The Vibrant Soundbridge is a means to rehabilitate patients with sensorineural hearing loss. It differs from hearing aids in that it uses mechanical energy rather than acoustic sound to deliver better sound quality to the inner ear. The implant’s crucial component is a floating mass transducer that is directly fixed to the incus to drive it, which is introduced into the middle ear through a facial recess approach. Although this is a newer technology, studies thus far have demonstrated better hearing results compared with hearing aids in terms of functional gain and speech intelligibility, and better outcomes on subjective assessments.
Key points
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The Vibrant Soundbridge is an option for amplification for patients with mild to severe sensorineural hearing loss.
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The device is most commonly placed through a mastoidectomy and facial recess approach. It is directly fixed to the incus to vibrate the ossicular chain.
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Overall, patients have increased functional gain and speech intelligibility and report better satisfaction compared with traditional amplification via hearing aids.
Introduction
For years, patients diagnosed with mild-to-severe sensorineural hearing loss were offered hearing aids as the best treatment. However, acoustic feedback and occlusion effect have frequently left many patients dissatisfied with amplification, despite advances in signal processing and device miniaturization. In 2000, the US Food and Drug Administration (FDA) approved the Vibrant Soundbridge (VSB), the first active implantable middle ear device available in the United States and Canada. The commercial release of the device in Europe preceded this in February 1998. The principle of middle ear implants is to bypass the tympanic membrane and impart mechanical vibrations directly to the ossicular chain to improve signal coupling.
The VSB device is a partially implanted electromagnetic device from Vibrant Med El (Med El Corporation, Innsbruck, Austria). The VSB system consists of 2 parts that provide electromagnetic, direct-drive amplification when coupled. The first is an externally worn digital Audio Processor that picks up sound signal and amplifies it to a level appropriate for the sensorineural hearing loss. The earlier version of the processor, the AP 304, is no longer available. Its successor was the AP 404, which is now an alternative to the most current processor called the Amadé. Both of these processors are fully digital. The Amadé features output gain capability of up to 54 dB versus 45 dB of the AP 404. In addition, it has directional microphone capability as well as the option to select 1 of 3 programs most suitable to the listening environment. The amplified sound is then transmitted to the receiver coil of the second component, the implanted vibrating ossicular prosthesis (VORP). At the VORP’s distal end is the floating mass transducer (FMT), which is fixed to the incus and directly drives it via mechanical motion ( Fig. 1 A). The FMT comprises 2 electromagnetic coils sealed in a titanium housing that contains a magnet and is smaller than a grain of rice (see Fig. 1 B). It is specifically designed to avoid mass-loading the ossicular chain.
Introduction
For years, patients diagnosed with mild-to-severe sensorineural hearing loss were offered hearing aids as the best treatment. However, acoustic feedback and occlusion effect have frequently left many patients dissatisfied with amplification, despite advances in signal processing and device miniaturization. In 2000, the US Food and Drug Administration (FDA) approved the Vibrant Soundbridge (VSB), the first active implantable middle ear device available in the United States and Canada. The commercial release of the device in Europe preceded this in February 1998. The principle of middle ear implants is to bypass the tympanic membrane and impart mechanical vibrations directly to the ossicular chain to improve signal coupling.
The VSB device is a partially implanted electromagnetic device from Vibrant Med El (Med El Corporation, Innsbruck, Austria). The VSB system consists of 2 parts that provide electromagnetic, direct-drive amplification when coupled. The first is an externally worn digital Audio Processor that picks up sound signal and amplifies it to a level appropriate for the sensorineural hearing loss. The earlier version of the processor, the AP 304, is no longer available. Its successor was the AP 404, which is now an alternative to the most current processor called the Amadé. Both of these processors are fully digital. The Amadé features output gain capability of up to 54 dB versus 45 dB of the AP 404. In addition, it has directional microphone capability as well as the option to select 1 of 3 programs most suitable to the listening environment. The amplified sound is then transmitted to the receiver coil of the second component, the implanted vibrating ossicular prosthesis (VORP). At the VORP’s distal end is the floating mass transducer (FMT), which is fixed to the incus and directly drives it via mechanical motion ( Fig. 1 A). The FMT comprises 2 electromagnetic coils sealed in a titanium housing that contains a magnet and is smaller than a grain of rice (see Fig. 1 B). It is specifically designed to avoid mass-loading the ossicular chain.
Candidacy for surgery
In the United States, The VSB System is indicated for adults 18 years and older who have moderate-to-severe sensorineural hearing loss that desire an alternative to an acoustic hearing aid. European centers are implanting children older than 3 years of age. Ideal candidates for middle ear implants are patients with high-frequency sensorineural hearing loss that have tried conventional amplification without success because of acoustic feedback, the occlusion effect, or inadequate high-frequency amplification. These limitations can be particularly pronounced in patients with good low-frequency hearing thresholds. Although cochlear implants have been available for profound sensorineural hearing loss, otologists could offer only hearing aids to patients with moderate-to-severe sensorineural hearing loss. The VSB is a surgical solution for these patients. Fig. 2 shows Med El Corporation’s criteria for candidacy in patients with sensorineural hearing loss.
Preoperative planning and preparation
It is important for both surgeon and audiologist to counsel the patient regarding the risks of surgery as well as the benefits and limitations of the device. Besides a history and physical examination, preoperative evaluation consists of a standard audiologic test battery, using a combination of aided and unaided conditions. These tests include tympanometry, acoustic reflex thresholds, pure-tone and bone-conduction thresholds as well as speech testing. CT imaging is not mandatory but advisable. Facial nerve monitoring is especially useful in cases of congenital temporal bone anomalies or revision surgeries. Patients can undergo VSB implantation on an outpatient basis.
Surgical technique
Patient Preparation
The patient is positioned as is routine for otologic procedures. Preoperative sedative followed by anesthesia is administered and facial nerve monitoring electrodes are applied. The postauricular area is shaved and disinfected. A silicone VORP template oriented in a 45° posterosuperior axis is placed on the skin to determine optimal implant position ( Fig. 3 A). The VORP should not lie under the auricle, which can be ensured by marking the skull with methylene blue and placing the VORP posterior to this point. In addition, the VORP transition should sit at the posterior edge of the intended mastoidectomy (see Fig. 3 B). The incision is marked on the skin and should be 2 cm from the edge of the template (see Fig. 3 C, D).
Procedural Approach
The surgical procedure consists of implanting the VORP and attaching the FMT. Elements of the procedure are similar to cochlear implantation: the middle ear is accessed through a facial recess approach after simple mastoidectomy, and the device is seated in the skull to avoid migration. A discussion of the procedure warrants familiarity with the components (see Fig. 1 ). The VORP consists of a magnet with coil, demodulator, VORP transition, conductor link, and FMT at the distal end. The FMT has a clip with which it attaches to the incus.
After an incision is made, a pericranial flap is elevated. To ensure proper attachment of the magnet, the total thickness of the skin overlying the receiving coil should not exceed 7 mm. A portion of the pericranial flap can be excised to achieve the appropriate thickness, but care must be taken to have continuous fascial coverage over the demodulator, the transition, and the conductor link. A sterilized VORP template is placed on the skull to verify sufficient exposure.
Next, a simple mastoidectomy is performed to the point that the short process of the incus is visualized. Bony overhangs are left at the periphery to help with conductor link retention. A device seat is then drilled, which allows the transition of the conductor link to slope deeply in the mastoid cavity. The conductor link should be as medial to the skull surface as possible. The VORP template is positioned using the previously marked reference so that the critical positioning of the transition point is correct ( Fig. 4 ). As in a cochlear implant, a channel is drilled from the seat to the mastoidectomy cavity for the VORP transition. Tie-down holes are created to fixate the demodulator (see Fig. 4 ).
A facial recess is drilled and enlarged with inferior extension, to allow introduction of the FMT. A 2.5- to 3.0-mm burr approximates the size of the FMT and should pass through the recess as a test of adequate space. Care is taken to preserve the incus buttress so that the ligament attached to the short process is not violated.
The VORP is introduced into the field, at which point monopolar cautery is no longer used. It is positioned so that the FMT lies in the mastoidectomy defect. The demodulator is sutured in place. The FMT is then advanced through the mastoidectomy and positioned so that its clip is over the superior portion of the incus long process. The axis of the FMT should be parallel to the axis of motion of the stapes and must be in intimate contact with the incudostapedial joint ( Fig. 5 ). Special forceps ( Fig. 6 ) are used to close the clip to encircle the incus. At this point, if the attachment is too loose, the clip can be tightened with fine alligator forceps. An alternative method advocated by the senior author is to elevate a tympanomeatal flap to augment exposure for tightening because this is difficult even through a widened facial recess.
