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The International Journal of Sports Physical Therapy | Volume 11, Number 6 | December 2016 | Page 877
ABSTRACT
Patellofemoral pain (PFP) has historically been a complex and enigmatic issue. Many of the factors thought
to relate to PFP remain after patients’ symptoms have resolved making their clinical importance difficult to
determine. The tissue homeostasis model proposed by Dye in 2005 can assist with understanding and imple-
menting biomechanical interventions for PFP. Under this model, the goal of interventions for PFP should be
to re-establish patellofemoral joint (PFJ) homeostasis through a temporary alteration of load to the offended
tissue, followed by incrementally restoring the envelope of function to the baseline level or higher.
High levels of PFJ loads, particularly in the presence of an altered PFJ environment, are thought to be a factor
in the development of PFP. Clinical interventions often aim to alter the biomechanical patterns that are
thought to result in elevated PFJ loads while concurrently increasing the load tolerance capabilities of the
tissue through therapeutic exercise. Biomechanics may play a role in PFJ load modification not only when
addressing proximal and distal components, but also when considering the involvement of more local factors
such as the quadriceps musculature.
Biomechanical considerations should consider the entire kinetic chain including the hip and the foot/ankle
complex, however the beneficial effects of these interventions may not be the result of long-term biome-
chanical changes. Biomechanical alterations may be achieved through movement retraining, but the inter-
ventions likely need to be task-specific to alter movement patterns. The purpose of this commentary is to
describe biomechanical interventions for the athlete with PFP to encourage a safe and complete return to
sport.
Level of Evidence: 5
Keywords: Foot, hip, knee, rehabilitation, running
IJSPT
CLINICAL COMMENTARY
CURRENT CONCEPTS IN BIOMECHANICAL
INTERVENTIONS FOR PATELLOFEMORAL PAIN
Richard W. Willy, PhD, PT, OCS1
Erik P. Meira, PT, DPT, SCS, CSCS2
1 Department of Physical Therapy, East Carolina University,
Greenville, NC, USA
2 Black Diamond Physical Therapy, Portland, OR, USA
CORRESPONDING AUTHOR
Richard Willy
Assistant Professor
Department of Physical Therapy
College of Allied Health Sciences
East Carolina University
Greenville, NC 27834
Fax: 252-744-6240:
E-mail: willyr@ecu.edu
The International Journal of Sports Physical Therapy | Volume 11, Number 6 | December 2016 | Page 878
BACKGROUND
Patellofemoral pain (PFP) has historically been a
complex and enigmatic issue. Many factors have
been identified to correlate with symptoms includ-
ing variations in strength, flexibility, patellar track-
ing, quadriceps angle, and patellofemoral joint (PFJ)
morphology. There are also known correlations with
psychological factors such as depression, fear-avoid-
ance, and anxiety which complicate the presenta-
tion further.1
Factors thought to relate to PFP often remain after
patients’ symptoms have resolved making their
clinical importance difficult to determine.2 Further
complicating assessment, the pain source in PFP
may involve multiple structures and is highly con-
troversial.2 As such, a thorough clinical assessment
of an individual is paramount to fostering successful
patient outcomes in this population. Although this
commentary will explore biomechanical interven-
tions for PFP, this pathology may be better under-
stood in the context of the tissue homeostasis model.
HOMEOSTASIS MODEL OF
PATELLOFEMORAL PAIN
In 2005, Dr. Scott Dye proposed a tissue homeostasis
model for understanding PFP.2 When any tissue is in
homeostasis, it is maintaining a constant physiologi-
cal condition of its internal environment. Although
very successful at self-regulation, sufficient disrup-
tion of homeostasis can result in pathophysiologic
processes. Instead of considering the presentation of
PFP strictly from a perspective of structural failure,
Dye suggested that the pathophysiologic processes
that occur in response to sudden bouts of increased
training loads or stressors should be seen as the true
driver of symptoms.2
Homeostasis can be described as a zone, or “envelope
of function”, where the tissue is capable of tolerating
loads.2 It has been suggested that this zone is estab-
lished through chronic loads to which the PFJ and
related structures have adapted in response to con-
sistent and incremental exposure.3 Acute increases
in training loads that exceed the established enve-
lope of function are thought to disrupt homeostasis
of the PFJ, ultimately resulting in pain. A central
tenet of the envelope of function is that high PFJ
loads are not inherently dangerous; rather loads that
exceed a tissue’s conditioned capacity may be what
are potentially injurious. Indeed, acute increases
in training load that exceed chronic training loads
appear to play a role in the development of many
sports-related injuries.3,4
Once this homeostasis of the tissue is disrupted
by sudden increases in training loads, the PFJ and
associated structures may no longer tolerate levels
of loading even during routine activities, such as
descending stairs or previously well-tolerated run-
ning distances.2 The goal of intervention at this
point should be to re-establish homeostasis through
a temporary alteration of PFJ loads, followed by
incrementally restoring the envelope of function to
the baseline level or, preferably, higher. The biome-
chanical interventions described in this commentary
can be particularly helpful at temporarily reducing
loads while trying to re-establish homeostasis of the
PFJ.6 Further, an understanding of the biomechanics
of therapeutic interventions for PFP can also assist
the clinician with planning a rehabilitation program
that incrementally restores a patient’s envelope
of function. The purpose of this commentary is to
describe biomechanical interventions for the athlete
with PFP to encourage a safe and complete return
to sport.
BIOMECHANICAL OVERVIEW OF
PATELLOFEMORAL PAIN
High levels of patellofemoral loads, particularly in
the presence of an altered PFJ environment,7 are
thought to be a factor in either the development or
chronicity of PFP.8-10 A PFJ that has relatively low
PFJ contact area11 or diminished cartilage thickness
and properties,7,12 transfers greater loads to the sub-
chondral bone.8 Indeed, individuals with PFP dem-
onstrate increased water content13 and metabolic
activity14 in the subchondral bone of the patella.
Therefore, clinical interventions often aim to alter
the biomechanical patterns that are thought to result
in elevated PFJ loads while concurrently increasing
the load tolerance capabilities of the tissue through
therapeutic exercise.
Interventions that address biomechanical loading of
the PFJ should encompass multiple loading param-
eters. Clinicians should familiarize themselves with
the sport-specific loading demands that their athlete
The International Journal of Sports Physical Therapy | Volume 11, Number 6 | December 2016 | Page 879
mometry during testing, either handheld (isometric)
or isokinetic. Handheld dynamometry is a reliable
measure of quadriceps strength (ICC=0.72)24 with
even greater reliability when straps are used to sta-
bilize the dynamometer (ICC=0.96).25 As clinicians
in non-research settings typically lack access to iso-
kinetic dynamometers, the use of an inexpensive
handheld dynamometer is highly advisable in the
assessment of quadriceps strength in athletes with
PFP.
Progressive quadriceps strengthening is a foundation
of rehabilitation of the athlete with PFP. In high qual-
ity studies, there is consistent evidence that progres-
sive quadriceps strengthening improves symptoms
and function in these patients.26 Progressive quadri-
ceps resistance exercises have been shown to reduce
PFP by 44-90%.26,27 While targeted strengthening
of the vastus medialis oblique (VMO) is often pre-
scribed, there is inconclusive evidence supporting its
superiority to generalized quadriceps strengthening
for the treatment of individuals with PFP. 26,28 There-
fore, the authors of this commentary have considered
the literature on generalized quadriceps strengthen-
ing and VMO-targeted strengthening together.
The results of a quadriceps strengthening program
may be enhanced through the use of patellar tap-
ing or bracing. The effect of patellar taping on PFJ
kinematics and PFP remains somewhat controver-
sial. Although the application of patellar tape results
in large and immediate reductions in pain,29 pain
reductions occur with either directionally applied
or non-directionally applied tape.30 These findings
are suggestive of a non-biomechanical mechanism
for the reduction in pain that is often observed with
patellar taping. Patellar taping may enhance the
ability to perform quadriceps resistance exercises in
individuals with PFP,31 presumably by reducing pain-
related quadriceps inhibition. Thus, patellar taping
may enable greater PFJ loading during quadriceps
resistance exercises that would ordinarily result in
pain.29 In support of this rationale, recent system-
atic reviews indicate that patellar taping enhances
patient outcomes, but only in the first 12 weeks of
rehabilitation6,32 when pain would be expected to be
the greatest. Patellar bracing may also have a simi-
lar influence on outcomes in individuals with PFP
through the 6 and 12 week time points.33 As such,
with PFP may experience. Running, for instance, is
a highly repetitive activity in which relatively high
loads of 4-5.5 times body weight15-17 are applied to
the PFJ at a moderately high rate18 (Figure 1). Thus,
a rehabilitation program for the running athlete
with PFP should include components that expose
the extensor mechanism to high loads at a relatively
moderate rate, with an emphasis on repetition. In
contrast to running, the jumping athlete likely expe-
riences PFJ reaction forces well in excess of 10 times
body weight19 applied at a much higher rate, but with
fewer repetitions. A well-planned rehabilitation pro-
gram for any athlete with PFP should reflect these
sport-specific demands to ensure a durable return
to sport.
CONSIDERING THE QUADRICEPS
Quadriceps weakness is an established risk factor for
the development of PFP20 across a variety of popu-
lations. Quadriceps weakness may be indicative of
inadequate chronic training loads and, ultimately, a
PFJ that has a relatively low envelope of function.
Individuals who develop PFP have been found to
have quadriceps strength deficits of 6-12% compared
with healthy control participants20-23 which are unde-
tectable via manual muscle testing. As such, out-
come measures documenting quadriceps strength
in this population should utilize some form of dyna-
Figure 1. The patellofemoral joint and related structures expe-
rience three aspects of loading a) the peak load per step, b) how
quickly this load is applied (rate of loading and 3) the total accu-
mulation of load during an activity. These metrics are impor-
tant to consider in the development of rehabilitation programs
for individuals with patellofemoral pain.
The International Journal of Sports Physical Therapy | Volume 11, Number 6 | December 2016 | Page 880
exercises. Specifically, clinicians should consider
carefully the interactions between external moment
arms, external and internal loads, knee joint angles
and articular contact area of the PFJ when prescrib-
ing quadriceps strengthening exercises. In either
open or closed kinetic chain, contact area of the PFJ
is the lowest in the first 20 degrees of knee flexion
and steadily increases as knee flexion increases.11,40
Interestingly, the external moment arm acting
on the knee also increases as an individual moves
deeper into a closed kinetic chain squat. As a result,
PFJ stress (the quotient of PFJ reaction force and
PFJ contact area) increases fairly linearly from full
knee extension to approximately 45 degrees of knee
flexion during a squatting maneuver.41,42 However,
PFJ reaction forces increase rapidly from approxi-
mately 45 degrees to 100 degrees of knee flexion with
either a squat or leg press43 with a disproportionate
lower rate of increase in PFJ contact area.40 The net
result is that PFJ stress is considerably higher when
squatting and leg presses in knee flexion angles in
excess of approximately 45 degrees when compared
with squatting with comparatively less knee flexion
(Figure 2 and 3A).41 Thus in the early stages of reha-
bilitation of PFP, the PFJ is particularly well-suited
to closed chain loads, in approximately the first 45
degrees of knee flexion.41
Quadriceps strengthening can also be achieved with
open kinetic chain exercises. However, PFJ loads
during open chain exercises are highly dependent
on the configuration of force application. During
open chain knee extension with a weight attached
to the ankle, the external moment arm increases as
the knee nears full extension. This loading configu-
ration results in a highly variable level of external
resistance throughout the knee extension motion
(EXT-VR) as shown in Figures 2 and 3B. Thus, PFJ
reaction forces increase rapidly as the knee nears
full extension in the open chain43 whereas PFJ con-
tact area decreases precipitously. This loading sce-
nario results in a large increase in PFJ stress in the
last 20 degrees of knee extension, which is exactly
opposite of what occurs during a squatting maneu-
ver.41 In contrast, a knee extension machine that
uses a cable system applies external resistance in a
fairly uniform manner throughout the knee range of
motion, via a constant external moment arm (EXT-
CR) as shown in Figure 2 and 3C.41,44 Knee exten-
it appears that recovery from PFP may be bolstered
by the addition of patellar taping or patellar bracing,
but only in the first 6-12 weeks of a patellofemoral
rehabilitation program.
THE QUADRICEPS STRENGTHENING
PARADOX
Despite the consistent improvements in pain asso-
ciated with quadriceps strengthening, the mecha-
nism behind reported pain reductions is unclear. For
instance, quadriceps strengthening exercises may
potentially expose the PFJ to high reaction forces
which are thought to exacerbate PFP. Conversely,
it has been proposed that quadriceps strengthening
may alter patellar kinematics, potentially increasing
the contact area between the patellar and trochlear
articular surfaces. To date, preliminary evidence
suggests that eight weeks of quadriceps strengthen-
ing may result in increased contact area of the PFJ.34
Thus, quadriceps strengthening may reduce PFJ
stress by increasing the contact area of the PFJ.
Ultimately, the process of quadriceps strengthening,
rather than the quadriceps strength gains that result,
may reduce PFP by improving load tolerance of the
patient and the PFJ structures. For instance, quadri-
ceps strengthening results in a desirable increase in
glucosaminoglycan content in articular cartilage of
the knee.35 In an animal model, eccentric quadriceps
muscle contractions result in protective adaptations
in distal femoral articular cartilage.36 Taken together,
these findings suggest that a loading program may
increase the tissue quality of the articular cartilage
of the PFJ. Emerging evidence also suggests that
progressive loading of the PFJ may reduce local
hyperalgesia37 and may alter central pain processing
in individuals with PFP.38,39 Therefore, progressive
quadriceps strengthening may improve a patient’s
envelope of function by enhancing load tolerance of
the PFJ. Clearly, further study is necessary to bet-
ter understand the mechanisms of pain reduction
that are observed in individuals with PFP that result
from a quadriceps strengthening program.
THE BIOMECHANICS OF QUADRICEPS
STRENGTHENING
Prescription of quadriceps strengthening for the
treatment of PFP requires a working knowledge of
the biomechanics of various progressive resistive
The International Journal of Sports Physical Therapy | Volume 11, Number 6 | December 2016 | Page 881
of the quadriceps45 necessitates peak quadriceps
forces estimated at 5 times body weight during the
stance phase of endurance-paced running.46 Muscle
forces of this magnitude are attainable with select
rehabilitation exercises. Single leg squats performed
to at least 65 degrees of knee flexion without added
weight yields peak quadriceps forces of approxi-
mately 4-5 times body weight.47 However, squats to
this depth of knee flexion may result in pain in indi-
viduals with PFP41 and peak knee flexion during run-
ning rarely exceeds 40-45 degrees,47 Thus, clinicians
should opt for added weight to a single leg squat to
attain peak quadriceps that are relevant to running.
Adding resistance to body weight exercises is abso-
lutely required if a clinician wishes to attain peak
quadriceps forces that are of same magnitude as
those seen during jumping. For instance, a bilateral
drop vertical jump results in peak quadriceps forces
of 7 times body weight.48
Provided the added resistance is sufficient, open
kinetic chain knee extension exercises can also
generate peak quadriceps forces that are similar to
forces noted during running and other activities. For
instance, therapists may find it difficult to provide
sport-relevant resistance between 45-90 degrees of
knee flexion41 with the EXT-VR load configuration.
Once past the early stages of rehabilitation, the
constant resistance supplied by a knee extension
machine using the EXT-CR configuration may thus
provide the best means to strengthen the quadri-
ceps between 45-90 degrees of knee flexion in the
athlete recovering from PFP (Figure 3C). For closed
kinetic chain, exercises that involve squatting or leg
presses between 0 and 45 degrees of knee flexion
may be the best means to strengthen the quadri-
ceps with moderate levels of PFJ stress. With either
squatting or open chain knee extension exercises,
clinicians should aim to incrementally increase the
range of motion and level of resistance in response
to improvements in pain in the patient to restore the
envelope of function of the PFJ.
TREATMENTS FOR PROXIMAL
CONTRIBUTIONS TO PATELLOFEMORAL
PAIN
Female athletes with PFP often demonstrate greater
hip adduction, hip internal rotation, and contralat-
eral pelvic drop during sporting tasks.6,49-51 These
sion machines with constant resistance exhibits
PFJ stress values in terminal knee extension that
are proportional to those observed during the same
range of motion with a knee extension with variable
resistance.41 Interestingly, a performing knee exten-
sions between 90-50 degrees of knee flexion with
a constant resistance configuration results in PFJ
stress levels that are intermediate to PFJ stress esti-
mated during closed chain squatting or open chain
knee extension through the same range of motion.41
When selecting appropriate resistance levels, clini-
cians should keep in mind that large internal muscle
forces often result from counteracting much lower
external loads. Regardless of the sport, clinicians
should seek to achieve activity-relevant quadriceps
loads with therapeutic exercise in athletes with PFP
prior to return to sport initiation. During running,
for instance, peak vertical ground reaction forces are
typically around 2.5 times body weight, yet the exter-
nal moment arm acting on the knee is rather large.
In contrast, the much smaller internal moment arm
Figure 2. Patellofemoral joint stress during three different
types of quadriceps strengthening exercises: EXT-VR represents
a free weight attached to the distal lower leg. EXT-CR represents
a knee extension machine that applies constant resistance.
Squat relates to a squatting maneuver. Patellofemoral joint
strees is dependent on the external moment arm, amount of
resistance and the direction of force application. Figure reprinted
with permission from Powers CM, Ho KY, Chen YJ Souza RB,
Farrokhi S. Patellofemoral joint stress during weight-bearing
and non-weight-bearing quadriceps exercises. J Orthop Sports
Phys Ther. May 2014; 44(5): 320-327.
The International Journal of Sports Physical Therapy | Volume 11, Number 6 | December 2016 | Page 882
drop and reposition the femur, via reduced hip adduc-
tion and medial rotation. Smartphone applications
and open source movement analysis software provide
the means to readily analyze an athlete’s mechanics
in the clinic. During running, close proximity of the
medial femoral condyles during midstance (Figure
4), known as a “reduced knee window,”58 is suggestive
of excessive hip adduction and hip internal rotation
of the stance limb. Results of movement analyses can
assist with clinical decision making in developing tar-
geted rehabilitation programs.
Reduced posterolateral hip strength is often observed
in individuals with PFP.1,59 As the posterolateral hip
musculature controls contralateral pelvic drop, hip
mechanics are thought to reduce PFJ contact area,
ultimately resulting in an increase in PFJ stress.50
Real-time magnetic resonance imaging studies sug-
gest relative lateral tracking of the patella as the
femur adducts and internally rotates during a squat-
ting or step down maneuver in females with PFP.52-55
Contralateral pelvic drop is thought to increase ten-
sion in the lateral patellar retinaculum56 via the
iliotibial band,57 potentially contributing to lateral
patellar tracking.
Recent literature has evaluated interventions designed
to address the proximal mechanisms of PFP. Proposed
interventions to address the proximal mechanism
contribution to PFP aim to reduce contralateral pelvic
Figure 3. The interaction between external loads and the external moment arm during common quadriceps strengthening exercises.
Figure 3A: During the single leg squat, the external moment arm (MA) increases as the depth of the squat also increases resulting in
increasing quadriceps forces and patellofemoral joint stress through 90 degrees of knee fl exion. Corresponds with “Squat” in Fig. 2.
Figure 3B: Patient performing open chain knee extension with a weight mounted at the levle of the lower leg (non tap fi gure). The
external moment arm (MA) increases as the knee extends, resulting in increasing quadriceps forces and patellofemoral joint stress as
the knee nears full extension. Corresponds with “EXT-VR” in Fig. 2. Figure 3C: During open chain knee extension on knee extension
machine with a cable and weight stack system, the external moment arm (MA) remains constant throughout the range, resulting in
relatively stable quadriceps forces and patellofemoral joint stress. Corresponds with “EXT-CR” in Fig. 2.
The International Journal of Sports Physical Therapy | Volume 11, Number 6 | December 2016 | Page 883
There is a growing body of evidence of moderate to
high quality that supports the prescription of pos-
terolateral hip strengthening for the treatment of
PFP.6,74 Hip strengthening programs result in moder-
ate to large reductions in PFP with moderate to large
improvements in function in the short- to medium-
term.74 To date, only one study has evaluated long-
term outcomes after a hip strengthening program
for PFP.69 At one-year post-intervention, Fukuda and
colleageus reported that individuals who completed
a hip and quadriceps strengthening program dem-
onstrated greater improvements in PFP and lower
limb function compared with quadriceps strength-
ening alone.69 Evaluating interventions for PFP that
employ hip strengthening can also be challenging
as the quadriceps are also loaded during most hip
strengthening exercises, such as step ups or single leg
squats.68 Future study that delineates hip strength-
ening and quadriceps strengthening exercises is
needed to better understand the mechanism(s) of
pain reduction noted after these rehabilitation pro-
grams. As proximal strengthening does not appear
to alter proximal mechanics, non-biomechanical
mechanisms may explain the reduction in PFP that
is widely reported with rehabilitation programs that
employ hip strengthening.
When approached from a tissue homeostasis perspec-
tive, long-term correction of proximal mechanics
may not be required. As higher levels of hip adduc-
tion75 and internal rotation76 increase PFJ stress,
these mechanics may hinder recovery from PFP.
However, precipitating factor in the development
of PFP in many athletes may be the application of
load beyond the amount that the PFJ has been con-
ditioned to tolerate. For example, a runner may have
always had elevated hip adduction and internal rota-
tion, yet the actual culprit for the development of
PFP may be increasing running mileage faster than
the PFJ and associated structures can adequately
adapt. Along these lines, an athlete who runs with
greater levels of hip adduction and hip internal rota-
tion may be more susceptible to rapid changes in
training loads than a runner who does not exhibit
similar mechanics. Thus, the promising clinical out-
comes of proximal exercise interventions for PFP
may be better explained as simply the systematic
conditioning of the PFJ and supportive musculature
adduction, and hip internal rotation, it is not surpris-
ing that hip strengthening is often prescribed for the
treatment of PFP.6,60,61 Interestingly, posterolateral
hip strengthening does not appear to reduce exces-
sive proximal mechanics in either asymptomatic62,63
or symptomatic individuals.64,65 While these findings
might be surprising, prospective data fail to sup-
port deficits in posterolateral hip strength as a risk
factor for the future development of PFP.59 In fact,
data from two large prospective studies suggest that
individuals who go on to develop PFP actually had
greater posterolateral hip strength.21,66 As reduced
hip strength is observed in individuals with active
PFP, but not before pain develops, hip strength defi-
cits may actually be the result of PFP, rather than
the cause of PFP.59 Also noteworthy, posterolateral
hip strength is not a strong predictor of frontal and
transverse plane hip mechanics during running or
stepdown maneuvers.67
Figure 4. Runner with patellofemoral pain demonstrating
reduced space between the medial femoral condyles i.e., reduced
knee window, suggestive of high levels of hip adduction and hip
internal rotation of the right lower extremity.
The International Journal of Sports Physical Therapy | Volume 11, Number 6 | December 2016 | Page 884
a proximal mechanism during running. This crite-
rion for enrollment in the respective studies under-
scores the importance of a targeted intervention in
response to a thorough clinical gait analysis.58
Cueing a modest increase in step rate (cadence) dur-
ing running has been shown to reduce PFJ contact
forces and stress in individuals with and without
PFP.16,81-83 Clinically, most runners find that employ-
ing modest increases in running cadence is a rela-
tively easy skill to learn. An increase in step rate
by 5-10% over preferred levels reduces PFJ loads in
part by decreasing peak knee flexion and quadriceps
forces during the stance phase of gait.16,81 Again, a
clinical gait analysis is highly recommended in
determining runners who would benefit the most
from an increase in step rate. Specifically, runners
who exhibit high amounts of vertical oscillation of
the estimated center of mass between flight phase
and mid-stance, have footfalls that are far in front of
the estimated center of mass, and reach high levels
of knee flexion during stance phase may benefit the
most from an increase in step rate.81,84 An increase
in step rate also results in a reduction in peak hip
adduction, albeit smaller in magnitude than the
aforementioned kinematic and mirror feedback
to tolerate more load rather than actually changing
hip frontal and transverse plane mechanics.62
MOVEMENT RE-EDUCATION FOR THE
TREATMENT OF PFP
When attempting to restore tissue homeostasis,
reducing PFJ loads through movement re-education
may be particularly helpful in the early to intermedi-
ate stages of rehabilitation. Recent work suggests that
various mechanics associated with PFP are modifi-
able with the use of motor learning techniques. As
a premise for movement re-education for the proxi-
mal mechanism of PFP, individuals with PFP demon-
strated delayed onset and reduced duration of gluteus
medius activation.77,78 Thus, currently described
movement re-education interventions for the proxi-
mal mechanism aim to alter the neuromuscular con-
trol of the gluteal musculature in an effort to control
proximal mechanics, if implicated. In contrast to hip
strengthening, movement re-education has been
shown to reduce proximal mechanics during running
and other functional tasks, such as step descent or a
single leg squat.49 Providing mirror and verbal feed-
back, for instance, has been shown to be effective
at reducing contralateral pelvic drop, hip adduction
and hip internal rotation during a single leg squat.62
Interestingly, changes in proximal mechanics during
a single leg squat did not transfer to running.62 Thus,
patients are able to achieve improved control of proxi-
mal mechanics during common therapeutic exercises
may not necessarily transfer these movement skills
to an unrelated task, such as running. These findings
suggest that changes in lower extremity mechanics
require a motor learning component and that move-
ment retraining likely needs to be task-specific.
The movement re-education literature for the
treatment of PFP has largely focused on retraining
running gait. Proximal mechanics79,80 have been
targeted in published gait retraining studies with
runners with PFP. Realtime kinematic80 or mirror
feedback,79 coupled with verbal cueing, result in
reductions in hip adduction and contralateral pelvic
drop in female runners with PFP (Figure 5). These
reductions in proximal mechanics were accompa-
nied by improvements in reported pain and lower
limb function that were associated with large effect
sizes.49 Importantly, these previous investigations
targeted females with PFP who also demonstrated
Figure 5. Open source software and a webcam can be used to
provide real-time feedback on frontal plane running mechanics.
This video technique is useful if the treadmill has a large con-
troller console that prevents the runner from seeing their refl ec-
tion in a full-length mirror.
The International Journal of Sports Physical Therapy | Volume 11, Number 6 | December 2016 | Page 885
studies.85,86 Thus, running with increased step rate
primarily reduces PFJ forces through a reduction in
quadriceps forces rather than a large effect on lat-
eral tracking of the PFJ.
Adopting a forefoot strike pattern during running
has also been suggested as a means to reduce PFJ
loads.82,87 However, clinicians should be aware, that
conversion to a forefoot strike increases the demand
of the ankle plantarflexors while reducing demand of
theknee extensors. Adopting a forefoot strike pattern
has been shown to result in 11% greater Achilles ten-
don forces per step, which equates to an additional
47.7 times body weight impulse loading of the Achil-
les tendon per mile of running.88 Because adopting a
5-10% increase in running cadence reduces PFJ loads
by 10-20%16,82 while also reducing Achilles tendon
loads,89 cueing an increase in running cadence may be
preferred over adoption of a forefoot running pattern.
Clinical reasoning should guide movement re-educa-
tion prescription. If frontal and transverse plane hip
mechanics are thought to be the main biomechani-
cal factor contributing to a runner’s current PFP, then
visual feedback to cue reductions in these mechanics
are warranted. If sagittal plane running mechanics are
primarily implicated in a runner’s PFP, then cueing an
increase in step rate during running may be the most
effective gait modication. Clinically, cueing a reduc-
tion in proximal mechanics can easily be done with
a full-length mirror or with a live video stream. Sim-
ilarly, cueing an increase in steprate can be accom-
plished via matching the rhythm of a metronome82,86
or in response to real time feedback from commer-
cially available wrist mounted running computers85
that calculate step rate via an accelerometer mounted
in a footpod or within the device itself (Figure 6).
THE ROLE OF FOOT ORTHOSES IN THE
TREATMENT OF PATELLOFEMORAL PAIN
While there appears to be some support for the use
of foot orthoses for the treatment of PFP,90 the bio-
mechanical rationale supporting their use is less
clear. For instance, a 6° medially wedged orthosis
did not reduce peak frontal plane kinematics or
joint moments of the knee or hip in runners with
and without PFP.91 Interestingly, greater standing
calcaneal eversion posture was not predictive of any
changes in frontal plane hip or knee mechanics in
response to orthotics.91 Despite these findings, foot
orthoses, combined with exercise therapy, resulted
in improved outcomes over six weeks in individuals
with PFP compared with exercise therapy alone.90
In an interesting clinical trial, Lewinson and col-
leagues randomized runners with PFP to either
medially or laterally wedged foot orthoses. Regard-
less of foot orthoses assignment, both groups of run-
ners reported 33% reductions in PFP after six weeks
of using the foot orthoses during routine training
runs.92 Non-uniform reductions in frontal plane knee
moments during running with the foot orthoses
were observed across the cohorts.92 These data, con-
sidered along with aforementioned studies, suggest
that foot orthoses may enhance short term outcomes
in PFP rehabilitation programs, but clinical results
may be due to either individualized responses or
non-biomechanical mechanisms. Patients with PFP
who experience a reduction in pain with the use of
foot orthoses may be able to tolerate greater levels
of resistance during therapeutic exercies, potentially
improving their envelope of function.
BIOMECHANICAL CONSIDERATIONS FOR
RETURN TO SPORT
As described previously, peak quadriceps loads asso-
ciated with an athlete’s sport of choice are readily
achieved with targeted resistance exercises. How-
Figure 6. Commercially available running computer enables
the real-time calculation of running cadence (step rate).
The International Journal of Sports Physical Therapy | Volume 11, Number 6 | December 2016 | Page 886
To guide clinical decision making, a criterion-based
progression should be implemented that evaluates
pain during activity and in the 24 hours after the
return to sport session. There are no formal guide-
lines available for acceptable pain in athletes with
PFP completing a return to sport program. Care
should be taken during return to sport tasks to avoid
acute aggravation of knee pain, which can increase
hyperalgesia in individuals with PFP.37 Thus, it is the
authors’ recommendation that pain should remain
at or below 2/10 on the visual analog scale during
return to sport activity, with trace to absent pain
after the activity session.
CONCLUSION
The mechanisms of PFP are complex and enigmatic.
The presentation may be best described by consid-
ering a tissue homeostasis model. Biomechanical
interventions that reduce PFJ loading may be most
helpful during early rehabilitation to allow progres-
sive quadriceps strengthening as tissue homeostasis
is re-established.
Biomechanical considerations should include the
entire kinetic chain including the hip and the ankle,
however the beneficial effects of these interven-
tions may not be the result of long-term biome-
chanical changes. True biomechanical alterations
may be achieved through movement retraining, but
the interventions must be extremely specific to the
desired task.
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