Cross-cultural translation and validation of the Spanish version of the patellofemoral pain and osteoarthritis subscale of the KOOS (KOOS-PF)

The aim of this study was to translate to Spanish the patellofemoral pain and osteoarthritis subscale of the knee injury and osteoarthritis outcome score (KOOS-PF) and validate this Spanish version of a disease-specific patient-reported outcome measure (PROM) for patellofemoral pain. The KOOS-PF was translated to Spanish and sixty patients with patellofemoral pain and/or osteoarthritis accepted to complete the questionnaire. 1-week later 58 patients answered the questions again for the test-retest reliability validation and finally 55 patients completed 1-month later for the responsiveness assessment. The Spanish version showed very good internal consistency (Cronbach's alpha: 0.93) and test-retest reliability (intraclass correlation coefficient: 0.82). Responsiveness was confirmed, showing a strong correlation with the global rating of change (GROC) score (r 0.64). The minimal detectable change was 11.1 points, the minimal important change was 17.2 points, and there were no floor or ceiling effects for the score.