Centre for Rehabilitation Science, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, UK
Correspondence to: C. J. McCarthy. E-mail: christopher.j.mccarthy{at}man.ac.uk
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Abstract |
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Methods. Patients with knee osteoarthritis (n = 214) were recruited for inclusion in a randomized controlled trial investigating two methods of exercise provision. Before treatment, patients completed the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Short Form 36 health survey (SF-36) questionnaires and were timed whilst performing an 8 m walk, ascending and descending a set of gymnasium stairs and completing a test of transferring in and out of a chair. A group of 15 patients also undertook a replicate testretest reliability study of the above outcome measures. Standardized response means were calculated for the ALF, WOMAC and SF-36 from data from the clinical trial.
Results. The ALF takes 10 min to administer and demonstrated excellent intra-tester reliability, with excellent intra-class correlation coefficient (ICC) statistics (ICC2,k 0.99; 95% CI 0.980.99), and low standard error of measurement (0.86 s) and smallest detectable difference (9.5%) values. Criterion-related validity with the physical function dimensions of the WOMAC and SF-36 was good, with correlation coefficients of 0.59 and 0.53 respectively. Standardized response means were higher for the ALF (0.49) than for both the WOMAC (0.39) and the SF-36 (0.12).
Conclusions. This work has demonstrated that the ALF can be used as a measure of physical function status and as a means of quantifying treatment response. The measure offers a simple and convenient outcome in the assessment and treatment of locomotor dysfunction. The ALF score is a reliable, valid and responsive outcome measure over 12 months and can be recommended for use in the evaluation of patients with knee osteoarthritis.
KEY WORDS: Locomotor function, Osteoarthritis, Validity, Reliability.
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Introduction |
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Objective assessment of locomotor function of timed walking, stair ascent and descent, and transferring to and from a chair has been used by several investigators in the field of knee osteoarthritis [710]. Recently the times of these individual activities have been aggregated to form one timed score, with the rationale that any single test imparts little information about the patient's overall functional ability, and that by aggregating the time of the activities a better objective assessment of the patient's overall functional capabilities can be obtained [9].
Whilst the individual locomotor functions of walking [11], stair ascent and descent [12] and transferring from sitting to standing [4] have established validity, the reliability, validity and responsiveness of an aggregated locomotor function score, comprising these three functions, has not been established.
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Methods |
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Patients
Two hundred and fourteen patients with knee OA were recruited for inclusion in a randomized controlled trial (RCT) investigating the long-term effect of two methods of exercise provision [13]. Patients were included if they met the American College of Rheumatology (ACR) clinical diagnostic guidelines for knee osteoarthritis [14, 15] and had radiological evidence of OA. Patients were excluded if they had knee OA secondary to inflammatory arthritis, had significant psychiatric or general medical morbidity that would either preclude their undertaking the exercises or their understanding of the nature of the exercise treatment, or had received an intra-articular steroid injection in the knee within 3 months. A convenience sample of 15 knee OA patients, meeting the same selection criteria, was used for a testretest reliability study. This study had received approval from the Central Manchester Local Research Ethics Committee and informed, written consent was obtained from all patients according to the Declaration of Helsinki.
Reliability study
A reliability study was conducted with a group of knee OA patients (n = 15). Patients attended for assessment and then undertook a replicate assessment within 1 week. The group undertook measurements of walking, stair ascent/descent and transferring, and completed the WOMAC and Short Form 36 health survey (SF-36) questionnaires at both assessments.
Outcome measures
The aggregated locomotor function (ALF) score
This outcome score was formed by summating the mean timed scores (seconds) from three locomotor functions (walking time, stair ascent and descent time) and time taken to transfer from sitting to standing.
Eight metre walk time
Patients were asked to walk, at their own naturally preferred comfortable pace, across the floor of the physiotherapy gymnasium. Following recommendations [16], a 10 m stretch of floor was used. An 8 m distance was marked on the gymnasium floor. Timing of the central 8 m allowed one or two steps at either end of the walk for untimed acceleration and deceleration, a process that has been shown to increase testretest reliability [16]. The time (s) taken to complete the distance was measured using a hand-held stopwatch (Zeon, UK). Patients were permitted to use walking aids if they required them. Three repetitions of the walk were undertaken and the times recorded. The mean of times was calculated and used for subsequent analysis.
Stair ascent and descent time
Patients were asked to ascend and then descend seven steps (four of 15 cm and three of 20 cm). Patients were instructed to undertake this task at their naturally preferred comfortable pace. The method that the patient employed to negotiate the stairs was recorded, i.e. whether they used alternate legs, used the banisters or always led with one leg. Patients were permitted to use the two banisters if they felt it necessary, as the use of banisters has been shown to not affect times [17]. Patients were timed (in seconds) using a hand-held stopwatch and repeated the test four times. The mean of the four repetitions was calculated and used for subsequent analysis. Four repetitions were used as the stairs used had steps of different heights; thus, by going over the steps in one direction and then the other the patients ascended and descended the different height steps twice.
Transferring time
Patients were asked to walk, at their own natural pace, a distance of 2 m to a chair and sit down, then immediately stand up and walk back to the start. Patients were timed (in seconds) using a hand-held stopwatch as they approached and retreated from the chair. The chair had no arms and a seat height of 0.46 m, typical of a toilet seat height [18]. Patients undertook three timed repetitions, the mean of which was calculated and used for subsequent analysis.
WOMAC
This is a tri-dimensional, disease-specific, self-administered health status measure [19]. The Likert scale version (LK3.0) of the questionnaire was used. Missing data and scoring procedures followed the WOMAC user guidelines [1].
SF-36
This is a 36-item questionnaire which measures health functioning on eight scales, including a physical functioning scale, and is among the most widely used measures of quality of life in studies of patients and populations [20]. Missing data and scoring procedures followed the SF-36 user guidelines [21].
Analysis
Testretest reliability
Data from these two assessments was then analysed for intra-rater reliability. To calculate useful indices of reliability, four statistics were calculated: intra-class correlation coefficients (ICC2,k) with 95% confidence intervals (CI), standard errors of measurement (SEM) and smallest detectable differences (SDD). The SDD is derived from the SEM and can be expressed in original units or as a percentage of the feature's grand mean. This statistic indicates the level of change (or percentage change) in a feature attributed with 95% certainty to a true change in the condition of the subject instead of that being caused by testretest errors [22].
Criterion-related validity analysis
To evaluate the strengths of the correlations between the new outcome measure and the two validated measures, the individual components and total ALF scores were correlated with the physical function dimensions of the WOMAC and SF-36 indexes, obtained at the subject's first assessment (n = 214). Correlations coefficients of around 0.2 were considered small, over 0.5 as moderate and over 0.8 as large [23].
Responsiveness analysis
The between-group standardized response means (SRM), obtained from the long-term review of a RCT evaluating the relative effectivenesses of two methods of providing exercise, were calculated and compared. The SRM was calculated by dividing the mean change score of the measure by the standard deviation of the change scores over the 12 month time period [24]. A larger SRM for an outcome measure would suggest greater responsiveness to the intervention by that outcome.
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Results |
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The standardized response means obtained from the RCT of exercise provision at 12 month follow-up were larger for the ALF (SRM = 0.49) than the physical function domains of the WOMAC (SRM = 0.39) and SF-36 (SRM = 0.12) (Friedman test 2 = 15.5, P<0.001).
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Discussion |
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If valid outcome measures are to be used in clinical practice, they must be appropriate for the patient population and convenient for the clinician. This work has demonstrated that a simple timed measure of locomotor function can be used as a measure of physical functioning and as a means of quantifying treatment response. The individual components of the ALF challenge the locomotor function of patients with knee OA, but are not so demanding that they cannot be completed. Consequently, the measure appears to offer the patient and clinician an appropriate, simple, quick (time to administer 10 min) and convenient outcome measure in the treatment of knee OA.
The use of the ALF score can be recommended for consideration as a clinical and research outcome measure with knee OA patients. Based on the evidence presented above, the ALF offers a valid, simple and convenient outcome measure which is responsive over 12 months and can be considered when planning treatment evaluation with OA patients.
The authors have declared no conflicts of interest.
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Acknowledgments |
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References |
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