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Evaluation of the Dutch version of the Foot and Ankle Outcome Score (FAOS): responsiveness and Minimally Important Change

  • Ankle
  • Published:
Knee Surgery, Sports Traumatology, Arthroscopy Aims and scope

Abstract

Purpose

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.

Level of evidence

Diagnostic study, Level I.

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Acknowledgments

We would like to thank Bas van der Heijden for his statistical assistance.

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Authors and Affiliations

  1. Department of Orthopedics, MC Slotervaart, Louwesweg 6, 1066 EC, Amsterdam, The Netherlands

    I. N. Sierevelt & D. Haverkamp

  2. Department of Orthopaedic Surgery, Orthopaedic Research Center Amsterdam, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam, The Netherlands

    I. C. M. van Eekeren, M. L. Reilingh & G. M. M. J. Kerkhoffs

  3. Department of Epidemiology and Biostatistics, EMGO Institute for Health and Care Research, VU University Medical Center, De Boelelaan 1089a, 1081 HV, Amsterdam, The Netherlands

    C. B. Terwee

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  1. I. N. Sierevelt
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  2. I. C. M. van Eekeren
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  3. D. Haverkamp
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Correspondence to I. N. Sierevelt.

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Sierevelt, I.N., van Eekeren, I.C.M., Haverkamp, D. et al. Evaluation of the Dutch version of the Foot and Ankle Outcome Score (FAOS): responsiveness and Minimally Important Change. Knee Surg Sports Traumatol Arthrosc 24, 1339–1347 (2016). https://doi.org/10.1007/s00167-015-3941-9

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  • DOI: https://doi.org/10.1007/s00167-015-3941-9

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