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A limited number of magnetically adjustable appliances are used in pediatric orthopedics to treat deformities of the spine and extremities.
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Magnetically Controlled Spine Growing Rods
These spinal distraction rods are designed for children with early onset scoliosis. Only a single such device is currently manufactured: the MAGEC® (MAGnetic Expansion Control) Spinal Deformity System (NuVasive).
Either single or dual rods may be implanted. The rods have an expansion device in their mid-portions containing a ratchet apparatus moved by neodymium magnets. The rod can be lengthened using an external magnetic remote controller placed over the spine. The MAGEC® rod is FDA- and CE-mark approved and rated MR Conditional at 1.5T only. Its magnets will create a substantial artifact, however, obscuring most of the chest. A second spine magnetic growing rod, the Phénix™, was implanted primarily in Europe and Australia between 2005 and 2015, having never received FDA approval. The company closed with the death of the inventor, but some legacy rods may occasionally be encountered. They are considered MR Unsafe. |
MAGEC® Spinal Growing Rods (from Cheung under CC-BY)
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Magnetic Limb Expandable Rods
The only currently produced device in this category is the PRECICE® System by NuVasive. It is intended for limb lengthening, fracture fixation, pseudarthrosis, mal/non-unions of long bones. Although labelled as MR Unsafe by the manufacturer, its mechanism and construction is nearly identical to the MR Conditional MAGEC®. Experimental testing shows the PRECICE® to have no safety concerns in 1.5T and 3.0T environments, so hopefully this restriction will be lifted in the future.
Two other interesting and promising magnetic expander devices for limb salvage surgery have been produced over the last decade — the MR Conditional REPIPHYSIS® (Wright Medical Technologies) and the MR Unsafe JTS® Extendible Implant (Stanmore Implants, UK). However, both companies have been acquired by Stryker during the last several years, and it appears a business decision has been made to discontinue their production. Legacy devices may rarely be encountered in practice.
References
Budd HR, Stokes OM, Meakin J, et al. Safety and compatibility of magnetic-controlled growing rods
and magnetic resonance imaging. Eur Spine J 2016; 25:678-582. [DOI LINK]
Cheung JPY, Cheung KMC. Current status of the magnetically controlled growing rod in treatment of early-onset scoliosis: What we know after a decade of experience. J Orthop Surg 2019; 27:1-10. [DOI LINK]
Gomez C, Nelson S, Speirs, Barnes S. Magnetic intramedullary lengthening nails and MRI compatibility. J Pediatr Orthop 2018; 38:e584-e587. [DOI LINK]
Ogg RJ, McDaniel CB, Wallace D, et al. MR safety and compatibility of a noninvasively expandable total-joint endoprosthesis. Magn Reson Imaging 2005; 23:789-794. [DOI LINK]
Budd HR, Stokes OM, Meakin J, et al. Safety and compatibility of magnetic-controlled growing rods
and magnetic resonance imaging. Eur Spine J 2016; 25:678-582. [DOI LINK]
Cheung JPY, Cheung KMC. Current status of the magnetically controlled growing rod in treatment of early-onset scoliosis: What we know after a decade of experience. J Orthop Surg 2019; 27:1-10. [DOI LINK]
Gomez C, Nelson S, Speirs, Barnes S. Magnetic intramedullary lengthening nails and MRI compatibility. J Pediatr Orthop 2018; 38:e584-e587. [DOI LINK]
Ogg RJ, McDaniel CB, Wallace D, et al. MR safety and compatibility of a noninvasively expandable total-joint endoprosthesis. Magn Reson Imaging 2005; 23:789-794. [DOI LINK]
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