Modeling sound transmission of human middle ear and its clinical applications using finite element analysis

We have developed a new finite element (FE) model of human right ear, including the accurate geometry of middle ear ossicles, external ear canal, tympanic cavity, and mastoid cavity. The FE model would be suitable to study the dynamic behaviors of pathological middle ear conditions, including changes of stapedial ligament stiffness, tensor tympani ligament (TTL), and tympanic membrane (TM) stiffness and thickness. Increasing stiffness of stapedial ligament has substantial effect on stapes footplate movement, especially at low frequencies, but less effect on umbo movement. Softer TTL will result in increasing umbo and stapes footplate displacement, especially at low frequencies (f < 1000 Hz). When the TTL was detached, the vibration amplitude of umbo increased by 6 dB at 600 Hz and two peaks (300 and 600 Hz) were found in the vibration amplitude of stapes footplate. Increasing the stiffness of tensor tympani resulted in a slightly decreased umbo amplitude at very low frequencies (f < 500 Hz) and significantly decreased displacement up to 12 dB at middle frequencies (1000 Hz < f < 4000 Hz). However, the amplitude change of stapes footplate is very sensitive to the TTL stiffness, especially at low frequency (f < 1000 Hz). The increased stiffness of TM resulted in reduced umbo and stapes footplate displacement at frequencies <1500 Hz and increased displacement at frequencies >1500 Hz. As (TM) thickness was increased, the umbo displacement was reduced, especially at very low frequencies (f < 600 Hz). Otherwise, the stapes displacement was reduced at all frequencies.