Ozden et al. translated and adapted the new Knee Society Score into Turkish and determined some psychometrical properties. They have conducted a valuable study but with some major shortcomings (1).
Firstly the authors state that they used recommendations by Beaton et al., although they don’t mention a pretest version in their study design; but only a pilot version exclusively in the discussion section. Beaton’s recommendations involve evaluating the prefinal version on at least 30–40 patients, which is of significant importance for the final shaping of the scoring tool (2).
Secondly, although sample size recommendations in the literature are inconsistent, and there is a lack of guidance regarding validation of scoring tools; the number of items in a questionnaire should be considered or at least 100 patients are needed for internal consistency, whereas 50 patients are required to effectively evaluate floor and ceiling effects (3, 4). On the other hand, authors included only 69 patients in total, i.e. from preoperative and postoperative patients groups in total. In detail, it is further explained that 11 of these patients, who were operated bilaterally, were included in preoperative as well as postoperative groups. This gives an actual total of 58 individuals, which is quite low for validating a 34-item questionnaire (3). Authors use of “number of patients” expression in tables indicates; however, number of knees included in total, which is very deceiving. Regarding validation studies, the number of knees is of a lesser interest but the actual number of patients because this is a study of psychometrical properties as stated in the title.
Thirdly, the new KSS has two forms to evaluate patients either in the preoperative or postoperative period with a different expectations section. Therefore, it is necessary to evaluate both forms in its respective aim, i.e. preoperative patients should be compared to corresponding preoperative scoring tool results and postoperative to its corresponding results. However, authors mixed both patient groups and stated only mean values from both groups and only than they have compared it with other scoring tools, i.e. they gave mean values of mixed preoperative and postoperative scores. This method is unique, but wrong in its methodology due to the reasons explained above. Furthermore, this approach makes it impossible to compare data from this study with any of the other studies out in the literature; because there are either exclusively preoperative or postoperative results in every other study, as it should normally be. The methodology in this study is therefore questionable and less creditable compared to other studies. Besides the methodological errors, there are also some issues with the obtained results. Firstly, the physical function domain of SF-36 should have ended in a positive correlation rather than a negative one when compared to the corresponding symptom domain of the new KSS. Furthermore, the functional activities domain of the new KSS shows almost no meaningful correlation with any of the corresponding functional domains of any other scoring tools, neither WOMAC nor KOOS or SF-36, which makes the cultural adaptation and successful translation process of this study questionable. Furthermore, although the authors claim that their results are “in conformity” with the literature, referenced French validation study includes major methodological mistakes that were addressed in a letter to the editor (5). Besides, the Japanese version does not have a reasonable correlation regarding the symptoms domain of the new KSS, because the authors failed to address issues mentioned in a recent study (4). The authors included only one center in their study, which limits the representativeness of the cohort used in this study. Even though the center would be a regional reference institution regarding the uniquely rich cultural and ethnic variabilities in Turkey, a multicenter study should have been considered.
Additionally, authors claim that their version is also aimed at Turkish speaking people living abroad, namely the European Union. This claim, however, requires further investigation because of the cultural settings. It is called external validity. Without investigating the external validity, this claim is not justified.
Last but not least, the psychometrical property is a term used to cover the validation of a scoring tool. Responsiveness is an important and relevant factor in this regard. However, it is not evaluated in this study. Therefore, it must have been inevitably mentioned in the discussion section since scoring tools are meant to reflect the effect of the performed intervention, and responsiveness is one of the major components of the psychometrical properties of a scoring tool.
Conclusion section, unfortunately, includes statements not investigated in this study. Because of the reasons explained above, a correction must be made to this study, whereas also a well-designed and executed new study is needed to validate the Turkish version of the new KSS for preoperative as well as postoperative versions.
Footnotes
Conflict of Interest: The author has no conflicts of interest to declare.
Financial Disclosure: The author declared that this study has received no financial support.
References
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