1993 Volume 96 Issue 3 Pages 457-465,547
The tympanic membrane is a biomembrane made of thin vibrant material. The tension and strength of the tympanic membrane rely mainly on the radial fibers in the lamina propria. Experimental myringotomy by linear incisions were made at right angles to the radial fiber bundles in the tympanic membrane of 54 guinea pigs. The healing process was observed chronologically by light, polarized light and electron microscopy for two years. The mechanical strength of recovery of the tympanic membranes were then studied using a microtension tester developed by our laboratory. The tensile direction was parallel to the radial fiber bundles of the tympanic membrane, and the tensile rate was 1×10-3m/sec.
1. Light microscopic observation showed that the radial fiber bundles did not reconstruct continuously even after two years. Polarized light microscopic observation showed that parts of the linear incision of the tympanic membrane contained polarized fibers in place of the normal radial fibers. Transmission electron microscopic observation of the tympanic membranes after four months showed that the radial fibers were cut off sharply, but that the lamina propria had regenerated with different fibers. Several fibroblasts were also observed. Scanning electron microscopic observation through the auditory canal after two years showed that thick masses of scar adhered to the site of the experimental incision of the tympanic membrane. This scar was composed of several layers of collagen fibers. The area of scar adhesion was also observed on the membrane facing the tympanic cavity, but it was thinner than the scars on the meatal side.
2. The tensile strength of the tympanic membrane recovered up to 40% of its original value after two weeks, up to 70% after two months, and up to 90% after four months. Through four to twelve months after trauma, the tensile strength of the experimental tympanic membranes had recovered to almost 100% of their original values.
The results indicate that the experimentally injured tympanic membrane of these guinea pigs underwent incomplete regeneration morphologically, but almost completely recovered tensile strength.