Magnetic Steering of Robotically Inserted Lateral-wall Cochlear-implant Electrode Arrays Reduces Forces on the Basilar Membrane In Vitro

Hypothesis: Undesirable forces applied to the basilar membrane during surgical insertion of lateral-wall cochlear-implant electrode arrays (EAs) can be reduced via robotic insertion with magnetic steering of the EA tip. Background: Robotic insertion of magnetically steered lateral-wall EAs has been shown to reduce insertion forces in vitro and in cadavers. No previous study of robot-assisted insertion has considered force on the basilar membrane. Methods: Insertions were executed in an open-channel scala-tympani phantom. A force plate, representing the basilar membrane, covered the channel to measure forces in the direction of the basilar membrane. An electromagnetic source generated a magnetic field to steer investigational EAs with permanent magnets at their tips, while a robot performed the insertion. Results: When magnetic steering was sufficient to pull the tip of the EA off of the lateral wall of the channel, it resulted in at least a 62% reduction of force on the phantom basilar membrane at insertion depths beyond 14.4 mm ( p < 0.05), and these beneficial effects were maintained beyond approximately the same depth, even with 10 degrees of error in the estimation of the modiolar axis of the cochlea. When magnetic steering was not sufficient to pull the EA tip off of the lateral wall, a significant difference from the no-magnetic-steering case was not found. Conclusions: This in vitro study suggests that magnetic steering of robotically inserted lateral-wall cochlear-implant EAs, given sufficient steering magnitude, can reduce forces on the basilar membrane in the first basilar turn compared with robotic insertion without magnetic steering.