KNEE Translation and validation of ‘The Knee Society Clinical Rating System’ into Spanish Oscar Ares • Enric Castellet • Francisco Macule ´ • Vicenc ¸ Leo ´n • Elvira Montan ˜ez • Alicia Freire • Pedro Hinarejos • Ferran Montserrat • Juan Ramon Amillo Received: 15 July 2012 / Accepted: 15 January 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract Purpose The Knee Society Clinical Rating System (KSS) is a questionnaire evaluating knee function itself and the patient’s ability to walk and climb stairs. The aim of our study is to present the validated translation of KSS into Spanish. Methods The validated method of translation–retrotrans- lation was used to translate KSS into Spanish. Three hun- dred and sixteen patients undergoing primary knee arthroplasty, before surgery and 6 months postoperative, completed the questionnaire (with an orthopedist’s help). Psychometric properties of feasibility (percentage of no answers), validity and sensitivity to change (test’s ability to detect change in patients’ functional status over time) were assessed. In the second part of the study, the translated version of KSS was compared with two already validated questionnaires (SF-36 and WOMAC). Results During the translation process, item 3 (ROM) presented low appropriateness and null comprehensibility. The alternative writing proposed was ‘for every 5°, we sum up 1 point, as if 8° were 1 point, to obtain the maximum scoring of 25 points you should bend more than 200°’. Feasibility: the item ‘malalignment’ obtained 15 % of missing item at visit 1. The percentage of invalid items was high in both visits (60 and 47 %). Validity: the coefficients of convergent correlation with WOMAC and SF-36 scales confirm the questionnaire’s validity. Sensitivity to change: significant differences were found in all cases between the mean scores comparing both visits. Conclusion The translated version 1.1 of KSS (final version) has shown to be feasible, valid and sensible to changes within the clinical practice of patients undergoing primary knees arthroplasty. Level of evidence Prognostic study, Level I. Keywords Knee society clinical rating system Á Translation Á Spanish Á Validation Á Transcultural adaptation Introduction Degenerative joint disease, also known as osteoarthritis (OA), is a chronic disease causing functional limitations and a decrease in quality of life. Treatment of this disease affecting the knee usually combines rehabilitation, anal- gesics and lifestyle modification. However, in the majority Electronic supplementary material The online version of this article (doi:10.1007/s00167-013-2412-4) contains supplementary material, which is available to authorized users. O. Ares (&) Á F. Macule ´ Orthopedic Department, Hospital Clinic Barcelona, University of Barcelona, Villarroel st. 170, 08036 Barcelona, Spain e-mail: arestraumatologia@gmail.com E. Castellet Hospital Vall d’Hebron, Barcelona, Spain V. Leo ´n Hospital de Cieza, Murcia, Spain E. Montan ˜ez Hospital Universitario Virgen de la Victoria, Malaga, Spain A. Freire Complexo Hospitalario Universitario A Corun ˜a, A Corun ˜a, Spain P. Hinarejos Á F. Montserrat Parc de Salut Mar. Hospital de La Esperanza, Barcelona, Spain J. R. Amillo Hospital de Viladecans, Barcelona, Spain 123 Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-013-2412-4