Considerations for design of future cochlear implant electrode arrays: Electrode array stiffness, size,

Abstract

Abstract-The level of hearing rehabilitation enjoyed by cochlear implant (CI) recipients has increased dramatically since the introduction of these devices. This improvement is the result of continual development of these systems and the inclusion of subjects with less severe auditory pathology. Developments include advanced signal processing, higher stimulation rates, greater numbers of channels, and more efficient electrode arrays that are less likely to produce insertion damage. New directions in the application of CIs, particularly in combined acoustic and electrical stimulation, and increasing performance expectations will place greater demands on future electrode arrays. Specifically, the next generation of arrays must be reliably inserted without damage, must maintain residual acoustic function, and may need to be inserted more deeply. In this study, we measured the mechanical properties of eight clinical and prototype human CI electrode arrays and evaluated insertion trauma and insertion depth in 79 implanted cadaver temporal bones. We found that the size and shape of the array directly affect the incidence of observed trauma. Further, arrays with greater stiffness in the plane perpendicular to the plane of the cochlear spiral are less likely to cause severe trauma than arrays with similar vertical and horizontal stiffness.

The Effects of Insertion Speed on Inner Ear Function during Cochlear Implantation: A Comparison Study

“…There are a number of variables related to hearing preservation that need to be clarified and investigated. These variables include electrode design, the use of hair cell protection, electrode insertion depth and the method of electrode insertion, which should be as atraumatic as possible [Ishii et al, 1995;Roland et al, 2005;Rebscher et al, 2008;Verbist et al, 2009]. Until recently, the electrode insertion speed and its impact on insertion characteristics has not been examined in detail, especially in the clinical setting [Majdani et al, 2010].…”

Cochlear Implants: System Design, Integration, and Evaluation

“…In many cases this damage results in decreased coupling efficiency and inconsistent channel-to-channel performance. Analysis of the forces that affect the occurrence of trauma and the angle at which an electrode contacts tissue have identified two primary mechanisms of injury [121][122][123][124][125][126]. First, damage most frequently occurs as a straight electrode, or curved electrode held on a stylet, contacts the outer wall of the scala tympani as it spirals away from the round window or cochleostomy through which the electrode was inserted.…”

“…In our trials at UCSF surgeons have observed little resistance to insertion and were confident that the electrodes were implanted with little or no trauma. Particularly in cases with the Advanced Bionics HiFocus™ electrode with positioner, subsequent dimensional analysis [127,149 ] and temporal bone evaluations indicate that many, or most, of these insertions exceeded the depth at which the electrode and positioner could be located without trauma. This disparity indicates that it is very difficult to sense the level of resistance that signals the initiation of injury with a large tapered electrode carrier.…”

Radiologic and Functional Evaluation of Electrode Dislocation from the Scala Tympani to the Scala Vestibuli in Patients with Cochlear Implants

“…Rebscher et al, 15 who tested the insertion damage in correlation to the stiffness of 8 different models of electrode arrays, showed that electrode arrays with proportionately greater stiffness in the vertical plane were less likely to produce severe trauma during insertion. Severe damage, defined as an electrode array dislocation from the scala tympani into the scala media or scala vestibuli, varied in straight electrodes from 0% to 37.5% and in spiral types from 0% to 38.9%.…”

“…Electrode arrays designed to position stimulating contacts near the modiolus appear to operate with lower current thresholds than previous devices that were located closer to the lateral wall of the scala tympani. [15][16][17] The charge units of maximum comfortable loudness level of the 2 groups were compared to determine whether an electrode dislocation was associated with higher stimulus charges.…”