Safety of orthopedic implants in magnetic resonance imaging: an experimental verification.

Magnetic resonance imaging (MRI) is an indispensable tool for musculoskeletal imaging. The presence of metal, however, raises concerns. The potential risks are loosening and migration of the implant, heating of the metal with surrounding tissue, causing thermal damage, and artifactual distortion which compromise the diagnostic value of the procedure. The aim of this study was to test experimentally the nature and extent of the first two of these effects in orthopedic implants. The degree of ferromagnetism was evaluated by deflection studies at the portals of a 0.25 Tesla permanent magnet and 1.0 Tesla clinical MRI scanner. None of the orthopedic implants exhibited any attraction. External fixator clamps, however, showed significant ferromagnetism. The heating of implants by "worst-case" scenario imaging sequences was insignificant. Many contemporary nonferromagnetic orthopedic implants can be imaged safely. It is prudent, however, to perform ex vivo deflection studies on a duplicate implant to confirm MR compatibility. With external fixator devices exhibiting strong ferromagnetism, MRI should be avoided. With expanding indications for MRI, orthopedic implants are unlikely to limit the potential of this powerful tool.