Investigation Into The Biomechanical Role Of The Ossicular Chain System During The Process Of Sound Transmission

The middle ear, which includes tympanic membrane, three ossicular bones (malleus, incus, and stapes) and affiliated tendons and muscles is a typical system of Newtonian mechanical system. Diseases such as otitis media and ossicular chain reconstruction surgery would alter the mechanical structure of the normal ossicular chain. So, the main objective of the research was to explore the middle ear dynamics for better understanding of sound transmission and for assessing the influence of diseases on the ossicular chain by using an accurate finite element model of the human middle ear.The research started with developing a systematic and accurate geometric modeling method that can be employed to reconstruct the ossicular chain of middle ear from the serial histological sections and micro-CT of a human temporal bone in the Computer-Aided Design (CAD) environment like SURFdriver, Microview ( a viewing and 3-D reconstruction software for imaging of micro-CT scanning) and Mimics software. Using the method, a solid model of human middle ear was constructed which revealed excellent accuracy in geometry.Then a finite element (FE) model of the ossicular system was built by using the geometric data translated from the CAD model and the published material parameters of the middle ear. More accurate and efficient meshes was remeshed using HyperMesh software and the remeshing tools of Mimics software, then the FE model was imported to ANSYS 10.0 where the statical, modal and harmonic properties were calculated and analyzed. The FE model was completed by adjusting physical parameters based on the umbo and stapedial footplate displacements comparing with published FE model results and laser Doppler vibrometry measurements. Finally, the accuracy of the FE model of ossicular chain was verified by comparing with sets of published experimental measurements. The results of these verifications demonstrated that the FE model constructed using the geometric modeling method developed in this research was reasonable in predicting the dynamic behaviors of the middle ear. Therefore, it was appropriate to employ the FE model to simulate the middle ear frequency response characteristics, which were the main concerns in the middle ear sound transmission investigation. The FE model of ossicular chain system was also applied preliminarily in resolving some clinical problems. In addition, a preliminary investigation was carried out to measure the natural frequencies of stapes by laser doppler vibrometry. It was found that the proper frequency distribution of the first 6 steps was close to the results calculated from the FE model of the ossicular chain.These results suggested that the FE model of the ossicular chain was very useful in the study of the middle ear mechanics.