Safety and image artifact of external fixators and magnetic resonance imaging.

External fixators commonly used in orthopaedic trauma and reconstruction may pose a potential safety hazard to patients exposed to magnetic resonance imaging. This interaction with the scanner depends on fixator composition, magnetism, and geometry. Image artifact produced by devices during scanning may diminish the diagnostic quality of the image. A mail survey of 91 radiologists' and 167 radiological technologists' current practices identified an absence of consensus regarding protocols for scanning patients who had external fixators in place. Eighteen external fixators were tested. Force was measured during exposure to the magnetic field at 30 cm from the magnetic resonance imaging portal, at the portal, and 30 cm inside the portal. The recordings ranged from 0 to 2.2 kg. Three fixators did not generate measurable forces and therefore are considered safe for the magnetic resonance imaging based on previously published safety standards. Ten devices did not produce measurable forces until placed at the portal, indicating that these fixators may be considered safe, providing the scanned area is distant to the fixator. To investigate image artifact, the fixators were placed on a phantom model and scanned. There was substantial variation among the fixators and image quality produced, depending on fixator composition and geometry.