Hip Osteoarthritis ROM

Long-Term Effect of Exercise Therapy and Patient Education on Impairments and Activity Limitations in People With Hip Osteoarthritis: Secondary Outcome Analysis of a Randomized Clinical Trial Ida Svege, Linda Fernandes, Lars Nordsletten, Inger Holm, May Arna Risberg

Background. The effect of exercise on specific impairments and activity limitations in people with hip osteoarthritis (OA) is limited.

Objective. The study objective was to evaluate the long-term effect of exercise therapy and patient education on range of motion (ROM), muscle strength, physical fitness, walking capacity, and pain during walking in people with hip OA.

Design. This was a secondary outcome analysis of a randomized clinical trial.

Setting. The setting was a university hospital.

Participants. One hundred nine people with clinically and radiographically evident hip OA were randomly allocated to receive both exercise therapy and patient education (exercise group) or patient education only (control group).

Intervention. All participants attended a patient education program consisting of 3 group meetings led by 2 physical therapists. Two other physical therapists were responsible for providing the exercise therapy program, consisting of 2 or 3 weekly sessions of strengthening, functional, and stretching exercises over 12 weeks. Both interventions were conducted at a sports medicine clinic.

Measurements. Outcome measures included ROM, isokinetic muscle strength, predicted maximal oxygen consumption determined with the Astrand bicycle ergometer test, and distance and pain during the Six-Minute Walk Test (6MWT). Follow-up assessments were conducted 4, 10, and 29 months after enrollment by 5 physical therapists who were unaware of group allocations.

Results. No significant group differences were found for ROM, muscle strength, predicted maximal oxygen consumption, or distance during the 6MWT over the follow-up period, but the exercise group had less pain during the 6MWT than the control group at 10 months (mean difference��8.5 mm; 95% confidence interval��16.1, �0.9) and 29 months (mean differ- ence��9.3 mm; 95% confidence interval��18.1, �0.6).

Limitations. Limitations of the study were reduced statistical power and 53% rate of adherence to the exercise therapy program.

Conclusions. The previously described effect of exercise on self-reported function was not reflected by beneficial results for ROM, muscle strength, physical fitness, and walking capacity, but exercise in addition to patient education resulted in less pain during walking in the long term.

I. Svege, PT, PhD, Norwegian Research Center for Active Reha- bilitation, Department of Ortho- paedics, Oslo University Hospital, Kirkeveien 166, 0450 Oslo, Nor- way. Address all correspondence to Dr Svege at: ida.svege@ ous-hf.no.

L. Fernandes, PT, PhD, Norwegian Research Center for Active Reha- bilitation, Department of Ortho- paedics, Oslo University Hospital, and Department of Orthopaedic Surgery and Traumatology, Institute of Clinical Research, Uni- versity of Southern Denmark, Odense, Denmark.

L. Nordsletten, MD, PhD, Depart- ment of Orthopaedics, Oslo Uni- versity Hospital, and Institute of Clinical Medicine, Faculty of Med- icine, University of Oslo, Oslo, Norway.

I. Holm, PT, PhD, Department of Orthopaedics, Oslo University Hospital, and Institute of Health and Society, Faculty of Medicine, University of Oslo.

M.A. Risberg, PT, MA, PhD, Nor- wegian Research Center for Active Rehabilitation, Department of Orthopaedics, Oslo University Hospital.

[Svege I, Fernandes L, Nordsletten L, et al. Long-term effect of exer- cise therapy and patient educa- tion on impairments and activity limitations in people with hip osteoarthritis: secondary outcome analysis of a randomized clinical trial. Phys Ther. 2016;96:818 – 827.]

© 2016 American Physical Therapy Association

Published Ahead of Print: December 17, 2015

Accepted: December 6, 2015 Submitted: February 11, 2015

Research Report

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Osteoarthritis (OA) of the hip ispresent in 5% to 11% of the gen-eral adult population, and preva- lence increases with age.1– 4 Pain, stiff- ness, and functional impairments are the major presenting complaints, often resulting in various degrees of activity limitations and decreased quality of life.5

Compared with people who are healthy, people with mild to moderate hip OA have demonstrated reduced hip range of motion (ROM), reduced knee extension muscle strength, and reduced walking capacity.6,7

Exercise therapy has been recom- mended as a first-line treatment modality for lower limb OA8 –10 and has been dem- onstrated to have a beneficial effect on self-reported hip function in patients with hip OA.11–14 Accordingly, a previ- ous publication based on the same trial as the present study reported that people who had hip OA and received exercise therapy in addition to patient education had better self-reported hip function over a 16-month follow-up period than people who had hip OA and received patient education only, whereas no effect on self-reported pain was demon- strated.13 However, few studies have evaluated the treatment effect with out- come measures representing specific impairments and activity limitations, and the results regarding whether exercise therapy can improve muscle strength, flexibility, and functional performance in patients with hip OA are conflict- ing.12,14 –16 Furthermore, because the specific exercise therapy program applied in the present study was aimed at improving self-perceived function as well as impairments and activity limita- tions,17 the evaluation of its effect on these specific secondary outcome mea- sures was of particular interest. Hence, the objective of this exploratory study was to evaluate the long-term effect, for people with hip OA, of a 12-week pro- gram including both exercise therapy and patient education or patient educa- tion only on selected secondary out- comes of impairments and activity limi- tations (including hip ROM, isokinetic concentric knee and hip muscle strength, indirectly measured oxygen consumption, walking capacity, and pain during walking). We hypothesized that

people in the group receiving exercise therapy would demonstrate better results for the selected outcome measures.

Method Study Design and Participants This exploratory study represents a sec- ondary outcome analysis of a single-blind randomized controlled trial evaluating, for people with hip OA, the effect of both exercise therapy and patient educa- tion or patient education only. The results for the primary outcome mea- sure, the pain subscale of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), at the 16-month follow-up assessment were published previously, along with the results for WOMAC stiffness, WOMAC function, and a health-related quality-of- life questionnaire (Medical Outcomes Study 36-Item Short-Form Health Survey questionnaire [SF-36]).13 No additional beneficial effect was found for WOMAC pain. Furthermore, the short-term results for biomechanical outcome measures and the long-term results, evaluated as the 6-year risk for total hip replacement, were recently published.18 Inclusion cri- teria were age of 40 to 80 years, hip pain for 3 months or longer, radiographically verified minimum joint space (in accor- dance with Danielsson criteria19: �4 mm for people �70 years old and �3 mm for people �70 years old), and a Harris Hip Score20 of 60 to 95 points. In people with bilateral hip OA, the more painful hip was defined as the index joint. Exclu- sion criteria were total hip replacement (THR) in the index joint, knee pain or knee OA, low back pain, rheumatoid arthritis, osteoporosis, cancer, cardiovas- cular disease leading to lack of tolerance of exercise, dysfunction in lower extrem- ities, pregnancy, or lack of understand- ing of Norwegian.

Participants were recruited from the orthopedic outpatient clinics of 2 hospi- tals, one sports medicine clinic, and gen- eral practitioners and through advertise- ment in a newspaper. Screening for inclusion was conducted at a university hospital by an orthopedic surgeon, who rated all radiographs, and a physical ther- apist, who rated hip symptoms by using the Harris Hip Score. Randomization was

performed in accordance with a computer-generated randomization list (block length�10, allocation ratio�1:1) designed by a statistician. Participants were assigned to treatment groups by a research coordinator, who was not involved in enrollment or treatment, through drawing of numbered and sealed envelopes. Allocation was con- cealed until the baseline assessment and patient education were performed. All participants signed a written informed consent form before enrollment.

Interventions All enrolled participants initially attended a patient education program developed for people with hip OA and provided in the form of a “hip school” previously described by Klassbo et al.21

The patient education program consisted of 3 group sessions over a 3-week period, led by 2 physical therapists educated in the method. Thereafter, participants were randomized to either an exercise group (n�55) or a control group (n�54). The exercise therapy program provided to participants in the exercise group was specifically designed for peo- ple with hip OA and was described in detail elsewhere.17 The program con- sisted of warm-up, strengthening exer- cises, functional exercises, and stretch- ing exercises. Participants were asked to perform the exercise therapy program 2 or 3 times per week for 12 weeks, and supervision by a physical therapist was provided at least once weekly. There- fore, the total intervention period, con- sisting of both the patient education pro- gram and the exercise therapy program, was 15 weeks. Adherence to the exer- cise therapy program was based on train- ing diaries; the cutoff for satisfactory adherence was at least 20 sessions (�80%).

Participants in the control group attended a 2-month follow-up visit at a physical therapy clinic as part of the patient education program. They did not have access to the exercise therapy pro- gram during the intervention period.

Both interventions were carried out at a sports medicine clinic. Two physical therapists were engaged in supervising participants during the exercise therapy

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program. The physical therapists were experienced in treating people with osteoarthritis; before the start of the study, they underwent training in the delivery of the specific exercise program.

Outcome Measures Outcome measures included hip ROM, isokinetic concentric muscle strength of knee and hip flexion and extension, the Astrand test, and distance and pain dur- ing the Six-Minute Walk Test (6MWT), as assessed with a visual analog scale (VAS). Follow-up assessments were conducted 4, 10, and 29 months after enrollment at the Norwegian School of Sport Sciences, Oslo, Norway (baseline assessment and

follow-up assessments at 4 and 10 months), and at a sports medicine clinic (follow-up assessment at 29 months). Five physical therapists administered all outcome assessments after undergoing training to ensure a standardized ap- proach to the assessments.

Hip passive ROM in the index joint was measured by use of a half-circle 1-degree- increment plastic goniometer with a movable arm. Flexion, abduction, and adduction were measured in the supine position, with a strap fixating the pelvis and opposite thigh.22 Internal rotation and external rotation were measured in the prone position, with the hip extended, the knee flexed at 90 degrees,

and a strap fixating the pelvis.22 Exten- sion was measured in the position of the modified Thomas test.22,23 Aggregated ROM was calculated by adding the mea- sured degrees of the 6 hip movements.

Isokinetic concentric muscle strength of hip and knee flexion and extension was tested by use of an isokinetic dynamom- eter (REV9000 [Technogym SpA, Gam- bettola, Italy] at baseline assessment and 4- and 10-month follow-up assessments; Biodex 6000 [Biodex Medical Systems Inc, Shirley, New York] at 29-month follow-up assessment). Isokinetic con- centric knee flexion and extension mus- cle strength was tested with the partici- pant in a sitting position, with straps fixating the trunk and thigh (Fig. 1). The knee joint testing range was set to 5 to 85 degrees of knee flexion. Isokinetic con- centric hip flexion and extension muscle strength was tested with the participant in the supine position, with the opposite leg extended at the knee and hip, and a strap fixating the pelvis and opposite thigh (Fig. 1). The hip joint testing range was set to 35 to 75 degrees of hip flex- ion. The test protocol included a 4-repetition warm-up followed by 20 sec- onds of rest before the 5 test repetitions. The angular velocity was 60 degrees per second, and the highest peak torque value of the 5 test repetitions, measured in newton-meters, for the index leg was used.

Aerobic capacity was assessed by use of the Astrand test, a submaximal bicycle ergometer test. We calculated the pre- dicted maximal oxygen consumption in accordance with the nomogram described by Astrand and Ryhming.24

The load and sitting position were adjusted for each participant, and the bicycle ergometer was calibrated to kilo- pascals before each test. Heart rate was corrected for sex and age,25 and pre- dicted maximal oxygen consumption was expressed in liters per minute.

In the 6MWT,26 participants walked back and forth in a 20-m-long corridor. Partic- ipants were instructed to walk as far as possible, without running, over a 6-minute period. A stopwatch was used to monitor time, and walking distance was registered in meters. Immediately

Figure 1. Setup for isokinetic muscle strength testing. (Top) Starting position for assessment of knee extension and flexion muscle strength. (Bottom) Starting position for assessment of hip extension and flexion muscle strength.

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after the 6MWT, participants were asked to score the hip pain they had experi- enced during walking on a VAS ranging from 0 to 100 mm, with 0 representing no pain and 100 representing extreme pain.

Activity level was assessed with the Phys- ical Activity Scale for the Elderly (PASE). The PASE is a self-administered, 7-day recall questionnaire used to assess phys- ical activity.27 The Norwegian version, which consists of 24 questions yielding a total score of 0 to 315, was used.28 In addition, participants reported the mean number of times per week they engaged in exercise or physical activity at base- line and at the 4-month follow-up assessment.

Sample Size Sample size calculations were based on the pain subscale of the WOMAC (VAS version), the predefined primary out- come measure. On the basis of a between-group difference of greater than or equal to 15 points, a standard deviation of 23, a 5% significance level, 90% power, and a dropout rate of 10%, at least 54 participants per group were needed.13 Calculations to evaluate statis- tical power for the secondary outcome measures were not conducted before the start of the study.

Masking The researchers, the 5 outcome asses- sors, and the physical therapists who provided the patient education program remained unaware of group allocations throughout the trial. The participants and the 2 physical therapists who pro- vided the exercise therapy program were aware of group allocations. Partic- ipants in the control group did not have access to the exercise therapy program during the intervention period and there- fore could not cross over to the exercise therapy group. After completion of the 4-month follow-up assessment, partici- pants in the control group could visit any physical therapist they wanted for treat- ment and supervision, and the specific exercise therapy program used in this trial was provided if participants requested it.

Data Analysis Analyses were performed with IBM SPSS Statistics, version 19.0 (IBM Corp, Armonk, New York). The significance level was set to .05. All analyses were intention-to-treat analyses and included all participants enrolled in the study, regardless of adherence to the patient education program or the exercise ther- apy program.

We applied a repeated-measures study design with one between-group factor (intervention at 2 levels: patient educa- tion, patient education plus exercise therapy) and one within-subject factor (occasion at 4 levels: baseline, 4 months, 10 months, 29 months). The interven- tion � occasion interaction term evalu- ated the extent to which intervention effectiveness differed over the total follow-up period (linear mixed model; variance component covariance struc- ture with occasion and occasion � inter- vention as fixed effects and occasion as random-effect intercept and slope). If this interaction was statistically signifi- cant, then we performed occasion-

specific between-group comparisons (Student t test) to identify at which occa- sions the groups differed.

Because many participants had under- gone THR during the follow-up period, we conducted a missing-value analysis to evaluate the pattern of missing observa- tions. The analysis revealed that missing data were not completely at random. Therefore, we conducted a sensitivity analysis—a linear mixed model with the last-observation-carried-forward tech- nique—to account for the poorer preop- erative results for participants who had undergone THR.

Role of the Funding Source This study was supported by EXTRA funds from the Norwegian Foundation for Health and Rehabilitation, through the Norwegian Rheumatism Association, and by grants from Oslo University Hospital.

Results Between April 2005 and October 2007, 59 women and 50 men with a mean age

Table 1. Baseline Characteristics of Study Participantsa

Characteristic

Exercise Therapy Group (n�55)

Control Group (n�54)

Age (y), X (SD) 58.4 (10.0) 57.2 (9.8)

Women, n (%) 31 (56.4) 28 (51.9)

Body mass index (kg/m2), X (SD) 24.6 (3.2) 24.9 (3.8)

Minimum joint space in target jointb (mm), X (SD) 2.1 (1.0) 1.9 (1.1)

Pain duration (mo), X (SD) 47.3 (53.3) 49.5 (50.9)

Harris Hip Score,c X (SD) 79.6 (7.7) 76.9 (8.2)

Bilateral radiographically evident hip OA, n (%) 38 (69.1) 38 (70.4)

THR of contralateral hip at enrollment, n (%) 4 (7.3) 2 (3.7)

Hereditary OA or known OA in family, n (%) 17 (30.9) 21 (38.9)

�12 y of education, n (%) 43 (78.2) 35 (64.8)

Work status, n (%)

Employed 35 (63.6) 36 (66.7)

On sick leave 8 (14.5) 5 (9.3)

Retired 12 (21.8) 9 (16.7)

a OA�osteoarthritis, THR�total hip replacement. b The minimum joint space in the hip joint was assessed in accordance with Danielsson criteria.19 Radiographically evident hip OA was defined as a minimum joint space of �4 mm for people �70 years old and �3 mm for people �70 years old. c The Harris Hip Score is a clinician-administered tool for evaluating hip pain, hip function, and hip range of motion and is scored from worst to best on a scale of 0 –100.20

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of 57.8 years (SD�9.9) were enrolled in the study (Tab. 1). The number of par- ticipants attending each follow-up assess- ment and the reasons for not attending are shown in Figure 2. Participants in the exercise group completed a median of 20 (first to third quartiles�16 –24) exer- cise sessions over the 12-week period; 53% completed at least 20 sessions (�80% adherence). One participant dis- continued exercise after 3 sessions because of increasing pain. No other adverse events occurred.

The results of the repeated-measures analysis revealed that there was a signif-

icant intervention � occasion interac- tion for pain on the VAS during the 6MWT (P�.018) (Tab. 2). No significant differences were found for the remaining secondary outcome measures. Overall, the estimated means for each group improved or remained relatively unchanged over the follow-up period (Tab. 3). The results of the sensitivity analysis corresponded to the findings of the main analysis (data not shown).

We conducted occasion-specific between-group comparisons for pain on the VAS during walking on the basis of the significant finding of the repeated-

measures analysis. No between-group difference was present at the 4-month follow-up assessment, but the exercise therapy group reported less pain during walking at the 10-month follow-up assessment (P�.043) and the 29-month follow-up assessment (P�.043).

Participants in both groups reported that they were engaged in exercise or physi- cal activity 3.2 and 3.7 times per week at the baseline and 4-month assessments, respectively. No group difference was found for the total PASE score over the 29-month follow-up period (P�.397).

Discussion The main findings of the present study were that a 12-week exercise therapy program given in addition to patient edu- cation provided no beneficial long-term effect over patient education only for ROM, muscle strength, indirectly mea- sured maximal oxygen uptake, or dis- tance covered in the 6MWT. Participants who received both exercise therapy and patient education reported significantly less pain during the 6MWT at the 10- and 29-month follow-up assessments than participants who received patient educa- tion only.

In line with our findings, Juhakoski et al14 and Bennell et al16 reported that exercise therapy had no significant short- term or long-term effect on hip ROM or lower limb muscle strength. Further- more, no effect of exercise has been demonstrated for various walking tests or stair walking tests.12,14 –16 On the other hand, French et al15 reported that patients who were given exercise ther- apy achieved better aggregated ROM than people in a control group. In gen- eral, the lack of an additional effect of exercise therapy on ROM, muscle strength, and walking ability in the pres- ent study may be partially explained by the relatively small deficits presented by participants at baseline relative to people who were healthy and normative data.6,7,29 –33 Together with participants’ high levels of physical activity at base- line, these data indicate that the potential for improvement was somewhat limited. The exercise effect may also have been compromised by the fact that only 53% of participants were adherent to the

Figure 2. Enrollment, randomization, and follow-up assessments of study participants.

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exercise program. Additionally, the exer- cises included in the program may have been ineffective for initiating changes in the selected secondary outcome mea- sures, and the dosage, progression, and execution of the exercises may have been inadequate. Furthermore, the PASE score and the reported engagement in exercise or physical activity were similar in the 2 groups and did not increase substantially from the baseline assess- ment to the 4-month follow-up assess- ment. These data may suggest that par- ticipants in the exercise group did not increase their overall exercise dosage by adding the specific exercise therapy pro- gram to their usual activities but rather that they replaced some of their previous weekly activities with 2 weekly sessions of exercise therapy.

Impaired ROM has been demonstrated in people with hip OA relative to people who are healthy6,7 and normative data29

and has been found to be associated with hip function and disability.6,7,34 There- fore, flexibility and stretching exercises were included in the exercise therapy program. The lack of a manual compo- nent during stretching may have resulted in an inadequate stimulus and, therefore, may account for the lack of effect on ROM. Hoeksma et al35 reported that man- ual therapy and stretching had a better effect on ROM than exercise, whereas French et al15 reported that manual ther- apy in addition to exercise was as effec- tive as exercise only.

Despite the fact that resistance exercises represented a key component of the exercise therapy program, no between- group difference in isokinetic concentric muscle strength of the knee and hip was found. The exercise therapy program applied in the present study comprised 7 resistance exercises,17 and participants were instructed to perform 3 sets with 8

repetitions, aimed at 70% to 80% of the 1-repetition maximum.36 The lack of an effect on isokinetic muscle strength may have been related to inadequate dosage and progression of the strengthening exercises. Only 53% of participants were adherent to the exercise therapy pro- gram, suggesting that many did not exer- cise frequently enough, as 2 or more ses- sions per week seem to be required to achieve increased muscle strength.37

Additionally, resistance and progression may have been insufficient, resulting in an intensity below the required 60% to 80% of the 1-repetition maximum.37

However, Fukumoto et at38 found that high-velocity strength training and low- velocity strength training were equally beneficial for improving strength in patients with hip OA. Furthermore, the strengthening component of the func- tional exercises included in the exercise therapy program may have been inade-

Table 2. Estimated Mean Differences Between Exercise Therapy Group and Control Groupa

Variable

Estimated Mean Difference (95% Confidence Interval)

Between Exercise Therapy Group and Control Groupb at:

P c4 mo 10 mo 29 mo

Hip ROM in index joint (°)

Aggregated 15.6 (�3.2, 34.4) 8.5 (�12.1, 29.1) �5.4 (�28.8, 18.0) .252

Extension 0.1 (�3.1, 3.3) �1.7 (�5.2, 1.8) 0.9 (�4.9, 3.0) .888

Flexion 4.7 (�1.4, 10.9) 2.1 (�4.6, 8.8) 0.5 (�7.2, 8.1) .072

Internal rotation 3.0 (�2.9, 8.9) 4.7 (�1.7, 11.1) 0.1 (�7.2, 7.4) .543

External rotation 5.4 (0.5, 10.3) �0.1 (�5.4, 5.2) �2.9 (�9.0, 3.1) .116

Abduction 2.3 (�1.0, 5.5) 1.8 (�1.7, 5.3) 0.4 (�4.4, 3.6) .393

Adduction 1.4 (�1.2, 4.0) 1.7 (�1.1, 4.6) �1.7 (�4.9, 1.6) .468

Isokinetic muscle strength in index leg, peak torque (N�m)

Knee extension 3.3 (�12.3, 18.9) �11.6 (�28.5, 5.2) �5.7 (�25.5, 14.1) .672

Knee flexion �1.8 (�11.3, 7.7) �7.1 (�17.4, 3.2) �4.1 (�16.2, 7.9) .647

Hip extension �4.9 (�27.3, 17.5) �23.1 (�49.4, 3.2) �6.0 (�35.4, 23.4) .450

Hip flexion �0.3 (�12.3, 11.8) �12.2 (�26.3, 1.9) 1.9 (�17.7, 13.9) .472

Predicted V̇O2max (L/min) �0.1 (�0.2, 0.4) �0.1 (�0.2, 0.4) �0.2 (�0.1, 0.6) .464

Walking capacity and pain

6MWT for distance (m) �0.2 (�40.7, 40.3) �1.8 (�46.6, 42.9) 8.7 (�42.7, 60.0) .801

Pain on VAS during 6MWT (mm) �4.4 (�11.3, 2.4) �8.5 (�16.1, �0.9) �9.3 (�18.1, �0.6) .018d

a ROM�range of motion, V̇O2max�maximal oxygen consumption, 6MWT�Six-Minute Walk Test, VAS�visual analog scale. b Mean for control group subtracted from mean for exercise group. c Linear mixed model (variance component model) with time and time � group as fixed effects and time as random-effect intercept and slope. P values are for time � group. d Significance level: P�.05.

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quate to improve maximum isokinetic concentric muscle strength.

The Astrand bicycle ergometer test and the 6MWT for distance can both be con- sidered to represent levels of physical fitness. No between-group difference was found for either of them over the study period. Walking speed and dis- tance have been suggested to be some- what decreased in patients with hip OA relative to people who are healthy.6,7,39

However, the 6MWT results for partici- pants in the present study were compa- rable to normative values for adults who are healthy,31–33,40 suggesting that the potential for improvement was some- what limited. Furthermore, specific exer- cises targeting walking activities or spe- cific types of training aimed at increasing cardiovascular fitness were not included in the exercise therapy program. Results regarding the importance of quadriceps muscle strength for walking speed are inconsistent,41,42 but it has been sug- gested that resistance training may

improve walking capacity in patients with lower limb OA.38,43

The previously reported results for the primary outcome measure of the ran- domized trial on which the present study was based revealed that exercise therapy had no additional effect on WOMAC pain over patient education only.13 Although the WOMAC can be considered to rep- resent an overall measure of self- perceived pain, including pain at rest, the assessment of pain during the 6MWT was included to evaluate activity-related pain. Activity-related pain is an important component of OA,44 but previous studies reported conflicting results regarding the effect of exercise therapy on levels of activity-related pain.12,15,16 In the present study, exercise therapy seemed to pro- vide a beneficial long-term effect on pain during walking, with the exercise group having 8.5 mm and 9.3 mm less pain on the VAS during the 6MWT at the 10- and 29-month follow-up assessments, respec- tively. The overall threshold for minimal

clinically important improvement on the VAS in patients with hip OA was esti- mated to be �15.3 mm45 but was found to be affected by the degree of symptom severity. In patients with less pain at baseline, comparable to that of partici- pants with mild to moderate symptoms at the time of enrollment in the present study, the threshold was estimated to be �7.2 mm.45 These data indicate that the mean estimated between-group differ- ences at the 10- and 29-month follow-up assessments were clinically relevant.

Although no additional effect of exercise therapy was revealed for the primary out- come measure (WOMAC pain), partici- pants who received exercise therapy and patient education had better self- reported physical function than those who received patient education only.13,46 Furthermore, we demonstrated a lower 6-year risk for THR surgery in the exercise group,46 indicating a favorable effect of exercise therapy on disease pro- gression. The lack of an effect of exercise

Table 3. Outcome Measures at Baseline and Follow-Up Assessments for Exercise Therapy Group and Control Groupa

Variable

X (SD) for:

Exercise Therapy Group Control Group

Baseline (n�55)

4 mo (n�54)

10 mo (n�48)

29 mo (n�40)

Baseline (n�54)

4 mo (n�50)

10 mo (n�39)

29 mo (n�28)

Hip ROM (°)

Aggregated 234.6 (43.8) 235.3 (49.4) 231.9 (55.2) 216.8 (44.7) 222.0 (46.6) 219.6 (43.6) 223.4 (52.5) 222.1 (51.9)

Extension 1.5 (7.9) 1.8 (8.3) 1.9 (9.7) 7.3 (6.5) 1.6 (8.6) 1.7 (7.9) 3.6 (8.6) 8.2 (7.1)

Flexion 126.5 (13.8) 123.3 (15.3) 119.8 (16.4) 116.0 (13.4) 119.1 (17.3) 118.5 (15.3) 117.7 (17.6) 115.5 (17.0)

Internal rotation 33.2 (14.4) 35.3 (14.5) 33.5 (15.9) 28.5 (14.0) 32.8 (15.6) 32.3 (15.7) 28.8 (16.0) 28.3 (13.7)

External rotation 27.7 (13.4) 31.9 (12.7) 32.0 (15.5) 24.4 (10.5) 24.4 (11.2) 26.5 (11.7) 32.1 (13.0) 27.3 (9.5)

Abduction 23.9 (8.6) 23.7 (7.5) 24.2 (7.9) 23.3 (8.4) 22.2 (9.0) 21.4 (7.1) 22.4 (9.3) 23.7 (8.6)

Adduction 21.9 (6.1) 20.7 (6.4) 20.5 (7.0) 17.4 (7.8) 21.9 (6.8) 19.3 (5.7) 18.8 (6.3) 19.0 (7.9)

Isokinetic muscle strength, peak torque (N�m)

Knee extension 116.7 (35.9) 123.4 (38.9) 120.2 (38.3) 136.8 (38.8) 120.6 (44.2) 120.1 (43.8) 131.1 (41.9) 142.5 (40.1)

Knee flexion 67.7 (24.4) 69.6 (25.1) 69.2 (24.3) 76.9 (23.0) 68.7 (24.4) 71.4 (25.5) 76.0 (26.4) 81.1 (25.1)

Hip extension 157.0 (58.4) 158.5 (56.4) 152.3 (49.2) 145.6 (51.1) 163.7 (65.9) 163.4 (60.4) 173.6 (64.1) 147.3 (61.5)

Hip flexion 91.4 (31.2) 90.7 (27.7) 84.0 (27.8) 85.0 (25.4) 96.1 (36.5) 90.9 (35.5) 96.8 (32.6) 84.3 (31.8)

Predicted V̇O2max (L/min) 2.3 (0.1) 2.4 (0.1) 2.3 (0.1) 2.3 (0.1) 2.4 (0.1) 2.5 (0.1) 2.4 (0.1) 2.6 (0.1)

Walking capacity and pain

6MWT for distance (m) 632.6 (103.8) 668.1 (99.5) 688.3 (16.6) 669.6 (88.4) 657.4 (95.0) 668.3 (100.4) 690.2 (101.3) 660.9 (141.1)

Pain on VAS during 6MWT (mm)

23.1 (20.2) 15.1 (16.7) 12.8 (17.6) 14.4 (16.7) 19.4 (14.9) 19.6 (16.0) 21.3 (20.5) 23.7 (19.7)

a ROM�range of motion, V̇O2max�maximal oxygen consumption, 6MWT�Six-Minute Walk Test, VAS�visual analog scale.

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therapy on ROM, muscle strength, indi- rectly measured maximum oxygen con- sumption, and the 6MWT for distance and the results reported in previous pub- lications for this trial appear to be some- what inconsistent. In summary, benefi- cial effects of exercise therapy were demonstrated for self-reported function, pain during walking, and the need for THR (ie, less need), whereas no addi- tional effects on self-reported pain, ROM, muscle strength, aerobic fitness, or walk- ing capacity were found. Perceived pain during activity may influence self- reported physical function,47 whereas pain is taken into account to a lesser extent in observer-driven clinical and performance-based tests.48 Joint pain in early OA is typically described as being exacerbated by activity and relieved by rest.44 Hence, the favorable effect on pain during walking in the present study may be associated with the previously demonstrated effect on self-reported physical function.13 However, the bene- ficial results were not reflected by changes in ROM, muscle strength, or the 6MWT. It has been suggested that even if high-intensity strength training produces larger maximal strength adaptations, it does not necessarily improve physical function more than low-intensity train- ing.37 Furthermore, the task specificity of the functional exercises in the exercise therapy program may have been decisive for the improvement of self-perceived physical function but may have had a limited effect on the specific measures of ROM and muscle strength.

The findings of the present study are applicable to people with symptomatic and radiographically evident hip OA, with mild to moderate symptoms, but without concomitant knee or back pain.

In participants with symptomatic and radiographically evident hip OA, increas- ing impairments and a mean decline in physical performance over time could have been expected. However, the esti- mated mean results suggested that both groups remained relatively stable over time. For a comparison of the treatment effect with the time-dependent course of the disease, a control group offered “no treatment” should have been included. Furthermore, the high standard devia-

tions in both groups at all follow-up assessments and the wide confidence intervals for the estimated means indi- cated that large individual differences were present at all follow-up assessments and for the treatment effect.

Self-reported outcome measures are fre- quently used to evaluate functional impairments and the treatment effect for OA, but according to Wright et al,48

observer-based outcome measures of function can provide supplementary information concerning physical func- tion. Hence, self-reported and observer- based outcome measures of function can be considered to be complementary rather than competing.49 The secondary outcome measures used in the present study were chosen on the basis of the reduced ROM, isokinetic knee extension muscle strength, and walking capacity in patients with hip OA relative to people who are healthy7 and normative data.29,30 Acceptable reliability has been demonstrated for the 6MWT50 and isoki- netic knee muscle strength assess- ments,51,52 whereas poorer intrarater and interrater reliability and relatively large measurement errors have been reported for ROM assessments.53–55 One previous study reported acceptable reli- ability for isokinetic hip muscle strength assessments, but the protocol in that study differed from our protocol in that it had a larger hip joint testing range.56

Recently, a consensus-derived set of performance-based tests for assessing physical function in patients with hip or knee OA were suggested as suitable out- come measures for use in clinical trials of patients with lower limb OA: the 30-s chair stand test, the 40-m fast-paced walk test, a stair-climb test, the Timed “Up & Go” Test, and the 6MWT.49 Further stud- ies evaluating the appropriateness of clinical and performance-based outcome measures in clinical trials and studies evaluating the effect of exercise interven- tions with various outcome measures in patients with hip OA are therefore encouraged.

The present study had some limitations. The power calculation was based on the predefined primary outcome of this ran- domized clinical trial, the WOMAC pain score at the 16-month follow-up assess-

ment.13 Post hoc power calculations based on estimated smallest detectable changes or minimal important changes for aggregated ROM,53 isokinetic knee extension muscle strength,57 the 6MWT,50,58 and pain on the VAS sug- gested that the numbers of participants needed in the groups were 66, 60, 42 to 119, and 80, respectively. Hence, the study was underpowered for detecting long-term group differences in the sec- ondary outcome measures. During the follow-up period, 18% of participants in the exercise group and 32% of partici- pants in the control group underwent THR. Therefore, the estimates for the long-term follow-up assessments must be interpreted cautiously, as the presum- ably poorer preoperative results for par- ticipants who underwent THR were not taken into account. This situation may have led to an overestimation of the mean estimates at the latest follow-up assessments in both groups. More impor- tantly, the fact that more participants (with poorer preoperative results) in the control group underwent THR may have resulted in an underestimation of the group differences in favor of the exercise therapy group. This situation, in addition to the overall reduced statistical power because of the small sample size and a considerable number of missing values during the long-term follow-up period, may have increased the risk of type II errors. Furthermore, multiple tests— be- cause of the repeated use of several sec- ondary outcome measures over a 29-month follow-up period—increased the risk of type I errors. Hence, the pres- ent study should be interpreted as an exploratory study, and future studies are needed to verify or reject the study hypothesis.

Changes in isokinetic muscle strength during the follow-up period must be interpreted with caution, as a different device was used for isokinetic strength assessment at the 29-month follow-up assessment. For the assessment of isoki- netic muscle strength of the hip, the test- ing range was small because of the tech- nical limitations of the REV6000; the testing range was set at 35 to 75 degrees of hip flexion and, therefore, repre- sented only about 32% of the mean total ROM in the sagittal plane. Furthermore,

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the fact that 5 different testers per- formed the outcome assessments increased the risk of measurement errors.

In general, masking of patients and care providers and adequate placebo treat- ments are difficult to apply in studies evaluating the effect of exercise interven- tions, including the present study. The rationale for providing the patient edu- cation program to all participants in the present study, including participants in the control group, was primarily based on ethical considerations. The placebo effect of exercise treatment has not been fully estimated but has been suggested to be of some significance.16 However, the efficacy of patient education interven- tions has been found to be negligible or small9; therefore, patient education may be considered to have served as a pla- cebo in the present study.

The present study was carried out at a sports medicine clinic, with a limited number of physical therapists involved in treating participants. These physical therapists had a particular interest in the field of active rehabilitation and were trained in providing the applied interven- tions. Therefore, the findings of the pres- ent study cannot be generalized to all physical therapists. However, the avail- ability of thorough descriptions of both the patient education program21 and the exercise therapy program17 enables ther- apists to acquire knowledge about these treatment modalities.

In conclusion, exercise therapy in addi- tion to patient education provided no long-term benefits over patient educa- tion only for hip ROM, muscle strength, aerobic fitness, and walking capacity, but participants who attended the exercise therapy program reported significantly less pain during walking at the 10- and 29-month follow-up assessments.

The authors express their thanks to the peo- ple who participated in this trial. The authors thank physical therapists Karin Rydevik, Sig- mund Ruud, Emilie Jul-Larsen Aas, and Marie Moltubakk for their contributions in leading the patient education program, supervising participants during the exercise therapy intervention, and conducting the outcome

assessments and research coordinator Kristin Bølstad for study management. They thank physical therapist and postdoctoral fellow Ingrid Eitzen for valuable discussions during the preparation of the article. They also acknowledge the Norwegian Sports Medi- cine Clinic, Oslo, Norway, for supporting the Norwegian Research Center for Active Reha- bilitation with rehabilitation and test facilities and research staff.

The study was approved by the Regional Medical Research Ethics Committee and was carried out in accordance with the Declara- tion of Helsinki.

This study was supported by EXTRA funds from the Norwegian Foundation for Health and Rehabilitation, through the Norwegian Rheumatism Association, and by grants from Oslo University Hospital.

Original trial registration: ClinicalTrials.gov NCT00319423; additional trial registration for the long-term follow-up study: Clinical- Trials.gov NCT01063777.

DOI: 10.2522/ptj.20140520

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