Effect of Silastic sheeting over the round window niche on sound transmission in the intact human middle ear.

BACKGROUND: Silastic sheeting is commonly used in middle ear surgery to prevent the formation of adhesions between the tympanic membrane and the medial bony wall of the middle ear cavity. This sheeting is often placed, advertently or inadvertently, so as to cover the round window niche. The effects of mechanically shielding the round window niche in the presence of an intact tympanic membrane and ossicular chain have not been empirically studied to date. OBJECTIVE: To investigate the effect of acoustically shielding the round window with 1 mm thick Silastic sheeting on middle ear sound transmission in otherwise intact cadaveric human temporal bones. METHODS: Using a fresh human cadaveric temporal model, a computerized laser Doppler vibrometry system was used to measure vibrations at the umbo and on the stapes footplate in response to sound introduced into the ear canal. Stapes displacement was used as a measure of sound transmission. The measurements were repeated after shielding the round window using 1 mm thick Silastic sheeting. RESULTS: We found that shielding the round window with Silastic produced no significant difference in the measurements at the stapes footplate. At the umbo, a slight increase in vibrations at 250 to 500 Hz was measured after shielding. This was on the order of 3 dB and was not statistically significant. CONCLUSION: In the presence of an intact tympanic membrane and ossicular chain, shielding the round window with Silastic sheeting has no clinically significant effect on sound transmission by the human middle ear.