title: The patellofemoral pain and osteoarthritis subscale of the KOOS (KOOS-PF): development and validation using the COSMIN checklist.
abstract: BACKGROUND
  Patellofemoral pain and osteoarthritis are prevalent and associated with substantial pain and functional impairments. Patient-reported outcome measures (PROMs) are recommended for research and clinical use, but no PROMs are specific for patellofemoral osteoarthritis, and existing PROMs for patellofemoral pain have methodological limitations. This study aimed to develop a new subscale of the Knee injury and Osteoarthritis Outcome Score for patellofemoral pain and osteoarthritis (KOOS-PF), and evaluate its measurement properties.
  
  
  METHODS
  Items were generated using input from 50 patients with patellofemoral pain and/or osteoarthritis and 14 health and medical clinicians. Item reduction was performed using data from patellofemoral cohorts (n=138). We used the COnsesus-based Standards for the selection of health Measurements INstruments guidelines to evaluate reliability, validity, responsiveness and interpretability of the final version of KOOS-PF and other KOOS subscales.
  
  
  RESULTS
  From an initial 80 generated items, the final subscale included 11 items. KOOS-PF items loaded predominantly on one factor, pain during activities that load the patellofemoral joint. KOOS-PF had good internal consistency (Cronbach's α 0.86) and adequate test-retest reliability (intraclass correlation coefficient 0.86). Hypothesis testing supported convergent, divergent and known-groups validity. Responsiveness was confirmed, with KOOS-PF demonstrating a moderate correlation with Global Rating of Change scores (r 0.52) and large effect size (Cohen's d 0.89). Minimal detectable change was 2.3 (groups) and 16 (individuals), while minimal important change was 16.4. There were no floor or ceiling effects.
  
  
  CONCLUSIONS
  The 11-item KOOS-PF, developed in consultation with patients and clinicians, demonstrated adequate measurement properties, and is recommended for clinical and research use in patients with patellofemoral pain and osteoarthritis.
authors.affiliation: School of Allied Health, College of Science, Health and Engineering, La Trobe University, Victoria, Australia.
authors.forename: Kay M
authors.initials: KM
authors.lastname: Crossley
authors.affiliation: Department of Family Practice, Centre for Hip Health and Mobility, University of British Columbia, Vancouver, Canada.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Macri
authors.affiliation: Department of Physiotherapy, The University of Melbourne, Parkville, Australia.
authors.forename: Sallie M
authors.initials: SM
authors.lastname: Cowan
authors.affiliation: School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Australia.
authors.forename: Natalie J
authors.initials: NJ
authors.lastname: Collins
authors.affiliation: Department of Sports Science and Clinical Biomechanics, Musculoskeletal Function and Physiotherapy, University of Southern Denmark, Odense, Denmark.
authors.forename: Ewa M
authors.initials: EM
authors.lastname: Roos
mesh_terms: D000328:Adult; D000368:Aged; D057189:Checklist; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000175:diagnosis*; D010147:Pain Measurement / Q000379:methods*; D046788:Patellofemoral Pain Syndrome / Q000175:diagnosis*; D000071066:Patient Reported Outcome Measures; D015203:Reproducibility of Results; D055815:Young Adult
keywords: Knee; Measurement; Osteoarthritis; Questionnaire