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Modern Rheumatology
ISSN: 1439-7595 (Print) 1439-7609 (Online) Journal homepage: http://www.tandfonline.com/loi/imor20
Exercise therapy in patients with hip
osteoarthritis: Effect on hip muscle strength
and safety aspects of exercise—results of a
randomized controlled trial
Benjamin Steinhilber, Georg Haupt, Regina Miller, Pia Janssen & Inga Krauss
To cite this article: Benjamin Steinhilber, Georg Haupt, Regina Miller, Pia Janssen & Inga Krauss
(2016): Exercise therapy in patients with hip osteoarthritis: Effect on hip muscle strength and
safety aspects of exercise—results of a randomized controlled trial, Modern Rheumatology,
DOI: 10.1080/14397595.2016.1213940
To link to this article: http://dx.doi.org/10.1080/14397595.2016.1213940
Published online: 03 Aug 2016.
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Download by: [University of Technology Sydney]
Date: 04 August 2016, At: 00:57
http://www.tandfonline.com/imor
ISSN 1439-7595 (print), 1439-7609 (online)
Mod Rheumatol, 2016; Early Online: 1–10
ß 2016 Japan College of Rheumatology
DOI: 10.1080/14397595.2016.1213940
ORIGINAL ARTICLE
Exercise therapy in patients with hip osteoarthritis: Effect on hip muscle
strength and safety aspects of exercise—results of a randomized
controlled trial
Benjamin Steinhilber1,2, Georg Haupt1, Regina Miller1, Pia Janssen1, and Inga Krauss1
Downloaded by [University of Technology Sydney] at 00:57 04 August 2016
1
Department of Sports Medicine, University Hospital, Tuebingen, Germany and 2Institute of Occupational Medicine, Social Medicine and Health
Services Research, University Hospital, Tuebingen, Germany
Abstract
Purpose: To evaluate the effect of an exercise therapy concept (the Tübingen exercise therapy
approach THüKo) for increasing hip muscle strength (HMS) in patients with hip osteoarthritis
(OA), and to investigate whether patients do adhere to the intervention and if there are any
adverse events related to the intervention.
Methods: A total of 210 hip OA patients (89 females, 121 males) were randomized into a
12-week exercise intervention (THüKo) including group sessions (1/week) and home exercising
(2/week), a placebo ultrasound group (1/week) or a control group (no treatment). HMS was
measured as isometric peak torque of hip abduction, adduction, flexion, and extension.
Adherence to exercise and safety aspects were monitored as additional outcomes.
Results: Baseline adjusted post intervention HMS of the THüKo group were higher compared to
the control group (differences of 0.11–0.27 Nm/kg, p50.01) and to the placebo ultrasound
group (differences of 0.09–0.19 Nm/kg, p50.01). Adherence to exercise was high (about 90%).
No subject had to refuse from training because of an exercise related adverse event and
exercise related pain was only of intermittent nature without sustainable adverse effects.
Conclusions: The Tübingen exercise therapy approach has shown to have a significant positive
effect on HMS. Its implementation has shown to be feasible and safe according to the
percentage of exercise participation and the absence of sustainable adverse events.
Introduction
Keywords
Dose-response, Gender, Hip, Osteoarthritis,
Strength training
History
Received 1 April 2016
Accepted 10 July 2016
Published online 2 August 2016
joint function [16,17]. Therefore, retaining and increasing HMS
is recommended in international guidelines for the management
of hip OA [18–20]. These guidelines further recommend
introducing patients into exercise programs that can be proceeded
autonomously after an initial period with professional support.
Such programs may increase long-term adherence to exercise and
address the economic burden of therapy costs in hip OA by
reducing cost-intensive face to face contacts between therapist
and patient [21].
The authors of this article recently reported scientific evidence
of the effectiveness of an exercise intervention in terms of selfreported pain reduction and improvement in PF in patients
suffering from hip OA [22]. The present article aims for the
analysis of the effects of the Tübingen exercise therapy approach
(THüKo) on HMS in comparison to sham ultrasound and a nontreated control. Additionally adherence and safety aspects of
THüKo were analysed.
Patients with hip osteoarthritis (OA) suffer from joint pain [1,2]
and exhibit decreased levels of physical function (PF) [3], which
result in impairments in quality of life [4,5]. A factor that is
suggested to interact with both pain and PF is the strength of the
surrounding hip joint muscles. Commonly, patients with hip OA
have reduced hip muscle strength (HMS) compared to their contralateral hip joint in case of unilateral hip OA [6] and healthy agematched persons [7,8]. These impairments in HMS are mentioned
to be the result of disuse atrophy [6,8], reflex arthrogenous
inhibition of muscle contraction [9], and infiltration of noncontractile material such as fat in the muscle [10]. Cross-sectional
studies reported an association of low HMS and reduced levels of
PF in hip OA [3,11]. A 5-year epidemiologic follow-up study [12]
indicated that reduced HMS fosters limitations of daily living.
Some authors even consider weak hip muscles as a risk factor for
idiopathic hip OA [13,14] similar to knee OA where quadriceps
weakness increases the risk for becoming knee OA [15].
Strengthening exercise programs are suggested to be one of
the most promising approaches to improve OA-related pain and
Materials and methods
Participants
Correspondence to: Benjamin Steinhilber, Institute of Occupational
medicine, Social Medicine and Health Services Research, University
Hospital, Wilhelmstrasse 27, 72074 Tuebingen, Germany. E-mail:
[email protected]
A total of 218 hip OA patients (mean age 58.7 yr, standard
deviation (SD) 10 yr; females ¼ 89, males ¼ 129) were recruited
between 2010 and 2012 by newspaper advertisements and the
outpatient clinic of the University Hospital. Sample size was based
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2
B. Steinhilber et al.
Mod Rheumatol, 2016; Early Online: 1–10
Box 1. Inclusion and exclusion criteria for the study.
Study design and study arms
Inclusion criteria
Age between 18 and 85 years
Osteoarthritis (OA) of one or both hip joint(s) (clinical criteria of the
American College of Rheumatology)
The subject gives voluntary consent to study participation after
receiving oral and written information about study content and
objectives
The subject has the time available to undertake the exercises and attend
the measurings
The subject is physically fit for the intervention measure (as ascertained
during the examination conducted by the principal investigator)
‘‘Fitness’’ in this setting relates to the physical as well as the
psychological condition of the subject. (Subjects will not be excluded
if they have one hip endoprosthesis, as long as the contralateral hip is
affected by osteoarthritis according to the listed criteria.)
The subject has capacity to consent
Measurements of the prospective study with a test-retest design
were taken at baseline (t0) and immediately after the twelve week
intervention period (t1). At t0 subjects were randomly assigned to
an exercise intervention (Tübinger Hüftkonzept THüKo, the
Tübingen exercise therapy approach), a control group receiving
no intervention (CG), a placebo ultrasound group (PUG), and an
experimental ultrasound group (UG). The rationale for including a
placebo control is based on the fact, that placebo interventions in
osteoarthritis are effective for pain relieve and improvements in
self-reported joint function and stiffness [25]. It was therefore of
special interest, if the exercise intervention has superior effects to
attention control alone. An experimental ultrasound group with a
small sample size was further included for ethical reasons.
Randomization was stratified by sex. Allocation concealment
was guaranteed by using a sealed opaque envelope that neither the
investigators nor the participants were able to view. Patients of
PUG and UG were single-blinded to the treatment applied.
Randomization ratio of UG was 1:10 compared with the respective
other groups. Due to its experimental characteristic, UG was not
included into data analysis.
Exclusion criteria
Unstable anchoring of endoprosthetic hip joint
Hip dislocation after endoprosthetic joint replacement
Further disorders affecting the lower extremities or lower back that
require treatment by a physician/therapist and which are not
connected to the OA and are currently being treated
The presence of osteoarthritis in several joints (for example, hip and
knee) is NOT an exclusion criterion
Medication or alcohol misuse
Participation in a clinical study in the preceding 4 weeks
Lack of compliance
Acute illness
Use of walking aids
Previous trauma in the hip and pelvis area with accompanying
development of secondary osteoarthritis
Known endocrinological causes of hip osteoarthritis
Confirmed metabolic causes of hip osteoarthritis
State after aseptic bone necrosis (Perthes’ disease)
Cardiocirculatory disorders or other comorbidities that result in severely
restricted everyday physical capacity and that are contraindications
to physical exertion (for example, heart failure NYHA III–IV,
terminal renal failure stage IV)
Medical exercise therapy, physiotherapy on resistance machines in the
preceding 3 months, with a total treatment frequency of more than
six units
Systematic group or individual therapy to treat the osteoarthritis
(systematic in the sense of a minimum of 1/week for 30 min or
more) in the preceding 3 months
Physical therapy to treat the osteoarthritis (systematic in the sense of
regular, prescribed application at least 1/week) in the preceding
3 months
Newly initiated exercise/movement therapy in the preceding 3 months
(sports and movement therapy defined as taking place a minimum of
1/week, getting out of breath, minimum duration 30 min)
Corticosteroid injection into the hip joint in the preceding 12 months
on the subscale bodily pain of the 36-item Short Form questionnaire, which was the primary outcome of this trial [23]. The
present article focuses on the secondary outcome HMS of this
study. All participating subjects gave their written informed
consent and the study received approval from the local ethics
committee. The study was registered by the German Clinical Trials
Register DRKS00000651. Inclusion criteria were age between 18
and 85 years and OA in at least one hip joint. Further, subjects had
to be able to walk safely without walking aids and must have had a
stable implantation of the artificial hip joint, if present in the contra
lateral hip. Hip OA was assessed according to the clinical criteria
of the American College of Rheumatology [24]. Exclusion criteria
were the beginning of any kind of exercise or physical therapy
within 3 months prior to the present study and any operation at the
lower extremities during the last 3 months prior to the present
study. A complete list of all in- and exclusion criteria are given in
Box 1.
Exercise intervention
The Tübingen exercise therapy approach (THüKo) comprised 12
supervised institutional group sessions and 24 unsupervised homebased sessions within 12 weeks. The weekly indoor institutional
group exercise sessions were supervised by a physical therapist
and lasted 60–90 min. The maximum number of participants per
group was restricted to 15. The sessions contained physical, social,
and cognitive elements. Physical elements aimed for mobilization,
strengthening, and improvement of postural control. The 24 home
sessions included a progressive exercise program (two sessions per
week) with exercises for mobilization, physical perception of
movements, balance, and strengthening. Strengthening exercises
accounted for about two-third of the training and were well
balanced for hip abduction (HAB), hip adduction (HAB), hip
flexion (HF), and hip extension (HE) with a progressive increase
in exercise intensity throughout the program. All strengthening
exercises were performed with the subjects’ own bodyweight, an
elastic latex band, a ball, and weight-cuffs (examples are depicted
in Figure 1). Some of the strengthening exercises were conducted
for each lower extremity separately and some were performed
bilaterally. The intensity of exercises was controlled and
quantified by the subjects’ subjective rating using the 15 category
Borg perceived exertion scale (Borg-Scale) from 6 to 20, where 6
is equivalent to no exertion ‘‘very very light’’ and 20 is equivalent
to maximum exertion ‘‘very very hard’’ [26]. In order to enable
the participants to exercise with the required exercise intensity
throughout the program, exercises were provided with two
performance levels (basic and difficult, see Figure 1) [27]. The
program included three phases. Phase I was an adaptation phase
(weeks one to three), phase II addressed strength endurance
(weeks four to eight) and phase III aimed to stimulate improvements in cross-sectional area (weeks nine to twelve). During the
adaptation phase subjects should exercise with exercise intensity
below 30% of their maximum voluntary contraction (MVC)
leading to low levels of perceived exertion. The strength
endurance phase (phase II) is characterized by subjects performing
exercises with 2–3 series and 20–25 repetitions, corresponding to
30–40% MVC. The third phase includes exercises with 3–4
series and 10–15 repetitions, corresponding to 70% MVC. The
percentage MVC is estimated by the number of repetitions that can
be conducted appropriately but with a subjective exertion level of
at least 14 on the Borg-Scale at the end of each set [22,23].
Exercise therapy in hip OA
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DOI: 10.1080/14397595.2016.1213940
3
Figure 1. Examples for exercise therapy [27].
Placebo ultrasound
The placebo ultrasound group received sham ultrasound onceweekly for 15 min. The transducer was gently moved over the hip
region. The used ultrasound gel had no active component and the
ultrasound itself was invisibly turned off.
Outcome criteria
Hip muscle strength (HMS). The Isomed 2000 (D&R GmbH,
Hemau, Germany) isokinetic dynamometer was used to measure
isometric peak torque for HAB, HAD, HF, and HE. Subjects were
placed in a lateral position for HAB/HAD and in a supine position
for HF/HE testing. The angles of the isometric measurements were
0 hip abduction for HAB, 20 hip abduction for HAD, 20 hip
flexion for HF, and 40 hip flexion for HE. All measurements
(prior and after the intervention period) were conducted at the
same time of the day to control for circadian variation in
performance. Details regarding standardization and procedures of
the applied strength measurements are reported by Steinhilber
et al. [28]. For each measure of HMS, the mean of both legs was
calculated and relativized to subject’s body weight (Nm/kg).
Adherence, dosage and safety of the interventions. Subjects of
the THüKo had to fill out exercise logs including exercise
frequency, duration, perceived exertion, and pain for each home
session. The therapist supervising the institutional sessions monitored adherence to the sessions and was asked to report any adverse
event in the context of the group sessions and to inquire information
on any adverse event in the context of the home exercises. In PUG
adherence was monitored by the person who applied the placebo
ultrasound. Dosage was pre-specified by the protocol.
Adherence was considered as the relation of intended exercise
and ultrasound sessions, respectively and the number of completed
sessions by all participating subjects.
Dosage of exercise was quantified using information on
duration, sets and repetitions of exercises and perceived exertion.
Safety was quantified by analyzing withdrawals from exercise due
to exercise related reasons, reports to the instructor on any adverse
event in the context of the group sessions and the home based
exercises as well as given information on perceived pain in the
context of exercising. Pain levels were assessed before, during,
and after exercising using an 11-point numerical rating scale (0–
10), where 0 indicated ‘‘no pain’’ and 10 ‘‘severe pain’’.
Anthropometric data. Gender, age, body height, body weight,
and body mass index (BMI) were determined.
Statistics
Data were analyzed by intention-to-treat with the last observation
carried forward. Alpha level for statistically significance was set to
0.05. Normal distribution was rated according to histograms,
normal quantile plots, skewness and curtosis for all metric
variables. Statistical analyses were done using JMP 10.0.0
software (SAS Inc., Cary, NC). Group differences at baseline
were tested by the Kruskal–Wallis Test. An analysis of covariance
(ANCOVA) was used to evaluate changes between experimental
groups in each isometric peak torque measure from t0 to t1.
Baseline peak torque values were used as covariates [29] and
group as well as the interaction term group*baseline peak torque
was included in the statistical model as independent factors.
Tukey–Kramer HSD (honestly significant difference) tests were
used for post-hoc comparison in case of significant model effects.
Differences of the adjusted post values between the experimental
groups were expressed in percent (Equation 1):
Equation 1: Calculation of percentage differences between
adjusted post values of different groups.
xGroupA xGroupB
100:
ðxGroupA þ xGroupB Þ=2
Effect sizes (ES) were calculated according to Cohen [30]
between all experimental groups (Equation 2).
4
B. Steinhilber et al.
Mod Rheumatol, 2016; Early Online: 1–10
Equation 2: Calculation of effect sizes and pooled SD.
ES ¼
ðx2 x1 ÞGroupA ðx2 x1 ÞGroupB
SDpooled
;
SDpooled
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ðnGroupA 1ÞSD2GroupA þ ðnGroupB 1ÞSD2GroupB
,
¼
nGroupA þ nGroupB 2
Downloaded by [University of Technology Sydney] at 00:57 04 August 2016
where x2 is the non-adjusted mean value after the intervention
period (t1) and x1 is the baseline (t0) mean value. SDpooled was
calculated with SD values from the non-adjusted values at
baseline.
In addition, an exploratory data analysis was performed by a
descriptive statistical approach to examine possible differences
between male and female subjects. Therefore, the adjusted post
values of the four isometric peak torque measures (which can be
obtained by gender specific ANCOVA as described above) were
given as mean percentage difference between experimental groups
for male and female subjects separately.
Adherence to exercise for the whole sample and each gender
separately was quantified in a descriptive manner by evaluating
the exercise logs regarding training frequencies, as well as
medians and the first and third quartiles for subjective exhaustion
after exercise and perceived pain.
Figure 2. Dropout flow-chart.
Exercise therapy in hip OA
DOI: 10.1080/14397595.2016.1213940
Table 1. Characterization of the study population.
Variable
Group
Mean (SD)
n
THüKo
CG
PUG
THüKo
CG
PUG
THüKo
CG
PUG
THüKo
CG
PUG
THüKo
CG
PUG
70
68
70
58 ± 19
60 ± 9
58 ± 10
80 ± 14
82 ± 13
83 ± 17
173 ± 9
173 ± 9
174 ± 10
27 ± 4
27 ± 3
27 ± 4
Age (yr)
Body weight (kg)
Body height (cm)
Downloaded by [University of Technology Sydney] at 00:57 04 August 2016
BMI (kg/m2)
5
statistically significant difference between PUG and CG, the
gender-specific analysis was not applied (Figure 3).
Baseline group differences*
Adherence and dosage of interventions
n.s.
n.s.
n.s.
n.s.
THüKo: exercise group following the Hip Concept Tübingen; CG: control
group; PUG: placebo ultrasound group; BMI: body mass index; SD:
standard deviation; n.s.: not statistically significant.
*Group differences were tested by the Kruskal–Wallis test.
Results
Dropouts and extreme values
Figure 2 shows dropouts and reasons for dropouts. 210 subjects
were randomly allocated to the experimental groups THüKo, CO,
and PUG. Therefore, two subjects could not be analyzed because
of missing values at t0: one subject in the THüKo group was not
able to perform maximum peak torque measurements at t0 due
to its physical condition after obstruction of the intestines, and
one subject of the PUG was lost for data analysis due to failed
storing of the measurement results at t0. 15 subjects were analyzed
intention-to-treat because of non-participation at t1. The characteristics of the finally analyzed population (n ¼ 208) are shown in
Table 1.
Effects on hip muscle strength
Baseline strength values, which were not normally distributed,
were similar between all experimental groups. The residuals of
each HMS measure were normally distributed and the interaction
term group*baseline peak torque had no effect. The data therefore
comply with the requirements to perform the ANCOVA. Table 2
illustrates HMS values for t0 and t1.
The ANCOVA revealed statistically significant increased HMS
of the THüKo group compared to CG and PUG in the adjusted
peak torque values at t1 for all muscle groups (differences ranged
from 7 to 15% (p50.01)). The differences in HF and HE between
the THüKo group and CG were slightly higher than between the
THüKo group and PUG (Table 2). No statistically significant
differences were found between PUG and CG. Effect sizes
indicate a medium effect of the exercise intervention. Additionally,
a small effect of sham ultrasound appeared in two isometric peak
torque measures (Table 3).
The mean percentage change in HMS (Nm/kg) for male and
female subjects from the THüKo group showed strength improvements for both genders compared to CG and PUG. However, the
effect of the THüKo intervention on HMS seemed to be more
pronounced in male subjects. Males from the THüKo group
increased HMS by 11 and 10% compared to male subjects from
CG and PUG while HMS in female subjects increased 9 and 4%
compared to CG and PUG, respectively. Since there was no
A total of 64 of 70 subjects completed the ultrasound program
with an adherence of 92%. 65 of 70 subjects from the THüKo
group completed the exercise program. Adherence (n ¼ 70) to the
group sessions was 89% (males 90%, females 89%). According to
the exercise logs, adherence to the home-based exercise program
was 91% (males 95%, females 88%).
Exercise logs further indicated that subjects were able to
exercise with the required exercise intensity with low levels of
perceived exertion during phase I and higher levels of perceived
exertion during phase II and III. Males and females documented
similar exertion levels in all phases (Table 4).
Safety
No participant of the THüKo group had to withdraw from the
program due to exercise related adverse events. Overall, lowmedian pain levels during exercising increased throughout the
12-week intervention period (phase I ¼ 1, phase II ¼ 2, phase
III ¼ 3). In contrast, median pain levels directly before and after
exercising decreased from three in phase I to two in phases II and
III. In males the median pain level in phase I was 1 and in phase II
and III it was 2. Females reported a median pain level of 1 in phase
I, 3 in phase II and 4 during phase III (Table 4).
Discussion
The aim of this randomized controlled clinical trial was to
investigate the effect of an exercise therapy program (the Tübingen
exercise therapy approach THüKo) with a substantial part of
home-based strengthening exercises on hip muscle strength
(HMS) in comparison to a non-treated control group (CG) and a
sham ultrasound group (PUG). Additionally, a report on adherence
to exercise and on safety aspects was provided.
The results show a statistically significant increase of HMS in
the THüKo group. Baseline adjusted peak torque values were 7–
15% higher compared to CG and PUG. Although not tested for
statistical significance, increases in HMS were more pronounced
in male subjects.
The study design of this trial has a lot in common with a study
from Bennell et al. They recently published data of a twelve week
individualized multimodal physiotherapeutic intervention for
patients with hip OA [31]. Aside of manual therapy techniques,
education and advice in the context of 10 supervised sessions, four
to six home exercises for strengthening, stretching and range of
motion, as well as functional balance and gait drills were part of
the program. Patients were introduced into the home exercises by
supervised physiotherapeutic sessions and were then asked to
continue autonomously at home four times a week. Three sets of
hip abductor and quadriceps strengthening should be carried out in
each training session and could be supplemented by another
strengthening exercise for hip extensors and/or hip rotators
[31,32]. Effects of this physiotherapeutic program were compared
to a sham ultrasound treatment for the hip joint (once a week for
twelve weeks with duration of 15 min). Both interventions reduced
self-reported pain and improved PF. However, the effect of the
active intervention was not superior to the effect induced by sham
ultrasound which raises questions about the additional effect of a
multimodal physiotherapeutic treatment as an active agent in
comparison to attention control alone. In this regard, it has to be
mentioned that the active intervention induced no statistically
significant increase in muscle strength. By the authors own
0.83
p50.0001
0.82
p50.0001
0.80
p50.0001
0.83
p50.0001
1.68 (0.68)
1.61 (0.70)
0.08 (0.30)
1.69
(1.61–1.76)
1.18 (0.34)
1.14 (0.34)
0.03 (0.16)
1.15
(1.12–1.18)
1.25 (0.43)
1.28 (0.46)
0.03 (0.20)
1.34
(1.29–1.39)
1.28 (0.36)
1.28 (0.40)
0.00 (0.16)
1.30
(1.26–1.35)
CG
mean (SD)
1.87 (0.64)
1.86 (0.64)
0.01 (0.29)
1.76
(1.69–1.83)
1.21 (0.31)
1.20 (0.32)
0.01 (0.13)
1.18
(1.15–1.21)
1.37 (0.41)
1.38 (0.42)
0.02 (0.22)
1.34
(1.29–1.39)
1.33 (0.38)
1.33 (0.40)
0.00 (0.16)
1.31
(1.27–1.35)
PUG
mean (SD)
1.74 (0.77)
1.93 (0.87)
0.19 (0.33)
1.95
(1.88–2.03)
1.17 (0.29)
1.26 (0.33)
0.08 (0.14)
1.27
(1.23–1.30)
1.33 (0.48)
1.46 (0.49)
0.13 (0.22)
1.45
(1.40–1.50)
1.31 (0.41)
1.42 (0.44)
0.11 (0.19)
1.42
(1.38–1.46)
THüKo
mean (SD)
0.27
(0.14–0.39)
0.12
(0.06–0.17)
0.11
(0.02–0.19)
0.12
(0.05–0.18)
mean (CI)
15
9
8
8
%
difference THüKo–CG
p50.001
p50.001
0.007
p50.001
p Value
0.19
(0.07–0.32)
0.09
(0.03 – 0.14)
0.11
(0.03–0.19)
0.11
(0.04–0.18)
mean (CI)
10
7
8
8
%
difference THüKo – PUG
p50.001
0.002
0.006
p50.001
p Value
0.07
(0.05–0.20)
0.03
(0.03–0.09)
0.00
(0.09–0.08)
0.00
(0.07–0.07)
mean (CI)
5
2
0
0
%
difference PUG–CG
0.339
0.447
0.997
0.996
p Value
B. Steinhilber et al.
THüKo: exercise group following the Hip Concept Tübingen; CG: control group; PUG: placebo ultrasound group; ANCOVA: analysis of covariance; SD: standard deviation; 95%CI: confidence interval.
*Differences in baseline values between groups were not statistically significant.
**Baseline adjusted post-intervention values.
Hip extension (Nm/kg)
baseline*
Post-intervention
change (post baseline)
ANCOVA**
Hip flexion (Nm/kg)
baseline*
Post-intervention
change (post baseline)
ANCOVA**
Hip adduction (Nm/kg)
baseline*
Post-intervention
change (post baseline)
ANCOVA**
Hip abduction (Nm/kg)
Baseline*
Post-intervention
change (post baseline)
ANCOVA**
ANCOVA
r2 adj.
p Value
Table 2. Isometric hip muscle peak torque between the experimental groups.
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6
Mod Rheumatol, 2016; Early Online: 1–10
Exercise therapy in hip OA
DOI: 10.1080/14397595.2016.1213940
Table 3. Effect sizes of hip muscle strength between the experimental
groups.
Isometric peak
ES
ES
ES
torque measure (THüKo and CG) (THüKo and PUG) (PUG and CG)
Hip
Hip
Hip
Hip
abduction
adduction
flexion
extension
0.3
0.2
0.4
0.4
0.3
0.3
0.3
0.3
0
0
0.1
0.1
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THüKo: exercise group following the Hip Concept Tübingen; CG: control
group; PUG: placebo ultrasound group; ES: effect size: 0.1 ¼ small
effect, 0.3 ¼ medium effect, 0.5 ¼ large effect.
Figure 3. Differences in experimental groups for male and female hip OA
patients. THüKo: the Tübingen exercise therapy approach; m: males; f:
females.
admission, the combination of several exercise modalities reduced
the dose of each of them. As such, the dosage of the applied
exercises seemed to be too low to stimulate strength adaptations
and superior treatment effects compared to placebo ultrasound
[31,33]. In contrast, results of the present study show that exercise
dosage was sufficient to improve HMS. Furthermore, the effects
on pain and PF exceeded the effects by the sham ultrasound
treatment [22]. This finding underlines the importance of an
adequate composition and dosage of exercise therapy programs.
Three aspects may be responsible for the differences in
strength adaptations between the present study and the study by
Bennell et al.
(1) Low quality of exercise performance and low intensity can
reduce the stimulus on target muscle and mitigate the impact of an
exercise on strength adaptations [34,35]. The exercises applied in
the present study were preliminary evaluated in a pilot study [28].
Subjects tended to exercise with an insufficient intensity.
Consequently, in the present study, efforts were increased to
support subjects’ motor learning in order to perform exercises with
high performance quality and to support subjects’ ability to rate
and adapt exercise intensity on the basis of perceived exertion.
Patients were precisely introduced into the exercises during the
group-based sessions and the first three weeks of home training
focused on low intensity exercises to allow motor learning. We
therefore hypothesized that subjects of the present study had a
higher standard in exercise performance and were more compliant
to the given exercise requirements. Subsequently, exercise
7
instructions, motor learning and control of exercise intensity
seem to be important for an effective strengthening intervention
program.
(2) Aside of movement quality and exercise intensity, frequency and amount of exercises are relevant aspects of exercise
dosage. Frequency of strengthening exercises was higher in the
study of Bennell et al. [31] with four weekly home sessions in
comparison to one group-based session and two home-based
sessions in the THüKo program. However, adherence to exercise
was higher in our study (91% compared to 85%) and the amount of
exercises throughout the study period was larger as well: A rough
estimate indicates that each subject of the study by Bennell et al.
performed about 1500 repetitions for each target muscle or muscle
group. The overall amount of repetitions including all exercises
was about 3000 repetitions [31]. Subjects of the present study
performed a similar amount of repetitions per muscle group (about
1300), but a distinctively greater overall amount (about 6000
repetitions). Since the repetitions per exercise for a given muscle
group were comparable between the two studies, it is remarkable
that an increase in muscle strength only occurred in the present
study. The higher overall amount of exercise repetitions might
account for this difference. Exercises for a target muscle
simultaneously co activate other muscles [36,37]. Therefore,
subjects from the THüKo group may have gained from additional
stimuli by muscle co activation provided by the high overall
amount of exercise repetitions.
(3) Half of the applied exercises in the study by Bennell et al.
[31] did not directly address the hip muscles. In contrast, exercises
of THüKo specifically focused on the muscles surrounding the hip
joint. Studies demonstrated that all major hip muscles are affected
by hip OA [8,34,38]. Therefore, it seems reasonable that impaired
HMS is more adequately addressed by joint specific exercises.
At this point, it cannot be evaluated whether higher quality,
intensity control, frequency, amount or specification of exercises
improved exercise effectiveness in the present study. The results of
these two studies illustrate the shortcomings of the current
literature in exercise therapy for hip OA. Although strength
training is recommended as first-line treatment in hip OA its
optimum dosage (type, intensity, frequency, duration) still has to
be defined [39] and in order to increase complexity of this issue it
has to be mentioned that people may respond differently to the
very same exercise intervention. In this regard French et al.
conducted a secondary analysis of data from a multicenter
randomized controlled trial to identify potential predictors of
response to exercise therapy with or without adjunctive manual
therapy in patients with hip OA [40]. Although French and
colleagues failed to identify predictors, secondary analyses of trials
with adequate sample sizes may provide hints or at least research
hypotheses in order to further improve person-tailored exercise
therapy programs in hip OA.
The explorative analysis of gender effects indicated a more
pronounced effect of the exercise intervention on HMS in male
subjects. This could be partly explained by findings from exercise
logs. Males of the THüKo group reported 7% higher adherence to
home exercising and less perceived pain than female subjects.
However, this minor incongruence between males and females
might not be the only reason attributable to greater strength
improvements in males. Häkkinen et al. found a positive
correlation of serum testosterone levels and changes in maximal
strength of the knee extensor muscles during a 6-month strength
training in two groups of women (age 40 and 70). They concluded
that a low level of testosterone, especially in older women, might
be a factor that limits strength development [41]. In general higher
age is reported to be a significant factor related to less adaptation
to resistance exercises [42,43] and might be pronounced in female
subjects at the age of menopause. On average, female subjects
8
B. Steinhilber et al.
Mod Rheumatol, 2016; Early Online: 1–10
Table 4. Exercise modalities and outcomes of the exercise logs of the home-based strengthening exercises.
Phase I Phase II Phase III
Downloaded by [University of Technology Sydney] at 00:57 04 August 2016
Exercise modalities of strengthening exercises
Week
Sessions per week
Exercises per session
Sets per exercise
Repetitions per exercise
Exercise intensity (Borg value at the end of a set)
Results from exercise logs
Perceived exertion (Borg value: 6–20)
Q3
Median
Q1
Median male
Median female
Pain before exercising (0–10)
Q3
Median
Q1
Pain after exercising (0–10)
Q3
Median
Q1
Pain during exercising (0–10)
P75
Median
P25
Median male
Median female
Phase I
adaptation
Phase II
strength endurance
PhaseIII
cross-sectional area
1–3
2
9–10
1
30
–
4–8
2
4
2–3
20–25
14
9–12
2
4
3–4
10–15
14
1
2
10
1
30
–
2
2
9
1
30
–
3
2
10
1
30
–
4
2
4
2
20
14
5
2
4
2
25
14
6
2
4
3
20
14
7
2
4
3
25
14
8
2
4
3
25
14
9
2
4
3
15
14
10
2
4
3
15
14
11
2
4
4
10
14
12
2
4
4
10
14
11
9
7
9
11
16
14
12
14
14
16
15
13
15
14
11
9
7
9
9
12
9
7
9
11
12
10
8
9
11
15
13
12
14
13
16
14
12
14
14
16
14
12
14
13
16
14
13
15
14
16
14
13
15
14
17
14
13
15
14
17
15
13
15
15
17
14
13
15
14
16
14
13
14
15
4
3
1
3
2
1
4
2
1
4
2
2
4
3
1
4
3
1
3
2
1
4
2
1
4
2
1
3
2
1
3
2
1
4
2
1
4
2
1
4
2
1
4
2
1
4
3
2
4
2
1
4
2
1
4
3
2
4
3
1
4
2
2
4
3
2
4
2
1
4
2
1
4
2
1
4
2
2
4
3
2
4
2
1
4
3
1
5
2
1
3
1
0
1
1
4
2
1
2
3
4
3
1
2
4
2
1
0
1
0
2
1
0
1
1
3
1
0
1
2
4
3
1
2
3
4
3
1
2
3
4
2
0
2
2
4
2
0
2
3
4
2
0
2
3
4
3
1
2
4
5
2
0
2
4
5
3
0
2
4
5
3
1
2
4
Q1: first quartile; Q3: third quartile.
from the THÜKo group were 5 years older than male subjects.
Therefore, different testosterone levels and age may contribute to
lower effects of the intervention on HMS in female subjects. These
finding have to be considered with caution since the study was not
specifically designed to evaluate effects of THüKo between male
and female subjects. Nonetheless, sex-related responses to exercise
therapy in OA patients should be considered in future research
projects because they may imply gender-specific therapeutic
concepts as already indicated in two previous reviews on exercise
therapy in knee OA [44,45].
Finally, we want to comment on the safety of the intervention.
Only few data are available on safety aspects of exercise
interventions in OA. It can generally be assumed that exercise is
a safe treatment option with only few contra-indications that are
mainly related to co-morbidities. Pain may increase, especially at
the beginning of the intervention period and falls may occur while
exercising, especially in person with reduced postural control and
gait disturbances [46,47]. In our study, no sustainable adverse
event was reported and no subject had to refuse from training
because of an exercise related adverse event. Low-pain levels
during exercising slightly increased throughout the exercise
program, whereas pain levels before and after exercising slightly
decreased. Almost exclusively, median pain levels during exercise
were lower than pre- and post-exercise measures. Pain levels can
be classified as low since subjects were not restricted from
training. Aside of this general assumption, monitored increases in
pain during the progressive exercise program may be related to
higher exercise intensity which also increased throughout the
home exercises. This has to be considered when informing
participants about potential pain experiences during exercising.
Subjects of the present study were given three hierarchically
ordered recommendations to cope with notably increased pain
during exercising: (1) Subjects should maintain repetitions and
intensity but the exercise should be performed in a different body
posture as provided by the exercise program. (2) If no mitigation
of pain could be achieved by (1), subjects should reduce exercise
intensity. (3) If exercising was still too painful this exercise should
be removed from the current session. In any case the therapist who
instructed the group sessions had to be contacted in order to
control exercise performance or provide an alternative exercise.
We cannot report how often subjects applied these recommendations as this was not monitored in detail. However, this procedure
has face validity to be a helpful tool for hip OA patients to cope
with pain during exercise.
Conclusion
The Tübinger Hip concept—a 12-week exercise intervention
specifically designed for patients with hip OA—can increase hip
muscle strength with superior effects in comparison to a nontreated control and a placebo ultrasound group. Its safety was
demonstrated and it can therefore be concluded, that a wellinstructed exercise programs is safe and feasible. This statement
has to be limited to patients that do not need gait aids. This study
underlines the importance of training programs focusing on
strengthening exercises in the treatment of hip OA. Further
research is needed to evaluate predictors for exercise effectiveness
such as gender aspects in order to provide person-tailored exercise
therapy concepts.
Acknowledgements
The authors thank Artzt company for providing the exercise
materials.
Conflict of interest
The authors report no conflicts of interest. The authors alone are
responsible for the content and writing of this article.
Exercise therapy in hip OA
DOI: 10.1080/14397595.2016.1213940
Downloaded by [University of Technology Sydney] at 00:57 04 August 2016
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