In Vivo Imaging of Cochlear Implant Electrode Orientation Relative to Scalar Tilt

Visualization of cochlear implant (CI) electrode contact position offers insights into electrode-cochlea biomechanics. Prior in vivo imaging studies have assessed electrode distances to a fixed modiolar axis, but electrodes' orientation within the cochlear canal and their relationship to the scala tympani's dynamic anatomical tilt have not been investigated. This study employed in vivo flat-panel computed tomography (FPCT) imaging to examine the flexibility and dynamic behavior of lateral wall arrays.

This retrospective cohort study included eight MED-EL FLEX28 CI users. FPCT images were acquired, and reconstructions were aligned to a standardized cochlear coordinate system. Vectors perpendicular to electrode contacts were used to estimate contact orientation using mid-modiolar image slices and 3D renderings. Anatomical landmarks were used to calculate scalar tilt.

A significant correlation was observed between scalar tilt and contact orientation (r = -0.44, p < 0.0001). The scala tympani exhibited its greatest tilt relative to the X-Y plane in the hook region, then transitioned to a parallel orientation at approximately 180° angular depth before increasing tilt again between 180° and 360°. Electrode arrays demonstrated rotational alignment with the scala between 180° and 360° angular insertion depth.

Flexible lateral wall electrode arrays accommodate the natural anatomical tilt of the scala tympani, with contact orientation aligning to cochlear structures for much of the insertion trajectory. This in vivo analysis provides new insights into the biomechanical interactions of electrode arrays within the cochlea and may have implications for structure preservation, spectral resolution, and CI stimulation patterns.

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