The rationale for FLEX (cochlear implant) electrode with varying array lengths

Abstract

With cochlear implantation (CI) being the standard of care for profoundly deaf cases, more and more patients with low frequency residual hearing are currently being treated with CI. In view of preserving the residual hearing, the ultimate aim of both the surgeons and the CI companies is to achieve zero-degree of electrode insertion trauma. Variations in the size and shape of cochlea, cross-sectional dimensions of ST, electrode insertion techniques with and without metal stylet rod and the experience level of the operating surgeons, all play a role in the electrode array related insertion trauma. An effective electrode design must include flexible array to accommodate the cochlear shape variation, electrode with variety of array lengths to support the concept of cochlear size specific electrode array and finally smaller cross-sectional dimensions of electrode array in matching the cross-sectional dimensions of ST. As per published reports, FLEX electrode array design offers minimal degree of electrode insertion trauma along with the possibility of patient specific electrode array length matching their cochlear size. Looking at the cross-sectional dimensions of FLEX electrode array along with its volume, it appear to be highly safe to the cochlea by not taking too much volume inside the ST. To offer additional support, otological pre-planning software tool like OTOPLAN is now clinically available in measuring the cochlear size in finding the best electrode array match along with the possibilities of anatomy based post-operative speech processor fitting.

Finite Element Modeling of Residual Hearing after Cochlear Implant Surgery in Chinchillas

“…It is desirable to create longer electrodes as they allow the patient to sense a wider range of frequencies more effectively [8,46]. Results from this study support the theory that cochlear implants can have minimal effect on the mechanics of the basilar membrane, even when inserted into the apex of the cochlea.…”

“…However, it is also known that CI surgery can cause varying levels of trauma or cochlear obstruction that affect the residual mechanical function of the inner ear [7]. The magnitude of this disruption could be partially dependent on the insertion depth of the implant [8,5].…”

Morphometric Analysis and Linear Measurements of the Scala Tympani and Implications in Cochlear Implant Electrodes

“…Detailed manufacturing information regarding the linear length at which each stimulating electrode was positioned, as well as the height and width at each stimulating electrode position, was obtained directly from Cochlear Limited for the Slim Modiolar and Slim Straight electrodes. Identical information for the MED-EL FLEX 28 was gathered from a review by Dhanasingh in 2021 (24).…”

Recent Advances in Cochlear Implant Electrode Array Design Parameters

“…Their placement in the cochlea and their inability to totally cover the human hearing range are among the biggest issues. Due to limited number of electrodes and channels of conventional CIs (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), further research on integrating more channels should be carried out [121]. Channel interactions occur when adjacent electrodes are too close to each other; therefore, increasing the number of stimulations has been considered unnecessary, and it has been propounded that using more than eight channels is not effective on speech perception [121].…”

“…However, current CIs have limitations regarding the stiffness of the electrode arrays, having an insufficient number of electrodes, and providing a sub-optimal hearing experience [ 10 , 11 ]. Recent work on improving these concerns enabled CI designs that can provide a personalized sound experience [ 12 , 13 , 14 ]. Although electrode arrays and electrode materials vary between different designs, electrode shapes remain the same, mainly being square, rectangular, and spherical [ 9 ].…”