Degradation of biodegradable orthopedic screws does (not) elevate tissue heating under Magnetic Resonance Imaging:...

Magnesium (Mg) alloy screws represent promising biodegradable orthopedic implants owing to their biocompatibility, mechanical strength, and gradual resorption, thereby obviating the need for secondary removal surgery. However, their electrical conductivity raises safety concerns during magnetic resonance imaging (MRI) used for the assessment of healing progress and potential complications, where exposure to radiofrequency (RF) energy may induce tissue heating. As Mg implants degrade, evolving geometry and material phase may alter electromagnetic behavior, deposition of RF energy and potential heating. This study systematically examined the effects of key degradation mechanisms-volume reduction, surface roughening, formation of a magnesium hydroxide layer, and implant fractures-on MRI-induced heating. High-resolution electromagnetic field simulations at 3.0 T (ASTM F2182 phantom and realistic human voxel model) were complemented by thermal modeling and experimental MRI heating measurements using real-world screws. Volume loss and edge smoothing reduced maximum 1g-specific absorption rate (SAR_1g) by up to 12%, while surface roughness (RMS = 0.5 mm) reduced SAR1g by -0.28% through increased surface impedance. Degradation layer caused minimal SAR change (<0.5%). Screw fractures increased localized SAR_1g by up to 19.1% but redistributed heat more uniformly across the implant, lowering peak temperatures compared to intact screws. In the human voxel model, fractured screws remained below the IEC safety limits under maximum permissible RF exposure with a maximum temperature elevation of 38.9 °C, whereas non-fractured screws exceeded 40 °C. Our results demonstrate that Mg screw degradation generally mitigates MRI heating risks. In conclusion, engineered degradation features may enhance MRI safety, providing design guidance for next-generation biodegradable orthopedic implants.