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Introduction of a classification system for patients with patellofemoral instability (WARPS and STAID)

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

Abstract

Purpose

The primary purpose of this paper is to introduce the WARPS/STAID classification system for patellofemoral instability. The secondary purpose is to establish the validity and reliability of the WARPS/STAID classification system.

Methods

Patients (n = 31) with a confirmed diagnosis of patellofemoral instability underwent a thorough knee history and physical examination with 3 raters. The raters graded each component of the WARPS/STAID classification system on a visual analogue scale (VAS). A single Global VAS WARPS/STAID score was graded after all other components of the classification system were completed. Intraclass correlation coefficient (ICC 2, 3) was calculated for each metric of the classification scale and for the Global score. Concurrent validity was assessed by correlating the WARPS/STAID score with the Kujala score. Subjects were assigned to one of three categories (WARPS, STAID, or mixed characteristics) according to the Total WARPS/STAID score to determine the level of agreement between the three raters.

Results

Intraclass correlation coefficient (ICC 2, 3) of the WARPS/STAID classification continuum ranged between 0.73 and 0.91 for the individual metrics of the classification. The ICC (2, 3) for the Global WARPS/STAID score was 0.75. The mean Kujala score (m = 61, SD 18) was significantly correlated with the total WARPS/STAID score (r = 0.387, p < 0.05). The majority of subjects were assigned to either the WARPS or STAID categories.

Conclusion

This study introduced the WARPS/STAID classification system and established both validity and reliability in subjects with patellofemoral instability.

Level of evidence

II.

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Authors and Affiliations

  1. Banff Sport Medicine, PO Box 1300, Banff, AB, T1L 1B3, Canada

    Laurie A. Hiemstra, Sarah Kerslake, S. Mark Heard & Gregory M. L. Buchko

  2. Department of Surgery, University of Calgary, Calgary, Canada

    Laurie A. Hiemstra & S. Mark Heard

  3. Department of Physical Education and Recreation Studies, Mount Royal University, Calgary, Canada

    Mark Lafave

  4. Department of Physical Therapy, University of Alberta, Edmonton, Canada

    Sarah Kerslake

Authors
  1. Laurie A. Hiemstra
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  2. Sarah Kerslake
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  3. Mark Lafave
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  4. S. Mark Heard
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  5. Gregory M. L. Buchko
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Correspondence to Laurie A. Hiemstra.

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Hiemstra, L.A., Kerslake, S., Lafave, M. et al. Introduction of a classification system for patients with patellofemoral instability (WARPS and STAID). Knee Surg Sports Traumatol Arthrosc 22, 2776–2782 (2014). https://doi.org/10.1007/s00167-013-2477-0

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  • DOI: https://doi.org/10.1007/s00167-013-2477-0

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