(865) Optimal Sites for Bone-Conduction Stimulation After Tympanoplasty Using a Drillable 3D Head Model

Introduction: Bone-conduction hearing relies on complex skull vibration mechanisms that can be altered by middle ear surgery, and although stimulation near the external auditory canal is advantageous in normal anatomy, the optimal site after tympanoplasty remains unclear. Therefore, this study aimed to identify the optimal bone-conduction stimulation sites after different tympanoplasty procedures using a drillable three-dimensional head model.

Methods: A drillable 3D whole-head model simulating conductive and mixed hearing loss was used. Three surgical conditions were evaluated: no drilling, canal wall up (CWU), and canal wall down (CWD) tympanoplasty. Bone-conduction stimulation was applied at three lateral skull sites near the external auditory canal at frequencies from 250 to 2000 Hz. Promontory vibration velocity was measured using laser Doppler vibrometry. Six measurements were obtained for each condition and averaged for analysis. Statistical comparisons were performed using one-way ANOVA.

Results: Clear stimulus-synchronized promontory vibrations were observed at 250–2000 Hz, whereas higher frequencies were excluded due to noise. In the CWU condition, stimulation near the external auditory canal consistently produced significantly higher promontory vibration velocities across most frequencies. In contrast, the CWD condition showed no consistent relationship between stimulation site and vibration velocity. Comparisons between surgical conditions demonstrated generally reduced vibration velocities in the CWD model compared with CWU.

Conclusions: Preservation of the posterior canal wall appears to enhance bone-conduction efficiency by enabling more direct transmission of skull vibrations to the promontory. Stimulation near the external auditory canal may be optimal in CWU cases, whereas bone-conduction stimulation might be applied at arbitrary sites in CWD cases.
Further validation under clinically relevant conditions, including cadaveric studies, is required to optimize implantation strategies for bone-conduction hearing devices.