Middle ear implants rely on accurate characterization of sound transmission from the tympanic membrane to the inner ear. Standard middle ear transfer function (METF) measurements typically expose the stapes footplate through the tympanic cavity while keeping the inner ear intact. However, studies have shown that inner ear impedance, surgical manipulations, and single-point laser Doppler vibrometry (LDV) measurements can introduce instability into METF assessments. These challenges affect the precision of middle ear mechanics research and complicate efforts to evaluate implant performance. Based on these challenges, there is a pressing need to develop a more stable and reproducible method for assessing METF under controlled conditions.
Researchers from Peking Union Medical College Hospital, Chinese Academy of Medical Sciences, have developed a new experimental approach to measure the middle ear transfer function more accurately. The study, published (DOI: 10.26599/JOTO.2025.9540034) in Journal of Otology in November 2025, introduces a trans-petrous vestibular method that removes inner ear interference and enables precise multi-point LDV measurements of the stapes footplate. Using 36 validated human temporal bone specimens, the team established a stable reference range for METF, offering a more reliable framework for future middle ear implant research.
The research team conducted detailed biomechanical experiments on 40 fresh-frozen human temporal bone specimens, ultimately selecting 36 that met strict structural and mechanical criteria. Unlike conventional approaches that measure vibrations from the tympanic side, the new protocol exposed the vestibular surface of the stapes footplate through a controlled trans-petrous route. This allowed perpendicular LDV alignment and multi-point measurements at the anterior, middle, and posterior regions of the footplate—capturing complex rocking and frequency-dependent motion patterns often missed by single-point methods.
Pure-tone acoustic stimuli (0.25–10 kHz) were delivered through the ear canal, while the LDV simultaneously recorded stapes velocity and ear-canal sound pressure to calculate METF. The resulting reference range demonstrated high stability across specimens and frequency bands. Additional tests showed that common surgical manipulations, such as mastoidectomy, tympanic membrane elevation, and exposure of ossicular structures, did not significantly alter the METF. This confirms the robustness of the new measurement framework and its compatibility with clinical procedures.
By eliminating inner ear impedance effects and enhancing spatial resolution of stapes motion, the method addresses critical limitations of existing protocols and provides a more accurate representation of middle ear mechanics, particularly in the high-frequency range.
According to the research team, the new trans-petrous vestibular approach represents a major step toward improving the reliability of middle ear biomechanics research. They emphasize that multi-point, vertically aligned LDV measurements offer a clearer picture of complex stapes footplate motion, reducing the variability introduced by inner ear loading. The researchers also note that the expanded METF reference range, derived from a larger-than-typical sample size, provides a stronger statistical foundation for evaluating implant designs. This methodological refinement is expected to support more precise, reproducible assessments in both experimental and clinical settings.
The establishment of a validated METF reference range offers important implications for future auditory research. It provides a standardized benchmark for selecting suitable temporal bone specimens, ensuring consistency across implant evaluation studies. The method is particularly valuable for assessing passive middle ear implants, piston prostheses, and reconstructive surgical procedures that require accurate quantification of stapes movement. Beyond improving implant design, this approach may aid in optimizing personalized hearing interventions and advancing biomechanical models of human hearing. Future studies incorporating three-dimensional vibrational mapping and multi-center data collection could further strengthen its role in auditory biomechanics.
About Journal of Otology
Journal of Otology is an open access, peer-reviewed journal that publishes research findings from disciplines related to both clinical and basic science aspects of auditory and vestibular system and diseases of the ear. This journal welcomes submissions describing original experimental research that may improve our understanding of the mechanisms underlying problems of basic or clinical significance and treatment of patients with disorders of the auditory and vestibular systems. In addition to original papers the journal also offers invited review articles on current topics written by leading experts in the field. The journal is of primary importance for all scientists and practitioners interested in audiology, otology and neurotology, auditory neurosciences and related disciplines. Journal of Otology welcomes contributions from scholars in all countries and regions across the world.
