Revealing the Effects of Tympanic Membrane Implant Mechanical Properties on High-Frequency Hearing Loss After Clinical Myringoplasty: A Finite Element Analysis.

Myringoplasty is most commonly used to treat tympanic membrane (TM) perforation. Clinical data have shown that unexplained high-frequency (above 3 kHz) hearing loss often occurs after myringoplasty. In this paper, a finite element (FE) model of the partial external and middle ear (ME) of the human ear, which considers the actual perforation and TM implants, is developed to reveal the mechanical mechanism of high-frequency hearing loss after implantation of temporalis fascia and cartilage commonly used in myringoplasty. The SFP displacement is proposed to evaluate the myringoplasty effect, which is proved to be better than the current practice of laser Doppler vibrometer (LDV) of umbo vibration. The model-derived results can replicate the phenomenon of better low-frequency (below 1 kHz) hearing recovery and severe high-frequency hearing loss after myringoplasty. Numerical results show that a temporalis fascia and cartilage implant, whose stiffness is smaller compared with normal PT, fails to fully restore hearing above 3 kHz, where higher-order vibration modes appear early, with more severe localization of TM energy and weakening of TM sound transmission. Moreover, the excessive thickness of implants compared to normal pars tensa (PT) leads to a decrease in the first resonant frequency (RF) and the high-frequency magnitude of the SFP displacement. Furthermore, the numerical study shows that TM implants with modulus higher than 45 MPa and density smaller than 1200 kg/m can restore high-frequency hearing better. This study has implications for choosing and designing the appropriate TM implants for myringoplasty.