Clinical studies were conducted on the partially implantable middle ear implant (MEI)or implantable hearing aid. In 23 out of 30 MEI-implanted ears the hearing level was improved by more than 20 dB. Twenty three implanted patients were utilizing the MEI, and the benefit of MEI was 1) no need of ear plugs,2) no acoustic feedback,3) quality sound transmission because of direct coupling, and 4) hearing improvement by MEI was better than conventional hearing aids especially in 4000 Hz. MEI was considered safe from the follow-up in these 30 cases since implantation, which revealed no complications such as elevation of bone conduction thresholds, vertigo, and acute inflammation. We recommend the middle ear implant or implantable hearing aid, under study, as a useful approach to a certain group of mixed hearing loss.

View full abstract

The partially implantable hearing aid (PIHA) utilizing the piezoelectric bimorph ossicular vibrator reported here consists of two units, external and internal unit. The electlet microphone in the external unit converts sound signals into electrical signals which are fed into the external link coil after amplification. The outer link coil then excites transcutaneously the internal link coil by means of electromagnetic induction. The ossicular vibrator of piezoelectric bimorph is then activated by receiving electroacoustic signals from the internal link coil. Direct coupling of the vibrator to the stapes allows highly efficient transmission of acoustic signals to the inner ear. As a result the patients can hear the natural quality of sound without feed back, troubles due to occlusion of the external ear canal and fatigue.
The Ehime type internal component (E-type) was primarily designed to implant it using the intact canal wall technique preserving the posterior ear canal and the ear drum. This original technique is termed the type 1 implant operation. During the last four years we developed a surgical method which enables the device implantable in the ear missing the bony external auditory canal, the ear was previously operated on by a radical mastoidectomy. This new method of operation has been named the type 2 implant operation. Since the first time we applied the device to a patient in 1984, we have implanted the device into 34 patients. The types 1 and 2 operations were performed in 25 and 7 patients, respectively. In the remaining 2 patients, the device was implanted in the radical mastoid cavity under the tympanomeatal skin flap. In the first chapter, the methods of operation together with the indication and the preoperative cautions were described in detail. In the second chapter, the surgical results were described with respect to clinical advantages and audiological benefits. The overall success rate was 88%. The surgical failures included retroauricular skin atrophy in 4 patients, insufficient sensitivity in 2, disconnection between the vibrator and stapes in 2 and recurrence of cholesteatoma in 1. Among them, reimplantation was attempted in 4 patients with satisfactory result. Each problematic patient was reported. Prevention and countermeasures of the problems are described.

View full abstract