Tympanosclerosis, grommets and shear stresses.

This paper deals with grommet induced tympanosclerosis. In the first part, patients from a controlled trial of the treatment of bilateral glue ear using unilateral grommet insertion are reviewed 15 years later. Tympanosclerosis due to grommet insertion is summated using computer graphics. Two areas of maximal tympanosclerosis are found, anteriorly and posteriorly midway between the annulus and the umbo. These maximal areas join inferiorly in the classical horse shoe shape. In an attempt to identify reasons for this distribution, the structure of the lamina propria is reviewed, and the changes that occur in tympanosclerosis considered. With this in mind, the tympanic membrane is modelled using finite element methodology to determine the areas of maximal shear stresses. These are found to be in the same position as tympanosclerosis. Such stresses would be increased by the weight of a grommet in situ. These stresses will damage the fibrils interconnecting between the fibrous layers of the lamina propria and this may lead to tympanosclerosis. This raises the question of whether a lighter grommet would decrease the incidence of grommet-induced tympanosclerosis.