Resident Physician Vanderbilt University Medical Center Nashville, Tennessee
Hypothesis: This study evaluated the utility of the pull-back technique in improving perimodiolar positioning of a pre-curved cochlear implant electrode with simultaneous insertion force profile measurement and direct observation of dynamic electrode behavior in a cadaveric cochlea through an intact, semi-transparent basilar membrane.
Background: Pre-curved electrodes with closer proximity to the modiolus have improved outcomes compared to straight electrodes. The effectiveness of the pull-back technique in further improving perimodiolar positioning and the insertion force profile have not been adequately studied.
Methods: The bone overlying the scala vestibuli was removed in 15 fresh cadaveric temporal bones, leaving the scala tympani unviolated. Each specimen was then mounted to a force sensor and robotic insertions of Cochlear532/632 electrodes were performed. Force profiles were obtained during standard insertion, over-insertion, and pullback with simultaneous video recording of the electrode through the semi-transparent basilar membrane.
Results: Standard insertion resulted in a mean peak force of 0.14 N (95% CI 0.10-0.18) and occurred at either sheath insertion (n=11, 73.3%) or complete electrode insertion (n=4, 26.7%). Over-insertion was associated with a peak force of 0.18 N (95% CI 0.14-0.21) which was not significantly higher than standard insertion (P = 0.18). Pull-back had a mean peak force of 0.10 N (95% CI 0.06-0.14), which was significantly lower than standard insertion (P = 0.02). Six temporal bones (40%) demonstrated visibly improved perimodiolar positioning.
Conclusions: Pull-back technique was not associated with significantly higher insertional forces compared to standard insertion. This study demonstrated improved perimodiolar positioning compared to standard insertion in 40% of temporal bones studied.
*Professional Practice Gap & Educational Need: Various electrode insertion techniques have been proposed in order to position the electrode closer to the modiolus, thereby improving postoperative hearing outcomes. Here, we investigate the utility of the pull-back technique in a micro-dissected cadaveric cochlea with simultaneous measurement of force profile and video recording of electrode behavior, allowing for direct observation of the effects of the technique on electrode positioning.
*Learning Objective: For the pre-curved electrode, the pull-back technique may improve perimodiolar positioning. Gentle over-insertion followed by electrode pull-back does not lead to significantly increased forces compared to standard insertion.
*Desired Result: Cochlear implant surgeons should consider using the pull-back technique when inserting pre-curved electrodes. The technique involves a gentle over-insertion followed by pulling the electrode back to the standard insertion depth to achieve close contact of the electrode with the modiolus.