INTRODUCTION
Persons with chronic conditions of aging such as osteoarthritis are a large and growing proportion of the population.1 Even though regular exercise has proven health and functional benefits, inactivity increases as patients age. Certainly, in patients with osteoarthritis, regular exercise can improve pain control, proprioception, strength, stability, and endurance, all of which improve functional independence. Until recently, however, evidence on exercise and osteoarthritis has been equivocal.2 Many retrospective studies alleged a possible negative relation between sports participation and certain occupations3,4,5; poor study design, however, has left the general applicability of their results in question. This perception may have limited the use of exercise for these patients, despite published guidelines, including those of the American College of Rheumatology.6
Treatment guidelines for osteoarthritis of the knee have considered exercise as an important nonpharmacologic approach.6 In addition, it directly reduces disability and corrects walking.7
Since the publication of the above treatment guidelines,6 several new randomized trials of exercise treatment of osteoarthritis of the knee have been published. I describe the current evidence for the benefits of exercise in the treatment of osteoarthritis of the knee. Efforts have been made to identify key determinants of effect, including elements of the training program, quality of the studies, and appropriateness of the outcome measures used.
METHODS
Literature search
A comprehensive computer-assisted search of the medical, sport, and rehabilitation literature between June 1966 and January 2000 was conducted using MEDLINE search systems. A highly sensitive search strategy of randomized controlled trials8 and systematic reviews was used. References of relevant review articles and trials were screened to identify articles not found in the main search. The literature search was conducted using the subject headings osteoarthritis and exercise and text words osteoarthritis or arthritis and knee or physical training. For more details of the search strategy, see the previously published article in British Journal of Sports Medicine.
Criteria for studies considered for inclusion
Trial reports that met the following criteria were eligible:
The trial concerned patients with osteoarthritis of the knee, and this was assessed using either clinical or radiologic criteria (or a combination).
Treatment had been allocated using a randomized procedure.
At least 1 of the treatments had included exercise. Exercise treatment was defined as a range of activities to improve strength, range of motion, endurance, balance, coordination, posture, motor function, or motor development. Exercise treatment can be performed actively, passively, or against resistance.9 No restrictions were made as to type of supervision or group size. Additional interventions were allowed.
At least 1 of the following measures had been included: pain, self-reported disability, observed disability, and patient's global assessment of effect.
Results had been published as a full report.
Trial reports were excluded if they concerned perioperative exercise treatment or if intervention groups received identical exercise treatment and, therefore, no contrast existed between intervention groups. No restrictions were made about the language of publication.
RESULTS
Study selection
Sixty-nine publications were initially identified. Thirty-seven studies were excluded because of methodologic criteria, 8 were excluded because they included review material, 4 were concerned with perioperative exercise treatment, and 2 included data reported in previous publications. Consequently, 18 publications on 17 trials (table) were included in this review.2,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26
Methodologic quality of the studies
Because of the nature of exercise treatment, neither care providers nor patients can be blinded to the treatment. The most prevalent shortcomings of exercise interventions concerned concomitant interventions: the design of 9 trials did not control for concomitant interventions on physical treatment strategies or medications, and 8 trials did not report these concomitant interventions. Many trials lacked sufficient information on several validity criteria: concealment of treatment allocation, level of compliance, control for concomitant interventions in the design, and blinding of outcome assessment.
Were the studies informative?
Information on adverse effects of exercise treatment on long-term (>6 months after randomization) outcome assessment was often missing in trial reports. In 3 trial reports, long-term follow-up was mentioned, but no results were presented. Other common deficiencies were in reporting on specification of eligibility criteria and description of the interventions.
Were the studies adequately powered?
The sample size and power of the trials varied widely. Nine trials compared groups of fewer than 25 patients, whereas 5 compared more than 100 patients (median group size, 39). Five studies2,10,14,20,22 were designed with sufficient power (>0.80) to detect medium-sized effects. Two studies19,27 were designed with power (0.67 and 0.71, respectively) almost sufficient to detect medium-sized effects.
OUTCOMES
Is exercise treatment effective?
Most trials identified were designed to study differences between exercise treatment and placebo treatment or no treatment. One also aimed to study differences between different exercise treatment interventions.17
Important outcomes in exercise interventions
Eight trials explicitly studied the differences between exercise interventions.13,17,18,20,22,23,24,25 Pain was assessed in all 8 trials. Three outcome measures were used. In 4 studies, information was given on the timing of pain assessment in relation to the days of exercise. In 1 study, outcome assessment preceded treatment,25 whereas in another, pain was assessed the week after the completion of treatment.26 Self-reported disability was assessed in 5 trials12,18,20,22,24 and walking in 4 trials.12,17,21,25
Data included assessment of aerobic walking program, aerobic hydrotherapy, and a nonaerobic program directed at range of motion. There was no evidence in favor of the type of exercise treatment program over another.
Pain
Pain was used as an outcome measure in 14 trials, and in these trials, 4 different outcome measures were used to assess pain. No information was available on timing of the pain assessment in relation to the days of exercise. In 1 trial, data presentation was insufficient to calculate the effect size.17 One trial included 2 comparisons between exercise treatment interventions (aerobic exercise and resistance exercise) and a placebo treatment.10
Clinical setting
In the 5 trials with sufficient power,2,10,14,20,22 participants and content of the intervention differed. Radiographic evidence indicated a mild or moderate stage of disease, and patients were recruited through physicians; community-based recruitment was also used. The trial of van Baar et al9 concerned supervised individual treatment, including strengthening exercises, range-of-motion exercises, and functional training over 12 weeks, whereas Ettinger et al10 used 3 months' supervised treatment followed by a home-based program for 12 months, and Petrella and Bartha14 and O'Reilly et al28 used only home-based exercise. Exercises included aerobic or resistance exercises,2,10 whereas Petrella and Bartha14 used a progressive resistance program over 8 weeks. In the trials of Ettinger et al10 and van Baar et al,2 the supervised part of the intervention took 12 weeks to complete. This would seem to impose a greater burden on the care provider to deliver the program than in the trials of Petrella and Bartha14 and O'Reilly et al.28
Kovar et al27 studied two 4-week exercise programs: individual weight-bearing exercises and supervised group treatment consisting of nonweight-bearing exercises. This study concerned patients with knee osteoarthritis for a mean duration of more than 10 years, and participants were recruited from the community and the clinic. The intervention concerned an 8-week supervised group treatment that mainly consisted of “fitness walking.” Other studies examined patients with knee osteoarthritis according to the criteria of the American College of Rheumatology, who were recruited from both the community and the clinic,15 and patients with knee osteoarthritis (not specified), who were recruited in the clinic,13 and included exercise interventions consisting of a 12-week walking program15 or an 8-week strength training program monitored on a dynamometer.13
Thus, the evidence indicates a small to moderate beneficial effect of exercise treatment on pain in knee osteoarthritis. This effect was found in participants with minimal to moderate osteoarthritis recruited from both community and clinic who were being treated with various types of exercise treatment for at least 8 weeks (see box headed “Patient type”).
Self-reported disability
Self-reported disability was measured in 6 trials. Three different measures were included. In 1 trial,13 data presentation was insufficient to calculate the effect of exercise on disability. In 2 trials with sufficient power,2,10 small effects were observed on disability.
Of the 3 trials with low power,15,19,27 a large effect was observed in 2.19,27
It can be concluded that evidence indicates a small benefit of exercise on self-reported disability. This effect was found in participants with minimal to moderate osteoarthritis who were recruited from both the community and the clinic and were being treated with various types of exercise.
Walking
Walking was assessed in 8 trials. In these trials, 5 different assessments were used. In 2 trials,13,17 data presentation was insufficient to calculate the effect size. In 3 trials with sufficient power,2,10,22 a small beneficial effect of exercise treatment on walking performance was observed. Petrella and Bartha observed increased walking at self-pace and self-paced stepping (2 measures of clinical relevance) following their exercise intervention.14
The evidence indicates a small beneficial effect of exercise treatment on walking performance, and Petrella and Bartha showed a significant effect on both self-selected speed of walking and stepping,14 both clinically relevant functional outcomes as recommended by Outcome Measures in Rheumatoid Arthritis Clinical Trials (OMERACT).29
Patient global assessment of effect
In only 2 trials was global assessment of effect by the patient used as the outcome measure.3,10 This indicates a need for future studies to integrate beneficial effects of exercise according to patients' global assessment.
DISCUSSION
Summary
Recent guidelines have advocated the inclusion of exercise in the treatment of osteoarthritis of the knee.6 Past reports of exercise as a cause of osteoarthritis of weight-bearing joints,3,4,5 however, may have reduced implementation among physicians. Lack of standard protocols, outcome measures, and maintenance strategies may also have contributed to poor implementation of exercise.
Table 1.
Summary of selected studies on the effect of exercise on osteoarthritis of the knee
| Study | Design | Intervention (group(s) (nos.) | Duration/sessions | Duration of sessions | Intensity | Pain | Disability | Walking |
|---|---|---|---|---|---|---|---|---|
| Bautch et al,15 1997 | RND | Low RE and education (n = 15) | 12 wk/3 per wk | 1 hr | 3 reps each exercise and increase to 10 at 4 wk | VAS present | AIMS | Walking based on 50% performance of Balke test |
| Education (n = 5) | ||||||||
| Callaghan et al,17 1995 | RND | Control sham electrical stimulation (n = 9) 20-min PT, 3 sets of 10 exercises (n = 9) Education; sit-to-stand, step-downs (n = 9) | 4 wk/2 per wk | 20 min | Not given | VAS present | Clinical measures of swelling, ROM | Time to complete 50 m |
| Chamberlain et al,18 1982 | RND | RE plus diathermy (hospital) (n = 7) | 12 wk/3 per wk | Not given | Graduated RE | No | No | Maximum weight and endurance |
| RE at home (n = 7) | ||||||||
| Messier et al,11 1997 | RCT | Aerobic exercise (n = 144) | 18 mo: 3 mo inpatient, then 12 mo homebased/3 per wk | 1 hr | 50%-70% HR | No | Self-reported disability score, x-ray score | 6-min walk, stair climbing, muscle strength |
| RE (n = 146) | Same | 1 hr | 1.1-kg start, increase 1-2 sets of 12 reps for 3 d | |||||
| Education (n = 149) | ||||||||
| Jan and Lai,19 1991 | RND | Ultrasound* Short-wave diathermy* Ultrasound and RE* Short-wave diathermy and RE* | 8 wk/3 per wk | Not given | Not given | No | No | Functional capacity; peak torque |
| Sylvester,20 1989 | RCT | Supervised walking (n = 47) Standard of care (n = 45) | 8 wk/3 per given | Not given | Not given | Not given | AIMS | 6-min walk test |
| Ettinger et al,10 1997 | RCT | Aerobic (walking) (n = 40) | 12 wk/3 per wk | 60 min (30 min plus warm up) | HR at 60%-80% max on treadmill | AIMS, Tennessee selfconcept scale | Trunk flexibility | Walking tolerance on treadmill |
| Aquatics†, (n = 40) | ||||||||
| ROM control exercise (n = 40) | ||||||||
| Minor et al,12 1989 | RCT | Home-based isokinetic exercise (n = 60) | 8 wk/daily | Graduated reps and sessions per day | As per graduated protocol | WOMAC, VAS rest and after exercise tests | SF-36‡ | Self-paced walk and step test |
| Control (n = 60) | ||||||||
| de Vet et al,21 1995 | RND | Hydrotherapy including pool walking (n = 7) | 6 wk/2 per wk | 30 min | Not given | VAS present | Philadelphia QOL, gait analysis, ROM | Not given |
| Short-wave diathermy plus walking, cycling, step-downs (n = 7) | ||||||||
| van Baar et al,2 1998 | RCT | Exercise tailored to patient (n = 100) | 12 wk/1-3 per wk | 30 min | Not given | VAS over last week | Self-reported disability, NSAID use, strength | Video of common tasks, NSAID use |
| Education (n = 101) | ||||||||
| RND = randomized, not specified; RE = resistance exercise; reps = repetitions; VAS, visual analog scale; AIMS, arthritis measurement scale; ROM = range of motion; PT = physical therapy; RCT = randomized controlled trial; HR = heart rate; WOMAC = Western Ontario McMaster pain scale; QOL = quality of life; NSAID = nonsteroidal anti-inflammatory drug. | ||||||||
Number of patients in each group not given.
Aquatics refers to water exercise.
SF-36 refers to Medical Outcomes Study 36-item short-form health survey.
Background and rationale
Two recent well-designed intervention studies have shown that regular physical activity in patients with osteoarthritis reduced disability2,10; however, 18 months after the study, exercise adherence had declined by half.11 Nonparticipation in and withdrawal from exercise programs remain a problem among patients with multiple chronic conditions.12 Hence, programs that are specifically designed to meet the needs of subgroups may effect long-term behavior change and the adoption of exercise in this population. A large randomized multicenter study by Ettinger et al10 showed that older patients who engage in either resistance or aerobic exercise achieved better pain control and functional outcomes at 18 months than those who only attended an educational program. However, patients continued to take various arthritis medications during the study, and no attempt was made to control for the class of medication. This may make decisions about inclusion of exercise difficult for practitioners.
Table 2.
| Patient type |
|---|
|
Table 3.
| Exercise type |
|---|
|
Petrella and Bartha recently reported the effect of a brief home-based progressive resistance exercise program for patients with unilateral osteoarthritis of the knee.14 This program consisted of a series of 3 exercises completed over 10 minutes a day using common household items. Compliance with the program at 2 months was more than 96%, no adverse events were reported, and pain and physical functioning measured using a self-paced walking activity increased significantly from baseline.
Despite these positive findings, no dose-response relation has been established between aerobic or resistance exercise and osteoarthritis. In addition, issues of long-term adherence and efficacy for exercise in the treatment of osteoarthritis are still unresolved.
Key findings
Seventeen randomized controlled trials of the effectiveness of exercise treatment in osteoarthritis of the knee were assessed. It can be concluded that exercise is effective in patients with osteoarthritis of the knee. Available evidence indicates beneficial effects on all studied outcome measures: pain, self-reported disability, observed disability in walking, self-selected walking and stepping speed, and patients' global assessment of effect. Effect-size values indicated small effects on both disability outcome measures, a small to moderate effect on pain, and a moderate to large effect according to patients' global assessment of effect. Because pain and disability are the main symptoms in patients with osteoarthritis, exercise treatment seems to be indicated.
Conclusions are based on a few studies. Only 5 randomized controlled trials had sufficient power.2,10,14,20,22 Furthermore, trials often did not include all relevant outcome measures, especially with regard to observed disability—that is, walking—and a patient's global assessment of effect. In addition, several different instruments have been used for assessing specific outcome measures. The recently published list of candidate instruments provided by Bellamy et al can be seen as a first step to the standardization of assessment.29
Minimal information is available on the long-term effects of exercise treatment on osteoarthritis of the knee (see box headed “Exercise type”). This lack of information about long-term effects is a remarkable omission because the clinical impression is that the effects disappear over time.
The evidence is insufficient to draw conclusions on the optimal content of an exercise treatment intervention. The 3 trials with sufficient power showed beneficial effects of different types of exercise treatment: aerobic exercise, resistance exercise, and mixtures of several types of exercise treatment.2,10,14 Results from trials comparing effects of different exercise treatment programs are inconclusive.12,17,18
Methodologic assessment showed some major threats to the validity of clinical trials of exercise treatment. Blinding of providers and patients was absent in all studies. As a consequence of the nature of exercise treatment, blinding of both providers and patients is not possible. Therefore, blinding of outcome measures is vital. In only half of the trial reports, however, was blinding of outcome assessment explicitly reported. Another possible source of bias is the commonly occurring absence of information on adherence to the intervention. This hampers the interpretation of a study with negative results. It remains unclear whether the exercise treatment intervention was ineffective because of the intervention itself or the participants' failure to adhere to the treatment.
In conclusion, the available evidence indicates beneficial short-term effects of exercise treatment in patients with osteoarthritis of the knee. Given the limited number of studies available, this conclusion applies to patients with mild to moderate osteoarthritis recruited from both outpatient settings and the community. Beneficial effects have been found for various types of exercise treatment and recommended for patients with mild to moderate osteoarthritis of the knee. Physicians should promote physical activity in their patients with osteoarthritis of the knee. Exercise can reduce symptoms, potentiate concomitant medications, and improve health in general.
Further research could expand these findings. In particular, additional clinical trials are needed to study the long-term effectiveness of exercise treatment. In the design and conduct of these trials, specific attention should be paid to a sufficient sample size, adherence to exercise treatment, controls for cointerventions, blinded outcome assessment, and adequate data analysis, including an intention-to-treat analysis. The incorporation of a standard set of outcome measures29,30 in combination with the adoption of a standard for reporting of results31 will greatly enhance evidence of synthesis in this area.
Summary points
Exercise is indicated for patients with mild/moderate osteoarthritis of the knee, but limited studies are available
Standard interventions and outcomes measures are needed
Physicians should stress behavior change for long-term benefit
Long-term efficacy has not been established
Strategies to promote exercise adoption for general health should be the goal of physicians and their patients
Competing interests: None declared
This article was published in Br J Sports Med 2000;34:326-331
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