Mechanisms of electrode fold-over in cochlear implant surgery when using a flexible and slim perimodiolar electrode array.

OBJECTIVES: This study evaluates the design of a thin perimodiolar cochlear implant electrode array (CI532) and assesses insertion-related rotation and fold-over.

METHODS: The study consisted on a cochlear model and temporal bone insertion studies. Twenty insertions were studied, under four different surgical insertion conditions in vitro, the intracochlear disposition of the electrode array and presence of tip fold over were recorded. Also, eight fresh human temporal bones were studied after insertion in two conditions: correct alignment of the electrode array during the insertion and misaligned. These surgical situations were investigated within this study using a video recording of the dynamics of insertion techniques and X-ray, including fluoroscopy, Cone Beam CT, and digital imaging analysis.

RESULTS: For electrodes inserted with a correct surgical technique, the placement was perfect, within the scala tympani. The wrapping factor was 0.53, and the perimodiolar distance was below 0.3 mm, with a mean insertion depth of 405°.

CONCLUSIONS: A perimodiolar position can be achieved with the new CI532 electrode array. The new electrode also seems to be reliable for atraumatic intracochlear placement in scala tympani (ST).