Mode shapes of a damaged and repaired tympanic membrane as analysed by the finite element method

This work makes use of recent finite element discretization of the human tympanic membrane where the known anisotropy of the tympanic membrane is implemented by a series of thin beam elements superimposed on thin shell membrane elements. These thin beam elements were introduced in order to simulate the fibre structure of the tympanic membrane. The onset of tympanosclerosis has been modelled as a gradual increase in tympanic membrane density and modulus in the affected area. This increased density results in a fall of 55% of the first natural frequency for only a 16% area of drum sclerosis. Additionally the amplitude response is significantly reduced. Repair of the membrane was simulated by removal of the fibre system from the affected area. Under these circumstances the natural frequencies virtually return to the healthy state but the mode shapes of vibration do not. The repair to the membrane, although not significantly altering frequency values, has resulted in a disruption to the normal mode shape patterns with consequences in the movements conveyed to the stapes and cochlear fluids.