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Open Access Research article

Minimal detectable change for mobility and patient-reported tools in people with osteoarthritis awaiting arthroplasty

Justine M Naylor123*, Andrew Hayen3, Edward Davidson4, Danella Hackett5, Ian A Harris123, Gihan Kamalasena1 and Rajat Mittal2

Author Affiliations

1 Orthopaedic Department, Liverpool Hospital, Sydney, Australia

2 School of Public Health and Community Medicine, University of New South Wales, Sydney, Australia

3 Ingham Institute of Applied Medical Research, Sydney, Australia

4 Physiotherapy Department, Nepean Hospital, Sydney, Australia

5 Physiotherapy Department, Fairfield Hospital, Sydney, Australia

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BMC Musculoskeletal Disorders 2014, 15:235  doi:10.1186/1471-2474-15-235

Published: 11 July 2014

Abstract

Background

Thoughtful use of assessment tools to monitor disease requires an understanding of clinimetric properties. These properties are often under-reported and, thus, potentially overlooked in the clinic. This study aimed to determine the minimal detectable change (MDC) and coefficient of variation per cent (CV%) for tools commonly used to assess the symptomatic and functional severity of knee and hip osteoarthritis.

Methods

We performed a test-retest study on 136 people awaiting knee or hip arthroplasty at one of two hospitals. The MDC95 (the range over which the difference [change] for 95% of patients is expected to lie) and the coefficient of variation per cent (CV%) for the visual analogue scale (VAS) for joint pain, the six-minute walk test (6MWT), the timed up-and-go (TUG) test, the Knee Injury and Osteoarthritis Outcome Score (KOOS) and the Hip Disability and Osteoarthritis Outcome Score (HOOS) subscales were calculated.

Results

Knee cohort (nā€‰=ā€‰75) - The MDC95 and CV% values were as follows: VAS 2.8 cm, 15%; 6MWT 79 m, 8%; TUG +/-36.7%, 13%; KOOS pain 20.2, 19%; KOOS symptoms 24.1, 22%; KOOS activities of daily living 20.8, 17%; KOOS quality of life 26.6, 44. Hip cohort (nā€‰=ā€‰61) - The MDC95 and CV% values were as follows: VAS 3.3 cm, 17%; 6MWT 81.5 m, 9%; TUG +/-44.6%, 16%; HOOS pain 21.6, 22%; HOOS symptoms 22.7, 19%; HOOS activities of daily living 17.7, 17%; HOOS quality of life 24.4, 43%.

Conclusions

Distinguishing real change from error is difficult in people with severe osteoarthritis. The 6MWT demonstrates the smallest measurement error amongst a range of tools commonly used to assess disease severity, thus, has the capacity to detect the smallest real change above measurement error in everyday clinical practice.

Keywords:
Osteoarthritis; Arthroplasty; Clinimetrics; Patient-reported outcome measures; Timed mobility tests