Table of Contents
Bone conduction implants can improve hearing in patients with conductive or mixed hearing loss as well as in cases of single-sided deafness (SSD). The Bonebridge implant is comprised of three components: a magnet, an internal transducer, and an external audio processor. The patient in this case previously underwent resection of a vestibular schwannoma via a middle fossa craniotomy in an attempt to preserve hearing. Unfortunately, the patient ultimately lost hearing in the right ear, resulting in SSD. Here, we demonstrate the step-by-step surgical technique for the Bonebridge implant to allow sound transmission from the patient’s deaf ear to the contralateral cochlea via bone conduction.
Bone conduction implants are used in patients who have conductive or mixed hearing loss, as well as in cases of single-sided deafness. The Bonebridge device is an active transcutaneous bone conduction implant that has both internal and external components.1 The implanted portion consists of both a magnet and a bone conduction-floating mass transducer (BC-FMT), while the external component is an audio processor. The internal and external components are connected transcutaneously via a magnet, and a hearing aid battery powers the audio processor externally.1 This transcutaneous connection is unique in that there is no defect in the skin or soft tissue that is present with prior versions of bone conduction implants. The audio processor detects sound and transmits it to the implant via the magnet, which in turn vibrates within the bone, resulting in ‘active’ bone conduction of sound.1 The Bonebridge may be performed in patients over the age of five years (> 12 in the United States), who have conductive or mixed unilateral hearing loss that meets specific pure tone average threshold requirements.1, 2 Hearing loss in the affected side can be severe, but the contralateral ear should have a relatively normal hearing (bone conduction threshold above 20 dB from 500 Hz to 3 kHz). It is also indicated in patients who have conductive or mixed hearing loss and have a bone pure tone average less than or equal to 45 dB at 500 Hz, and 1, 2, and 3 kHz.2
This patient developed unilateral deafness after a middle fossa craniotomy for resection of a vestibular schwannoma.
Hearing loss is grossly evaluated using the Weber and Rinne tests. These tests make use of a tuning fork to differentiate between conductive and sensorineural hearing loss.
The Weber test is performed by placing a vibrating tuning fork over the forehead or incisor at the midline. The patient is asked to identify on which side the vibrations are heard more loudly. If the patient has conductive hearing loss, the sound will localize to the impaired ear. If the patient has sensorineural hearing loss, the sound will localize to the better hearing ear, indicating a sensorineural hearing loss in the opposite ear.3, 4
The Rinne test is used to differentiate between sensorineural and conductive hearing loss. The test is performed by placing the vibrating tuning fork over the mastoid bone behind the ear (bone conduction) until the patient can no longer hear, and then quickly moving the tuning fork just lateral to the external auditory canal (air conduction). In patients with normal hearing or sensorineural hearing loss, air conduction will be perceived as louder than bone conduction. In patients with conductive hearing loss, the bone conduction will be greater than the air conduction.3, 4 The Rinne test can also be performed by placing the tuning fork on the mastoid and lateral to the EAC at separate times and asking at which location the patient perceives the sound to be louder.3, 4 These tests, however, are not without limitations, and there is substantial variation in their accuracy.5 Additionally, only a single frequency (typically 512 Hz) is tested.
The gold standard for diagnosis of hearing loss is by a pure-tone audiogram with appropriate masking techniques and word recognition scores. It differentiates between conductive and sensorineural hearing loss and also provides hearing threshold cutoffs that help to define the severity of the hearing loss and the frequencies of hearing that are most affected.6
Computed tomography (CT) must be completed prior to Bonebridge implantation to assess for temporal bone suitability for implantation of the BC-FMT and in order to rule out a retrocochlear pathology.1 Some surgeons elect to use 3D CT analysis to create a temporal bone well template. Others have even created 3D printed models of the temporal bone for planning in complex cases.7
Unilateral hearing loss can be conductive, sensorineural, or mixed, and is differentiated by Weber and Rinne tests as well as an audiogram. Etiologies of conductive hearing loss are numerous and include otosclerosis, ossicular dislocation, superior semicircular canal dehiscence, congenital malformation, and middle ear effusion. Etiologies of sensorineural hearing loss include presbycusis, Meniere’s disease, infectious causes, and a retrocochlear pathology such as a vestibular schwannoma. Any patient that presents with unilateral or asymmetric sensorineural hearing loss requires further evaluation to detect any retrocochlear pathology. In the setting of these findings, an MRI is required to further evaluate and confirm the diagnosis.8 Surgical resection of a vestibular schwannoma can result in reduced or complete loss of hearing. The risk of this loss varies based upon the surgical approach. Both middle fossa craniotomy and retrosigmoid approaches allow for hearing preservation, but these rates vary widely and depend on both surgeon and patient/tumor factors.
Patients with SSD may be treated with a variety of devices. These range from hearing aids, bone conduction implants, and even cochlear implants. One option for patients with single-sided deafness is air conduction contralateral routing of signal (CROS) hearing aids. These devices route sound from the non-functioning ear to the functional ear. These devices, however, are only accepted by 10–20% of patients, with 80–90% of patients with unilateral hearing loss opting for bone conduction implant.2
The traditional type of bone conduction implant is the percutaneous, bone-anchored hearing aid (BAHA). These devices consist of an osseointegrated titanium screw and an abutment, which protrudes through the soft tissue and skin. While these devices are effective in the treatment of conductive/hearing loss and single-sided deafness, they are associated with complications such as infection around the titanium screw, skin overgrowth, and wound dehiscence.9
These complications are more likely to occur with percutaneous devices compared with transcutaneous devices that do not communicate with an outside environment. The advantages of the Bonebridge include improved cosmesis and earlier activation time (2–4 weeks) as the device does not require osseointegration.1 There are no significant differences between the two devices for functional gain and word recognition scores.9, 10
Passive bone conduction devices rely on the vibration of the skin and soft tissue and do not vibrate the bone directly. Like the Bonebridge, they are transcutaneous, but the sound is captured from the environment and transformed into an electrical signal that then stimulates the magnet and does not directly stimulate the bone of the skull.11 One study compared the passive and active devices and found that there were similar cutaneous complications with transcutaneous as the BAHA.
This patient had SSD, one of the three primary indications for Bonebridge placement.
The ideal outcome of her surgery would be a noticeable improvement in her ability to hear. One review study found that the patients, with conductive or mixed loss hearing and were treated with the Bonebridge implant, had a functional gain from 24 to 37 dB, which was stable over time.1, 2
Single-sided deafness is the newest indication for Bonebridge implantation, and there are fewer studies that evaluate outcomes in these patients. However, the smaller studies that have been completed demonstrate improved speech recognition in both quiet and noisy environments.12
In addition to an age requirement, patients should have conductive, mixed, or unilateral hearing loss that meets the previously defined pure tone average threshold requirements.1, 2 Patients with ear canal atresia have been shown to benefit substantially as they have a large air-bone gap with a preserved inner ear mechanism. Similarly, patients with otosclerosis, ear canal stenosis, or a chronic draining ear that prevents usage of traditional hearing aids, will also benefit.1, 2
After Bonebridge implantation, patients will have a large artifact on MRI that significantly affects the ability to assess both the ipsilateral as well as the contralateral cranial vaults.13
Single-sided deafness was added to the list of indications for bone conduction implants in the 2000s.2 The development of transcutaneous bone conduction implants such as the Bonebridge implant allowed for substantial reductions in complications associated with the more traditionally used percutaneous models, which have been in use since the 1970s.2, 9 The Bonebridge device was first implanted in 2011.2
The procedure can be done under either local or general anesthesia.1 Approaches include a mastoid, retrosigmoid, or middle fossa placement. For the mastoid approach, a standard postauricular incision is performed. Exposure of both the posterior canal and the mastoid cortex should be accomplished. These landmarks, along with the temporal line, will help to identify the sinodural angle, which is the ideal site for implantation of the BC-FMT.2 Care is then taken to measure where the device will sit within the mastoid. Preoperative assessment with CT can assist in ensuring appropriate location planning. The site is then prepared for the implant using a drill. The drill depth is determined by the patient’s anatomy. In cases where the patient has a thin mastoid (i.e. dura or sigmoid in close proximity), a lift may be necessary in order to avoid compression of these structures. A lift is a thin washer that can be attached to the wings of the BC-FMT, ranging from 1–4 mm in thickness.2 A subperiosteal pocket is created adjacent to the drilled site in the mastoid to accommodate the coil portion of the device, similar to site preparation for a cochlear implant receiver/stimulator. Two pilot holes are then created with the drill bit that is included in the Bonebridge kit. The BC-FMT is secured with two screws, and the wound is subsequently closed in layers.
The surgery lasts less than an hour, with minimal blood loss, and is performed on an outpatient basis. The cosmetic result is excellent as the incision is hidden behind the ear. There are no permanent external components compared with percutaneous models.1 An external device is connected via a magnet to allow for the conduction of signals from the external environment.
The Bonebridge provides substantial benefit to patients, with improved hearing outcomes and relatively few complications.2 Adverse events after implantation are rare, but include pain, dizziness, tinnitus, or minor skin infections. These complications typically resolve within a few days with medical management.2 Patients with SSD typically note improvements in speech recognition in quiet and noisy environments, both objectively and subjectively. Patients are also found to be generally satisfied with their devices.2
The Bonebridge implant continues to be a well-tolerated, safe, and effective option for the treatment of patients with unilateral, mixed, or conductive hearing loss.
Stryker 5 diamond drill
Bonebridge implant kit
Nothing to disclose.
The patient referred to in this video article has given their informed consent to be filmed and is aware that information and images will be published online.
- Miller ME. Osseointegrated Auditory Devices: Bonebridge. Otolaryngol Clin North Am. 2019;52(2):265-272. doi:10.1016/j.otc.2018.11.006.
- Sprinzl GM, Wolf-Magele A. The Bonebridge Bone Conduction Hearing Implant: indication criteria, surgery and a systematic review of the literature. Clin Otolaryngol. 2016;41(2):131-143. doi:10.1111/coa.12484.
- Recommended procedure for Rinne and Weber tuning-fork tests. British Society of Audiology. Br J Audiol. 1987;21(3):229-230. doi:10.3109/03005368709076410.
- Sheehy JL, Gardner G Jr, Hambley WM. Tuning fork tests in modern otology. Arch Otolaryngol. 1971;94(2):132-138. doi:10.1001/archotol.1971.00770070368009.
- Kelly EA, Li B, Adams ME. Diagnostic Accuracy of Tuning Fork Tests for Hearing Loss: A Systematic Review. Otolaryngol Head Neck Surg. 2018;159(2):220-230. doi:10.1177/0194599818770405.
- Davies RA. Audiometry and other hearing tests. Handb Clin Neurol. 2016;137:157-176. doi:10.1016/B978-0-444-63437-5.00011-X.
- Mukherjee, P., Cheng, K., Flanagan, S. et al. Utility of 3D printed temporal bones in pre-surgical planning for complex BoneBridge cases. Eur Arch Otorhinolaryngol 274, 3021–3028 (2017). doi:10.1007/s00405-017-4618-4.
- Reiss M, Reiss G. Zur Differentialdiagnose der einseitigen Schwerhörigkeit [Differential diagnosis of unilateral hearing loss]. Praxis (Bern 1994). 2000;89(6):241-247.
- Gerdes T, Salcher RB, Schwab B, Lenarz T, Maier H. Comparison of Audiological Results Between a Transcutaneous and a Percutaneous Bone Conduction Instrument in Conductive Hearing Loss. Otol Neurotol. 2016;37(6):685-691. doi:10.1097/MAO.0000000000001010
- Ihler F, Blum J, Berger MU, Weiss BG, Welz C, Canis M. The Prediction of Speech Recognition in Noise With a Semi-Implantable Bone Conduction Hearing System by External Bone Conduction Stimulation With Headband: A Prospective Study. Trends Hear. 2016;20:2331216516669330. Published 2016 Oct 3. doi:10.1177/2331216516669330.
- Zernotti ME, Di Gregorio MF, Galeazzi P, Tabernero P. Comparative outcomes of active and passive hearing devices by transcutaneous bone conduction. Acta Otolaryngol. 2016;136(6):556-558. doi:10.3109/00016489.2016.1143119.
- Salcher R, Zimmermann D, Giere T, Lenarz T, Maier H. Audiological Results in SSD With an Active Transcutaneous Bone Conduction Implant at a Retrosigmoidal Position. Otol Neurotol. 2017;38(5):642-647. doi:10.1097/MAO.0000000000001394.
- Steinmetz C, Mader I, Arndt S, Aschendorff A, Laszig R, Hassepass F. MRI artefacts after Bonebridge implantation. Eur Arch Otorhinolaryngol. 2014;271(7):2079-2082. doi:10.1007/s00405-014-3001-y.
Table of Contents
- Implant Template
So we're going to do a MED-EL Bonebridge today. I'm going to show you the steps in that. Start out with a postauricular incision, standard postauricular incision. And- let's expose the mastoid. It's all the way to the tip. So this woman has single-sided deafness- after a- acoustic neuroma with the- that we were not able to preserve hearing on. And- it was done through a middle fossa approach, so her mastoid is intact. So this would be a good opportunity for a Bonebridge. I'll take a bipolar. The other problem here- not holding the ear- if you can't hold the ear- yeah, if you can, that would be great. So we'll dry it up some. So other opportunities for doing a Bonebridge- it can be done if a mastoidectomy has been done, but then you have to go above the linea temporalis, and it's a little different approach than what we're going to show today. So someone who's never had a mastoidectomy, and has single-sided deafness, the mastoid approach for Bonebridge is- very good- a very good option. Dry up all these little bits here. Okay. I will take a Bovie. Basically just expose the mastoid like we would for a cochlear case or a- a cochlear implant. So I make a T-shaped incision at the linea temporalis, and then bisecting the mastoid- mastoid tip. Alright, can I have a Lempert? Hold the ear. So, I will- use this Lempert elevator. To expose everything up to the ear canal. You see there? And I'll take a Weity. Okay, let me have a- Let's make this incision a little bit more anterior. I'll take a Bovie. So this exposure is very similar to what we would do for a- a mastoidectomy or a cochlear implant. Let me see a Bovie? so like a cochlear implant, I'm event- the- eventually gonna make a pocket underneath the muscle for the receiver stimulator to- package to sit. So, she's had a middle fossa craniotomy, so there's a little bit of scarring up there, but that's okay, we're not going to need to be in that area. Alright, so, at this point, what I want to do is measure for where the implant will go. So see, I have the ear canal right here, all exposed. And this is the middle fossa, linea temporalis here, there's the edge of her craniotomy, right there. So the implant- the device will sit right about here. So here's a measuring stick.
Marking- and I'll need a marking pen to measure out where… And this is 16 mm. And I've measured on her CT scan, preoperative CT scan, where- how much room I have. And she has a very large mastoid. So there's plenty- plenty of room, and depth, and also in- in width- in an anterior/posterior direction.
So what I'll do is I'll start with a 5 diamond, and I'll drill the seat- for the implant. So you're using a 5 cutter to start? This is a 5 cutting- 5 cutting bit. Water down. Up. That'll be good. Can I have the bed towards me some more? Okay, good. That's perfect. Alright. So basically I'm just going to drill a circle. Can I get a face shield? Alright, water on. So basically… You don't want to get through the ear canal. So, the depth of the implant is 9 mm. So, you want it to sit in here 9 mm. And I measured the distance to the- sigmoid in this patient, there should be plenty of room. So, let me measure it. So, I push it in, and there's- I could still go deeper, there's 2 lines there, which tells me it's still 2 mm- I have 2 more millimeters. Now, if this was as far as I could go because of either sigmoid sinus or- if we avoid middle fossa because of the dura, then I would need a 2 mm lift. So the number of lines here tell me how many lifts I need, but if I think I can drill deeper and get- get it fully in, which would then show that I don't need any lifts. So I have- I have more room here. We really just need a couple more milliliters, and it'll be… And that I believe is the sigmoid right there. That might be as far as I can go there. I just want to make sure all ledges are taken down. So we can see there's the sigmoid sinus... the air cells. So that's about as deep as it can go right there. Alright, so let me measure it again. Water off. So now it's in all the way. And the other thing I'm looking for is- are these screws flush with the bone? And what I want to be able to do- is- I should be able to pass- not be able to pass- a Rosen needle underneath it. Can I have a Rosen? So I can feel that's really solid on the bone, but I can't inferiorly, or superiorly. So, this tells me to me that I can go all the way in, see there's no- if as far as I went was like that, that would tell me I need 1, 2, 3, 4 lifts. But this was able to be pushed all the way in with these screw guides flush with the bone. So that tells me that's exactly how I want it. So, I'm not going to need any lifts on this one. So what I need to do now- let me have an irrigation? Is I want to make a pocket for the receiver.
Let's clean it up a little bit. So- let me- yeah, so then- this device hooks onto here, and this tells me the angle that I want. So I want this stimulator… You can take it off the stick if you'd like to, so you can manipulate it a little easier. Press and pull. So you press and then pull it out. And so- I'm going to determine the angle where I want these to sit. So this sits on here- and the device can bend. This plastic one shows you the angles that it can go, so I'm going to want this to sit like that, so that there'll be a little bit of an angle bend at the joint between the receiver and the can. So, that's pretty- not much of a bend will be needed. Alright, so what I need to do now- let me see- is make a pocket for the device. And let me have a- let me have a Bovie? There's a little bit of scarring here. Sarah, can I have you come up here and hold this up like this for me? So, she's had this prior craniotomy, so there's a little bit of a scarring here. Hold that like that. Yeah, lift it up, I want to make a little… Okay, now I'll take a- Lempert. So very similar to a cochlear implant pocket. That should be good. Alright, and then I'll use this. I'll use this tester. I'll slide this under. And see that it'll fit just like that. So the pocket's perfect sized. The bone- this will be flushed with the bone. I don't need any lifts. Okay, you can let go Sarah.
So now, I want to make my pilot holes. So what we use is- there's several ways of doing it, You can use self-drilling screws, or you can use a drill system like the Baha with the drill bit that comes with the- that comes with the- the MED-EL Bonebridge kit. So you open the kit. And- here's the bit. And this fits in. So it's anchored like that. And- just like that. So, what I'll need is this back. There we go. Alright, so now we have our 2 holes drilled. There. There and there. And now we put the device in.
Oh, so that's- okay. Do you have a suction? And do we have the screws handy? So it bends a little bit. So, I'll take my first. Screw. Should I hand it to you like this, or? -No. Pop this part off. Yeah, and then you get the screwdriver. Just screw it with... Yeah, right. We'll put a little bit of a- more of a bend in there. So these are self-drilling, self-tapping screws. Loosen- don't want it- just loosen it just a little bit. Get the other hole lined up. You have the screwdriver, empty screwdriver? That's going to get it. Alright. I'll take the other screw. There we go. Now tighten them up. There we go. Tightened up. Do you want to show the torque wrench for your? Oh yeah, so then we have a torque wrench, so we take this bit. and- oh. You take this into here. Okay. On the inside. In is up. In is- right. This goes in here, and we go to 25? 10 to 20. 10 to 20. There we go. 20. Alright, so... When do you see them back? I will see her back in a couple of weeks. A lot of it depends on, you know, the availability of audiology to do the activation. We'd like to try and do it on the same day. Any time the swelling comes down, correct? Yeah. 2-4 weeks, typically. So as you can see, the hole for the template is bigger than the can. So it's okay for there to be some space around it. It's the anchors of the screw in this bone that is actually doing all the work. It doesn't need to have contact with the bone around it. So that's where all the action happens. Perfect. Alright, so now we close it up.