Chapter 9. Borderline cases: bone-conduction device versus middle ear implant versus cochlear implant

9.0 Introduction

During a round table discussion on borderline cases (CI2024, in Las Palmas), an overview was presented of Nijmegen studies aiming at borderline areas between conventional hearing aids (behind-the ear device or BTE) and implantable hearing devices: Cochlear implant (CI), middle ear implant (MEI) and implantable bone-conduction device (BCD). 

Four borderline areas are addressed

–Sensorineural hearing loss:

  • Severe/profound hearing loss: when switching from BTE to CI?
  • If the hearing loss is moderate to severe, what is the better option: a BTE or MEI?

–Conductive/mixed hearing loss, 

  • What is the best amplification option? A BTE or BCD or MEI?
  • In case of mixed hearing loss with a severe sensorineural component, when switching from a powerful BCD/MEI to a CI?

The focus is on device benefit in terms of speech recognition in quiet. 

 

9.1 Sensorineural hearing loss

9.1.1 When switching from a BTE to a CI in severe/profound sensorineural hearing loss? 

 

The concept of ‘equivalent hearing loss’ is used, comparing speech recognition score of CI users with speech recognition scores of a large group of BTE users with varying degrees of sensorineural hearing loss (Snik et al., 1997). The speech measure chosen in this overview (and in all Nijmegen studies) is the (unilateral) phoneme recognition score in quiet obtained with monosyllables (MPS), presented at a normal conversational level (65 dB SPL; Snik, 2007, Verhaegen et al., 2008). 

In order to determine the ‘equivalent hearing loss’, data of (53) BTE users with moderate to profound sensorineural hearing loss were gathered; Appendix 9.1 presents the selection criteria and the BTE-fitting procedure. In Figure 1, individual, unilateral MPS scores are presented as a function of the PTA3 (mean hearing loss at 0.5, 1 and 2 kHz); the MPS of the ear with the best hearing (lowest PTA3) is presented. The blue line connects median MPS scores of the BTE users divided into classes, according to their PTA3.  These data will be used for a comparison with CI data.

Figure 1. The individual MPS values as a function of the PTA3 of the BTE users and the median (p50) and p25 MPS data of the group of CI users (dotted lines). MPS stands for Monosyllables Phoneme Scores

 

Table 1 presents MPS scores, obtained one-year after cochlear implantation of 139 successive but selected CI users with postlingual onset. Inclusion criteria and details about the types of CI used are presented in Appendix 9.1. The Table presents the median and mean MPS as well as the p25 MPS (the 25e percentile). The p50 (median) and p25 values are indicated in Figure 1 as dotted lines. The figure shows that the median and the p25 MPS values are ‘equivalent’ to those of BTE users with a PTA3 of 75 dB HL and 85 dB HL (expressed in multiples of 5 dB), respectively. In other words, if a CI candidate has a PTA3 > 85 dB HL, then the chance that his/her MPS with CI is higher than with his/her BTE is >75%. If the PTA3 is 75 dB SPL, the chance level is 50%. This suggests that the p25 value (and thus 85 dB HL value) might be the better criterion. 

 

Table 1. The median, p25 and mean MPS scores and the related word recognition scores (WRS) of the CI users

measure MPS WRS
median (p50) 77% 57%
p25 63% 30%
mean 75% 53%
mean, from a later study* 79% 60%

* more recent data from a Nijmegen study (Huinck et al., 2019), see Appendix 9.1 for details

The last line of the table shows the outcome of a study carried out one decade later, by Huinck et al. (2019). They studied the advantage of relatively early implantation by comparing the MPS of two groups of CI users. Group 1 comprised CI users selected using rather conventional inclusion criteria (speech recognition with BTE less than 30% and/or PTA3 > 85 dB HL). Their data are presented in Table 1, last line and are rather well comparable to those used in the previous analysis.

Huinck et al. used the data of Group1 for a comparison with CI users selected according to more relaxed criteria (MPS with BTE between 30% and 60% and/or PTA3 between 65 dB HL and 85 dB HL). The one-year post-implant MPS of the second group was significantly higher than that of Group 1; viz. 85% versus 79%. The authors suggested that relatively early implantation is beneficial, which was ascribed to less ‘auditory deprivation’. 

This suggests that the less conservative PTA3 > 75 dB HL criterion might be the better choice. 

9.1.2 Moderate to severe sensorineural hearing loss, better results with a MEI or a BTE?

 

Nowadays, regarding MEIs, only the Vibrant Soundbridge is widely used (VSB; Med-El, Innsbruck, Austria). In Nijmegen the VSB has (only) been applied if a BTE was contraindicated (owing to chronic external otitis; Snik and Cremers, 2001). MPS data were gathered and used to answer the question which device is more powerful, a BTE or a VSB. The same straightforward method was performed as in the previous section; Figure 2 presents the MPS as a function of the PTA3 of 30 patients, fitted with a VSB (for details regarding inclusion criteria and devices used, see Appendix 9.1). A best-fit line is presented; the full black line. The blue line in the figure is copied from Figure 1, referring to BTE users. Evidently, the VSB scores are below the BTE scores. E.g., at a PTA3 of 65 dB HL, the MPS with VSB is approx. 25% worse than that obtained with BTE, increasing to 45% at 75 dB HL.

The figure suggests that, if the PTA3 exceeds 50-60 dB HL, a BTE should be fitted for better speech recognition, unless a BTE is contraindicated. Compared with the p50 MPS from CI users, the ‘equivalent hearing loss’ is approx. 60 dB HL, so, if a BTE is contraindicated, cochlear implantation might be considered if the PTA3 exceeds 60 dB HL. 

Although the capacity of the VSB is limited, it should be noted that this device is highly appreciated by patients with moderate sensorineural hearing loss and chronic external otitis. They can use this device all day without pain or itching (Snik and Cremers, 2001). The Med-El Company advocates the present VSB only for patients with sensorineural hearing loss suffering from chronic external otitis.

Figure 2.  The individual MPS of MEI users plotted as a function of the PTA3. For reference purposes, more recent literature data (Maier et al., 2015); mean MPS versus mean PTA3, presented as a red dot (see Appendix 9.1 for details) 

 

9.2 Conductive and mixed hearing loss

 

9.2.1 What is the best option: a BTE or a BCD? 

 

Most often, the cause of a (chronic) conductive/mixed hearing loss is aural atresia/stenosis or a chronic draining ear. In either case, a BTE is contraindicated. However, in other aetiologies like otosclerosis or tympanosclerosis, a BTE might be used. 

Whether a (powerful) BTE or a BCD is more effective, depends on the width of the air-bone gap. Assume a powerful BTE is used with a mean maximum output (MPO) of 112 dB HL and a mean gain of 50 dB. If the air-bone gap is e.g. 55 dB, then the effective MPO is really limited: viz. 112 minus 55 thus 57 dB HL, and the effective gain is -5 dB. Even the less powerful conventional BCDs can provide such a MPO and gain. 

The MPO and gain of a BCD are not affected by the width of the air-bone gap. The mean MPO of more powerful BCDs like the percutaneous BCD (pBCD; see section 9.2.2) is significantly higher than that 57 dB HL; a MPO of 85 dB HL with a mean gain of up to 20 dB is achievable.

Mylanus et al. (1998) and de Wolf et al (2010) compared outcomes (MPS) obtained with powerful BTEs and pBCDs in (Nijmegen) patients with conductive/mixed hearing loss. They found that if the air-bone gap exceeds 30-35 dB the pBCD provided higher gain and therefore better speech scores than the BTE; below 30 dB the BTE provided the best result.

In other words, if a BTE is not contraindicated while the mean air-bone gap exceeds 35 dB, then a powerful (thus percutaneous) BCD might be the better amplification option.

 

9.2.2 If a BCD is indicated, which type of BCD should be used? In other words, can we rank today’s BCDs?

 

Before discussing the capacity of BCDs, an overview of the different types that are  available. 

  1. The non-surgical, conventional BCD, which is kept in place by a softband, steal headband or adhesive coupling. Such devices are referred to as transcutaneous passive BCDs, e.g., the Baha Softband (Cochlear BAS, Goteborg, Sweden), Ponto Softband (Oticon Medical, Askim, Sweden) and the Adhear (Med-EL, Innsbruck, Austria)
  2. BCD with magnetic coupling, requiring a surgically placed subcutaneous magnet for coupling purposes. This device is also referred to as a transcutaneous passive device, e.g., the Sophono device (Medtronic, Minneapolis, USA) and the Baha Attract (Cochlear BAS; see Figure 3) 
  3. Another transcutaneous approach consists of an actuator (the vibrator) implanted subcutaneously in the mastoid, driven by an externally worn audio-processor. This type of BCD is referred to as a transcutaneous active BCD. Available devices nowadays: the Bonebridge (Med-E; see Figure 3), the Osia (Cochlear BAS) and the Sentio (Oticon Medical)

Figure 3. Different types of BCDs

 

  1. The percutaneous BCD (pBCD) with a skin penetrating implant, connecting the BCD to the skull without attenuation caused by the damping tissue. Available devices: the Baha (Cochlear BAS) and the Ponto (Oticon Medical; see Figure 3). It should be noted that (only) for the pBCDs more powerful audio-processors are available besides the standard processors.

 

The different types of BCDs are not equivalents. In contrast to BTEs, all BCDs (and MEIs) have a limited capacity. E.g., the loudest sound that BCDs can produce (the MPO or maximal power output) varies between 50 dB HL and 85 dB HL, while men can tolerate sounds up to 105-115 dB HL.

The MPO of BCDs and also that of the VSB have been studied. Table 2 gives a literature overview. The table shows that data from different studies are rather consistent. It should be noted that in contrast to the other BCDs and VSB, the MPO of pBCD can easily be derived from the available data sheets, following the procedure introduced by Carlsson and Hakansson (1997). 

The Table doesn’t provide the MPO of the passive transcutaneous devices. Their mean MPO lays between 50 dB HL and 60 dB HL (Van Barneveld et al., 2018); included in the Table are only the more powerful options.

What are the consequences of a low MPO? Figure 4 presents the audiogram of a patient with mixed hearing loss. Bone conduction thresholds are shown as well as loudness discomfort levels. The patient was fitted with a passive tBCD with magnetic coupling as the bone-conduction thresholds laid well within the application range of that device. Measured MPO values are also displayed. The mean bone conduction threshold is 32 dB HL and the mean MPO of the tBCD is 55 dB HL. Consequently the ‘auditory window’ with this BCD, is just 23 dB (55 minus 32 dB HL). 

Figure 4. Audiogram of a patient with mixed hearing loss. As a BCD is applied, only the bone conduction thresholds are relevant. MPO values are also displayed 

Figure 5.  On the right side, the (simplified) audiogram with (mean) MPO levels of different types of BCDs. Now, on the left, the level of every-day sound sources, expressed in dB HL. Arrows indicate  ‘projections’ of the (grey) speech area into the patient’s auditory window. tBCD: transcutaneous passive BCD; pBCD: percutaneous BCD; BCD-SP: pBCD with powerful sound processor.

 

Figure 5, left side, presents the outside world with all kinds of sounds, expressed in dB HL. The grey area represents the speech area (normal conversational speech at 65 dB SPL). Evidently, projecting properly relevant sounds (not only speech at normal conversational level, but also with raised voice or someone talking at some distance or the patient’s own voice and the other sounds) in the narrow ‘auditory window’ of 23 dB is not easily possible. 

Now, the right figure also shows the MPO of more powerful BCD solutions (values taken from Table 2). With a standard pBCD, the auditory window becomes 37 dB and if a more powerful processor is used, like the Baha 5 SP, then the window becomes 55 dB, the maximum achievable window with todays BCDs. With the VSB, this window is 50 dB. Thus, from an audiological point of view, pBCD is the best option followed by the VSB device. As Figure 5 shows, the speech area is approx. 35 dB wide. This value is used to define application ranges for different types of BCD and the VSB. We use the following assumption: for a given patient, a specific BCD can be used only if the ‘auditory window’ is at least 35 dB. Simply means that the highest acceptable PTA4bc (average bone-conduction threshold at 0.5, 1, 2 and 4 kHz) is the mean MPO value minus 35 dB. Table 3 gives an overview; it should be noted that, at date, the MPO of the relatively new transcutaneous active BCDs (Osia en Sentio) is not known yet (not published). 

Evidently, the different types of BCDs and the VSB are not equivalents; if the PTA4bc of a transcutaneous passive BCD user exceeds 20-25 dB HL, then an update to a percutaneous device might significantly improve the patient’s performance. Another option is to apply a VSB. For Bonebridge users with a PTA4bc exceeding 30 dB HL, a pBCD or VSB are the next options. 

 

9.2.3 In severe mixed hearing loss, when to switch to a CI?

 

Following the same procedures as used before, Figure 6 presents the MPS versus PTA3 (bone-conduction) of 26 patients with mixed hearing loss with moderate to severe sensorineural component using the most powerful BCD at that time, the Baha Cordelle (Verhaegen et al., 2009). For selection criteria etc. see Appendix 9.1. The PTA3 for bone conduction varied between 30 dB HL and 75 dB HL. As the figure shows, when using the CI-p50 (77%), the ‘equivalent hearing loss’ is 60 dB HL. 

Figure 6. Individual MPS values as a function of PTA3 if 26 users of the most powerful pBCD

 

Verhaegen et al. (2009) also presented the data of the first five Nijmegen patients switching from a Baha Cordelle to a CI. Two of them suffered from advanced otosclerosis and external otitis and three from chronic middle ear problems. The MPS of these five patients improved significantly from 10% (range 0 to 30%) with BCD to 75% (range 60% to 90%) with the CI. 

Regarding advanced otosclerosis, performance with a CI might be worse than in patients with normal cochlear anatomy (Rotteveel et al., 2010). Poor performance is caused by anomalies of the cochlea leading to problems with the insertion of the electrode array. This might lead to a partial insertion. Because of poor bone quality, facial nerve stimulation might occur. Then, certain electrodes have to be switched off (Rotteveel et al., 2010). Therefore, the MPS scores of CI users with otosclerosis are worse than those of patients with a normal bony structure; the p50 and p25 MPS values for CI users with otosclerosis are 55% and 40% respectively (Rotteveel et al., 2010), thus more than 20% below those of CI users with anatomically normal cochleae (Figure 1). Using Figure 6 the otosclerosis-specific p50 and p25 (not shown) result in ‘equivalent hearing loss’ values of 70 dB HL and 75 dB HL, respectively.

Cochlear implantation in the other group of patients with severe mixed hearing loss, suffering from chronic middle ear problems, is also challenging. Nevertheless, cochlear implantation in such patients remains of utmost importance, as it is a ‘last resort’ solution. 

 

9.2.4 Which acoustic implantable device to use for patients with conductive/mixed hearing loss?

 

Previous sections clearly suggest that the pBCD is the best option from an audiological point of view. That device has some other specific advantages as well, but also a disadvantage. The advantages:

  1. Of course application of a pBCD requires surgery, however minimal invasive surgery, in contrast to all the other implantable options. Implantations have even been performed in outpatient clinics 
  2. pBCD is the only implantable device that can be updated when hearing deteriorates. Besides the standard sound-processor, power and superpower processors are available
  3. The distortion of MRI images is limited in contrast to most other implantable BCDs and VSB. Explantation of MEIs and active tBCDs because of MRI have been reported 

Disadvantage of pBCDs are infections around the percutaneous implant and implant loss owing to poor fixation in the skull bone (poor osseo-integration).

Elaborations.

Regarding point 1: Minimal invasive surgery lowers the burden for the patient and the costs of the intervention. At the other end, placing a MEI in patients with conductive/mixed hearing loss might be challenging, especially in patients with congenital anomalies (e.g., aural atresia) and in patients with chronic otitis media. In the latter case, subtotal petrosectomy is a required first surgical step (Verhaert et al., 2013).

Regarding point 2: Longevity is an important issue, especially when treating elderly people. This is illustrated in Table 4, which shows the effectiveness of several types of BCDs and the VSB in relation to age of patients with mixed hearing loss. Few data were found on the deterioration of the sensorineural component in patients with mixed hearing loss. Therefore, as an approximation, we used age-related hearing thresholds taken from the ISO standard (ISO 7029, 2017), with an additional cochlear loss of 20 dB HL owing to cochlear damage caused by middle ear infections and/or medical treatments in the past (group ISO 7029+; see Appendix 9.1 for details). We used these data for illustrating the effect of aging on the effectiveness of several devices.  

 

Table 4. Effective use of devices in progressive (cochlear) hearing loss in patients with cochlear damage caused by chronic otitis media in the past (ISO 7029+). 

  

device PTAbc max,

dB HL

ISO 7029+

years

Passive tBCD* 25 up to 50 
Active tBCD** 30 up to 60
VSB 45 up to 80
pBCD 50 up to ±85

* with magnetic coupling; ** the Bonebridge

 

Table 4 shows that when using a passive tBCD with magnetic coupling, the PTAbc max for applying that device (25 dB HL; taken from Table 3) is passed at age 50 years. Evidently, the pBCD and VSB are the best solutions as they might be used effectively life long.

Disadvantages of percutaneous implantation are skin problems around the implant and implant loss, leading to revision surgeries. Through the years, the number of revisions has dropped, owing to more than 35 years of experience with percutaneous implants. New implantation procedures have been introduced as well as optimized implants. Table 5, 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 at least twice a year, later on. Apart from planned visits, additional visits took place at the patient’s initiative. Dun et al. (2012) published data on medical complications of 903 successive adult patients, implanted from the start in 1988 up to 2008. Table 5 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, 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 a specific new, improved percutaneous implant and/or implant procedure (Nelissen et al., 2014; Kruyt et al., 2018; see Table 5). Indeed, further progress has been made, as relatively less revision surgeries were needed. 

It should be noted that the follow-up period of the latter two studies is relatively short, 3 years. However, as has been shown by Dun et al., most complications occur in the first year post implantation. 

The last columns of the table presents data related to skin problems around the percutaneous implant (percentage of visits with some skin reaction). Severity of skin reaction was 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).  Indeed, skin problems remain common; however, the percentage of serious skin problems requiring some type of intervention is decreasing (Holgers grades 2 to 4; last column). 

 

Table 5.  Number of revisions related to the total follow-up period and the percentage of soft tissue reactions

Author, year n revisions Summed follow-up relatively All skin reactions3 Holgers grade > 2
Dun, 2012 9031 1452 4.267 yrs 1 in 30 yrs 15% 4,3%
Wazen, 2008 218 23 990 yrs 1 in 43 yrs 4
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%

1only the adults; 2revisions because of soft tissue problems plus lost implants; 3Holgers grades 1 to 4; 4no Holgers grades reported 

 

Similar systematic studies on complications with the other types of BCDs and MEIs are lacking. 

It is suggested, based on the data of Table 5, that one revision surgery in 40 years might be considered as the standard for all implantable devices.

 

9.3. Concluding remarks

 

Fortunately, nowadays several amplification options are available for deaf and hearing-impaired patients for whom conventional amplification (BTE) is no longer effective or contra-indicated (CI, BCD, MEI). Thanks to the investigators and the companies that put these devices into the market! 

Regarding the future; a main concern is the costs of these interventions; each update of any implantable device comes with a higher price. Cost is a major issue; already in 1998, Daniels & Sabin concluded: ’no country in the world can afford all of the medical care that providers can render to populations’ (Daniels and Sabin, 1998). In other words, there is a great need for better affordable hearing devices including implants, see also the ‘World report on hearing’ (WHO, 2021).

 

Appendix 9.1 

 

Section 9.1.1. Regarding the 53 BTE users: the inclusion criteria were: age between 18 and 70 years, with flat or mildly sloping audiogram (difference in threshold between 0.5 kHz and 4 kHz less than 40 dB HL) with hearing thresholds < 110 dB HL up to 4000 Hz (to exclude patients with dead regions), using BTEs for at least 3 years. They were all fitted with state-of-the-art digital hearing devices using the NAL-NL fitting rule in the Nijmegen clinic, using one and the same validation protocol (Snik, 2007; Verhaegen et al., 2008).  

Selection criteria for the 139 CI users: postlingual deafness with normal cochlear anatomy. Age: between 18 and 70 years. Devices used were the Cochlear CI (N22, N24, Freedom) and Advanced Bionics CI (C1, 90K), almost equally divided. The patients were implanted between 1990 and 2009. Same evaluation protocol was used as for the BTE users. Evidently, the included data are relatively old data, however, comparable to that for a group of 52 CI users implanted in Nijmegen between 2010 and 2016, using similar conservative inclusion criteria. Their mean MPS was 79% (Huinck et al., 2019), close to MPS of reference CI group (75%).

   

Section 9.1.2. Regarding the 30 VSB users: inclusion criteria were: age 18-70 years, with flat or mildly sloping audiogram (difference in threshold between 0,5 kHz and 4 kHz less than 40 dB HL) and with hearing threshold < 80 dB HL up to 4 kHz, using their VSB for at least 1 year. The patients were fitted between 1998 and 2008 (unilaterally) with the AP303 or AP404 speech processor. For the fitting, the NAL rule was applied. The evaluation protocol was the same as used to test the BTE users (Snik, 2007; Verhaegen et al., 2008). 

Evidently, the included data are relatively old data. Maier et al. (2015) presented data of a more recently implanted group (their group 1, n=34). They were fitted with the Amade speech processor, using the NAL fitting rule. Individual data were not presented: in Figure 2, the average MPS is presented at the average pre-intervention PTA3 (red symbol). This average MPS is in agreement with the Nijmegen data (data-point on the best fit line) suggesting that the MPS values used might still be relevant. Note that Maier et al. reported the mean WRS using monosyllables; that score was expressed as a MPS, using a look-up table. 

 

Section 9.2.3. The study group comprised 26 patients, using the most powerful BCD at that time, the Baha Cordelle (Verhaegen et al., 2008). The inclusion criteria were: age 18-70 years, with flat or mildly sloping bone-conduction audiogram and measurable bone conduction thresholds up to 2 kHz. They were all using a pBCD for more than a year. The mean MPO of the Baha Cordelle (0.5 to 4 kHz) is 82 dB HL, 1 to 4 dB below that of more recent powerful pBCDs, as presented in Table 2. 

 

Section 9.2.4. Deterioration of hearing loss in aging patients with chronic middle ear problems. 

For subjects with pure sensorineural hearing loss, ISO 7029 describes the deterioration of hearing sensitivity owing to aging, however, only for otologically normal subjects (ISO, 2017). In case of chronic middle ear problems, progression in cochlear hearing loss might follow the ISO 7029 norm, however, with an additional cochlear loss owing to either the infections or medical interventions in the past. We assessed that additional cochlear loss by comparing the bone-conduction thresholds of patients between 50 and 70 years, using a BCD, with the age-specific ISO 7029 thresholds. The assumption is that cochlear damage caused by the middle ear problems is reduced significantly by using a BCD instead of a BTE (e.g., Macnamara et al., 1996). 

Three studies with relevant data were identified. Table A9.1 shows that the ‘additional sensorineural hearing loss’ is approx. 20 dB (note: the ISO thresholds used were the average for those of men and women).

 

Table A9.1. Bone conduction thresholds compared to age-specific ISO 7029 norms of patients with mixed hearing loss using BCDs; the additional cochlear loss.

Study; first

author

n (ears) 0.5 kHz

dB

1 kHz 

dB

2 kHz

dB

4 kHz

dB

mean 

dB

Bosman, 2013 18 15  20 25 20  20 
Flynn, 2012 20 15 20  20  10  17 
Pfiffner, 2011*  44 19

*their group C; no frequency specific data available

 

References

 

Bosman AJ, Snik AF, Hol MK, Mylanus EA. Evaluation of a new powerful bone-anchored hearing system: a comparison study. J Am Acad Audiol. 2013 Jun;24(6):505-13.

 

Carlsson PU, Håkansson BE. The bone-anchored hearing aid: reference quantities and functional gain. Ear Hear. 1997 Feb;18(1):34-41. 

 

Daniels N, Sabin J. The ethics of accountability in managed care reform. Health Aff (Millwood). 1998 Sep-Oct;17(5):50-64.

 

Dun CA, Faber HT, de Wolf MJ, Mylanus EA, Cremers CW, Hol MK. Assessment of more than 1,000 implanted percutaneous bone conduction devices: skin reactions and implant survival. Otol Neurotol. 2012 Feb;33(2):192-8. 

 

Flynn MC, Hedin A, Halvarsson G, Good T, Sadeghi A. Hearing performance benefits of a programmable power baha® sound processor with a directional microphone for patients with a mixed hearing loss. Clin Exp Otorhinolaryngol. 2012 Apr;5 (Suppl 1):S76-81. 

 

Ghoncheh M, Busch S, Lenarz T, Maier H. A Novel Method to Determine the Maximum Output of Individual Patients for an Active Transcutaneous Bone Conduction Implant Using Clinical Routine Data. Ear Hear. 2024 Jan-Feb 01;45(1):219-226. 

 

Huinck WJ, Mylanus EAM, Snik AFM. Expanding unilateral cochlear implantation criteria for adults with bilateral acquired severe sensorineural hearing loss. Eur Arch Otorhinolaryngol. 2019 May;276(5):1313-1320. 

 

ISO 7029, 2017. Acoustics. Statistical distribution of hearing thresholds related to age and genders. Third edition, 2017-01, International Organization for Standardization, Geneva, Switzerland

 

Kruyt IJ, Monksfield P, Skarzynski PH, Green K, Runge C, Bosman A, Blechert JI, Wigren S, Mylanus EAM, Hol MKS. Results of a 2-Year Prospective Multicenter Study Evaluating Long-term Audiological and Clinical Outcomes of a Transcutaneous Implant for Bone Conduction Hearing. Otol Neurotol. 2020 Aug;41(7):901-911.

 

Macnamara M, Phillips D, Proops DW. The bone anchored hearing aid (BAHA) in chronic suppurative otitis media (CSOM). J Laryngol Otol Suppl. 1996;21:38-40.

 

Maier H, Hinze AL, Gerdes T, Busch S, Salcher R, Schwab B, Lenarz T. Long-term results of incus vibroplasty in patients with moderate-to-severe sensorineural hearing loss. Audiol Neurootol. 2015;20(2):136-146. 

 

Maier H. Improving the evidence base of audiological indication ranges from pre-clinical and clinical measurements. Keynote, Osseo, Denver, US, 2023.

 

Mertens G, Desmet J, Snik AF, Van de Heyning P. An experimental objective method to determine maximum output and dynamic range of an active bone conduction implant: the Bonebridge. Otol Neurotol. 2014 Aug;35(7):1126-30.  

 

Mylanus EA, van der Pouw KC, Snik AF, Cremers CW. Intraindividual comparison of the bone-anchored hearing aid and air-conduction hearing aids. Arch Otolaryngol Head Neck Surg. 1998 Mar;124(3):271-6. 

 

Nelissen RC, Stalfors J, de Wolf MJ, Flynn MC, Wigren S, Eeg-Olofsson M, Green K, Rothera MP, Mylanus EA, Hol MK. Long-term stability, survival, and tolerability of a novel osseointegrated implant for bone conduction hearing: 3-year data from a multicenter, randomized, controlled, clinical investigation. Otol Neurotol. 2014 Sep;35(8):1486-91. 

 

Pfiffner F, Caversaccio MD, Kompis M. Audiological results with Baha in conductive and mixed hearing loss. Adv Otorhinolaryngol. 2011;71:73-83. 

 

Rotteveel LJ, Snik AF, Cooper H, Mawman DJ, van Olphen AF, Mylanus EA. Speech perception after cochlear implantation in 53 patients with otosclerosis: multicentre results. Audiol Neurootol. 2010;15(2):128-36. 

 

Snik A. Auditory implants, 2024, www.snikimplants

 

Snik AFM, Vermeulen AM, Brokx JP, Beijk C, van den Broek P. Speech perception performance of children with a cochlear implant compared to that of children with conventional hearing aids. I. The “equivalent hearing loss” concept. Acta Otolaryngol. 1997 Sep;117(5):750-4. 

 

Snik AFM. Hearing impairment in the high-tech era. Inaugural lecture, Radboud University Nijmegen. Thieme MediaCenter, Nijmegen, 2007; ISBN 90-9021439-9.

 

Snik AFM, Cremers CW. Vibrant semi-implantable hearing device with digital sound processing: effective gain and speech perception. Arch Otolaryngol Head Neck Surg. 2001 Dec;127(12):1433-7. 

 

van Barneveld DCPBM, Kok HJW, Noten JFP, Bosman AJ, Snik AFM. Determining fitting ranges of various bone conduction hearing aids. Clin Otolaryngol. 2018 Feb;43(1):68-75.

 

Verhaegen VJ, Mulder JJ, Mylanus EA, Cremers CW, Snik AF. Profound mixed hearing loss: bone-anchored hearing aid system or cochlear implant? Ann Otol Rhinol Laryngol. 2009 Oct;118(10):693-7.

 

Verhaegen VJ, Mylanus EA, Cremers CW, Snik AF. Audiological application criteria for implantable hearing aid devices: a clinical experience at the Nijmegen ORL clinic. Laryngoscope. 2008 Sep;118(9):1645-9. 

 

Verhaert N, Mojallal H, Schwab B. Indications and outcome of subtotal petrosectomy for active middle ear implants. Eur Arch Otorhinolaryngol. 2013 Mar;270(4):1243-8.

 

Wazen JJ, Young DL, Farrugia MC, Chandrasekhar SS, Ghossaini SN, Borik J, Soneru C, Spitzer JB. Successes and complications of the Baha system. Otol Neurotol. 2008 Dec;29(8):1115-9. 

 

Wazen JJ, Wycherly B, Daugherty J. Complications of bone-anchored hearing devices. Adv Otorhinolaryngol. 2011;71:63-72. 

 

WHO 2021. World report on hearing. Geneva: World Health Organization; 2021. Licence: CC BY-NC-SA 3.0 IGO.

 

Zwartenkot JW, Snik AF, Mylanus EA, Mulder JJ. Amplification options for patients with mixed hearing loss. Otol Neurotol. 2014 Feb;35(2):221-6.

 

Chapter 10. A rather technical update, March 2021

Are today’s implantable hearing devices better than conventional devices for patients with conductive or mixed hearing loss?

Introduction

In March 2014, we published a paper in ENT & Audiology news, with the same title. The present overview should be considered as an update. Since 2014, several new implantable hearing devices have been introduced, existing device types have been further developed and, unfortunately, some devices have been withdrawn from the market. Below, an overview is given of devices, which are available early 2021, with the focus on their effectiveness; only acoustical implantable devices are considered. The central question is: what are the choices for a patient with a particular hearing loss? In this overview, a division is made between patients with conductive/mixed hearing loss (part 1) and those with sensorineural hearing loss (part 2). This overview can be considered as a summary of the website snikimplants.nl. In the present text, regularly, a reference is given to a specific (sub)chapter of the website for more detailed information; these references are colored red.

Part 1; patients with conductive and mixed hearing loss

Patients with conductive or mixed hearing loss become candidates for amplification if reconstructive surgery is not an option or might lead to poor post-surgical hearing thresholds (see e.g. Nadaraja et al., 2013). The amplification options available nowadays are: the conventional acoustic behind-the-ear devices (BTE) or in-the-ear devices, conventional (non-surgical) bone-conduction devices (BCDs), (semi-)implantable BCDs and active middle ear implants with their actuator coupled to one of the cochlear windows. This overview aims primarily at comparing the audiological capacity (effectiveness) of non-surgical and implantable BCDs, mainly based on literature reviews.

1.1 The limitations of air-conduction devices in conductive and mixed hearing loss

BTEs are effective hearing devices for sensorineural hearing loss, however, less effective, if the patient has an additional attenuation (air-bone gap) on top of the sensorineural hearing loss. Obviously, if the gain of a BTE, measured on an ear simulator, is 50 dB and the maximum output is 115 dB SPL (representative values), and if the hearing impaired patient has sensorineural hearing loss with additionally an air-bone gap of 45 dB, then the gain reduces to just 5 dB (50-45) and the maximum output to just 70 dB SPL (115-45). Wardenga et al. (2020), studying patients with otosclerosis or tympanosclerosis (no contra-indication for using an air-conduction device) indeed showed that the width of the air-bone gap is an important success factor for a BTE fitting.

Fitting a conventional BCD is not necessarily more effective than a BTE, as the bone-conduction route is far less effective than the air-conduction route. Amongst others, Skoda-Türk and Welleschik (1981) showed that the bone-conduction route is even approximately 50 dB less effective. In other words, the first 50 dB produced by the amplifier of such a traditional BCD are ‘lost’, making this solution in principle as (in)effective as a BTE for the patient with a 50 dB air-bone gap. So, both options are not effective; however, if the air-bone gap is limited, below 50 dB HL, then the BTE might be the better choice.

In the case of a malformed, atretic ear or chronically inflamed middle ear, BTEs cannot or should not be used, and thus, BCDs are the next option.

1.2 Conventional, transcutaneous BCDs

Figure 1 shows a conventional BCD, which comprises a sound processor (in a BTE housing) and, separately, the actuator (bone vibrator). The actuator is pressed against the skin, behind the ear, by means of the steel spring headband. This traditional set-up has been updated during the last decades. Instead of the steel headband to keep the actuator in place, a so-called softband has been introduced, specifically developed for young children (Baha Softband; Verhagen et al., 2008). Nowadays, the BCD manufacturers have such a solution available.

figure 2.2

Figure 1, a traditional, conventional bone-conduction device; source Internet

More recently, a BCD with a magnetic coupling (needing surgery; see section 1.2.1) and a BCD with an adhesive coupling, the Adhear device, were introduced (e.g. Favoreel et al. 2020; Osborne et al. 2020).

Below, a comparison is made of these devices, based on a systematic review of published papers (period: 2005-early 2021). Papers presenting audiological data, comparing two different types of the above-introduced BCDs, were included. The search string included device names, and ‘bone-conduction’ and ‘hearing thresholds’. The following eight papers were identified and included in this overview: Verhagen et al., (2008); Christensen et al. (2010); Denoyelle et al. (2015); Powell et al. (2015); Giannantonio et al. (2018); Skarzynski et al. (2019); Favoreel et al. (2020) and Osborne et al. (2020).

The hypothesis is that the new coupling options are approximately as effective as the traditional coupling with the steel headband.

Verhagen et al. (2008) and Christensen et al. (2010) compared the Baha Softband with traditional BCDs with steel headband. Combining these 2 studies (in total n=22) a small difference in aided thresholds was seen of 2.3 dB in favor of the softband. Favoreel et al. (2020), Osborne et al. (2020) and Skarzynski et al. (2019) compared the Adhear with the softband. Combining the data from these 3 studies (n=37), a minor difference was found of 1.6 dB, in favor of the Adhear. So, the ‘traditional’ transcutaneous BCD has been updated and, as such, is still on the market. A major advantage of these devices is that surgery (implantation) is not involved. 

1.2.1 Conventional BCDs, transcutaneous solutions that require surgery

In 2011, another type of coupling was introduced; the magnetic coupling (Sophono device; e.g. Denoyelle et al., 2015). In contrast to coupling the actuator with a headband or with an adhesive, surgery is involved. One magnet is placed subcutaneously, connected to the skull, behind the pinna, and the other magnet is attached to the actuator of the BCD. Some years later, the Baha Attract was released with the same type of coupling (e.g. Powell et al., 2015). Denoyelle et al. (2015) compared the (pre-surgery worn) Baha Softband and the Sophono device. No differences in aided thresholds were found. Aided thresholds obtained with the Baha Attract and Sophono were compared in two other studies (Powell et al. 2015; Giannantonio et al. 2018). After pooling their data (n=32) a difference of 3 dB was found in favor of the Baha Attract.

Next, the mean aided threshold (0.5, 1, 2, 4 kHz) was calculated for all subjects from any of the studies, using one of the non-implantable transcutaneous solutions (in total n=109) and, separately, those using a semi-implantable transcutaneous device with magnetic coupling (n=79). The calculated mean aided threshold was 28 dB HL (s.d. of 3 dB HL, range 20-33 dB HL) and 29 dB HL (s.d. of 2 dB HL, range 25-33 dB HL), respectively. Therefore, as hypothesized, in terms of aided thresholds, all these transcutaneous BCDs seem to be equally effective. So, the type of coupling doesn’t play a part. It should be noted that the reported aided thresholds, in the range of 25-30 dB HL, are relatively poor, especially for young children, who need to develop speech and language (see section 1.6).

Apart from effectiveness, other factors play a role in the selection of a particular BCD, like ease of device use, costs, cosmetics and whether or not the device is comfortable to use. If implanted, additional factors that should be considered as well are: the stability and safety of the implanted part of the BCD, extra costs and MRI compatibility.

The softband is easier to use and better accepted than a steel headband (Verhagen et al., 2008); in contrast to the softband, skin problems occurred more frequently with headband, owing to the rather high local pressure to keep the actuator in place and effective, with the steel headband (Snik et al., 2005). With the adhesive BCDs, problems with the skin have been reported as well. Neumann et al. (2019) reported that 2 of the 12 subjects using the Adhear device discontinued using their device owing to persistent irritation of the skin, while other studies reported no skin problems with the adhesive BCD (Favoreel et al., 2020). Concerning the BCDs with the magnetic coupling; reviewing the literature, Bezdjian et al. (2017) reported that skin problems occurred in 29% of subjects using the Sophono device; in 3.5% of the subjects these problems were severe. Dimitriadis et al. (2017) reported minor skin problems in 4 % of their Baha Attract users and serious skin problems in 3 %.

In short, skin problems are not uncommon and might occur with all these transcutaneous devices; however, the percentage of serious problems leading to non-use or even revision surgery is low.

Regarding children, it should be noted that the youngest age at which the Sophono and Baha Attract magnets can be implanted is 5 years, according to the manufacturers. So, for young children (< 5 years), only the non-surgical options remain.

1.3 BCDs with percutaneous coupling

Two more types of BCD are available that bypass the skin and subcutaneous layers. These layers attenuate the vibrations produced by any transcutaneous BCDs. These two types of BCD comprise a BCD with percutaneous coupling to the skull and a BCD with its actuator implanted, under the skin, connected by a transmission link to an externally-worn sound processor (see below, section 1.3.1).

In the late eighties a percutaneous coupling for BCDs was developed as an alternative for the transcutaneous coupling. Hakansson et al. (1984) showed that their newly developed percutaneous coupling was approx. 15 dB more effective than the transcutaneous coupling, because the vibration-attenuating skin and subcutaneous layers were bypassed. Nowadays, there is a choice between the percutaneous Cochlear Baha devices and Oticon Ponto devices. Apart from the standard sound processor, more powerful BCD processors are available, what is of importance for longevity of the treatment (Chapter 4.2). Regarding aided thresholds obtained with the first generations Baha compared to those of the conventional BCDs, a systematically difference of 6-10 dB was found in favor of the Baha (Cremers et al., 1992; Snik et al., 2004). Recently, a comparison was made between more homogenous groups, viz. children with conductive loss. Aided thresholds were more than 10 dB better with Baha (Chapter 7.2.1).

Another approach to compare BCDs, instead of studying aided thresholds, is to compare maximum output levels (MPO) of different types of BCDs (Chapter 2.3). The MPO, or the loudest sound that a BCD can produce, is a device-characteristic, objective measure. In comparison BTEs, the MPO of BCDs is rather limited; the MPO of BTEs might be 120 dB SPL (average at 0.5, 1, 2 and 4 kHz, which equals approx. 115 dB HL). Transcutaneous BCDs have a MPO, expressed in dB HL, just around 55 dB HL (e.g. Sopohono device; Chapter 2.3). The Baha Attract is an exception, whenever a power processor (BP110) is used instead of the standard processor; the measured MPO was 64 dB HL.

The MPO of standard percutaneous BCD processors is approx. 67 dB HL, while the MPO of the more powerful processors is significantly higher, up to 80-85 dB HL (Chapter 2.3). All these MPO values are limited, restricting the patient’s dynamic range of hearing with the device switched on. The patient’s dynamic range of hearing is, by definition, the difference in dB HL between the hearing (bone-conduction) thresholds and the MPO of the fitted BCD. Studying the MPO of all the different types of BCD leads to similar conclusion regarding effectiveness as that drawn from studying aided thresholds. That was expected because, to deal with that limited MPO which causes distortions of loud sounds, a lower gain setting than usual might be chosen by the subject. Doing so, on the one hand distortions will be less audible, while on the other hand aided thresholds will be worse. Indeed, Cremers et al. (1992), comparing conventional BCDs with headband, with the percutaneous Baha, showed that the aided thresholds were approx. 10 dB better with percutaneous Baha, while harmonic distortion, measured in the sound field, was significantly less with Baha, ascribed to the higher MPO.

Percutaneous BCSs are the most powerful type of BCD on the market (early 2021).

Problems with the skin around the percutaneous implant are not uncommon. A recent study showed that adverse skin reactions, needing treatment, occurred in 15% of the patients (Langerkvist et al., 2020). Complication leading to revision surgery also occur; the longer the follow-up, the higher the chance. To related revisions with follow-up, the revision ratio was introduced (Chapter 5.1.2), being the accumulated follow-up periods of all subjects in the study divided by the number of revision surgeries in that group. That ratio proved to vary between studies and surgical procedures. The traditional surgical approach includes thinning of the skin around the percutaneous implant; in this case, in adults, the ratio was 1 revision in 43/77 years of follow-up (2 studies). Recently, other approaches have been introduced, mainly to simplify the surgical procedure (no thinning of the skin layers). Then the ratio is somewhat less: 1 revision in 30/55 years (also 2 studies). These ratios seem to be acceptable. Complication rates are higher in children; see section 1.6.

1.3.1 Transcutaneous device with the actuator (vibrator) implanted, connected to the skull

In 2001, another concept was introduced; the actuator of the BCD was totally implanted, rigidly connected to the skull. That actuator is connected to the externally sound processor by a transmission link. The first device on the market was the Bonebridge device. Huber et al. (2013) studying BCD devices in cadaver heads, measuring vibration of the cochlear promontory, concluded that the Bonebridge device was as effective as the standard Baha device (BP100). In agreement with that, Gerdes et al. (2016), comparing two groups of patients, one group using the Bonebridge and the other the percutaneous Baha, reported that aided threshold and several speech recognition scores were identical. Comparing the MPOs of the two devices (the standard Baha and the Bonebridge), a difference of 4 dB was seen in favor of the Baha (Chapter 2.3).

As said before, all these MPO values are limited, restricting the patient’s dynamic range of hearing with the device. To deal with that, compression amplification is often used. In principle, compression amplification is advocated for patients with a limited dynamic hearing range caused by physiological factors. Compression can also be used to minimize the consequences of a limited dynamic range caused by a low MPO of the fitted device. However, the better option, instead of using compression, is to apply a more powerful BCD. Recently, another transcutaneous device with the actuator connected to the skull was introduced, the Osia device (Cochlear Company). This rather new device will be discussed soon on the website Snikimplants.nl.

1.4 Active middle ear implants 

Another option instead of a BCD is to use an active middle ear implant with its actuator coupled to one of the cochlear windows; nowadays, the only available option is the Vibrant Soundbridge device (Chapter 2.3). Regarding the audiological outcomes: the MPO is approx. 85 dB HL (Chapter 2.3) thus in the same range as the most powerful percutaneous BCD, the Baha 5 SP. Regarding aided thresholds, using data from a literature search (including a.o. 14 studies with VSB and 18 studies with percutaneous BCD, in patients with mixed hearing loss (Chapter 3, last paragraphs), a spread in outcomes is seen, however, not a structural difference between these two types of devices. This suggests that fitting either a percutaneous BCD or a VSB leads to similar aided thresholds. Both devices worked well in patients with mixed hearing loss with a sensorineural hearing loss component of up to 50-55 dB HL.

The main theoretical advantage of a VSB is that in contrast to a BCD, only the cochlea of the implanted ear is stimulated. With a BCD, owing to the low attenuation of the bone-conducted vibrations through the skull bone, the contralateral cochlea is stimulated as well, although to a lesser degree, referred to as ‘cross’ stimulation. The limited research looking into ‘cross’ stimulation shows no clear advantage of the VSB (regarding directional hearing, see Agterberg et al., 2014); however, no firm conclusion can be drawn yet.

Implantation of the VSB in an atretic ear might be challenging owing to the abnormal anatomy (Mancheno et al., 2017). In chronic inflamed middle ear, first of all, the inflammation should be dealt with, e.g. by a subtotal petrosectomy with obliteration of the middle ear with abdominal fat. Then the VSB can be applied effectively (Chapter 5.2). So, in contrast to BCD, VSB implantation in conductive/mixed hearing loss is more demanding. Regarding complications, post-VSB implantation, again, the relation between reported revision surgeries and the accumulated follow-up time was determined (5 studies). The ratio varied from one revision in 15 years up to one in 28 years (Chapter 5.1.2), thus worse than those found for percutaneous BCDs (see above section 1.3). It should be noted that most of the included studies presented combined data of the VSB applied in conductive/mixed hearing loss and in sensorineural hearing loss.

1.5. Conclusion

For optimal treatment for a particular patient with conductive or mixed hearing loss, choosing the best BCD, BTE or the VSB, is a challenge. Given the effectiveness and the limitations of the different options, counseling is of utmost importance. Transcutaneous BCDs are less vulnerable to skin reactions compared to percutaneous BCDs. Furthermore, the complications with percutaneous implant might require revision surgery. However, the percutaneous BCD is by far the most powerful BCD solution, thus leading to better hearing. As the processor of percutaneous devices can be changed for more powerful processors, the percutaneous BCD might be used life long, in contrast to the other types of BCDs (Chapter 4.2). For children choosing the best option is even more challenging; see next section. Compared to BCD implantation, VSB implantation is more complicated and complications requiring revision surgery are relatively high. On the other hand, as for percutaneous BCDs, longevity is not a major issue.

1.6 Application of BCDs in children

For hearing impaired children, counseling is even more important. For young children, good hearing is essential: the better the hearing the higher the chance that the child will develop normally. According to Northern and Downs (1991), indeed, children need normal hearing (15 dB HL or less) to ensure normal development of speech and language. This statement is in agreement with anecdotal data presented by Verhagen et al. (2008). Therefore, when counseling the parents of a child with a hearing loss, sufficiently powerful amplification options should be advocated.

In case of a congenital conductive hearing loss, whenever the tympanic membrane is at least partly visible (typically the air-bone gap will be near 40 dB HL), BTEs might be an effective solution. A transcutaneous BCD with headband or softband should be used in all the other cases. Nowadays, the adhesive coupling is also an option. As the aided sound field thresholds (mean data of 28-29 dB HL; see above) are significantly above the target of 15 dB HL, replacement of the transcutaneous BCD with the more powerful percutaneous BCD or Bonebridge, should remain on the agenda and, meanwhile, speech and language development should be monitored (Verhagen et al., 2008). The use of percutaneous BCDs involves implantation of a skin penetrating titanium coupling. Concerning the youngest age at which such implantation is feasible, thickness of the skull plays an important role: 3 mm or more is preferred (Snik et al., 2005). This implies that the child must be approximately 4 years old. Even then, loss of implants is a problem. Recently, a literature review was published aiming at complications and implant loss in children (comprising 952 percutaneous implants; Kruyt et al., 2020). Implant loss occurred in 14% and revision surgery was needed in 17% of the implants. However, implant loss with more recently introduced new percutaneous implants with a wider diameter, seemed to be better than that of older types, viz. 8,2% versus 25,5%. Although these figures are significantly worse than the reported complication rates with transcutaneous devices, the higher effectiveness of percutaneous devices should be taken into account while counseling. However, once more, it should be noted that, on the average, aided thresholds in children with conductive hearing loss, using percutaneous BCDs, are more than 10 dB HL better than those in children using conventional transcutaneous BCDs (see review, Chapter 7.2.1).

The VSB with the transducer coupled to one of the cochlear windows has been applied in children as young as 2 months (Mandala et al., 2011). Since then, little has been published. Only one paper was found (with n>5); Leinung et al. (2017) presented results obtained in 13 young children with aural atresia with an average age of 2.5 years. While the mean bone conduction threshold (at 0.5, 1, 2, 4 kHz) of the whole group was 8 dB HL, the mean aided threshold was just 40 dB HL, which is rather poor. In order to advocate VSB implantation in toddlers and young children, more evidence is needed. Studying elderly children, in total 60 children from 4 studies, a better mean aided threshold was found, viz. 31 dB HL, which still is approx. 10 dB worse than that of percutaneous BCDs (Chapter 7.2.1). That figure might improve with growing surgical experience.

In summary, regarding children, choices have to be made, based on the child’s development, audiological aspects (effectiveness) and the drawbacks of the devices. Good hearing is of utmost importance and, as long as the rehabilitation is not optimal in audiological terms, monitoring the child’s progress remains of prime importance.

It should be noted that application of bilateral BCDs in children with bilateral conductive hearing loss, congenital or acquired, is of utmost importance (Chapter 6.2); the vast majority of the children accepts two devices. Papers on bilateral application of the VSB in children are scares. Application of a BCD in unilateral congenital conductive hearing loss, however, is still debatable; profit is limited and non-use is unacceptably high, even with a percutaneous BCD (Chapter 6.2). Within four years after implantation about 40% of the children stopped using the BCD and 25% used it occasionally. Similar long-term data on the use of VSB in such children is lacking.

However, binaural hearing scores in patients with unilateral acquired conductive hearing loss using a percutaneous BCD were much better than those found in congenital cases (adult data; Agterberg et al., 2011). This suggests that previous experience with bilateral input is an important success factor.

Part 2; Acoustic implants for patients with sensorineural hearing loss

The BTE is the standard treatment for patients with mild to severe sensorineural hearing loss; whenever the hearing loss is severe/profound, cochlear implantation is the treatment of choice.

An alternative amplification option for patients with moderate/severe sensorineural hearing loss is an active middle ear implant. Nowadays, two semi-implantable devices, the Vibrant Soundbridge (VSB; Chapter 2) and the Maxum device (Ototronix, USA), and one fully implantable device, the Esteem device (Envoy Medical, St. Paul, MN, USA) are on the market. In 2014, two reviews of the literature were published comparing these devices amongst others, with BTEs; it was reported that no structural audiological benefit was found compared to BTEs (Chapter 8.1). As the implantable devices are expensive and involve surgery, the cost-utility ratio of these devices is unfavorable compared to BTEs. Since the two reviews of the literature were published, in 2014, to our knowledge, just two more clinical trials with audiological data were published; one regarding the Maxum device and one with the Esteem device, as published by company-independent research groups. In contrast, since 2014, 11 papers were identified with audiological data obtained in patients with sensorineural hearing loss using the VSB.

Although these middle ear implants have, on the average, no convincing audiological advantages compared to BTEs, they might be of major benefit for patients who cannot use a BTE (e.g. patients that don’t tolerate ear molds owing to chronic external otitis; see e.g. VSB fact sheet, Med-El, 2015)Edfelt et al. (2014) even showed that for such patients the application of the VSB device is cost effective.

Nijmegen, March, 10th 2021, Ad Snik, Martijn Agterberg

References

Agterberg MJH, Hol MKS, Cremers CWRJ, Mylanus EAM, van Opstal AJ, Snik AFM. Conductive hearing loss and bone conduction devices: restored binaural hearing? Adv Otorhinolaryngol. 2011;71:84-91.

Agterberg MJ, Frenzel H, Wollenberg B, Somers T, Cremers CW, Snik AF. Amplification options in unilateral aural atresia: an active middle ear implant or a bone conduction device? Otol Neurotol. 2014 35:129-35.

Van Barneveld D, Kok H, Noten J, Bosman A, Snik A. Determining fitting ranges of various bone conduction hearing aids. Clin Otolaryngol. 42018;3:68-75.

Bezdjian A, Bruijnzeel H, Daniel SJ, Grolman W, Thomeer HGXM. Preliminary audiologic and peri-operative outcomes of the Sophono™ transcutaneous bone conduction device: A systematic review. Int J Pediatr Otorhinolaryngol. 2017;101:196-203.

Christensen L, Smith-Olinde L, Kimberlain J, Richter GT, Dornhoffer JL. Comparison of traditional bone-conduction hearing AIDS with the Baha system. J Am Acad Audiol 2010;21:267-73.

Cremers CW, Snik FM, Beynon AJ. Hearing with the bone-anchored hearing aid (BAHA, HC 200) compared to a conventional bone-conduction hearing aid. Clin Otolaryngol Allied Sci. 1992;17:275-9.

Denoyelle F, Coudert C, Thierry B, Parodi M, Mazzaschi O, Vicaut E, Tessier N, Loundon N, Garabedian EN. Hearing rehabilitation with the closed skin bone-anchored implant Sophono Alpha1: results of a prospective study in 15 children with ear atresia. Int J Pediatr Otorhinolaryngol. 2015;79:382-7.

Dimitriadis PA, Hind D, Wright K, Proctor V, Greenwood L, Carrick S, Ray J. Single-center Experience of Over a Hundred Implantations of a Transcutaneous Bone Conduction Device. Otol Neurotol. 2017;38:1301-1307.

Edfelt L, Stromback K, Grendin J et al., Evaluation of the cost-utility in middle ear implantation in the ‘Nordic’ school; a multi-center study in Sweden and Norway. Acta Otolaryngol. 2014;134:19-25.

Favoreel A, Heuninck E, Mansbach AL. Audiological benefit and subjective satisfaction of children with the ADHEAR audio processor and adhesive adapter. Int J Pediatr Otorhinolaryngol. 2020;129:109729.

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;37:685-91.

Giannantonio S, Scorpecci A, Pacifico C, Marsella P. A functional and anatomical comparison between two passive transcutaneous bone conduction implants in children. Int J Pediatr Otorhinolaryngol. 2018;108:202-207.

Håkansson B, Tjellstrom A, Rosenhall U. Hearing thresholds with direct bone conduction versus conventional bone conduction. Scand Audiol 1984;13:3-13.

Huber AM, Sim JH, Xie YZ, Chatzimichalis M, Ullrich O, Röösli C. The Bonebridge: preclinical evaluation of a new transcutaneously-activated boneanchored hearing device. Hear Res. 2013;301:93-9.

Kruyt IJ, Bakkum KHE, Caspers CJI, Hol MKS. The efficacy of bone-anchored hearing implant surgery in children: A systematic review. Int J Pediatr Otorhinolaryngol. 2020;132:109906.

Lagerkvist H, Carvalho K, Holmberg M, Petersson U, Cremers C, Hultcrantz M. Ten years of experience with the Ponto bone-anchored hearing system-A systematic literature review. Clin Otolaryngol. 2020;45:667-680.Leinung M, Zaretsky E, Lange BP, Hoffmann V, Stöver T, Hey C. Vibrant Soundbridge® in preschool children with unilateral aural atresia: acceptance and benefit. Eur Arch Otorhinolaryngol. 2017;274:159-165.

Mancheño M, Aristegui M, Sañudo JR. Round and Oval Window Anatomic Variability: Its Implication for the Vibroplasty Technique. Otol Neurotol. 2017;38:e50-e57.

Mandalà M, Colletti L, Colletti V. Treatment of the atretic ear with round window vibrant soundbridge implantation in infants and children: electrocochleography and audiologic outcomes. Otol Neurotol. 2011;32:1250-5.

Nadaraja GS, Gurgel RK, Kim J, Chang KW. Hearing outcomes of atresia surgery versus osseointegrated bone conduction device in patients with congenital aural atresia: a systematic review. Otol Neurotol. 2013;34:1394-9.

Nelissen RC, Mylanus EA, Cremers CW, Hol MK, Snik AF. Long-term Compliance and Satisfaction With Percutaneous Bone Conduction Devices in Patients With Congenital Unilateral Conductive Hearing Loss. Otol Neurotol. 2015;36:826-33.

Neumann K, Thomas JP, Voelter C, Dazert S. A new adhesive bone conduction hearing system effectively treats conductive hearing loss in children. Int JPediatr Otorhinolaryngol. 2019;122:117-125.

Northern JL, Downs MP. Hearing in children. Williams & Wilkins, 1991; Chapter 1.Osborne MS, Child-Hymas A, McDermott AL. Longitudinal study of use of the pressure free, adhesive bone conducting hearing system in children at a tertiary centre. Int J Pediatr Otorhinolaryngol. 2020;138:110307.

Powell HR, Rolfe AM, Birman CS. A Comparative Study of Audiologic Outcomes for Two Transcutaneous Bone-Anchored Hearing Devices. Otol Neurotol. 2015;36:1525-31.

Skarzynski PH, Ratuszniak A, Osinska K, Koziel M, Krol B, Cywka KB, Skarzynski H. A Comparative Study of a Novel Adhesive Bone Conduction Device and Conventional Treatment Options for Conductive Hearing Loss. Otol Neurotol. 2019;40:858-864.

Skoda-Türk R, Welleschik B. Luft- oder Knochenleitungshören? Zur Hörgeräteversorgung von Schalleitungsschwerhörigen. Laryngol Rhinol Otol (Stuttg). 1981;60:478-83.

Snik AF, Bosman AJ, Mylanus EA, Cremers CW. Candidacy for the bone-anchored hearing aid. Audiol Neurootol. 2004;9:190-6.

Snik AF, Mylanus EA, Proops DW, Wolfaardt JF, Hodgetts WE, Somers T, Niparko JK, Wazen JJ, Sterkers O, Cremers CW, Tjellström A. Consensus statements on the BAHA system: where do we stand at present? Ann Otol Rhinol Laryngol Suppl. 2005;195:2-12.

Verhagen CV, Hol MK, Coppens-Schellekens W, Snik AF, Cremers CW. The Baha Softband. A new treatment for young children with bilateral congenital aural atresia. Int J Pediatr Otorhinolaryngol. 2008;72:1455-9.

Vogt K, Frenzel H, Ausili SA, Hollfelder D, Wollenberg B, Snik AFM, Agterberg MJH. Improved directional hearing of children with congenital unilateral conductive hearing loss implanted with an active bone-conduction implant or an active middle ear implant. Hear Res. 2018;370:238-247.

VSB fact sheet (VORP 503/Samba). The Vibrant Soundbridge system. Med-El website, downloads; visited June 2015.

Wardenga N, Diedrich V, Waldmann B, Lenarz T, Maier H. Hearing Aid Treatment in Patients with Mixed Hearing Loss. Part I: Expected Benefit and Limitations after Stapes Surgery. Audiol Neurootol. 2020;25:125-132.

Blog 2019-2: Percutaneous bone conductor or (active) middle ear implant to treat mixed hearing loss? Osseo presentation

Introduction

To rehabilitate patients with mixed hearing loss, implantable devices like the Vibrant Soundbridge middle ear implant (VSB) or percutaneous bone conductors (BCDs) have been applied. Such implantable devices become the next option whenever conventional hearing devices (e.g. behind-the-ear device) or reconstructive surgery are not possible or probably not effective (e.g. in case of aural atresia or chronic draining ears). Using recent publications, describing clinical trails, a comparison is made between audiological outcomes obtained with either power BCDs and VSBs. Studies in patients with severe mixed hearing loss were considered only if the mean sensorineural hearing loss component was at least 35 dB HL (arbitrary choice).

Medline was used to find relevant studies, published between 2016 and early 2019. Of the 30 detected studies, 25 studies were excluded (see Materials and Methods in the appendix) and five studies remained:

Busch et al. (2016) studied 78 patients with mixed hearing loss using the VSB with its actuator coupled to either the round window (RW) or the oval window (OW); Lee et al., (2017) and Zahnert et al. (2019) also published VSB data, including 19 and 24 patients, respectively. Bosman et al. (2018) published data on the application of a recently introduced percutaneous power BCD, viz. the Baha 5SP, applied in 10 patients and  Bosman et al. (2019) published also data on another percutaneous power BCD, the Ponto 3SP device, applied in 18 patients.

Separately, for reference purposes, data obtained with the Codacs middle ear implant device were included (Lenarz et al., 2013). This device, developed for severe mixed hearing loss was on the market from 2013 until 2018. It was the most powerful middle ear implant (MEI) ever. In contrast to the other devices, the maximum power output (MPO) of the Codacs is so high that it had to be limited when applied in patients (Lenarz et al., 2013; 2014).

The Methods and Materials section is added as an appendix.

Results

Figure 1 presents the frequency-specific gain values related to the (bone-conduction) threshold; it should be noted that a VSB with actuator coupled to the cochlea and BCDs directly stimulate the cochlea, bypassing the impaired middle ear (and thus the air-bone gap). Therefore, to assess the effectiveness of the device fitting, only the ‘effective gain’ is of importance, defined as the cochlear (bone-conduction) thresholds minus the aided thresholds (e.g. Busch et al., 2016; Snik, 2018).

The figure presents the ‘effective gain’ divided by the cochlear hearing loss, referred to as the gain-threshold (GT) ratio, plotted as a function of frequency (0.5 kHz to 4 kHz). If GT=0, it means that the aided threshold and the cochlear thresholds coincide, indicating no ‘compensation’ of the cochlear hearing loss. Regarding the VSB, the subfigure at the right shows the calculated results using Zahnert et al. (2019), Lee et al. (2017) and Busch et al. (2016), separately. As these curves show a similar trend, data were averaged after weighting for the number of patients per study. The mean VSB data in the left subfigure show the highest GT ratio at 2 kHz with roll-off in higher and lower frequencies. For the Baha 5SP, a broader frequency response is seen comparable to that of the Ponto 3SP; obviously, the latter device is less powerful (lower GT values).

The target GT ratio (0.45), according to the well-validated NAL-RP fitting procedure, is also indicated (Dillon, 2012; see also Appendix). Systematic differences are seen between the measured GT ratios and that NAL-target GT ratio, especially in the high and low frequencies.  At 2 kHz the measured values are closest to the NAL-GT target.

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Figure 1. The gain-threshold (GT) ratio presented as a function of frequency. Results of the included studies are shown (individual data of the 3 VSB studies, presented in right subfigure, were averaged). According to the NAL-RP fitting rule, the target GT ratio is approx. 0.45 (indicated in the figure)

The NAL fitting rule is well established for sensorineural hearing loss (Dillon, 2012). However, compared to conventional behind-the-ear devices, BCDs and middle ear implants have a limited dynamic range caused by a relatively low MPO (maximal power output). Therefore, a modified, pragmatic version of the NAL fitting rule has been introduced for these implantable devices (Snik et al., 2019, see Appendix), meant primarily for validation purposes. Figure 2 shows target-aided thresholds as obtained with this pragmatic validation rule, minus the measured aided thresholds. A value of 0 means that the result is adequate according to that rule; negative values indicate insufficient gain. Mean (pooled) VSB data and, separately, the results of the Ponto 3SP study and Baha 5SP study are presented. In agreement with Figure 1, an obvious discrepancy is found at 0.5 kHz for the VSB device. The Ponto 3 SP has relatively little gain at 2 kHz.

The Baha 5SP seems to be an adequate device with a rather flat curve around 0; as Figure 2 shows, the Ponto 3SP device lags behind by approx. 6 dB, what might be ascribed to the difference in MPO of the two BCDs. The MPO of the Baha 5SP is approximately 9 dB higher than that of the Ponto 3SP (Schwartz, 2018). The MPO of the VSB and the Baha 5SP are rather comparable (Chapter 2 in Snik, 2018).

As a reference, Codacs data are added in both figures, showing that the best resemblance is found with the Baha 5SP.

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Figure 2. The difference between prescribed aided thresholds and measured aided thresholds as a function of frequency. The modified NAL-procedure was used. Pooled VSB data are presented, and, separately, the data of the two percutaneous BCD studies

Apart from aided thresholds, three studies presented aided speech recognition scores in quiet, however, measurement conditions and the tests used were divers. Importantly, in all studies, monosyllabic words were applied. Busch et al. (2016) and Zahnert et al. (2019) presented word scores obtained at a presentation level of 65 dB SPL, using the Freiburger monosyllable test. Bosman et al. (2018; 2019) reported only speech-in-noise data. From their databases, Dutch NVA monosyllable test scores were retrieved comprising phoneme score obtained at 60 dB SPL. These data were converted into word scores and corrected for presentation level. Lee et al. (2017) presented the words at variable levels, viz. the individual patient’s most comfortable listening level. Therefore, these data were excluded. Table 1 shows the outcomes.

Table 1. Speech recognition scores at 65 dB SPL presentation level

WRS PS score and calculated WRS Correction 60 à 65 dB SPL
VSB Zahnert* 67%
VSB Busch* 78%
Ponto 3SP*** 75%/52% 75%
Baha 5SP*** 69%/44% 70%
Codacs** 75%

Note WRS: word recognition score, * Freiburger monosyllable test; (Busch et al., 2013). ** WRS obtained with different monosyllable tests (different languages; Lenarz et al., 2013; Lenarz et al., 2014); *** NVA monosyllable test (PS at 60 dB SPL corrected to WRS at 60 dB SPL using WRS=PR2.3; correction for 65 instead of 60 dB SPL using WRS increases by 5 % per dB)

In summary, referring to Figure 2, for patients with mixed hearing loss around 35-45 dB HL, the achieved aided thresholds related to the prescribed values with either Codacs, VSB or the percutaneous Baha 5SP and Ponto 3SP are rather comparable and relatively close to prescribed values using the adaptive NAL rule (except the VSB at 0.5 kHz and the Ponto 3SP at 2 kHz). Speech recognition, a supra threshold outcome measure, is also rather comparable between systems.

Closing remarks

It is acknowledged that the VSB outcomes depend on the efficacy of the actuator coupling to the cochlea (e.g. Busch et al., 2016). Recently, a new coupling option has been developed (Lenarz et al., 2018; Mueller et al., 2018), which has a positive effect on the frequency response of the VSB, boosting gain and output with 10-15 dB around 1 kHz.

For the percutaneous BCDs, the coupling of the processor to the skull is more or less standardized and, therefore, not a major source of variance between subjects.

To choose a device, the audiological performance is highly relevant but also of importance is the invasiveness and complexity of the surgery, medical and technical complications and its risks, longevity, cost etc. Regarding the Baha 5SP, with high volume setting, it might be advised to use the behind-the-ear processor away from the ear, with a clip connected to clothing, to deal with feed-back. That might be considered as a draw back. Regarding de application of a middle ear implant, the status and anatomy of the middle ear is of importance as it might affect effective application (e.g. Manchero et al., 2017).

Note that the conclusions drawn are valid for the present devices/processors. If more powerful processors or more effective actuators are introduced or if better coupling techniques are being developed, conclusions might change.

Appendix.

Materials and methods

Search strategy

This review was carried out in accordance with PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses; Moher et al., 2009). Medline (Pubmed) was used to find relevant studies, published between 2016 and early 2019. Search string was: ((soundbridge OR ponto OR baha) AND (mixed hearing) NOT transcutaneous). Thirty manuscripts were identified; based on the abstracts, 20 manuscripts were excluded because: the focus was on cochlear implantation (1), comprised a review, no original data (5), case reports and how-we-do-it reports (4). Manuscripts dealing with medical/surgical issues (8), technical issues (1) and application in pure sensorineural hearing loss (1) were excluded as well. The full text of the remaining 10 manuscripts was reviewed. One more manuscript was excluded because the mean cochlear hearing loss was below 35 dB HL (Iwasaki et al., 2017), three manuscripts were excluded as the bone-conduction thresholds and/or aided thresholds were not presented frequency specific (essential information for the present analyses; Brkic et al., 2019; Olszewski et al., 2017; Monini et al., 2017) and one manuscript with just 5 relevant patients (Gregoire et al., 2018). Five studies were included; regarding VSB: Busch et al. (2016); Zahnert et al. (2019) and Lee et al. (2017). Regarding BCD, two studies were identified: Bosman et al. (2018) and Bosman et al. (2019). Unfortunately, Bosman et al., didn’t present the aided thresholds; these were retrieved from their database.

Table 2 gives an overview of some number of subjects per study and mean age at intervention.  For reference purposes, data obtained with the Codacs middle ear implant were included (Lenarz et al., 2013; Lenarz et al., 2014; Busch et al., 2013). This device was the most powerful middle ear implant, on the market from 2013 to 2018. Mean age of the 43 patients (of the 3 evaluative studies) was 59 years.  On the average, the patients using BCDs are older than those using the MEIs.

Table 2. Some patient characteristics

Study; first author Lee, 2017 Busch, 2016 Zahnert, 2019 Bosman, 2018 Bosman, 2019
n 19 78 24 18 10
Device VSB VSB VSB Ponto 3SP Baha 5SP
Age, years 55±17 57±17 55 (34-75) 64 (22-80) 70 (59-77)

Note. n: number of patients; PTAbc: calculated mean bone-conduction threshold at 0.5, 1, 2, 4 kHz. Regarding the age at implantation, mean age is presented with standard deviation or the median age with range between brackets

Table 3. The mean bone-conduction thresholds (in multiples of 5 dB) per type of implant.

Thresholds (dB HL): 0.5 kHz 1kHz 2kHz 4kHz
VSB, n=121 30 dB HL 35 40 45
Baha 5SP n=10 30 40 50 55
Ponto 3SP n=18 30 40 45 50
Codacs n=43 45 45 50 50

Gain measurement

BCDs as well as the MEIs with its actuator coupled to one of the cochlear windows stimulate the cochlea directly, bypassing the impaired middle ear. Therefore, the air-bone gap doesn’t play any role when fitting these devices and, to evaluate audiological benefit, the ‘effective gain’ is of importance. The ‘effective gain’ is defined as the cochlear (bone-conduction) thresholds minus the aided thresholds (e.g. Busch et al., 2016; Snik, 2018).  The ‘effective gain’ assesses which proportion of the cochlear hearing loss is ‘compensated’ by the device. By definition, the often-used ‘functional gain’ equals the ‘effective gain’ plus the air-bone gap, and is mainly dominated by the width of the air-bone gap. In contrast, the ‘effective gain’ is a measure of the quality of the device fitting and can be compared to target gain values as prescribed by generally used, validated prescription procedures.

Given a certain hearing loss, obviously, the required ‘effective gain’ depends on the cochlear hearing thresholds (the higher the hearing loss, the higher the gain should be). Therefore, the ‘effective gain’ divided by the cochlear threshold (the gain/threshold ratio or GT ratio) is calculated; according to the widely used NAL-RP hearing aid fitting rule, this ratio should be approximately 0.45 for 1, 2 and 4 kHz, for proper amplification (Dillon, 2012).

However, for mixed hearing loss cases, that target GT ratio of 0.45 is not easily reached, owing to, amongst others, the limited highest sound level that can be produced by BCDs or VSBs (limited output), characterised by the ‘maximum power output’ or MPO of these devices. Therefore, a pragmatically adapted NAL procedure has been introduced for these implants, to be used for validation purposes (Snik et al., 2019). This pragmatic procedure was based on the NAL rule (Dillon, 2012) and optimized using data of 31 published clinical trials, regarding all types of BCDs and active middle ear implants. Consequently, this adapted NAL rule is device independent. The assumption is that appropriate (sufficiently powerful) implantable devices have been chosen (regarding the MPO) and that amplification is (predominantly) linear. In short, following the NAL fitting procedure, aided thresholds should equal 0.55 times the cochlear (bone-conduction) threshold; a margin of 5 dB was added. However, at 1, 2 and at 4 kHz the aided threshold should be 25 dB HL or less. This latter adaptation is based on the statement that, in case of (predominant) conductive hearing loss, de first 20 dB can be missed (Dillon, 2012). Regarding 0.5 kHz, following the NAL-RP rule, calculated target aided threshold is 5 dB higher than that at 1 and 2 kHz, thus an (second) additional margin of 5 dB is set for 0.5 kHz only. Table 4 shows the thus prescribed aided thresholds as a function of the cochlear hearing loss and target aided word scores as calculated assuming the target aided thresholds are reaches, while using the SII procedure (speech-intelligibility index, Killion & Mueller, 2010).

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Table 4. Target aided thresholds and word scores using the adapted NAL rule.a

 

References

Bosman AJ, Kruyt IJ, Mylanus EAM, Hol MKS, Snik AFM. On the evaluation of a superpower sound processor for bone-anchored hearing. Clin Otolaryngol. 2018;43:450-455. doi: 10.1111/coa.12989.

Bosman AJ, Kruyt IJ, Mylanus EAM, Hol MKS, Snik AFM. Evaluation of an abutment-level superpower sound processor for bone-anchored hearing. Clin Otolaryngol. 2019 Epub ahead of printing. doi: 10.1111/coa.13084.

Brkic FF, Riss D, Auinger A, Zoerner B, Arnoldner C, Baumgartner WD, Gstoettner W, Vyskocil E. Long-Term Outcome of Hearing Rehabilitation With An Active Middle Ear Implant. Laryngoscope. 2019;129:477-481. doi:10.1002/lary.27513.

Busch S, Kruck S, Spickers D, Leuwer R, Hoth S, Praetorius M, Plinkert PK, Mojallal H, Schwab B, Maier H, Lenarz T. First clinical experiences with a direct acoustic cochlear stimulator in comparison to preoperative fitted conventional hearing aids. Otol Neurotol. 2013 Dec;34(9):1711-8.

Busch S, Lenarz T, Maier H. Comparison of Alternative Coupling Methods of the Vibrant Soundbridge Floating Mass Transducer. Audiol Neurootol. 2016;21:347-355. doi: 10.1159/000453354.

Dillon H. Hearing aids, Chapter 10, 2012; Thieme Verlag, Stuttgart

Grégoire A, Van Damme JP, Gilain C, Bihin B, Garin P. Our auditory results using the Vibrant Soundbridge on the long process of the incus: 20 years of data. Auris Nasus Larynx. 2018;45:66-72. doi: 10.1016/j.anl.2017.02.007.

Killion MC, Mueller HG. A new count-the-dots method. Hear J. 2010;63(1):10-17.

Iwasaki S, Usami SI, Takahashi H, Kanda Y, Tono T, Doi K, Kumakawa K, Gyo K, Naito Y, Kanzaki S, Yamanaka N, Kaga K. Round Window Application of an Active Middle Ear Implant: A Comparison With Hearing Aid Usage in Japan. Otol Neurotol. 2017;38:e145-e151. doi: 1097/MAO.0000000000001438.

Lee JM, Jung J, Moon IS, Kim SH, Choi JY. Benefits of active middle ear implants in mixed hearing loss: Stapes versus round window. Laryngoscope. 2017;127:1435-1441. doi: 10.1002/lary.26244.

Lenarz T, Verhaert N, Desloovere C, Desmet J, D’hondt C, González JC, Kludt E, Macías AR, Skarżyński H, Van de Heyning P, Vyncke C, Wasowski A. A comparative study on speech in noise understanding with a direct acoustic cochlear implant in subjects with severe to profound mixed hearing loss. Audiol Neurootol. 2014;19(3):164-74.

Lenarz T, Zimmermann D, Maier H, Busch S. Case Report of a New Coupler for Round Window Application of an Active Middle Ear Implant. Otol Neurotol. 2018 Dec;39(10):e1060-e1063.

Lenarz T, Zwartenkot JW, Stieger C, Schwab B, Mylanus EA, Caversaccio M, Kompis M, Snik AF, D’hondt C, Mojallal H. Multicenter study with a direct acoustic cochlear implant. Otol Neurotol. 2013 Sep;34(7):1215-25.

Mancheño M, Aristegui M, Sañudo JR.Round and Oval Window Anatomic Variability: Its Implication for the Vibroplasty Technique.Otol Neurotol. 2017 Jun;38(5):e50-e57.

Müller M, Salcher R,  Prenzler, Nhomas Lenarz, Hannes Maier. Redesign of the Hannover Coupler: Optimized Vibration Transfer from Floating Mass Transducer to Round Window.  Biomed Res Int 2018; article ID 3701954

Moher D, Liberati A, Tetzlaff J, Altman DG; PRISMA Group. Preferred reporting  items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med 2009;6:e1000097.

Monini S, Bianchi A, Talamonti R, Atturo F, Filippi C, Barbara M. Patient satisfaction after auditory implant surgery: ten-year experience from a single implanting unit center. Acta Otolaryngol. 2017;137:389-397. doi: 10.1080/00016489.2016.1258733.

Olszewski L, Jedrzejczak WW, Piotrowska A, Skarzynski H. Round window stimulation with the Vibrant Soundbridge: Comparison of direct and indirect coupling. Laryngoscope. 2017;127:2843-2849. doi: 10.1002/lary.26536.

Schwartz, J. MPO Available to the patient: A comparison of the Cochlear™ Baha® 5 Power, Cochlear Baha 5 SuperPower and the Oticon Medical Ponto 3 SuperPower.  26-4-2018.  http://pronews.cochlearamericas.com/mpo-available-to-the-patient/

Snik AFM. Auditory implants. Where do we stand at present? 2018; http:\\www.snikimplants.nl

Snik A, Maier H, Hodgetts B, Kompis M, Mertens G, van de Heyning P, Lenarz T, Bosman A. Efficacy of Auditory Implants for Patients With Conductive and Mixed Hearing Loss Depends on Implant Center. Otol Neurotol. 2019;40:430-435. doi: 10.1097/MAO.0000000000002183.

Zahnert T, Mlynski R, Löwenheim H, Beutner D, Hagen R, Ernst A, Zehlicke T, Kühne H, Friese N, Tropitzsch A, Luers JC, Todt I, Hüttenbrink KB. Long-Term Outcomes of Vibroplasty Coupler Implantations to Treat Mixed/Conductive Hearing Loss. Audiol Neurootol. 2019;23:316-325. doi: 10.1159/000495560.

 

 

Blog 2019-1: Percutaneous bone conductor or (active) middle ear implant to treat mixed hearing loss? No clear winner yet

Introduction

To rehabilitate patients with mixed hearing loss, implantable devices like the Vibrant Soundbridge middle ear implant (VSB) or percutaneous bone conductors (BCDs) have been applied. Such implantable devices become the next option whenever conventional hearing devices (e.g. behind-the-ear device) or reconstructive surgery are not possible or probably not effective (e.g. in case of aural atresia or chronic draining ears). Using recent publications, describing clinical trails, a comparison is made between audiological outcomes obtained with either power BCDs and VSBs. Studies in patients with severe mixed hearing loss were considered only if the mean sensorineural hearing loss component was at least 35 dB HL (arbitrary choice).

Medline was used to find relevant studies, published between 2016 and early 2019. Of the 30 detected studies, 25 studies were excluded (see Materials and Methods at the end of this blog for details) and five studies remained:

Bush et al. (2016) published data 58 patients with mixed hearing loss using the VSB with its actuator coupled to either the round window (RW) or the oval window (OW); Lee et al., (2017) and Zahnert et al. (2019) also published such VSB data, on 19 and 24 patients, respectively. Bosman et al. (2018) published data on the application of a recently introduced percutaneous power BCD, viz. the Baha 5SP, applied in 10 patients; Bosman et al. (2019) published also data on another percutaneous power BCD, the Ponto 3SP device, applied in 18 patients.

The Methods and Materials section is added at the end of this blog.

Results

Figure 1 presents the frequency-specific gain values related to the (bone-conduction) threshold; it should be noted that BCDs as well as VSBs with actuator coupled to the cochlea, directly stimulate the cochlea, bypassing the impaired middle ear (and thus the air-bone gap). Therefore, to assess the effectiveness of the device fitting, only the ‘effective gain’ is of importance, defined as the cochlear (bone-conduction) thresholds minus the aided thresholds (e.g. Busch et al., 2016; Snik, 2018).

The figure presents the ‘effective gain’ divided by the cochlear hearing loss thus the bone-conduction threshold, referred to as the gain-threshold (GT) ratio, plotted as a function of frequency (0.5 kHz to 4 kHz). If GT=0, it means that the aided threshold and the cochlear thresholds coincide, indicating no ‘compensation’ of the cochlear hearing loss. Regarding the VSB, the subfigure at the right shows the calculated results using Zahnert et al. (2019), Lee et al. (2017) and Busch et al. (2016), separately. As these curves show a similar trend, data were averaged after weighting for the number of patients per study. The mean VSB data in the left subfigure show the highest GT ratio at 2 kHz with roll-off in higher and lower frequencies. For the Baha 5SP, a broader frequency response is seen comparable to that of the Ponto 3SP; obviously, the latter device is less powerful (lower GT values).

The target GT ratio, according to the well-validated NAL-fitting procedure, is also indicated (Dillon, 2012; see also Materials an Method section at the end of this manuscript). Systematic differences are seen between the measured GT ratios and that NAL-target GT ratio, especially in the high and low frequencies. At 2 kHz the measured values are closest to the NAL-GT target. 

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Figure 1. The gain-threshold (GT) ratio presented as a function of frequency. Results of the included studies are shown (individual data of the 3 VSB studies, presented in right subfigure, were averaged). According to the NAL-RP fitting rule, the target GT ratio is approx. 0.45 (indicated in the figure) 

The NAL fitting rule is well established for sensorineural hearing loss (Dillon, 2012). However, compared to conventional behind-the-ear devices, BCDs and middle ear implants have a limited dynamic range caused by a relatively low MPO (maximal power output). Therefore, a modified, pragmatic version of the NAL fitting rule has been introduced for these implantable devices (Snik et al., 2019; Materials and Methods section), meant primarily for validation purposes. Figure 2 shows target-aided

3

Figure 2. The difference between prescribed aided thresholds and measured aided thresholds as a function of frequency. The modified NAL-procedure was used. Pooled VSB data are presented, and, separately, the data of the two percutaneous BCD studies

thresholds (obtained with this pragmatic validation rule) minus the measured aided thresholds. A value of 0 means that the result is adequate according to that rule; negative values indicate insufficient gain. Weighted means are presented of the pooled VSB studies and, separately, the results of the Ponto 3SP study and Baha 5SP study. In agreement with Figure 1, most obvious discrepancies are found at 0.5 kHz and 4 kHz, especially for the VSB device, in the order of 15-20 dB. The Baha 5SP seems to be the most adequate device with a rather flat curve around 0; according to Figure 2, the Ponto 3SP device lags behind by approx. 10 dB, what might be ascribed to the difference in MPO of the two BCDs. The MPO of the Baha 5SP is approximately 9 dB higher than that of the Ponto 3SP (Schwartz, 2018). The MPO of the VSB and the Baha 5SP are rather comparable (Chapter 2 in Snik, 2018).

Apart from aided thresholds, all the five studies presented aided speech recognition scores in quiet, however, measurement conditions and the tests used were divers. Nevertheless, in all the studies monosyllabic words were used. Bush et al. (2016) and Zahnert et al. (2019) presented word scores (WRS) obtained at a presentation level of 65 dB SPL. Bosman et al. (2018; 2019) reported phoneme scores (PS) of words presented at 60 dB SPL; which can be recalculated to a word score at 65 dB SPL (applying WRS=PS2.3 and using the slope of the speech performance-intensity curve: 6% per dB). Lee et al. (2017) measured word scores presented at the patient’s most comfortable listening level instead of at a fixed level and, thus, cannot be used for a comparison.

Table 1 shows the outcomes.

Table 1. Speech recognition scores

Study/test VSB, Zahnert VSB, Bush Ponto 3SP Baha 5SP
WRS 65 dB SPL 67% 78%
PS at 60 dB SPL calculated WRS at 65 dB SPL 75%

80%

69%

75%

Note WRS: word recognition score, PS: phoneme score

In summary, for patients with mixed hearing loss, the achieved (effective) gain with either VSB or the percutaneous Baha 5SP show similar results in the mid frequencies (Figures 1 and 2), however, at 4 kHz and especially at 0.5 kHz, best results are found with the Baha 5SP. Regarding speech recognition, results are rather similar (Table 1; the WRS data at 65 dB SPL input). Therefore, from an audiological point of view, differences between devices are limited.

Closing remarks

It is known that the VSB outcomes depend on the efficacy of the actuator coupling to the cochlea (e.g. Busch et al., 2016). New coupling options are being developed (e.g. Lenarz et al., 2018), which might have a positive effect on the frequency response. Another way to deal with the peaked frequency response is to lower the gain of the VSB device in the mid frequencies. However, that is only an option if the implanted device has sufficient reserve.

For the percutaneous BCDs, the coupling of the processor to the skull is more or less standardized and therefore not a major source of variance between subjects.

To choose a device, the performance is highly relevant but also of importance is the status of the middle ear (can a VSB be placed?), invasiveness and complexity of the surgery, risk of medical and technical complications, longevity, cost etc. Regarding the Baha 5SP, with high volume setting, it might be advised to use the behind-the-ear processor away from the ear, with a clip connected to clothing, to deal with feed-back. That might also be considered as a draw back.

Note that the conclusions drawn are valid for the present devices/processors. If more powerful processors or more effective actuators are introduced or if better coupling techniques are developed, conclusions might change.

Appendix.

Materials and methods

Search strategy

This review was carried out in accordance with PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses; Moher et al., 2009). Medline (Pubmed) was used to find relevant studies, published between 2016 and early 2019. Search string was: ((soundbridge OR ponto OR baha) AND (mixed hearing) NOT transcutaneous). Thirty manuscripts were identified; based on the abstracts, 20 manuscripts were excluded because: the focus was on cochlear implantation (1), comprised a review, no original data (5), case reports and how-we-do-it reports (4). Manuscripts dealing with medical/surgical issues (8), technical issues (1) and application in pure sensorineural hearing loss (1) were excluded as well. The full text of the remaining 10 manuscripts was reviewed. One more manuscript was excluded because the mean cochlear hearing loss was below 35 dB HL (Iwasaki et al., 2017), three manuscripts were excluded as the bone-conduction thresholds and/or aided thresholds were not presented frequency specific (essential information for the present analyses; Brkic et al., 2019; Olszewski et al., 2017; Monini et al., 2017) and one manuscript with just 5 relevant patients (Gregoire et al., 2018). Five studies were included; regarding VSB: Bush et al. (2016); Zahnert et al. (2019) and Lee et al. (2017). Regarding BCD, two studies were identified: Bosman et al. (2018) and Bosman et al. (2019).

Table 2 gives an overview of some relevant patients’ characteristics of these 5 studies (age and mean cochlear or bone-conduction thresholds). On the average, the patients using BCDs are older than those using the VSB.

Table 2. Some patient characteristics

Study; first author Lee, 2017 Busch, 2016 Zahnert, 2019 Bosman, 2018 Bosman, 2019
n 19 78 24 18 10
Device VSB VSB VSB Ponto 3SP Baha 5SP
Age, years 55±17 57±17 55 (34-75) 64 (22-80) 70 (59-77)
PTAbc dB HL 45 37 40 38 44

Note. n: number of patients; PTAbc: calculated mean bone-conduction threshold at 0.5, 1, 2, 4 kHz. Regarding the age at implantation, mean age is presented with standard deviation or the median age with range between brackets

Gain measurement

BCDs as well as the VSB with its actuator coupled to one of the cochlear windows stimulate the cochlea directly, bypassing the impaired middle ear. Therefore, the air-bone gap doesn’t play any role when fitting these devices and, to evaluate audiological benefit, the ‘effective gain’ is of importance. The ‘effective gain’ is defined as the cochlear (bone-conduction) thresholds minus the aided thresholds (e.g. Busch et al., 2016; Snik, 2018). The ‘effective gain’ assesses which proportion of the cochlear hearing loss is ‘compensated’ by the device. By definition, the often-used ‘functional gain’ equals the ‘effective gain’ plus the air-bone gap, and is mainly dominated by the width of the air-bone gap. In contrast, the ‘effective gain’ is a measure of the quality of the device fitting and can be compared to target gain values as prescribed by generally used, validated prescription procedures.

Given a certain hearing loss, obviously, the required ‘effective gain’ depends on the cochlear hearing thresholds (the higher the hearing loss, the higher the gain should be). Therefore, the ‘effective gain’ divided by the cochlear threshold (the gain/threshold ratio or GT ratio) is calculated; according to the widely used NAL-RP fitting procedure, this ratio should be approx. 0.45 for 1, 2 and 4 kHz, for proper amplification (Dillon, 2012).

However, for mixed hearing loss, that NAL-prescribed target GT ratio is not easily reached, owing to, amongst others, the limited highest sound level that can be produced by BCDs or VSBs (limited output), characterised by the ‘maximum output’ or MPO of these devices. Therefore, a pragmatically adapted NAL procedure has been introduced for these implants, to be used for validation purposes (Snik et al., 2019). This pragmatic procedure was based on 31 published clinical trials, regarding all types of BCDs and active middle ear implants and, consequently, this new procedure is device independent. The assumption is that appropriate (sufficient powerful) implantable devices have been chosen (regarding the MPO) and that amplification is linear. In short, aided thresholds should equal 0.55 times the cochlear threshold (following the NAL-RP fitting procedure) plus a margin of 5 dB with a minimum value of 25 dB HL at 1, 2 and 4 kHz (margins to deal with the limited MPO of the devices; Snik et al., 2019). Regarding 0.5 kHz, following the NAL-RP rule, calculated target aided threshold is 5 dB higher than that at 1 and 2 kHz, thus an additional margin of 5 dB is set at 0.5 kHz.

References

Bosman AJ, Kruyt IJ, Mylanus EAM, Hol MKS, Snik AFM. On the evaluation of a superpower sound processor for bone-anchored hearing. Clin Otolaryngol. 2018;43:450-455. doi: 10.1111/coa.12989.

Bosman AJ, Kruyt IJ, Mylanus EAM, Hol MKS, Snik AFM. Evaluation of an abutment-level superpower sound processor for bone-anchored hearing. Clin Otolaryngol. 2019 Epub ahead of printing. doi: 10.1111/coa.13084.

Brkic FF, Riss D, Auinger A, Zoerner B, Arnoldner C, Baumgartner WD, Gstoettner W, Vyskocil E. Long-Term Outcome of Hearing Rehabilitation With An Active Middle Ear Implant. Laryngoscope. 2019;129:477-481. doi:10.1002/lary.27513.

Busch S, Lenarz T, Maier H. Comparison of Alternative Coupling Methods of the Vibrant Soundbridge Floating Mass Transducer. Audiol Neurootol. 2016;21:347-355. doi: 10.1159/000453354.

Dillon H. Hearing aids, 2012; Thieme Verlag, Stuttgart

Grégoire A, Van Damme JP, Gilain C, Bihin B, Garin P. Our auditory results using the Vibrant Soundbridge on the long process of the incus: 20 years of data. Auris Nasus Larynx. 2018;45:66-72. doi: 10.1016/j.anl.2017.02.007.

Iwasaki S, Usami SI, Takahashi H, Kanda Y, Tono T, Doi K, Kumakawa K, Gyo K, Naito Y, Kanzaki S, Yamanaka N, Kaga K. Round Window Application of an Active Middle Ear Implant: A Comparison With Hearing Aid Usage in Japan. Otol Neurotol. 2017;38:e145-e151. doi: 1097/MAO.0000000000001438.

Lee JM, Jung J, Moon IS, Kim SH, Choi JY. Benefits of active middle ear implants in mixed hearing loss: Stapes versus round window. Laryngoscope. 2017;127:1435-1441. doi: 10.1002/lary.26244.

Lenarz T, Zimmermann D, Maier H, Busch S. Case Report of a New Coupler for Round Window Application of an Active Middle Ear Implant. Otol Neurotol. 2018;39:e1060-e1063. doi: 10.1097/MAO.0000000000001996

Moher D, Liberati A, Tetzlaff J, Altman DG; PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med 2009;6:e1000097.

Monini S, Bianchi A, Talamonti R, Atturo F, Filippi C, Barbara M. Patient satisfaction after auditory implant surgery: ten-year experience from a single implanting unit center. Acta Otolaryngol. 2017;137:389-397. doi: 10.1080/00016489.2016.1258733.

Olszewski L, Jedrzejczak WW, Piotrowska A, Skarzynski H. Round window stimulation with the Vibrant Soundbridge: Comparison of direct and indirect coupling. Laryngoscope. 2017;127:2843-2849. doi: 10.1002/lary.26536.

Schwartz, J. MPO Available to the patient: A comparison of the Cochlear™ Baha® 5 Power, Cochlear Baha 5 SuperPower and the Oticon Medical Ponto 3 SuperPower. 26-4-2018. http://pronews.cochlearamericas.com/mpo-available-to-the-patient/

Snik AFM. Auditory implants. Where do we stand at present? 2018; http://www.snikimplants.nl, see chapters 2, 3 and 4.

Snik A, Maier H, Hodgetts B, Kompis M, Mertens G, van de Heyning P, Lenarz T, Bosman A. Efficacy of Auditory Implants for Patients With Conductive and Mixed Hearing Loss Depends on Implant Center. Otol Neurotol. 2019;40:430-435. doi: 10.1097/MAO.0000000000002183.

Zahnert T, Mlynski R, Löwenheim H, Beutner D, Hagen R, Ernst A, Zehlicke T, Kühne H, Friese N, Tropitzsch A, Luers JC, Todt I, Hüttenbrink KB. Long-Term Outcomes of Vibroplasty Coupler Implantations to Treat Mixed/Conductive Hearing Loss. Audiol Neurootol. 2019;23:316-325. doi: 10.1159/000495560.

Blog 2018-4: Unsubstantiated claimed ‘equivalence’ of newly introduced BCDs (bone-conduction devices) to established BCDs

Introduction.

Originally, (conventional) bone-conduction devices (BCDs) comprised a bone
vibrator pressed against the skin in the mastoid region. This so-called
transcutaneous coupling works, but is not effective at all. Therefore, these
conventional BCDs needed very powerful amplifiers. Nevertheless, the gain and
output was limited and these devices were only applied if there was no
acceptable alternative, thus as a ‘last resort’ solution (e.g. in case of aural atresia
or chronic draining ears).
The first implantable BCD, the Baha, introduced in the late eighties, was more
powerful, owing to its (efficient) percutaneous coupling, bypassing the vibration-
attenuating skin and subcutaneous layers (Hakannson et al., 1985).

Effectiveness.

At that time, to establish the effectiveness of the Baha device, within-subject, pre-
post intervention studies were performed comparing Baha with the patient’s
own conventional BCD, and the beneficial outcomes were accepted by the
authorities as convincing evidence. Reimbursement was admitted in many
countries, e.g. by the FDA, with the restriction that the sensorineural hearing loss
component (SNHLc) had to be less than 45 dB HL.

Equivalence claims.

Since then, several new types of implantable BCDs have been developed and
marketed on the basis of presumed equivalence to Baha (e.g. implantable
transcutaneous devices). These devices have achieved approval based on the
assumption of equivalence, rather than based on clinical trials demonstrating
their effectiveness, and the same restriction as applied for Baha (SNHLc &lt;45 dB
HL) was claimed. However, these implantable transcutaneous BCDs cannot
compete with Baha regarding gain and output (Chapter 3 and 4.1, this website;
van Barneveld et al., 2018); this means that the &lt;45 dB HL criterion is an
overestimation. Table 4.1, Chapter 4.1, this website, presents the more realistic
criteria, per device type, based on objective data, (partly) validated by published
clinical data.

Widely, the equivalence rule is under debate owing to serious problems with
other implants (breast implants, pace makers etc.) that were allowed to the
market based on the equivalence principle, without appropriate effectiveness
studies (e.g. https://www.theguardian.com/society/2018/nov/25/revealed-
faulty-medical-implants-harm-patients-around-worldreference). To deal with
this public debate, before the introduction of a new device, effectiveness studies

should be performed aiming at the capacity (in audiological terms) and stability
of that implantable hearing device.

References

Håkansson B, Tjellström A, Rosenhall U, Carlsson P. The bone-anchored hearing
aid. Principal design and a psychoacoustical evaluation. Acta Otolaryngol.
1985;100(3-4):229-39.
van Barneveld DCPBM, Kok HJW, Noten JFP, Bosman AJ, Snik AFM. Determining
fitting ranges of various bone conduction hearing aids. Clin Otolaryngol.
2018;43(1):68-75.

Blog 2018-2: How to quantify the gain (amplification) of a bone-conduction device; comment to the systematic review by Bezdjian et al. (2017)

During the last decades, several new types of bone-conduction devices (BCDs) have been released for patients with conductive or mixed hearing loss. One rather recent innovation is the semi-implantable (transcutaneous) Sophono device (Medtronic; Jacksonville, Fl, USA), which is based on the Otomag device (Siegert et al., 2013; chapter 2, this website). This device makes use of a transcutaneous magnetic coupling between the externally worn conventional BCD and the skull. Recently, Bedzjian et al. (2017) reviewed published clinical experience with this device. Their overview aimed at ‘functional improvement’ and peri-operative medical issues. The Bedzjian et al. paper has been discussed before (Snik, 2018); below, that discussion is elaborated.

The ’auditory’ or ‘functional’ gain

The ‘functional improvement’ or ‘auditory gain’, as introduced by the authors, was defined as the difference between aided and unaided sound-field thresholds. In sensorineural hearing loss, the ‘auditory gain’, better known as the ‘functional gain’, is a measure of the amplification provided by the (air-conduction) device. That is not the case for conductive or mixed hearing loss when using a BCD; BCDs directly stimulate the cochlea, bypassing the impaired middle ear and thus the air-bone gap. Owing to the definition of ‘auditory gain’, however, the width of that air-bone gap directly affects the ‘auditory gain’.

To illustrate this: in case of aural atresia, assuming a total hearing loss of 70 dB HL and a mean ‘auditory gain’ of 30 dB, the aided thresholds are poor, viz. 40 dB HL. In case of mild conductive hearing loss of 40 dB HL, e.g. owing to chronic otitis, an ‘auditory gain’ of 30 dB implies near-normal hearing with the device. Obviously, the latter patient has more adequate amplification, although the ‘auditory gain’ is the same for either patient. As has been suggested before, it is more useful to analyse the aided thresholds in relation to the cochlear thresholds (bone-conduction thresholds, see Appendix 2.3, this website).

Bedzjian et al. (2017) reported that the ‘auditory gain’, averaged over studies, was 31.6 dB and they concluded that this was a satisfactory result. However, it only indicates that the BCDs did work but obviously not how adequately the BCDs were fitted.

Averaging the ‘auditory gain’ over studies is also debatable because some studies comprised patients with conductive hearing loss and other studies patients with single-sided deafness. In single-sided deaf patients, the BCD is implanted at the deaf side and works as a (transcranial) CROS device, a totally different application than a BCD for conductive hearing loss. Reading the original papers, its is clear that in single-sided deaf patients the ‘auditory gain’ was defined as the thresholds of the normal ear that was blocked with an ear plug minus the aided thresholds obtained with the CROS-BCD. Thus, to determine the ‘auditory gain’ the thresholds of the blocked normal ear were considered as ‘unaided thresholds’.
Clearly, the ‘auditory gain’ of a CROS-BCD, defined as the thresholds of the blocked normal ear minus the aided thresholds obtained with the CROS-BCD, doesn’t assess the benefit of the CROS-BCD as, amongst others, it depends directly on how effectively the normal ear was blocked. Nevertheless, oftenb done (references)

In summary. To illustrate the real capacity of any BCD, aided thresholds* should be related to bone-conduction thresholds for patients with conductive or mixed hearing loss. For patients with single-sided deafness, aided thresholds should be compared to the air-conduction thresholds of the normal hearing ear to see whether or not cross stimulation with the BCD compensates effectively the acoustic head shadow (see also previous blog 2018-1).
The ‘auditory gain’ or ‘functional gain’ is not an appropriate measure to assess the effectiveness of any BCD fitting.

* Note that using aided thresholds to assess the gain of a device is not straightforward if non-linear amplification (compression) is applied, see Appendix 2, this website. Using Bezdjiran et al.’s data, it seems to be justified to use the aided threshold to assess gain, as amplification seemed to be linear. That is concluded from the fact that the reported mean unaided minus aided free-field tone thresholds (assessing gain for low-level sounds) was comparable to the mean unaided minus aided speech reception thresholds (assessing gain for mid-level sounds), namely 31.6 dB versus 33.6 dB.

References

1. Bezdjian A, Bruijnzeel H, Daniel SJ, Grolman W, Thomeer HGXM, Preliminary audiologic and peri-operative outcomes of the Sophono™ transcutaneous bone conduction device: A systematic review, Int. J. Pediatr. Otorhinolaryngol. 101 (2017) 196-203.

2. Siegert R, Kanderske J, A new semi-implantable transcutaneous bone conduction device: clinical, surgical, and audiologic outcomes in patients with congenital ear canal atresia, Otol. Neurotol. 34 (2013) 927-934.

3. Snik A. How to quantify the ‘auditory gain’ of a bone conduction device; comment to the systematic review by Bezdjian et al. Int. J. Pediatr. Otorhinolaryngol. (2018). E-pub ahead of publication

Blog 2018-1: Implantable transcutaneous bone conductors or percutaneous bone conductors; a free choice? Review of the paper by Cedars et al., 2016

The Baha bone-conduction device (BCD) was developed in the eighties for patients with conductive and mixed hearing loss. When this device is percutaneously coupled, the BCD is a powerful hearing solution (see Chapters 2 and 3, this website) and is generally considered as the gold standard. However, in a number of patients, problems occurred with the skin around the percutaneous implant. Although well manageable in adults (Chapter 5, this website) this has lead to revision surgeries, most frequently in children.

Therefore, new transcutaneously coupled BCDs have been developed (Sophono, Attract). These devices are attached with a magnetic coupling instead of a percutaneous one, with one magnet implanted, connected to the skull. The advantage is that the skin remains intact, however, the price that has to be paid is decreased efficiency of approx. 15 dB, owing to damping of the BCD’s vibrations by skin and subcutaneous layers. The first device on the market was the Otomag device, developed by Siegert et al. Since 2009 this device is known as the Sophono device (Medtronic, Boulder, US). The Baha Attract, introduced 4 years later, uses the same type of coupling (Cochlear BAS, Gothenburg, Sweden; see Chapters 2,3).

Cedars et al. (2016) published a well-documented paper entitled ‘Conversion of traditional osseointegrated bone-anchored hearing aids to the Baha Attract in four paediatric patients’ (2016). That paper was discussed before (Snik, 2017). The reason for the conversion was medical problems ascribed to the percutaneous coupling. Their Figure 5 showed that owing to the conversion, the aided thresholds worsened by 10 to 20 dB. That is quite a high price. Firstly, let us consider the aided thresholds of the child (number 4) with bilateral conductive hearing loss. Using the aided thresholds (data from Figure 5, Cedars et al.), the audibility of speech can be assessed as well as the expected word recognition score, see Figure 1, below. The count-the-dots approach was used (Mueller & Killion, 1991) resulting in an audibility index of 0.78 and 0.35, for the original percutaneous application and the new transcutaneous application, respectively. The related word recognition score can be determined using that audibility index, and is 95% when fitted with a BCD and 60% when fitted with the Attract. Adults with good linguistic skills might be able to deal with deterioration from 95% to 60%, but for children, who need to develop speech and language, it is problematic.

Slide1

Figure 1. The aided thresholds obtained with, in red, the percutaneous BCD and in black, the transcutaneous BCD. The grey area presents the speech area, taken from Mueller & Killion (1990). The audibility index can be determined by counting the dots in the grey area (max. is 100) and divide it by 100

BCDs are also applied in patients with single-sided deafness (SSD). If someone is talking at the deaf side, it is poorly understood owing to acoustic head shadow. This is a high frequency phenomenon; attenuation is approx. 5 dB in the low frequencies and around 10-15 dB, up to 3-4 kHz. Above that frequency, increased attenuation is found, exceeding 25 dB HL at 4-6 kHz (see the classical data of Shaw, 1974). To deal with this, amongst others, a CROS-BCD can be applied. The BCD is placed at the deaf side and works as a transcranial CROS device (e.g. Hougaard et al., 2017).
However, with a transcutaneous CROS-BCD, owing to dampening of the vibrations by the skin and subcutaneous layers, especially in the high frequencies, effective CROS stimulation might be low. Cedars et al. presented data of 3 children with SSD (patients 1 to 3; owing to incomplete data only the results of patients 1 and 2 are discussed) who were using a percutaneous CROS-BCD that was replaced by a transcutaneous one. To obtain CROS-aided thresholds, the normal hearing ear was blocked during the measurements.
Figure 2 shows the original CROS-aided thresholds minus the air-conduction thresholds (normal hearing ear) for the transcutaneous (full lines) and the percutaneous CROS device (broken lines), presented as a function of frequency. Within these two patients an obvious difference is seen between the devices. Attenuation is seen especially with the transcutaneous CROS. That attenuation is worse than the attenuation caused by head shadow, using Shaw’s data (the blue line); in other words, when stimuli are presented at the impaired side, unaided thresholds are better than transcutaneous CROS aided thresholds. The Figure indicates that for these two patients, the application of the transcutaneous CROS-BCD is not an effective solution, in contrast to the percutaneous application (although, unfortunately, information above 4 kHz is missing).

Slide2

Figure 2. Attenuation caused by head shadow (in blue, according to Shaw, 1974), the attenuation of the percutaneous CROS-BCD (broken lines) and transcutaneous CROS-BCD (full lines) of the two patients (P1 in red and P3 in black) calculated from Figure 5, Cedars et al. (2016)

Hougaard et al. (2017) reported non-use and relatively low daily use of the Baha Attract in their 13 adult patients with SSD, and suggested that it probably could be ascribed to poor compensation of head shadow. Furthermore, Hougaard et al. also reported aided thresholds of seven more patients with conductive hearing loss using the transcutaneous Baha. They concluded that the aided thresholds were worse compared to published aided thresholds with the percutaneous Baha. This is in agreement with the data of Cedars et al.’s patient 4.

In summary, indeed problems with the skin around a percutaneous implant are recurrent and annoying. The 12 reported clinical visits for patient 4 in Cedar et al. (2016) might obviously be worrying and upsetting for both the child and the parents. However, according to the review above, in audiological terms, a transcutaneous solution is a major step backwards. Furthermore, transcutaneous BCDs are not free of medical complications either (e.g. Cedars et al., 2016).

The search for the best bone-conduction device, especially for children, should be continued; the options are 1) usage of percutaneous BCDs with more skin-friendly implants, better implantation procedures and improved after care, 2) transcutaneous BCDs with significantly more powerful (and feedback-free) processors.

References
E. Cedars, D. Chan, A. Lau, et al., Conversion of traditional osseointegrated bone-anchored hearing aids to the Baha Attract in four pediatric patients, Int. J. Pediatr. Otrhinolaryngol. 91 (2016) 37-42.
G. Mueller, M. Killion, An easy method for calculating the Articulation Index, Hear. J. 43 (9) (1990) 14-17.
E.A.G. Shaw, The external ear, in: W.D. Keidel, W.D. Neff (Eds.), Handbook of Sensory Physiology, vol. V/1, Springer Verlag, New York, 1974, pp. 455-490.
Snik A. Letter to the editor. Int J. Pediatr. Otorhinolaryngol. 2017;93:172.
Hougaard DD, Boldsen SK, Jensen AM, Hansen S, Thomassen PC. A multicentre study on objective and subjective benefits with a transcutaneous bone-anchored hearing aid device: first Nordic results. Eur. Arch. Otorhinolaryngol. 2017;274:3011-3019.
Dimitriadis PA, Carrick S, Ray J. Intermediate outcomes of a transcutaneous bone conduction hearing device in a paediatric population. Int J Pediatr Otorhinolaryngol. 2017;94:59-63.

Appendix.
It should be noted that using aided thresholds to assess the performance (gain) of a device is not straightforward if non-linear amplification is applied (see appendix 2, this website). Whether or not non-linear amplification was used in the reviewed studies was not reported. With regard to the Hougaard et al. data, it seems that amplification was linear, which is concluded from the fact that the reported ‘gain’ derived from free-field tone thresholds (19.8 dB), was comparable to the gain derived from the ‘supra-threshold’ speech reception thresholds (estimated from their Figure 4b), being 20 dB. That is indicative for linear amplification. Such an analysis was not possible with the data of Cedars et al., as supra threshold measures were lacking.

Chapter 8. Sensorineural hearing loss

Part 2. Challenges and limitations of implantable hearing devices (auditory implants) for sensorineural hearing loss 

8. Sensorineural hearing loss 

8.1 Auditory implants for moderate to severe sensorineural hearing loss

To rehabilitate sensorineural hearing loss, conventional air-conduction hearing aids are the first choice (e.g. behind-the-ear devices or BTEs; Figure 2.1, chapter 2). If the sensorineural hearing loss is not too severe, it is possible to make conversational speech audible again with BTEs. However, speech recognition might still be compromised, especially in noisy situations, despite appropriate amplification owing to the associated deprived processing of speech cues in the cochlea (referred to as cochlear distortion; Plomp, 1978). Today’s digital devices might deal with that; algorithms have been developed that might enhance speech sounds relative to noise, like noise reduction algorithms and adaptive directionality of the microphone (Dillon, 2012).

For patient with severe to profound sensorineural hearing loss (>70-80 dB HL), BTEs might no longer be sufficiently effective because proper restoration of the audibility of speech is not possible and/or because of significant cochlear distortions. Then, cochlear implantation becomes the next treatment option (Hoppe et al., 2015; Huinck et al., 2019). The 70-80 dB HL limit is based on speech recognition tests; above that limit, word score is probably significantly better with a cochlear implant than with a BTE.

An alternative amplification option for patients with a hearing loss below 70-80 dB HL is an (acoustic) auditory implant (Verhaegen et al., 2008). High sound fidelity, high output with less feedback problems and no occluding earmolds were claimed advantages of such auditory implants over BTEs (e.g. Goode, 1995). Since the late nineties, several different types of auditory implants have been introduced for patients with sensorineural hearing loss (Snik, 2011). Nowadays (end 2020), only two semi-implantable devices are still on the market, viz. the Vibrant Soundbridge (VSB; Figure 2.6, chapter 2) and the Maxum device (Ototronix, USA; Pelosi et al., 2014). The latter device comprises a permanent magnet connected surgically to the stapes, in the middle ear. The driver is an electro-magnetic coil placed in a deep fitted in-the-ear hearing aid. Early 2020, the competitor of the VSB, the semi-implantable Cochlear MET device, was taken off the market.

In addition to semi-implantable devices, one fully implantable device is on the market, namely the Esteem device (Envoy Medical, St. Paul, MN, USA; Marzo et al., 2014). Another fully implantable device was the Cochlear Carina, which also was withdrawn from the market early 2020. Rather recently, several systematic reviews were published aiming at the claimed advantages of auditory implants over BTEs. Pulcherio et al. (2014) concluded that, comparing the Carina and Esteem devices to BTEs, no structural audiological benefit was found. As these implantable devices are expensive and involve implant surgery and regularly revision surgery (every 5-10 years, to replace the battery), the cost-benefit ratio of these devices is unfavorable compared to BTEs. Another review by Kahue et al. (2014), comparing published audiological outcomes obtained with middle ear implants (including the VSB and Maxum devices) and BTEs, concluded that a surplus value of the middle ear implants could not be established. Since these reviews were published, screening the literature, just one more clinical trial was found with the Maxum device as well as one with regard to the Esteem device, published by company-independent research groups. Barbara et al. (2018b) reported on 3 patients using the Maxum device; compared to BTEs, two patients had equal speech recognition scores and the third patient had a 10% higher word score with the Maxum device. Regarding the Esteem device, Barbara et al (2018a) published an overview of their outcomes. The patient group described in this paper overlapped with that of a previous paper of the same authors, which was included in the above-mentioned systematic reviews by Kahue et al. and Pulcherio et al.

It might be concluded that compared to BTEs, today’s middle ear implants have no convincing audiological advantages, except for patients who don’t tolerate the earmold of BTEs owing to e.g. external otitis (consensus statement, see Magnan et al., 2005). The recent systematic reviews indicate that that statement remains valid. Some manufacturers of middle ear implants refer to that conclusion (e.g. VSB fact sheet, 2015)Edfelt et al. (2014) showed that for such patients the application of the VSB device is (even) cost effective. Note that according to the set-up of the Maxum device, it is not an option for patients with external otitis. No papers could be identified on the Esteem device applied in patients with external otitis. In contrast, the VSB device is widely applied.

In summary:

There is no convincing evidence that today’s auditory implants for patients with sensorineural hearing loss led to better speech recognition than BTEs, however, such devices (except the Maxum device) might (cost-) effectively be used in patients with sensorineural hearing loss who don’t tolerate earmolds.

To help patients with sensorineural hearing loss and chronic external otitis, bone-conduction devices (BCD) have been applied as well; with a BCD, the ear canal remains open. Bone conduction works but it is not really effective (see Chapter 2). Indeed, studies with the most powerful type of BCD, the percutaneous BCD (Baha), applied in such patients showed insufficient amplification (Snik et al., 1995). Stenfelt et al. (2000) studied the use of Baha in patients with an another reason, namely in patients with a predominant high-frequency sensorineural hearing loss, enabling an open-ear fitting. They also concluded that Baha was not powerful enough. No papers were found on the effectiveness of today’s more powerful BCDs (e.g. the percutaneous super power devices) in such patients.

In summary

To help patients with sensorineural hearing loss in need for amplification, bone-conduction devices have insufficient power 

8.2 Capacity of VSB with today’s sound processors

In contrast to the Maxum and Envoy Esteem devices, the VSB has been widely applied. With the more recent sound processors (Amade or Samba for VSB), improvements in sound quality have been achieved compared to the older processors. Concerning speech recognition, Figure 8.2 shows the %-correct score at normal conversational level (65 dB SPL) of 14 patients using these updated VSB processors. Patients with ski-slope audiograms were excluded, following Verhaegen et al., 2008. The drawn lines are taken from that latter study, based on the speech performance of patients with previous-generation sound processors. The figure shows that the new data points are close to the line or somewhat better (line taken from Verhaegen et al.). Busch et al. (2016) reported a similar conclusion. As a reference, Verhaegen et al showed that with BTE, applied in patients with similar hearing loss, the mean speech score was higher, e.g. at 65 dB HL the mean phoneme score was 90% with BTE versus 70% with VSB.

SNHL PS65vsPTA enkel VSB

Figure 8.1. Speech recognition-in-quiet scores (presentation level 65 dB SPL; phoneme scores) as a function of the hearing loss of 14 VSB-Amade/Samba users (squares). The drawn line is the best fit from a previous study (Verhaegen et al., 2008).

A problem of using auditory implants with an open ear canal, like the VSB, might be interference between the vibrations of the middle ear ossicles generated by the implant’s actuator and direct sounds that activate the ossicles in the normal way. It should be noted that owing to the digitally processing of digital audio processors, the amplified sounds are delayed, typically by 4 ms to 10 ms. That implies that the direct and processed sounds are not in phase for most frequencies, leading to a distorted sound. This phenomenon also occurs when fitting digital BTE devices with open earmolds (Groth & Sondergaard (2004) and Stone et al. (2008)). The latter study showed that the (annoying) interference depends on (and can be adjusted by) the gain level of the device, compression settings and on frequency. The lower the processing delay, the better. Studies looking into this interference when using middle ear implants have not been published yet.

8.3 References chapter 8

Barbara M, Filippi C, Covelli E, Volpini L, Monini S. Ten years of active middle ear implantation for sensorineural hearing loss. Acta Otolaryngol. 2018a;138(9):807-814.

Barbara M, Volpini L, Filippi C, Atturo F, Monini S. A new semi-implantable middle ear implant for sensorineural hearing loss: three-years follow-up in a pilot patient’s group. Acta Otolaryngol. 2018b;138(1):31-35.

Busch S, Lenarz T, Maier H. Comparison of Alternative Coupling Methods of the Vibrant Soundbridge Floating Mass Transducer. Audiol Neurootol. 2016;21(6):347-355.

Carlsson PU, Håkansson BE. The bone-anchored hearing aid: reference quantities and functional gain. Ear Hear. 1997;18:34-41

Dillon H. Hearing aids. 2012, Thieme Verlag, Stuttgart, Germany

Edfelt L, Stromback K, Grendin J, et al., Evaluation of cost-utility in middle ear implantation in the ‘Nordic School’; a multicenter study in Sweden and Norway. Acta Otolaryngol. 2014;134:19-25

Goode RI. Current status and future of implantable electromagnetic hearing aids. Otolaryngol Clin N Am. 1995;28:141-146

Groth J, Sondergaard MB. Disturbance caused by varying propagation delays in non-occluding hearing aid fittings. Int J Audiol. 2004;43:594-599

Huinck WJ, Mylanus EAM, Snik AFM. Expanding unilateral cochlear implantation criteria for adults with bilateral acquired severe sensorineural hearing loss. Eur Arch Otorhinolaryngol. 2019;276(5):1313-1320.

Kahue CN, Carlson ML, Daugherty JA, Haynes DS, Glasscock ME 3rd. Middle ear implants for rehabilitation of sensorineural hearing loss: a systematic review of FDA approved devices. Otol Neurotol. 2014;35(7):1228-37.

Marzo SJ, Sappington JM, Shohet JA. The Envoy Esteem implantable hearing system. Otolaryngol Clin North Am. 2014;47(6):941-52.

Magnan J, Manrique M, Dillier N, Snik A, Hausler R. International consensus on middle ear implants. Acta Otolaryngol. 2005;125:920-921

Pelosi S, Carlson ML, Glasscock ME 3rd. Implantable hearing devices: the Ototronix MAXUM system. Otolaryngol Clin North Am. 2014;47(6):953-65.

Plomp R. Auditory handicap of hearing impairment and the limited benefit of hearing aids. J Acoust Soc Am. 1978;63:533-549

Pulcherio JO, Bittencourt AG, Burke PR, Monsanto R, de Brito R, Tsuji RK, Bento RF. Carina® and Esteem®: a systematic review of fully implantable hearing devices. PLoS One. 2014;17;9(10)

Rameh C, Meller R, Lavielle JP, Deveze A, Magnan J. Long-term patient satisfaction with different middle ear hearing implants in sensorineural loss. Otol Neurotol 2010;31:883-892

Snik  A, Implantable hearing devices for conductive and sensorineural hearing impairment. In: F-G Zeng et al. (eds.) Auditory Prosthesis. New Horizons. Springer Handbook of Auditory Research 39, 2011:85-108

Snik AF, Mylanus EA, Cremers CW. Bone-anchored hearing aids in patients with sensorineural hearing loss and persistent otitis externa. Clin Otolaryngol Allied Sci. 1995;20:31-35

Stenfelt S, Håkansson B, Jönsson R, Granström G. A bone-anchored hearing aid for patients with pure sensorineural hearing impairment: a pilot study. Scand Audiol. 2000;29:175-185

Stone MA, Moore BCJ, Meisenbacher K, Derleth RP. Tolerable hearing aid delays. V. Estimation of limits for open canal fittings. Ear Hear. 2008;29:601-617

Verhaegen VJ, Mylanus EA, Cremers CW, Snik AF. Audiological application criteria for implantable hearing aid devices: a clinical experience at the Nijmegen ORL clinic. Laryngoscope. 2008;118(9):1645-1649

VSB fact sheet (VORP 503/Samba). Vibrant soundbridge System. Med-El website, downloads, 2015