Exploring the effect of cadaver head fixation in bone conduction hearing: Insights from finite element modeling

This study investigates the effects of head fixation method on bone conduction (BC) responses using a full head finite element model validated against experimental data. Boundary constraint variables, including fixation strength, location, height, and neck support, were systematically analyzed by varying material Young's modulus, adjusting fixation positions, and modifying the vertical position of fixation points. Among them, fixation strength had the most significant impact on ipsilateral and contralateral cochlear promontory velocities. Firm fixation minimized interface deformation, enabling the skull's intrinsic mechanical properties to shape promontory velocities, while loose fixation produced uniform responses regardless of skull properties. Fixation location and height showed minimal effects on ipsilateral and contralateral promontory velocities, and neck support strength exhibited negligible influence due to the dominance of soft tissue compliance. Furthermore, since the Young's modulus of the skull can vary across cadaver specimens, its influence on bone conduction responses under different boundary constraints was also examined by changing of Young's modulus of the cortical bone. Young's moduli of the cortical bone significantly influenced both ipsilateral and contralateral promontory velocities under firm fixation conditions but had limited effects under loose fixation conditions. Transcranial attenuation was largely unaffected by boundary constraints, reflecting the skull's intrinsic deformation behavior. These findings highlight the critical role of head fixation method strength in BC experiments. Under loose fixation, promontory velocities were little affected by fixation location, height, or Young's modulus of the cortical bone. By contrast, firm fixation amplifies the effect of Young's modulus of cortical bone on promontory velocity and transcranial attenuation, making it more suitable for isolating intrinsic skull behavior. These findings demonstrate that fixation strategy must be chosen to align with the objectives of BC research.