Fresh Tympanic Membrane Perforations Heal Without Significant Loss of Strength

Abstract

The mechanical and structural properties of the tympanic membrane change after a perforation has healed. In previous studies, efforts have been made to enhance the healing process of tympanic membrane perforations. The strength of the healed perforation has been tested with moiré interferometry in gerbils, but in no other species. A laser myringotomy was made on 10 Sprague-Dawley rats and 10 CBA mice, and assessments were made after 2 or 4 weeks with moiré interferometry and light and electron microscopy. The mean peak displacement at pressure loads of +350 daPa and of -350 daPa did not differ significantly in the healed perforations as compared with the untouched tympanic membranes. Morphologic assays showed fivefold increased thickness at the site of the perforation due to invaded fibroblasts and extracellular matrix. Moiré interferometry was successfully performed in the rat ears, whereas in mouse ears the method was not easily applicable due to technical difficulties. The stress-strain curve of the rat tympanic membrane displays an S-shape. The strength of the spontaneously healed tympanic membrane after myringotomy was not significantly impaired. The site of the perforation became significantly thickened at 2 and 4 weeks post-myringotomy. This information is of clinical importance, because recently closed perforations will be challenged by pressure gradient in everyday life.