The effect of ventilation tubes on stresses and vibration motion in the tympanic membrane: a finite element analysis

There have been very few analyses of the biomechanical behaviour of ventila tion tubes, or grommets, even though clinical studies have indicated that t ube design and material determines extrusion rates and may influence tympan osclerosis. This paper reports a comprehensive biomechanical analysis of th e effect of a grommet on the tympanic membrane. Analytical and computer sim ulation techniques (finite element analysis) are used to determine the chan ges in the vibratory motion and stresses in the membrane when a Reuter-Bobb in ventilation tube is inserted. It is found that the presence of a ventila tion tube significantly affects the motion of the membrane in the neighbour hood of the implant. When the effect of implant material is investigated, i t is found that the amplitude of motion of a heavier metal implant is less than a lighter polymeric implant. If it is true that higher motion predispo ses towards early extrusion, then the lighter implant (polyethylene) is pre dicted to have a higher extrusion rate. Regarding the maximum stresses in t he tympanic membrane, they form a crescent-shaped region in the anterior an d posterior quadrants in the regions where tympoansclerosis is observed. Th e magnitude and pattern of the stress is predicted not to depend significan tly on the presence of the tube. This suggests that tympanosclerosis is not determined by the implant per se and therefore that no tube design feature can be expected to prevent it.