Translation and validation of the new knee society knee scoring system into Spanish: Spanish KSS translation.

Purpose: The aim of the study was to translate and validate the English version of the 'Knee Society Knee Scoring System' developed in 2011 (2011 KSS) into Spanish. This new KSS version considers patient satisfaction and expectations before and after knee arthroplasty. Moreover, the questionnaire allows a better characterization of a younger and more diverse population.

Methods: A cross-cultural adaptation process was carried out to obtain the Spanish version of the questionnaire. After that, patients undergoing primary knee arthroplasty answered the translated questionnaire before and 6 months after surgery. Psychometric properties including feasibility, validity, reliability, and sensitivity to change were then assessed, and the questionnaire was compared with prior KSS, as well as with SF-12 and WOMAC, all of them already validated to Spanish.

Results: In the cross-cultural adaptation process, alternative translations of some items in 'Patient Expectative' and 'Functional Activities' sections were suggested. One hundred and seventy-six patients answered the resulting 1.0 version. Feasibility: 'Charnley Functional Classification', 'Deduction for flexion contracture and extensor lag', the question 'Do you use these aids because of your knees?', and 'Advanced activities (total)' obtained a high number of missing items. Eighty-eight patients (50%) in the preoperative visit and 141 patients (86.5%) after surgery had at least one missing answer. Internal validity: although the analysis suggests the presence of more than one dimension, there was a dimension that explained a higher percentage of variance, which was more noticeable in the postoperative visit. Convergent validity: correlation coefficients with prior KSS, SF-12, and WOMAC confirm the questionnaire's validity. Reliability: Cronbach's alpha for the new KSS was 0.841 and 0.861 in visit 1 and 2, respectively, and higher than that for prior KSS. Sensitivity to change: statistically, significant differences were found between the mean scores between both visits.

Conclusion: The proposed Spanish version of 2011 KSS is valid, reliable, and sensible to change in patients undergoing primary knee arthroplasty. Moreover, it has higher internal consistency (reliability) than the prior KSS. It should be emphasized its correct filling by both health professional and patients LEVEL OF EVIDENCE: II.