Comment on “Robot-Assisted versus Conventional Total and Unicompartmental Knee Arthroplasty: A Meta-analysis of Radiological and Functional Outcomes”

摘要

We read with interest the article “Robot-Assisted versus Conventional Total and Unicompartmental Knee Arthroplasty: A Meta-analysis of Radiological and Functional Outcomes” by Chin et al[1] and appreciate the authors for their work; however, we found that the analysis of some data in this article is not appropriate.The authors used meta-analysis to synthesize the mechanical axis deviation and component angle deviations, which is very innovative, but there are statistical errors. When synthesizing continuous variables into weighted mean difference (WMD), it is not accurate to directly use the difference between an angle and its target value, but to include the absolute value of the difference between this angle and its target value in the calculation.Take the coronal tibial component angle as an example. Assuming that its target value is 90 degrees, and the original data of groups A and B conform to the normal distribution ([Table 1]), then group A is often expressed as 90.2?±?3.83, and group B is often expressed as 91.8?±?0.84. If the WMD is directly synthesized using deviations, that is, 0.2?±?3.83 for group A and 1.8?±?0.84 for group B are used for synthesizing the data, it will be concluded that group A has better control of the coronal tibial component angle. However, the correct method should be as follows: 1). to obtain the difference between each original data and its target value; 2). to obtain its absolute value of the difference; 3). to include the absolute deviation in the calculation. In this way, 3.0?±?1.87 for group A and 1.8?±?0.84 for group B are used for synthesizing the data, and we could reach the conclusion that group B is actually better ([Fig. 1]). Table 1 The coronal tibial component angle of groups A and B Raw data Deviations Absolute deviations Group A ?a1 86.0 86.0–90 |86.0–90| ?a2 87.0 87.0–90 |87.0–90| ?a3 90.0 90.0–90 |90.0–90| ?a4 93.0 93.0–90 |93.0–90| ?a5 95.0 95.0–90 |95.0–90| Mean?±?SD 90.2?±?3.83 0.2?±?3.83 3.0?±?1.87 Group B ?b1 90.5 90.5–90 |90.5–90| ?b2 91.5 91.5–90 |91.5–90| ?b3 92.0 92.0–90 |92.0–90| ?b4 92.5 92.5–90 |92.5–90| ?b5 92.5 92.5–90 |92.5–90| Mean?±?SD 91.8?±?0.84 1.8?±?0.84 1.8?±?0.84 Abbreviation: SD, standard deviation. Fig. 1 The forest plot of coronal tibial component angle. By reading the article and the references it cited, we found that the authors used the above-mentioned direct synthesizing method, and the subsequent results and conclusions are based on this inappropriate statistical method, which needs to be further verified.Publication HistoryArticle published online:24 August 2020? 2020. Thieme. All rights reserved.Thieme Medical Publishers, Inc.333 Seventh Avenue, 18th Floor, New York, NY 10001, USA.