Relations Between Scalar Shift and Insertion Depth in Human Cochlear Implantation

Objective:The intracochlear position of an electrode array may influence the outcome after cochlear implantation. The design of the electrode array can increase the risk of trauma causing penetration of the basilar membrane or shift of the electrode array into the scala vestibuli. The aim of the present study was to identify a scalar shift after implantation of two different electrode arrays developed by one manufacturer.Study Design:Retrospective analysis.Setting:Tertiary referral center.Patients and Intervention:Cochlear implant recipients implanted between 2010 and 2014 and receiving either a mid-scala (n=30) or a perimodiolar (n=30) electrode array.Main Outcome Measure:Occurrence of scalar shift in association with the electrode type.Results:Scalar shift occurred in 26.7% (8 of 30) of the patients implanted with a perimodiolar electrode array and in 6.7% (2 of 30) of the patients implanted with the mid-scala electrode array. The mean insertion depth in the patients experiencing scalar shift after implantation of the mid-scala electrode was much deeper (21.590.34mm) when compared with the mean insertion depth of the patients with scalar shift after implantation with a perimodiolar electrode array (17.85 +/- 2.19mm). There tends to be a correlation between the cochlear length and the occurrence of a scalar shift. However, the number of patients with scalar shift in the mid-scala group is rather small.Conclusion:Based on the presented data, more patients implanted with a perimodiolar electrode array have a scalar shift when compared with the midscalar electrode array.