patella is pulled superiorly and posteriorly, causing
compression onto the femur.9 6 As the patella attempts to move superiorly, the weight of
the tibia and foot cause resistance to the movement resulting in an inferiorly and
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posteriorly directed force on the patella through the patellar ligament (patellar ligament
force). Therefore, for each quadriceps contraction, both the quadriceps muscle and the
patella ligament act to force the patella against the femur. This resulting compression
force is the PFJRF.
Figure 2.6. Diagram of the patellofemoral joint reaction force (PFJRF)
and its increase as a result o f the increase in compression force from both
the quadriceps force (QF) and the patellar ligament force (PLF) with
increased knee flexion.
Reilly and Martens1 2 8 provided the first experimental analysis of the PFJRF
during functional activities, with several others following1 0 2 ,1 3 1 ,1 4 3 Resulting reports
provide some general characteristics of the PFJRF. Firstly, reports support a general
tendency for the PFJRF to increase in magnitude with increasing knee flexion angles.1 0 2
As the knee flexes, more of the quadriceps force produces compression of the patella
onto the femur (Figure 2.6).1 0 0 Matthews et al1 0 2 investigated the effect of joint angle on
PFJRF by calculating the magnitude of the PFJRF in six different knee flexion angles
during a squatting activity. As the subject squatted from 5° to 90°, the PFJRF increased
from less than 700N to more than 3000N.1 0 2 Reilly and Martens, using a deep squat
23
QF
PFJRI
PFJRF
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motion with knee flexion of 130° calculated the PFJRF to be about 6000N.1 2 8 Steinkamp
et al calculated the PFJRF for typical patellofemoral joint rehabilitation exercises both
open and closed chain (non-weight bearing and weight bearing respectively), utilizing a
similar peak knee extensor moment in an attempt to hold the quadriceps force constant
These authors found that the PFJRF differed considerably as a result of knee flexion
angle. For the open chain task, the peak moment occurred when the knee was fully
extended and the PFJRF was more than five times body weight (3500N). However, this
value for PFJRF was less than half of the 14 times body weight (9800N) found for the leg
press exercise which achieved a similar peak knee extensor moment at 90° knee
flexion.1 4 3 Thus, PFJRF does increase with both quadriceps force and with knee flexion
angle.
The second characteristic of the PFJRF is its heavy dependence on the quadriceps
force, with larger quadriceps forces increasing the PFJRF regardless of the joint angle. To
determine the effect of quadriceps force on PRJRF, comparison can be made of the
PFJRF during activities utilizing similar knee flexion angles. PFJRF has been calculated
during level walking at a knee angle of approximately 15° (loading response).1 0 2 ,1 2 8 Both
investigators utilized the same quadriceps forces and knee flexion angles previously
reported for the walking task, with new model parameter inputs for the PFJRF
calculation. The resulting PFJRF was 422N and 314N, values less than half that found
during an isometric squat at 15° of knee flexion.1 0 2 ,1 2 8 The differences between the two
walking studies could be attributed to the different model inputs o f limb length and
weight. Comparison the two different magnitudes of PFJRF given similar knee flexion
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angles, could be attributed only to the magnitude of the quadriceps force and/or the
patellar ligament force.
To determine the effect of the PFJRF on the patella during common tasks, the
magnitude of the PFJRF also has been assessed during both activities o f daily living and
during sporting activities.3 9 ,4 6 ,1 3 1 Scott & Winter1 3 1 and Flynn & Soutas-Little4 6 both
assessed running activities, while Erickson and Nissell assessed the PFJRF during
cycling.3 9 The magnitude of PFJRF reached more than 4250N, which is, for an averaged
sized man (700N), more than six times body weight. The daily activities assessed
included walking up and down ramps, and up and down stairs. PFJRF during walking up
a ramp was less than half of that calculated for walking down a ramp (about 1250N or
more than 1.8 times body weight).1 0 2 Walking upstairs involved a larger PFJRF than
either walking up or down a ramp with values ranging from more than 2.5 times body
weight to more than 3.7 times body weight.1 0 2 Walking downstairs resulted in a PFJRF
greater than four times body weight1 0 2 ,1 2 8 These values for PFJRF indicate that the
patella experiences significant amounts of compressive force on a daily basis. With the
inclusion of sporting activities, the patellofemoral joint must withstand compressive
forces reaching 14 times body weight.1 4 3 This significant compressive load on the patella
may be a risk factor for development of patellofemoral joint pathology.
Mechanical Lever Arm
The mechanical lever arm of a force is the distance between an arbitrary reference
point and the point of application of the force. As the knee joint goes through flexion and
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extension, recall that the patella moves inferiorly and superiorly causing the contact point
between the patella and the femur to change. This changing location of the patellar
contact area causes the patella to change how it provides mechanical advantage through
the knee range of motion.6 2 ,9 6 ,9 7 ’1 4 7 ,1 5 8 Therefore, while an equilibrium state exists
between the quadriceps force and the patellar ligament force (equation 2.8), neither the
two forces, nor the two lever arms (Jqf or (J plf) are equal to each other. The patella
behaves as a rigid body, acting as a lever, with the fulcrum being the point of the patella
in contact with the femur. As the contact changes with flexion and the contact area
moves proximally on the patella, the mechanical advantage for the quadriceps tendon is
reduced. This fulcrum function of the patella allows the force in the quadriceps tendon to
be different from the force in the patellar ligament.
This lever action of the patella was first described by Maquet using a simple line
drawing.1 0 0 Prior to Maquet’s publication, it was believed that the patella functioned as a
simple pulley to change the direction but not the magnitude of the quadriceps force. In
fact, the bulk of the publications in this area have been completed using a patella modeled
as a simple pulley..1 0 2 ,1 2 8 This mechanical advantage associated with the fulcrum action
of the patella should be considered when calculating the forces acting on the patella. In
general, when calculating equations o f motion, the perpendicular relationship between the
force and the lever arm are required to obtain the moment or caused by the acting force.
Measurement of a perpendicular lever arm from the center of rotation of the knee joint to
the quadriceps tendon or to the patellar ligament, however, will not reflect the fulcrum
effect of the patella (Figure 2.7). Grood et al coined the term quadriceps “effective” lever
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Figure 2.7. A) The knee extensor mechanism divided into its two parts, the
tibiofemoral joint and the patellofemoral jo in t Each diagram shows three
forces, the fulcrum (indicated by the solid dot), and the moment arms of the
levers. Note that the location of the fulcrum of the patellofemoral joint
determines the lever arms for the quadriceps force (Fq) and the patellar
ligament force (Fp). The joint reaction force (Fp) and (F r) for the
patellofemoral joint and tibiofemoral joint respectively, and the weight o f the
limb (W ) are also indicated. From Grood, ES et al Biomechanics of the Knee-
Extension Exercise: Effect of Cutting the Anterior Cruciate Ligament JB one
Joint Surg Am 66-A:725-733,1984. (Reprinted with permission.)
arm6 2 to distinguish the actual perpendicular measure from an adjusted measure which
does consider the fulcrum effect (Figure 2.7). These authors reported that the quadriceps
effective lever arm can be determined by multiplying the actual lever arm by a ratio of
the force in the quadriceps tendon to the force in the patellar ligament.6 2 Models using
the quadriceps lever arm should include the adjustment for the patellar fulcrum action to
accurately assess the forces acting on the patella. Comparison o f published reports of the
two lever arms (actual and effective) reveals that the actual (perpendicular) lever arm is
usually longer than effective (Figure 2.8).6 2 ’9 6 ’ 9 7 ’1 4 7 ’1 5 8 Therefore, measurements based on
the actual lever arm will tend to underestimate the quadriceps force.
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2.50
I 2.00-
E
< 1.50 -
fc
§ I.OQq;
209
1.98
1.70
1.55
0.8'
■ 2 -8 3 0.75
a
g 0.50
g 0.00
a
-0.50
-0.15
0.00 20.00 40.00 60.00 80.00 100.00
Knee Joint Angle (deg)
Figure 2.8. Difference between actual (perpendicular) quadriceps lever
arm and effective quadriceps lever arm, which considers the fulcrum
action o f the patella.
Contact Area
The motion of the patella during knee flexion causes the point of contact between
the patella and the femur to move, resulting in the fulcrum action of the patella.
Therefore, only a portion o f the patella contacts the femur at any one point in the range of
motion.
Contact area has been determined primarily in cadaver studies, as the available
methods to quantify contact area have been invasive.7 ,6 8 ,7 9 FUJI pressure sensitive
film,7 ,3 1 ,7 7 casting,7 ,4 9 ,1 3 3 and dyeing techniques7 ,5 0 ,1 0 2 are the most common methods to
assess patellofemoral joint contact area. FUJI film presents the investigator with the
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ability to quantify the contact area results, but does not easily localize the contact area
onto the patella. Both dye (including ink) and casting methods rely on qualitative
comparisons, or require custom software for analysis. However, they provide a means of
localization of the contact area onto the patella and/or femur.
The magnitude of the contact area between the patella and femur during full knee
extension is about 0.8cm2.5 0 ,1 3 3 Contact area generally increases with increased knee
flexion angle until 60° (Figure 2.9) then reduces slightly with increasing flexion.5 0 For
S
90°
M
Figure 2.9. Location of the patellofemoral joint contact area at 0°, 45° and 90°
of knee flexion. The superior (S), medial (M), and lateral (L) borders of the
patella are designated.
example, knee flexion o f 30°, results in a mean area of 2.2cm2 or 17% of the articular
surface of the patella, averaging reports of patellofemoral joint contact area.6 8 ,1 3 3 As knee
flexion increases, contact area increases to a mean of 2.9S and 2.93cm2 for 60° and 90° of
knee flexion respectively.6 8
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03451
The magnitude of the contact area also may change with the amount of force
applied through the quadriceps tendon,7 7 although this finding has been refuted.4 For
example, as Hehne increased the knee extension force from 500N to 2S00N contact area
(measured with Fuji film) increased at 30° of knee flexion from 0.8cm2 to 2.3cm2 and at
60° from 0.85cm2 to 3.9cm2.7 7 In contrast, with force changes from 700N to 1500N, no
significant change in contact area was measured using a transducer implanted into the
patellofemoral joint.4
Reports on the location of the contact area on the patella and femur through range
of motion show a gradual change in location from the inferior pole o f the patella to the
superior patella and then to the lateral margins of the patella.6 8 7 6 In full extension, only
the inferior tip of the patella makes contact with the femur. With increasing knee flexion,
contact area gradually moves to a more superior position on the patella (Figure 2.9).7 6
Some authors have reported the contact area to reach the superior margin of the patella by
90 degrees,7 6 while others reported the contact to be just superior to mid patella at this
knee angle.7 6 With knee flexion beyond 100°, contact area changes from a bean shaped
area across the medial and lateral patellar facets to two separate contact areas, one
medial, and one lateral along the patellar margins.7 6 This change in the shape and
distribution of contact area with high flexion angles results from the contact between the
lateral margins of the patella with more inferior portions of the femoral condyles.1 3 3 The
change in contact area occurs as the patella is displaced inferiorly with knee flexion.
While most reports on contact area are based on cadaver studies, one investigator
has recently attempted to quantify the patellofemoral joint contact area in vivo using
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magnetic resonance imaging (MRI).2 8 ,1 3 3 Initial comparison of this MRI contact area
measurement with invasive contact area measurement tools has been favorable.2 8 ,1 3 3 The
MRI methodology presented, however, relies on extensive mathematical reconstruction
o f the joint surfaces and custom software not yet available to other researchers or
clinicians. Therefore, while MRI may be a successful tool as a method for quantifying
contact area in vivo, a method would need to be developed for its use.
Patellofemoral Joint Stress
Patellofemoral joint stress is defined as the PFJRF per unit area of contact
between the patella and the femur.7 9 Stress has been directly measured, using FUJI film
in cadaver specimens.7 7 In addition, patellofemoral joint stress has been calculated by
assessing the PFJRF and dividing by contact area obtained from reports in the
literature.1 0 2 ,1 4 3
To date, only one study has estimated the patellofemoral stress during walking.1 0 2
These authors combined cadaver measurements of contact area (methylene blue dye
method) with quadriceps forces and joint angles previously reported in the literature.1 0 2
Using a patellofemoral joint model (assuming a pulley function of the patella), the
patellofemoral joint stress was estimated to be nearly 2MPa for level walking. Estimates
of ramp and stair walking were as high as S.SMPa1 0 2
Steinkamp et al compared the patellofemoral joint stress between open and closed
chain knee rehabilitation exercises, again using contact area obtained from cadaveric
studies.1 4 3 The open chain (knee extension exercise) and closed chain (leg press exercise)
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motions tested were estimated to cause peak joint stress of 23 to 24MPa. However, the
peak stress during the knee extension exercise occurred when the knee was fully
extended. Thus, the stress was acting on the inferior portion of the patella. In contrast,
during the leg press exercise, peak stress occurred when the knee was flexed to 90°.1 4 3
Thus, the stress was acting near the superior pole of the patella. Further analysis of the
stress over four joint angles revealed that stress was minimal in during the knee extension
exercise when the knee was flexed to 90°. Similarly, during the leg press exercise, stress
was minimal during full knee extension.1 4 3 This has important clinical implications in
that the two exercises may be utilized during rehabilitation in the range of motion which
causes the least patellofemoral joint stress. Thus the full knee range of motion from 0° to
90° can be exercised while maintaining low levels of joint stress.
PATHOLOGY OF THE PATELLOFEMORAL JOINT
INCIDENCE AND CLINICAL PRESENTATION
Patellofemoral pain (PFP) is a widespread problem affecting one out of every four
people5 0 ,1 0 3 and is reported to be one of the most common knee pathologies.3 2 ,4 7 ,8 6 ,1 2 7
While symptoms of PFP vary between patients, some findings are considered
characteristic. Pain is the most prevalent complaint, usually described as being
retropatellar or along the medial or lateral patellar borders.4 7 ,1 4 5 Other complaints include
knee instability (not associated with ligamentous laxity), swelling, or locking of the
patellofemoral jo in t1 2 ,1 4 5 ,1 5 4 Activities associated with aggravating the pain include
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sustained knee flexion (called moviegoers knee),34,1 0 3 ,1 1 2 ,1 5 4 and strenuous activity such as
running, jumping, deep squatting, and walking up or down stairs.2 7 ,3 4 ,1 3 7
Extensive literature exists regarding the treatment of persons with PFP, both
surgical1 1 ,2 1 -2 3 ,4 3 ,4 4 ,6 3 ,7 8 ,1 1 5 ,1 4 4 ,1 5 7 and conservative.8 4 ,9 2 ,1 0 3 ,1 2 4 ,1 3 7 In fact, more than 100
surgical options for treatment of PFP have been reported. This large number of surgical
procedures indicates that there is no surgical treatment of choice for persons with PFP.
Furthermore, the extensive discussion on surgical treatment indicates that conservative
care, which centers on stretching and strengthening the quadriceps and correcting
alignment and tracking problems of the patellofemoral joint also is limited in its success.
If any one method were consistently found to be successful, a consensus would be
reached in the existing literature. This lack of consensus in treatment may be attributed
to a lack of consensus on the etiology of PFP.
ETIOLOGY
There have been several theories regarding the etiology of PFP, including
chondromalacia patellae (softening of the cartilage),5 7 ,8 1 alignment and tracking disorders
of the patellofemoral joint or lower extremity,5 4 ,8 1 ,8 4 ,1 1 2 ,1 4 5 a reduction in the magnitude or
change in the timing of the vastus medialis obliquus (VMO) muscle versus the vastus
lateralis (VL) muscle,1 0 1 ,1 0 3 ,1 4 2 ,1 5 1 and excessive mechanical stress on the patellofemoral
joint.5 4 ,5 7 ,5 9 ,7 6 However, most of these theories have been at least partially refuted in the
scientific literature. For example, chondromalacia patellae, although present in many
patients with PFP, has not correlated well with pain since chondromalacia has been
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documented as being present in the absence of pain1 1 0 and absent in the presence of
pain.2 0 Similarly, several investigators have documented the presence of PFP in the
absence of alignment and tracking problems of the patellofemoral joint or lower
extremity.1 3 6 While imbalance in muscle activity and tiraing continues to be a subject of
strong clinical controversy, the bulk of the scientific literature refutes differences in both
magnitude1 2 ,8 7 ,9 9 ’1 1 2 ’1 2 0 ,1 4 5 and timing5 6 ,8 8 ,1 0 7 ,1 2 0 ,1 4 5 of the VMO activity when compared
with the VL.
Mechanical Stress Theory
In contrast, the theory suggesting that mechanical factors cause excessive stress
on the patellofemoral joint has not been either supported or refuted in persons with PFP.
Mechanical stress is a theory sufficiently encompassing to include most other proposed
causative factors under its umbrella. For instance, alignment and tracking problems are
associated with an increase in patellofemoral joint stress4 9 ,6 8 ,9 4 ,1 2 4 while chondromalacia
patellae may be a result of excessive patellofemoral joint stress.5 4 ,5 7 Chondromalacia
may occur as the excessive stress causes a breakdown of the articular cartilage. Although
some dismiss this cartilage degeneration as a source of pain because it is aneural, the
damage to chondral components is known to trigger a release o f lysosomes and local
effusion. This inflammation, in turn, may cause a stretching of soft tissue structures,
which contain nerve endings and cause pain.2 0 In addition, the cellular damage disrupts
the ability of the cartilage to absorb and transmit load, thereby forcing the subchondral
bone to experience abnormal loading. These loads lead to a stiffening of the subchondral
bone and further disruption in the function of load absorption and transmission.2 0 ,5 7
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Thus, subchondral bone (rich in nerve endings), may become painful prior to visual
evidence o f cartilage damage. In addition, Goodfellow et al reported that cartilage may
intially denegenerate at either the surface layer or the basilar layer, adjacent to the
subchondral bone,S 7 further supporting the theory that pain may exist without visual
evidence of damage. Thus, if breakdown o f cartilage occurs at the basilar layer, or the
subchondral bone becomes involved in pathology early, the stress theory becomes
consistent with reports that some persons with PFP have no objective findings.2 0 ,9 3
Theoretically, there is considerable merit to the hypothesis that excessive stress causes
PFP, however, there is no current report comparing the patellofemoral joint stress
between persons with and without PFP.
Mechanism o f Elevated Patellofemoral Joint Stress
Stress is defined as the force per unit area of contact. With respect to the
patellofemoral joint, the force is the patellofemoral joint reaction force (PFJRF) or the
force perpendicular to the joint surface while the area is the amount of contact between
the femoral trochlea and the patellar facets.6 1 ,1 4 3 Therefore, an increase in patellofemoral
joint stress requires either an increase in the PFJRF or a decrease in the contact area.
Factors capable of decreasing the contact area or increasing the PFJRF become critical to
an understanding of elevated patellofemoral joint stress.
Increased Patellofemoral Joint Reaction Force
Along with decreased contact area, increased PFJRF may result in greater
magnitudes of patellofemoral joint stress. A few anatomical considerations have been
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reported that may affect PFJRF. In brief, these anatomical factors include patellar alta,
quadriceps muscle cross sectional area, lever arm, and tendon length.1 3 ,2 6 ,7 4 ,1 4 0 More
common causes of increased PFJRF include the task requirement regarding the
quadriceps muscle activity (level of vigor)3 5 * 3 7 ,1 3 9 and the knee flexion angle.2 ,1 6 ,6 1 ’ 7 9 ,1 0 0 ,1 0 2
Recall that the PFJRF is calculated as the vector sum of the quadriceps force and
the patellar ligament force (Equation 2.7). Therefore, increases in the amount of
quadriceps force can increase the PFJRF. Such an increase in quadriceps force occurs by
increasing the vigor of the activity. For example with a change in activity from walking
to running, the PFJRF may increase from just over 300N to nearly 4000N.1 2 8 A less
dramatic increase may occur by contacting the floor more heavily during walking.1 4 1
Additional activities associated with higher PFJRF include squatting,1 2 8 leg press and
extension exercises,1 4 3 and stair climbing.1 2 8 While many of these activities are hobbies
for most people, stair climbing is a necessity of daily living and may require PFJRF
between 2.5 and 4.3 times body weight, or 1250N to more than 3000N, a value very near
the magnitude estimated for running.1 2 8 This high PFJRF makes stair climbing the most
difficult activity of daily living for persons with PFP, and the pain associated with stair
ascent or descend may force these people to limit or curtail this function.
Knee flexion angle is a second major factor associated with increased magnitude
of PFJRF. As the knee flexion angle increases, the proportion of the quadriceps force
and patellar ligament force that causes compression increases (Figure 2.7). Therefore, as
knee flexion increases, the PFJRF will rise accordingly. Matthews et al1 0 2 estimated the
PFJRF during isometric squatting at increasing knee flexion angles. They reported a
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nearly linear increase in PFJRF from less than SOON in 5° of flexion to nearly 4000N in
90° of flexion.1 0 2
Decreased Patellofemoral Joint Contact Area
Reduction in patellofemoral joint contact area can occur for many reasons but all
factors may be divided into two main categories, 1) those associated with anatomic
anomalies and 2) those associated with function. While there are unlimited functional
activities on which the basic concepts of a reduction in contact area may be appreciated,
these concepts will be discussed only in terms of gait, one of the most important
functional activities.
Anatomical Factors in Reduced Contact Area
Reduced patellofemoral joint contact area has been associated with bony or soft
tissue anomalies present in the patellofemoral joint or the lower
extremities.2 0 ,2 1 ’ 6 8 ,8 1 ,1 0 5 * 1 1 8 ,1 2 4 ,1 5 8 Of these anomalies, those directly affecting the
component parts of the patellofemoral joint are the most important and include patellar
shape2 0 ,9 3 ,1 5 3 and the shape of the femoral trochlea.2 1 ,3 6 ,4 2 Of the three main patellar types
described by Wiberg,1 5 3 the type two patella (lateral facet is twice the size of the medial
facet) is the most conforming patellar shape, therefore yielding increased area of contact
since the opposing surfaces are congruent.5 0 ,1 3 2 In contrast, altering the proportional size
of the lateral facet as in Wiberg’s type one or type three patellae may cause a reduction in
contact area as a result of decreased joint surface congruity.5 0 ,5 4 ,7 7 ,1 3 2
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Similarly, dysplasia of the femoral trochlear groove decreases the congruity of
joint surfaces area2 1 ’ 4 2 and allows increased lateral displacement of the patella, changing
the contacting surfaces4 2 and may result in reduced patellofemoral joint contact area. For
example, dysplasia of the lateral femoral condyle may result in decreased anterior
projection and a loss of bony support in the patellofemoral joint4 2 The smaller lateral
condyle is insufficient to resist the normal bowstring effect created by the anatomical
alignment of the femur on the patella, resulting in lateral displacement of the patella4 2
and, therefore, altered contact area.
Bony anomalies may occur in the femur, tibia, or foot and still indirectly impact
the patellofemoral joint and the contact area. Since the quadriceps muscles attach to the
femur and the patellar ligament to the tibia, anomalies affecting the femur or the tibia will
alter the alignment of the patellofemoral joint and affect the joint congruency during
function by changing the resting position of the femur under the patella or the position of
the patella on the femur.2 0 ,6 1 ,1 4 5 ,1 5 8 These lower extremity bony anomalies include
excessive femoral anteversion or retroversion,9 4 change in the Q-angle,7 6 ,8 4 varus or
valgus knee angulation,8 4 tibial rotations,2 4 ,7 8 and foot alignment.1 2 3
Besides bony anomalies contributing to reduced contact area, soft tissue changes
also affect contact area. One of the common soft tissue anomalies is patellar ligament
length. Normal length of the patella in comparison to the patellar ligament is about a 1:1
ratio (1.02 + .13).' Ratios more than 20% larger (patella alta) will cause the patella to
contact the femur abnormally, or not at all, in the early ranges of knee flexion.1 ,2 0 ,1 5 8 This
results from the patella resting higher on the femur, and therefore incongruent with the
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femoral trochlea it contacts.1 ,2 0 '1 5 8 In contrast, for ratios 20% smaller than normal (patella
baja), there has been no report regarding the impact on patellofemoral joint contact area.
Another common soft tissue abnormality is hypomobility of the lateral soft tissue
restraints, including as the lateral retinaculum or iliotibial band, or hypermobility of the
medial soft tissue restraints. Both cause the patella to rest more laterally and reduce the
joint congruency.4 1 ,5 2 ’ 5 3 ,9 8 ,1 2 4 * 1 5 5 Thus, instead of having contribution to contact area from
the medial patellar facet on the medial femoral trochlea, contact is isolated to the lateral
facet and trochlea as it abuts on the lateral lip of the trochlear groove.9 8 ,1 2 4 ,1 5 5
Functioned Factors in Reduced Contact Area
In addition to structural or anatomical factors that effect patellofemoral joint
contact area, there are functional movement patterns that may reduce contact area. Since
the patellofemoral joint functions in coordination with the tibiofemoral joint, motion of
the patellofemoral joint is dependent on the motion of the tibiofemoral
jo in t1 5 ’ 6 6 ’ 6 7 ,9 1 ,9 8 ’1 3 5 ,1 4 9 In fact, contact area of the patellofemoral joint is dependent on the
knee flexion angle of the tibiofemoral joint With earlier knee flexion angles,
patellofemoral joint contact is smaller and located on the lower portion of the patella.7 6 ,1 3 2
As the knee angle increases, the magnitude of the contact area increases nearly linear,
through about 60°. As the knee continues to flex to 90°, contact area may remain about
the same or slightly increase.5 0 Therefore, as the knee joint is flexed during initial weight
acceptance in walking, the amount of contact area will depend on the amount of knee
flexion, if all other factors are held constant Since persons with PFP have been reported
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to adopt gait strategies that include smaller knee flexion angles during this weight
acceptance phase in comparison to control subjects,1 0 8 '1 1 9 the smaller angle may
functionally reduce the contact area and cause increased patellofemoral joint stress in this
population.
To assess the contribution of contact area to the magnitude of patellofemoral joint
stress, the contact area of individuals must be evaluated. Currently, the tools available
for such an analysis are invasive and therefore, not available for in-vivo
analysis.7 6 ,7 7 ’ 9 0 ’1 3 3 ’1 5 2 However, one investigator has pioneered the use of MRI in the in-
vivo assessment of contact area.2 8 The custom software required for such an analysis is,
however, not currently available. Therefore, development of an MRI tool to assess
patellofemoral joint contact area in-vivo is necessary before any patellofemoral joint
stress analysis can be performed.
The many factors capable of contributing to elevated patellofemoral joint stress
make understanding the magnitude of stress challenging. However, the first step is to
confirm the role of stress in persons with PFP by quantifying and comparing
patellofemoral joint stress between persons with and without PFP. Furthermore,
evaluation in each individual of the magnitude of the contact area utilized, as well as the
knee flexion angle itself, may provide important information regarding contributing
factors to elevated joint stress. It is possible, however, that patellofemoral joint stress in
someone with PFP may be similar to that of someone without PFP. In this case, the
person suffering from PFP may be overusing their patellofemoral joint with their
selection of, and participation in, daily activities.
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Overuse and Patellofemoral Pain
Articular cartilage is designed to absorb and transmit forces in such a manner as
to protect the bony surfaces they overlay.4 5 ,8 0 ,8 9 ,1 2 6 1 3 4 As force is applied to cartilage, the
surface deforms as fluid is pressed out of the cartilage. When the force is removed, the
cartilage imbibes the fluid and the surface reforms its original shape. In the presence of
continuous or repetitive forces, there may be insufficient time for the cartilage to recover
causing a gradual breakdown o f the integrity of the cartilage over time.8 0 ,1 6 1 With such
an overuse history, there may be no current evidence of excessive patellofemoral joint
stress, but rather, the continual or repetitive overuse is causing micro-breakdown of the
cartilage1 2 6 and the associated chemical changes.9 3
SU M M ARY O F PATELLOFEM ORAL PATHOLOGY
The patellofemoral joint is pathological in one out of every four individuals, yet
there is no current consensus on the etiology of PFP. The hypothesis that PFP is caused
by excessive mechanical stress is theoretically sound, yet has not been tested in a
pathological population. Investigation into this hypothesis would require assessment of
both individual contact area and PFJRF, since increased patellofemoral joint stress may
be a function of either decreased contact area or increased PFJRF. Further interpretation
of the results of such a comparison would require assessment o f potential reasons for the
increase in patellofemoral joint stress.
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CHAPTER m
QUANTIFICATION OF PATELLOFEMORAL JOINT CONTACT
AREA USING MAGNETIC RESONANCE IMAGING: A
COMPARISON TO THE FUJI FILM TECHNIQUE IN
CADAVERIC SPECIMENS
The use of contact area obtained from cadaveric specimens for biomechanical
modeling does not permit investigators to assess the inter-subject variability in contact
area as a result of patellofemoral pathology or malalignment. Developing a non-invasive
technique to evaluate contact area will assist researchers and/or clinicians in obtaining
patient specific contact area data to be used in biomechanical analyses and clinical
decision making.
This chapter will describe such a method for quantifying patellofemoral joint
contact area using magnetic resonance imaging (MRI) and to compare this method with
the current gold standard, Fuji pressure sensitive film. Furthermore, the reliability of this
MRI method also is described. The techniques described in this chapter will be used in
Chapters m and IV to quantify patellofemoral joint stress.
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INTRODUCTION
Excessive patellofemoral joint stress has been hypothesized to contribute to
articular cartilage wear and patellofemoral joint pain.5 5 From a mechanical standpoint,
patellofemoral joint stress is defined as the patellofemoral joint reaction force divided by
the area of contact between the patella and the trochlear surface of the femur. Using
biomechanical methods and mathematical equations to derive the patellofemoral joint
reaction force, several investigators have estimated patellofemoral joint stress during
various activities.7 9 ,1 0 2 ,1 3 1 ’1 4 3 In these studies, patellofemoral joint contact area was
obtained from cadaveric specimens.
The use of cadaveric contact area data in estimating patellofemoral joint stress
poses significant problems. For example, cadaveric specimens are generally from an
older population and do not reflect the typical age ranges of persons with patellofemoral
pain.1 8 ’ 2 8 ,4 9 ’ 5 6 ,1 4 8 ’1 5 6 ,1 5 9 Perhaps more importantly, however, is that inter-subject variability
in contact area as a result of patellar malalignment cannot be considered. This is of
significant concern especially since a malaligned patella can substantially alter contact
area and joint stress.4 9
Given the limitation associated with the use of contact area from cadaver
specimens in estimating patellofemoral joint stress, there is a need for an in-vivo method
to obtain such data. The purpose o f the present study was to describe a method for
quantifying patellofemoral joint contact area using magnetic resonance imaging (MRI).
The validity of this technique was established in cadaver specimens by comparing the
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contact area obtained from MRI with contact area obtained using Fuji pressure sensitive
film. A secondary purpose of this study was to report on the repeatability of the MRI
method. Information obtained from this study will assist researchers and/or clinicians in
obtaining patient specific contact area data to be used in biomechanical analyses and
clinical decision making.
METHODS
Six fresh frozen unmatched human cadaver knees were used in this study. Each
specimen consisted of an intact knee joint with % of the length of the tibia and femur
retained. Prior to preparation, specimens were thawed at room temperature. Throughout
preparation and testing, each specimen was kept moist using 4% saline solution.
SPECIM EN DISSECTIO N AND LOADING
To expose the suprapatellar pouch, longitudinal incisions were made along the
lateral borders of the central quadriceps tendon and the quadriceps muscle group was
separated from the anterior aspect of the femur. A 5-cm incision was made in the
superior patellofemoral joint capsule to accommodate the Fuji film packets.
To simulate a compressive load across the patellofemoral joint, a custom loading
apparatus (constructed of non-ferromagnetic material) was designed. Each specimen was
supported on a base that held the knee in 30° of flexion (Figure 3.1). The tibia and the
femur were secured to the base with rubber tubing. To take up the slack in the quadriceps
tendon, a plastic screw was inserted into the proximal femur and a small circle of surgical
tubing (3-cm diameter) was sutured to the deep portion of the quadriceps tendon and
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looped around the plastic screw. Surgical tubing threaded through a plastic cap secured
to the anterior patella, was looped around wooden dowels in the support base to provide a
compressive force through the patellofemoral joint (Figure 3.1).
Figure 3.1 Custom loading apparatus used to provide patellofemoral joint
loading during assessment of contact area. The compressive force through the
patellofemoral joint was provided by a plastic cap secured to the patella (1)
and rubber tubing anchored to the base of support (2). The slack in the
quadriceps tendon was taken up by suturing rubber tubing to the quadriceps
tendon and securing the tubing to a plastic screw inserted into the proximal
femur 131
A SSESSM E N T O F CONTACT AREA
Patellofemoral joint contact area was assessed using the MRI and the Fuji film
techniques. Both methods were employed simultaneously using the methods outlined
below.
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Magnetic Resonance Imaging
Images of the patellofemoral joint were obtained using a 1.5T magnet (GE
Medical Systems, Milwaukee, Wisconsin) and a three-dimensional spoiled gradient
recalled echo (3D SPGR) imaging sequence. The following parameters were employed:
TR=60ms, TE=20ms, Flip Angle=30°, NEX=1.5, matrix size: 512 X 224 X 28, field of
view: 20 cm X 20 cm and chemically selective fat suppression. Each slice was 2 mm
thick and contiguous with adjacent slices.
Fuji Film
Contact pressure patterns were obtained using Fuji pressure sensitive film (Fuji
Photo Film Co., Tokyo, Japan) with a pressure range of 2-6kgf7cm2. The film was cut to
size (5.0 cm x 5.0 cm) and placed inside a protective polyethylene envelope (250 /an
thick). The polyethylene envelope prevented contamination and allowed contact area to
be obtained within a fully lubricated joint.
PROCEDURE
Following specimen dissection and mounting on the loading apparatus, a Fuji film
packet was inserted into the patellofemoral joint through the incision in the suprapatellar
pouch. A compressive force was then applied to the specimen using the technique
described above. On the average, the compressive force used in this stuffy resulted in
peak patellofemoral joint stress of 5.53 + 2.1 MPa. As the purpose of this study was to
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compare the two methods of assessing contact area, no attempt was made to control the
magnitude of the compressive forces between specimens.
Prior to imaging, two five-inch receive only extremity coils were secured
vertically on either side of the patella. Sequential images were then obtained, ensuring
that the entire patellofemoral joint was imaged. Total imaging time was approximately
11 minutes. Upon completion of scanning, the patellofemoral joint was unloaded and the
Fuji film packet removed. Any film with evidence of crinkling artifact was discarded, a
new film inserted, and the MRI procedure repeated.
To determine the measurement reliability for both the MRI and Fuji film
techniques, the procedures (as outlined above) were repeated three times in one
specimen. A new Fuji film packet was used for each of these three trials.
Data Analysis
Q uantification o f C ontact A rea using M RI
Sequential sagittal plane images were displayed for analysis using Signa Advantage
Medical Imaging Software (GE Medical Systems, Milwaukee, Wisconsin). The section
of the image containing the patella and surrounding portion of the femur was isolated and
magnified. (Figure 3.2A). Patellofemoral joint contact was defined as areas of patella
and trochlear surface approximation in which no distinct separation could be found
between the cartilage borders of the two structures. Since cartilage brightness is
enhanced on fat supressed images, the definition of contact area was operatively defined
as ‘white on white’.
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The line of contact between the patella and femur was measured and recorded
using the same software used to display the images (Figure 3.2B). When the line of
contact was curved, separate straight-line segments were measured. To obtain the contact
area for each slice, the length of the line of contact was multiplied by the 2 mm slice
thickness. Contact areas calculated from each image were summed to obtain the total
patellofemoral joint contact area, with values reported in units of cm2. Measurements
were made twice and averaged for final analysis. All MRI measurements were made by
the same investigator.
Figure 3.2 A) Representative sagittal plane image of the patellofemoral joint,
magnified 2.5 times normal size. B) The blue line indicates contact between the
patella and femur.
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Quantification o f Contact Area using F uji Film
The exposed Fuji film was processed by scanning the resulting print on a Hewlett
Packard Scan Jet lie Color Scanner and analyzed using National Institutes of Health
IMAGE (Bethesda, MD) version 1.6 software. Using a scale provided by the
manufacturer, the software was calibrated for the film sensitivity, temperature during data
collection, and for the hardware used in processing. This program converted the Fuji film
pressure image into a scaled image with 256 levels of gray, which was used for the
determination o f the contact area. The contact area was identified, and the number of
pixels in the image were counted. The pixels were converted into area and reported in
units of cm2 . A preliminary study revealed the accuracy of the color scanner to be within
0.5% for quantification of contact area. Measurements were made twice and averaged
for final analysis.
Statistical Analysis
The reliability o f contact area measurements obtained from MRI and the Fuji film
technique was assessed using the Intraclass Correlation Coefficient (ICC).8 The ICC also
was used to assess the agreement between the two methods. All statistical analyses were
performed using BMDP statistical software.
RESULTS
For the reliability portion of this study, the ICC for the repeated MRI trials was
0.87. The ICC for the values obtained from the repeated Fuji film trials was 0.99. The
ICC value indicating the level o f agreement between the MRI and the Fuji film
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techniques was 0.96. When averaged across all specimens, the contact area obtained
through MRI was 2.94 + 1.01 cm2 while the contact area obtained through the Fuji film
technique was 3.04 + 0.95 cm2. The average individual specimen difference between the
two methods was 10.7% (Figure 3.3).
DISCUSSION
■ FUJI BMRI
5.00
4.00
C 300
s
w
2 2.00
<
w
§ 1.00
< 3
0.00
1 2 3 4 5 6
Specimen
Figure 3 J Comparison of the mean contact area measurements
between Fuji film and MRI for all six specimens.
The reliability o f both techniques was found to be excellent, with the Fuji film
technique being more reproducible than the MRI method. The lower ICC value using
MRI reflects a greater amount of measurement error, however, this value falls well within
the acceptable range for clinical and experimental methods.1 1 6 Whether or not the same
level of reproducibility would be obtained between different investigators (inter-rater
reliability) has yet to be determined.
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Based on the high ICC values, comparison of the patellofemoral joint contact area
between the MRI and Fuji film techniques was found to be excellent, with the overall
average difference across all specimens being less than 5%. In comparison, the average
within specimen difference was 10.7%. The lower overall average difference across all
specimens was the result of the MRI measurement being greater than the Fuji film
measurement in three of the specimens and less than the Fuji film measurement in the
remaining three specimens. The lack of consistency in the direction o f the differences
between the MRI and Fuji film techniques (i.e. MRI greater or less than Fuji film)
indicates that the MRI method did not apply a consistent bias to measurement of contact
area. In other words, the MRI technique did not consistently overestimate nor
underestimate contact area when compared to the Fuji film technique.
The magnitude of the individual specimen differences is reflective of the intrinsic
error or variability associated with measuring contact area using MRI. Such variability is
directly related to image resolution, the quality of the articular cartilage within the
specimen, and the state of joint lubrication. Every effort was made to externally lubricate
each specimen with saline solution during the study. However, several of the specimens
evaluated demonstrated varying degrees of cartilage degeneration based on visual
inspection. In some images, this degeneration resulted in gaps in the contacting surfaces,
making evaluation of contact area difficult However, the use of multiple line segments
to quantify contact area in such specimens likely yielded a more accurate result in
comparison to methods using mathematical representations of the shape of the articular
surfaces, which tend to smooth over such surface defects.
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The average contact area from MRI obtained in this study (3.19 cm2) compares
favorably with that previously reported in the literature at a comparable knee flexion
angle.6 8 ,6 9 ,7 6 ,1 0 2 ,1 3 3 This suggests that the loading apparatus used in this current
investigation was capable of producing compressive loads comparable to other in-vitro
methods. In fact, the compressive load produced an average stress value comparable to
what has been reported during stair ambulation.1 4 This suggests that a physiological
loading of the joint was obtained.
CONCLUSION
MRI assessment of patellofemoral joint contact area was found to be highly
reproducible, and comparable to the established Fuji film technique, suggesting that this
method may be a valuable tool in evaluating the patellofemoral joint contact area. Future
investigations should consider assessment of normal and pathological joints for
etiological studies of patellofemoral joint disease. This method also may be utilized to
determine age specific, pathology specific, or activity level specific contact areas for
relevant study populations. Finally, assessment of patellofemoral joint contact area
following patellofemoral joint surgery may allow surgeons to assess the impact of
specific procedures on patellofemoral joint mechanics.
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CHAPTER IV
PATELLOFEMORAL JOINT STRESS DURING LEVEL WALKING
IN PERSONS WITH AND WITHOUT PATELLOFEMORAL PAIN
Patellofemoral pain affects about 25% of the population, yet its etiology is
unknown. Although the cause of patellofemoral joint pathology is believed to be related
to elevated joint stress (force per unit area), this hypothesis has not been adequately
tested and causative mechanisms have not been clearly defined. Knowledge of the
biomechanical factors contributing to patellofemoral joint pain may improve treatment
techniques and guide development of prevention strategies.
The purpose of this chapter was to determine if individuals with patellofemoral
pain (PFP) demonstrate elevated patellofemoral joint stress compared to pain-free
controls during free and fast walking. Furthermore, the biomechanical factors
contributing to patellofemoral joint stress will be analyzed to determine their role in PFP.
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INTRODUCTION
Patellofemoral pain (PFP) is the most common lower extremity complaint
encountered in orthopaedic practice.3 2 Despite its high incidence however, management of
this disorder remains highly controversial. Given as such, proposed treatment approaches
have been numerous with varied outcomes. The primary reason for this inconsistency
has been the lack of consensus concerning the etiology of this disorder. Although the
cause of patellofemoral joint pathology is believed to be related to elevated joint stress
(force per unit area),5 5 this hypothesis has not been adequately tested and causative
mechanisms have not been clearly defined.
Traditionally, quantification of PFJRF and contact area have been made
experimentally using in-vitro cadaveric models.4 ,1 6 ,6 4 ’ 7 6 ,9 4 Although such studies have
been valuable in providing information regarding patellofemoral joint mechanics, the use
of simulated non-physiologic muscle loading has made extrapolation to the in-vivo
condition questionable. More recently, mathematical modeling has been employed to
quantify the forces experienced by the patellofemoral joint Using either static or
dynamic approaches, many studies have incorporated kinematic and/or kinetic data
obtained from healthy subjects to determine quadriceps force and joint reaction force
during various activities.4 ,7 1 ,7 3 ,7 6 ,7 9 ,1 0 2 ,1 4 3 ,1 4 8 Surprisingly, no such data have been obtained
from a PFP population.
In contrast, only a few studies have attempted to quantify patellofemoral joint
stress. Using calculated PFJRF’s, investigators have utilized patellofemoral joint contact
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areas obtained from cadaver studies to derive stress.4 ,7 9 ’1 0 2 ,1 4 3 Although this approach
may be sufficient for the assessment of the "normal" condition, the fact that contact area
is most likely influenced by patellar alignment and may vary significantly from person to
person, makes the use of cadaveric data in a patient population inappropriate. The
implication being that a relatively small change in contact area could result in a large
change in stress.
To date, no study has compared the patellofemoral joint stress between subjects
with PFP and pain-free controls. In-vivo evaluation of patellofemoral joint biomechanics
will afford important information regarding the factors contributing to joint stress in this
population, and may provide data that can be used to guide treatment. For example, if
increased patellofemoral joint stress is found to be related to increased joint reaction
force, treatment may be directed toward altering the force (i.e. changing the gait pattern
or activity). In contrast, if increased patellofemoral joint stress is found to be related to
decreased contact area between the patella and the femur (a result of abnormal patellar
alignment) treatment may focus on restoring normal tracking (i.e. through either surgical
or non-operative approaches). Currently, classification of patients with PFP based on
biomechanical factors contributing to elevated patellofemoral joint stress has not been
attempted.
Using an imaging based biomechanical model of the patellofemoral joint (which
takes into consideration the inherent variability in patellofemoral joint contact areas
between individuals), the purpose of this study was to test the hypothesis that persons
with PFP would demonstrate elevated patellofemoral joint stress compared to pain-free
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controls during free and fast walking. A secondary purpose of this study was to identify
the biomechanical variables contributing to elevated patellofemoral joint stress in this
population.
METHODS
SU BJECTS
Twenty subjects were recruited for this study, 10 individuals with a diagnosis of
PFP (five males and five females) and 10 individuals without PFP (five males and five
females). There were no significant group differences with respect to average age,
height, or weight (Table 4.1).
Table 4.1 Subject Characteristics, means (standard deviations), PFP =
patellofemoral pain group.
PFP Control
Male
(n=5)
Female
(n-5)
Combined
(n=10)
Male
(n=5)
Female
(n=5)
Combined
(n=10)
Age (years) 38.2(7.7) 36.0(13.4) 37.1(10.4) 32.2(7.0) 31.8(8.1) 32(7.1)
Height (cm) 178.9(10.7) 166.1(6.4) 67.9(17.8) 177.7(10.4) 163.7(7.4) 67.2(4.4)
Weight (kg) 78.1(16.0) 63.4(8.4) 70.8(14.3) 78.1(7.9) 57.6(12.3) 67.9(14.5)
Subjects with PFP were recruited from orthopaedic dimes in the Los Angeles
area. For purposes of this study, PFP subjects were screened to rule out ligamentous
instability, internal derangement, or patellar tendonitis. Subjects were accepted into the
study if they met the following inclusion criterion 1) pain originating specifically from
the patellofemoral articulation (vague or localized) and 2) reproducible pain with at least
two of the following functional activities commonly associated with PFP: a) stair ascent
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or descent, b) squatting, c) kneeling, d) prolonged sitting, e) isometric quadriceps
contraction.1 1 9 ’1 2 1 Subjects with PFP were excluded from participation if they reported
having any of the following: 1) previous history of knee surgery; 2) history of traumatic
patellar dislocation; 3) any neurological involvement that would influence gait; 4) any
implanted biological devices, such as pacemakers, cochlear implants, clips which could
interact with the magnetic field during imaging.
Subjects in the comparison group were recruited from the University of Southern
California, and matched for gender to those in the PFP group. Inclusion criterion for
participation in the comparison group were as follows: 1) no history or diagnosis of knee
pathology or trauma; 2) no knee pain with any of the activities described as inclusion
criterion for the PFP group; 3) no limitations present that would influence gait; and 4) no
implanted biological devices, such as pacemakers, cochlear implants, clips which could
interact with the magnetic field during imaging.
Prior to participation, all subjects were fully informed as to the nature of the
study, and signed a human subjects consent form approved by the Institutional Review
Board of the University of Southern California Health Sciences campus.
PROCEDURE
All subjects completed two phases of data collection. Phase one consisted of MRI
assessment to determine patellofemoral joint contact area, while phase two consisted of
comprehensive gait analysis. Data obtained from both data collection sessions were
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required as input variables into a biomechanical model to quantify patellofemoral joint
stress.
Magnetic Resonance Imaging
All imaging was performed at the Los Angeles County / University of Southern
California Imaging Science Center. Images of the patellofemoral joint were obtained
using a 1.5T magnet (GE Medical Systems, Milwaukee, Wisconsin) and a three-
dimensional spoiled gradient recalled echo (3D SPGR) imaging sequence. The following
parameters were employed: TR=60ms, TE=20ms, Flip Angle=30°, NEX=1.5, matrix
size: 512 x 224 x 28, field of view: 20 cm x 20 cm and chemically selective fat
suppression. Each slice was 2 mm thick and contiguous with adjacent slices.
Prior to scanning, subjects removed any metal such as jewelry and hair clips.
Subjects were positioned supine in the MRI Bore with the knee in 0° of knee flexion.
One receive-only extremity coil was secured on each side of the patellofemoral joint
Subjects rested quietly while the scan was performed. Following completion of the first
scan, subjects were re-positioned and the scan repeated with the knee supported in three
additional knee flexion angles 20°, 40°, and 60°. Total imaging time was 44 minutes.
Gait Analysis
Gait analysis was performed at the Musculoskeletal Biomechanics Research
Laboratory at the University of Southern California. Three-dimensional motion was
obtained using a six-camera (Vicon) motion analysis system (Oxford Metrics LTD,
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Oxford, England). Kinematic data were sampled at 60 Hz and recorded digitally on an
IBM 166 MHz personal computer. Reflective markers (20 mm spheres) placed at
specific anatomical landmarks were used to determine sagittal plane motion of the lower
extremity. Ground reaction forces were collected at a rate o f2500 Hz using two AMTI
force plates (Model #OR6-6-l, Newton, Mass). The force plates were situated within the
middle of the 10-meter walkway with the pattern of tile flooring camouflaging their
location.
Subjects were appropriately attired to permit marker placement directly on the
skin of the subject. The involved limb was instrumented for subjects with PFP, while the
right lower extremity was instrumented for subjects without PFP. Anthropometric
measures were obtained from each subject for use in calculating lower extremity kinetics
using inverse dynamics equations. Reflective markers were then taped to the following
landmarks: sacrum, anterior superior iliac spine (ASIS) bilaterally, lateral thigh, lateral
femoral epicondyle, lateral tibia, lateral malleolus, 2n d metatarsal head, and posterior
calcaneous.
Subjects were instructed to walk along a 10-meter walkway with the middle 6
meters being used for data collection. Three trials of self-selected free and self-selected
fast walking velocities were obtained. A trial was considered successful if the subject’s
instrumented foot landed within either force plate (without targeting). All kinematic and
kinetic data were collected simultaneously.
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DATA A N ALYSIS
Patellofemoral Joint Contact Area
Sequential sagittal plane images of the patellofemoral joint were displayed for
analysis using Signa Advantage medical imaging software (GE Medical Systems,
Milwaukee, Wisconsin). The section of the image containing the patella and surrounding
portion of the femur was enlarged to 2.5 times normal view to enhance visualization of
the contact area. Contact was defined as areas of patella and femoral approximation in
which no distinct separation could be found between the cartilage borders o f the two
structures.7 0 Since cartilage is relatively bright on the 3D SPGR images obtained, the
definition of contact area was operatively defined as ‘white on white’.
The line of contact between the patella and femur was measured and recorded
using the electronic calipers within the same software used to display the images. When
the line of contact was curved, separate straight-line segments were measured. To obtain
the contact area for each slice, the length was multiplied by the 2-mm slice thickness.
Contact areas calculated from each image were summed to obtain the total patellofemoral
joint contact area, with values reported in mm2. This method has been shown to be
reliable and comparable to contact area obtained using Fuji pressure sensitive film in
cadaver specimens.7 0 Contact area measurements were made twice and averaged. All
MRI measurements were made by the same investigator.
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Knee Joint Kinematics and Kinetics
Reflective markers were identified manually using VICON Clinical Manager
(VCM) software and then automatically digitized. The same software was used to
calculate knee joint kinematics and kinetics in the sagittal plane. Only data
corresponding to the force plate step was used.
To calculate the net joint moment at the knee (sagittal plane), anthropometric
data, ground reaction forces, and kinematics were utilized to solve inverse dynamics
equations. To facilitate comparison between subjects and groups, the net knee joint
moments were normalized by body mass and reported in units of Nm/kg. Data obtained
from the three trials were averaged.
Biomechanical Model
A patellofemoral joint model was developed to utilize input from mechanical
analysis of the lower extremity and patellofemoral joint contact area from the MRI. An
overview of the model is illustrated (Figure 4.1). Input variables for the model algorithm
included knee joint flexion angle, knee extensor moment, and patellofemoral joint contact
area.
The first step of the algorithm was to calculate the quadriceps force. The
effective lever arm (LA) for the quadriceps muscle group was determined for each knee
joint angle position using an equation fit to the data from van Eijden and colleagues
(Equation 4.1).1 4 8 At each joint angle, the knee extensor moment (Mect) was divided by
the lever aim to obtain quadriceps force (QF) (Equation 4.2).
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Quadriceps Effective
Lever Arm *
Relationship bctweeen
QF and PFJRF **
Knee Joint Angle
Net Knee Joint
Moment
Patellofemoral
Joint Contact Area
Patellofemoral Joint
Stress
Patellofemoral
Joint Reaction
Force (PFJRF)
Figure 4.1. Flow chart of patellofemoral joint model. *Data obtained from
van Eijden and colleagues.7 3 **Data obtained from van Eijden and
colleagues.3 1
Equation 4.1 = (g.OE-OS*3 - O.Oi:**2 + 0.2&c + 0.046)
x = tibiofemoral joint angle
r2 = .99
Equation 4.2 =
0 = knee flexion angle
/ =1 to x
x = number of frames of data
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The second step of the algorithm was to calculate the patellofemoral joint reaction
force (PFJRF). A constant (k) was then calculated for each joint angular position by
fitting an equation to the data reported by van Eijden and colleagues (Equation 4.3).1 4 7
This constant was multiplied by the QF to obtain the patellofemoral joint reaction force
(PFJRF) (Equation 4.4).
Equation 4 3 k (x) = (4.62E-01 + 1.47E-03X-3.84E-05X2) /
( l-l 62E-02x+1.55E-04JT-6.98E-07X3)
x= tibiofemoral joint angle
r = 9 9
Equation 4.4 PFJRF{et )= k * QFfa )
k = constant
0 = knee flexion angle
/ = 1 to J C
x = number of frames of data
Using the four contact area points obtained from MRI, the final step of the
algorithm was to calculate patellofemoral joint stress. A straight line was fit between
each two consecutive data points to provide approximate patellofemoral joint contact area
values for each knee flexion angle from 0° to 60°. Patellofemoral joint stress was then
calculated by dividing the PFJRF by the contact area for the knee flexion angle
corresponding to the PFJRF value (Equation 4.5).
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Equation 4.5 P FJ s t r e s s (# i)= P F J R F fa )* A R E A fa )
AREA - PFJ contact area
9 = knee flexion angle
/ = 1 to J C
x = number of frames of data
The model output was PFJRF, patellofemoral joint stress, and utilized contact
area (contact area corresponding to knee flexion angle), all normalized to the gait cycle.
The patellofemoral joint stress-time integral was calculated by taking the area under the
patellofemoral joint stress curve as a function of the entire gait cycle. Similarly, the
PFJRF-time integral was the area under the PFJRF curve as a function of the entire gait
cycle. The mean utilized contact area was calculated by taking the average of the utilized
contact area over the gait cycle.
STATISTIC AL A N A LYSIS
Biomechanical variables used for statistical analysis included peak patellofemoral
joint stress, patellofemoral joint stress-time integral, peak PFJRF, PFJRF-time integral,
peak knee extensor moment, peak knee joint flexion angle during stance, and mean
utilized contact area. Stride characteristics used for statistical analysis included velocity,
stride length, and cadence.
Comparisons between groups were made using trimmed means and Yuen's test
for comparison of two independent groups with unequal variances.1 6 0 This analysis was
repeated for each variable. All significance levels were set at p<.05. All statistics were
computed using a custom macro written in Microsoft Excel *97.
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RESULTS
STRID E CH ARACTERISTICS
There were no significant differences in free or fast walking velocities between
the PFP group and the control group (Table 4.2). Similarly, there were no significant
group differences in cadence or stride length during free or fast walking (Table 4.2).
Table 4.2. Stride characteristics. Means (standard deviations) for free and fast
walking. PFP = patellofemoral pain group
FreeVtalking Fast Vtalking
PFP (n=10) Control (n=10 PFP (n=10) Control (n=10
Velocity (m/min) 81.7(7.8) 83.0(6.7) 109.7(9.0) 108.2(5.8)
Stride Length (m) 1.3(0.1) 1.4(0.1) 1.5(0.1) 1.6(0.1)
Cadence (step/min) 117.9(3.6) 121.1(6.9) 142.8(11.2) 139.9(7.0)
KNEE KINEM A TICS
There were no significant differences in knee kinematics between the PFP group
and the control group during either free or fast walking (Figure 4.2A. 4.2B).
N E T KNEE JO IN T M OM ENTS
During free walking, the peak knee extensor moment was significantly less in the
PFP group when compared to the control group (0.43 vs. 0.57 Nm/kg; p = 03) (Figure
4.3A). In contrast, there were no significant group differences in the peak knee extensor
moment during fast walking (Figure 4.3B).
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PATELLOFEM ORAL JO IN T REAC TIO N FORCE
During free walking, peak PFJRF was significantly less in the PFP group when
compared to the control group (7.5 vs. 9.5 N/kg; p = 05) (Figure 4.4A). However, there
was no significant difference in the PFJRF-time integral between the PFP group and the
control group (Figure 4.4A). During fast walking, there were no significant group
differences with respect to the peak PFJRF or the PFJRF-time integral (Figure 4.4B).
UTILIZED PATELLOFEM ORAL JO IN T CONTACT AREA
During free walking, the mean utilized contact area was significantly less in the
PFP group when compared to the control group (138.3 vs. 225.5 mm2 , p = 03) (Figure
4.5A). Similarly, during fast walking, the mean utilized contact area was significantly
less in the PFP group when compared to the control group (144.2, vs. 240.5 mm2, p =.02)
(Figure 4.5B).
PATELLOFEM ORAL JO IN T STR E SS
During free walking, there was no significant difference in the peak
patellofemoral joint stress between the PFP group and the control group (Figure 4.6A).
However, the PFP group demonstrated a significantly larger patellofemoral joint stress
time integral when compared with the control group (51.4 vs. 22.4 MPa • %Gait Cycle,
p=.05) (Figure 4.6A).
During fast walking, peak patellofemoral joint stress was significantly greater in
the PFP group when compared to the control group (6.6 vs.: 3.1 MPa, p=.02) (Figure
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4.6B). As with free walking, the PFP group also demonstrated a significantly larger
patellofemoral joint stress-time integral when compared with the control group (67.9 vs.
33.1 MPa • %Gait Cycle, p=.002) (Figure 4.6B).
DISCUSSION
The primary purpose of this study was to test the hypothesis that subjects with
PFP would demonstrate elevated patellofemoral joint stress during level walking when
compared to individuals without PFP. This hypothesis was supported by the finding that
during free and fast walking, subjects in the PFP group demonstrated a patellofemoral
joint stress-time integral more than twice that of the control group. The patellofemoral
joint stress time integral provides a meaningful comparison of the patellofemoral joint
stress over the entire gait cycle, as this variable represents the pressure experienced by
the patellofemoral joint over a single stride.
In contrast to the patellofemoral joint stress-time integral, there was no significant
difference in peak patellofemoral joint stress during free walking, however, there was a
definite trend with higher values being evident in the PFP group. In fact, the average
peak patellofemoral joint stress for the PFP group was more than 2.S times larger than the
average peak patellofemoral joint stress for the control group. The lack of statistical
significance can be attributed to the high variability among the PFP subjects, and the
relatively small sample size. Peak patellofemoral joint stress during fast walking was
however, significantly larger in the PFP group (2.1 times greater) when compared with
the control group. Since cartilage degeneration is related to the magnitude, duration, and
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frequency of the applied load,4 3 ’ 8 9 ’1 3 4 ’1 6 1 the results o f this study suggest that elevated joint
stress may be a predisposing factor with respect to the development of PFP.
A secondary purpose of this study was to identify the biomechanical variables
contributing to elevated patellofemoral joint stress in the PFP group. Considering that
patellofemoral joint stress is defined as force per unit area, elevated stress may be a
function of either high PFJRF or low patellofemoral joint contact area. In the present
study, the elevated patellofemoral joint stress in the PFP group was attributed to a
significantly smaller contact area, as the PFJRF was diminished during free walking and
similar during fast walking (when compared to the control group).
As measured in the current study, the utilized patellofemoral joint contact area
could be influenced by the knee joint angle during gait or by an abnormal position of the
patella within the femoral trochlea. In general, patellofemoral joint contact area
decreases with knee extension,3 0 ,5 8 however comparison of knee kinematics throughout
the gait cycle revealed no group differences. This suggests that the decrease in contact
area in the PFP group may have been more a function of decreased joint congruency.
This finding has important clinical implications, since treatments aimed at altering
patellar alignment (i.e. changing patellofemoral joint congruence), may be beneficial in
improving contact area, thereby reducing the detrimental effects of elevated joint stress.
The diminished PFJRF in the PFP group during free walking was primarily a
function of a reduced knee extensor moment as the knee motion did not vary between
groups. The lower PFJRF and knee extensor moment are indicative of a quadriceps
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avoidance gait pattern, which has been suggested by Powers and colleagues to be a
strategy by which subjects with PFP reduce the muscular forces acting across the
patellofemoral joint.1 2 0 The reduced knee extensor moment could not be explained by a
reduction in knee flexion angle or by walking velocity, as no group differences were seen
in these variables. Instead, we hypothesize that a subtle forward trunk lean may have
been used by the PFP group to reduce the knee extensor moment. Although not
measured, such a maneuver would bring the body center of mass closer to the knee joint
center and subsequently reduce the demand on the knee extensors. This premise is
consistent with the findings of Ernst et al.4 0 Despite the apparent effort to reduce
quadriceps demand, such compensation did not translate into diminished patellofemoral
joint stress. However, a more normal knee extensor moment would likely have resulted
in greater differences in patellofemoral joint stress between the PFP and the control
groups.
Further analysis of the patellofemoral joint stress curve revealed an unexpected
bimodal curve. Two stress peaks were noted in each subject, one during weight
acceptance, and the second during early swing. The peak during weight acceptance was
generally higher in magnitude than the second peak, and was driven primarily by the
magnitude of the knee extensor moment and subsequent PFJRF (which also peaked at
this time), as well as the relatively small contact area associated with the smaller knee
flexion angles. The second peak occurred during a period of the gait cycle when the
rectus femoris has been reported to be active as a hip flexor,1 1 3 resulting in a
corresponding peak in the knee extensor moment and corresponding PFJRF. Passive
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restraint from soft tissue tautness (including that of the rectus femoris) also may have
contributed to the knee extension moment during this phase of the gait cycle.
A reduced knee extensor moment was not evident during fast walking, which
suggests that quadriceps avoidance was not achieved during the higher demand activity.
Subsequently, increases in the PFJRF and patellofemoral joint stress were observed in the
PFP group during fast walking. This finding is consistent with increased clinical
complaints of pain with functional activities requiring higher quadriceps force, such as
fast walking, stairs, and running.
In light of the findings reported in the current study, there are several limitations
that should be noted. Our results, while supporting the proposed hypothesis, may not be
generalized to the entire PFP population as only 10 subjects were evaluated. In addition,
the model used in this study assumed a planar representation of the patellofemoral joint
for calculation of patellofemoral joint stress. While the error associated with such an
assumption is not known, any error would be consistent across both groups, making
comparisons between populations possible. Finally, the MRI technique utilized to assess
patellofemoral joint contact area was performed with the quadriceps muscle group
relaxed and may not be representative of the magnitude of contact area present with
quadriceps contraction. Future study is needed to explore potential differences in contact
area with the quadriceps relaxed and contracted.
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CONCLUSION
Subjects with PFP exhibited higher patellofemoral joint stress during the gait
cycle when compared to subjects without PFP. These findings are consistent with the
hypothesis that increased patellofemoral joint stress is a predisposing factor with respect
to development of PFP. Elevated patellofemoral joint stress in the PFP group was a
function of decreased patellofemoral joint contact area, as the PFJRF was comparable
between groups. Clinically, these findings indicate that treatment designed to alter the
magnitude of the contact area between the patella and the femur may be beneficial to
reduce the patellofemoral joint stress during level walking.
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CTRL
% Gait Cycle
CTRL
100
% Gait Cycle
Figure 4.2. Comparison of knee joint flexion angle between groups during (A) free walking and (B) fast walking. No
significant differences were found between the patellofemoral pain (PFP) and the control (CTRL) groups.
^ 4
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CTRL
CTRL
Figure 43. Comparison of knee joint moments between groups (A) free walking and (B) fast walking. Positive values
indicate knee extensor moment, negative values indicate knee flexor moment. ‘Indicates peak knee extensor moment
significantly smaller in the patellofemoral pain (PFP) group compared to the control (CTRL) group.
1
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-PFP CTRL
15
12
9
6
3
0
— r
100 60 80 20 40 0
% Gait Cycle
PFJRF-time Integral (p=.06)
PFP: 84.6 N/kg*%Gait Cycle
CTRL: 107.2 N/kg*%Gait Cycle_______
B.
£
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g
£
PFP CTRL
15
12
9
6
3
0
100 80 0 20 40 60
•/•Gait Cycle
PFJRF-time Integral (p>. 1)
PFP: 135.5 N/kg*%Gait Cycle
CTRL: 146.9 N/kg*%Gait Cycle_____
Figure 4.4. Comparison of patellofemoral joint reaction force (PFJRF) between groups during (A) free walking and (B)
fast walking. ^Indicates significantly smaller peak PFJRF in the patellofemoral pain (PFP) group compared with the
control (CTRL) group.
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A.
PFP CTRL
500
400
i 300
m
t
<
200
100
■ T — i
40 60 100 0 20 80
% Gail Cycle
B.
PFP CTRL
20 40 60
% Gait Cycle
80 100
Figure 4.5. Comparison of utilized patellofemoral joint (PFJ) contact area between groups during (A) free walking
and (B) fast walking. "Indicates average utilized PFJ contact area is significantly less in the patellofemoral pain (PFP)
group compared to the control (CTRL) group during free and fast walking.
■vj
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b
Vi
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■ -CTRL PFP
8
6
4
2
■ I
0
I
60 80 100 0 20 40
•/•Gait Cycle
PFJ Stress-time Integral
PFP; 51.42 MPa*%Gait Cycle
CTRL; 22.36 MPa*%Gait Cycle
B.
PFP** CTRL
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20 80 100 0 40 60
% Gait Cycle
PFJ Stress-time Integral
PFP: 67.91 MPa*%Gait Cycle
CTRL; 33.05 MPa*%Gait C ycle_____
Figure 4.6. Comparison of patellofemoral joint (PFJ) stress between groups (A) free walking and (B) fast walking.
•Indicates peak PFJ stress in the patellofemoral pain (PFP) group is significantly greater than the control (CTRL)
group. ^Indicates the PFJ stress time integral (area under the curve) is significantly greater in the PFP group
compared to the control group during free and fast walking.
■ 'j
O n
CHAPTER V
PATELLOFEMORAL JOINT STRESS DURING STAIR ASCENT
AND DESCENT IN PERSONS WITH AND WITHOUT
PATELLOFEMORAL PAIN
PFP is a common syndrome causing pain and functional limitations during stair
climbing and other activities requiring high levels of quadriceps activity. Ascending and
descending stairs, are two of the most painful activities of daily living for persons with
PFP. Whether or not the pain associated with stair ambulation is the result of elevated
joint stress (force per unit area) has not been explored.
This chapter will compare the patellofemoral joint stress in persons with and
without PFP during stair ascending and descending tasks. Information obtained from this
study will be useful in understanding the biomechanical mechanisms contributing to
functional deficits in the PFP population.
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INTRODUCTION
Patellofemoral pain (PFP) affects approximately one of four people in the general
population.3 2 The clinical presentation of PFP varies between individuals, but some
features are considered representative. For example, pain is commonly described as
being retropatellar or along the medial and lateral borders of the patella. Symptoms are
typically exacerbated with sustained sitting (movie-goers knee) and activities requiring
high levels of quadriceps activity (i.e. running, squatting, and negotiating stairs).1 3 8 ,1 5 4
From a functional standpoint, ascending and descending stairs is one of the most painful
activities of daily living for persons with PFP.
It has been reported that stair climbing places a higher demand on the knee when
compared to level walking as demonstrated by an increased knee extensor moment (an
indication of quadriceps demand) and greater range of knee motion.5 ,6 As the
patellofemoral joint reaction force (PFJRF) is dependent on the magnitude of the
quadriceps force and the knee flexion angle,5 5 the compressive force acting between the
patella and femoral trochlea during stair ascent and descent would be expected to be
significant In fact, Matthews & colleagues have reported that the PFJRF during stair
ambulation is more than three times that of level walking.2 9 The increased PFJRF
associated with stair ambulation suggests that patellofemoral joint stress (force per unit
contact area) would be elevated as well. Elevated patellofemoral joint stress in the PFP
population is of significant concern as stress is thought to be the factor responsible for
articular cartilage degeneration and wear.5 5 ,1 0 0
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Whether or not individuals with PFP demonstrate higher magnitudes of
patellofemoral joint stress compared to non-painful individuals has not been explored.
Evidence does exist however, suggesting that this may be the case. Hebert et al. reported
that individuals with PFP demonstrated increased knee extensor moments during a
squatting activity when compared to control subjects.6 5 This finding implies that the
PFJRF may be elevated as well. In addition, PFP has been reported to be associated with
patellar malalignment,9 '5 4 ,5 5 which can result in reduced patellofemoral joint contact
area4 9 ,6 8 ,9 4 and an increase in patellofemoral joint stress.
Using an imaging based biomechanical model of the patellofemoral joint (which
takes into consideration the inherent variability in patellofemoral joint contact areas
between individuals) the purpose of this study was to quantify patellofemoral joint stress
in persons with and without PFP during stair ascent and descent. It was hypothesized that
persons with PFP would demonstrate higher patellofemoral joint stress compared to
individuals without PFP. Information obtained from this study may be useful in
understanding the biomechanical mechanisms contributing to functional deficits in the
PFP population.
METHODS
SU BJECTS
Twenty subjects were recruited for this study, 10 individuals with a diagnosis of
PFP (five males, five females) and 10 individuals without PFP (five males, five females)
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There were no significant group differences with respect to average age, height, or weight
(Table 4.1).
The PFP subjects were recruited from orthopaedic clinics in the Los Angeles area.
For purposes of this study, PFP subjects were screened to rule out ligamentous instability,
internal derangement, or patellar tendonitis. Subjects were accepted into the study if they
met the following inclusion criterion 1) pain originating specifically from the
patellofemoral articulation (vague or localized) and 2) reproducible pain with at least two
of the following functional activities commonly associated with PFP: a) stair ascent or
descent, b) squatting, c) kneeling, d) prolonged sitting, e) isometric quadriceps
contraction.1 1 9 ,1 2 0 Subjects with PFP were excluded from participation if they reported
having any of the following: 1) previous history of knee surgery; 2) history of traumatic
patellar dislocation; 3) any neurological involvement that would influence gait; 4) any
implanted biological devices, such as pacemakers, cochlear implants, clips which could
interact with the magnetic field during imaging.
Subjects in the comparison group were recruited from the University of Southern
California, and matched for gender to those in the PFP group. Inclusion criterion for
participation in the comparison group were as follows: 1) no history or diagnosis of knee
pathology or trauma; 2) no knee pain with any o f the activities described as inclusion
criterion for the PFP group; 3) no limitations present that would influence gait; and 4) no
implanted biological devices, such as pacemakers, cochlear implants, clips which could
interact with the magnetic field during imaging.
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Prior to participation, all subjects were fully informed as to the nature of the
study, and signed a human subjects consent form approved by the Institutional Review
Board of the University of Southern California Health Sciences campus.
PROCEDURE
All subjects completed two phases of data collection. Phase one consisted of MRI
assessment to determine patellofemoral joint contact area, while phase two consisted of
comprehensive motion analysis during stair ascent and stair descent Data obtained from
both data collection sessions were required as input variables into a biomechanical model
to quantify patellofemoral joint stress.
Magnetic Resonance Imaging
All imaging was performed at the Los Angeles County / University of Southern
California Imaging Science Center. Images of the patellofemoral joint were obtained
using a l.ST magnet (GE Medical Systems, Milwaukee, Wisconsin) and a three-
dimensional spoiled gradient recalled echo (3D SPGR) imaging sequence. The following
parameters were employed: TR=60ms, TE=20ms, Flip Angle=30°, NEX=1.5, matrix
size: 512 X 224 X 28, field of view: 20 cm X 20 cm and chemically selective fat
suppression. Each slice was 2 mm thick and contiguous with adjacent slices.
Prior to scanning, subjects removed any metal such as jewelry and hair clips.
Subjects were positioned supine in the MRI Bore with the knee in 0° o f knee flexion.
One receive-only extremity coil was secured on each side of the patellofemoral joint.
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Subjects rested quietly while the scan was performed. Following completion of the first
scan, subjects were re-positioned and the scan repeated with the knee supported in three
additional knee flexion angles 20°, 40°, and 60°. Total imaging time was 44 minutes.
Motion Analysis
Motion analysis was performed at the Musculoskeletal Biomechanics Research
Laboratory at the University of Southern California. Three-dimensional kinematics were
obtained using a six-camera motion analysis system (Vicon, Oxford Metrics LTD,
Oxford, England). Movement was sampled at 60Hz and recorded digitally on an IBM
166 MHz personal computer. Reflective markers (20 mm spheres) placed at specific
anatomical landmarks were used to determine motion of the pelvis and lower extremity.
Ground reaction forces were collected at a rate o f2500 Hz using an AMTI force plate
(Model #OR6-6-l, Newton, Mass). This force plate was situated as the first of a three-
step staircase (step height = 20.5 cm, tread = 27.5 cm) (Figure 5.1).
Subjects were appropriately attired to permit marker placement directly on the
skin of the subject The involved limb was instrumented for subjects with PFP, while the
right lower extremity was instrumented for subjects without PFP. Anthropometric
measures were obtained from each subject for use in calculating lower extremity kinetics
using inverse dynamics equations. Reflective markers were then taped to the following
landmarks: sacrum, anterior superior iliac spine (ASIS) bilaterally, lateral thigh, lateral
femoral epicondyle, lateral tibia, lateral malleolus, 2nd metatarsal head, and posterior
calcaneous.
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Staircase Level
1) step #3-
2) start position -
Floor Level: (Force
1) step#1 -ascent
2) step #2-
Staircase Level 1:
1) step #2 - ascent
2) step#1-descent
Subfloor Level:
1 ) start position -
2) step #3-
Figure 5.1. Force plate and portable staircase set up arrangement. This
arrangement permitted the force plate to become one of the steps during stair
ascent and descent
Subjects were allowed several practice trials to accommodate to the stair
apparatus. All participants were instructed to walk in a step over step fashion at a self
selected pace. Two trials for each ascending stairs and descending stairs were obtained
for each subject. A trial was considered successful if the subject’s instrumented foot
landed within the force plate. All kinematic and kinetic data were collected
simultaneously.
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DATA ANALYSIS
Patellofemoral joint Contact Area
Sequential sagittal plane images of the patellofemoral joint were displayed for
analysis using Signa Advantage medical imaging software (GE Medical Systems,
Milwaukee, Wisconsin). The section of the image containing the patella and surrounding
portion of the femur was enlarged to 2.5 times normal view to enhance visualization of
the contact area. Contact was defined as areas of patella and femoral approximation in
which no distinct separation could be found between the cartilage borders of the two
structures. Since cartilage is relatively bright on the 3D SPGR images obtained, the
definition of contact area was operatively defined as ‘white on white’.7 0
The line of contact between the patella and femur was measured and recorded
using the same software used to display the images. When the line of contact was
curved, separate straight-line segments were measured. To obtain the contact area for
each slice, the length was multiplied by the 2-mm slice thickness. Contact areas
calculated from each image were summed to obtain the total patellofemoral joint contact
area, with values reported in mm2. This method has been shown to be reliable and
comparable to contact area obtained using Fuji pressure sensitive film in cadaver
specimens.7 0 Contact area measurements were made twice and averaged. All MRI
measurements were made by the same investigator.
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Knee Joint Kinematics and Kinetics
Reflective markers were identified manually using VICON Clinical Manager
(VCM) software and then automatically digitized. The same software was used to
calculate knee joint kinematics and kinetics in the sagittal plane. Only data
corresponding to the force plate step was used.
To calculate the net joint moment at the knee, anthropometric data, ground
reaction forces, and kinematics were used to solve inverse dynamics equations. To
facilitate comparison between subjects and groups, the net knee joint moments were
normalized by body mass and reported in units of Nm/kg. Data obtained from the two
trials were averaged.
Biomechanical Model
A patellofemoral joint model was developed to utilize input from mechanical
analysis of the lower extremity and patellofemoral joint contact area from the MRI. An
overview of the model is illustrated (Figure 4.1). Input variables for the model algorithm
included knee joint flexion angle, knee extensor moment, and patellofemoral joint contact
area.
The first step of the algorithm was to calculate the quadriceps force. The
effective lever arm (LA) for the quadriceps muscle group was determined for each knee
joint angle position using an equation fit to the data from van Eijden et al (Equation
I J O
4.1). At each joint angle, the knee extensor moment (M ext) was divided by the lever
arm to obtain quadriceps force (QF) (Equation 4.2).
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The second step of the algorithm was to calculate the patellofemoral joint reaction
force (PFJRF). A constant (k) was then calculated for each joint angular position by
fitting an equation to the data reported by van Eijden et al (Equation 4.3).1 4 7 This
constant was multiplied by the QF to obtain the patellofemoral joint reaction force
(PFJRF) (Equation 4.4).
Using the four contact area values obtained from MRI, the final step in the
algorithm was to calculate patellofemoral joint stress. A straight line was fit between
each two consecutive data points to provide approximate patellofemoral joint contact area
values for each knee flexion angle from 0° to 60°. For knee flexion angles greater than
60°, the straight line fit between contact area at 40° and 60° was extrapolated out to the
maximum knee flexion angle measured. Patellofemoral joint stress was then calculated
by dividing the PFJRF by the contact area for the knee flexion angle corresponding to the
PFJRF value (Equation 4.5).
The model output was PFJRF, patellofemoral joint stress, and utilized contact
area (contact area corresponding to knee flexion angle), all normalized to the stance
phase of stair ambulation. The patellofemoral joint stress-time integral was calculated by
taking the area under the patellofemoral joint stress curve as a function of the stance
phase. Similarly, the PFJRF-time integral was the area under the PFJRF curve as a
function of the stance phase. The mean utilized contact area was calculated by taking the
average of the utilized contact area over the stance phase.
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STATISTICAL ANALYSIS
Variables used for statistical analysis included cadence, peak patellofemoral joint
stress, patellofemoral joint stress-time integral, peak PFJRF, PFJRF-time integral, peak
knee extensor moment, peak knee joint flexion and extension angle, and mean utilized
contact area.
Comparisons between groups were made using trimmed means and Yuen's test
for comparison of two independent groups with unequal variances.1 6 0 This analysis was
repeated for each variable and significance levels were set at p<.05. All statistics were
computed using a custom macro written in Microsoft Excel '97.
RESULTS
CADENCE
During stair ascent, the PFP group adopted a significantly slower cadence
compared with the control group (115.9 vs. 142.1 steps/min; p=.016). Similarly, the PFP
group demonstrated a significantly reduced cadence compared with the control group
during stair descent (115.4 vs. 153.6 steps/min; p=.004).
K NEE KINEMA TICS
There were no significant differences in knee kinematics between the PFP group
and the control group during stair ascent or stair descent (Figure 5.2A, 5.2B).
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N E T KN EE JO IN T M OM ENTS
During stair ascent, the PFP group demonstrated a significantly lower peak knee
extensor moment when compared to the control group (0.81 vs. 1.16 Nm/kg; p=.04)
(Figure 5.3 A). The same trend was observed during stair descent (0.98 vs. 1.12 Nm/kg),
however this difference was not statistically significant (p=.09) (Figure 5.3B).
PATELLOFEM ORAL JO IN T REAC TIO N FORCE
During stair ascent, peak PFJRF was significantly less in the PFP group when
compared to the control group (25.0 vs. 37.3 N/kg; p=.02) (Figure 5.4A). In addition, the
PFJRF-time integral, during stair ascent, was significantly less in the PFP group when
compared to the control group (288.2 vs. 501.9 N/kg * % Stance Phase; p=.01XFigure
5.4A). In contrast, there was no significant group difference with respect to the peak
PFJRF during stair descent although a trend was observed toward smaller PFJRF-time
integral in the PFP group (464.4 vs. 605.9 N/kg * % Stance Phase; p=07) (Figure 5.4B).
UTILIZED PATELLOFEM ORAL JO IN T CONTACT AREA
There were no significant differences in the mean utilized contact area between
the PFP and the control group during stair ascent or stair descent (Figure 5.5A, 5.5B).
PATELLOFEM ORAL JO IN T STR E SS
During stair ascent, there was no significant difference in peak patellofemoral
joint stress between the PFP group and the control group (Figure 5.6A). Furthermore,
there was no significant group difference with respect to the patellofemoral joint stress-
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time integral (Figure S.6A). Similarly, during stair descent there was no significant
group difference for either peak patellofemoral joint or the patellofemoral joint stress-
time integral (Figure 5.6B). Although peak patellofemoral joint stress was not
significantly different between groups, the time at which peak patellofemoral joint stress
occurred was significantly earlier for the PFP group when compared to the control group
(50 vs. 76 % Stance Phase; p^.05) (Figure 5.6B).
DISCUSSION
As persons with PFP typically complain o f pain during stair ambulation, it was
hypothesized that these individuals would demonstrate elevated patellofemoral joint
stress when compared to individuals without PFP. This hypothesis was not supported by
the current study as no significant group differences were found for either peak
patellofemoral joint stress or patellofemoral joint stress-time integral during stair ascent
or descent
When evaluating the individual components of patellofemoral joint stress,
however, group differences were observed. During stair ascent, peak PFJRF and the
PFJRF-time integral were significantly reduced in the PFP group, with values being 33%
and 43% lower respectively, than the control group. The reduced PFJRF in the PFP
group was attributed to a 50% reduction in the peak knee extensor moment as there were
no differences in knee kinematics.
The lower knee extensor moment and PFJRF are suggestive of quadriceps
avoidance, which has been proposed by Powers and colleagues to be a compensatory
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strategy by which subjects with PFP reduce the forces acting across the patellofemoral
joint.1 2 0 The reduced knee extensor moment was likely achieved through a significant
reduction in stair climbing cadence as moments have been shown to be influenced by
walking speed.1 1 3 Although not measured, altered segment alignment, such as forward
trunk lean, could have been an additional strategy to reduce the knee extensor moment.
Such a strategy, as reported by Erast et al, would bring the body center of mass closer to
the knee joint center subsequently reducing the moment about the knee joint4 0
Despite the fact that the PFJRF was reduced in the PFP group during stair ascent,
patellofemoral joint stress was similar between groups. This discrepancy can be
explained by the trend toward decreased utilized contact area in the PFP group.
Although not statistically significant the observed 14% reduction in contact area helped
offset the decrease in stress that would be expected with a reduction in PFJRF (the result
being a stress curve comparable to the control group).
In contrast to stair ascent there was no significant difference in the peak PFJRF
during stair descent. Despite the lower cadence in the PFP group (75% of normal) there
was only a trend towards decreased knee extensor moment and PFJRF-time integral.
The lack of a significant difference in the PFJRF during stair descent as found in stair
ascent may be related to differences in compensation options between these two tasks.
For example, subjects with PFP selected a similar cadence during the two tasks (115.9
and 115.4 steps/min respectively for stair ascent and stair descent) yet the peak knee
moment during stair ascent was less than 83% of the peak during stair descent A similar
yet larger difference was noted in peak PFJRF, with the peak during stair ascent 76% as
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large as that during stair descent. Thus, the increase in the knee moment and PFJRF
during stair descent was not a function of cadence and must be attributed to other factors.
Although the patellofemoral joint stress-time integral during stair descent was
similar between groups, the pattern of patellofemoral joint stress was different, with peak
patellofemoral joint stress occurring significantly earlier in the stance phase for the PFP
group. This early peak in patellofemoral joint stress may be explained by the reduced
utilized contact area at lesser knee flexion angles in the PFP group. Given similar shaped
PFJRF curves, the smaller utilized contact area would result in greater peak
patellofemoral joint stress during the first 60% of the stair descent stance phase. As the
knee flexion angle increased (during the last 40% stair descent stance phase) the
patellofemoral joint contact area in the PFP group also increased (relative to the control
group), resulting in decreased patellofemoral joint stress late in the stance phase. The
decreased contact area in the PFP group at lesser knee flexion angles (i.e. 0°-30°) is
consistent with the premise that patellar malalignment and subsequent reduction in
contact area would likely be evident before the patella becomes firmly seated in the
trochlear groove.6 8
Comparison of the ascending and descending stair conditions revealed that peak
patellofemoral joint stress values were similar although slightly larger during stair
descent However, the patellofemoral joint stress-time integral was more than 1.5 times
greater during descending stairs when compared to ascending stairs. As the
patellofemoral joint stress-time integral represents the stress experienced by the
patellofemoral joint over the stance phase, a larger integral is indicative of greater overall
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joint pressure. The greater patellofemoral joint stress-time integral during stair descent is
consistent with clinical complaints, as patients frequently report greater pain during stair
descent compared to stair ascent.
Caution must be made in generalizing these findings to the entire PFP population
as only 10 subjects were evaluated. It is likely that the degree of compensation during
stair ambulation may vary depending on the severity of pain complaints and the nature of
the injury. In addition, the model used in this study assumed a planar representation of
the patellofemoral joint for calculation of patellofemoral joint stress. While the error
associated with such an assumption is not known, any error would be consistent across
both groups, making comparisons between populations valid. Finally, the MRI technique
utilized to assess patellofemoral joint contact area was performed with the quadriceps
muscle group relaxed and may not be representative of the magnitude of contact area
present with quadriceps contraction. Future study is needed to explore potential
differences in contact area with the quadriceps relaxed and during activation.
CONCLUSION
Subjects with PFP did not demonstrate increased patellofemoral joint stress
during stair ascent and descent when compared to a pain free control group. During stair
ascent, stress was modulated by a reduction in the PFJRF which was accomplished
through a reduction in the knee extensor moment and a slower cadence. During stair
descent, although adopting a similar cadence to that in stair ascent, subjects with PFP
demonstrated higher peak knee moment and peak PFJRF, which accounted for the lack of
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significant differences during stair descent. These findings suggest that individuals with
PFP employ compensatory strategies to maintain normal levels o f joint stress during stair
ambulation.
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- « e , 60
PFP CTRL
% Stance
CTRL
100
100
% Stance
Figure 5.2. Knee joint angle plotted as a function of the stance phase for both the patellofemoral pain group (PFP)
and the control group (CTRL) during (A) ascending stairs and (B) descending stairs. There was no significant
difference between groups for peak knee flexion or peak knee extension.
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V
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-PFP CTRL
1.5
0.5
0
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PFP CTRL
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£ 0.5
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Figure 5.3. Net knee joint moment plotted as a function of the stance phase for both the patellofemoral pain group
(PFP) and the control group (CTRL) during (A) ascending stairs and (B) descending stairs. ^Indicates that peak
extension moment is significantly smaller in the PFP group when compared with the CTRL group.
V ©
in
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- - - PFP**
% Stance
PFJRF integral:
PFP: 288.2 N/kg * %Stance
CTRL: 501.9 N/kg *%Stance
CTRL
30
20
0 20 40 60 80 100
B
-PFP CTRL
40
30
20
10
0
0 20 60 80 40 100
% Stance
PFJRF integral:
PFP: 464.4 N/kg * %Stance
CTRL: 605.9 N/kg * %Stance
Figure 5.4. Pateltofemoral joint reaction force (PFJRF) plotted as a function of the stance phase for both the
patellofemoral pain group (PFP) and the control group (CTRL) during (A) ascending stairs and (B) descending stairs.
“Indicates that peak PFJRF is significantly smaller in the PFP group when compared with the CTRL group.
**Indicates that the PFJRF-time integral is significantly smaller in the PFP group when compared with the CTRL
group.
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- - PFP CTRL
600
400
« o
£
< 200
0 20 60 40 80 100
% Stance
B
. . . PFP
% Stance
CTRL
600
I 4 0 0
| 200
20 40 100 0 60 80
Figure 5.5. Utilized pateHofemoral joint (PFJ) contact area plotted as a function of the stance phase for both the
patellofeinoral pain group (PFP) and the control group (CTRL) during (A) ascending stairs and (B) descending stairs.
There was no significant difference between groups.
V O
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<»
E
•PFP CTRL
8
6
4
2
0
0 20 40 60
% Stance
PFJ Stress Integral:
PFP: 88.6 MPa ♦ % Stance
CTRL: 100 MPa *% Stance
80 100
B
PFP CTRL
8
6
4
2
0
0 20 40 60 100
% Stance
PFJ Stress Integral:
PFP: 159.3 MPa *% Stance
CTRL: 140.6 MPa *% Stance
Figure S.6. Patellofemoral joint (PFJ) stress plotted as a function of the stance phase for both the patellofemoral pain
group (PFP) and the control group (CTRL) during (A) ascending stairs and (B) descending stairs. "Indicates that the
time to peak PFJ stress was significantly earlier in the PFP group when compared with the CTRL group.
VO
00
SUMMARY AND CONCLUSIONS
The purpose of this dissertation was to assess the prevailing hypothesis that
patellofemoral joint stress is a causative factor in PFP. To assess patellofemoral joint
stress in vivo, both PFJRF and patellofemoral joint contact area had to be quantified since
patellofemoral joint stress is defined as (PFJRF * patellofemoral joint contact area). To
measure patellofemoral joint stress, it was first necessary to develop a reliable and valid
technique to quantify the patellofemoral joint contact area in-vivo. Once a technique was
established, patellofemoral joint stress and its component factors could be determined in
persons with PFP and compared with a control group. Patellofemoral joint stress was
quantified during level walking, an activity not usually reported as painful, followed by
ascending and descending stairs, an activity known to aggravate PFP. The hypothesis
being tested was that persons with PFP would exhibit greater patellofemoral joint stress
when compared to a control group. It was further expected that the differences between
groups would be larger during the higher demand activity of stair ambulation.
To assess the patellofemoral joint contact area in-vivo, an MRI method was
developed and the contact area obtained from the MRI method was compared to the
contact area obtained from the current (invasive) gold standard, Fuji pressure sensitive
film. The results of this comparison indicated that the MRI technique was both a valid
and reliable tool for assessing contact area. MRI permitted comparison of patellofemoral
joint eontact area between groups and allowed for an individualized assessment of
patellofemoral joint stress.
99
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The hypothesis of elevated patellofemoral joint stress in persons with PFP was
supported by the data obtained during free and fast walking, in that subjects with PFP
demonstrated significantly higher patellofemoral joint stress-time integrals, with values
more than twice that of the control group. Furthermore, the peak patellofemoral joint
stress was significantly higher in the PFP group during fast walking and there was a trend
toward higher peak patellofemoral joint stress in free walking in the PFP group when
compared with the control group. The higher patellofemoral joint stress in the PFP group
was primarily attributed to a reduction in utilized patellofemoral joint contact area during
level walking. The group with PFP selected a similar walking velocity as that of the
control group, used similar knee joint kinematics, yet the utilized contact area was
significantly different. Since the lower extremity mechanics were similar between
groups, the decrease in contact area in the PFP group appeared to be more a function of
decreased joint congruency.
In contrast to level walking, individuals with PFP did not demonstrate elevated
patellofemoral joint stress compared to the control group during either stair ascent or stair
descent. The PFP group did, however, demonstrate some evidence of compensation in
that they selected a significantly slower walking cadence (an indication of speed) during
both stair ascent and descent when compared to the control group. In addition, the PFP
group demonstrated a significantly smaller knee extension moment and PFJRF during
stair ascent and a trend toward a smaller knee extension moment and PFJRF in stair
descent This combination of findings, slower cadence and reduced knee extensor
moment is evidence o f a quadriceps avoidance pattern which has been suggested to be a
100
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compensatory strategy by which subjects with PFP attempt to reduce the forces acting on
the patellofemoral jo in t1 2 1
The findings for level walking are consistent with the premise that increased
patellofemoral joint stress is a predisposing factor with respect to development of PFP,
while the findings for stair climbing indicate a compensatory strategy. The difference in
the results between level walking and stair climbing may be explained by the fact that
stair climbing is an activity that typically aggravates symptoms of PFP, while level
walking usually is not considered to aggravate PFP symptoms.
These data suggest that there may be a limit to the amount of patellofemoral joint
stress that individuals with PFP are able to tolerate. Subjects in the PFP group utilized
similar lower extremity movement patterns as those in the control group even though
they resulted in significantly higher patellofemoral joint stress-time integrals during level
walking. However, when faced with the greater demand stair ambulation, persons with
PFP no longer continued to use lower extremity mechanics similar to the control group.
Subjects with PFP instead altered their gait pattern to attempt to minimize the stresses
experienced by the patellofemoral joint.
Clinically, these findings indicate that persons with PFP utilize less contact area
in the patellofemoral joint during level walking when compared to the control group.
Therefore, treatment designed to alter the magnitude of the contact area between the
patella and the femur would be beneficial to reduce the patellofemoral joint stress during
these activities. Furthermore, during stair ascent, stress was modulated by a reduction in
101
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the PFJRF, which was accomplished through a reduction in the knee extensor moment
and a slower cadence. These findings suggest that individuals with PFP employ
compensatory strategies during stair ambulation to maintain normal levels of joint stress.
102
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BIBLIOGRAPHY
1. Aglietti P, Insall JN, Cerulli G: Patellar pain and incongruence. I: Measurements
o f Incongruence. Clinical Orthopaedics and Related Research 1983; 176:217-
224.
2. Aglietti P, Menchetti PPM. Biomechanics of the patellofemoral joint, in Scuderi
GR (ed): The Patella. New York, Springer-Verlag; 1995:25-48.
3. Agur AMRed: Grant’ s Atlas o f Anatomy, Baltimore, Williams & Wilkins;
1991:255.
4. Ahmed A, Burke DL, Yu A: In-vitro measurement of static pressure distribution
in synovial joints- Part II: Retropatellar surface. Journal o f Biomedical
Engineering 1983; 105:231 -236.
5. Andriacchi TPP, Andersson BJM, Fermier RWBS, Stem DD, Galante JOM: A
Study of Lower-Limb Mechanics during Stair-Climbing. The Journal o f Bone
and Joint Surgery 1980;62-A:749-757.
6. Asplund DJ, Hall SJ: Kinetics and myoelectric activity during stair-climbing
ergometry. Journal o f Orthopaedic and Sports Physical Therapy 1995;22:247-
253.
7. Ateshian GA, Kwak SD, Soslowsky U , Mow VC: A stereophotogrammetric
method for determining in situ contact areas in diarthrodial joints, and a
comparison with other methods. Journal o f Biomechanics 1994;27:111-124.
8. Bartko JJ: On various intraclass correlation reliability coefficients. Psychological
Bulletin 1976;83:762-765.
9. Biloff C: Patellofemoral malalignment. The Journal o f Manual and Manipulative
Therapy 1995;3:39-43.
10. Blauth M, Tillmann B: Stressing on the human femoro-patellar joint. I.
Components of a vertical and horizontal tensile bracing system. Anatomy and
Embryology 1983;168:117-123.
11. Blazina ME, Fox JM, Del Pizzo W, Broukhim B, Ivey FM: Patellofemoral
replacement Clinical Orthopaedics and Related Research 1979;144:98-102.
12. Boucher JP, King MA, Lefebvre R, Pepin A: Quadriceps femoris muscle activity
in patellofemoral pain syndrome. American Journal o f Sports Medicine
1992;20:527-532.
103
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
13. Brand RA, Pedersen DR, Friederich JA: The sensitivity of muscle force
predictions to changes in physiologic cross-sectional area. Journal o f
Biomechanics 1986;19:589-596.
14. Brechter JHPC: Patellofemoral joint stress during stair ascent and descent:
comparison of persons with and without patellofemoral pain. Proceedings o f the
American Society fo r Biomechanics 2000;24:27-28.(Abstract)
15. Brossmann J, Muhle C, Schroder C, et al: Patellar tracking patterns during active
and passive knee extension: evaluation with motion-triggered cine MR imaging.
Radiology 1993;187:205-212.
16. Buff H-U, Jones LC, Hungerford DS: Experimental determination of forces
transmitted through the patello-femoral joint Journal o f Biomechanics
1988;21:17-23.
17. Callaghan MJ, Baltzopoulos V: Anterior knee pain: the need for objective
measurement. Clinical Biomechanics 1992;7:67-74.
18. Callaghan MJ, Baltzopoulos V: Gait analysis in patients with anterior knee pain.
Clinical Biomechanics 1994;9:79-84.
19. Carson WGJr, James SL, Larson RL, Singer KM, Wintemitz WW: Patellofemoral
disorders: physical and radiographic evaluation. Part I: Physical examination.
Clinical Orthopaedics and Related Research 1984a;185:165-177.
20. Carson WGJr, James SL, Larson RL, Singer KM, Wintemitz WW: Patellofemoral
disorders: physical and radiographic evaluation. Part II: Radiographic
examination. Clinical Orthopaedics and Related Research 1984b; 185:178-186.
2 1. Casscells SW: The arthroscope in the diagnosis of disorders of the patellofemoral
joint Clinical Orthopaedics and Related Research 1979;144:45-50.
22. Ceder LC, Larson RL: Z-plasty lateral retinacular release for the treatment of
patellar compression syndrome. Clinical Orthopaedics and Related Research
1979;144:110-113.
23. Childers JC, Jr., Ellwood SC: Partial chondrectomy and subchondral drilling for
chondromalacia. Clinical Orthopaedics and Related Research 1979;144:114-120.
24. Ching D, Lee T, Sandusky MD, Powers CM, Hicks KS, McMahon PJ: Effect of
tibial rotation on in-situ strain in the peripatellar reinaculum and patellofemoral
contact pressures. Orthopaedic Research Society 1998;815
25. Chrisman OD, Snook GA, Wilson TC: A long-term prospective study of the
Hauser and Roux-Goldthwait procedures for recurrent patellar dislocation.
Clinical Orthopaedics and Related Research 1979;144:27-30.
104
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
26. Clamann HP: Motor unit recruitment and the gradation of muscle force. Physical
Therapy 1993;73:830-843.
27. Clement DB, Tauton JE, Smart GW, McNicol KL: A survery of overuse running
injuries. Physician and Sports Medicine 1981;9:47-58.
28. Cohen ZA, McCarthy DM, Kwak SD, et al: Knee cartilage topography, thickness,
and contact areas from MRI: in-vitro calibration and in-vivo measurements.
Osteoarthritis Cartilage 1999;7:95-109.
29. Cook TM, Farrell KP, Carey LA, Gibbs JM, Wiger GE: Effects of restricted knee
flexion and walking speed on the vertical ground reaction force during gait.
Journal o f Orthopaedic and Sports Physical Therapy 1997;25:236-244.
30. Crosby BE, Insall J: Recurrent dislocation of the patella: relation of treatment to
osteoarthritis. Journal o f Bone and Joint Surgery 1976;58-A:9-13.
31. D'Agata SD, Pearsall AW, IV, Reider B, Draganich LF: An in vitro analysis of
patellofemoral contact areas and pressures following procurement of the central
one-third patellar tendon. American Journal o f Sports Medicine 1993;21:212-
219.
32. Devereaux M, Lachmann S: Patellofemoral arthralgia in athletes attending a
sports injury clinic. Britain Journal o f Sports Medicine 1984; 18:18-21.
33. Dillon PZ, Updyke WF, Allen WC: Gait analysis with reference to
chondromalacia patellae. Journal o f Orthopaedic and Sports Physical Therapy
1983;5:127-131.
34. Douchette SA, Child DD: The effect of open and closed chain exercise and knee
joint position on patellar tracking in lateral patellar compression syndrome. The
Journal o f Orthopaedic and Sports Physical Therapy 1996;23:104-110.
35. Dufek JS, Bates BT: The evaluation and prediction of impact forces during
landings. Medicine an Science in Sports and Exercise 1990;22:370-377.
36. Eilert RE: Dysplasia of the patellofemoral joint in children. American Journal o f
Knee Surgery 1999;12:114-119.
37. Elftman H: Forces and energy changes in the leg during walking. American
Journal o f Physiology 1939;125:339-356.
38. Engin AE, Korde MS: Biomechanics of normal and abnormal knee joint Journal
o f Biomechanics 1974;7:325-334.
39. Ericson MO, Nisell R: Patellofemoral joint forces during ergometric cycling.
Physical Therapy 1987;67:1365-1369.
105
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
40. Ernst G, Kawaguchi J, Saliba E: Effect of patellar taping on knee kinetics of
patients with patellofemoral pain syndrome. Journal o f Orthopedic and Sports
Physical Therapy 1999;29:661-667.(Abstract)
41. Fabbriciani C, Schiavione Panni A, Delcogliano A: Role of arthroscopic lateral
release in the treatment of patellofemoral disorders. Arthroscopy 1992;8:531-536.
42. Farahmand F, Senavongse W, Amis AA: Quantitative study of the quadriceps
muscles and trochlear groove geometry related to instability of the patellofemoral
joint. Journal o f Orthopaedic Research 1998;16:136-143.
43. Ficat RP, Ficat C, Gedeon P, Toussaint JB: Spongialization: A new treatment for
diseased patellae. Clinical Orthopaedics and Related Research 1979; 144:74-83.
44. Fielding JW, Liebler WA, Urs K, Wilson SA, Puglisi AS: Tibial tubercle transfer:
a long-range follow-up study. Clinical Orthopaedics and Related Research
1979;144:43-44.
45. Finlay JB: Energy absorbing ability o f articular cartilage during impact. Medical
& Biological Engineering &Computing 1979;17:397-403.
46. Flynn TW, Soutas-Little RW: Patellofemoral joint compressive forces in forward
and backward running. The Journal o f Orthopaedic and Sports Physical Therapy
1995;21:277-282.
47. Fox TA: Dysplasia of the quadriceps mechanism: Hypoplasia of the vastus
medialis muscle as related to the hypermobile patella syndrome. Surgical Clinics
o f North America 1975;55:199-226.
48. Frankel VH, Burstein AH, Brooks DB: Biomechanics of internal derangement of
the knee. Journal o f Bone and Joint Surgery l971;53-A:945-962.
49. Fujikawa K, Seedhom BB, Wright V: Biomechanics of the patello-femoral joint.
Part II: a study of the effect of simulated femoro-tibial varus deformity on the
congruity of the patello-femoral compartment and movement of the patella.
Engineering in Medicine 1983a; 12:13-21.
50. Fujikawa K, Seedhom BB, Wright V: Biomechanics of the patello-femoral joint.
Part I: a study o f the contact and the congruity of the patello-femoral
compartment and movement of the patella. Engineering in Medicine 1983b; 12:3-
11.
51. Fukubayashi T, Kurosawa H: The contact area and pressure distribution pattern of
the knee. Acta Orthopaedica Scandinavia 1980;51:871-879.
52. Fulkerson JP: Evaluation of the peripatellar soft tissues and retinaculum in
patients with patellofemoral pain. Clinics in Sports Medicine 1989;8:197-202.
106
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
53. Fulkerson JP, Gossling HR: Anatomy of the knee joint lateral retinaculum.
Clinical Orthopaedics and Related Research 1980;153:183-188.
54. Fulkerson JP, Hungerford DS: Disorders o f the Patellofemoral Joint, Baltimore,
Williams & Wilkins; 1990:
55. Fulkerson JP, Shea KP: Mechanical basis for patellofemoral pain and cartilage
breakdown, in Ewing JW (ed): Articular Cartilage and Knee Joint Function:
Basic Science and Arthroscopy. New York, Raven Press; 1990:93-101.
56. Gilleard W, McConnell J, Parsons D: The effect of patellar taping on the onset of
vastus medialis obliquus and vastus lateralis muscle activity in persons with
patellofemoral pain. Physical Therapy 1998;78:25-32.
57. Goodfellow J, Hungerford DS, Woods C: Patello-femoral joint mechanics and
pathology. II. Chondromalacia Patellae. Journal o f Bone and Joint Surgery
1976;58-B:291-299.
58. Goodfellow J, Hungerford DS, Zindel M: Patello-femoral joint mechanics and
pathology. I. Functional Anatomy of the patello-femoral joint. Journal o f Bone
and Joint Surgery 1976;58-B:287-290.
59. Grana WA, Coniglione: Knee disorders in runners. The Physician and Sports
Medicine 1985;13:127-133.
60. Gray H: Gray's Anatomy, Philadelphia, Lea & Febiger, 1984:
61. Grelsamer RP, Klein JR: The biomechanics of the patellofemoral joint. Journal
o f Orthopaedic and Sports Physical Therapy 1998;28:286-298.
62. Grood ES, Suntay WJ, Noyes FR, Butler DL: Biomechanics of the knee-extension
exercise: effect of cutting the anterior cruciate ligament. Journal o f Bone and
Joint Surgery 1984;66-A:725-733.
63. Hall JE, Micheli U , McManama GB: Semitendinosus tenodesis for recurrent
subluxation or dislocation of the patella. Clinical Orthopaedics and Related
Research 1979;144:31-35.
64. Haut R: Contact pressures in the patellofemoral joint during impact loading on the
human flexed knee. Journal o f Orthopaedic Research 1989;7:272-280.
65. Hebert U , Gravel D, Arsenault AB, Tremblay G: Patellofemoral pain syndrome:
the possible role of an inadequate neuromuscular mechanism. Clinical
Biomechanics 1994;9:93-97.
107
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
66. Heegaard J, Leyvraz P-F, Cumier A, Rakotomanana L, Huiskes R: The
biomechanics of the human patella during passive knee flexion. Journal o f
Biomechanics 1995;28:1265-1279.
67. Heegaard J, Leyvraz P-F, Van Kampen A, Rakotomanana L, Rubin PJ,
Blankevoort L: Influence of soft structures on patellar three-dimensional tracking.
Clinical Orthopaedics and Related Research 1994;299:235-243.
68. Hefzy MS, Jackson WT, Saddemi SR, Hsieh Y-F: Effects of tibial rotations on
patellar tracking and patello-femoral contact areas. Journal o f Biomedical
Engineering 1992;14:329-343.
69. Hehne H-JM: Biomechanics of the patellofemoral joint and its clinical relevance.
Clinical Orthopaedics and Related Research 1990;258:73-85.
70. Heino JG, Powers CM, Terk MR, Lee TQ: Measurement of patellofemoral joint
contact area using magnetic resonance imaging. Transactions o f the Orthopaedic
Research Society 1999;45:99(Abstract)
71. Hirokawa: Three-dimensional mathematical model analysis of the patellofemoral
joint Journal o f Biomechanics 1991;24:659-671.
72. Hirokawa S: Three-dimensional mathematical model analysis of the
patellofemoral joint. Journal o f Biomechanics 1991;24:659-671.
73. Hirokawa S, Solomonow M, Lu Y, Lou Z-P, D'Ambrosia R: Anterior-posterior
and rotational displacement of the tibia elicited by quadriceps contraction. The
American Journal o f Sports Medicine 1992;20:299-306.
74. Hoy MG, Zajac F, Gordon ME: A musculoskeletal model of the human lower
extremity: the effect of muscle, tendon, and moment arm on the moment-angle
relationship of musculotendon actuators at the hip, knee, and ankle. Journal o f
Biomechanics 1990;23:157-169.
75. Hsu RWW, Himeno S, Covertry MB, Chao EYS: Normal axial alignment of the
lower extremity and load-bearing distribution at the knee. Clinical Orthopaedics
and Related Research 1990;215-227.
76. Huberti HH, Hayes WC: Patellofemoral contact pressures: the influence of Q-
angle and tendofemoral contact. The Journal o f Bone and Joint Surgery
1984; 16A:715-723.
77. Huberti HH, Hayes WC, Stone JL, Shybut GT: Force ratios in the quadriceps
tendon and ligamentum patellae. Journal o f Orthopaedic Research 1984;2:49-54.
108
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
78. Hughston JC: Proximal and distal reconstruction of the extensor mechanism for
patellar subluxation. Clinical Orthopaedics and Related Research 1979; 144:36-
42.
79. Hungerford DS, Barry M: Biomechanics of the patellofemoral joint. Clinical
Orthopaedics and Related Research 1979;144:9-15.
80. Hunter W: Of the structure and disease of articulating cartilage. Clinical
Orthopaedics and Related Research 1995;317:3-6.
81. Insall JN: Chondromalacia patellae: patellar malalignment syndrome.
Orthopaedic Clinics o f North America 1979;10:117-127.
82. Insall JN: Current Concepts Review Patellar Pain. Journal o f Bone and Joint
Surgery 1982;64-A: 110-114
83. Insall JN, Bullough PG, Burstein AH: Proximal "tube” realignment of the patella
for chondromalacia patellae. Clinical Orthopaedics and Related Research
1979;144:63-69.
84. Insall JN, Falvo KA, Wise DW: Chondromalacia Patellae: a prospective study.
Journal o f Bone and Joint Surgery 1976;58-A: 1 -8.
85. Jordan G, Schwellnus MP: The incidence of overuse injuries in military recruits
during basic training. Military Medicine 1994; 159:421-426.
86. Kannus P, Aho H, Jarvinen M: Computerized recording of visits to an outpatients
sports clinic. American Journal o f Sports Medicine 1987;15:79-85.
87. Karst GM, Jewett PD: Electromyographic analysis of exercises proposed for
differential activation of medial and lateral quadriceps femoris muscle
components. Physical Therapy 1993;73:286-295.
88. Karst GM, Willett GM: Onset timing of electromyographic activity in the vastus
medialis oblique and vastus lateralis muscles in subjects with and without
patellofemoral pain syndrome. Physical Therapy 1995;75:813-823.
89. Kempson GE: The mechanical properties o f articular cartilage, in Sokoioff L (ed):
The Joints and Synovial Fluid. New York, Academic Press; 1980:177-238.
90. Kettelkamp DB, Jacobs AW: Tibiofemoral contact area - determination and
implications. Journal o f Bone and Joint Surgery 1972;54-A:349-356.
91. Koh TJ, Grabiner MD, De Swart RJ: In vivo tracking of the human patella.
Journal o f Biomechanics 1992;25:637-643.
109
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
92. Laprade J, Culham E, Brouwer B: Comparison of five isometric exercises in the
recruitment of the vastus medialis oblique in persons with and without
patellofemoral pain syndrome. Physical Therapy 1998;27:197-204.
93. Laurin CA, Dussault R, Levesque HP: The tangential x-ray investigation of the
patellofemoral joint Clinical Orthopaedics and Related Research 1979; 144:16-
26.
94. Lee TQ, Anzel SH, Bennett KA, Pang D, Kim WC: The influence of fixed
rotational deformities of the femur on the patellofemoral contact pressures in
human cadaver knees. Clinical Orthopaedics 1994;302:69-74.
95. Levine J: Chondromalacia patellae. Physician and Sports Medicine 1979;7:41-
49.
96. LiebFJ, Perry J: Quadriceps Function. An anatomical and mechanical study
using amputated limbs. Journal o f Bone and Joint Surgery 1968;50-A:1535-
1548.
97. Lindahl O, Movin A: The mechanics of extension o f the knee joint. Acta
Orthopaedica Scandinavia 1967;38:226-234.
98. Luo Z-P, Hsu H-C, Rand JA, An K-N: Importance of soft tissue integrity on
biomechanical studies of the patella after TKA. Transactions o f the ASME
1996;118:130-132.
99. MacIntyre DL, Robertson GE: Quadriceps muscle activity in women runners with
and without patellofemoral pain syndrome. Archives o f Physical and Medical
Rehabilitation 1992;73:10-14.
100. Maquet P: Mechanics and osteoarthritis of the patellofemoral joint Clinical
Orthopaedics and Related Research 1979;144:71-73.
101. Mariani P, Caruso I: An electromyographic investigation of subluxation of the
patella. Journal o f Bone and Joint Surgery 1979;6 IB: 169-171.
102. Matthews LS, Sonstegard DA, Henke JA: Load bearing characteristics of the
patello-femoral joint. Acta Orthopaedica Scandinavia 1977;18:511-516.
103. McConnell J: The management of chondromalacia patellae: a long term solution.
The Australian Journal o f Physiotherapy 1986;32:215-223.
104. McMinn RMH, Hutchings RT: Color Atlas o f Human Anatomy, Chicago, Year
Book Medical Publishers, Inc.; 1977:263.
110
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
105. Minkoff J, Fein L: The role of radiography in the evaluation and treatment of
common anarthrotic disorders of the patellofemoral joint. Clinics in Sports
Medicine 1989;8:203-260.
106. Mori Y, Kuroki Y, Yamamoto R, Fujimoto A, Okumo H, Kubo M: Clinical and
histological study of patellar chondropathy in adolescents. Arthroscopy
1991;7:182-197.
107. Morrish GM, Wolcdge RC: A comparison o f the activation of muscles moving
the patella in normal subjects and in patients with chronic patellofemoral
problems. Scandinavian Journal o f Rehabilitation and Medicine 1997;29:43-48.
108. Nadeau S, Gravel D, Hebert LJ, Arsenault AB, Lepage Y: Gait study of patients
with patellofemoral pain syndrome. Gait and Posture 1997;5:21-27.
109. Nagamine R, Otani T, White SE, McCarthy DS, Whiteside LA: Patellar tracking
measurement in the normal knee. Journal o f Bone and Joint Surgery
1995;13:115-122.
110. O'Neill DB, Micheli LJ, Warner JP: Patellofemoral stress: a prospective analysis
of exercise treatment in adolescents and adults. American Journal o f Sports
Medicine 1992;20:151-156.
111. Outerbridge RE, Dunlop JAY: The problem of chondromalacia patellae. Clinical
Orthopaedics and Related Research 1975;110:177-196.
112. Papagelopoulos PJ, Sim FH: Patellofemoral pain syndrome: diagnosis and
management. Orthopedics 1997;20:148-157.
113. Perry J: Gait Analysis: Normal and Pathological Function, Thorofare, NJ, Slack,
Inc.; 1992:
114. Perry J, Antonelli D, Ford W: Analysis of knee-joint forces during flexed-knee
stance. Journal o f Bone and Joint Surgery 1975;57-A:961-967.
115. Pickett JC, Stoll DA: Patellaplasty or patellectomy? Clinical Orthopaedics and
Related Research 1979;144:103-106.
116. Portney L, Watkins M: Foundations o f Clinical Research: Applications to
Practice, Norwalk, Conn., Appleton & Lang; 1993:
117. Powers CM, Lilley JC, McMahon PJ, Lee TQ: The effect of anatomically based
extensor loading on the biomechanics o f the patellofemoral joint. Orthopaedic
Research Society 1998;
118. Powers, Christopher M The role of the vasti in patellar kinematics and
patellofemoral pain. 203. 1996. University of Southern California. (Dissertation)
111
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
119. Powers CM, Heino JG, Rao S, Perry J: The influence of patellofemoral pain on
lower limb loading during gait Clinical Biomechanics 1999; 14:722-728.
120. Powers CM, Landel R, Perry J: Timing and intensity of vastus muscle activity
during functional activities in subjects with and without patellofemoral pain.
Physical Therapy 1996;76:946-955.
121. Powers CM, Landel R, Sosnick T, et al: The effects of patellar taping on stride
characteristics and joint motion in subjects with patellofemoral pain. Journal o f
Orthopaedic and Sports Physical Therapy 1997;26:286-291.
122. Powers CM, Lilley JC, Lee TQ: The effects of multi-plane loading of the extensor
mechanism on the patellofemoral joint Clinical Biomechanics 1998;13:616-624.
123. Powers CM, Maflucci R, Hampton S: Rearfoot posture in subjects with
patellofemoral pain. Journal o f Orthopaedic and Sports Physical Therapy
1995;22:155-160.
124. Puniello MS: Iliotibial band tightness and medial patellar glide in patients with
patellofemoral dysfunction. Journal o f Orthopaedic and Sports Physical Therapy
1993;17:144-148.
125. Radin EL: A rational approach to the treatment of patellofemoral pain. Clinical
Orthopaedics and Related Research 1979;144:107-109.
126. Radin EL, Paul IL, Lowy M: A comparison of the dynamic force transmitting
properties of subchondral bone and articular cartilage. The Journal o f Bone and
Joint Surgery l970;52-A:444-456.
127. Reider B, Marshall JL, Ring B: Patellar tracking. Clinical Orthopaedics and
Related Research 1981;157:143-148.
128. Reilly DT, Martens M: Experimental analysis of the quadriceps muscle force and
patello-femoral joint reaction force for various activities. Acta Orthopaedica
Scandinavia 1972;43:126-137.
129. Renstrom AF: Knee pain in tennis players. Clinics in Sports Medicine
1995;14:163-175.
130. Schutzer SF, Ramsby GR, Fulkerson JP: The evaluation o f patellofemoral pain
using computerized tomography: a preliminary study. Clinical Orthopaedics and
Related Research 1986;204:286-293.
131. Scott SH, Winter DA: Internal forces at chronic running injury sites. Medicine
and Science in Sports and Exercise 1990;22:357-369.
112
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
132. Seedhom BB, Takeda T, Tsubuku M, Wright V: Mechanical factors and
patellofemoral osteoarthrosis. Annals o f Rheumatic Diseases 1979;38:307-316.
133. Seedhom BB, Tsubuku M: A Technique for the study of contact between visco
elastic bodies with special reference to the patello-femoral joint Journal o f
Biomechanics 1977;10:253-260.
134. Setton LA, Zhu W, Mow VC: The biphasic poroviscoelastic behavior of articular
cartilage: role of the surface zone in governing the compressive behavior.
J.Biomechanics 1993;26:581-592.
135. Shellock FG, Foo TKF, Deutsch AL, Mink JH: Patellofemoral joint: evaluation
during active flexion with ultrafast spoiled GRASS MR imaging. Radiology
1991;180:581-585.
136. Shellock FG, Mink JH, Deutsch AL, Foo TKF: Kinematic MR imaging of the
patellofemoral joint: comparison of passive positioning and active movement
techniques. Radiology 1992;184:574-577.
137. Shelton GL: Conservative management of patellofemoral dysfunction. Sports
Medicine: Musculoskeletal Problems 1992;19:331-347.
138. Shelton GL, Thigpen LK: Rehabilitation of patellofemoral dysfunction: a review
of literature. Journal o f Orthopaedic and Sports Physical Therapy 199l;l4:243-
249.
139. Simpson KJ, Jameson EG, Odum S: Estimated patellofemoral compressive forces
and contact pressures during dance landings. Journal o f Applied Biomechanics
1996;12:1-14.
140. Singerman R, Davy DT, Goldberg VM: Effects of patella alta and patella infera
on patellofemoral contact forces. Journal o f Biomechanics 1994;27:1059-1065.
141. Skinner SR, Antonelli D, Perry J, Lester DK: Functional demands on the stance
limb in walking. Orthopaedics 1985;8:355-361.
142. Souza DR, Gross MT: Comparison of vastus medialis obliquus:vastus lateralis
muscle integrated electromyographic ratios between healthy subjects and patients
with patellofemoral pain. Physical Therapy 1991;71:310-316.
143. Steinkamp LA, Dillingham MF, Markel MD, Hill JA, Kaufman KR:
Biomechanical considerations in patellofemoral joint rehabilitation. American
Journal o f Sports Medicine 1993;21:438-444.
144. Steurer PA, Gradisar LA, Hoyt WA, Chu M: Patellectomy: a clinical study and
biomechanical evaluation. Clinical Orthopaedics and Related Research
1979;144:84-90.
113
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
145. Thomee R, Augustsson J, Karlsson J: Patellofemoral pain syndrome. A review of
current issues. Sports Medicine 1999;28:245-262.
146. Tria AJJr, Alicea JA: Embryology and anatomy of the patella, in Scuderi GR (ed):
The Patella. New York, Springer-Verlag; 1995:11-24.
147. van Eijden TMGJ, de Boer W, Weijs WA: The orientation of the distal part of the
quadriceps femoris muscle as a function of the knee flexion-extension angle.
Journal o f Biomechanics 1985; 18:803-809.
148. van Eijden TMGJ, Kouwenhoven E, Verburg J, Weijs WA: A mathematical
model of the patellofemoral joint. Journal o f Biomechanics 1986;19:219-229.
149. van Kampen A, Huiskes R: The three-dimensional tracking pattern of the human
patella. Journal o f Orthopaedic Research 1990;8:372-382.
150. Veress SA, Lippert FG, Hou MCY, Takamoto T: Patellar tracking patterns
measurement by analytical x-ray photogrammetry. Journal o f Biomechanics
1979;12:639-650.
151. Voight M, Wieder DL: Comparative reflex response times of vastus medialis
obliquus and vastus lateralis in normal subjects and subjects with extensor
mechanism dysfunction: An electromyographic study. American Journal o f
Sports Medicine 1991;19:131-137.
152. Walker PS, Hajek JV: The load-bearing area in the knee joint. Journal o f
Biomechanics 1972;5:581-589.
153. Wiberg G.: Roentgenographic and anatomic studies on the femoro-patellar joint.
Acta Orthopaedica Scandinavia 1941; 12:319-410.
154. Wilk KE, Davies GJ, Mangine RE, Malone TR: Patellofemoral disorders: a
classification system and clinical guidelines for nonoperative rehabilitation.
Journal o f Orthopaedic and Sports Physical Therapy 1998;28:307-322.
155. Winslow J, Yoder E: Patellofemoral pain in female ballet dancers: correlation
with iliotibial band tightness and tibial external rotation. Journal o f Orthopaedic
and Sports Physical Therapy 1995;22:18-21.
156. Witvrouw E, Sneyers C, Lysens R, Victor J, Bellemans J: Reflex response times
of vastus medialis oblique and vastus lateralis in normal subjects and in subjects
with patellofemoral pain syndrome. Journal o f Orthopaedic and Sports Physical
Therapy 1996;24:160-166.
157. Worrell RV: Prosthetic resurfacing o f the patella. Clinical Orthopaedics and
Related Research 1979;144:91-97.
114
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
158. Yamaguchi GT, Zajac FE: A planar model of the knee joint to characterize the
knee extensor mechanism. Journal o f Biomechanics 1989;22:1-10.
159. Yates C, Grana WA: Patellofemoral pain- a prospective study. Orthopedics
1986;9:663-667.
160. Yuen K: The two sample trimmed t for unequal population variances. Biometrika
1974;61:165-175.
161. Zimmerman NB, Smith DG, Pottenger LA, Cooperman DR: Mechanical
disruption of human patellar cartilage by repetitive loading in vitro. Clinical
Orthopaedics and Related Research 1988;229:302-307.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
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Asset Metadata

Creator Brechter, Jacklyn Heino (author)

Core Title Factors contributing to patellofemoral joint stress: a comparison of persons with and without patellofemoral pain

School Graduate School

Degree Doctor of Philosophy

Degree Program Biokinesiology

Degree Conferral Date 2000-12

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

Tag biophysics, medical,health sciences, rehabilitation and therapy,OAI-PMH Harvest

Language English

Contributor Digitized by ProQuest (provenance)

Advisor Powers, Christopher (committee chair), [illegible] (committee member), Azen, Stanley (committee member), Perry, Jacquelin (committee member)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-143671

Unique identifier UC11329547

Identifier 3054715.pdf (filename),usctheses-c16-143671 (legacy record id)

Legacy Identifier 3054715-0.pdf

Dmrecord 143671

Document Type Dissertation

Rights Brechter, Jacklyn Heino

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 au...

Repository Name University of Southern California Digital Library

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