Cross-Cultural Adaptation and Validation of Fulkerson Knee Instability Scale into Spanish in Patellofemoral Pain

Background/Objectives: The aim of this study was to cross-culturally adapt to Spanish and to analyze the psychometric properties of Fulkerson Knee Instability Scale in Patellofemoral Pain. Methods: A Cross-cultural adaptation and validation study has been carried out following the recommendations of COnsensus-based Standards for the selection of health Measurement Instruments (COSMIN). The sample consisted of seventy-five Spanish subjects with Patellofemoral Pain, implying 106 affected knees. Cross-cultural adaptation involved both cultural and linguistic adaptation of the Fulkerson Knee Instability Scale. Psychometric properties evaluated were: validity (construct and external), reliability (internal consistency, test-retest and agreement), discriminant ability and feasibility. Results: Construct validity showed strong correlation between Fulkerson Scale and both Knee injury and Osteoarthritis Outcome Score for Patellofemoral pain and osteoarthritis (r=0.83) and Kujala Patellofemoral Score (r=0.79). Correlation coefficients assessing discriminant validity between Fulkerson and descriptive data were all r<0.4. Cronbach α evaluating internal consistency and Intraclass correlation coefficient assessing test-retest reliability were both 0.618 (CI95%: 0.534-0.692). Standard error of the mean and Smallest detectable change were 10.13 and 8.82, respectively. Bland-Altman plots showed that >90% of the cases were within the limits of agreement. No floor or ceiling effects were found. Assessing feasibility, Fulkerson was understandable in general and completed by all participants. Conclusions: The Spanish version of Fulkerson Knee Instability Scale is a valid, reliable and feasible functional assessment tool for Spanish subjects with patellofemoral pain according to its psychometric properties.