title: Minimal detectable change for mobility and patient-reported tools in people with osteoarthritis awaiting arthroplasty.
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 (n = 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 (n = 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.
authors.affiliation: Orthopaedic Department, Liverpool Hospital, Sydney, Australia. Justine.Naylor@sswahs.nsw.gov.au.
authors.forename: Justine M
authors.initials: JM
authors.lastname: Naylor
authors.forename: Andrew
authors.initials: A
authors.lastname: Hayen
authors.forename: Edward
authors.initials: E
authors.lastname: Davidson
authors.forename: Danella
authors.initials: D
authors.lastname: Hackett
authors.forename: Ian A
authors.initials: IA
authors.lastname: Harris
authors.forename: Gihan
authors.initials: G
authors.lastname: Kamalasena
authors.forename: Rajat
authors.initials: R
authors.lastname: Mittal
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D004185:Disability Evaluation; D005080:Exercise Test; D005260:Female; D006621:Hip Joint / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009517:New South Wales; D015207:Osteoarthritis, Hip / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D020370:Osteoarthritis, Knee / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D010147:Pain Measurement; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013997:Time Factors; D014850:Waiting Lists