Thank you for your letter. We certainly agree with your underlying concern about the length of follow-up being relatively short, however, this is the nature of a new technology that had only been approved for use in the United States (where nearly all cases were derived from) for 5 years at the time of data collection. As the number of MCGR cases has increased every year since 2013, the average follow-up time was less than the 2.5 years that might be expected if the case rate was constant. We acknowledged in the published paper that the two major limitations of this study were the short follow-up and the unexpectedly low rate of rod fracture, leading to concern about lack of reported complications in the registry, and any conclusions are tempered by these limitations. Additionally, as you suggest, looking at the impact of failure to lengthen as a modifier of these outcomes would be interesting, but this data are not readily available for all patients in the registry. Certainly, repeating this study with longer follow-up will be important as we move forward.
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Roye, B., Marciano, G., Matsumoto, H. et al. Author’s response to letter to the editor regarding “Is rod diameter associated with the rate of rod fracture in patients treated with magnetically controlled growing rods?”. Spine Deform (2021). https://doi.org/10.1007/s43390-021-00355-x