Results

SUBJECTS

The response rate to the postal survey was 81.9% with 28.7% of subjects reporting knee pain.7 Four hundred and seventy four of these subjects were telephoned, of whom 131 were pain free at the time of the telephone contact and 43 were unwilling to participate. Of the 300 subjects with knee pain who attended the baseline assessment, 191 subjects were recruited into the intervention study, of which 113 were randomised to the exercise group and 78 to the control group (fig 1). Of the 109 subjects not recruited, 35 were unwilling to participate and 74 were excluded (already performing quadriceps exercises n=24, clinical inflammatory arthropathy n=12, pain referred from back or hip n=12, serious injury in last six months n=7, previous knee replacement n=5, unable to complete study because of imminent move or hospitalisation n=5, pain free (WOMAC score=0) at first assessment n=4, medical condition preventing exercise n=5. One hundred and eighty subjects (94.2%) attended for reassessment; 108 exercisers and 72 controls. The proportion of men and women in each group was similar (exercise group 64.8% women, control group 68.1% women). Table 1shows other baseline characteristics. Mean values were similar for all data with the exception of activation where standard deviations were wide. Radiographs were obtained on 161 subjects (89.4%) who completed the study. Frequency of subjects with ⩾ grade 1 osteophyte (in either knee in any compartment) was high in both groups (75.3% in exercise group, 78.1% in control group). Osteophyte (⩾ grade 1) was more common in the patellofemoral compartment (73.9% of subjects) than in the tibiofemoral compartment (52.8% of subjects). Grade 2 osteophyte or above was less common, occurring in 66 subjects (40.9%). Analgesic usage was similar in the two groups. Values were obtained for all outcome variables for each subject and hence the results presented relate to the 108 subjects in the exercise group and 72 subjects in the control groups.

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Figure 1

Summary data for study recruitment and completion.

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Table 1

Baseline data (means and standard deviations) on subjects completing the study

Discussion

A reduction in pain has been shown with a home exercise programme, which is consistent for all measures of pain. Pain has not been the primary outcome measure in previous studies and has been omitted completely in some.15 One study reported a 35% reduction in pain,6 while other studies have reported unquantified improvements.4 Varying methods of assessments make direct comparison difficult. Nevertheless, the larger effect in the Fisher study in comparison with this study is not surprising, given the intensity of the exercise programme and the degree of supervision. A similar reduction in pain to this study was documented in one of the few controlled studies.16 Although a secondary outcome measure, physical function is nevertheless important. The magnitude of change is less than in reported hospital based trials,6but is still significant. Similar results in terms of function have been reported from a large study of community derived subjects with knee OA. As with other studies, however, the exercise programme was hospital based and intensively supervised.17

It is not clear how much of this improvement in pain and function relates to change in muscle strength. The improvements in strength were modest. Fisher and colleagues reported increases in strength of 14–35%.6 ,18 Other studies have demonstrated improvements of 13–29%.15 ,16 It may be that the exercise programme in this study lacked intensity. As it was home based and required minimal supervision, it was designed with safety in mind. Alternatively, the difference may be because of differences in measurement. Several studies have exercised at the same muscle length used for measurement.15 ,16 As some degree of specificity exists, this will maximise measured increases in strength.19 A third possibility is compliance, particularly as this was a home programme. Drop out rate was small, however, and over 70% of subjects in the intervention group completed 75% of the programme, a figure that compares favourably with other studies of home exercise.20 ,21 Only one previous study has reported change in muscle activation after rehabilitation in a similar population.22 A reduction of 15% was demonstrated but was achieved with an intensive, supervised exercise programme. The reduction in muscle strength in the control group is difficult to explain. As control subjects were advised of the benefit of exercise in general, it is unlikely that they reduced their levels of activity. Alternatively, as it was a voluntary measure, they may have been less motivated than the exercise group. The lack of blinding of the assessor may also have been implicated although efforts were made to encourage all subjects.

The possibility that improvements in pain and disability may, at least in part, relate to factors other than muscle strength, must be considered. With the exception of muscle strength, outcome measures were self assessed and may therefore, as with all exercise studies, be influenced by lack of subject blinding. It was also impossible for the assessor to be blinded to treatment group in this study. While, as mentioned, this could have influenced assessment of muscle strength, it is unlikely to have had a major effort on the other more important outcome measures. Reduction in levels of anxiety and depression were apparent in the exercise group. It is not clear whether this was a primary or secondary effect. Contact with a therapist may have had an effect on psychological outlook. Positive effects on pain and disability in OA have previously been reported with telephone contact.23 Alternatively, self perceived reduction in pain and disability may lead to improved mental health. Such an effect has been demonstrated previously following aerobic exercise.24

Reductions in weight are also apparent in the exercise group. Two small studies have demonstrated a positive effect on symptoms after weight reduction.25 ,26 It is possible, however, that this represents a secondary effect because of improvements in physical activity. Analgesic usage is unlikely to account for improvements in pain. Baseline assessments were similar in the groups, and analgesic requirements tended to reduce in the exercise group.

The trend towards greater improvements in pain and function in the subjects most compliant with the exercise programme adds support for strength gain being the key factor. The improvement in WOMAC pain score in the least compliant group is, however, somewhat contradictory. It is possible that these subjects stopped exercising because of clinical improvement. While numbers are small, there is some evidence for this, with 35% of this group reporting improvement, compared with none in the next most compliant group.

Distinguishing between clinical and statistical significance is important in any clinical trial. Levels for statistical significance reached in the current study are borderline. This may in part relate to “placebo effect”, as pain scores were reduced in the control group, an effect that is well recognised in osteoarthritis trials. As baseline measures were similar between groups it would have been possible to analyse within group differences. This would, however, have required additional comparisons with the inherent risk of type I errors. An alternative and perhaps more important influence in terms of statistical outcome is the dispersion of outcome values. Deviations and hence confidence intervals were wide in comparison with previously reported figures in hospital referred populations. As power calculation were based on a slightly lower standard deviation than measured, a power of 80% has not been achieved. Nevertheless for several reasons the result can be regarded as clinically significant. Subjects were highly heterogeneous in terms of age, muscle strength, severity of pain, and radiological change. Overall the population had less pain than in previous studies. In addition this was a simple low cost package of exercise with minimal supervision. A mean reduction in pain of 22% may, in this context, be considered to have clinical importance.

This study has focused on knee pain rather than structural change. Although most subjects did have evidence of osteophytosis, these results may not be generalisable to a population with severe radiographic OA. As pain is the most common reason for seeking medical intervention, however, these results are highly pertinent to the primary care setting.