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The effects of hip muscle strengthening on knee load, pain, and function in people with knee osteoarthritis: A protocol for a randomised, single-blind controlled trial

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Lower limb strengthening exercises are an important component of the treatment for knee osteoarthritis (OA). Strengthening the hip abductor and adductor muscles may influence joint loading and/or OA-related symptoms, but no study has evaluated these hypotheses directly. The aim of this randomised, single-blind controlled trial is to determine whether hip abductor and adductor muscle strengthening can reduce knee load and improve pain and physical function in people with medial compartment knee OA. 88 participants with painful, radiographically confirmed medial compartment knee OA and varus alignment will be recruited from the community and randomly allocated to a hip strengthening or control group using concealed allocation stratified by disease severity. The hip strengthening group will perform 6 exercises to strengthen the hip abductor and adductor muscles at home 5 times per week for 12 weeks. They will consult with a physiotherapist on 7 occasions to be taught the exercises and progress exercise resistance. The control group will be requested to continue with their usual care. Blinded follow up assessment will be conducted at 12 weeks after randomisation. The primary outcome measure is the change in the peak external knee adduction moment measured during walking. Questionnaires will assess changes in pain and physical function as well as overall perceived rating of change. An intention-to-treat analysis will be performed using linear regression modelling and adjusting for baseline outcome values and other demographic characteristics. Results from this trial will contribute to the evidence regarding the effect of hip strengthening on knee loads and symptoms in people with medial compartment knee OA. If shown to reduce the knee adduction moment, hip strengthening has the potential to slow disease progression. Australia New Zealand Clinical Trials Registry ACTR12607000001493.
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BMC Musculoskeletal Disorders
Open Access
Study protocol
The effects of hip muscle strengthening on knee load, pain, and
function in people with knee osteoarthritis: a protocol for a
randomised, single-blind controlled trial
Kim L Bennell*
1
, Michael A Hunt
1
, Tim V Wrigley
1
, David J Hunter
2
and
Rana S Hinman
1
Address:
1
Centre for Health, Exercise & Sports Medicine, School of Physiotherapy, University of Melbourne, Australia and
2
New England Baptist
Hospital, Boston, MA, USA
Email: Kim L Bennell* - k.bennell@unimelb.edu.au; Michael A Hunt - mhunt@unimelb.edu.au; Tim V Wrigley - timw@unimelb.edu.au;
David J Hunter - djhunter@caregroup.harvard.edu; Rana S Hinman - ranash@unimelb.edu.au
* Corresponding author
Abstract
Background: Lower limb strengthening exercises are an important component of the treatment
for knee osteoarthritis (OA). Strengthening the hip abductor and adductor muscles may influence
joint loading and/or OA-related symptoms, but no study has evaluated these hypotheses directly.
The aim of this randomised, single-blind controlled trial is to determine whether hip abductor and
adductor muscle strengthening can reduce knee load and improve pain and physical function in
people with medial compartment knee OA.
Methods/Design: 88 participants with painful, radiographically confirmed medial compartment
knee OA and varus alignment will be recruited from the community and randomly allocated to a
hip strengthening or control group using concealed allocation stratified by disease severity. The hip
strengthening group will perform 6 exercises to strengthen the hip abductor and adductor muscles
at home 5 times per week for 12 weeks. They will consult with a physiotherapist on 7 occasions
to be taught the exercises and progress exercise resistance. The control group will be requested
to continue with their usual care. Blinded follow up assessment will be conducted at 12 weeks after
randomisation. The primary outcome measure is the change in the peak external knee adduction
moment measured during walking. Questionnaires will assess changes in pain and physical function
as well as overall perceived rating of change. An intention-to-treat analysis will be performed using
linear regression modelling and adjusting for baseline outcome values and other demographic
characteristics.
Discussion: Results from this trial will contribute to the evidence regarding the effect of hip
strengthening on knee loads and symptoms in people with medial compartment knee OA. If shown
to reduce the knee adduction moment, hip strengthening has the potential to slow disease
progression.
Trial Registration: Australia New Zealand Clinical Trials Registry ACTR12607000001493
Published: 7 December 2007
BMC Musculoskeletal Disorders 2007, 8:121 doi:10.1186/1471-2474-8-121
Received: 18 October 2007
Accepted: 7 December 2007
This article is available from: http://www.biomedcentral.com/1471-2474/8/121
© 2007 Bennell et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0
),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Background
Osteoarthritis (OA) is a chronic, localised joint disease
affecting approximately one-third of adults, with the dis-
ease prevalence increasing with advancing age [1]. Con-
comitant with this high prevalence is a large economic
cost, with direct and indirect costs estimated to be $23.9
billion in Australia in 2007 [2]. Indeed, given the chang-
ing demographics of the adult population [3], expecta-
tions are for the prevalence of disease and its burden on
the health care system to increase in coming decades [4]
The knee is the most common weightbearing joint
affected by OA, with the disease predominantly affecting
the medial compartment of the tibiofemoral joint [5,6].
Patients with knee OA frequently report symptoms of
knee pain and stiffness as well as difficulty with activities
of daily living such as walking, stair-climbing and house-
keeping [7]. Ultimately, pain and disability associated
with the disease lead to a loss of functional independence
and a profound reduction in quality-of-life.
To date, most knee OA research examining treatment for
knee OA has focused on surgical or pharmacological strat-
egies. Although effective, these types of interventions have
many potential side effects and are expensive [8]. Thus,
recent knee OA clinical guidelines reinforce the impor-
tance of non-pharmacological strategies in the manage-
ment of the condition [9,10]. However, there is an
absence of high quality evidence to support the use of
such therapies [9]. Given that surgical replacement of the
knee is the only recognized treatment for end-stage struc-
tural degeneration of the joint, there is an urgent need to
develop new treatment interventions capable of effec-
tively reducing the personal and societal burden of knee
OA.
Increased loading across the joint has been implicated in
the progression of knee OA severity [11]. The role of gait
analysis in the quantification of dynamic joint load has
received much attention in the literature in light of the dif-
ficulty in performing in vivo measurement of joint loading
during movement [12-14]. From this research, the exter-
nal knee adduction moment, an indirect measure of load
in the medial compartment of the tibiofemoral joint [15],
has emerged as an important and widely accepted biome-
chanical marker of knee load.
Cross-sectional studies demonstrate that patients with
knee OA have a higher peak knee adduction moment dur-
ing walking when compared to healthy age-matched con-
trols [16,17]. It is also likely that the higher prevalence of
medial compared with lateral tibiofemoral joint OA is the
result of differences in the relative loading within the tibi-
ofemoral joint. The external knee adduction moment
determines load distribution across the medial and lateral
tibial plateaus [18-20], with force across the medial com-
partment almost 2.5 times that of the lateral [15]. It has
also been reported that for patients with knee OA, the
magnitude of the adduction moment is predictive of clin-
ical outcomes such as severity of knee pain [21] and radi-
ographic disease [22]. Lastly, longitudinal studies have
demonstrated that as little as a one-unit increase in the
adduction moment is associated with up to a 6.5-fold
increase in the risk of disease progression [11]. Given the
importance of the knee adduction moment with regard to
both symptom severity and disease progression in knee
OA, conservative strategies to reduce the knee adduction
moment constitute a logical rehabilitative approach.
A variety of exercise programs for knee OA have been
described in the literature. These have included general
aerobic exercise programs such as walking or cycling as
well as more specific programs involving strengthening of
particular muscle groups and/or flexibility exercises. Stud-
ies investigating the effects of strengthening in patients
with knee OA have generally focussed on improving
quadriceps strength [23-25]. However, little attention has
been paid to improving the strength of other lower limb
muscle groups such as the hip abductors and adductors.
Due to the lack of research investigating their efficacy,
such exercises are not routinely prescribed for knee OA.
Recent evidence, however, suggests that hip abductor and
adductor muscle strength may be important for reducing
the knee adduction moment [26-28]. During walking,
these muscles stabilise the pelvis on the hip joint in the
frontal plane. The position of the pelvis can alter the posi-
tion of the body's centre of mass and thereby alter loads at
the knee joint. It is postulated that during single leg stance
support in gait, weakness of the ipsilateral hip abductors
may drop the pelvis toward the contralateral swing leg
which can shift the body's centre of mass away from the
knee joint centre and increase the knee adduction
moment. Importantly, a recent longitudinal cohort study
found that people with a lower external hip adduction
moment (suggesting weaker hip abductor muscles) dem-
onstrated more rapid knee OA progression [26].
Less is known about the hip adductor muscles in relation
to knee OA but they may also help reduce the knee adduc-
tion moment, particularly in a varus malaligned knee. By
virtue of their attachment to the distal medial femoral
condyle, the adductors could eccentrically restrain the ten-
dency of the femur to move further into varus. Yamada et
al.[29] found that patients with knee OA demonstrated
stronger hip adductors compared with age-matched con-
trols, and that those with more severe OA had even
stronger adductors than their less severe counterparts.
They hypothesised that this increased strength may be due
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to greater use of the hip adductors in an attempt to lower
the knee adduction moment.
Given that hip muscle strength has the potential to alter
knee load, we hypothesise that hip muscle strengthening
may be a novel intervention for rehabilitation of knee OA
patients that slows disease progression and reduces symp-
toms. However, this has not been evaluated to date. The
primary aim of this trial is to determine whether strength-
ening of the hip muscles in people with medial compart-
ment knee OA reduces knee joint loading as quantified by
the peak external knee adduction moment. The secondary
aim is to determine whether hip strengthening can reduce
knee pain and improve function. It is hypothesised that a
12-week program of strengthening the hip abductor and
adductor muscles will i) reduce the knee adduction
moment; and ii) improve pain and physical function.
Methods/Design
Design
This will be a single-blind randomised controlled trial
(Figure 1). Potential participants will undergo telephone
screening followed by clinical examination by a physio-
therapist to ensure eligibility. A screening x-ray will be per-
formed to quantify knee joint alignment and assess
disease severity. Eligible participants will then be stratified
by disease severity (Kellgren and Lawrence grade 2, 3 and
4) [30] and randomly allocated in permuted blocks of 4
to 6 to hip strengthening or control groups. The randomi-
sation sequence will be generated a priori using the ran-
dom number function in Excel by an independent
investigator not directly involved in assessment of partici-
pants. Allocation will be sealed in opaque and consecu-
tively numbered envelopes held in a central location.
These will be opened in sequence by a person not
involved in the study after recruitment and baseline test-
ing of participants.
Participants
88 men and women (approximately 30 each of KL grades
2, 3, and 4) aged over 50 years will be recruited from the
community via advertisements in local clubs, libraries,
and the print and radio media in metropolitan Mel-
bourne, Australia and from our database of people who
have registered their interest in participating in research
studies. Eligibility will be confirmed by radiographic and
clinical examination. People with tibiofemoral joint OA
fulfilling American College of Rheumatology classifica-
tion criteria [31] and reporting average knee pain on walk-
ing >3 on an 11-point scale (0 = no pain; 10 = maximal
pain) will be included. Other inclusion criteria will be: (i)
knee alignment 182° on a standardised semiflexed
standing posteroanterior knee x-ray (which corresponds
to a mechanical axis angle of 180° on a full leg x-ray,
indicating varus alignment) [32]; (ii) predominance of
pain/tenderness over the medial region of the knee and;
(iii) medial compartment radiographic OA defined as at
least Grade 1 medial joint space narrowing or Grade 1
medial tibial or femoral osteophytes [33].
Exclusion criteria will include: (i) questionable radio-
graphic knee OA (Kellgren and Lawrence Grade 1 [30]);
(ii) lateral tibiofemoral joint space width less than
medial; (iii) symptoms originating predominantly from
the patellofemoral joint as determined by clinical exami-
nation; (iv) knee surgery or intra-articular corticosteroid
injection within 6 months; (v) current or past (within 4
weeks) oral corticosteroid use; (vi) systemic arthritic con-
ditions; (vii) history of hip or tibiofemoral/patellofemo-
ral joint replacement or tibial osteotomy; (viii) any other
muscular, joint or neurological condition affecting lower
limb function; (ix) planning to commence exercise or
other treatment for knee OA in the next 12 months; (x)
Trial protocolFigure 1
Trial protocol.
Telephone screening
Ineligible
Fail inclusion criteria
Meet exclusion criteria
Xray and clinical
screening
Ineligible
Fail inclusion criteria
Meet exclusion criteria
0 weeks Consent, baseline assessment and
randomisation
(n=88)
Hip
Strengthening
Group
Control Group
(usual care)
Weekl
y
Logbooks completed by all patients
12 weeks Final assessment
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unable to ambulate without a gait aid and; (xi) non-Eng-
lish speaking.
Ethical approval has been obtained from the University of
Melbourne Human Research Ethics Committee (HREC
No. 0709220) and from the Department of Human Serv-
ices Victoria, Radiation Safety Committee. All participants
will provide written informed consent.
Interventions
All participants will be requested to refrain from seeking
other forms of treatment during the trial. However, due to
ethical considerations, analgesia will be permitted as
required.
Hip strengthening group
Participants will perform a series of 6 exercises designed to
strengthen the hip abductor and adductor muscles (Table
1) at home, five times per week for 12 weeks. Strengthen-
ing will be limited to the limb with the test knee for 5 of
the 6 exercises. In participants with bilateral knee OA,
only the most symptomatic knee will be assessed and
treated. Participants will attend one of 6 musculoskeletal
physiotherapy clinics located around metropolitan Mel-
bourne to receive appropriate instruction of exercises,
monitoring, and safe progression of resistance. Partici-
pants will visit the physiotherapist on 7 occasions, occur-
ring at 1, 2, 3, 4, 5, 7, and 10 weeks following the baseline
assessment. These will be individual sessions lasting 30
minutes initially and 15 minutes for subsequent visits.
The exercises will be standardised and the therapists will
be trained to deliver the exercises prior to the study. The
therapists will adjust the intensity of the exercises accord-
ingly as determined by the participant s ability to com-
plete 10 repetitions for a given exercise.
Control group
Control group participants will not receive any additional
intervention or complete any home exercises during the
12 week study. They will be requested to continue their
usual care.
Outcome assessment
Participants will be assessed at baseline and at 12 weeks
by an assessor blinded to group allocation. Age, gender,
duration of knee OA symptoms, previous treatment, sur-
gery and medication use for knee OA will be obtained at
the baseline assessment. Radiographic disease severity
will be assessed from the baseline x-ray using the Kellgren
and Lawrence grading system [30]. Skyline knee x-rays
performed in nonweightbearing at 20° knee flexion will
also be obtained to assess severity of OA within the patel-
lofemoral joint. X-rays will be evaluated according to oste-
ophytes and joint space narrowing based on a 4 point
scale [33].
Gait measures
Participants will undergo three-dimensional gait analyses
where they will be instructed to walk barefoot at their self-
selected normal speed that will be monitored by two pho-
toelectric beams. For the follow-up assessment, partici-
pants will again be instructed to walk at their self-selected
speed, but will also perform additional trials constrained
to the speed exhibited at baseline if the self-selected speed
varies by more than 5% between test sessions. Kinematic
data will be collected using a Vicon motion analysis sys-
tem with eight M2 CMOS cameras (1280 × 1024) operat-
ing at 120 Hz (Vicon, Oxford, UK). The standard Plug-In-
Gait marker set will be used (anterior superior iliac spine,
posterior superior iliac spine, mid-lateral thigh, lateral
knee joint, lateral shank, lateral malleolus, second meta-
tarsal head, and over the posterior calcaneus). Additional
markers will be placed anteriorly at the sternal notch and
posteriorly over the spinous processes of T2 and T10 to
construct a local segment coordinate system fixed to the
thorax. Lastly, medial knee and ankle markers will be
included during a static standing trial to determine rela-
tive positioning of joint centres. Kinetic data will be col-
lected using a single, floor-mounted 0R6-6-2000 force
Table 1: Hip abductor and adductor muscle strengthening exercises
Exercise Dosage
Abduction in sidelying 3 sets of 10 at a 10 RM resistance
Unilateral hip abduction performed in sidelying with the use of ankle cuff weights
Abduction in standing 3 sets of 10 with moderate resistance band
Unilateral hip abduction performed in standing with the use of resistance band
Standing wall isometric hip abduction 3 sets of 10 with 5 second holds
Performed in unipedal stance with the opposite limb in 90 degrees of hip and knee flexion. Exercises will be done for both
limbs.
Adduction in sidelying 3 sets of 10 at a 10 RM resistance
Unilateral hip adduction performed in sidelying with the use of ankle cuff weights if possible
Abduction in standing 3 sets of 10 with moderate resistance band
Unilateral hip abduction performed in standing with the use of resistance band
Towel squeezes 3 sets of 10 with 5 second holds
Bilateral isometric hip adduction against a rolled-up towel in sitting
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plate at a sampling rate of 1080 Hz (Advanced Mechanical
Technology Inc., Watertown, MA), in synchrony with the
cameras. Net joint moments will be calculated via inverse
dynamics (Vicon Plug-In-Gait v1.9).
The primary outcome measure will be the peak external
knee adduction moment during the stance phase of gait,
normalised to body weight and height (Nm/BW*HT %).
Test-retest reliability in our laboratory for the knee adduc-
tion moment is excellent (intra-class correlation coeffi-
cients (ICC(3,5)) of 0.92–0.97, in 11 elderly patients with
knee pain tested one week apart). Other variables of inter-
est (see Table 2) will include the peak external hip adduc-
tion moment during stance, maximum contralateral
pelvic drop, and trunk lean angulation in the frontal
plane. A total of five trials will be obtained for the test
limb and all data reported will be averaged across the 5 tri-
als at each test session.
Strength measures
Participants will undergo isometric strength assessment of
hip abduction, adduction, extension, flexion, internal
rotation and external rotation as well as knee extension.
After a single, submaximal trial for each movement, par-
ticipants will be instructed to perform 3 trials each of 5
seconds duration, separated by 15 seconds of rest. The
maximum force output from the 3 trials will be recorded.
All force data will be converted to Nm by multiplying by
the resistance lever arm and normalized to body mass
(Nm/kg).
Maximal isometric hip abduction and adduction torque
will be measured with the participant positioned supine
on a height-adjustable examination table, and with ade-
quate stabilization of the pelvis and contralateral limb.
The study limb will be positioned in slight abduction with
no hip or knee flexion. A handheld dynamometer (HHD)
(Nicholas MMT, Lafayette Instruments, Lafayette, IN) will
Table 2: Measures collected in the trial
Primary Outcome Measurement
Peak external knee adduction moment 3-D motion analysis and force plate system average of 5 walking trials at
self-selected speed
Secondary Outcomes Measurement
Gait Analysis
Peak external hip adduction moment 3-D motion analysis and force plate system average of 5 walking trials at
self-selected speed
Peak pelvic obliquity and lateral trunk lean angle 3-D motion analysis and force plate system average of 5 walking trials at
self-selected speed
Strength
Isometric muscle strength of hip abductors, adductors, flexors, and
rotators
Hand held dynamometer
Isometric quadriceps muscle strength KinCom dynamometer
Symptoms
Pain, stiffness and physical function in past 48 hours WOMAC Osteoarthritis Index – Likert version
Average pain over past week in standing, walking and overall 11 point horizontal numeric rating scale (end descriptors of 0 = no pain
and 10 = worst pain possible)
Average restriction over past week in activities of daily living 11 point horizontal numeric rating scale (end descriptors of 0 = no
restriction and 10 = maximum restriction)
Perceived rating of change for pain and for function over 12 week trial Ordinal scale (1-much worse, 2-slightly worse, 3-no change, 4-slightly
better, 5-much better) at study completion
Function
Standing balance Step test number of times can step foot up and down off 15 cm step in
15 secs
Overall function Timed stair ascent and descent
Other Measures Measurement
Physical activity levels Physical Activity Scale for the Elderly (PASE)
Compliance (exercise group only) Number of physiotherapy visits Completion of home exercises via log-
book
Adverse effects Log-book and open probe questioning
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be placed 5 cm proximal to the lateral and medial femoral
condyles for the hip abduction and adduction trials,
respectively.
Maximum isometric hip extension strength will be meas-
ured in the same participant position as used during
abduction and adduction testing, except that the test limb
will be raised off the bed and supported by a padded cuff
[34]. A force transducer connected to an electronic incli-
nometer will be suspended from the ceiling using a chain,
and the transducer-inclinometer device will be attached to
the padded cuff. The angle of the chain will be 70 degrees
from the horizontal and the involved hip will be flexed 20
degrees to ensure that the test limb is perpendicular to the
force transducer. Participants will then perform isometric
hip extension while force data are recorded from the force
transducer.
Hip strength for flexion, internal rotation, and external
rotation will be measured with the participant stabilized
securely to a chair and the hips and knees flexed to 90
degrees. The HHD will be placed immediately proximal to
the superior pole of the patella for tests of hip flexion
strength and immediately proximal to the medial and lat-
eral malleoli for external and internal hip rotation
strength, respectively.
Quadriceps isometric muscle strength at 60° of knee flex-
ion will be assessed using the Kin-Com 125-AP
dynamometer (Chattecx Corporation, Chattanooga, TN,
USA). Participants will be seated in a standardised posi-
tion and stabilized to the testing apparatus with straps as
well as a thigh block. The lever arm axis of rotation will be
aligned with the lateral femoral condyle for each patient.
All of the above strength tests have demonstrated excel-
lent test-retest reliability in our lab (ICC
2,2
= 0.84–0.98)
based on a subgroup of patients who were tested on 2 sep-
arate occasions separated by an average of 14 days (range
12–23 days).
Self-report measures
Overall average knee pain in the past week will be self-
assessed by a single, 11-point horizontal numeric rating
scale with terminal descriptors of (0 = no pain; 10 = max-
imal pain). Similar scales will be used to measure average
pain in the past week for each of walking and standing.
Such measurement has demonstrated reliability in
patients with knee OA [35].
Self-reported knee pain, stiffness and difficulty with phys-
ical function will be measured using the Western Ontario
and McMaster Universities (WOMAC) Osteoarthritis
Index [36], a valid, reliable, and responsive disease-spe-
cific instrument. The WOMAC consists of 24 questions
covering pain (scored 0–20), stiffness (scored 0–8) and
physical function (scored 0–68), where higher scores indi-
cate worse symptoms.
Participants will rate their perceived change in pain and in
physical function over the 12 weeks (compared to base-
line) on an ordinal scale (1-much worse, 2-slightly worse,
3-no change, 4-slightly better, 5-much better). Scales of
this kind are frequently used as an external criterion for
comparison with changes in scores of other outcomes
[37]. Measuring patient perceived improvement using a
rating of change scale has been shown to be a clinically
relevant and stable concept for interpreting truly mean-
ingful improvements from the individual perspective
[38].
Objective measures of function
Observed functional tests will include the step test and a
timed stair ascent/descent task. The step test is a func-
tional, dynamic test of standing balance [39]. Participants
will stand barefoot on the study leg in front of a 15 cm
step and will be instructed to step the opposite foot on
and off the step as quickly as possible over 15 seconds.
The number of times the foot can be placed up onto the
step and returned to the floor is recorded, with higher
scores indicating better balance. The stair ascent/descent
task involves ascending and descending a set of stairs with
six steps (each 17.5 centimetres in height). Participants
will be instructed to climb up, turn around at the top of
the stairs and climb down at their usual pace and the total
time taken will be recorded, with longer time taken indi-
cating poorer physical function.
Other measures
Physical activity will be measured using the Physical Activ-
ity Scale for the Elderly (PASE) which assesses both the
level and type of recreational and occupational physical
activity undertaken by participants over the previous
week. The PASE was developed and has been validated in
samples of older adults (age 55+ years) [40]. Scores on the
PASE range from 0 to over 400, and higher scores indicate
higher activity levels.
In addition to adverse effects over the course of the trial,
use of medications and other therapies will be recorded by
each participant in a personal logbook.
Sample size calculations
Our sample size of 88 ensures adequate power to detect
significant changes in the peak knee adduction moment
after 12 weeks. We estimate a change in the peak knee
adduction moment after a strengthening program to be
between 5 and 10%. Based on our participants with knee
OA from previous studies, a 7.5% reduction equates to an
absolute change of approximately 0.3 Nm/BW*HT %.
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Estimates of the standard deviation of change scores are
0.4 Nm/BW*HT % based on data obtained from ongoing
studies in our laboratory investigating conservative treat-
ment for knee OA as well as other published reports [41].
Thus, a total of 38 patients per group are required to detect
a 0.3 Nm/BW*ht % change with 90% power (2 sided test,
alpha = 0.05). We also assume an attrition rate of approx-
imately 15% for the duration of the study, suggesting that
44 patients per group will be required.
Statistical analysis
Data will be assessed in a blinded fashion. All analyses
will be conducted on an intention-to-treat principle using
all randomised participants. Missing data will be replaced
by the last score carried forward. Demographic character-
istics and baseline data will be summarised by descriptive
statistics. For outcomes measured on a continuous scale,
differences in mean change from baseline to 12 weeks
between groups will be evaluated using linear regression
modelling while adjusting for baseline levels of the out-
come measure. For the knee adduction moment, gait
speed, disease severity (KL grade), and pain will also be
included as covariates. Model assumptions will be
checked by standard diagnostic plots [42]. Participant rat-
ing of perceived change will be compared between the two
groups by calculating the relative risks and their 95% con-
fidence intervals using log binomial regression [43].
Discussion
This study uses a single-blind randomised controlled trial
design to investigate whether strengthening of the hip
abductor and adductor muscles for 12 weeks in people
with medial knee OA and varus malalignment reduces the
knee adduction moment during walking gait. As a second-
ary aim, it will evaluate whether hip muscle strengthening
also improves disease-associated symptoms, namely knee
pain and physical function.
Lower limb muscle strengthening has recently received
increased interest as an inexpensive treatment for knee OA
due to its ability to reduce knee pain and improve physical
function [23], and also because of its potential ability to
reduce knee joint load. The novelty of the present study is
the focus on hip strengthening. The hip muscles, particu-
larly the abductors, play an important role in stablization
of the pelvis and trunk. Indeed, movement of the contral-
ateral pelvis or lateral leaning of the trunk over the stance
limb, which may occur as a result of hip muscle weakness,
has been suggested to adversely influence the magnitude
of the knee adduction moment [26]. Thus, hip muscle
activity appears to be an important, yet understudied,
contributor to knee joint load.
We have chosen a series of six exercises to strengthen the
hip abductors and adductors based on ease of perform-
ance and isolation of the targeted musculature. We have
purposely avoided any exercises that involve components
of internal or external rotation or that require muscles
other than the abductors or adductors as the prime mover.
It is acknowledged that human gait requires movement
and stabilization in all three planes of movement, but we
have focused on only the frontal plane given the estab-
lished importance of kinematics and kinetics in this plane
on knee OA pathophysiology [13,44].
Some authors propose that gait biomechanics in people
with knee OA may be influenced by KL grade [45], sug-
gesting a possible confounding influence of disease sever-
ity on the effects of interventions in this patient
population. Thus, we will recruit equal numbers of partic-
ipants with mild (KL grade 2), moderate (KL grade 3), and
severe knee OA (KL grade 4) and perform post hoc explor-
atory subgroup analyses. Indeed, a potential benefit of our
design is the identification of groups of patients in which
conservative treatment such as hip muscle strengthening
may or may not be beneficial.
The peak external knee adduction moment was chosen as
the primary outcome measure in this study due to its asso-
ciation with medial compartment knee joint load and
knee OA progression [11,15]. Thus, it represents a non-
invasive, functional means to quantify knee joint loading
and serves as a biomarker for disease progression [46].
Given the design of the study, measurement of muscle
strength also constitutes an important outcome measure.
To ensure that strength gains are limited to the hip abduc-
tors and adductors, measurement of hip flexion, exten-
sion, rotation (both internal and external), and knee
extension will also be conducted. Isometric muscle
strength measured with isokinetic and handheld
dynamometry have both been shown to be valid and reli-
able in a clinical setting [47]. Lastly, objective and self-
report measures of function, as well as self-reported meas-
urement of pain will provide clinically relevant estimates
of change in knee OA symptoms with our novel hip
strengthening intervention. Therefore, this study will
quantify the effects of hip strengthening on biomechani-
cal, functional, and clinical attributes of knee OA.
It is anticipated that testing of all participants will be com-
pleted by the end of 2008. The results from this trial will
contribute to evidence based recommendations for the
usefulness of hip muscle strengthening in the manage-
ment of medial knee OA.
Competing interests
The author(s) declare that they have no competing inter-
ests.
BMC Musculoskeletal Disorders 2007, 8:121 http://www.biomedcentral.com/1471-2474/8/121
Page 8 of 9
(page number not for citation purposes)
Authors' contributions
KB, DH and RH conceived and designed the trial protocol.
KB, DH, RH and TW procured the project funding. MH is
the research assistant on the project. KB and MH drafted
the manuscript and RH and TW contributed to the man-
uscript. All authors read and approved the final manu-
script.
Acknowledgements
This trial is being funded by the National Health and Medical Research
Council (Project #454686).
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pub
... Studies investigating the effects of strengthening in patients with OA of the knee have generally focused on improving quadriceps strength 13,27 . However, little attention has been devoted to improving the strength of other lower limb muscle groups such as the hip abductors and adductors 5 . ...
... It is postulated that during single leg stance support in gait, weakness in the ipsilateral hip abductors may drop the pelvis toward the contralateral swing leg, which can shift the body's centre of mass away from the centre of the knee joint and increase the knee adduction moment. Importantly, a recent longitudinal cohort study found that individuals with a lower external hip adduction moment (suggesting weaker hip abductor muscles) demonstrated more rapid progression of knee OA 5,7 . Patients with knee OA demonstrated stronger hip adductors compared with agematched controls, and individuals with more severe OA had even stronger adductors than their counterparts with less severe OA. ...
... Individuals with more severe OA had even stronger adductors than their counterparts with less severe OA. Previous investigators hypothesized that this increased strength was due to greater use of the hip adductors in an attempt to lower the knee adduction moment 5,30,42 . ...
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... It is postulated that during single leg stance support in gait, weakness of the ipsilateral hip abductors may drop the pelvis toward the contralateral swing leg which can shift the body's centre of mass away from the knee joint centre and increase the knee adduction moment. Importantly, a recent longitudinal cohort study found that people with a lower external hip adduction moment (suggesting weaker hip abductor muscles) demonstrated more rapid knee OA progression 8,20 . ...
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... A redução da dor em pacientes com OA submetidos a exercícios resistidos vem sendo atribuída ao aumento de força muscular e estabilidade na articulação acometida, 40 assim como à consequente redução de carga articular. 41 Entretanto, nos programas de curta duração onde também se observa redução da dor, este fato pode ser atribuído ao contato frequente com um profissional de saúde e à redução da ansiedade e depressão proporcionados pela participação. 42 Um estudo comparou os efeitos de ER dinâmicos e isométricos sobre a dor e função de pacientes com AO, 23 e concluiu que ambas as intervenções são eficazes para reduzir a dor e aumentar a funcionalidade. ...
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