title: Evaluation of the Dutch version of the Foot and Ankle Outcome Score (FAOS): Responsiveness and Minimally Important Change.
abstract: OBJECTIVE
  The aim of this study was to evaluate the responsiveness of the Foot and Ankle Outcome Score (FAOS) and provide data on the Minimally Important Change (MIC) in patients 1 year after hindfoot and ankle surgery.
  
  
  METHODS
  Prospective pre-operative and 1 year post-operative FAOS scores were collected from 145 patients. A patient's global assessment and a longitudinal derived Function Change Score were used as external anchors. To assess responsiveness, effect sizes (ES) and Standardized Response Means (SRM) were calculated and hypotheses on their magnitudes were formulated. Additional ROC curve analysis was performed, and the Area Under the Curve (AUC) was calculated as a measure of responsiveness. MIC values were estimated using two different methods: (1) the mean change method and (2) the optimal cut-off point of the ROC curve.
  
  
  RESULTS
  Responsiveness was supported by confirmation of 84% of the hypothesized ES and SRM and almost all AUCs exceeding 0.70. MIC values ranged from 7 (symptoms) to 38 (sport) points. They varied between calculation methods and were negatively associated with baseline values. A considerable amount of MIC values did not exceed the smallest detectable change limit, indicating that the FAOS is more suitable at group level than for longitudinally following individual patients.
  
  
  CONCLUSIONS
  The FAOS demonstrated good responsiveness in patients 1 year after hindfoot and ankle surgery. Due to their wide variation, MIC estimates derived in this study should be interpreted with caution. However, these estimates can be of value to facilitate sample size calculation in future studies.
  
  
  METHODS
  Diagnostic study, Level I.
authors.affiliation: Department of Orthopedics, MC Slotervaart, Louwesweg 6, 1066 EC, Amsterdam, The Netherlands. I.Sierevelt@gmail.com.
authors.forename: I N
authors.initials: IN
authors.lastname: Sierevelt
authors.affiliation: Department of Orthopaedic Surgery, Orthopaedic Research Center Amsterdam, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands.
authors.forename: I C M
authors.initials: IC
authors.lastname: van Eekeren
authors.affiliation: Department of Orthopedics, MC Slotervaart, Louwesweg 6, 1066 EC, Amsterdam, The Netherlands.
authors.forename: D
authors.initials: D
authors.lastname: Haverkamp
authors.affiliation: Department of Orthopaedic Surgery, Orthopaedic Research Center Amsterdam, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands.
authors.forename: M L
authors.initials: ML
authors.lastname: Reilingh
authors.affiliation: Department of Epidemiology and Biostatistics, EMGO Institute for Health and Care Research, VU University Medical Center, De Boelelaan 1089a, 1081 HV, Amsterdam, The Netherlands.
authors.forename: C B
authors.initials: CB
authors.lastname: Terwee
authors.affiliation: Department of Orthopaedic Surgery, Orthopaedic Research Center Amsterdam, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands.
authors.forename: G M M J
authors.initials: GM
authors.lastname: Kerkhoffs
mesh_terms: D000328:Adult; D000842:Ankle / Q000601:surgery*; D005260:Female; D005500:Follow-Up Studies; D005528:Foot / Q000601:surgery*; D006801:Humans; D008297:Male; D009426:Netherlands; D000071066:Patient Reported Outcome Measures; D011446:Prospective Studies; D015203:Reproducibility of Results
keywords: Foot and Ankle Outcome Score (FAOS); Minimally Important Change (MIC); PROM; Questionnaires; Responsiveness