title: Introduction of a classification system for patients with patellofemoral instability (WARPS and STAID).
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  This study introduced the WARPS/STAID classification system and established both validity and reliability in subjects with patellofemoral instability.
  
  
  METHODS
  II.
authors.affiliation: Banff Sport Medicine, PO Box 1300, Banff, AB, T1L 1B3, Canada, hiemstra@banffsportmed.ca.
authors.forename: Laurie A
authors.initials: LA
authors.lastname: Hiemstra
authors.forename: Sarah
authors.initials: S
authors.lastname: Kerslake
authors.forename: Mark
authors.initials: M
authors.lastname: Lafave
authors.forename: S Mark
authors.initials: SM
authors.lastname: Heard
authors.forename: Gregory M L
authors.initials: GM
authors.lastname: Buchko
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000145:classification* / Q000175:diagnosis; D008297:Male; D057071:Patellofemoral Joint; D015203:Reproducibility of Results; D055815:Young Adult
references.citation: Osteoarthritis Cartilage. 2005 Nov;13(11):1029-36
references.pmid: 16154776
references.citation: J Knee Surg. 2012 Nov;25(5):411-6
references.pmid: 23150352
references.citation: Arthroscopy. 1993;9(2):159-63
references.pmid: 8461073
references.citation: Am J Sports Med. 2003 Jul-Aug;31(4):487-92
references.pmid: 12860533
references.citation: Psychol Bull. 1979 Mar;86(2):420-8
references.pmid: 18839484
references.citation: J Bone Joint Surg Am. 1989 Apr;71(4):506-13
references.pmid: 2703510
references.citation: Clin Orthop Relat Res. 2007 Feb;455:93-101
references.pmid: 17279039
references.citation: Med Sci Sports Exerc. 2008 Apr;40(4):606-11
references.pmid: 18317388
references.citation: Sports Med Arthrosc Rev. 2007 Jun;15(2):61-7
references.pmid: 17505319
references.citation: Knee Surg Sports Traumatol Arthrosc. 2011 Apr;19(4):663-70
references.pmid: 21153544
references.citation: Eur Radiol. 2012 Nov;22(11):2347-56
references.pmid: 22645041
references.citation: Sports Med Arthrosc Rev. 2007 Jun;15(2):82-8
references.pmid: 17505323
references.citation: Am J Sports Med. 2010 Nov;38(11):2248-54
references.pmid: 20716682
references.citation: Clin Sports Med. 2002 Jul;21(3):499-519
references.pmid: 12365240
references.citation: J Bone Joint Surg Am. 2003 Nov;85(11):2138-44
references.pmid: 14630842
references.citation: J Bone Joint Surg Am. 1990 Oct;72(9):1424-9
references.pmid: 2229126
references.citation: Am J Sports Med. 2000 Jul-Aug;28(4):472-9
references.pmid: 10921637
references.citation: Arthroscopy. 2010 Jul;26(7):926-35
references.pmid: 20620792
references.citation: Knee Surg Sports Traumatol Arthrosc. 1994;2(1):19-26
references.pmid: 7584171