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Source: Wikimedia Commons and Nevit Dilment

New Data Increases Concerns Over MAGEC Rod Failure

Tracey Romero • Thu, January 18th, 2018

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Magnetically controlled growing rods have become a popular choice for treatment of early onset scoliosis, however concerns have been raised over reports of metallosis, a type of metal poisoning, around failed MAGnetic Expansion Control (MAGEC) spinal growing rods, a type pf magnetically controlled growing rods.

A study, “Analyses of Explanted Magnetically Controlled Growing Rods from Seven UK Spinal Centers,” which was published in the January 2018 issue of the journal Spine analyzed explanted MAGEC rods to better understand why this is occurring.

After analyzing 34 MAGEC rods from 18 children recruited from seven United Kingdom spinal centers that were explanted for complications like failure of rod lengthening and maximum rod distraction reached, Thomas Joyce, Ph.D., professor of Orthopaedic Engineering, School of Engineering at Newcastle University in the United Kingdom and colleagues found that all 34 MAGEC rods had substantial titanium debris inside.

In addition, 91% of the MAGEC rods showed measurable wear of the extending bar, towards the magnet end. In 74% of the rods, there was also damage to the radial bearing. And in 53% of the rods, O-ring seal failure was observed.

Externally, all the rods showed “growth marks” on the extending bar component which indicated the growth of the rod in vivo.

The researchers wrote, “The combination of high volumes of titanium wear debris alongside O-ring seal damage likely accounts for the metallosis reported clinically around some MAGEC rods. Based on this explant data, a failure mechanism in MAGEC rods due to the natural off axis loading in the spine was proposed.”

Joyce told OTW in an interview, “The natural spine allows motion in many directions. We can bend to the left or the right, lean forwards or backwards, and twist our upper bodies to look to the left or the right. Such complexity is magnified in children with scoliosis, whose spines have not grown as we would expect. MAGEC rods essentially connect the top of the spine to the bottom of the spine. Ideally they allow growth in a straight line. However, scoliotic spines and spines in general are not straight, and this lack of straightness, along with all the natural movements of the spine, produce the off axis loading we refer to in our paper.

He added that he was surprised that all the explanted rods “showed a similar damage mode, despite different implantation times and different implanting surgeons”.

“This damage mode was the external marks which we termed ‘growth marks’, and the internal signs of wear which often resulted in copious amounts of metal wear debris.”

When asked if there was a way to modify the rods to make them safer to use, Joyce said, “The MAGEC rods essentially consist of a solid bar within a tube. In the MAGEC rods we examined, the bar is only supported at the bottom of the tube. If it were to be supported at the top of the tube too, this would minimize the effects of the off axis loading.”

He said, “MAGEC rods have several potential benefits, mostly based around a reduction in the number of surgeries. But they are a new technology that needs to be independently and thoroughly assessed. In this way, surgeons will be able to make a fully informed decision as to the benefits and drawbacks. Our independent research continues and this is one of the next steps we’d advocate, alongside setting up a registry, or registries, so that these spinal implants can be tracked over time and their performance assessed.”

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