This article describes outcomes for the Otologics active middle ear implant for the semi-implantable and fully implantable (Carina, Otologics LLC, Boulder, CO) devices. Inclusion and exclusion criteria are reported in detail for surgical and audiologic management. Results from the clinical trial demonstrated no change for unaided air and bone conduction thresholds and no significant change in monosyllabic word scores or sentences in noise. Experiments are reported for conductive and mixed types of hearing losses in animal and human cadaveric models. These devices are in their infancy, and further study is needed to better identify candidates and develop appropriate expectations.
Key points
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Active middle ear implants increase our rehabilitation armamentarium available in situations in which traditional amplification is not adequate.
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The adoption of traditional amplification remains a problem for a variety of reasons.
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Use of an implantable middle ear prosthesis requires a major commitment from the patients, families, surgeon, audiologist, and educator, particularly if and when future candidacy expands to include the young pediatric age range.
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The reliability of implantable devices has greatly improved with newer generations of the implants, but failures do still occur.
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The best results are achieved in settings with trained surgeons, audiologists, and educators working together with implant patients.
A video of Otologics surgery accompanies this article at http://www.oto.theclinics.com/
Introduction
The World Health Organization estimates that approximately 600 million people are affected with hearing loss worldwide. Of these, 250 million suffer from moderate to severe hearing losses. In the United States, 28 million Americans have hearing loss severe enough to impact communications. The magnitude of the problem worldwide is overwhelming in how one begins to rehabilitate these hard-of-hearing and deaf individuals.
Traditional hearing aids have seen major advances in recent years, both in fidelity of sound and cosmetic appearance. Although most of the hard-of-hearing population could benefit from traditional amplification, only 15% to 20 % actually use these devices. Even in the severely affected group with marked compromise of communication skills, only 55% use hearing aids. All health care workers are familiar with the many rationales for not wearing amplification devices. Aesthetic appearance, cost, discomfort in wearing, restriction in activities, quality of sound, and medical conditions (such as canal deformity, chronic external otitis, and chronic middle ear disease) are common complaints from our patients. This lack of adoption of even new hearing aid technology has encouraged manufacturers to develop a new line of technology that is implantable to alleviate these common problems.
The active middle ear prostheses use semi-implantable and fully implantable technology to stimulate the inner ear. In the past decade, rapid advances have been made in the field; these are available in the market place for patients with mild to severe hearing losses. Implantable devices fall into 4 general categories: acoustic osseointegrated prostheses, active middle ear prostheses, cochlear implants, and auditory brainstem implants, along with hybrid devices. This article centers on the semi-implantable and fully implantable Otologics LLC devices, now Cochlear Corporation (Sydney, Australia) active middle ear prostheses.
Introduction
The World Health Organization estimates that approximately 600 million people are affected with hearing loss worldwide. Of these, 250 million suffer from moderate to severe hearing losses. In the United States, 28 million Americans have hearing loss severe enough to impact communications. The magnitude of the problem worldwide is overwhelming in how one begins to rehabilitate these hard-of-hearing and deaf individuals.
Traditional hearing aids have seen major advances in recent years, both in fidelity of sound and cosmetic appearance. Although most of the hard-of-hearing population could benefit from traditional amplification, only 15% to 20 % actually use these devices. Even in the severely affected group with marked compromise of communication skills, only 55% use hearing aids. All health care workers are familiar with the many rationales for not wearing amplification devices. Aesthetic appearance, cost, discomfort in wearing, restriction in activities, quality of sound, and medical conditions (such as canal deformity, chronic external otitis, and chronic middle ear disease) are common complaints from our patients. This lack of adoption of even new hearing aid technology has encouraged manufacturers to develop a new line of technology that is implantable to alleviate these common problems.
The active middle ear prostheses use semi-implantable and fully implantable technology to stimulate the inner ear. In the past decade, rapid advances have been made in the field; these are available in the market place for patients with mild to severe hearing losses. Implantable devices fall into 4 general categories: acoustic osseointegrated prostheses, active middle ear prostheses, cochlear implants, and auditory brainstem implants, along with hybrid devices. This article centers on the semi-implantable and fully implantable Otologics LLC devices, now Cochlear Corporation (Sydney, Australia) active middle ear prostheses.
Requirement for active middle ear prostheses
Semi-implantable and fully implantable active middle ear prostheses all require common components: a sensory pick up mechanism, processing electronics, a power source, communication system, and a stimulator. The approach has varied with companies, but the needs remain the same. Although technology in implantable devices has made major strides, challenges remain in developing microphone technology, a translating stimulator, and an implantable power source.
In semi-implantable devices, the microphone, processing electronics, and power source can all be maintained externally with information and power being delivered transcutaneously via a telecommunication coil or magnetic induction. In these devices, many of the technological problems have been solved; the results rely more on signal processing than microphone and battery technology.
In fully implantable devices, these challenges have slowed down the introduction of this technology into the hard-of-hearing patient population. The development of a fully implantable microphone has been one of the major stumbling blocks in all implantable hearing devices. A microphone must be sensitive to ambient sounds, ignoring biologic noises while implanted under a layer of skin and subcutaneous tissue. Adding 6 mm of soft tissue over a microphone decreases its effectiveness by tenfold, thus requiring an enlargement of the microphone system by tenfold. The sensitivity to biological noises and skull vibrations, as during voicing or chewing, is increased 100 fold under 6 mm of soft tissue. Thus, some cushioning of the microphone is required to temper the biological sounds.
Battery technology has made major advances in the past decade. The power source needs to be capable of delivering at least 16 hours of device use without recharging to be an effective amplifier for patients. It should be safe and provide sufficient power for all operating conditions over the life of the implant. It is now feasible to have a small battery sufficient to drive active middle ear prostheses for 24 plus hours between charges. Larger batteries similar to cardiac pacemaker technology can last 5 to 7 years without recharging before requiring replacement.
Electrodes in cochlear implants have now been implanted in patients with devices lasting for several decades. This development is a relatively straightforward technological development when compared with an active middle ear prosthesis. Stimulating the intact inner ear requires a translating system that converts sound energy into movements of the ossicular chain or tympanic membrane. These constantly moving devices must be engineered to survive in a hostile biological system with host protective mechanisms, such as inflammation and fibrosis chronically attempting to wall off the foreign body and protect the host.
Manufacturers have used a variety of techniques to solve these problems. Success has been achieved, though often at the sacrifice of other elements of the system. One must appreciate that we are still in the initial developmental stages, similar to the period of very early cochlear implants; great developments are here and yet to come.
The Otologics LLC has transferred their intellectual properties for the hearing devices to Cochlear Corporation. All the work reported next used devices supplied by Otologics LLC; therefore, the name Otologics is used in referring to the device. This device should not be confused with the present Cochlear Corporation products, such as the Baha or Cochlear Nucleus cochlear implants (Cochlear Corporation, Sydney, Australia). Cochlear Corporation is currently marketing the latest generation of the Carina (Cochlear Boulder, Otologics LLC, Boulder CO) in Europe and South America.
Otologics middle ear transducer (semi-implantable)
The Otologics Middle Ear Transducer (MET), has a button external processor that provides power and sound stimulation through a transcutaneous coil to the implanted digital electronics hermetically sealed package and transducer ( Fig. 1 ). The stimulator is an electromagnetic transducer that is mounted in a titanium bracket anchored to the mastoid bone with the transducer tip loaded against the body of the incus ( Fig. 2 ). Power to the internal device and sound signals are transmitted transcutaneously through a radio coil from the external button to the implant digital electronics processing the sound and controlling movement of the transducer. Sound induces translation of the transducer with resultant stimulation of the ossicular chain through incus movement.
Otologics Carina (fully implantable)
The Otologics Carina has a traditional microphone implanted in the cortical bone of the mastoid and attached to the implant canister through a dependent lead. The hermetically sealed implant canister contains the electronics package and battery ( Fig. 3 ). A traditional communication coil used in other implant technology along with a magnet allows recharging the battery and adjustments of software algorithms, along with volume of sound. The transducer is electromagnetically driven and is loaded against the body of the incus, mechanically translating to stimulate the ossicular chain. It is anchored securely to the mastoid via a titanium bracket, and the degree of incus loading is adjusted by a feedback loop system to assure sustained contact with maximal compliance of the system ( Fig. 4 ). As the pickup sensor is located remotely to the external and middle ear, the ossicular chain is not disrupted.
