Magnetic Resonance Imaging (MRI) is a commonly accepted and widely used diagnostic medical procedure. It is often safe to perform MRI on an individual that has an orthopaedic implant device. The main issues affecting the safety of passive implants (medical devices that serve their function without the supply of power) in the MR environment involve magnetically induced displacement force and torque and radio frequency (RF) induced heating. The MR static field induces displacement forces and torques on ferromagnetic materials. However, both ferromagnetic and non-ferromagnetic metallic devices of certain geometries may experience heating caused by interactions with the RF field. Of secondary concern is the possibility of image artefacts that can compromise image quality.
Zimmer metallic implants are manufactured using one or more of the following non-ferromagnetic materials: commercially pure titanium (CP Titanium), Ti-6Al-4V alloy, Ti-6Al-7Nb alloy, several Co-Cr alloys (ASTM F75, F562, and F90), tantalum (Trabecular Metal™ Material), and the following implant grade stainless steels: 316L, REX 734, 22-13-5 and Biodur 108. Zimmer’s internal testing has revealed that although each metallic material exhibits a small but measurable magnetic attraction in the 1.5 Tesla and 3.0 Tesla environments, the maximum magnetic force exerted on a device (stainless steel) is less than 25% of the force exerted on the device due to gravity (Ref. Zimmer Research Report_WA_2179_10_Rev.1). None of the metallic materials exhibited any torque movement in 1.5 Tesla and 3.0 Tesla MR environments. Therefore, no movement or deflection of Zimmer devices manufactured from the aforementioned metallic materials is expected in 1.5 Tesla and 3.0 Tesla MR environments.
The polymer (plastic) and ceramic materials used in the manufacture of some Zimmer implants are non-metallic and non-ferromagnetic and pose no risk of movement or deflection due to exposure to the MR environment.
In regards to RF induced heating, one recent publication states “…..to date, there has been no report of a patient being seriously injured as a result of excessive heat that developed in a "passive" metallic implant or device. However, heating is potentially problematic for implants that have an elongated shape or those that form a conducting loop of a certain diameter” (Ref. F. G. Shellock, “Reference Manual for Magnetic Resonance Safety, Implants, and Devices”, 2008 edition, pg:136). The RF induced heating of Zimmer implants is currently being tested and the results will be made available upon completion.
Patients should note that there are several different manufacturers and generations of MRI systems available, and Zimmer cannot make any claims regarding the safety of Zimmer implants and devices with any specific MR system.
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