The perceived angle of the round window affects electrode insertion trauma in round window insertion – an anatomical study

Abstract Conclusion: In this study round window (RW) insertion of cochlear implant was performed with a lower degree of trauma in 86.6% of cases. Therefore RW insertion is a valid option to be considered in selected cochlear implant patients, especially when hearing preservation is a goal. In most cases drilling of the overhangs is required. Objectives: To systematically examine the potential for minimizing electrode insertion trauma with RW insertion. Methods: Fifteen temporal bones were inserted with a 0.5 mm electrode analog in an anterior or antero-inferior vector from a reference point along the facial recess. Surface preparation of the inferior segment of the basal turn was performed and the point of first contact was analyzed using computerized morphometric software. The same software was used to measure the RW dimensions before and after drill down of the bony overhangs. An insertion was considered ‘traumatic’ if the point of first contact was the medial wall of the scala, whereas ‘less traumatic’ was an insertion in which the point of first contact was the inferior or posterior wall of the scala. Results: Less traumatic insertion was achieved in 13 of the 15 bones, and in these the mean RW angle, as observed from a surgical point of view, was 137°. The mean RW angle in the traumatic insertion group was 147°. The difference was statistically significant.