Techniques to improve the efficiency of a middle ear implant: effect of different methods of coupling to the ossicular chain.

HYPOTHESIS: Coupling and placement of actuators onto the ossicular chain have a significant influence on active middle ear implant (AMEI) performance.
BACKGROUND: AMEIs have proved to be effective in treating moderate-to-severe sensorineural hearing loss as well as mixed and conductive loss. Here, we assess the effect on performance of an AMEI prosthesis using 5 different methods of coupling to the ossicular chain in 6 temporal bones.
METHODS: The AMEI provided direct vibratory stimuli to the incus using the following methods: 1) tip of the transducer in contact with incus body (baseline condition), 2) tip of the transducer placed in a laser-drilled hole in the incus body, 3) the àWengen clips (straight and articulated) crimped to the transducer and attached to the incus long process, 4) a 0.5-mm diameter cylinder placed in contact with the incus long process, and 5) a bell-shaped prosthesis in contact with the head of the stapes. Performance in each condition was assessed by measuring the resultant stapes velocities (HEV) from which the maximum equivalent ear canal sound pressure levels (L(Emax)) were computed.
RESULTS: Relative to the baseline condition, which produced L(Emax) of 112 to 126 dB SPL for frequencies of 0.25 to 8 kHz, the other coupling methods produced similar or substantially improved (increased L(Emax)) performance. Best performance was achieved by providing vibratory stimulation to the head of the stapes directly with the bell-shaped tip where performance improved significantly by 16 to 22 dB.
CONCLUSION: Stapes velocities produced by AMEI transducers may be increased depending on the tip used to couple the transducer to the ossicular chain and the placement of the stimulating tip along the incus. Improvement in coupling the transducer to the incus and stapes produced significant improvements in the transfer of vibratory stimuli to the ossicular chain.