Dynamic Behavior and Insertional Forces of a Precurved Electrode Using the Pull-Back Technique in a Fresh Microdissected Cochlea

Abstract

Hypothesis This study evaluated the utility of the pull-back technique in improving perimodiolar positioning of a precurved cochlear implant (CI) electrode array (EA) with simultaneous insertion force profile measurement and direct observation of dynamic EA behavior. Background Precurved EAs with perimodiolar positioning have improved outcomes compared with straight EAs because of lowered charge requirements for stimulation and decreased spread of excitation. The safety and efficacy of the pull-back technique in further improving perimodiolar positioning and its associated force profile have not been adequately demonstrated. Methods The bone overlying the scala vestibuli was removed in 15 fresh cadaveric temporal bones, leaving the scala tympani unviolated. Robotic insertions of EAs were performed with simultaneous force measurement and video recording. Force profiles were obtained during standard insertion, overinsertion, and pull-back. Postinsertion CT scans were obtained during each of the three conditions, enabling automatic segmentation and calculation of angular insertion depth, mean perimodiolar distance (M avg), and cochlear duct length. Results Overinsertion did not result in significantly higher peak forces than standard insertion (mean [SD], 0.18 [0.06] and 0.14 [0.08] N; p = 0.18). Six temporal bones (40%) demonstrated visibly improved perimodiolar positioning after the protocol, whereas none worsened. M avg significantly improved after the pull-back technique compared with standard insertion (mean [SD], 0.34 [0.07] and 0.41 [0.10] mm; p < 0.01). Conclusions The pull-back technique was not associated with significantly higher insertional forces compared with standard insertion. This technique was associated with significant improvement in perimodiolar positioning, both visually and quantitatively, independent of cochlear size.