Lower Extremity Injury Rates on Artificial Turf Versus Natural Grass Playing Surfaces: Letter to the Editor

Dear Editor:

We are writing to express our concerns regarding the recently published article titled, “Lower Extremity Injury Rates on Artificial Turf Versus Natural Grass Playing Surfaces: A Systematic Review.” ² We highly appreciate the diligent effort invested into conducting a systematic review on this important topic. However, we kindly suggest that certain aspects be taken into consideration that might limit the clarity, reliability, and validity of the article’s conclusions.

First, and most important, the article lacks information on effect sizes, their statistical significance, and the sample size of the included studies. Reporting this information for each included study would be valuable for prioritizing certain results for summary and synthesis. ¹ Therefore, including effect sizes, statistical significance and sample size of the studies would contribute considerably to enhance interpretability of the summarized findings, limit risk of bias, and enhance transparency.

Our second point of concern is the risk of bias assessment for the included studies. A more recent systematic review and meta-analysis on injuries sustained on artificial turf compared with grass found that the risk of bias was a pervasive issue. ³ We deeply value the reporting of the level of evidence and assessment of the cohort selection processes. However, it would have been beneficial if the authors had reported the cohort selection process for each study and preferably used a more comprehensive quality assessment of the included studies, such as the ROBINS-I (Risk of Bias in Nonrandomized Studies–of Interventions) tool. ⁵ A thorough evaluation of the risk of bias would have provided valuable insights into the quality and potential sources of bias in the literature.

Moreover, when results are summarized in the figures and the Results section, the relevant studies are not cited. This omission makes it challenging to locate and verify the articles mentioned and hinders interpretation of the presented results. For instance, in Figure 6 and the Results section, we are unable to determine which of the included studies report comparable injury rates between the old generation turf type and natural grass. In addition to the previously mentioned lack of reporting of relevant statistical data, such as effect and sample sizes, the lack of citations in the reporting of results limits the possibility to draw meaningful conclusions based on the summarized studies.

Furthermore, the authors argue that they did not conduct a meta-analysis because of heterogeneity of the included studies. However, they do not report an estimate of the suspected heterogeneity. Reporting the results of heterogeneity analyses would have offered readers the possibility of checking whether the observed heterogeneity between characteristics of individual included studies would also reflect statistical heterogeneity between the results from individual studies. The reporting of heterogeneity statistics would have increased transparency and reinforced the decision not to conduct or interpret results from meta-analysis. Moreover, given the large number of included studies, it might have been possible to conduct meta-analyses within smaller subsets of studies, that were considered similar enough for data synthesis. ¹ Subgroup analyses could have mitigated heterogeneity and might have provided important insights into the effect estimates within specific subgroups of studies.

Additionally, although the authors state that the systematic review was conducted according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, ⁴ they do not provide specific reasons for exclusion of full-text articles. This omission hinders the transparency of the study methodology.

Finally, the authors acknowledge in the Discussion section that their study should be interpreted as a “global snapshot of the literature.” We fully agree with the authors that “a more comprehensive overview of the literature may provide valuable information.” However, considering our earlier mentioned concerns, we believe that the lack of specific and quantified results diminishes the practical implications and relevance of the presented findings. Including more comprehensive and specific information from the analyzed studies would have greatly enhanced the usefulness and applicability of the results.

We sincerely appreciate the authors’ efforts in conducting this systematic review. However, we identified relevant flaws in the conduct and reporting of this systematic review that considerably limit interpretation of the results and prevent a deeper understanding of injuries on different playing surfaces.

M. Oudmaijer, BSc O. Koolen, BSc L. van der Meij, BSc S. Kloprogge, MSc H. Gerger, PhDRotterdam, the Netherlands