CLINICS 2011;66(3):367-372
DOI:10.1590/S1807-59322011000300001
CLINICAL SCIENCE
Influence of patellofemoral pain syndrome on
plantar pressure in the foot rollover process
during gait
Sandra Aliberti,I Mariana de S.X. Costa,I Anice de Campos Passaro,I Antônio Carlos Arnone,II
Rogério Hirata,III Isabel C. N. SaccoI
I
Laboratory of Biomechanics of the Human Movement and Posture; Physical Therapy, Speech and Occupational Therapy Department, School of Medicine,
University of São Paulo, São Paulo, Brazil. II Orthopedics Clinic, University Hospital, University of São Paulo, São Paulo, Brazil. III Research Assistant at the
Center for Sensory-Motor Interaction (SMI), Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
BACKGROUND: Patellofemoral Pain Syndrome is one of the most common knee disorders among physically active
young women. Despite its high incidence, the multifactorial etiology of this disorder is not fully understood.
OBJECTIVES: To investigate the influence of Patellofemoral Pain Syndrome on plantar pressure distribution during
the foot rollover process (i.e., the initial heel contact, midstance and propulsion phases) of the gait.
MATERIALS AND METHODS: Fifty-seven young adults, including 22 subjects with Patellofemoral Pain Syndrome (30
¡ 7 years, 165 ¡ 9 cm, 63 ¡ 12 kg) and 35 control subjects (29 ¡ 7 years, 164 ¡ 8 cm, 60 ¡ 11 kg), volunteered for
the study. The contact area and peak pressure were evaluated using the Pedar-X system (Novel, Germany)
synchronized with ankle sagittal kinematics.
RESULTS: Subjects with Patellofemoral Pain Syndrome showed a larger contact area over the medial (p = 0.004) and
central (p = 0.002) rearfoot at the initial contact phase and a lower peak pressure over the medial forefoot
(p = 0.033) during propulsion when compared with control subjects.
CONCLUSIONS: Patellofemoral Pain Syndrome is related to a foot rollover pattern that is medially directed at the
rearfoot during initial heel contact and laterally directed at the forefoot during propulsion. These detected
alterations in the foot rollover process during gait may be used to develop clinical interventions using insoles,
taping and therapeutic exercise to rehabilitate this dysfunction.
KEYWORDS: Patellofemoral pain syndrome; Biomechanics; Gait; Plantar Pressure; Lower extremity.
Aliberti S, Costa MSX, Passaro AC, Arnone AC, Hirata R, Sacco ICN. Influence of patellofemoral pain syndrome on plantar pressure in the foot rollover
process during gait. Clinics. 2011;66(3):367-372.
Received for publication on August 26, 2010; First review completed on October 1, 2010; Accepted for publication on November 9, 2010
E-mail: icnsacco@usp.br
Tel.: 55 11 3091-8426
frequently cited intrinsic factors include femoral trochlear
anatomic alterations, weakness and/or imbalance of the
quadriceps, peripatelar soft-tissue tightness and lower
extremity dynamic misalignments.1,4 The most commonly
cited lower extremity dynamic misalignments are excessive
hip adduction and internal rotation as well as excessive
and/or prolonged rearfoot pronation during locomotion.6,7
PFPS is believed to be related to a reduction in the contact
area in the patellofemoral joint; this reduction occurs due to
alterations in the dynamic alignment of the tibiofemoral
joint.8 One theory states that excessive and/or prolonged
pronation of the rearfoot leads to excessive medial rotation
of the tibia in a closed kinetic chain.7 This medial rotation of
the tibia would induce a compensatory medial rotation of
the femur to maintain the relative lateral rotation of the
tibial plateau in relation to the femoral condyles, which are
associated with knee extension during the midstance phase
of gait. When the femur medially rotates, the compression
INTRODUCTION
Patellofemoral Pain Syndrome (PFPS) is one of the most
common knee dysfunctions among physically active young
women. Despite its high incidence, rehabilitation is challenging, as the multifactorial etiology of this syndrome is not
fully understood.1-3
PFPS is believed to originate from a combination of
extrinsic and intrinsic risk factors.1,4,5 The most commonly
described extrinsic risk factors related to PFPS include the
surface used for running or physical activity practice, sport
shoes and the volume and intensity of training.5 The most
Copyright ß 2011 CLINICS – This is an Open Access article distributed under
the terms of the Creative Commons Attribution Non-Commercial License (http://
creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the
original work is properly cited.
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CLINICS 2011;66(3):367-372
The PFPS subjects experienced pain in the patellofemoral
joint region for at least two months (4¡3 years). Their pain
occurred during at least one of the following situations:
resisted contraction of the femoral quadriceps, squatting,
prolonged sitting and descending or ascending stairs.
Subjects were excluded from the study if they had undergone any previous knee surgery, had a history of patellar
dislocation or had any other limitations that would
influence gait. The control subjects had no history or
diagnosis of knee pathology or trauma, no knee pain with
any of the activities mentioned and no limitations that
would influence gait.
Overall exclusion criteria for both groups were a
discrepancy of 1 cm21 or greater in lower leg length and
major foot deformities. The arch index was evaluated to
exclude major arch alterations (planus, equinus planus and
extra cavus feet) that could interfere with gait mechanics.22
Knee pain intensity in individuals with PFPS was
measured with a Visual Analogue Pain Scale (VAS), in
which subjects rated their current pain on a 10-cm
horizontal scale that ranged from ‘‘no pain’’ on the left to
‘‘worst pain imaginable’’ on the right. The VAS was shown
to be a reliable, valid and responsible means of assessing
pain in studies of PFPS.23-25 The intensity of knee pain in the
PFPS group was 1.7¡2.3 cm, and the control subjects
presented a knee pain intensity equal to 0.0 cm. To better
characterize knee function in PFPS and CG subjects, each
individual was evaluated with the Lysholm Functional
Knee Scale; the average (median) Lysholm score was 70 for
the PFPS group and 98 for the CG.24,25
As PFPS is common in physically active individuals, the
subjects in both groups answered a questionnaire about
how many time they have been physically active, frequency
and duration of physical activity; they were considered
physically active when their physical activity frequency was
at least three times a week.26 Both groups had similar scores
for physically activity (GC = 51.3%, PFPS = 40.0%; p = 0.422),
practice time (GC = 5¡5 years, PFPS = 5¡2 years; p = 0.330),
frequency (GC = 3¡1 days/week, PFPS = 2¡1 days/week;
p = 0.246) and duration (GC = 85¡30 min, PFPS = 68¡
22 min; p = 0.534).
between the lateral surface of the patella and the lateral
femoral condyle rises. As a result, patellofemoral joint stress
increases.6,9
Kinematic studies that have investigated the relationship
between excessive /prolonged foot pronation and rearfoot
eversion with PFPS have produced controversial findings.
Some authors observed greater pronation in subjects with
PFPS during locomotor activities,13-15 while others could not
confirm the coexistence of excessive rearfoot pronation and
PFPS.5,16 One of the potential limitations of these studies
was that rearfoot motion could not be differentiated from
forefoot motion. Total foot pronation is composed of two
events, rearfoot eversion during weight acceptance and
midfoot/forefoot loading during early midstance. Models
that show the foot as a rigid segment may miss information
related to its flexibility during the foot rollover process in
locomotor tasks.16
Alternatively, an indirect way of evaluating the kinetic
chain results of the foot rollover process during gait is to
assess plantar pressure distribution during the gait subphases. Higher pressures on the medial areas of the plantar
surface as well as excessive pronation during running were
associated with the development of lower limb injuries.17
Thijs et al.18 evaluated plantar pressure in soldiers during
barefoot gait and observed a relationship between PFPS and
lateralized support of the feet, suggesting that individuals
who developed PFPS exhibited a heel strike in a lesspronated position and a foot rollover that was more directed
toward the lateral side of the foot. This study evaluated a
specific military population that was going through an
intense training period, and the authors commented that
caution should be used when generalizing these findings.
The plantar pressure distribution findings and their
relationship to lower limb injuries and pain suggest that
there is not a consensus in the literature and more
investigation is needed.
To our knowledge, no studies have investigated plantar
pressure distribution during the subphases of the foot
rollover process in a PFPS population. This investigation
may identify the phases of the foot rollover process during
which plantar loading and foot contact alterations occur and
may contribute to elucidating foot mechanics in PFPS
individuals.
This study aimed to investigate the influence of
Patellofemoral Pain Syndrome on plantar pressure distribution during the initial heel contact, midstance and propulsion phases of gait.
Gait Measurement
The contact area and peak pressure were evaluated
during barefoot gait using the Pedar-X System (Novel,
Munich, Germany) synchronized to the ankle sagittal
angular variation. This variation was evaluated by an
electrogoniometer that was instrumented with a strain gage
(model SG110/A, Biometrics, Gwent, England) and fixed to
the ankle joint according to the manufacturer’s instructions
(Goniometer and torsiometer operating manual. Gwent:
Biometrics Ltd; 2002).
The insoles of the Pedar-X System were 2.5 mm thick and
contained a matrix of 99 capacitive pressure sensors with a
spatial resolution of 1.6 to 2.2 cm;2 the insoles were placed
inside an anti-skid sock.27 Prior to the tests, the insoles were
calibrated according to the manufacturer’s instructions, and
the zero setting procedure was performed as recommended
by Novel prior to data acquisition.28
The electrogoniometer was calibrated with the ankle in its
mechanically neutral position while the subject stood in a
relaxed posture with his or her body weight equally
distributed in both feet and in stationary equilibrium; the
output value was defined as the zero angle of the
MATERIALS AND METHODS
Subjects
Fifty-seven adults of both sexes volunteered for the study
and were divided into two groups: the control group (CG)
(n = 35; 29¡7 yrs; 164¡ 8 cm; 60¡11 kg; 32 women) and the
PFPS group (PFPS) (n = 22; 30¡7 yrs; 165¡9 cm; 63¡12 kg;
20 women). The sample power calculation was based on the
primary outcome (the pressure variables) with an expected
proportion of PFPS development of 30%, a power of 80%
and an alpha error of 5%.19,20 The groups did not differ in
mean age (p = 0.698), height (p = 0.935), or body mass
(p = 0.734). All participants gave their written informed
consent, and the Local Ethics Committee approved the
study (protocol n.1237/05).
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Aliberti S et al.
goniometer. Forward motion of the lower segment was
regarded as flexion (positive values) and backward motion
as extension (negative values).
Before data acquisition, the subjects were instructed to
walk freely in a self-selected cadence on a 10-meter
walkway to reproduce their daily gait and adapt to the lab
environment and to the equipment attached to their feet.
The self-selected cadence was converted into an audible
digital signal using a metronome. The participants kept a
similar cadence between trials based on the audio feedback
provided by the metronome; this procedure helped avoid
great differences in gait cadence between trials. The
cadences performed during the gait trials did not differ
between the groups (CG = 108¡3 steps/min; PFPS = 107¡
3 steps/min; p = 0.871). A total of 15 steps were recorded,
and the mean was used for statistical purposes.
Pedar and electrogoniometer data were acquired and
synchronized using a 12-bit analog-to-digital converter
(AMTI, DT3002) at a sampling rate of 100 Hz. Both signals
were synchronized by a TTL (transistor-transistor logic)
signal that was emitted by the Pedar Sync Box. This box
emitted 0 volts (V) when at least 20 kPa was detected by the
Pedar System while the foot was in contact with the surface
and 5 V when the pressure was lower than 20kPa while the
foot was in the swing phase.
Although the Pedar-X system is most appropriate for
evaluating shod gait, we used the insoles to evaluate
barefoot gait as reported by Nurse and Nigg.29 Barefoot
gait analysis was performed because our intention was to
investigate the complex behavior of the foot-floor interaction30,31 without any other interference such as the subject’s
shoes. Additionally, the Pedar-X system could acquire
multiple steps without requiring the subject to alter their
gait to make contact with any platform.32
The contact area (cm2) and peak pressure (kPa) were
evaluated in six plantar areas that were adjusted proportionally to the length and width of each subject’s foot with
the Novel Multiprojects software (Novel, Munich,
Germany). The plantar surface was first divided into three
larger areas, the rearfoot (30% of the foot length), midfoot
(30% of the foot length) and forefoot (40% of the foot length),
according to the scheme established by Cavanagh and
Ulbrecht.33 The rearfoot was subdivided into the medial
(30% of the rearfoot width), central (40% of the rearfoot
width) and lateral rearfoot (30% of the rearfoot width) areas,
and the forefoot was subdivided into the medial (55% of the
forefoot width) and lateral forefoot (45% of the forefoot
width).34
Figure 1 - Synchronization between the Pedar-X System and the
ankle electrogoniometer through the synchronizer box of the
Pedar-X System.
to extension of the ankle and the toe-off instant (as seen in
the pressure data).
Statistical inferential analysis was performed with
Statistica v.7 software (Statsoft Inc.). For statistical purposes,
pressure data from only one foot per subject were analyzed
and compared. In the control group, a foot was randomly
chosen for analysis, while in the PFPS group, the chosen foot
corresponded to the painful knee in subjects with unilateral
pain and the most painful knee in subjects with bilateral
pain.
Plantar pressure variables followed a normal distribution
(Shapiro-Wilk’s Test), and variances were homogeneous
(Levene’s Test). Groups and areas were compared using
2 three-way ANOVAs (2X3X6) that considered the gait
DATA ANALYSIS
The stance phase of the gait was divided into three
subphases using a customized mathematical function
developed using Matlab software (v.7.1). The initial heel
contact phase was defined as the time interval between the
first foot contact with the ground (as seen in the pressure
data) and the deflection instant in the transition from
extension to flexion of the ankle angular variation curve.
The midstance phase was defined as the time interval
between the prior ankle deflection instant (extension to
flexion) and the deflection instant in the transition from the
flexion to extension of the ankle. The propulsion phase was
the interval between the last deflection instant from flexion
Figure 2 - Subphases of the gait stance obtained from ankle
sagittal angular variation: the initial heel contact occurred
between A and B, the midstance phase occurred between B
and C, and the propulsion phase occurred between C and D.
Positive values denote ankle flexion, and negative values denote
extension.
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Figure 3 - Mean values of the contact area (cm2) in six plantar areas (MR = medial rearfoot, CR = central rearfoot, LR = lateral rearfoot,
M = midfoot, MF = medial forefoot and LF = lateral forefoot) during initial contact, midstance and propulsion. (CG = control group,
PFPS = patellofemoral pain syndrome, * p,0.05, # p , 0.1).
Figure 4 - Mean values of the peak pressure (kPa) in six plantar areas (MR = medial rearfoot, CR = central rearfoot, LR = lateral rearfoot,
M = midfoot, MF = medial forefoot and LF = lateral forefoot) during initial contact, midstance and propulsion. (CG = control group,
PFPS = patellofemoral pain syndrome, * p,0.05).
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subphases (3) and the plantar areas (6) as repeated measurements; these analyses were followed by a Newman-Keuls
post-hoc test. The level of significance was set at a = 5% and
marginal significance was set at 1% , a , 5%.
revealing changes in this pattern that would be difficult to
perceive through a clinical visual observation of gait. The
decision to divide the foot rollover mechanism into three
phases allowed us to investigate in more detail what was
happening at initial contact, midstance and propulsion in this
population. The rollover pattern observed in the PFPS
individuals was different from that observed in the healthy
individuals and could induce alterations in the load attenuation within the kinetic chain of the lower limbs. Plantar
pressure that is medially distributed at the initial contact and
laterally distributed during propulsion would probably
result in torque alterations in the lower kinetic chain.
A plantar contact that is medially oriented in the rearfoot
is probably related to an everted rearfoot and could lead to
an excessive medial rotation of the tibia. This rotation could
induce a compensatory medial rotation of the femur and a
lateralization of the patella in relation to the femur,
increasing the patellofemoral joint stress.7 This medially
directed contact in the rearfoot has already been detected in
individuals with PFPS during stair descent.34 Plantar
pressure that is laterally distributed during propulsion is
probably related to a greater re-inversion that is performed
to provide a rigid lever for push-off, as the more everted
initial contact leads to a less stable foot.17 This event can
possibly cause lower limb torque modification during gait,
inducing alterations in the load attenuation within the
kinetic chain.
This detailed characterization of the rocker mechanism is
clinically relevant because these findings can be used to
develop clinical interventions such as insoles, taping and
therapeutic exercises useful for the rehabilitation of this
dysfunction.
Furthermore, this study evaluated a population that was
predominantly female who participated in this study and
exhibited similar levels of physical activity compared with
the control group, which decreased the possibility that
gender and variable levels of physical activity interfered
with our results.
RESULTS
The PFPS group showed a greater contact area at the
medial (p = 0.004) and central (p = 0.002) rearfoot during
initial heel contact, a greater contact area at the medial
(p = 0.072) and lateral (p = 0.005) forefoot in the midstance
and a greater contact area at the lateral forefoot in the
propulsion phase (p = 0.079).
The PFPS group also presented a smaller peak pressure at
the medial forefoot during propulsion than the CG (p =
0.003).
DISCUSSION
Our main findings showed that subjects with PFPS
presented larger contact areas at the medial and central
rearfoot during initial heel contact, at the medial and lateral
forefoot in the midstance, and at the lateral forefoot during
propulsion. PFPS individuals also presented a smaller peak
pressure at the medial forefoot that was followed by a larger
contact area at the lateral forefoot during propulsion.
These results suggest that PFPS individuals exhibit a foot
rollover process characterized by an initial heel contact that
is performed more medially at the rearfoot and a propulsion
phase that is performed more laterally at the forefoot. In the
midstance, the larger contact area at both the medial and
lateral forefoot suggests that PFPS individuals have a
greater excursion of the foot during this phase both
medially and laterally.
According to Willems et al.,17 this laterally directed
support during propulsion, which causes the terminal
push-off to occur laterally rather than predominantly across
the hallux as expected, occurs because an increase in
eversion during initial heel contact leads to a less stable
foot. Consequently, a greater re-inversion is performed to
provide a rigid lever for optimal push-off. Willems et al.17
performed a prospective study of physically active subjects
who developed exercise-related injuries. Plantar pressure
and rearfoot 3D kinematics were evaluated, and the
researchers observed a foot rollover pattern during running
that was similar to what we observed during gait. Subjects
who developed injuries showed a more central initial
contact that was associated with a more everted rearfoot
as well as a more laterally directed propulsion. In our study,
PFPS individuals presented a more medially directed
initial contact and more laterally directed support during
propulsion. This result may also be attributed to a greater
evertion of the rearfoot at heel strike followed by an increase
in supination during the propulsion phase.
The laterally directed propulsion observed in this study,
inferred from the larger lateral forefoot contact area and the
smaller peak pressure at the medial forefoot during
propulsion, is compatible with the pattern reported by
Thijs et al.18 These authors prospectively evaluated plantar
pressure during the gait of military subjects who developed
PFPS. They observed a more lateralized foot rollover pattern
in subjects who developed PFPS than in subjects who did
not develop the disorder.
The present study contributes to discussions about the
influence of PFPS in the foot rollover mechanism during gait,
CONCLUSION
Individuals with PFPS exhibit a foot rollover pattern that
is medially directed at the rearfoot during initial heel
contact and laterally directed at the forefoot during
propulsion. These alterations during the foot rollover
process can be used to develop clinical interventions that
use insoles, taping and therapeutic exercise to rehabilitate
this dysfunction.
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