Manual Therapy xxx (2014) 1e5

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Manual Therapy
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Original article

Trunk biomechanics and its association with hip and knee kinematics
in patients with and without patellofemoral pain
Theresa Helissa Nakagawa a, *, Carlos Dias Maciel b, Fa

bio Viadanna Serra
~o a
a
Department of Physical Therapy, Federal University of Sa~o Carlos, Sa
~o Carlos, SP, Brazil
b ~o Paulo, Sa
Department of Electrical Engineering, University of Sa ~o Carlos, SP, Brazil

a r t i c l e i n f o a b s t r a c t

Article history: Patellofemoral pain (PFP) is a common lower extremity condition observed in sports clinics. Recently, it
Received 20 January 2014 has been suggested that trunk motion could affect hip and knee biomechanics in the frontal plane. Thus,
Received in revised form the purpose of the study was compare trunk kinematics, strength and muscle activation between people
25 August 2014
with PFP and healthy participants. In addition, the associations among trunk biomechanics, hip and knee
Accepted 28 August 2014
kinematics were analysed. Thirty people with PFP and thirty pain-free individuals participated. The peak
ipsilateral trunk lean, hip adduction, and knee abduction were evaluated with an electromagnetic
Keywords:
tracking system, and the surface electromyographic signals of the iliocostalis and external oblique muscle
Electromyography
Hip joint
were recorded during single-leg squats. Trunk extension and trunk flexion with rotation isometric
Muscle strength strength and side bridge tests were quantified using a handheld dynamometer. Compared with the
Patella control group, the PFP group demonstrated increased ipsilateral trunk lean, hip adduction and knee
abduction (p ¼ 0.02e0.04) during single-leg squat accompanied with decreased trunk isometric strength
(p ¼ < 0.001e0.009). There was no between-group difference in trunk muscle activation. Only in the
control group, ipsilateral trunk lean was significantly correlated with hip adduction (r ¼ 0.66) and knee
abduction (r ¼ 0.49); also, the side bridge test correlated with knee abduction (r ¼ 0.51). Differences in
trunk, hip and knee biomechanics were found in people with PFP. No relationship among trunk, hip and
knee biomechanics was found in the PFP group, suggesting that people with PFP show different
movement patterns compared to the control group.
© 2014 Elsevier Ltd. All rights reserved.

1. Introduction increasing the laterally directed force acting on the patella (Powers,
2003).
Patellofemoral pain (PFP) is one of the most common lower In people with PFP, increased ipsilateral trunk lean has been
extremity conditions observed in sports medicine clinics (Baquie hypothesised to compensate for hip abductor muscle weakness
and Brukner, 1997). PFP is particularly prevalent in physically to control hip adduction by elevating the contralateral pelvis
active young adults (Taunton et al., 2002). It has been suggested during functional activities (Dierks et al., 2008). However, it has
that the patellofemoral joint may be influenced by other lower also been suggested that ipsilateral trunk lean could affect knee
extremity joints (Powers et al., 2003). Excessive knee valgus, kinetics in the frontal plane (Hunt et al., 2008). In fact, it has
resulting from hip adduction and knee abduction, is believed to been shown that when performing increased ipsilateral trunk
increase the dynamic quadriceps angle, which reflects the frontal lean during gait, healthy volunteers have demonstrated
plane forces acting on the patella (Powers, 2010). The abnormal increased hip and knee abduction moments (Mundermann et al.,
motion of the femur and the tibia in the frontal plane would be 2008). Note that previous results have suggested that increased
expected to adversely affect the patellofemoral joint mechanics by knee abduction moment during landing contributes to an
increased incidence of PFP (Myer et al., 2010). A higher knee
abduction moment might increase the dynamic quadriceps angle
and consequently increase the lateral vector force acting on the
* Corresponding author. Departamento de Fisioterapia, Universidade Federal de patella, which would result in greater stress on the lateral
S~ ~o Carlos, SP, Brazil.
ao Carlos, Rodovia Washington Luis, km 235, CEP: 13565-905, Sa compartment of the patellofemoral joint (Powers, 2003, 2010).
Tel.: þ55 16 3306 6575; fax: þ55 16 3361 2081.
Although there is evidence of increased trunk movement in the
E-mail addresses: helissa2000@yahoo.com.br, helissa8@gmail.com
(T.H. Nakagawa). frontal plane in people with PFP during gait, the relation among

http://dx.doi.org/10.1016/j.math.2014.08.013
1356-689X/© 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Nakagawa TH, et al., Trunk biomechanics and its association with hip and knee kinematics in patients with and
without patellofemoral pain, Manual Therapy (2014), http://dx.doi.org/10.1016/j.math.2014.08.013
2 T.H. Nakagawa et al. / Manual Therapy xxx (2014) 1e5

the trunk, hip and knee kinematics in the frontal plane has not the lower rib, at the L2 level (Hermens et al., 1999). For the external
been investigated in people with PFP. oblique abdominis muscle, the electrode was placed midway be-
It has recently been demonstrated that persons with PFP per- tween the anterior superior iliac spine and the rib cage (Ekstrom
formed greater ipsilateral trunk lean during weight-bearing activ- et al., 2007).
ities (Nakagawa et al., 2012; Noehren et al., 2012). Trunk muscle The EMG data obtained during the single-leg squat were nor-
strength and muscle activation could influence trunk kinematics in malised to the maximal voluntary isometric contraction (MVIC).
people with PFP; thus, it is important to investigate whether trunk The participants performed one practice trial prior to the collection
muscle strength and activation are altered during functional ac- of three 5-s MVICs for the iliocostalis muscle and the external
tivities and how those potential differences in trunk muscle oblique abdominis muscle and rested for 30 s between the trials
strength and activation may influence trunk, hip and knee kine- (Bolgla et al., 2010). The handheld dynamometer (Lafayette In-
matics in people with and without PFP. Also, the associations struments, Lafayette, IN, USA) was used to simultaneously measure
among trunk biomechanics, hip adduction and knee abduction the trunk extension (Fig. 1A) and trunk flexion with rotation
should be analysed in both groups. strength (Fig. 1B) generated during each MVIC (Bolgla et al., 2010).
The purpose of this study was to compare trunk extension, The participants were required to obtain three measurements with
flexion with rotation and lateral flexion isometric strength; ilio- a variability of ± 10%; otherwise, another trial was performed
costalis and external oblique muscle activation and ipsilateral trunk (Bolgla et al., 2010). For the iliocostalis muscle (Fig. 1A), the par-
lean, hip adduction, knee abduction during a single-leg squat be- ticipants were in the prone position with their hands folded behind
tween people with PFP and healthy participants. In addition, the their necks (Muller et al., 2010). The handheld dynamometer was
associations among trunk biomechanics, hip adduction and knee positioned between the scapulae, under a nylon strap secured
abduction were analysed in both groups. It was hypothesised that around the upper trunk and the examination table, which was used
the participants with PFP would present lower isometric trunk to resist trunk extension. A second adjustable nylon strap, which
muscle strength and diminished activation of the iliocostalis and was placed on the distal thighs and secured firmly around the
external oblique muscles when compared with the control partic- underside of the table, was used to stabilise the participant on the
ipants. It was expected given previous findings that people with PFP examination table. For the external oblique abdominis muscle
would present increased trunk, hip, and knee frontal plane motion. (Fig. 1B), the participant performed an oblique curl-up, attempting
It was also hypothesised that lower trunk muscle strength, lower to move the shoulder toward the opposite knee (Ekstrom et al.,
trunk muscle activation and greater ipsilateral trunk lean would be 2007). The handheld dynamometer was positioned on the ster-
associated with lower hip adduction and greater knee abduction in num, under a nylon strap secured around the upper trunk and the
both groups. examination table, which was used to resist trunk flexion with
rotation. A second adjustable nylon strap was placed on the distal
2. Methods

Sixty participants between the ages of 18e35 participated in this

study. The PFP group consisted of 20 females and 10 males
(mean ± SD age, 22.7 ± 3.4 years, height, 171.3 ± 9.2 cm, and body
mass, 65.3 ± 10.3 kg). The control group also consisted of 20 fe-
males and 10 males (age, 22.3 ± 3.0 years, height, 168.6 ± 8.6 cm,
and body mass, 63.3 ± 9.8 kg). The groups were matched for age,
height and body mass (p > 0.05).
All of the participants with PFP reported an insidious onset of
symptoms (>3 months). Furthermore, the participants reported
readily reproducible peripatellar or retropatellar pain while per-
forming at least 2 of the following activities: stair ascent or descent,
running, kneeling, squatting, prolonged sitting, jumping, or iso-
metric quadriceps contraction. Participants with no history of knee
injury or pain were selected for the control group. The exclusion
criteria for all groups included a previous history of knee surgery; a
history of back, hip or ankle joint injury or pain; patellar instability;
signs or symptoms of meniscal or knee ligament involvement, and
any neurological condition that would affect movement. Prior to
the data collection, all participants provided written informed
consent and the experimental protocol was approved by the
Institutional Review Board of the xxxxxxx. In the participants with
PFP who reported bilateral symptoms, the lower extremity re-
ported to be most affected was tested. The corresponding limb of
each gender- and age-matched control participant was tested.
The electromyographic signals (EMG) of the trunk muscles were
sampled at 2000 Hz using surface electrode DE-3.1 sensors (Delsys
Inc., Boston, MA, USA) and interfaced with an amplifier Bagnoli™ 8-
channel system (Delsys Inc., Boston, MA, USA). The EMG activity
was recorded unilaterally between a frequency band from 20 to
500 Hz. Before the electrode placement, the skin was shaved,
abraded and cleaned with isopropyl alcohol. For the iliocostalis
muscle, the electrode was placed 1 finger width medially from the Fig. 1. (A) Trunk extension isometric strength test position. (B) Trunk flexion with
line from the posterior spinal iliac superior to the lowest point of rotation isometric strength test position. (C) Side bridge test position.

Please cite this article in press as: Nakagawa TH, et al., Trunk biomechanics and its association with hip and knee kinematics in patients with and
without patellofemoral pain, Manual Therapy (2014), http://dx.doi.org/10.1016/j.math.2014.08.013
 T.H. Nakagawa et al. / Manual Therapy xxx (2014) 1e5 3

thighs and secured firmly around the underside of the table. In Kinematic data were filtered at 6 Hz using a fourth-order zero-
order to avoid pain or discomfort during the iliocostalis and lag low-pass Butterworth filter (Willson and Davis, 2008). The Euler
external oblique abdominis muscle MVICs, a piece of foam padding angles were calculated using the joint coordinate system defini-
measuring 5 mm thick was positioned between the handheld tions as recommended by the International Society of Biome-
dynamometer and the participant's skin (Fig. 1A and B). No chanics (Wu et al., 2002). The kinematic variables of interest
participant reported any discomfort when performing the MVICs. consisted of peak ipsilateral trunk lean, peak hip adduction, and
For the side bridge test (Fig. 1C), the participants were posi- peak knee abduction during the single-leg squat. Data were aver-
tioned as described by McGill et al. (1999). The handheld dyna- aged across the 3 trials. The ICCs (3,1) and SEM for the kinematic
mometer was positioned on the iliac crest, under a nylon strap measurements were 0.93 (0.07 ) for ipsilateral trunk lean, 0.92
secured around the pelvis and the examination table. Strong verbal (1.83 ) for hip adduction, and 0.92 (1.81 ) for knee abduction.
encouragement was given throughout the MVIC testing. The testing All statistical analyses were performed using the SPSS software
order was randomised to account for ordering bias. (version 19, SPSS Inc., Chicago, IL, USA). The data were analysed
For the trunk extension and trunk flexion with rotation iso- with respect to their normality of distribution using the Shapir-
metric strength tests and the side bridge test, the maximum oeWilk W test. Independent t-tests were used to test for group
strength measurement obtained during 3 trials was used for the differences in strength, EMG and kinematics. The Pearson's pro-
analysis. All strength data recorded in kg were normalised for body ductemoment correlation coefficient was used to examine the re-
weight (Ireland et al., 2003). The intraclass correlation coefficients lationships between each dependent variable (i.e, peak hip
[ICCs (3,1)] and standard errors of measurement (SEM) for the adduction and knee abduction) and the independent variables
strength measurements were 0.77 (5.4% BM) for trunk extension, (peak ipsilateral trunk lean, trunk extension isometric strength,
0.80 (6.9% BM) for trunk flexion with rotation, and 0.80 (8.9% BM) trunk flexion with rotation isometric strength, side bridge test,
for the side bridge test. iliocostalis EMG, and external oblique abdominis EMG). The alpha
The raw EMG signals were band pass filtered at 35e500 Hz, and level was set at 0.05.
a 60-Hz notch filter was applied. The data were full-wave rectified
and a moving 75-ms average window smoothing algorithm was 3. Results
used to generate a linear envelope (Souza and Powers, 2009), with
the maximum amplitude across the MVICs representing 100% ac- Group comparisons and data distribution analysis for all vari-
tivity (Bolgla et al., 2010). The averaged EMG data collected during ables are presented in Table 1. The PFP group presented decreased
the single-leg squat were expressed as a percentage of the EMG trunk extension and trunk flexion with rotation isometric strength,
during the MVIC. The kinematic and EMG data were reduced using and side bridge test compared with the control group
custom MATLAB software (The MathWorks, Natick, MA). The (p ¼ < 0.001e0.009). There was no between-group difference in the
average of the three trials for the kinematic and EMG variables was iliocostalis and external oblique muscle activation during the single
used for the statistical analysis. leg squat. Peak ipsilateral trunk lean, hip adduction and knee
The three-dimensional joint kinematics of the trunk, hip and abduction were greater in the PFP group compared to the control
knee were quantified using the Flock of Birds® (miniBird® hard- group (p ¼ 0.02e0.04). Pearson's correlation coefficients among the
ware, Ascension Technology Corporation, Burlington, VT) inte- kinematic, electromyographic and strength variables are presented
grated with the MotionMonitor™ software (Innovative Sports in Table 2. Peak ipsilateral trunk lean was negatively correlated with
Training, Inc., Chicago, IL). Electromagnetic sensors were placed on peak hip adduction and positively correlated with peak knee
the sternum, sacrum, distal lateral thigh and anteromedial aspect of abduction in the control group only. In addition, the side bridge test
the proximal tibia. Kinematic data were collected at 90 Hz. values negatively correlated with the peak knee abduction values
Prior to data collection, the medial and lateral malleoli and during the single-leg squat in the control group. No significant
femoral epicondyles were digitised to determine the ankle joint correlation was found in the PFP group.
centre and the knee joint centre, respectively. The hip joint centre
was estimated using the functional approach (1999) After the 4. Discussion
digitisation process, a static trial was obtained to determine the
lower limb anatomical coordinate system. The trunk angle was Consistent with the hypothesis proposed, people with PFP
determined by the sternal sensor, sacral sensor, and the respective presented decreased trunk strength compared with the control
hip joint centre. The participants were instructed to squat to an participants. However, no difference in trunk muscle activation was
angle greater than 60  of knee flexion at a rate of 15 squats/minute found between the groups. People with PFP had a greater peak
(Willson and Davis, 2008), as monitored by a metronome. Three ipsilateral trunk lean, hip adduction and knee abduction when
trials were obtained on the tested side. A one-minute rest interval performing a single leg squat than healthy participants. In addition,
was provided between trials. significant associations among trunk kinematics, lateral trunk

Table 1
Group comparisons of the strength, electromyographic and kinematic variables.

PFP group (n ¼ 30) Control group (n ¼ 30) Mean difference 95% CI ShapiroeWilk p-value
Mean (SD) Mean (SD)

Trunk extension strength (% BM) 23.6 (7.2) 28.8 (7.9) 5.2 15.4e4.3 0.15 0.008a
Trunk flexion with rotation strength (%BM) 18.6 (9.1) 38.3 (13.9) 19.7 28.5e9.9 0.19 <0.001a
Side bridge test (% BM) 32.3 (15.2) 43.1 (16.2) 10.8 20.8e2.2 0.34 0.009a
Iliocostalis EMG (% MVIC) 15.3 (10.3) 25.3 (19.5) 9.9 18.4e0.2 0.28 0.09
External oblique EMG (% MVIC) 15.5 (13.5) 15.0 (11.6) 0.5 12.9e3.3 0.32 0.90
Peak ipsilateral trunk lean ( ) 9.8 (5.2) 6.9 (4.4) 2.9 2.7e3.1 0.21 0.02a
Peak hip adduction ( ) 24.0 (6.5) 19.2 (6.0) 4.8 4.6e5.1 0.40 0.04a
Peak knee abduction ( ) 10.5 (6.4) 6.8 (5.3) 3.6 3.4e3.8 0.13 0.03a

BM ¼ body mass, CI ¼ confidence interval, EMG ¼ electromyography, and MVIC ¼ maximal voluntary isometric contraction.
a
Significant difference, p < 0.05.

Please cite this article in press as: Nakagawa TH, et al., Trunk biomechanics and its association with hip and knee kinematics in patients with and
without patellofemoral pain, Manual Therapy (2014), http://dx.doi.org/10.1016/j.math.2014.08.013
4 T.H. Nakagawa et al. / Manual Therapy xxx (2014) 1e5

Table 2 such as onset time or duration of activation, as an earlier onset time

Pearson correlation coefficients (r) among the strength, electromyographic and ki- or a longer activation of the weak trunk muscles could help to
nematic variables in the PFP and control groups.
control the increased trunk motion.
Independent variables Groups Peak hip Peak knee Consistent with the results from previous studies (Nakagawa
adduction ( ) abduction ( ) et al., 2012; Noehren et al., 2012), the participants with PFP in the
Trunk extension strength (% BM) PFP 0.22 0.21 current study displayed greater ipsilateral trunk lean accompanied
Control 0.13 0.16 with greater hip adduction and knee abduction compared to the
Trunk flexion with rotation PFP 0.12 0.30
control participants. Excessive ipsilateral trunk lean, hip adduction
strength (%BM) Control 0.69 0.25
Side bridge test (% BM) PFP 0.12 0.37 and knee abduction could increase the dynamic quadriceps angle
Control 0.32 0.51a and the lateral forces acting on the patella and consequently produce
Iliocostalis EMG (% MVIC) PFP 0.27 0.08 detrimental effects on the patellofemoral joint (Powers, 2003, 2010).
Control 0.09 0.05
The findings from previous studies support the results in the current
External oblique EMG (% MVIC) PFP 0.22 0.10
Control 0.08 0.24
study that reported decreased isometric lateral trunk flexion
Peak ipsilateral trunk lean ( ) PFP 0.15 0.18 strength evaluated by the side bridge test in the PFP group compared
Control 0.66a 0.49a to the control group (Cowan et al., 2009; Willson and Davis, 2009).
BM ¼ body mass, EMG ¼ electromyography, and MVIC ¼ maximal voluntary iso- The altered lateral trunk strength could reduce the ability of people
metric contraction. with PFP to stabilise the hip and trunk in the frontal plane during
a
Significant relationship, p < 0.01. functional and athletic activities (McGill et al., 1999).
The finding of a significant negative correlation between peak
ipsilateral trunk lean and hip adduction in the control group may be
strength and hip and knee kinematics were found only in the explained by the elevated pelvis on the opposite side, which may
control group. It is possible that these differences between the PFP have occurred secondary to the ipsilateral trunk lean and the
and control participants may impact patellofemoral joint me- consequently decreased hip adduction during the single-leg squat
chanics; however, further investigation is necessary to clarify how (Dierks et al., 2008; Souza and Powers, 2009). Mundermann et al.
they might influence symptoms and function in people with PFP. (Mundermann et al., 2008) demonstrated that increased ipsilateral
To the best of the author's knowledge, this was the first study to trunk lean was accompanied by decreased hip adduction moments
demonstrate that people with PFP showed diminished capacity to during gait in healthy adults. Peak ipsilateral trunk lean was found
generate trunk extension and flexion with rotation strength to be positively associated with knee abduction in the control
compared to the control participants. Therefore, the PFP group may participants. In fact, it has been reported that increased ipsilateral
be also more vulnerable to the large external forces in the sagittal trunk lean may increase the valgus moment of the knee joint (Hunt
and transverse planes experienced by the trunk during functional et al., 2008; Mundermann et al., 2008). Finally, the importance of
and sports activities. Because the trunk comprises more than half the the lateral core stability, as measured by the side bridge test, was
body's mass, excessive motion of the trunk could impose greater supported by the results of the current study because the lower
loads at the knee and possibly increase the patellofemoral stress. For lateral trunk and hip strengths were associated with greater peak
example, it has been suggested that increased posterior trunk lean knee abduction during a single-leg squat.
during functional and sports activities could increase the knee Interestingly, a significant correlation was not found among the
flexion moment (Powers, 2010) and the demand on the quadriceps evaluated variables in the PFP group. One explanation for this
(Blackburn and Padua, 2009) that could lead to an increased patel- finding could be that the coupling of the trunk and pelvis move-
lofemoral joint compression. On the other hand, the increased ment is regulated by the lateral trunk musculature (MacKinnon and
contralateral trunk rotation could result in greater hip internal and Winter, 1993). For example, it is possible that a subgroup of people
knee external rotation moments that could be accompanied with with PFP who demonstrated greater deficits of the lateral trunk and
greater femoral, internal and tibial external rotation decreasing the hip strength and/or muscle activation would be unable to elevate
patellofemoral contact area (Salsich and Perman, 2007). their contralateral pelves while leaning their trunks laterally to
In addition, there was no difference in the iliocostalis and control the hip adduction excursion during the single-leg squats.
external oblique abdominis activation during the single-leg squat Corroborating with this hypothesis, in the current study, people
in the PFP group compared to the control group. We were not aware with PFP demonstrated increased ipsilateral trunk lean and hip
of any previous study that investigated trunk muscle activation adduction accompanied with decreased lateral trunk muscle
during functional activity in people with PFP in order to compare strength. Additionally, another subgroup of people with PFP could
the results. This findings of trunk muscle activation in combination have performed isolated contralateral pelvic drops, as a result of the
with the findings of decreased trunk muscle strength and increased hip abductor weakness or altered muscle activation, shifting the
ipsilateral trunk lean during the single-leg squat suggests that centre of mass more medially in relation to the stance limb
people with PFP were unable to compensate for the weak trunk (Powers, 2010). The increased perpendicular distance from the
muscles by increasing the magnitude of the muscle activity, i.e. resultant ground reaction force vector and the knee joint centre
increasing the number of active motor units and frequency of might have increased the varus moment at the knee (Powers, 2010).
activation (Robertson, 2004), of the iliocostalis and external oblique The different cited mechanisms (i.e. lateral trunk flexor/hip weak-
abdominis muscles when making an effort to control the excessive ness or decreased activation accompanied with increased lateral
excursion of the trunk in the frontal plane. It is important to note trunk lean and isolated contralateral pelvic drop accompanied with
that the lateral core stability is a product of both motor control and increased varus moment) possibly performed by different sub-
muscular capacity of the lumbo-pelvic-hip complex (Leetun et al., groups of people with PFP could explain the lack of correlation
2004). Thus, the lack of lateral core stability demonstrated in among trunk biomechanics, hip adduction and knee abduction in
people with PFP could have contributed to the greater ipsilateral the PFP group. Indeed, it has been recently hypothesized that
trunk lean that, consenquently, may have increased the knee subgroups of people with PFP present distinct biomechanical def-
abduction moment by moving the ground reaction force laterally icits and subgrouping this population would provide a rationale for
relative to the knee joint (Hunt et al., 2008; Hewett et al., 2009). researchers to develop targeted treatment interventions (Selfe
Future studies should also investigate other neuromuscular factors, et al., 2013; Keays et al., 2014).

Please cite this article in press as: Nakagawa TH, et al., Trunk biomechanics and its association with hip and knee kinematics in patients with and
without patellofemoral pain, Manual Therapy (2014), http://dx.doi.org/10.1016/j.math.2014.08.013
 T.H. Nakagawa et al. / Manual Therapy xxx (2014) 1e5 5

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Please cite this article in press as: Nakagawa TH, et al., Trunk biomechanics and its association with hip and knee kinematics in patients with and
without patellofemoral pain, Manual Therapy (2014), http://dx.doi.org/10.1016/j.math.2014.08.013