The magnetic attraction of lower extremity external fixators in an MRI suite

Objectives: To determine the magnetic attraction of 10 currently available lower extremity external fixators in the MRI suite and to test fixators with minimal or no magnetic attraction for the presence of temperature elevation during a 30-minute MRI scan. Design: Consecutive testing of selected tibial external fixation models in an identical manner. Setting: Level 1 trauma center. Constructs: Ten commercially available external fixators used for lower extremity injuries applied to saw bone tibia. Intervention: External fixators; suspended in testing apparatus were placed at three locations in the MRI suite for magnetic testing. Fixators with minimal attraction were scanned for 30 minutes. Main Outcome Measurements: Magnetic attraction was measured with a digital scale, and temperature measurements were obtained with a digital thermometer and thermocouple. Results: The llizarov with carbon fiber rings, Richards Hex-Fix, and Large Synthes External Fixator had <1 kg of magnetic attraction at all three locations. No component of these fixators experienced >2degrees of temperature elevation after a 30-minute MRI scan. The EBI Dynafix with Ankle Clamp, EBI Dynafix, and EBI Dynafix Hybrid along with the Hoffman II, Hoffman II Hybrid, llizarov with stainless steel rings, and Synthes Hybrid had >1 kg of magnetic attraction at all three locations. Conclusions: Many commercially available external fixators; have components and spring clamps that have significant magnetic attraction to the MRI scanner. Fixators that have <1 kg of attraction do not experience significant heating during MRL.