title: Assessing stability and change of four performance measures: a longitudinal study evaluating outcome following total hip and knee arthroplasty.
abstract: BACKGROUND
  Physical performance measures play an important role in the measurement of outcome in patients undergoing hip and knee arthroplasty. However, many of the commonly used measures lack information on their psychometric properties in this population. The purposes of this study were to examine the reliability and sensitivity to change of the six minute walk test (6MWT), timed up and go test (TUG), stair measure (ST), and a fast self-paced walk test (SPWT) in patients with hip or knee osteoarthritis (OA) who subsequently underwent total joint arthroplasty.
  
  
  METHODS
  A sample of convenience of 150 eligible patients, part of an ongoing, larger observational study, was selected. This included 69 subjects who had a diagnosis of hip OA and 81 diagnosed with knee OA with an overall mean age of 63.7 +/- 10.7 years. Test-retest reliability, using Shrout and Fleiss Type 2,1 intraclass correlations (ICCs), was assessed preoperatively in a sub-sample of 21 patients at 3 time points during the waiting period prior to surgery. Error associated with the measures' scores and the minimal detectable change at the 90% confidence level was determined. A construct validation process was applied to evaluate the measures' abilities to detect deterioration and improvement at two different time points post-operatively. The standardized response mean (SRM) was used to quantify change for all measures for the two change intervals. Bootstrapping was used to estimate the 95% confidence intervals (CI) for the SRMs.
  
  
  RESULTS
  The ICCs (95% CI) were as follows: 6MWT 0.94 (0.88,0.98), TUG 0.75 (0.51, 0.89), ST 0.90 (0.79, 0.96), and the SPWT 0.91 (0.81, 0.97). Standardized response means varied from .79 to 1.98, being greatest for the ST and 6MWT over the studied time intervals.
  
  
  CONCLUSIONS
  The test-retest estimates of the 6MWT, ST, and the SPWT met the requisite standards for making decisions at the individual patient level. All measures were responsive to detecting deterioration and improvement in the early postoperative period.
authors.affiliation: School of Rehabilitation Science, McMaster University, Hamilton, ON, Canada. d.kennedy@utoronto.ca
authors.forename: Deborah M
authors.initials: DM
authors.lastname: Kennedy
authors.forename: Paul W
authors.initials: PW
authors.lastname: Stratford
authors.forename: Jean
authors.initials: J
authors.lastname: Wessel
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Gollish
authors.forename: Dianne
authors.initials: D
authors.lastname: Penney
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D019645:Arthroplasty, Replacement, Knee; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000503:physiopathology* / Q000601:surgery*; D020370:Osteoarthritis, Knee / Q000503:physiopathology* / Q000601:surgery*; D011184:Postoperative Period; D015203:Reproducibility of Results; D016896:Treatment Outcome; D016138:Walking