Reply to the Letter to the Editor: Translation and Validation of the German New Knee Society Scoring System.

To the Editor, We thankMr. Özden for giving us the opportunity to more comprehensively introduce our work, in which we translated and validated the newKneeSociety Score (KSS) in German [5]. There are several very interesting comments we will address on a point-by-point basis. In his letter, Mr. Özden noted that we should not have used the WOMAC as a scoring tool to comparatively analyze the new KSS in terms of construct validity because it doesn’t include an expectation and satisfaction section. Although it is a thoughtful critique, one should keep in mind that the new KSS has a unique satisfaction and expectation section, which no other scoring tool includes. But not all parameters can be present in all scoring tools. As stated in our study, construct validity is analyzed to reflect the consistency in the corresponding domains [5]. We analyzed construct validity using the well-known and widely used scoring tools such as WOMAC and SF-36 because: (1) There is no accepted reference method to reflect the status of patients before and after TKA and (2) these tests have been validated in previous studies [6, 8, 11]. Similar to our study, Noble and colleagues [8] used the Knee injury and Osteoarthritis Outcome Score and SF-12 to evaluate the construct validity of the new questionnaire. Neither measure includes any expectation or satisfaction sections. Other high-quality validation studies of the new KSS translated into Dutch and Korean languages used the WOMAC score for the same purpose as in our study [6, 11]. Mr. Özden also criticized the low correlation of patient expectations in our study. Indeed, we found a low correlation of patients’ expectations; this low correlation was already anticipated, as a similar result had been previously observed by others [6], which we noted in our paper [5]. We agree with Mr. Özden’s second comment, that long questionnaires may burden patients. As discussed in our paper: “like in all adaptation and validation studies, patients had to complete three separate scoring tools simultaneously, which may have resulted in missing or invalid responses as a result of an increase in responders’ burden” [5]. Previous studies have noted this issue [6, 11]. Indeed, there is a tension between respondent burden and the amount of detail one seeks in a patientreported outcomes questionnaire; more detail can be informative, but too much can represent an unreasonable imposition on patients’ time. Next, the author of the letter also mentioned total score calculations, which we noted in our Discussion section [5]. We presented total scores alongside all subdomain scores so as to make our findings comparable with other studies [6, 11]. The last two concerns are about sample size and the study design. We find the former comment valuable and appreciate the author’s concern regarding one of the most challenging issues in validation studies. Sample size is vitally important in terms of statistical (RE: Kayaalp ME, Keller T, Fitz W, Scuderi GR, Becker R. Translation and Validation of the German New Knee Society Scoring System. Clin Orthop Relat Res. 2019;477: 383-393). The authors certify that neither they, nor any members of their immediate families, have any commercial associations (such as consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. The opinions expressed are those of the writers, and do not reflect the opinion or policy of CORR or The Association of Bone and Joint Surgeons.