We found positive correlations between the OKS and the VAS (12 questions of the OKS, r = 0.692, p < 0.001; Factor 1, r = 0.708; p < 0.001; Factor 2, r = 0.566, p < 0.001). When we evaluated construct validity using the relationship between the OKS and SF-36 scores, we obtained an r value of −0.74. We observed convergent validity for the Korean OKS based on correlations (range, 0.5-0.8) between factor scores of the OKS and three domain scores (physical functioning, role physical, bodily pain). The strongest correlations were observed between the Factor 1 score of the OKS and the bodily pain score of the SF-36 (r = −0.698) and the Factor 2 score and the physical functioning score (r = −0.715). The correlation coefficients between factor scores of the OKS and other domain scores were relatively weak (r < 0.5), indicating adequate divergent validity. We found no ceiling effects for the Korean OKS. The worst score was 59 points in one patient and the best was 12 points in two patients.
The objectives of this study were to produce a Korean version of OKS by translation and adaption. Therefore, we translated a culturally adapted version of the OKS into the Korean language and validated this adapted version of the OKS in Korean patients who had TKAs. In addition, we determined whether the Korean version would show similar reliability and validity with the previous study [2-4, 6, 8, 13, 15-17].
Before interpreting our results, several limitations must be considered. First, our subjects were patients who underwent TKAs at only one arthroplasty center. Although access to the hospital is open to every patient and our patients are a mixture of urban and rural inhabitants, the current study cohort might not represent all people of our country because study samples were enrolled only from the southeastern area of country. Second, the time between the test and retest was relatively short, which might have positively biased our reliability results because the patients would not have had time to forget their answers on the earlier questionnaire. Finally, this validation was performed with patients who underwent TKAs for knee OA. Further investigation of the Korean OKS with patients after TKA is warranted to concomitantly assess the responsiveness of this measure.
The Korean version of the OKS was easily understood by the patients and administered. Our results show the Korean version of the OKS is a reliable and valid instrument for measuring outcome in Korean patients with TKAs, and its reliability levels were similar to those of the Chinese , Dutch , German , Japanese , Italian , and Swedish versions .
The reproducibility of each of the 12 items showed kappa statistics of agreement greater than 0.6. Although numerous OKS validation studies have been published [2-4, 6, 8, 13, 15-17], the average reproducibility of each OKS item was not reported. If the first and second questionnaires were assessed by the patients during clinic visits, it could decrease the average reproducibility of the questionnaire. The results can be explained by some patients probably having to wait much longer than others for the consultation before being seen by the interviewer. To avoid this bias, we mailed the VAS for pain, Korean version of the OKS, and SF-36 to 142 patients who underwent TKAs for knee OA. An ICC of 0.848 for the Korean version of the OKS is in accordance with other translated versions with ICCs ranging from 0.85 to 0.97 [4, 6, 8, 13, 15, 16].
Our data show the OKS could be translated into Korean without losing the psychometric properties of the original OKS version. Accordingly, the Korean version of the OKS appears to be a reliable and valid instrument for self-assessment of pain and function in patients who had TKAs. Therefore, we suggest this Korean version of the OKS can be used for future clinical studies in Korea.
We thank the staff from the outpatient clinics, and the patients who participated in this study. We also thank Sang Sup Lee PhD, Jerry G. Gebhard PhD, Sam Cho MD, Shi Hwan Park MD, and Tae Sik Goh MD for help with the translation process.
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Appendix 1: Korean version of the Oxford Knee Score (Symbol)