5.1 Stability (implant survival rates, medical complications) and MRI compatibility
Systematic studies on long-term implant stability are relatively scarce but not for percutaneous ‘BCDs’. Reported disadvantages of percutaneous implantation are implant loss and skin irritation around the percutaneous implant, which might lead to (revision) surgery. It should be noted that over the years, less complications occurred, owing to more than 30 years of experience with these implants. New implantation procedures have been introduced as well as optimized implants. Table 5.1, first line, presents Nijmegen data. Systematically, all minor and major complications have been documented for each patient, starting in 1988. Patients were seen at least 5 times during the first years after implantation and twice a year, later on. Apart from planned visits, additional visits took place at the patient’s initiative. Dun et al. (2012) analysed these data from the first successive 903 adult patients, implanted between 1988 and 2008. Table 5.1 shows that one revision surgery has been performed per 30 years of follow-up (column 5). Wazen et al. (2008) published a similar study. They started later with applying these implants, in 1998. That might be the reason why their result is better than that of Dun et al.
More recently, prospective multicentre studies have been published using new, upgraded percutaneous implants and/or implant procedures (Nelissen et al., 2014; Kruyt et al., 2018; see Table 5.1). Indeed, further progress has been made, as, relatively, less revision surgeries were needed.
In 2020 Lagerkvist et al. reviewed the literature, regarding, amongst others, the survival rate of the implants for percutaneous ‘BCDs’ (25 studies; altogether more than 1000 ‘BCD’ users). Using their data, the implant survival rate determined at 1-1.5 years post surgery (8 studies, 372 users) was 98,1% and at 3-5 years post surgery (3 studies, 130 users): 98,5%. In other words, with the more recent percutaneous implants and surgical techniques, the percutaneous-implant survival rate is high, close to 100%, and seems to be stable over time (Lagerkvist et al., 2020).
The last columns of the table presents data related to skin reactions around the percutaneous implant (percentage of visits with some kind of skin reaction). Generally, the severity of skin reaction is expressed in Holgers grades 1 to 4. Grade 2, red and moist tissue, requires local treatment; grades 3 and 4, more severe conditions, might require revision surgery (Wazen et al., 2011). As the table shows, indeed, skin problems remain rather common; however, the percentage of serious skin problems, requiring some type of intervention, is decreasing (Holgers grades 2 to 4; see last column).
Table 5.1. Number of revisions related to the total follow-up period and the percentage of soft tissue reactions
| Author, year | n | Summed revisions | Summed follow-up | Relatively | All skin reactions*** | Holgers grade > 1 |
| Dun, 2012 | 903* | 145** | 4.267 yrs | 1 in 30 yrs | 15% | 4,3% |
| Wazen, 2008 | 218 | 23 | 990 yrs | 1 in 43 yrs | **** | |
| Nelissen, 2014 | 52 | 2 | 156 yrs | 1 in 78 yrs | 23,1% | 1,8% |
| Kruyt, 2018 | 39 | 2 | 117 yrs | 1 in 58 yrs | 15,5% | 1,5% |
*only the adults; **revisions because of soft tissue problems plus lost implants; ***Holgers grades 1 to 4; ****no Holgers grades reported
It should be noted that the follow-up period of the latter two studies is relatively short. However, as has been shown by Dun et al., most complications occur in the first years post implantation.
Concerning MEIs, the number of medical complications and explantations have been reported by e.g., Bernardeshi et al. (2011), Colletti et al. (2013), Mlynski (2014) and Brkic et al. (2019), Sprinzl et al. (2021). The derived revision-surgery rates varied between 1 in 15 years up to 1 in 28 years of follow-up. ‘Teething problems’ might have played a role, especially with regard to surgical techniques and coupling options. Update: indeed, more recent data published by Vickers et al. (2023; multicentre UK data; 163 VSB users), showed a better result: one serious adverse event requiring surgery per 50 years of follow-up.
Sprinzl et al. (2021) and Vickers et al. (2023) also reported survival rates for VSB implants. Sprinzl et al. presented data of 46 patients; they distinguished two subgroups; see section 5.2.2. The implant survival rate of the whole group was 91% at 1-year post implantation and 73% at 4-years post implantation. Vickers et al. reported an implant survival rate of 92% at 1-year and 88% at 3-years post implantation. Vickers et al. also reported implant survival rates for the ‘Bonebridge’ (109 patients), viz. 97% at 1-year and 93% at 3-years post implantation. These survival rates are worse than those of implants for percutaneous ‘BCDs’ (as review by Lagerkvist et al., 2020; see section 5.1). The relatively poor outcome for the VSB is caused by the complicated and/or instable medical status of the patients’ middle ears, were the VSB actuator is located.
The survival rate of implants for percutaneous ‘BCDs’ is favourable compared to that of other implantable devices. However, problems with the skin around the percutaneous implant, leading to revision surgery, might occur. Owing to complicated and/or non-stable medical conditions of the middle ear, VSB-implant loss is relatively high; therefore, a ‘BCD’ might be a safer choice (especially in chronic otitis media; see section 5.2.2).
5.1.2 MRI compatibility
An important issue to consider when choosing an implantable device is MRI safety. MRI is a powerful and increasingly popular diagnostic tool. Statistics show that the incidence of MRI scanning increases steadily over the years. In 2020, the incidence was 66 MRI scans per 1000 habitants in the Netherlands.
Doshi et al. (2014) reviewed the literature and manufacturer’s information on MRI compatibility of percutaneous and transcutaneous ‘BCDs’ and MEIs. The percutaneous implant is MRI safe; in contrast, the MEIs are not MRI safe. Early 2015, a new VSB implant was introduced, the VORP 503, which is MRI safe up to 1.5T. The transcutaneous bone-conduction implants are MRI compatible either up to 1.5T (‘Bonebridge’, Baha Attract) or 3T (Sophono). It should be noted that with each upgrade, MRI safety is specified. Therefore, the data presented here might not be up to date.
Maybe more important is the degree of distortion of the MRI scan caused by the implanted device. The percutaneous implants affect the MRI image only locally (radius of 15 mm) while the transcutaneous implants, comprising magnets, distort the MRI scans more significantly, with a radius of 10 to 15 cm (Doshi et al., 2014). In contrast to damage to the implant by a MRI machine, the distortion of the MRI scan might not change when the devices are upgraded. The best options to minimise the distortion of the MRI image is a percutaneous ‘BCD’ and implants (e.g., Osia, active transcutaneous ‘BCD’; Cochlear) with a piezoelectric actuator instead of an electromagnetic one (Nassiri et al., 2024).
Concerning MRI compatibility, percutaneous ‘BCDs’ are the best option, as well as implanted devices with a piezoelectric actuator.
5.2. Application of implantable devices in certain groups of patients
5.2.1 Congenital middle ear and outer ear anomalies; surgical repair or amplification?
When counselling patients with hearing loss caused by congenital ear anomalies, firstly, reconstructive surgery should be considered. Congenital ear anomalies might vary from mild (middle ear anomalies) to severe (bony atresia of the ear canal) with associated AB-gaps (difference between air- and bone-conduction thresholds) from 40 to 65 dB. Amongst otologists, reconstructive surgery of congenital anomalies is considered as very challenging because of the deviating anatomy, and risk of complications. In audiometric terms, the profit is often limited and not stable over time. Theoretically, surgery is successful if the AB-gap is closed, but mostly, post intervention, an obvious AB-gap remains. To define a successful outcome after atresia repair, often, a rather conservative criterion is used: if the remaining AB-gap is 30 dB or less, the outcome is considered as sufficient (Nadaraja et al., 2013). In their systematic review (35 studies were included), Nadaraja et al. showed that this criterion is met in approx. 50% of the operated patients. Already in 1999, based on a review of the literature and expert opinions, Declau et al. (1999) concluded that atresia repair was only safe in experienced hands and the authors suggested that alternative options like ‘BCDs’ should be considered more often. That conclusion has been underlined by Evans & Kazahaya (2007). They reported that the majority (93%) of their operated patients with atresia of the ear canal still needed some type of hearing device. Further evidence came from the Nadaraja et al. study; they compared the outcomes of studies with percutaneous ‘BCD’ application (Baha) and surgical atresia repair. They concluded that the results with Baha were significantly better. More recently, a systematic review by Shannon et al. (2023) came to the same conclusion.
Apart from atresia of the ear canal, minor congenital (middle ear) anomalies might occur; e.g. isolated congenital stapes fixation or a mobile stapes with ossicular chain anomalies. Thomeer et al. (2010; 2011; 2012) published one-year post-intervention audiometric data; the mean remaining AB-gap was 15 to 20 dB. One year after surgery, 65% to 75% of the operated ears had a PTA (air conduction) of 30 dB HL or better. However, as stated by Thomeer et al., hearing thresholds might have been better with hearing devices. In case hearing aid fitting is considered in minor congenital middle ear anomalies, the first amplification option is a conventional BTE. If the AB-gap exceeds 30 dB HL, a percutaneous ‘BCD’ is the better option; the larger the AB-gap, the higher the profit of a percutaneous Baha/Ponto device over a BTE (for details, see Chapter 2, section 2.2).
In 2006, as an alternative amplification option, Colletti et al. (2006) introduced the VSB with its actuator (FMT) directly coupled to the round window of the cochlea (see also section 2.3). Amongst others, Frenzel et al. (2009) and Colletti et al. (2010) published their results with the VSB applied in patients with atresia of the ear canal and reported that this amplification option was safe and effective. Concerning this VSB application, several coupling options for the FMT to the cochlea have been introduced, either connected to the incus, if the stapes was mobile, or to the round window. If there is a choice, there is a preference for a coupling to the incus because of higher output (e.g. Hüttenbrink et al., 2008). A long-term evaluation showed that all FMT couplings were stable, with the best ‘effective gain’ for the incus coupling (Bush et al., 2017) (for the definition of ‘effective gain’ see Appendix 2).
Regarding the effectiveness of the different types of implants, a literature review was performed. Included were studies in patients with predominant conductive hearing loss, using acoustic implants; mostly children. For details of the review, see Chapter 7; the outcome of this review is presented in Table 7.1, which is copied and presented here as Table 5.2. For a comparison, hearing thresholds obtained after surgical atresia repair are presented as well (first line). The number of included studies, number of patients, (weighted) average bone-conduction thresholds and average aided thresholds (0.5 to 4 kHz) are presented.
Table 5.2 (same as Table 7.1)
| Treatment
|
studies | Patients,
cumulative |
Average bc
threshold |
Average post intervention
threshold with (range) |
| Atresia repair | 5 | 199 | 11 dBHL | 41 (33-47) dBHL |
| Percut. ‘BCD’ | 6 | 135 | 11 | 20 (15-22) |
| ‘Bonebridge’ | 7 | 100 | 10 | 27 (19-31) |
| ‘Sophono’ | 2 | 42 | 16 | 35 (35-36) |
| Conv. ‘BCD’ | 8 | 126 | 11 | 33 (27-45) |
| VSB | 4 | 60 | 11 | 31 (27-40) |
Percut. stands for percutaneous; conv. for conventional ‘BCD’ (‘BCD’ on softband); bc for bone conduction. Range refers to the range of outcomes of the individual studies
Note. Regarding the application of ‘BCDs’: there is no a priori reason to expect that its effectiveness depends on aetiology; however, the effectiveness of a VSB application might depend on the chosen coupling of the VSB to the cochlea, see e.g., section 5.2.3.
Table 5.2 shows that surgical atresia repair might lead to inferior hearing thresholds when compared to the application of percutaneous ‘BCDs’. Regarding transcutaneous ‘BCDs’, the ‘Bonebridge’ is the best option. Results with the VSB are somewhat disappointing.
5.2.2. Chronic otitis media with effusion and supprative otitis media
In most cases, otitis media with effusion (OME) is a transient disease, affecting mainly children. Mostly the OME recovers spontaneously; if not, grommets are inserted in the tympanic membrane. In some children, OME might be (semi) chronic, e.g., in children with Down syndrome and children with cleft palate (Sheenan & Hans, 2006), asking for longer lasting hearing solution. Then, provision of a hearing device might be beneficial. The OME-associated (conductive) hearing loss in such children typically varies between 15 dB HL and 35 dB HL what suggests that BTEs can be used effectively (see Chapter 2, section 2.2). A ‘BCD‘ on a headband or softband has also been advocated (Ramakrishnan et al., 2006). The advantage of a ‘BCD’ is that whenever the hearing loss fluctuates over time (not unlikely in case of OME), BTEs have to be refitted, in contrast to ‘BCDs’. Note, however, that aided thresholds with conventional transcutaneous ‘BCDs’ typically lay around 25-30 dB HL, thus close to the ‘unaided’ thresholds (Snik et al., 2008). Indeed, according to the data of Ramakrishnan et al. (2006), who provided children with OME with ‘BCDs’ on headbands, it was not a great success. More recently, an interesting new approach was launched; the use of commercially available bone-conduction headset with a remote microphone (Holland Brown et al., 2019; 2021). The authors state that this is an affordable and effective solution for children with OME waiting for treatment or recovery and for children with a fluctuating hearing loss.
Chronic supprative otitis media (CSOM) is a long-standing middle ear inflammation that results in periods of discharge from the ear. The tympanic membrane is perforated. CSOM might lead to a serious complication: cholesteatoma (benign collection of keratinized epithelium in the middle ear that can destroy vital structures).
Treatment of such patients is mainly focussed on the inflammation and, eventually, cholesteatoma removal. CSOM might lead to substantial conductive or mixed hearing loss. To improve hearing, the use of BTEs with occluding ear moulds might have an adverse effect on ear discharge. While BTEs are not a safe choice, percutaneous ‘BCDs’ can be used and the outcomes are favourable (Snik et al., 2005). Literature has shown that replacing BTEs by percutaneous ‘BCDs’ had a significant positive effect on the ear discharge (Macnamara et al. 1996; Mylanus et al. 1998; McDermott et al. 2002), which led to a significant reduction in outpatient visits (Hol et al., 2004). This is an important advantage in terms of cost-benefit as well as in patient’s convenience.
Another amplification option is a MEI with the actuator coupled to one of the cochlear windows. This requires an infection-free middle ear. MEIs (VSBs) have successfully been implanted after subtotal petrosectomy with obliteration of the ear cavity with abdominal fat (e.g. Linder et al. 2009 and Ihler et al., 2013). Minor technical and medical problems were reported. Ihler et al. reported one revision surgery in their 10 implanted patients. Mean gain at threshold level (or the ‘effective gain’; for its definition, see Appendix 2) was comparable to that of the VSB applications in other types of mixed hearing loss.
For the effectiveness of the different types of ‘BCDs’ ; see Table 5.2.
For patients with chronic running ears (CSOM) who need amplification, ’BCDs’ are the first treatment option. MEIs might be used as well, although implant surgery is complicated by the fact that a stable, infection-free middle ear has to be established, first of all.
5.2.3 Otosclerosis
Otosclerosis is a disease that leads to mixed hearing loss. Large variations in hearing loss have been reported and hearing loss might deteriorate over time at different rates (e.g. Rotteveel et al., 2004; Sziklai et al., 2009). The conductive part is caused by stapes fixation. Although some twenty-year-old patients with otosclerosis might already have a sensorineural hearing loss component (SNHLc) of 30 dB HL (Iliadou et al., 2006; Topsakal et al., 2006), approximately 90% of the patients suffer from a predominantly conductive hearing loss and a presbycusis-like deterioration of SNHLc with relatively early onset (Kursten et al., 1994; Aarnisalo et al., 2003; Topsakal et al., 2006). The other 10% suffer from an obvious mixed hearing loss; around 1.5% of these patients develop a profound SNHLc, exceeding 70 dB HL, referred to as ‘advanced otosclerosis’.
The generally accepted first treatment option is to place surgically a stapes prosthesis to restore the mobility of the ossicular chain (referred to as ‘stapedotomy’). This is considered as a safe and effective intervention that reduces the AB-gap to 10 dB in most cases. At the high frequencies, the outcome might be somewhat worse (e.g. Strömbäck et al., 2012).
If, after stapedotomy, amplification is still needed, then the first choice is a BTE. In case of advanced otosclerosis, a powerful BTE is needed (e.g. van Loon et al., 2014; Wardenga et al. 2020). VBS application with its actuator applied in the classical way (connected to the incus, moving in parallel to the stapes prosthesis) is also an option, as has been shown by Dumon et al. (2009) and Venail et al. (2007). Kontorinis et al. (2011) and Beltrame et al. (2009) also applied the VBS in patients with otosclerosis, however, with its actuator coupled to the round window.
Another option is the use of ‘BCDs’. Burell et al. (1996) used the percutaneous ‘BCD’ and called it: ‘the third option for otosclerosis’. Since then, little has been published on this application.
Finally, an option was to use the Codacs device (Lenarz et al., 2014); this device, specially developed for patients with advanced otosclerosis, is taken of the market 2020. However, still included in this analysis, as it was the most powerful acoustic implant ever.
A literature search was performed aiming at published audiometric outcomes, obtained with any of these amplification options (BTE, VSB, ’BCD’ or Codacs; summer 2015); little has been published, especially on BTE fittings after stapedotomy. Figure 5.1 gives an overview of the collected data. Concerning BTE, the data were retrieved from three studies in which stapedotomy was not performed or unsuccessful (Burell et al., 1996; Lenarz et al., 2013; Busch et al., 2013).
Figure 5.1. The mean device-aided thresholds presented versus the mean SNHLc of study groups of patients with otosclerosis using: BTEs (red symbols, 3 studies, n=27), Baha (yellow symbol, 1 study, n=7), VSB with the FMT coupled to the round window (open dots, 2 studies, summed n=7), VSB applied in the classical way in patients with a stapes prosthesis (green symbol, 2 studies, summed n=7) and, finally, Codacs device (black round, 3 studies, n=44). Typically, standard deviations (not indicated) varied between 4 dB and 6 dB in either direction. Target line for aided thresholds is presented as introduced in section 4.3, chapter 4
Figure 5.1 suggests that application of either the Codacs device (data from Lenarz et al., 2013; Lenarz et al., 2014; Busch et al., 2013) or the VSB with FMT coupled in the classical way (data from Venail et al., 2007; Dumon et al., 2009), are the most effective options because they the device aided hearing thresholds are closest to the target line. The studies with the FMT coupled to the round window (data from Kontorinis et al., 2011; Beltrame et al., 2009) seem to be less effective. This suggests that FMT applied in the classical way (with stapes prosthesis) is a better option.
For patients with advanced otosclerosis there is still a debate on the best option, stapedotomy plus a powerful BTE or cochlear implantation. Van Loon et al. (2014), reviewing the literature and their own data showed that for such patients, referred for cochlear implantation, stapedotomy with BTE fitting, should still be considered; in several CI (cochlear implant) candidates, stapedotomy with a BTE resulted in adequate speech perception. Interestingly, Kludt et al (2015) reported that patients suffering from advanced otosclerosis, fitted with the Codacs device (acoustic stimulation) had speech in noise scores much better than those of CI users, matched with respect to their cochlear thresholds. This suggests that acoustic stimulation might outperform electric stimulation in patients with severe cochlear hearing loss as found in advanced otosclerosis.
Another issue counselling such patients is that speech recognition after cochlear implantation might be below the expected ‘normal’ values, caused by unfavourable otosclerosis-related conditions. Bone formation within the otosclerotic cochlea might lead to problems with insertion of the CI’s electrode array. Furthermore, broad current spread might occur owing to poor bone quality of the cochlear shell (and therefore poor electrical isolation); this might cause unwanted stimulation of the nerves facialis when activating the CI (see also Chapter 9, section 9.2.3).
First treatment option for patients with otosclerosis is stapedotomy plus, eventually, the fitting of a BTE. Often, patients with advanced otosclerosis, referred for cochlear implantation, might still benefit from a stapedotomy and the fitting of powerful BTEs moreover as speech recognition scores with a CI might be non-optimal.