New developments in bone-conduction hearing implants: a review

Abstract

The different kinds of bone-conduction devices (BCDs) available for hearing rehabilitation are growing. In this paper, all BCDs currently available or in clinical trials will be described in categories according to their principles. BCDs that vibrate the bone via the skin are referred to as skin-drive devices, and are divided into conventional devices, which are attached with softbands, for example, and passive transcutaneous devices, which have implanted magnets. BCDs that directly stimulate the bone are referred to as direct-drive devices, and are further divided into percutaneous and active transcutaneous devices; the latter have implanted transducers directly stimulating the bone under intact skin. The percutaneous direct-drive device is known as a bone-anchored hearing aid, which is the BCD that has the largest part of the market today. Because of some issues associated with the percutaneous implant, and to some extent because of esthetics, more transcutaneous solutions with intact skin are being developed today, both in the skin-drive and in the direct-drive category. Challenges in developing transcutaneous BCDs are mostly to do with power, attachment, invasiveness, and magnetic resonance imaging compatibility. In the future, the authors assume that the existing percutaneous direct-drive BCD will be retained as an important rehabilitation alternative, while the transcutaneous solutions will increase their part of the market, especially for patients with bone-conduction thresholds better than 35 dB HL (hearing level). Furthermore, the active transcutaneous direct-drive BCDs appear to be the most promising systems, but to establish more detailed inclusion criteria, and potential benefits and drawbacks, more extensive clinical studies are needed.

Keywords: active; bone-conduction device; implantable; passive; percutaneous; transcutaneous.

Figure 1

Categorization of bone-conduction devices. Abbreviations: BAHA, bone-anchored hearing aid; BCI, bone-conduction implant.

Figure 2

Conventional skin-drive bone-conduction devices, attached with (A) a steel spring headband, and (B) with frames for glasses. Note: Images provided courtesy of (A) Starkey Hearing Technologies, (B) bruckhoff hannover gmbh.

Figure 3

Sophono^®, a passive transcutaneous skin-drive bone-conduction device. Note: Image provided courtesy of Sophono^®.

Figure 4

Baha^® Attract, a passive transcutaneous skin-drive bone-conduction device. Note: Image provided courtesy of Cochlear Bone Anchored Solutions AB.

Figure 5

Bone-anchored hearing aid, a percutaneous direct-drive bone-conduction device. Notes: (A) Ponto (Oticon Medical, Askim, Sweden); and (B) Baha^® BP100 (Cochlear Bone Anchored Solutions AB, Mölnlycke, Sweden). Images provided courtesy of Oticon Medical (A) and Cochlear Bone Anchored Solutions AB (B).

Figure 6

Bone-conduction implant, an active transcutaneous direct-drive bone-conduction device.

Figure 7

Bonebridge™, an active transcutaneous direct-drive bone-conduction device. Note: Image provided courtesy of MED-EL.

Figure 8

SoundBite™, an in-the-mouth bone-conduction device with implant for tooth attachment and behind-the-ear sound processor. Note: Image provided courtesy of Sonitus Medical.

Figure 9

Estimated maximum recommended preoperative bone-conduction thresholds, which include a “gray” zone depending on if an aided PTA of at least 30 or 35 dB HL is met. Abbreviations: BCI, bone-conduction implant; HL, hearing level; max, maximum; preop, preoperative; PTA, pure-tone average; PTA₄, four-frequency averages of PTA; PTAbc, pure-tone average for bone-conduction.