The Korean New KSS was found to be more responsive than the Korean WOMAC and Korean SF-36. All the domains of the Korean New KSS, except for expectation, showed a large change (> 0.8), calculated as SRM. This analysis showed that the Korean New KSS having a SRM of 2.03 (p < 0.001) was more responsive than the Korean WOMAC with a SRM of 1.88 (p < 0.001) and the Korean SF-36 physical and mental component summaries, with SRMs of 1.14 (p < 0.001) and 0.68 (p < 0.001) respectively. The SRM of the Korean KSS symptom score was 2.23 (p < 0.001) which was higher than the Korean WOMAC pain (2.12, p < 0.001) and SF-36 bodily pain scores (1.14, p < 0.001). Furthermore, regarding the functional scale, the Korean New KSS had a mean score of 1.85 (p < 0.001) which indicates that it was more responsive than the Korean WOMAC with a score of 1.75 (p < 0.001) and the SF-36 physical function score of 1.67 (p < 0.001) (Table 5).
Construct validity and responsiveness for age-matched control groups between the Korean New KSS, Korean WOMAC, and Korean SF-36 also showed good correlations. Gender analysis between the Korean New KSS and Korean WOMAC showed strong to moderate correlations with the exception of the expectation subscale which correlated weakly (Table 6). Similarly, the Korean New KSS and Korean SF-36 showed moderate to weak positive correlation when men and women were compared individually (Table 7). Furthermore, gender analysis of responsiveness showed that the Korean New KSS had higher SRMs when compared with the Korean WOMAC and Korean SF-36 (Table 8).
The recently developed 2011 KS Score is widely used for patients undergoing TKA. For a measure to be effective across cultures, it not only has to be translated well linguistically, but also has to be adapted culturally to maintain the content validity of the instrument . The current study was conducted to develop the Korean version of the 2011 KS Score for Korean-speaking patients who undergo TKA, which was developed through crosscultural adaptation, and to investigate its psychometric properties. Similar versions of the 2011 KS Score have been translated to Japanese , French , Dutch , and Chinese  through the process of crosscultural adaptation, and all have been shown to have good psychometric properties. The current study similarly shows that the Korean New KSS is a reliable, consistent, and valid instrument to evaluate the functional outcomes and expectations of Korean-speaking patients before and after TKA (Appendix 1. Supplemental material is available with the online version of CORR®.).
We acknowledge certain limitations of our study. First, because all three questionnaires were administered simultaneously 4 weeks preoperatively and 1 year postoperatively, the patients could have been affected by responder burden, which might lead to similar or missing responses. This was addressed by having a trained research assistant review the questionnaires for such responses in the presence of eligible patients without any attempt to influence the response. However, we acknowledge that by having research personnel assist in the administration of what is designed as a patient-reported outcomes tool, the performance with the Korean version of the KSS with respect to reliability and validity we observed in this study may be somewhat better than might be achieved with unassisted patients in general use. Second, the demographic features of TKA use in Korea, such as the predominance of older women, should be taken into account; further studies are needed to investigate these psychometric properties in Korean men, although we attempted to address that to some extent with our additional analysis. Third, although our translation methods were rigorous, certain inconsistencies might remain in the translation from one language to another. If better words or phrases are suggested, they should undergo validation by using the same standardized protocol.
The test-retest reliability was excellent for all the domains of the Korean New KSS, showing a high degree of concordance (ICC) and good to excellent internal consistency. Reliability refers to the degree to which test results have a brief internal consistency without any treatment change, and internal consistency is defined as the coherence among scale components. Some authors quote a period between 2 days and 2 weeks for the second application of a test, which is an adequate compromise between recall bias and change in disease condition . However, according to Terwee et al. , the appropriateness of the period chosen is not as important as the justification of the period described. In the current study, reliability and internal consistency were assessed by asking patients to complete the questionnaires twice during a 4-week interval. The Korean New KSS showed excellent reliability for all domains (ICC, 0.69-0.85), showing good reproducibility. It also showed good-to-excellent internal consistency in all the subscales (Cronbach's alpha, 0.83-0.92). Our study showed an ICC of 0.69 to 0.85, which is similar to the results of Japanese , French , and Dutch  studies that translated the 2011 KS Score to their respective languages, with ICCs ranging from 0.65 to 0.88, from 0.84 to 0.97, and from 0.73 to 0.92, respectively. Similarly, our study showed a Cronbach's alpha of 0.83 to 0.92, which also is in agreement with those of other translated versions of the 2011 KS Score and the original English KSS (Cronbach's alpha, 0.68-0.95) , showing g good-to-excellent reliability and internal consistency (Table 9). Although we could not provide comparative data regarding reliability for age-matched control groups as reliability in our study was assessed at an interval 4 weeks apart, our data regarding validity and responsiveness appear adequate to address the gender disparity of our study.
The Korean New KSS showed adequate construct validity when compared with the Korean WOMAC and Korean SF-36. Because no gold standard measure has been established to evaluate validity post-TKA, correlations between the preoperative scores of the Korean New KSS and those of the Korean WOMAC and Korean SF-36 were determined. These scoring systems were selected because their test validities have been proven in previous studies [2, 11]. All the domains of the Korean New KSS correlated well with the Korean WOMAC, except for the expectation subscale. All the domains tested showed strong or moderate correlation with the individual subscales of the Korean WOMAC. The satisfaction domain of the Korean New KSS showed a weak positive correlation with all the subscales of the SF-36 except general health, which might be expected owing to the high satisfaction rates post-TKA. Similarly, some studies have indicated that the current TKA population is physically more active than in the past and observed that some patients start participating in physical activities postoperatively, which they were not able to do preoperatively [1, 12]. Therefore, the activity domain becomes an important tool for post-TKA evaluation. In the current study, the activity domain of the Korean New KSS showed a strong positive correlation with physical function (r = 0.62, p < 0.001) and physical component summary (r = 0.52, p < 0.001), moderate with physical role (r = 0.46, p < 0.001), and weak with bodily pain (r = 0.26, p = 0.003) and the social function (r = 0.31, p = 0.001) component of the Korean SF-36. Similarly, the symptom domain also exhibited similar moderate positive correlation with physical function (r = 0.41, p < 0.001) and weak positive correlation with bodily pain, social function, and the physical component summary (r = 0.22, p = 0.016; r = 0.20, p = 0.025; and r = 0.26, p = 0.003, respectively). The expectation domain showed a similar correlation with the physical function and general health subscales of the Korean SF-36. Our study shows low levels of correlation when compared with the Dutch  and French studies  but similar correlations when compared with the Japanese version of the 2011 KS Score . A possible explanation for this finding could be the difference in cultural background between the European and Asian populations. Nevertheless, such differences in correlation coefficients do not reduce the usefulness of our study but rather indicate that further studies are needed to identify the reason for these findings and their effect on the instrument. Our data regarding age-matched control groups showed similar values for Korean men and women when construct validity was analyzed individually, thereby eliminating any gender-based biases from our study.
The Korean New KSS was the most responsive scale when compared with the Korean WOMAC and Korean SF-36. Responsiveness shows the ability of a scale to reflect changes in perioperative and postoperative results; the higher the responsiveness, the greater the ability of a scale to detect changes . Analysis also revealed that the Korean New KSS symptom score was more responsive when compared with the WOMAC pain and the SF-36 bodily pain scores. However, regarding the functional scale, the Korean New KSS was more responsive than the Korean WOMAC and the Korean SF-36. Similarly, for age-matched control groups, the Korean New KSS also was more responsive when compared with the Korean WOMAC and Korean SF-36, thereby confirming our current study population is representative of the Korean population undergoing TKA.
The Korean version of the 2011 KS Score appears valid, reliable, and responsive in Korean-speaking patients who undergo TKA for knee osteoarthritis. Therefore, it now can be used as a valuable metric to assess functional outcomes and expectations of Korean patients who undergo TKA. Because the population of men undergoing knee arthroplasty in Korea is small compared with that of women, further studies will be required to investigate the properties of the Korean New KSS among men.
1. Argenson JN, Parratte S, Ashour A, Komistek RD, Scuderi GR. Patient-reported outcome correlates with knee function after a single-design mobile-bearing TKA. Clin Orthop Relat Res.
2. Bae SC, Lee HS, Yun HR, Kim TH, Yoo DH, Kim SY. Cross-cultural adaptation and validation of Korean Western Ontario and McMaster Universities (WOMAC) and Lequesne osteoarthritis indices for clinical research. Osteoarthritis Cartilage.
3. Beck CT, Gable RK. Ensuring content validity: an illustration of the process. J Nurs Meas.
4. Bland JM, Altman DG. Measurement error. BMJ.
5. Collins NJ, Misra D, Felson DT, Crossley KM, Roos EM. Measures of knee function: International Knee Documentation Committee (IKDC) Subjective Knee Evaluation Form, Knee Injury and Osteoarthritis Outcome Score (KOOS), Knee Injury and Osteoarthritis Outcome Score Physical Function Short Form (KOOS-PS), Knee Outcome Survey Activities of Daily Living Scale (KOS-ADL), Lysholm Knee Scoring Scale, Oxford Knee Score (OKS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Activity Rating Scale (ARS), and Tegner Activity Score (TAS). Arthritis Care Res (Hoboken).
2011;63:suppl 11S208-228 10.1002/acr.206324336550.
6. Debette C, Parratte S, Maucort-Boulch D, Blanc G, Pauly V, Lustig S, Servien E, Neyret P, Argenson JN. French adaptation of the new Knee Society Scoring System for total knee arthroplasty. Orthop Traumatol Surg Res.
7. Ghanem E, Pawasarat I, Lindsay A, May L, Azzam K, Joshi A, Parvizi J. Limitations of the Knee Society Score in evaluating outcomes following revision total knee arthroplasty. J Bone Joint Surg Am.
8. Guillemin F. Cross-cultural adaptation and validation of health status measures. Scand J Rheumatol.
9. Guillemin F, Bombardier C, Beaton D. Cross-cultural adaptation of health-related quality of life measures: literature review and proposed guidelines. J Clin Epidemiol.
10. Hamamoto Y, Ito H, Furu M, Ishikawa M, Azukizawa M, Kuriyama S, Nakamura S, Matsuda S. Cross-cultural adaptation and validation of the Japanese version of the new Knee Society Scoring System for osteoarthritic knee with total knee arthroplasty. J Orthop Sci.
11. Han CW, Lee EJ, Iwaya T, Kataoka H, Kohzuki M. Development of the Korean version of Short-Form 36-Item Health Survey: health related QOL of healthy elderly people and elderly patients in Korea. Tohoku J Exp Med.
12. Huch K, Muller KA, Sturmer T, Brenner H, Puhl W, Gunther KP. Sports activities 5 years after total knee or hip arthroplasty: the Ulm Osteoarthritis Study. Ann Rheum Dis.
13. Insall J. Current concepts review: patellar pain. J Bone Joint Surg Am.
14. Koh IJ, Kim TK, Chang CB, Cho HJ, In Y. Trends in use of total knee arthroplasty in Korea from 2001 to 2010. Clin Orthop Relat Res.
15. Liang MH, Fossel AH, Larson MG. Comparisons of five health status instruments for orthopedic evaluation. Med Care.
16. Liu D, He X, Zheng W, Zhang Y, Li D, Wang W, Li J, Xu W. Translation and validation of the simplified Chinese new Knee Society Scoring System. BMC Musculoskelet Disord.
17. Marx RG, Menezes A, Horovitz L, Jones EC, Warren RF. A comparison of two time intervals for test-retest reliability of health status instruments. J Clin Epidemiol.
18. Nilsdotter AK, Lohmander LS, Klassbo M, Roos EM. Hip disability and osteoarthritis outcome score (HOOS): validity and responsiveness in total hip replacement. BMC Musculoskelet Disord.
19. Noble PC, Scuderi GR, Brekke AC, Sikorskii A, Benjamin JB, Lonner JH, Chadha P, Daylamani DA, Scott WN, Bourne RB. Development of a new Knee Society scoring system. Clin Orthop Relat Res.
20. Scuderi GR, Bourne RB, Noble PC, Benjamin JB, Lonner JH, Scott WN. The new Knee Society Knee Scoring System. Clin Orthop Relat Res.
21. Terwee CB, Bot SD, Boer MR, Windt DA, Knol DL, Dekker J, Bouter LM, Vet HC. Quality criteria were proposed for measurement properties of health status questionnaires. J Clin Epidemiol.
22. Straeten C, Witvrouw E, Willems T, Bellemans J, Victor J. Translation and validation of the Dutch new Knee Society Scoring System©. Clin Orthop Relat Res.
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