Computational study of the effects of orthopedic plates on gradient-induced peripheral nerve stimulation under MRI using electromagnetic and neurophysiological modeling.

PURPOSE: This study investigates the impact of orthopedic plates on peripheral nerve stimulation (PNS) during MRI, focusing on how the presence of implants affects PNS thresholds.

METHODS

A combination of anatomical electromagnetic and neurophysiological modeling was utilized. Electromagnetic fields in human body models were simulated, both with and without orthopedic plates. Simulations were performed under x-, y-, and z-axis gradient coils, with plates implanted at two clinically relevant locations. Nerve responses were modeled using an established neurophysiological model.

RESULTS

The presence of orthopedic implants significantly influenced nerve stimulation, leading to reductions in stimulation thresholds of up to 80%. Some of the reduced thresholds were close to the PNS limits outlined in International Electrotechnical Commission (IEC) 60601-2-33, suggesting a considerably reduced safety margin compared to cases without implants.

CONCLUSION

Orthopedic implants can substantially lower the activation thresholds of nearby nerves, with some thresholds approaching the PNS limits defined in IEC 60601-2-33 for MRI gradient field. This finding indicates a reduced safety margin for patients with implants, highlighting the need for more comprehensive safety assessments.