Middle-Ear Sound Transmission Under Normal, Damaged, Repaired, and Reconstructed Conditions.

Abstract

We hypothesize that current clinical treatment strategies for the disarticulated or eroded incus have the effect of combining the incus and stapes of the human middle ear (ME) into one rigid structure, which, while capable of adequately transmitting lower-frequency sounds, fails for higher frequencies. ME damage causes conductive hearing loss (CHL) and while great progress has been made in repairing or reconstructing damaged MEs, the outcomes are often far from ideal. Temporal bones (TBs) from human cadavers, a laser Doppler vibrometer (LDV), and a fiber-optic based micro-pressure sensor were used to characterize ME transmission under various ME conditions: normal; with a disarticulated incus; repaired using medical glue; or reconstructed using a partial ossicular replacement prosthesis (PORP). Repairing the disarticulated incus using medical glue, or replacing the incus using a commercial PORP, provided similar restoration of ME function including almost perfect function at frequencies below 4 kHz, but with more than a 20-dB loss at higher frequencies. Associated phase responses under these conditions sometimes varied and seemed dependent on the degree of coupling of the PORP to the remaining ME structure. A new ME-prosthesis design may be required to allow the stapes to move in three-dimensional (3-D) space to correct this deficiency at higher frequencies. Fixation of the incus to the stapes or ossicular reconstruction using a PORP limited the efficiency of sound transmission at high frequencies.