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How much does depth matter? Magnetically controlled growing rod distraction directly influenced by rod tissue depth



Magnetically controlled growing rod (MCGR) for the treatment of early-onset scoliosis (EOS) is a relatively innovative technique. MCGR benefits over traditional growing rods are known but limitations and complications are being revealed. The purpose of this study was to examine the importance of tissue depth on rod lengthening.


A single-institution retrospective review of 72 MCGR patients was performed. Ultrasound measured rod distraction. Differences in programmed and actual distraction, and complications were recorded. Tissue depths and achieved length were averaged and used to construct a regression to account for variability.


Percentage of std and offset orientation rod lengthening relative to the programmed distraction was inversely proportional to rod depth (std R = 0.50, p = 0.002) (offset R = 0.60, p < 0.001). Expected std rod lengthening achieved decreased by 1.46%/mm depth. Expected offset rod lengthening achieved decreased by 1.68%/mm depth. 28 pts (38.9%) sustained complications. Age, sex, BMI, standard tissue depth, and/or offset tissue depth had no predictive ability with respect to complications sustained (overall model R = 0.31, p = 0.36).


In a series of EOS surgical patients treated with MCGRs, the relationship between percentage of programmed lengthening achieved as well as total lengthening was inversely proportional to tissue depth of the rod. There was a trend towards increasing frequency of complications recorded with decreasing tissue depth though this was not significant. These data can help with surgical planning during MCGR placement.

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No funding was required. This was part of routine care.

Author information




CS: study conception and design, data analysis, manuscript draft, commented on previous versions of the manuscript, read and approved the final manuscript. SG: study conception and design, Material preparation, data collection, commented on previous versions of the manuscript, read and approved the final manuscript. VJ: study conception and design, commented on previous versions of the manuscript, read and approved the final manuscript. PS: study conception and design, commented on previous versions of the manuscript, read and approved the final manuscript.

Corresponding author

Correspondence to Peter F. Sturm.

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Ethical approval

This research study was conducted retrospectively from data obtained for clinical purposes. We consulted extensively with the IRB of Cincinnati Children’s Hospital Medical Center who determined that our study did not need ethical approval. An IRB official waiver of ethical approval was granted from the IRB of Cincinnati Children’s Hospital Medical Center.

Conflict of interest

The authors have no conflict of interest. Dr. Sturm reports other support from DePuy, a Johnson and Johnson Company, Nuvasive, and Green Sun Medical, outside the submitted work.

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As this was a retrospective chart review of routine care, no informed consent was required.

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Seidel, C.P., Gilday, S.E., Jain, V.V. et al. How much does depth matter? Magnetically controlled growing rod distraction directly influenced by rod tissue depth. Spine Deform (2021).

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  • Scoliosis
  • Magnetic growing rods
  • Early-onset scoliosis
  • Tissue depth