Elsevier

Physiotherapy

Volume 97, Issue 4, December 2011, Pages 302-308
Physiotherapy

Responsiveness of physical function outcomes following physiotherapy intervention for osteoarthritis of the knee: an outcome comparison study

https://doi.org/10.1016/j.physio.2010.03.002Get rights and content

Abstract

Objective

To compare the responsiveness of two self-report measures and three physical performance measures of function following physiotherapy for osteoarthritis of the knee.

Setting

Single centre study in acute hospital setting.

Methods

Patients referred for physiotherapy with osteoarthritis of the knee were recruited. The Western Ontario and McMaster Universities (WOMAC), Lequesne Algofunctional Index (LAI), timed-up-and-go test (TUGT), timed-stand test (TST) and six-minute walk test (6MWT) were administered at first and final physiotherapy visits. Wilcoxon Signed Rank tests were used to determine the effect of physiotherapy on each outcome. Responsiveness was calculated using effect size, standardised response mean and a median-based measure of responsiveness due to some outlying data.

Results

Thirty-nine patients with a mean age of 65.3 (standard deviation 6.9) years were investigated before and after a course of exercise-based physiotherapy. There was a significant improvement in all outcomes except the WOMAC scores. All measures demonstrated small effect sizes for all statistics (<0.50), except the 6MWT which was in the moderate range for one of the indices (standardised response mean 0.54). The LAI was more responsive than the WOMAC total score and the WOMAC physical function subscale for all responsiveness statistics, whilst the 6MWT was more responsive than the TST and the TUGT. The median-based effect size index produced the smallest effect sizes for all measures (0.1 to 0.43).

Conclusion

These results can be used to guide decision making about which physical function outcome measures should be used to evaluate effectiveness of rehabilitation of people with osteoarthritis of the knee at group level in a clinical setting.

Introduction

Responsiveness is a critical psychometric property of outcome measurement. Although there are numerous definitions of responsiveness [1], it is commonly defined as ‘the ability of an instrument to detect a clinically meaningful change over time’ [2], [3], [4] and is usually quantified by a statistical or numerical score [5]. There is no clear consensus on how responsiveness should be assessed [1], [6]. Two types of responsiveness have been described. Internal responsiveness is established by comparing a number of measures against each other, and can be measured using a variety of statistics. External responsiveness establishes how changes in a measure compare with corresponding changes in a reference measure [6]. In the absence of a criterion standard of change, researchers have suggested that the best way to establish responsiveness is to compare a number of measures using different responsiveness statistics [2], [7], [8]. The statistics used most commonly to measure internal responsiveness are the effect size [9] and the standardised response mean [10]. Both of these measures use means and standard deviations, thereby assuming normality of the data. The effect size divides the mean change score by the standard deviation of the baseline score, whilst the standardised response mean uses the standard deviation of the change score as the denominator. Some authors advocate the standardised response mean over the effect size [6], [11] as it incorporates the response variance and is an indicator of the ability of the measure to distinguish ‘signal’ from ‘noise’ [12]. However, other authors recommend using the effect size over the standardised response mean [1], [9], [13] as the aim is to describe the magnitude of change, rather than the statistical significance.

Physiotherapy is reported to be the most important non-pharmacological management option in osteoarthritis [14], and its main goals are to reduce pain and optimise physical functioning [15]. International scientific groups, such as the Outcome Measures in Rheumatology Group and the Osteoarthritis Research Society, have recommended evaluating pain, patients’ global assessment of disease status and function in clinical trials [16], [17]. Physical function can be measured by self-report or physical performance methods, and a combination of both is recommended to provide complimentary information [18] as they appear to examine different aspects of function [19].

The Western Ontario and McMaster Universities Index (WOMAC) [20] and the Lequesne Algofunctional Index (LAI) [21] are two commonly used disease-specific measures of function used in physiotherapy-based research for osteoarthritis of the knee [22], [23], [24], [25], and have undergone more psychometric evaluation than other self-report measures in osteoarthritis [26]. Although both measures have been validated, few studies have compared their responsiveness in patients with osteoarthritis. The LAI was more responsive than the WOMAC in patients with osteoarthritis of the knee undergoing exercise therapy [27], whilst the WOMAC was more responsive than the LAI 12 months after arthroplasty [28]. Physical function can also be measured through a range of timed physical performance tests, such as walking distance and sit-to-stand activities which are commonly limited in osteoarthritis of the lower limbs [18], [29]. Three commonly used measures include the timed-stand test (TST), timed-up-and-go test (TUGT) and 6-minute walking test (6MWT), which have all been used as outcomes in physiotherapy-based clinical trials of osteoarthritis [23], [30], [31], [32]. The 6MWT was more responsive than stair ascent and 10 m walking speed and following hip arthroplasty [33], and than TUGT after hip and knee arthroplasty [34].

No published studies have evaluated the comparative responsiveness of the aforementioned three performance measures and two self-report measures to physiotherapy intervention. There is an array of outcomes that measure physical function in osteoarthritis [26], [35], and it is important that outcomes demonstrate psychometric properties, including responsiveness. Outcomes that demonstrate highly responsive scores are preferable because they require smaller sample sizes in clinical trials [3]. Therefore, the aim of this study was to compare the responsiveness of two self-report measures of functional ability and three measures of physical performance before and after physiotherapy intervention for osteoarthritis of the knee.

Section snippets

Study population

Subjects with osteoarthritis of the knee who were referred for physiotherapy at St Vincent's University Hospital, Dublin, Ireland between July 2006 and February 2008 were invited to take part in the study. To be included, they were required to have a diagnosis of osteoarthritis of the knee according to the American College of Rheumatology criteria [36], and to have been referred for physiotherapy by a medical practitioner. They were excluded if they were unable to read or communicate

Statistical analyses

Data were analysed using Microsoft Excel (2003) and Statistical Package for the Social Sciences Version 15 (SPSS Inc, Chicago, IL, USA). Descriptive statistics including means, medians and standard deviations of baseline score, post-physiotherapy score and change score for each measure were used to summarise the data. Normality of change scores were assessed visually and using the Shapiro-Wilk statistic. Although the three self-report measures were normally distributed, the three physical

Results

In total, 46 subjects were recruited to the study. Seven of these failed to complete their course of physiotherapy. Therefore, 39 subjects who completed all outcomes at both assessment points were included in the final data analysis. Table 1 shows the patient characteristics of the study population. The mean number of physiotherapy attendances was 5.8 (range 3 to 8). All patients received exercise-based treatment as determined by presenting clinical signs and symptoms by the treating

Discussion

This is the first known study to evaluate the responsiveness of both self-report measures and physical performance measures of function following physiotherapy for osteoarthritis of the knee. As only some of the data were normally distributed, effect size using the median and interquartile range was estimated along with conventional effect size statistics. Q3/7 was chosen as it approximates with the standard deviation and is robust to outliers. All measures demonstrated small effect sizes for

Conclusion

In conclusion, the LAI was more responsive than the WOMAC for self-report function in osteoarthritis of the knee, whilst the 6MWT was most responsive in assessment of physical performance. However, all measures yielded small effect sizes. An alternative method for estimating responsiveness in the presence of outliers is presented, and these results were consistent with other responsiveness statistics used in this study. The results of this study may be used to inform researchers in choice of

Acknowledgements

The authors would like to acknowledge Ms Mairead Dockery, Senior Physiotherapist, St Vincent's University Hospital, Dublin for her assistance in data collection, and Professor Ronan Conroy, Senior Lecturer in Epidemiology, Royal College of Surgeons in Ireland, Dublin for his statistical advice.
Ethical approval: St Vincent's Healthcare Group research ethics committee (Reference Number R077).
Funding: Ms French is supported by a research grant from the Irish Health Research Board Fellowship for

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