Reduction of Insertion Trauma within Patients Implanted with a HiFocus Mid-Scala Electrode Array after Slowing Down Insertion Speed

Background. Minimizing intra-cochlear trauma is important in cochlear implantation in order to preserve residual hearing and to create optimal conditions for transmission of electric information to the neural structures. Cochlear morphology, physical properties of the array as well as surgical techniques are all likely to influence the amount of insertion trauma. In January 2015 a change of surgical procedure, meaning slowing down the insertion speed to 25 seconds or more, was implemented in our institution, based on new data showing a correlation between insertion speed and intra-cochlear pressure.

Objective. To evaluate the incidence of scalar translocation of HiFocus MS electrode arrays and the effect of insertion speed and surgical approach on insertion trauma.

Methods. The intra-cochlear position per electrode contact of 208 patients implanted with a HiFocus MS electrode array, were evaluated on spatially synchronized midmodiolar cross-sections of pre- and post-operative CT-images. A comparison of translocation rate was made between fast (25 seconds or less between markers) or slow insertions, and between pure and extended round window surgical approaches.

Results. A translocation rate of 25% (28/112) was found in the fast-implanted group against 11,5% (11/96) in the slow-implanted group (p = 0.013). From the 41 pure round window insertions, scalar translocations were found in 14 cochleae (34,1%). Inserted through an extended round window approach resulted in 25 of the 169 cochleae (14,8%), p = 0.006.

Conclusions. Insertion of a HiFocus Mid-Scala electrode array in 25 or more seconds or the use of an extended round window approach reduces intra-cochlear trauma.