Effects of Cartilage Overlay on the Tympanic Membrane: Lessons From a Temporal Bone Study for Cartilage Tympanoplasty.

Abstract

Placing cartilage grafts on different tympanic membrane (TM) locations will affect sound transfer function, and the effects will differ according to the part of the TM modified. Cartilage tympanoplasty is increasingly popular because of lower reperforation rates, and better long-term stability. In this temporal bone study, we investigated the effect of placing cartilage grafts over different parts of the normal TM on sound transmission. In 10 human fresh frozen temporal bones, umbo and stapes vibrations to acoustic stimuli from 250 to 8000 Hz were measured at multiple points using a scanning laser vibrometer. Four different cartilage arrangements were measured in each temporal bone. 1) Overlay condition leaving an umbo rim of normal TM (Umbo Rim). 2) Overlay condition leaving annular rim of normal TM (Annular Rim). 3) Overlay condition leaving both rims of normal TM (Two Rims). 4) Overlay condition leaving no normal TM exposed (No Rims). At low frequencies, there was a statistically significant decrease in velocity from baseline for the No Rims (umbo mean -4 dB; stapes -6 dB) and Umbo Rim (umbo -4 dB; stapes -3.7 dB) conditions. All conditions showed significant decreases for middle frequencies (umbo -4.0, -5.9, -7.4 and -6.3 dB; stapes -10.8, -6.6, -6.3 and -7.7 dB) and high frequencies (umbo -13.2, -3.0, -3.1 and -5.5 dB; stapes -4.6, -2.4, -2.6 and -3.5 dB). Results are in order for No Rims, Umbo Rim, Two Rims, and Annular Rim conditions. In the low frequencies, it seems to matter where the cartilage is placed, and in particular the annular rim of the TM seems to be important for the low-frequency acoustic transfer function. In the higher frequencies, all graft placements caused some drop at all frequencies. In all frequencies, effects were modest by clinical standards.