Magnetically Controlled Growing Rods: Influence on Intraoperative Fluoroscopic Imaging

Abstract

Case: A 7-year-old boy with severe congenital scoliosis and impending thoracic insufficiency syndrome underwent uneventful single magnetically controlled growing rod (MCGR) insertion and removal of his ipsilateral rib-based distraction implants at our institution. Intraoperative fluoroscopy imaging revealed an artifactual bend (S-distortion) of the rod actuator after placement. This artifact was eliminated by moving the image intensifier further from the patient. Conclusion: We attributed the S-distortion to influences of magnetic fields within the MCGR actuator onto the image intensifier. Surgeons should be aware of such implications which can lead to misleading imaging artifacts. This is a first reported case of such incident with MCGR.

Quantitative assessments of image intensifier distortion induced by weak (Sub‐Gauss) magnetic fields during fluoroscopically‐guided procedures

“…9 It is noteworthy that if the implant material contains a magnet component, such as the actuator in magnetically controlled growing rods (MCGRs), 10 the implant material will cause S-distortion in the II-produced images. 11 The S-distortion associated with Siemens Arcadic Orbic II model is smaller than the S-distortion associated with GE OEC 9900 Elite II model, while no measurable variation is found within a model, suggesting that the two II models have different designs in internal magnetic shielding. According to the technical specifications of these II models, internal mu-metal shielding is always installed in Siemens Arcadic Orbic II, while it is optional for GE OEC 9900 Elite II and likely not selected for our units.…”

“…However, the amount and pattern of S‐distortion should vary with the rotation angle of C‐arm because the impact of the magnetic force on electrons’ path would change 9 . It is noteworthy that if the implant material contains a magnet component, such as the actuator in magnetically controlled growing rods (MCGRs), 10 the implant material will cause S‐distortion in the II‐produced images 11 …”