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Clin Orthop Relat Res (2019) 477:2613-2614 DOI 10.1097/CORR.0000000000000988
Letter to the Editor
Published online: 1 October 2019Copyright © 2019 by the Association of Bone and Joint Surgeons
Reply to the Letter to the Editor: Translation and Validation of
the German New Knee Society Scoring System
Mahmut Enes Kayaalp MD, Ronald Becker MD, PhD
To the Editor,
We thank Mr. ¨Ozden for giving us the
opportunity to more comprehensively
introduce our work, in which we trans-lated and validated the new Knee Society
Score (KSS) in German [5]. There are
several very interesting comments we will address on a point-by-point basis.
In his letter, Mr. ¨Ozden noted that
we should not have used the WOMAC as a scoring tool to comparatively an-alyze the new KSS in terms of con-struct 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
con-sistency 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 ac-cepted 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 ques-tionnaire. 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. ¨Ozden 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 antic-ipated, as a similar result had been
previously observed by others [6],
which we noted in our paper [5].
We agree with Mr. ¨Ozden’s second
comment, that long questionnaires may burden patients. As discussed in our
paper:“like in all adaptation and
vali-dation studies, patients had to complete three separate scoring tools simulta-neously, 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 patient-reported outcomes questionnaire; more detail can be informative, but too much can represent an unreasonable
imposi-tion 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 re-garding 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 Sys-tem. 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 con-sultancies, 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 writ-ers, and do not reflect the opinion or policy of CORR®or The Association of Bone and Joint Surgeons®.
M. E. Kayaalp, Department of Orthopaedics and Traumatology, Cerrahpasa Faculty of Medicine, Istanbul University, Istanbul, Turkey
R. Becker, Department of Orthopaedics and Traumatology, University Hospital Brandenburg, Medical School Brandenburg Theodor Fontane, Brandenburg an der Havel, Germany
M. E. Kayaalp MD (✉), Department of Orthopaedics and Traumatology, Istanbul University-Cerrahpasa Faculty of Medicine, Kocamustafapasa Cd. 53, 34098 Istanbul, Turkey, Email: mek@mek.md
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Re-lated Research®editors and board members are onfile with the publication and can be viewed on request.
strength and is sometimes overlooked in the Turkish, Japanese and French
vali-dation studies of the new KSS [3, 4, 9].
The most important aspect in this regard is to include a sufficiently strong sample size for internal consistency as well as test-retest reliability.
Although it was thoroughly
explained in our paper [5], it must be
noted that there is no general consensus regarding the sample size to validate a
scoring tool [1]. However, it is
rec-ommended to include at least 100
patients for internal consistency [10].
Recommendations vary between two
to 20 patients per item [1, 2, 7],
al-though the author quoted only one book chapter, which recommended 10
patients per item [9]. Even if this would
be a rule, as the author suggested, other than a recommendation, our study would still be powerful enough with 100 patients, because 10 patients per item suggestion would be met consid-ering the domains of the new KSS. It should not be forgotten, that our anal-ysis was on domain scores as
sug-gested by Noble and colleagues [8], not
on total scores. Therefore, a total number of items is of less importance compared to patients per items in in-dividual domains. Additionally, con-sidering the test-retest reliability, our sample size was more than adequate for the analyses we performed as also
explained with detail in our paper [5].
Statistical power doesn’t depend on sample size alone but also on the study design. Evaluating the same patients in the pre- and post-operative periods
allow for a more-consistent analysis, since these studies are psychometrical
studies performed on individual
patients. This is more important in the case of the new KSS because the scoring tool has two separate forms for pre- and post-operative patients. Al-though some validation studies
over-looked this detail [9], we performed
separate analysis for both forms, which ensures an additional strength to our study. Therefore, the concern about the sample size cannot be applied to our study.
Finally, the reverse correlation be-tween the mental health and vitality domains of SF-36 with the symptoms domain of the new KSS caused some concern. However, as mentioned in our paper, these results were anticipated. Similar results were also previously
reported [8, 11], and referenced in our
paper [5].
References
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2. Hair JF, Anderson RE, Tatham RL, Black WC. Multivariate Data Analysis with Readings. Tulsa, OK: Petroleum Pub-lishing; 1995.
3. Kayaalp ME. Comment on: “French adaptation of the new Knee Society Scoring System for total knee arthro-plasty” by Debette C., Parratte S., Mau-cort-Boulch D., Blanc G., Pauly V., Lustig S., Servien E., Neyret P.,
Argenson JN. Orthop Traumatol Surg Res. 2014;100:531-534.
4. Kayaalp ME. Comment on Hamamoto et al.: Cross-cultural adaptation and vali-dation of the Japanese version of the new knee society scoring system for osteoar-thritic knee with total knee arthroplasty. J Orthop Sci. [Published online ahead of print June 17, 2019]. DOI:10.1016/j.jos. 2019.05.008.
5. 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: 383-339.
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London: Academic Press; 1979. 8. Noble PC, Scuderi GR, Brekke AC,
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9. ¨Ozden F, Tu˘gay N, Umut Tu˘gay B, Yalın Kılınç C. Psychometrical properties of the Turkish translation of the new knee society scoring system. Acta Orthop Traumatol Turc. 2019;53:184-188. 10. Terwee CB, Bot SD, de Boer MR, van der
Windt DA, Knol DL, Dekker J, Bouter LM, de Vet HC. Quality criteria were proposed for measurement properties of health status questionnaires. J Clin Epi-demiol. 2007;60:34-42.
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2614 Kayaalp & Becker Clinical Orthopaedics and Related Research®
