Hearing loss is a common disability among adults. In the aging population, 25% of individuals between age 65 and 74 and 50% of individuals age 75 and older have hearing problems. Overall, approximately 30 million adults in the United States have moderate-to-severe sensorineural hearing loss. For this group, acoustic amplification (a conventional hearing aid) is an important rehabilitative strategy that often restores hearing to a serviceable level.
Despite the potential benefits of acoustic amplification, many hearing-impaired patients do not accept hearing aids. Some common complaints about hearing aids include feedback annoyance, ear canal discomfort, stigma of wearing an external appliance, and psychological rejection. It is estimated that only 20% of individuals within the United States who may benefit from a hearing aid own one. Only half of those who own a hearing aid use their device on a long-term basis.
Advantages of Implantable Hearing Devices
The search for alternatives to conventional hearing aids motivated the development of implantable hearing devices that deliver sound energy more directly to middle and inner ear structures. This design eliminates many of the disadvantages of conventional hearing aids. Implantable hearing devices endeavor to deliver more natural sound quality, increase gains across the frequency spectrum, reduce feedback, improve comfort and cosmesis, and eliminate ear canal occlusion. Although the chapter is mainly devoted to implantable middle ear hearing devices (IMEHDs), a bone-anchored hearing aid (BAHA) is a common implantable alternative to the conventional hearing aid and is briefly discussed.
Risks associated with middle ear device implant surgery include sensorineural hearing loss, ossicular chain disruption, facial nerve injury, external canal laceration, and cerebrospinal fluid leak. Beyond surgical risks, other considerations associated with implantable hearing devices are higher costs compared with conventional hearing aids, incompatibility with magnetic resonance imaging (MRI), and uncertain need for future explantation (ie, device removal) and reimplantation. Nevertheless, emerging technologies in IMEHDs are very exciting for both patients and care providers.
Perioperative risks associated with BAHA surgery include cerebrospinal fluid leak and wound problems surrounding the osseointegrated implant. The most common long-term complication is skin overgrowth over the abutment, as common as one in five patients, and has been shown to correlate with incomplete skin graft survival in the early postoperative period. However, an important distinguishing feature of the BAHA from all middle ear implants is that it is safe in MRI scanners with forces up to 9.4 T. Because of its minimal risks, the BAHA has become a popular alternative for those with conductive and sensorineural hearing losses and cannot tolerate or use hearing aids.
Hearing Device Components
An IMEHD is a device that converts acoustic energy to mechanical energy and delivers it to a vibratory structure in the middle ear. The basic components of an IMEHD consist of an acoustic signal detector (receptor), a transmission ...