2025/11/27 by Wils, Irina, Mair, Tobias, Dobrev, Ivo +1
Neuroscience · Medicine · #Hearing Loss and Rehabilitation #Ear Surgery and Otitis Media #Hearing, Cochlea, Tinnitus, Genetics
paper · doi:10.5167/uzh-280884
Effective mechanical coupling between bone conduction implants and the skull is essential for optimal auditory stimulation. The Bonebridge™ (MED-EL, Innsbruck, Austria) uses cortical screws to secure the transducer to the mastoid bone. However, the biomechanical consequences of varying the attachment quality of the screws on cochlear activation remain unclear. Five Bonebridge implantations were performed, and five coupling conditions were evaluated: (1) both screws fixed, (2) only the superior screw fixed, (3) only the inferior screw fixed, (4) skin tension without screws, and (5) two screws, but neither fixed tightly. Cochlear activation was assessed by measuring pressure changes within the scala vestibuli and scala tympani using custom intracochlear acoustic receivers. Additionally, 3D velocity measurements via laser Doppler vibrometry were performed at multiple locations: the Bonebridge surface (4 points), the skull surface (4 points), and the cochlear promontory (1 point). A 1D scanning vibrometer further recorded vibratory responses on the implant and skull surfaces around the implant (450-500 points). Intracochlear pressure, promontory, and skull motion decrease when screws are removed, especially the top screw, with reductions of 5-25 dB above 3 kHz. Total harmonic distortions occur mostly for frequencies below 2 kHz, and increase from 2 % when both screws are fixed to 18 % when neither of the screws is fixed. The reduction of screw fixation weakens mechanical coupling, leading to reduced cochlear activation and worse audio quality. Thus, suboptimal coupling strategies may diminish auditory benefit for Bonebridge recipients, and during surgery, a firm attachment of both screws should be aimed for.