7.1 Introduction; children should not be treated as young adults

Counselling adults, who, according to their audiogram, should profit from amplification, is not always successful. Adults might deny their hearing problems or postpone a hearing aid trial. If their attitude is more positive, they might only be interested in hardly visible devices, even if speech recognition with such devices is not optimal.

For children, there is less room to move because the better the hearing the higher the chance that the child will develop normally. According to Northern and Downs (1991; their chapter 1), indeed, children need (sub)normal hearing (15 dB HL or less) to ensure normal development of speech and language. Therefore, when counselling the parents of a child with conductive or mixed hearing loss, sufficiently powerful amplification options should be advocated (see section 4.3).

The main purpose of (any) device fitting is optimising the audibility of speech (Amlani et al., 2002). A popular tool to assess the audibility of speech is the Speech Intelligibility Index (SII). SII is the proportion of normal speech that is audible to a patient with a specific hearing loss; the SII ranges from 0 to 100, zero means that normal speech is not audible and 100 means that the patient is able to fully hear normal speech. The SII is based on the idealised spectrum of conversational speech with a +/- 15 dB range, often referred to as the speech banana. The speech banana can be represented in the audiogram, see Figure 7.1. To calculate the SII, for each frequency band (1/3 octave wide), the proportion of speech in that band that is audible is weighted according to the contribution of that band to speech intelligibility (weighting factors indicated by the density of the dots in the figure). Next, these outcomes are summed for all 1/3 octave frequencies. In this simplified model, the speech banana stretches from 20 dB HL up to 50 dB HL, over a frequency range of 250 to 6000 Hz (Mueller and Killion, 1990; Killion and Mueller, 2010). The number of dots (max is 100 dots) is the SII; so, one dot counts for 1% of the ‘speech cues’. In the figure, post-intervention hearing thresholds are presented of two different interventions. Counting the dots shows that the SII is 90 and 22 for intervention 1 and 2, respectively. In their paper, Killion & Mueller (2010) also published a graph with the relationship between the SII and word recognition scores (their Figure 3). Using that graph, the SII of 90 and 22 matches with word recognition scores (WRS) of 95% and 20%, respectively. Evidently, treatment 1 is much more effective than treatment 2. The figure further suggests that when the maximum 15-dB-hearing-loss criterion of Northern & Downs is fulfilled, SII is 100, thus optimal.

Especially in children, hearing aid fitting should be bilaterally, as bilateral input leads to improved hearing in noise and might enable spatial hearing (see Chapter 6). Lately, statistics showed that children with bilateral compared to unilateral hearing devices developed better cognitive skills, which was caused by better perception of soft sounds and better speech perception in noisy places (de Raeve et al., 2015). The factor in between better hearing and better cognitive development is incidental learning. Most things that children learn are acquired in informal everyday situations.

Figure 7.1. Audiogram format with speech area according to Mueller and Killion (gray area). Post-intervention thresholds are shown of two different treatments, 1 (red line) and 2 (green line). The SII of the two interventions is determined by counting the dots above the hearing threshold (Source audiogram: Mueller and Killion, 1990).

Only approximately 1/3 of the knowledge of young children is acquired in structured quiet settings (e.g., in school). The remaining 2/3 is acquired during the day while playing, watching TV, talking with parents and other persons, etc. (de Raeve et al., 2015). Especially under these latter conditions, the children profit from bilateral hearing devices.

Probably, the observation that children with unilateral hearing loss (second ear normal) might display delayed educational development, has the same cause (Kuppler et al., 2013). This underlines that hearing with two ears is of utmost importance for the development of speech and language in children.

 

7.2 Literature review: why some interventions don’t work

Now, we will use the audibility of speech (thus the SII) to find the best intervention for a child with congenital conductive or mixed hearing loss. A literature search was carried out with as search terms: children, conductive hearing loss, mixed hearing loss, and (Baha or Ponto or Sophono or softband or ‘Vibrant Soundbridge’ or surgery or conventional bone conduction or ‘Bonebridge’). Next, those papers were selected in which 1. two interventions were compared, 2. with at least 10 children involved, 3. with a unilaterally fitted device and 4. published after 2006. Most of the included studies addressed children with congenital conductive hearing loss.

Figure 7.2. Mean device-aided thresholds versus the sensorineural hearing loss component (SNHLc) of several study groups of children fitted with: percutaneous ’BCDs’ (red symbols, 5 studies*; summed 86 children), transcutaneous ‘BCDs’ (yellow symbols; 4 studies*; 130 children) and children with atresia repair (blue symbols, 3 studies*; 109 children). The black dots refer to three studies* in which the VSB was used (however, without a comparison with another device; 54 children).

* see note at the end of this chapter for references.

Figure 7.2 shows data obtained in children with conductive or mixed hearing loss. Concerning the percutaneous ‘BCD’ devices, evidently applied in pure condictive hearing loss (SNHLc was around 10 dB HL) overall, a mean device-aided threshold of 19 dB HL was found. That is close to the value that is mentioned in the ‘Practise Guidelines’ for fitting percutaneous devices (17.5 dB HL; Roman et al., 2011) and the 15 dB HL, which is the upper limit for a handicapping hearing loss for young children according to Northern & Downs (1991). Concerning the transcutaneous ’BCDs’, viz. the combined data of conventional ’BCDs’ (three studies, 49 children), ’BCDs’ on softband (two studies, 23 children) and the Sophono ‘BCD’ (one study, 15 children) a mean value of 29 dB HL was found. That value was expected, owing to the 10 to 15 dB poorer effectiveness of transcutaneous stimulation compared to percutaneous stimulation (Hakansson et al., 1984). Only one study was identified concerning the Sophono device with a mean device-aided hearing threshold of 33 dB HL (Denoyelle et al., 2015). That mean aided threshold was close to the reported threshold in the original paper, introducing the Sophono device (Siegert & Kanderske, 2013; reporting a mean value of 27 dB HL; 27 children).

With regard to surgical atresia repair, the mean long-term hearing threshold is 41 dB HL (three studies). That value is in good agreement with data from Nadaraja et al. (2013) who performed a systematic review of the literature. It should be noted that the outcomes of two interventions displayed in Figure 7.1 are Farnoosh et al.’s data (2014), with intervention 1 referring to a percutaneous ‘BCD’ application and 2 to atresia repair. The pre-intervention audiograms of the two groups were similar.

On the left side of the figure, the SII is presented calculated according to Killion and Mueller (2010). It is obvious that SII is the highest when using percutaneous ’BCDs’; ranging from 85 to 100 (corresponding WRS: 93 to 100%). Results with the transcutaneous ’BCDs’ are lower. Spread is larger and the SII ranges from subnormal (75; WRS of 90%) to moderate(50; WRS of 70%). Children with such a low SII might be prone to developmental delays. The SII after reconstructive surgery is particularly low, below 50. Indeed, Evans & Kazahaya (2007) reported that 90% of their operated children still needed some kind of amplification after atresia-repair.

Concerning the use of the VSB with its actuator coupled to one of the cochlear windows, no studies were found that presented results compared to another amplification device. However, three studies on VSB application in children with conductive loss were identified with at least 10 children involved. The mean aided thresholds of these three studies with VSB users are presented in Figure 7.1 as black dots. These data are in the same range as those of the transcutaneous ’BCDs’ what is somewhat disappointing and might be described to the experimental character of these studies. More data are needed (see update 2020, new section 7.2.1). So far, the ‘Bonebridge’ has hardly been applied in children (Sprinzl & Wolf-Magele, 2015) and is not further considered here (see update 2020, new section 7.2.1).

Children with acquired conductive or mixed hearing loss because of chronic inflammation will benefit from amplification in the same way as children with congenital conductive hearing loss. Mostly, for this indication, BTEs are contraindicated for medical reasons.

Figure 7.2 presents data that can be used for counselling parents of children with conductive hearing loss. In short:

Reconstructive surgery in case of congenital atresia of the ear canal is, on the average, the least effective treatment. 

For children with predominantly conductive hearing loss, today’s percutaneous ’BCDs’ provide more adequate gain than transcutaneous ’BCDs’, what might enable a better spontaneous development.

7.2.1 Update of Figure 7.2 using data published between 2016 and 2020 

Update of the data presented in figure 7.2 is based on an additional search of the literature; search period: 2016 (end previous search period) until early 2020. For details of the selection process, see note at the end of this chapter. Seven additional studies were identified, describing 11 groups of persons with different treatments. Data of the latest evaluation moment were used. The table below presents all the data averaged (viz. the mean post-intervention thresholds and the mean bone-conduction thresholds (more precisely, the mean threshold at 0.5, 1, 2, 4 kHz of each study was used to calculate the average over studies) per type of treatment, including the data of the previous search (presented in Figure 7.2). Table 7.1 shows that the mean bone-conduction threshold (column 3) per type of treatment is rather comparable. The mean post-intervention thresholds (next column) varied between 20 dB HL and 41 dB HL.

Using all the studies (from the previous and new literature search) that presented frequency-specific post-intervention thresholds, the mean post-intervention threshold was calculated per frequency and per type of intervention to enable calculating the SII and the associated word recognition score (WRS). The last column of the table presenting the WRS, suggests once more that these treatments are not equivalents. As concluded before, especially, the outcomes of surgical atresia repair are disappointing followed by the passive transcutaneous ‘BCD’s. The results obtained with the ‘Bonebridge’ and percutaneous ‘BCD’ are the best.

The data in the table should be considered with some caution: regarding the Sophono device and the VSB, 2 and 4 studies, respectively, were identified.

 

Table 7.1

Treatment	studies	Subjects, cumulative	Mean bc threshold	Mean post intervention threshold with (range)	Estimated WRS; % correct
Atresia repair	5	199	11 dBHL	41  (33-47) dBHL	25%
Percut. ‘BCD’	6	135	11	20  (15-22)	95
‘Bonebridge’	7	100	10	27  (19-31)	90
Sophono	2	42	16	35  (35/36)	65
Conv. ‘BCD’	8	126	11	33  (27-45)	70
VSB	4	60	11	31  (27-40)	75

Percut. stands for percutaneous; conv. for conventional ‘BCD’, including ‘BCD’ on softband; bc for bone conduction; WRS for word recognition score

 

 

 

7.3 Age at intervention and implant stability in children

After neonatal hearing screening and a diagnosed bilateral conductive hearing loss few amplification options are available. When the tympanic membrane is visible, BTEs might be used. A transcutaneous ‘BCD’ with softband can be used in all the other cases. It is easier to use and thus better accepted than a steel headband (Hol et al., 2005). The position of the stimulating bone-vibrator over the skull can easily be changed. The ‘BCD’-aided thresholds with such devices typically lay between 25 dB HL and 30 dB HL (e.g., Verhagen et al., 2008; Denoyelle et al., 2015), which might be acceptable but only for learning speech at a basal level (Northern & Downs, 1991; Verhagen et al., 2008). Therefore, replacement of a ‘BCD’ on head/softband by a percutaneous ‘BCD’ or other more powerful solutions should remain on the agenda and, meanwhile, speech and language development should be monitored.

The use of percutaneous ’BCDs’ implies implantation of a skin-penetrating titanium implant, anchored in the skull, behind the ear. Concerning the youngest age at which such implantation is feasible, the thickness of the skull plays an important role. At least 3 mm is preferred (Snik et al., 2005). This implies that the child must be approximately 4 years old; nevertheless, even then, the loss of these implants is approx. 3 times higher than in adults (e.g., Dun et al., 2010). McDermott et al. (2009) reported that implant loss was high amongst the under fives and much less in older children. Other studies didn’t find such a distinct dependence of implant loss on age at implantation (de Wolf et al., 2008). 

The subcutaneous magnet, for the coupling of a Sophono or Baha Attract processor, can be implanted from age 5 onwards, according to the manufacturers. Bezdjian et al. reviewed the literature and found 3 serious adverse reactions in 99 patients using the Sophono device, mainly children (Bezdjian et al., 2017). Dimitriadis et al. (2016, 2017) reported that the complication rate with the Baha Attract was low, when compared to the percutaneous ‘BCD’.

VSB with the transducer placed in the ‘round-window’ niche of the cochlea has been applied in children as young as 2 months (Mandala et al., 2011). However, since 2011, little has been published. Only one paper was found (with at least 5 implanted children); Leinung et al. (2017) presented results obtained in 13 young children with atresia of the ear canal. Age at implantation varied from 1.3 to 4.2 years with an average 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 device-aided threshold was 40 dB HL, which is poor compared to the data presented in Table 7.1. In order to advocate VSB implantation in toddlers and young children, more evidence is needed.

The preferred age at intervention for reconstructive surgery (atresia repair) is 5-6 years and, furthermore, only relatively mild atresia-cases should be considered for surgery (e.g., Declau et al., 1999). Concerning stability, revision surgery might be necessary, up to one-third of the cases, as reported by Farnoosh et al. (2014). These authors compared atresia repair with percutaneous ‘BCD’ application, amongst other, with respect to medical complications. Percentage of revision surgery after atresia repair was almost 3 times higher than that after ‘BCD’ implantation. Therefore, it was suggested that, also in terms of medical aftercare, percutaneous ’BCDs’ might be a better choice than atresia repair.

 

7.4 Percutaneous or transcutaneous ’BCDs’ in children, counselling issues

When a child is approx. 4 years old, the conventional ‘BCD’ should be ‘upgraded’. Parents might choose for transcutaneous ‘BCD’ instead of percutaneous ‘BCD’, because of stability issues, daily care of the skin around the skin-penetrating-implant and/or emotional problems to accept titanium implants sticking out, through the skin. Then the remaining amplification options are to use either the Sophono device (Alpha 2 MPO) or the Baha Attract, applicable from age 4 or 5 years. First data showed that, as expected, the Baha Attract is as effective as Baha on a Softband (Kurz et al., 2014). Nowadays, as a sound processor, the Baha 5 power is advocated, which is more powerful than the standard Baha. The use of the Baha power processor will improve the MPO by several dBs. When bilateral transcutaneous ‘BCDs’ are used, in predominant conductive hearing loss, aided thresholds are expected between 25 dB HL and 35 dB HL, with corresponding SII values between 85 and 50 (corresponding WRS: 93% and 70%).  This might be just safe but suggests that these children should be followed-up more closely than bilateral percutaneous ‘BCD’ users concerning their speech and language development. It still remains of importance to keep a change to a percutaneous ‘BCD’ on the agenda.

Another suggestion that has been put forward to further support children with transcutaneous ’BCDs’ is the provision of an additional personal FM system. Those systems, coupled to the child’s ‘BCD’ might enable better speech recognition, however, can only be used effectively in structured situations like classrooms. 

*Note. References belonging to the studies summarised in Figure 7.2: Claros & Pujol, 2013; Frenzel et al., 2015; Verhagen et al., 2008; Farnoosh et al., 2014; Ricci et al., 2011; Denoyelle et al., 2015; Bouhabel et al., 2012; Evans & Kazahaya, 2007; Christensen et al., 2010; Mandala et al., 2011. The update of figure 7.2 (early 2020) was based on an additional literature search using Pubmed. The search string comprised the words: children, hearing, thresholds, and either a device name (Baha, Ponto, Bonebridge, Sophono, Vibrant Soundbridge) or atresia, surgery. Studies were excluded if aiming at subjects with just unilateral hearing loss, single-sided deafness or sensorineural hearing loss. The inclusion criteria used were: 1. either the aided PTA4 or the aided thresholds at 0.5, 1, 2, 4 kHz should have been reported, as well as bone-conduction thresholds and 2. group size should be more than 9. The newly identified studies comprised: Zhao et al., 2016; Fan et al., 2019, Bravo-Torres et al., 2018, Kulasegarah et al., 2018, Ren et al., 2019, Ahn et al., 2018, Zernotti et al., 2019, Ratuszniak et al., 2019.

6.1 Introduction

Binaural hearing refers to hearing with two ears. When listening with two ears instead of one, at least three advantages can be distinguished: 1) loudness summation, 2)) directional hearing and 3) binaural squelch. In normal hearing persons binaural hearing is obvious, based on accurate processing of the unilateral inputs, leading to a ‘fused’ percept (binaural hearing). That is not evident for patients using hearing devices. Bilateral input with hearing implants does not automatically result in binaural hearing.

An introduction of the three advantages of binaural hearing:

1. Loudness summation refers to improved hearing owing to summation of sound as heard by each ear: the input perceived by either cochlea is summed, leading to an increase in loudness of approx. 5 dB.
2. Localization of sounds, in the horizontal plane. To identify where a sound is coming from, the two ears have to work together. Interaural differences in perceived sounds are detected, caused by the different positions of the two ears with respect to the sound source. These interaural differences concern interaural loudness differences or ILD; owing to acoustic head shadow and interaural time differences or ITD, caused by a difference in arrival times of the sound at the two ears). The head, as an acoustic barrier, attenuates primarily high frequency sounds (> 2000 Hz). As a consequence, high-frequency sounds are being perceived as louder by the ear nearest to the sound source, creating an ILD. Below 1500 Hz, the head shadow causes little attenuation. Instead, ITDs (or, related, interaural differences in phase) are the relevant cue to localize a sound source. Sounds arrive earlier at the ear nearest to the sound source, creating the ITD. Owing to the limited distance between the two ears, the ITD varies between 0 ms (sounds from the front) to a maximum of 0.7 ms (by a sound presented at the very right or left).
3. Binaural squelch refers to central de-masking. Assume someone is listening to speech coming from the front and ambient noise also coming from the front. Then the noise might mask the speech. However, if the noise is coming from the left, then the speech sounds in the two ears will (still) be in phase (ITD=0). However, not the ambient noise (ITD= 0.7 ms, the maximum value). The differences in ITDs enables the perceptually separation (de-masking) of the speech and the ambient noise, referred to as binaural squelch.

Bilateral application of BTEs in patients with bilateral sensorineural hearing loss leads to bilateral input but not automatically to binaural hearing. The advantage of a second BTE might be worse than the advantage of listening with two ears (see e.g., Bogaert et al., 2006, studying sound localisation). Nevertheless, e.g., Boymans et al. (2008) showed an obvious benefit of bilateral BTEs in a large group of patients with bilateral sensorineural hearing loss, regarding sound localisation and the effective use of head shadow.

6.2 Binaural hearing with ‘BCDs’

When using the air-conduction route, the two ears can be stimulated independently because they are acoustically well isolated from each other. That is not the case for bone-conduction stimulation. The skull transmits the bone-conducted vibrations quite effectively, thus with little damping. Therefore, with one ‘BCD’, not only the ipsilateral cochlea is stimulated but also the contralateral cochlea. This is referred to as ‘cross-stimulation’ (i.e. cross-hearing). The attenuation in dB of the bone-conducted vibrations from one cochlea to the other varies widely with a median of just 5 dB. The variation between subjects is significant as well as within subjects, between the frequencies (Stenfelt, 2012). In other words, for bone-conduction stimulation, the cochleae are poorly acoustically isolated, however, just sufficiently to enable the detection of interaural differences, although, impaired (Stenfelt, 2005).

Table 6.1 presents data on binaural effects when changing from unilateral to bilateral listening in patients using ‘BCDs’ and, as a reference, normal hearing persons. In the latter case, unilateral hearing refers to hearing with one ear occluded. The first row of the Table presents the mean result (and standard deviations) of the ‘binaural’ outcomes as measured in normal hearing persons (Agterberg et al., 2011) and might be considered as standard values. The other rows present an overview of the outcomes of published Nijmegen studies concerning bilateral ‘BCD’ application in bilateral conductive/mixed hearing loss and unilateral ‘BCD’ application in unilateral conductive hearing loss, thus with a second normal hearing ear. All the patients and the normal hearing persons were evaluated with one and the same protocol. 

Binaural summation and speech in ambient noise were assessed using speech; directional hearing was tested using narrow-band noise with a short duration (1s) presented by one loudspeaker out of seven at a location between + 900 and – 900 azimuth (Agterberg et al., 2011). Concerning the binaural summation score, firstly, speech recognition was measured while the patient was listening with one ear (in unilateral cases with their normal ear; in bilateral cases with their left ear only, thus the ‘BCD’ on the right ear was turned off). To quantify binaural squelch, firstly, speech recognition in noise was measured while the patient was listening unilaterally. Speech was presented in front of the patient and the noise at the side of the only hearing ear. Secondly, the ‘BCD’ near the patient’s other ear was activated (in the normal hearing subjects, one ear had been occluded for the first measurement, which is open again for the second measurement). The presented score is the improvement between these two situations. The asterisks indicate values that differ significantly from 0. The next two columns show directional hearing results for low frequency sounds (relying on detection of ITDs) and for high frequency sounds (relying on the detection of ILDs), respectively. The mean absolute error is shown (0 means perfect localisation). Concerning these results: statistically significance was assessed by comparing the scores obtained in the unilateral listening situation (not shown) and bilateral listening situation. 

Let us consider bilateral ‘BCD’ application in bilateral hearing loss. According to the table, row 2, bilateral ‘BCD’ application does lead to the expected improvement in binaural summation (column 1) of, approximately, 4 dB. This result is in agreement with the literature (Janssen et al., 2012; review). Although not measured, binaural hearing in normal hearing subjects is around 5 dB. Obviously, here, the inevitable ‘cross-stimulation’ during bone-conduction stimulation, plays a minor role.

Table 6.1

	N	Binaural summation (dB)	Head shadow & squelch (dB)	Directional hearing, 0.5kHz (degrees)	Directional hearing, 3 kHz (degrees)
Controls	10	n.a.	4.6 ± 1.6*	7 ± 7^	8 ± 10^
Bilat CHL, bilat Baha, acquired	17	4.0 ± 2.1*	2.5 ± 1.8*	26 ± 8^	25 ± 8^
Unilat CHL, acquired	13	2.2 ± 1.5*	3.0 ± 1.7*	16 ± 10^	20 ± 12^
Unilat CHL, congenital	10	1.3 ± 2.4	1.1 ± 1.9	30 ± 13	31 ± 18

Note. N.a.: not available, CHL: conductive hearing loss.

* significantly different from 0 (p<0.05); ^significantly improved compared to the unilateral listening condition (p<0.05)

Considering row 3 (‘BCD’ application in acquired unilateral conductive hearing loss) a limited but significant binaural summation score was found, however, not for the unilateral congenital cases (row 4). Column 2 shows the binaural squelch/head shadow data. The bilateral conductive hearing loss patients (row 2) profit significantly, however, profit is approx. half that of the normal hearing persons (2.5 vs. 4.6 dB). For unilateral acquired conductive hearing loss, the outcome is approx. the same, while for the congenital cases, no significant benefit was found. 

Columns 3 and 4 comprise the outcome of the sound localisation tests; the mean absolute difference (in degrees) between the perceived location and the real location of the activated loudspeaker are presented. For normal hearing persons, an error of 7-80   was found, for the bilateral ‘BCD’ users approximately 250  and for the patients with unilateral acquired hearing loss using ‘BCD’, approximately 200. These three groups showed significantly improved scores when changing from unilateral hearing (mean unaided scores not presented but in the range of 46-660) to bilateral hearing. Probably, disturbing ‘cross-stimulation’ is the reason for the difference in score between the normal hearing persons and the bilateral ‘BCD’-users. Again, the unilateral congenital cases showed the worst scores, see next paragraph.

6.3 Unilateral congenital conductive hearing loss; elaborated outcomes

The localisation scores of the patients with congenital unilateral conductive hearing loss with their ‘BCD’ active were largely unchanged, namely 340 and 390 for 0.5 and 3 kHz without the ‘BCD’ and  300 and 310 for 0.5 and 3 kHz with the ‘BCD’. The most likely explanation is that these patients, being unilaterally hearing since birth, have learned to use some specific monaural cues rather effectively. For normal subjects such cues are less relevant because they are inferior, rather marginal binaural cues (as elaborated by Agterberg et al., 2012 and Vogt et al. 2020). Vogt et al. even showed that with a percutaneous ‘BCD’ turned on, these patients remained relying on monaural cues for sound localisation, despite the second input (via the ‘BCD’).

In an attempt to understand the moderate results of the patients with congenital onset of their hearing loss, we decided to study whether or not age at intervention played a role. The hypothesis was that maybe a sensitive period exists; the earlier implantation, the better the binaural results would be. Figure 6.1 shows the individual summed outcome of three binaural tests (the head shadow test and the two directional hearing scores) after expressing the outcomes into z-scores, using the standard deviations of the normal hearing persons. Results of 20 patients who used a ‘BCD’ for at least 3 months were available (Nelissen et al., 2015). Figure 6.1 shows the summed z-scores of these 20 patients as a function of age at implantation. For reference purposes the same procedure was applied to the data of the patients with acquired unilateral conductive hearing loss; a mean summed z-score of just over 10 was found in that group. The Figure shows that a value of 10 is achieved by just one of the patients with congenital unilateral hearing loss. Also negative summed z-scores were found, indicating a worse result with ‘BCD’ than without. A significant effect of age at intervention is not seen, while the spread in results is large.

Figure 6.1. Binaural advantage based on the use of head shadow and sound localisation. Summed z-scores are presented as a function of age at intervention. Data of the ‘BCD’ users that continued using their device and those who stopped are indicated by different symbols.

Fitting of a (percutaneous) ‘BCD’ in patients with a unilateral congenital conductive hearing loss, to enable binaural hearing, might result in a poor outcome; age at implantation doesn’t seem to play a role (in the age-range studied, from 4 years into adulthood).

Furthermore, Nelissen et al. (2015) reported that with a follow-up > 5 years, 65% of the patients had stopped using their ‘BCD’. An association was found between ‘long-term’ non-use and the ‘short-term’ (one-year post-intervention) summed ‘binaural advantage score’. The non-use was not related to age at intervention. It seems that several of these patients were not able to integrate the new input with that of the normal hearing ear, which is needed for a binaural percept. Thus, not surprisingly, the main reason to stop, as indicated by the patients, was complaints about interfering sounds/ambient noise when using the ‘BCD’ in situations with background sounds. Patients with unilateral acquired conductive hearing loss do benefit from ‘BCD’ application; obviously, they profit from their previously developed binaural abilities.

More recently, a review of the literature was published (Vogt et al., 2021) focussing on post-intervention binaural hearing abilities in children with congenital atresia of the ear canal. Interventions included not only a percutaneous ‘BCD’ but also all other types of implantable ‘BCDs’, MEIs like the VSB as well as surgical atresia repair. Surprisingly, all outcomes were disappointing, irrespective of the type of intervention (concerning binaural summation and/or binaural squelch and/or directional hearing). Vogt et al. discussed factors that might have played a role namely 1. age at treatment, 2. whether the treated ear was a ‘lazy’ ear, which means an ear with a not fully maturated neural network, and 3.  the role of the remaining asymmetry in hearing thresholds, post-intervention, as was seen generally. It was argued that the main problem might have been the remaining asymmetry in hearing after the interventions, which typically varied between 20 dB and 35 dB. This asymmetry might hinder the development of binaural hearing.

Concerning the binaural advantage of a MEI in unilateral conductive hearing loss, it should be noted that in contrast to a ‘BCD’, ‘cross-stimulation’ with a MEI is absent. Two publications were found in which outcomes obtained with the VSB MEI were compared to those with ‘BCDs’ in patients with congenital unilateral conductive hearing loss (Agterberg et al., 2014; Vogt et al. 2018). Agterberg et al. compared results of patients fitted either with a ‘BCD’ (n=4) or with a VSB (n=4). All were experienced device users. An anticipated better result with the ‘cross-stimulation-free’ VSB device in a directional hearing experiment could not be established. Same conclusion was drawn from a comparison between the VSB and an active transcutaneous ‘BCD’, the ‘Bonebridge’ device (Vogt et al., 2018). This suggests that ‘cross-stimulation’ is not a major issue for these patients.

Although unilateral congenital hearing loss in children might lead to developmental delays (in speech language development and performance in school), outcomes of today’s treatment options are grossly disappointing (Vogt et al., 2021). Nevertheless, some children experience improved hearing and are happy with that. No conclusive evidence was found regarding the role of age at treatment, degree of asymmetry in hearing after the treatment nor what intervention is the most effective one.

6.4. Bilateral application of ‘BCDs’ and MEI

Bilateral application in bilateral conductive hearing loss is not always considred (Wang et al. 2025), while it works, see Table 6.1, what is also reported by e.g., Janssen et al. (2012; systematic review) and Zeitooni et al, 2016. The latter study was carried out in normal hearing persons; binaural advantages were compared as obtained with stimuli/speech presented bilaterally over headphones (air-conduction route) and, separately, bilaterally by bone-conduction transducers (bone conduction route). The authors reported profit in both conditions, however the binaural advantage (using speech in noise) was approx. two times better with headphone presentation. This factor of 2 is in fair agreement with the difference as presented in column 2, Table 6.1, when comparing the outcomes of the normal hearing persons and the bilateral ‘BCD’ users.

A further question is whether or not (adult) patients with bilateral congenital conductive or mixed hearing loss do profit from fitting bilateral ‘BCDs’. Bosman et al. (2001) reported that the ‘binaural advantage’ as found in their patients with acquired bilateral conductive hearing loss (summarised in row 2, Table 6.1) and those of 6 congenital cases were grossly the same. This might suggest that early binaural auditory experience is not a prerequisite for effective use of bilateral ‘BCDs’ in bilateral conductive hearing loss. More recently, Den Besten et al. (2020) published data on a group of 7 children with bilateral congenital conductive hearing loss, all experienced users of bilateral percutaneous ‘BCDs’. They reported that all children showed improved sound localisation when using two instead of one ‘BCD’, however, localisation scores were moderate in most of the children. Agterberg et al. (2024) demonstrated accurate sound localization with bilateral MEIs in 4 of the 6 included patients. Den Besten et al. also presented data on none-use. Almost 85% of their group of bilaterally implanted children (n=33) used both percutaneous ‘BCD’ devices all the time.

Although transcutaneous ‘BCDs’ have been applied bilaterally, no systematic prospective evaluative study has been found in literature (early 2021).  As far as we know, studies are also missing on binaural hearing after bilateral application of MEIs, like the VSB, in patients with conductive or mixed hearing loss. Wolf-Magele et al. (2016) studied 10 bilateral VSB users, however 6 of them with sensorineural hearing loss, 4 with mixed loss and Koci et al (2016) reported directional hearing measurements in 10 bilateral VSB users; 8 of them had sensorineural hearing loss. Reported results of these mixed groups of VSB users are favourable, but the outcomes are not necessarily representative for patients with conductive or mixed hearing loss. So, specific studies are needed.

Note. A special remark has to be made concerning binaural summation in patients with bilateral conductive hearing loss using (two) devices instead of one. Improved hearing has been observed owing to binaural summation, in the order of 4 dB, see Table 6.1. This is of major importance; as the amplification of ‘BCDs’ is limited owing to the relatively low MPO, see Chapter 4, Figure 4.4 and related text. The ‘gain ratios’ for groups B and C as presented in that figure will improve significantly with the extra 4 dB of gain. For example, at 2 kHz, the NAL-prescribed value of approx. 0.45 is now reached for both devices of group C while for group B a value of 0.38 is found instead of 0.27. 

However, a problem might occur when fitting two devices. When programming two BTEs in bilateral pure sensorineural hearing loss, either BTE is programmed individually. When switching on both BTEs, overstimulation might occur owing to binaural summation. Generally, to deal with that, the volume and maximum output of the two BTEs is lowered; mostly, the software does this automatically. Evidently, for devices with limited MPO like the ‘BCDs’ and MEIs, such a lowering of gain and output is contra-productive and should be avoided.

In bilateral conductive or mixed hearing loss, the application of bilateral ‘BCD’s leads to binaural hearing, although not optimal, with somewhat better result in acquired cases than congenital cases. Device compliance is high.

So far, the patients in the bilateral ‘BCD’ studies had rather symmetric bone-conduction thresholds. It is not clear what might happen in case of asymmetric bone-conduction thresholds. The theoretical problem is that the better ear might be hindered or even over-stimulated by a ‘BCD’ device fitted at the side of the worse cochlea. No data are available on this issue. When using MEIs, such a problem might not occur.

6.5. Binaural hearing and adaptive sound processing

Today’s ‘BCDs’ and VSBs make use of, amongst others, adaptive sound processing like expansion- and/or compression amplification, noise reduction, feedback reduction and/or adaptive directional microphones. Interaural cues (ILDs and ITDs) might be distorted by independently working digital sound processors. Sound processing times are relatively long (3 to 9 ms) compared to the maximum possible ITD (0.7 ms), furthermore the bilateral devices are not synchronized. All these factors might deteriorate interaural cues, resulting potentially in poor horizontal localization (Bogaert et al., 2006; Beck & Sockalingam, 2010). In principle, these advanced sound processing options are not really necessary when fitting patients with good cochlear function (conductive or mixed hearing loss with mild to moderate SNHLc), because the auditory system can still sort out the important information. On the other hand, some of these processing options might be necessary, to deal with limitation of the devices such as feedback, the unnatural position of the microphone, audible microphone noise and the limited MPO.

It is not evident that patients with conductive hearing loss or mixed hearing loss with a minor to moderate sensorineural hearing loss component do profit from advanced adaptive sound processing. Side effects like deteriorated spatial hearing might occur. Conclusive research is lacking.

References

Agterberg MJH, Straatman L, Bruchhage KL, Jürgens T, Hollfelder D, Leichtle A. The Merits of Bilateral Application of Middle Ear Implants in Patients With Bilateral Conductive and/or Mixed Hearing Loss. Trends Hear. 2024;28:23312165241264466.

Den Besten CA, Vogt K, Bosman AJ, Snik AFM, Hol MKS, Agterberg MJH. The Merits of Bilateral Application of Bone-Conduction Devices in Children With Bilateral Conductive Hearing Loss. Ear Hear. 2020;41(5):1327-1332.

Vogt K, Wasmann JW, Van Opstal AJ, Snik AFM, Agterberg MJH. Contribution of spectral pinna cues for sound localization in children with congenital unilateral conductive hearing loss after hearing rehabilitation. Hear Res. 2020;385:107847.

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.

Vogt K, Desmet J, Janssen A, Agterberg M, Snik A. Unexplained variance in benefit of treatment of congenital unilateral aural atresia. Audiol Neurotol 2021; in press.

Wang Y, Zhu J, Liu Y, Wang D, Zhao S. Over three-year outcomes of Bonebridge implantation in children and adolescents with congenital bilateral conductive hearing loss. Auris Nasus Larynx. 2025;52(3):207-215.

Zeitooni M, Mäki-Torkko E, Stenfelt S. Binaural Hearing Ability With Bilateral Bone Conduction Stimulation in Subjects With Normal Hearing: Implications for Bone Conduction Hearing Aids. Ear Hear. 2016;37(6):690-702.

 

5.1 Stability (implant survival rates, medical complications) and MRI compatibility 

Systematic studies on long-term implant stability are relatively scarce but not for percutaneous ‘BCDs’. Reported disadvantages of percutaneous implantation are implant loss and skin irritation around the percutaneous implant, which might lead to (revision) surgery. It should be noted that over the years, less complications occurred, owing to more than 30 years of experience with these implants. New implantation procedures have been introduced as well as optimized implants. Table 5.1, first line, presents Nijmegen data. Systematically, all minor and major complications have been documented for each patient, starting in 1988. Patients were seen at least 5 times during the first years after implantation and twice a year, later on. Apart from planned visits, additional visits took place at the patient’s initiative. Dun et al. (2012) analysed these data from the first successive 903 adult patients, implanted between 1988 and 2008. Table 5.1 shows that one revision surgery has been performed per 30 years of follow-up (column 5). Wazen et al. (2008) published a similar study. They started later with applying these implants, in 1998. That might be the reason why their result is better than that of Dun et al.

More recently, prospective multicentre studies have been published using new, upgraded percutaneous implants and/or implant procedures (Nelissen et al., 2014; Kruyt et al., 2018; see Table 5.1). Indeed, further progress has been made, as, relatively, less revision surgeries were needed.

In 2020 Lagerkvist et al. reviewed the literature, regarding, amongst others, the survival rate of the implants for percutaneous ‘BCDs’ (25 studies; altogether more than 1000 ‘BCD’ users). Using their data, the implant survival rate determined at 1-1.5 years post surgery (8 studies, 372 users) was 98,1% and at 3-5 years post surgery (3 studies, 130 users): 98,5%. In other words, with the more recent percutaneous implants and surgical techniques, the percutaneous-implant survival rate is high, close to 100%, and seems to be stable over time (Lagerkvist et al., 2020). 

The last columns of the table presents data related to skin reactions around the percutaneous implant (percentage of visits with some kind of skin reaction). Generally, the severity of skin reaction is expressed in Holgers grades 1 to 4. Grade 2, red and moist tissue, requires local treatment; grades 3 and 4, more severe conditions, might require revision surgery (Wazen et al., 2011). As the table shows, indeed, skin problems remain rather common; however, the percentage of serious skin problems, requiring some type of intervention, is decreasing (Holgers grades 2 to 4; see last column).

Table 5.1. Number of revisions related to the total follow-up period and the percentage of soft tissue reactions

Author, year	n	Summed revisions	Summed follow-up	Relatively	All skin reactions***	Holgers grade > 1
Dun, 2012	903*	145**	4.267 yrs	1 in 30 yrs	15%	4,3%
Wazen, 2008	218	23	990 yrs	1 in 43 yrs	****
Nelissen, 2014	52	2	156 yrs	1 in 78 yrs	23,1%	1,8%
Kruyt, 2018	39	2	117 yrs	1 in 58 yrs	15,5%	1,5%

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

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

Concerning MEIs, the number of medical complications and explantations have been reported by e.g., Bernardeshi et al. (2011), Colletti et al. (2013), Mlynski (2014) and Brkic et al. (2019), Sprinzl et al. (2021). The derived revision-surgery rates varied between 1 in 15 years up to 1 in 28 years of follow-up. ‘Teething problems’ might have played a role, especially with regard to surgical techniques and coupling options. Update: indeed, more recent data published by Vickers et al. (2023; multicentre UK data; 163 VSB users), showed a better result: one serious adverse event requiring surgery per 50 years of follow-up.

Sprinzl et al. (2021) and Vickers et al. (2023) also reported survival rates for VSB implants. Sprinzl et al. presented data of 46 patients; they distinguished two subgroups; see section 5.2.2. The implant survival rate of the whole group was 91% at 1-year post implantation and 73% at 4-years post implantation. Vickers et al. reported an implant survival rate of 92% at 1-year and 88% at 3-years post implantation. Vickers et al. also reported implant survival rates for the ‘Bonebridge’ (109 patients), viz. 97% at 1-year and 93% at 3-years post implantation. These survival rates are worse than those of implants for percutaneous ‘BCDs’ (as review by Lagerkvist et al., 2020; see section 5.1). The relatively poor outcome for the VSB is caused by the complicated and/or instable medical status of the patients’ middle ears, were the VSB actuator is located.

The survival rate of implants for percutaneous ‘BCDs’ is favourable compared to that of other implantable devices. However, problems with the skin around the percutaneous implant, leading to revision surgery, might occur. Owing to complicated and/or non-stable medical conditions of the middle ear, VSB-implant loss is relatively high; therefore, a ‘BCD’ might be a safer choice (especially in chronic otitis media; see section 5.2.2).

5.1.2 MRI compatibility 

An important issue to consider when choosing an implantable device is MRI safety. MRI is a powerful and increasingly popular diagnostic tool. Statistics show that the incidence of MRI scanning increases steadily over the years. In 2020, the incidence was 66 MRI scans per 1000 habitants in the Netherlands.

Doshi et al. (2014) reviewed the literature and manufacturer’s information on MRI compatibility of percutaneous and transcutaneous ‘BCDs’ and MEIs. The percutaneous implant is MRI safe; in contrast, the MEIs are not MRI safe. Early 2015, a new VSB implant was introduced, the VORP 503, which is MRI safe up to 1.5T. The transcutaneous bone-conduction implants are MRI compatible either up to 1.5T (‘Bonebridge’, Baha Attract) or 3T (Sophono). It should be noted that with each upgrade, MRI safety is specified. Therefore, the data presented here might not be up to date.   

Maybe more important is the degree of distortion of the MRI scan caused by the implanted device. The percutaneous implants affect the MRI image only locally (radius of 15 mm) while the transcutaneous implants, comprising magnets, distort the MRI scans more significantly, with a radius of 10 to 15 cm (Doshi et al., 2014). In contrast to damage to the implant by a MRI machine, the distortion of the MRI scan might not change when the devices are upgraded. The best options to minimise the distortion of the MRI image is a percutaneous ‘BCD’ and implants (e.g., Osia, active transcutaneous ‘BCD’; Cochlear) with a piezoelectric actuator instead of an electromagnetic one (Nassiri et al., 2024).

Concerning MRI compatibility, percutaneous ‘BCDs’ are the best option, as well as implanted devices with a piezoelectric actuator.

5.2. Application of implantable devices in certain groups of patients

5.2.1 Congenital middle ear and outer ear anomalies; surgical repair or amplification?

When counselling patients with hearing loss caused by congenital ear anomalies, firstly, reconstructive surgery should be considered. Congenital ear anomalies might vary from mild (middle ear anomalies) to severe (bony atresia of the ear canal) with associated AB-gaps (difference between air- and bone-conduction thresholds) from 40 to 65 dB. Amongst otologists, reconstructive surgery of congenital anomalies is considered as very challenging because of the deviating anatomy, and risk of complications. In audiometric terms, the profit is often limited and not stable over time. Theoretically, surgery is successful if the AB-gap is closed, but mostly, post intervention, an obvious AB-gap remains. To define a successful outcome after atresia repair, often, a rather conservative criterion is used: if the remaining AB-gap is 30 dB or less, the outcome is considered as sufficient (Nadaraja et al., 2013). In their systematic review (35 studies were included), Nadaraja et al. showed that this criterion is met in approx. 50% of the operated patients. Already in 1999, based on a review of the literature and expert opinions, Declau et al. (1999) concluded that atresia repair was only safe in experienced hands and the authors suggested that alternative options like ‘BCDs’ should be considered more often. That conclusion has been underlined by Evans & Kazahaya (2007). They reported that the majority (93%) of their operated patients with atresia of the ear canal still needed some type of hearing device. Further evidence came from the Nadaraja et al. study; they compared the outcomes of studies with percutaneous ‘BCD’ application (Baha) and surgical atresia repair. They concluded that the results with Baha were significantly better. More recently, a systematic review by Shannon et al. (2023) came to the same conclusion.

Apart from atresia of the ear canal, minor congenital (middle ear) anomalies might occur; e.g. isolated congenital stapes fixation or a mobile stapes with ossicular chain anomalies. Thomeer et al. (2010; 2011; 2012) published one-year post-intervention audiometric data; the mean remaining AB-gap was 15 to 20 dB. One year after surgery, 65% to 75% of the operated ears had a PTA (air conduction) of 30 dB HL or better. However, as stated by Thomeer et al., hearing thresholds might have been better with hearing devices. In case hearing aid fitting is considered in minor congenital middle ear anomalies, the first amplification option is a conventional BTE. If the AB-gap exceeds 30 dB HL, a percutaneous ‘BCD’ is the better option; the larger the AB-gap, the higher the profit of a percutaneous Baha/Ponto device over a BTE (for details, see Chapter 2, section 2.2).

In 2006, as an alternative amplification option, Colletti et al. (2006) introduced the VSB with its actuator (FMT) directly coupled to the round window of the cochlea (see also section 2.3). Amongst others, Frenzel et al. (2009) and Colletti et al. (2010) published their results with the VSB applied in patients with atresia of the ear canal and reported that this amplification option was safe and effective. Concerning this VSB application, several coupling options for the FMT to the cochlea have been introduced, either connected to the incus, if the stapes was mobile, or to the round window. If there is a choice, there is a preference for a coupling to the incus because of higher output (e.g. Hüttenbrink et al., 2008). A long-term evaluation showed that all FMT couplings were stable, with the best ‘effective gain’ for the incus coupling (Bush et al., 2017) (for the definition of ‘effective gain’ see Appendix 2). 

Regarding the effectiveness of the different types of implants, a literature review was performed. Included were studies in patients with predominant conductive hearing loss, using acoustic implants; mostly children. For details of the review, see Chapter 7; the outcome of this review is presented in Table  7.1, which is copied and presented here as Table 5.2. For a comparison, hearing thresholds obtained after surgical atresia repair are presented as well (first line). The number of included studies, number of patients, (weighted) average bone-conduction thresholds and average aided thresholds (0.5 to 4 kHz) are presented.

Table 5.2 (same as Table 7.1)

Treatment	studies	Patients, cumulative	Average bc threshold	Average post intervention threshold with (range)
Atresia repair	5	199	11 dBHL	41  (33-47) dBHL
Percut. ‘BCD’	6	135	11	20  (15-22)
‘Bonebridge’	7	100	10	27  (19-31)
‘Sophono’	2	42	16	35  (35-36)
Conv. ‘BCD’	8	126	11	33  (27-45)
VSB	4	60	11	31  (27-40)

Percut. stands for percutaneous; conv. for conventional ‘BCD’ (‘BCD’ on softband); bc for bone conduction. Range refers to the range of outcomes of the individual studies

Note. Regarding the application of ‘BCDs’: there is no a priori reason to expect that its effectiveness depends on aetiology; however, the effectiveness of a VSB application might depend on the chosen coupling of the VSB to the cochlea, see e.g., section 5.2.3.

Table 5.2 shows that surgical atresia repair might lead to inferior hearing thresholds when compared to the application of percutaneous ‘BCDs’. Regarding transcutaneous ‘BCDs’, the ‘Bonebridge’ is the best option. Results with the VSB are somewhat disappointing. 

5.2.2.  Chronic otitis media with effusion and supprative otitis media

In most cases, otitis media with effusion (OME) is a transient disease, affecting mainly children. Mostly the OME recovers spontaneously; if not, grommets are inserted in the tympanic membrane. In some children, OME might be (semi) chronic, e.g., in children with Down syndrome and children with cleft palate (Sheenan & Hans, 2006), asking for longer lasting hearing solution. Then, provision of a hearing device might be beneficial. The OME-associated (conductive) hearing loss in such children typically varies between 15 dB HL and 35 dB HL what suggests that BTEs can be used effectively (see Chapter 2, section 2.2). A ‘BCD‘ on a headband or softband has also been advocated (Ramakrishnan et al., 2006). The advantage of a ‘BCD’ is that whenever the hearing loss fluctuates over time (not unlikely in case of OME), BTEs have to be refitted, in contrast to ‘BCDs’. Note, however, that aided thresholds with conventional transcutaneous ‘BCDs’ typically lay around 25-30 dB HL, thus close to the ‘unaided’ thresholds (Snik et al., 2008). Indeed, according to the data of Ramakrishnan et al. (2006), who provided children with OME with ‘BCDs’ on headbands, it was not a great success. More recently, an interesting new approach was launched; the use of commercially available bone-conduction headset with a remote microphone (Holland Brown et al., 2019; 2021). The authors state that this is an affordable and effective solution for children with OME waiting for treatment or recovery and for children with a fluctuating hearing loss. 

Chronic supprative otitis media (CSOM) is a long-standing middle ear inflammation that results in periods of discharge from the ear. The tympanic membrane is perforated. CSOM might lead to a serious complication: cholesteatoma (benign collection of keratinized epithelium in the middle ear that can destroy vital structures).

Treatment of such patients is mainly focussed on the inflammation and, eventually, cholesteatoma removal. CSOM might lead to substantial conductive or mixed hearing loss. To improve hearing, the use of BTEs with occluding ear moulds might have an adverse effect on ear discharge. While BTEs are not a safe choice, percutaneous ‘BCDs’ can be used and the outcomes are favourable (Snik et al., 2005). Literature has shown that replacing BTEs by percutaneous ‘BCDs’ had a significant positive effect on the ear discharge (Macnamara et al. 1996; Mylanus et al. 1998; McDermott et al. 2002), which led to a significant reduction in outpatient visits (Hol et al., 2004). This is an important advantage in terms of cost-benefit as well as in patient’s convenience.

Another amplification option is a MEI with the actuator coupled to one of the cochlear windows. This requires an infection-free middle ear. MEIs (VSBs) have successfully been implanted after subtotal petrosectomy with obliteration of the ear cavity with abdominal fat (e.g. Linder et al. 2009 and Ihler et al., 2013). Minor technical and medical problems were reported. Ihler et al. reported one revision surgery in their 10 implanted patients. Mean gain at threshold level (or the ‘effective gain’; for its definition, see Appendix 2) was comparable to that of the VSB applications in other types of mixed hearing loss. 

For the effectiveness of the different types of ‘BCDs’ ; see Table 5.2. 

For patients with chronic running ears (CSOM) who need amplification, ’BCDs’ are the first treatment option. MEIs might be used as well, although implant surgery is complicated by the fact that a stable, infection-free middle ear has to be established, first of all.

5.2.3 Otosclerosis

Otosclerosis is a disease that leads to mixed hearing loss. Large variations in hearing loss have been reported and hearing loss might deteriorate over time at different rates (e.g. Rotteveel et al., 2004; Sziklai et al., 2009). The conductive part is caused by stapes fixation. Although some twenty-year-old patients with otosclerosis might already have a sensorineural hearing loss component (SNHLc) of 30 dB HL (Iliadou et al., 2006; Topsakal et al., 2006), approximately 90% of the patients suffer from a predominantly conductive hearing loss and a presbycusis-like deterioration of SNHLc with relatively early onset (Kursten et al., 1994; Aarnisalo et al., 2003; Topsakal et al., 2006). The other 10% suffer from an obvious mixed hearing loss; around 1.5% of these patients develop a profound SNHLc, exceeding 70 dB HL, referred to as ‘advanced otosclerosis’.

The generally accepted first treatment option is to place surgically a stapes prosthesis to restore the mobility of the ossicular chain (referred to as ‘stapedotomy’). This is considered as a safe and effective intervention that reduces the AB-gap to 10 dB in most cases. At the high frequencies, the outcome might be somewhat worse (e.g. Strömbäck et al., 2012).

If, after stapedotomy, amplification is still needed, then the first choice is a BTE. In case of advanced otosclerosis, a powerful BTE is needed (e.g. van Loon et al., 2014; Wardenga et al. 2020). VBS application with its actuator applied in the classical way (connected to the incus, moving in parallel to the stapes prosthesis) is also an option, as has been shown by Dumon et al. (2009) and Venail et al. (2007). Kontorinis et al. (2011) and Beltrame et al. (2009) also applied the VBS in patients with otosclerosis, however, with its actuator coupled to the round window.

Another option is the use of ‘BCDs’. Burell et al. (1996) used the percutaneous ‘BCD’ and called it: ‘the third option for otosclerosis’. Since then, little has been published on this application.

Finally, an option was to use the Codacs device (Lenarz et al., 2014); this device, specially developed for patients with advanced otosclerosis, is taken of the market 2020. However, still included in this analysis, as it was the most powerful acoustic implant ever.

A literature search was performed aiming at published audiometric outcomes, obtained with any of these amplification options (BTE, VSB, ’BCD’ or Codacs; summer 2015); little has been published, especially on BTE fittings after stapedotomy. Figure 5.1 gives an overview of the collected data. Concerning BTE, the data were retrieved from three studies in which stapedotomy was not performed or unsuccessful (Burell et al., 1996; Lenarz et al., 2013; Busch et al., 2013).

Figure 5.1. The mean device-aided thresholds presented versus the mean SNHLc of study groups of patients with otosclerosis using: BTEs (red symbols, 3 studies, n=27), Baha (yellow symbol, 1 study, n=7), VSB with the FMT coupled to the round window (open dots, 2 studies, summed n=7), VSB applied in the classical way in patients with a stapes prosthesis (green symbol, 2 studies, summed n=7) and, finally, Codacs device (black round, 3 studies, n=44). Typically, standard deviations (not indicated) varied between 4 dB and 6 dB in either direction. Target line for aided thresholds is presented as introduced in section 4.3, chapter 4

Figure 5.1 suggests that application of either the Codacs device (data from Lenarz et al., 2013; Lenarz et al., 2014; Busch et al., 2013) or the VSB with FMT coupled in the classical way (data from Venail et al., 2007; Dumon et al., 2009), are the most effective options because they the device aided hearing thresholds are closest to the target line. The studies with the FMT coupled to the round window (data from Kontorinis et al., 2011; Beltrame et al., 2009) seem to be less effective. This suggests that FMT applied in the classical way (with stapes prosthesis) is a better option.

For patients with advanced otosclerosis there is still a debate on the best option, stapedotomy plus a powerful BTE or cochlear implantation. Van Loon et al. (2014), reviewing the literature and their own data showed that for such patients, referred for cochlear implantation, stapedotomy with BTE fitting, should still be considered; in several CI (cochlear implant) candidates, stapedotomy with a BTE resulted in adequate speech perception. Interestingly, Kludt et al (2015) reported that patients suffering from advanced otosclerosis, fitted with the Codacs device (acoustic stimulation) had speech in noise scores much better than those of CI users, matched with respect to their cochlear thresholds. This suggests that acoustic stimulation might outperform electric stimulation in patients with severe cochlear hearing loss as found in advanced otosclerosis.

Another issue counselling such patients is that speech recognition after cochlear implantation might be below the expected ‘normal’ values, caused by unfavourable otosclerosis-related conditions. Bone formation within the otosclerotic cochlea might lead to problems with insertion of the CI’s electrode array. Furthermore, broad current spread might occur owing to poor bone quality of the cochlear shell (and therefore poor electrical isolation); this might cause unwanted stimulation of the nerves facialis when activating the CI (see also Chapter 9, section 9.2.3).

First treatment option for patients with otosclerosis is stapedotomy plus, eventually, the fitting of a BTE. Often, patients with advanced otosclerosis, referred for cochlear implantation, might still benefit from a stapedotomy and the fitting of powerful BTEs moreover as speech recognition scores with a CI might be non-optimal.

4.1 Introduction

An attempt is made to develop a fitting model based on a ‘acceptable partial’ use of the
patient’s dynamic range of hearing. Audibility of normal conversational speech, with its 30
dB wide speech range, is an important factor in that model.

A new goal has been formulated: at least 35 dB of the patient’s ‘dynamic range of
hearing’ should be audible with a device; ensuring that, with proper amplification,
conversational speech is audible (Zwartenkot et al., 2014 and Rheinfeldt et al., 2015).
This criterion is indicated in Figure 4.1. The idea is that 35 dB HL is enough to hear
conversational speech adequately while the hearing device makes use of wide-dynamic
range compression as a kind of automatic volume control.

This criterion is referred to as the ‘DR>35 dB rule’. A second criterion is now introduced,
namely that at least 2/3 of the patient’s ‘dynamic range of hearing’ should be audible with
a minimum of 35 dB (referred to as the ‘DR 2/3 rule’). This criterion is based on the data
of Figure 3.2. Baha patients in that study were fitted with different types of linear devices
with volume wheel. Typically, their ‘dynamic range of hearing’ with the device equals
about 2/3 of the unaided range, up to 30 dB HL. This new criterion is illustrated by the
blue line in Figure 4.1.

Table 4.1 presents the MPO data taken from Table 2.1. The second and third columns of
this table indicate up to what mean SNHLc value the different devices fulfill the ‘DR&gt;35
dB rule’ or ‘the DR 2/3’. These values deviate from those advocated by the
manufacturers; typically by 10 to 20 dB.

Figure 4.1. The minimal desired mean MPO versus mean SNHLc. Red line presents the
minimal desired MPO if the device-aided ‘dynamic range of hearing’ has to be 35 dB at
least (DR>35 dB rule). The blue line gives such target values if at least 2/3 of the
dynamic range should be audible with a minimum of 35 dB (DR 2/3 rule).

Amongst others, Table 4.1 suggests that the Sophono Alpha 1 device can only be used
in pure conductive hearing loss: indeed Sylvester et al. (2013) studying a group of
Sophono users came to a similar conclusion. The table further suggests that
percutaneous ‘BCDs‘ (with their most powerful processors) and the VSB device have
approximately the same capacity.

Table 4.1

Device	Mean   MPO*	‘Max SNHLc’ if the ‘DR 2/3 rule’ is used	‘Max SNHLc’ if the “DR>35 dB rule” is used
Sophono Alpha 1	53 dB HL	5 dB HL	20 dB HL
‘Bonebridge’	64 dB HL	20 dB HL	30 dB HL
Standard Baha/ Ponto	70 dB HL	25 dB HL	35 dB HL
Super power Baha/Ponto	83-88 dB HL	45-50 dB HL	45-50 dB HL
‘Vibrant Soundbridge’	81dB HL	45 dB HL	45 dB HL
Codacs **	100 dB HL	> 65 dB HL	> 65 dB HL
Baha Attract/BP110	64 dB HL	20 dB HL	30 dB HL

* taken from Table 2.1
** no longer available

When using the milder criterion (DR &gt; 35 dB rule), the application range is broader, see
third column. As said before, a ‘working range’ of 35 dB might be just sufficient for proper
amplification of speech, in combination with wide-dynamic range compression (Rheinfeldt
et al., 2015). ‘Wide-dynamic range compression’ increases the amplification of low-level
sounds while keeping the high-level sounds at loud but comfortable levels. ’Wide
dynamic range compression’ is the standard choice for patients with pure sensorineural
hearing loss using BTEs, who have a limited ‘dynamic range of hearing’ because of
physiological conditions. When applying ‘BCDs’ or MEIs, ‘wide-dynamic range
compression’ is also used, although the limited ‘dynamic range of hearing’ is not caused
by physiological conditions but technical restrictions of the used devices (low MPO).
Evidently, the starting point when choosing an amplification option should be selecting a
device with a high MPO. Especially in children, powerful devices should be used, see
Chapter 5.

Importantly; it should be noted that the ‘max SNHLc’ values per device type, as
presented in the table, are in agreement with maximum SNHLc values as obtained from
clinical studies, as presented in Figure 3.3.c. Using the trend-curves indicated in that
figure, the maximum SNHLc per device type could be assessed as well, e.g., approx. 45
dB HL for VSB and 15-20 dB HL for the transcutaneous ‘BCDs’. This agreement
(between Figure 3.3.c and Table 4.1 data) validates the MPO-based ‘max SNHLc-
values’ for application, as presented in the Table 4.1.

Concerning the use of hearing devices for conductive and mixed
hearing loss, the limited MPO has to be taken into account. Patients
‘compensate’ for a low MPO by lowering the amplification of the device,
leading to an unintended decrease in perception of speech. In short,
today’s passive transcutaneous ‘BCDs’ can be used in patients with
normal cochlear function or with a limited mean SNHLc, the active
‘Bonebridge’ in patients with mean SNHLc below 25 dB HL and the
percutaneous ‘BCDs’ and VSB in patients with mean SNHLc up to 50
dB HL. These values are more conservative (less optimistic) than those claimed by the manufacturers and might change when more powerful
processors are released.

4.2. Implanting elderly patients; the best solutions

Owing to aging or a progressive (hereditary) cochlear hearing loss, the SNHLc
deteriorates over time. Using data on the age-related hearing deterioration enables the
estimation of ‘years of effective use’ of a particular device. However, little is known
(reported) on age-related hearing deterioration in patients with mixed hearing loss. One
paper was identified; Figure 4.2 shows age-related deterioration in hearing of patients
with mixed hearing loss, studied by Iliadou et al. (2006). They reported both air- and
bone-conduction thresholds for patients suffering form OTSC7. The figure presents the
mean SNHLc (0.5, 1, 2 and 4 kHz averaged) as a function of age; see the first two rows.
Data up to 60 years were presented; the indicated mean SNHLc at 70 and 80 years are
(non linear) extrapolations. The thick red lines indicate whether or not a certain device
can (still) be used effectively. E.g., the figure shows that the Baha, with its ‘max SNHLc’
of 50 dB HL, can be used effectively up to approx. 80 years (the ‘max SNHLc’ refers to
the maximum sensorineural hearing loss component for successful application see Table
4.1). The Ponto device and the VSB might be applied successfully up to an age of
approx. 75 years.

Probably, the mildest scenario is that of a patient with a stable conductive hearing loss
component and, additionally, presbycusis. Using the median age-related hearing
deterioration for men (ISO 7029; 2017), Figure 4.3 is obtained. It should be noted that if
the patient suffers from mixed hearing loss caused by chronic otitis media, they might
have an additional sensorineural hearing loss caused by the infections and/or treatments,
which is approx. 20 dB (mean value 0.5 to 4 kHz; see ee Table A9.1, Chapter 9, and
related text). Taken this 20 dB into account, the effective use decreases to 50 years for
the ‘Bonebridge’ and 75 years for VSB and the percutaneous ‘BCDs’ while for such
patients with an age of 50+, the passive transcutaneous ‘BCD’ with magnetic coupling is
not an effective option.

Figure 4.2. Effective device use for a patient with progressive hearing loss owing to otosclerosis (OTSC7), based on the ‘DR 2/3 rule’. SNHLc stands for the cochlear hearing loss of patients

Figure 4.3. Effective device use for a patient with stable conductive hearing loss component and a sensorineural component that deteriorates over time owing to presbycusis. The ‘DR 2/3 rule’ was applied

Again, the percutaneous ‘BCD’ and the VSB seem to be the better choice.
When choosing for a particular treatment, effectiveness in the long run is one of the
factors that should be considered. The expected degree of hearing deterioration over
time should be assessed from the patient’s history.

It should be noted that the conclusion drawn from Table 4.1 and Figures 4.2 and 4.3 are
valid for the specified device types. If more powerful audioprocessor are released,
conclusions might change.

Effectiveness in the long run is an often ignored but important factor
when counselling specifically elderly patients (if implant surgery is
involved).

4.3 Attempt to formulate a prescription procedure

So far, the evaluation of the capacity of various amplification options aimed at the
MPO, as a low MPO restricts the ‘aided dynamic range of hearing’ of the patient. As said
before, to deal with that limitation, compression is often used. Another technical limitation might be device noise as patients with predominant conductive hearing loss might hear it,
owing to normal cochlear sensitivity. In that case ‘expansion’ (reduced amplification for
soft sounds) can be used to make the noise inaudible (Dillon, 2012). Information on the
noise level of a device should be clearly indicated on datasheets, as is available for
percutaneous ‘BCDs’. Problems with the noise floor have been reported with some VSB
processors (e.g. Linder et al., 2009), which, according to the manufacturer, have been
solved in newer sound processors. For the Cochlear Codacs device, the noise floor is
approximately 40 dB HL (Cochlear’s data sheets), which can be lowered to 25 dB HL.
This should explicitly be taken into account when counselling this device for a given
patient.

To choose the best device for a given patient is of utmost important. Note that when
considering the application of a MEI, well-masked bone-conduction thresholds are
essential to ensure that the cochlea of the to-be-implanted ear is sensitive enough for
successful application of the implant. On the other hand, for the application of
‘BCDs’, unmasked bone-conduction thresholds of the to-be-treated ear should be
considered. Owing to the limited transcranial attenuation of bone vibrations, the ‘BCD’ will
stimulate the cochlea with the best sensitivity, which might be either the ipsilateral or
contralateral cochlea (Stenfelt, 2012). Consequently, the fitting should be based on the
unmasked bone-conduction thresholds.

Regarding device fitting, it should be realized that both a ‘BCD’ and a MEI, with its
actuator coupled to one of the cochlear windows, directly stimulate the cochlea. This
simply implies that we can use our knowledge on fitting conventional hearing devices
(e.g., BTEs) in pure sensorineural hearing loss; thus we can make use of the well-known
validated prescription rules, like the NAL and DSL rules (Dillon, 2012).

To develop a practice-based prescription procedure, we used published data. The
selected studies, used in Chapter 3 were used again. For each of the included studies,
the ‘amplification at cochlear level’ was calculated as a function of frequency. That
amplification, referred to as ‘effective gain’, is, by definition, the frequency specific bone-
conduction threshold (cochlear threshold) minus the device-aided threshold (for more
information, see Appendix 2.3). To obtain a relative amplification value, corrected for the
degree of hearing loss, the ‘effective gain’ was divided by the bone-conduction threshold,
referred to as the ‘gain ratio’. According to the NAL-RP, that ratio should be approx. 0.45
(with some minor corrections; Dillon, 2012).

Twenty papers were included, which provided all the data needed for the calculations.
Figure 4.4 presents the ‘gain ratios’, presented per device type and the degree of
cochlear loss (mean SHNLc). To deal with the discontinuities that we found when
evaluating Figures 3.2 and 3.3, the 20 studies were divided into 3 subgroups, according
to the mean SNHLc of the participants :group 1 comprised the studies in patients with a
mean SNHLc below 25 dB HL, group 2 those with SNHLc between 25 and 40 dB HL and
group 3 those with a SNHLc exceeding 40 dB HL; see Table 4.2. Using Table 4.1, for
each subgroup, the amplification options are added, third row.

Table 4.2. Subgroups to deal with the discontinuities observed in Figure 3.2

	Group 1	Group 2	Group 3
Mean SNHLc	< 25 dB HL	25 to 40 dB HL	> 40 dB HL
Figure 3.2 shows:	Negative gain	Intermediate	Positive gain
Amplification options based on Table 4.1 and noise floor data	Percutaneous ‘BCD’/VSB/’Bonebridge’	Percutaneous ‘BCD’/VSB	Percutaneous ‘BCD’/VSB
Hypothetical target for gain	Predominant conductive loss: compensate the air-bone gap!	Intermediate	‘Compensate’ the SNHLc as if it was a pure sensorineural loss

Furthermore, using Table 4.1 and noise level data, for each subgroup, the amplification options are listed.

Lines in Figure 4.4 are labeled according to device type.

Figure 4.4. The gain ratio (gain divided by threshold) as a function of frequency. Figure 4.4A presents the data of group 1 (BAHS stands for Baha and Ponto together: 1 study, n=20; VSB: 3 studies, n=34 and Bonebridge: 1 study, n=12), Figure 4.4B for group 2 (BAHS: 6 studies, n=113; VSB: 7 studies, n=97) and Figure 4.4C for group 3 (BAHS: 1 study, n=12; VSB: 3 studies, n=47).

Obviously, Figure 4.4 shows that all the ‘gain ratios’ are below 0.45, the value taken from the NAL-RP rule (valid at 1, 2, 4 kHz; Dillon, 2012). The figure also shows that the ‘gain ratio’ is the highest at 2 kHz, irrespective of device type and subgroup. Furthermore, it is evident that inter-group differences are large (compare subfigures A, B and C). Differences between hearing devices within groups are less outspoken.

These data have been used to develop the practice-based prescription procedure: for mixed hearing loss, it is assumed that the cochlear loss (SNHLc) should be ’compensated’, equally as prescribed for sensorineural hearing loss. For group 1 with predominant conductive hearing loss, thus without a SNHLc (close to) 0 ,  the amplification (and thus the ‘gain ratio’) should be (close to) 0. However, negative ‘gain ratios’ are seen (Figure 4.4.A), as we also saw in Figures 3.2 and 3.3. Related to this, Dillon argued that  in patients with a conductive hearing loss, not the whole AB gap should be compensated, but only partially (Dillon, 2012, Chapter 10.4). Following that reasoning, it is suggested that, based on our data (Figs 3.2 and 3.3), the device-aided thresholds might be 25 dB HL instead of the ideal value of (closer to) 0, for patients with a (sub) normal cochlear function. More details are found in Snik et al. (2019).

Table 4.3 presents the desired device-aided thresholds and ‘effective gain’, based on the data presented in Figure 4.4.

Table 4.3. Target values as a function of SNHLc for 1, 2 and 4 kHz

SNHLc (dB HL)	0	10	20	30	40	50	60
Target aided threshold (dB HL)	<25	<25	<25	<25	<25	<27	<33
Effective gain (aided minus cochlear thresholds dB)	-25	-15	-5	5	15	23	27

Following the NAL rule, amplification at 0.5 kHz might be set 8 dB lower than that at the higher frequencies (to deal with upward spread of masking; Dillon, 2012). 

What are the limitations of this proposed procedure? It should be noted that this evaluation is based on today’s hearing implants. Furthermore, the procedure has not (yet) been validated. 

This practice-based prescription procedure can be used irrespective of the type of device used. Prerequisite is that a device is chosen with sufficiently high MPO, as listed in Table 4.1, preferably following the ‘DR 2/3 rule’.

Importantly, note that for percutaneous ‘BCDs’, Hodgetts and Scollie (2017) developed a dedicated prescription rule, based on the DSL fitting rule. That procedure is the preferred option, taking, amongst others, the limited MPO of these ‘BCDs’ explicitly into account.

What is the effect of a relatively low MPO? Figure 3.1A (upper, right) shows the
audiogram of a patient with conductive hearing loss. Cochlear thresholds and the
loudness-discomfort-levels (LDLs), taken from Dillon and Storey (1998), are indicated in
Figure 3.1B (upper, left).

    

Figure 3.1. Figure A (upper left) shows the audiogram; figure B (upper, right) present the
cochlear thresholds and the LDLs. Figure C (lower figure) shows the MPO values
(labelled with ‘S’) of the applied transcutaneous ‘BCD’.

The patient’s dynamic range of hearing is, by definition, the difference between the
cochlear threshold and LDLs. Evidently, Figure 3.1C shows that the MPO values,
indicated by symbol S, split the patient’s dynamic range of hearing into two parts; an
audible part (45 dB wide, see vertical red arrows) and a second unused part (40 dB
wide). The speech area of the patient’s own voice is schematically indicated, with the
yellow part being ‘inaudible’. It should be noted that it is assumed that the amplification of
the device was 0 (which means that with the device, the AB-gap was ‘functionally’
‘closed’).. With that gain of 0 , the MPO values indicate that the ‘BCD’ saturates at 50-60
dB HL. Saturation causes annoying distortions. Patients can prevent distortions, by
turning down the volume (thus reducing the amplification). For instance, in this case, the
chosen reduction in amplification might be 20 dB. In that way, the louder part of the
patient’s own voice (yellow area), that range from 50 to 70 dB HL, will be perceived
undistorted, ranging from 30 to 50 dB HL. Now, the patient’s own speech fits nicely in the
patient’s ‘BCD’-aided dynamic range of hearing. However, that 20 dB attenuation
(negative amplification) negatively affects speech perception of someone else, talking at
a normal conversational level. Note that in the audiogram such a ‘negative gain’ of 20 dB
shows up as a ‘remaining AB-gap’ of 20 dB. This example underlines that it is better to
use a ‘BCD’ with a higher MPO, even in patients with a (sub)normal sensorineural
hearing loss component.

The choice for a ‘negative gain’ to deal with a relatively low MPO, proved to be a general
observation amongst patients using ‘BCDs’.

The next question is: in daily practise, what is the volume setting (chosen amplifications)
by ‘BCD’ users with varying degrees of cochlear hearing loss ? This question was
answered with the help of our Baha database by re-examined the data of 89 patients
using Baha devices (Snik et al., 2004). At that time, Baha devices with (predominantly)
linear amplification were used (Baha Compact, Classic, HC220, Cordelle) and with a
volume wheel that enabled the patients to choose their preferred amplification (Snik et
al., 2004).

Figure 3.2 The ‘Baha’-aided thresholds (at 0.5, 1 and 2 kHz averaged) as a function of
the mean SNHLc (sensorineural hearing loss component; same frequencies). For clarity,
individual data of the 89 Baha users were grouped into 12 classes of each 5 dB wide.
The diagonal line represents the (cochlear) hearing thresholds, thus the thresholds
without the Baha

Figure 3.2 shows that patients with (sub)normal cochlear function (low mean SNHLc) set
the volume of their Baha such that the gain is negative: the ‘Baha’-aided thresholds are
worse (higher) than the threshold without the ‘Baha’. This results in a remaining AB-gap
of around 10 dB, which is seen for SNHLc values up to approx. 25 dB HL.

Patients with more severe SNHLc need ‘positive’ amplification to be able to properly hear
other subjects talking, which, according to Figure 3.2, is found for SNHLc &gt; 30 dB HL.

It should be noted that with increasing mean SNHLc, more and more patients used the
more powerful Baha sound processors (Snik, 2014). Per patient, the type of Baha device
used was documented and, consequently, its MPO was known. The MPO values were
used to obtain the ‘input level at saturation’ or the sound level at which the MPO was
reached. This ‘input level’ is simply the MPO value minus the amplification of the Baha (output = input + amplification). The amplification itself is easily obtained by subtracting
the Baha-aided thresholds from the cochlear thresholds (thresholds without the Baha).
These calculated (individual) input levels at which the Baha devices saturate, (again)
grouped in the 12 classes, are presented in Figure 3.2 as the blue line (with label
‘saturation’). The figure clearly shows that the input level at saturation restricts the
dynamic range of hearing with the Baha significantly. Before discussing the
consequences, Figure 3.2 was redrawn, see Figure 3.2^bis.

   

Figure 3.2^bis Redrawn of Figure 3.2 with more details, see text

The left graph of Figure 3.2 bis  shows the remaining capacity of ear of patients with SNHLc
between 0 and 60 dB HL. As said before, the diagonal line presents the cochlear
thresholds while the dotted line presents the patient’s LDL. The right graph shows
the aided situation after Baha fitting, taken from Figure 3.2. The difference between aided
thresholds and input level at saturation is the patient’s aided dynamic range of hearing or
his ‘auditory window’ to the world.

The Baha-aided dynamic range of hearing is restricted; as an example, at a SNHLc of 45
dB HL, a patient’s unaided dynamic range of hearing is 50 dB HL (95-45 dB, left-hand graph, red arrow) and with the Baha, the dynamic range is only 35 dB HL (40 to 75 dB
HL, right-hand graph, red arrow).

The subfigure on the right side presents schematically sounds from the real auditory
world. Let us consider normal conversational speech. That level fluctuates between 25
dB HL and 55 dB HL (indicated in the subfigure, right-hand side; according to Killion &amp;
Christensen, 1998). Combining the right-side subfigure and the right-hand graph shows
that in the present patient group, the 30 dB speech range is only fully audible when the
mean SNHLc is 15 dB HL or less, while at a mean SNHLc of 60 dB HL, the audible
proportion of speech range has reduced to just 5 dB HL.

Furthermore, we learn from Figure 3.2 that the patients, irrespective of their mean
SNHLc, set the volume of their device such that the device saturates at input sound
levels of 70-75 dB HL. Indeed, this choice does enable undistorted perception of even
the loudest parts of normal conversational speech. So, the figure suggests that the
patients in this study don’t compromise with regard to the input level at saturation, but,
consequently, they do compromise with regard to the softest speech sounds that they
can hear.

As indicated before, the basic rule for desired amplificatiion in pure sensorineural hearing
loss equals approximately half the hearing loss(e.g., Dillon, 2012). As the figure shows,
that is not accomplished at all. E.g. at a mean SNHLc of 45 dB HL, the amplification is
only 7 dB (see Figure 3.2). The limited MPO plays an important, probably decisive role in
the low amplification setting, as chosen by the patients.s.

So far, the analysed data concerned the Baha device. Figure 3.3 presents similar data of
all implantable systems available (early 2017), including besides the Baha the
percutaneous Ponto (Oticon Medical, Askim, Sweden), the ‘Bonebridge’ (Med-El,
Innsbruck, Austria), Sophono (Medtronic, Boulder, Co, USA), the transcutaneous Baha
Attract (Cochlear BAS, Gothenburg, Sweden) and the Codacs device (Cochlear,
Mechelen, Belgium). A systematic review of the literature was carried out.

To find the most relevant studies it was decided, first of all, to use studies that had been
selected before by authors who published systematic reviews. This concerned reviews by
Colquitt et al., 2011; Verhaert et al., 2013; Nadaraja et al., 2013; Ernst et al., 2016;
Sprinzl and Wolf-Mangele, 2016 and Dimitriades et al., 2016. Only those studies were re-
considered that presented audiometric data; including air- and bone-conduction
thresholds as well as device-aided thresholds. Duplicates were removed as well as
studies with five patients or less and studies published before 2006. Unpublished
presentations were also excluded.

Using the reviews by Colquitt et al., Nadaraja et al. and Verhaert et al. Concerning the percutaneous Baha and Ponto mechanisms, nine publications met the inclusion criteria (Kompis et al., 2007; Priwin et al., 2007; Flynn et al., 2009; Fuchsman et al., 2010; Ricci et al., 2011; Marsella et al., 2011; Bouhabel et al., 2012; Concerning VSB using the reviews by Verhaert et al. and Ernst et al., 14 publications were included (Beltram et al. 2009; Streitberger et al. 2009; Colletti et al. 2011; Baumgartner et al., 2010; Frenzel et al., 2010; Beleites et al. 2011; Bernardeschi et al., 2011; ., 2013). Sprinzl andWolf-Mangele (2016) reviewed the outcomes of ‘Bonebridge’ application. Only two studies met the criteria (Sprinzl et al., 2013; Ihler et al., 2016). Dimitriades et al. (2016) reviewed the transcutaneous Baha Attract; three studies were included (Iseri et al., 2014; 2015; Briggs et al., 2015). Since the number of included publications regarding the Baha Attract and the ‘Bonebridge’ were low and the publications with the percutaneous Baha/Ponto outcomes were rather dated (&lt;2012), we performed an additional literature search, using Pubmed. For Bonebridge and Baha Attract, search terms were the respective device names together with &#39;2016&#39;; concerning ‘Bonebridge’, four studies were added (Gerdes et al., 2016; Baumgartner et al., 2016; Smerber et al., 2016; Zernotti et al., 2016), for Baha Attract, no further study with relevant audiometric data was found. Concerning Baha/Ponto, the sound-processor&#39;s names were used and the search period was 2011-2016. In contrast to the other devices, number of patients studied had to be ten or more. Seven studies were identified (Pfiffner et al., 2011; Flynn et al., 2012; Bosman et al., 2013; Kurz et al., 2013; Desmet et al., 2013; Kompis et al. 2014; Gerdes et al. , 2016). Concerning the Sophono device, a systematic review has not yet been published. Therefore, we searched for studies using only &#39;Sophono&#39; as search term and applying the introduced inclusion criteria. Six studies were included (Siegert and Kanderke, 2013; Sylvester et al., 2013; Hol et al., 2013; Denoyelle et al., 2015; Shin et al., 2016; Magliulo et al., 2015). Finally, data obtained with the Codacs device were included, which is the most powerful implantable device (Zwartenkot et al., 2014). Searching PubMed, three papers were identified comprising audiological data obtained in more than five patients (Busch et al., 2013; Lenarz et al., 2013; 2014).

Altogether, 48 studies were included in this analysis. Figure 3.3A  presents per study the
mean device-aided threshold at 0.5, 1, 2 and 4 kHz as a function of the mean cochlear
threshold, SNHLc, averaged over the same frequencies. Again, this figure shows that,
generally, when the (mean) SNHLc is below 25-30 dB HL, a remaining AB gap (data
points above the diagonal) is found, in agreement with Figure 3.2. Remarkably, Figure
3.3.b shows a rather large variability between studies.

Figure 3.3B presents the same data as Figure 3.3A; this time, trend-curves are
presented, drawn by eye through the data points for a each device. Considering the bleu
line, representing the trend for VSB, the VSB-aided thresholds are at a rather stable level
(25-30 dB HL) up to a SNHLc of approx. 45 dB HL. Above that value, the VSB-aided
thresholds seem to deteriorate exponentially, indicating that the device is no longer
powerful enough for such degrees of the SNHLc. For the Baha Attract and Sophono
devices, similar trends are seen, however, with lower cut-off SNHLc values, in between
15 dB HL and 20 dB HL. Obviously, these different types of hearing devices are not
equivalents, which conclusion is in line with the variance in objective MPO data, as
presented in Table 2.1.

For the Baha/Ponto devices, no clear cut-off value for SNHLc is found. This is caused by
the availability of several processors with increasing power, which have been applied in
the patients with more severe SNHLc.

Even taking this device-related limitation into account, an obvious variation between
studies is seen. This suggests that well-defined device-fitting procedures are needed.
This issue is the subject of the next chapter (chapter 4).

Figure 3.3.a.  Mean device-aided threshold (0.5, 1, 2, 4 kHz) as a function of the mean
SNHLc as obtained from 48 studies using the percutaneous Baha/Ponto devices (black
diamonds), the VSB (big blue dots), the ‘Bonebridge’ (red squares), the Baha Attract
(green triangles), the Sophono (small black dots) or the Codacs (green circles)

Figure 3.3.b. The same figure as Figure 3.3A, however, this time trend lines are indicated
for the VSBand the passive transcutaneous ‘BCDs’

2.1 Introduction

Nowadays, for patients with conductive hearing loss or mixed hearing loss, who need amplification, commonly used options are: 1. conventional acoustic behind-the-ear devices (BTE) or in-the-ear devices, 2. (semi-implantable) bone-conduction devices (‘BCD’) and 3. active middle ear implants with their actuator coupled to one of the cochlear windows; these implantable devices have been described in detail elsewhere (Snik, 2011).

The three options are neither equivalent nor interchangeable with respect to medical or anatomical restrictions and their technical capacities.

While there are several practical, medical, surgical and esthetical reasons to prefer one of these technologies over another, this chapter discusses one of the basal characteristics of these hearing devices, namely the maximum output capacity. Part of the following paragraphs has been published before (Zwartenkot et al. 2014, Snik, 2014, van Barneveld et al. 2017).

2.2. Air-conduction versus bone-conduction hearing aids; capacity of these devices

In principle, devices using either the air-conduction or bone-conduction route can be considered as amplification options for patients with conductive or mixed hearing loss. Generally, for patients with pure sensorineural hearing loss, BTEs are the first choice, fitted according to standardized procedures (Dillon, 2012).

Figure 2.1. A conventional BTE (behind-the-ear) hearing aid with earmould. Source: Internet

However, when an AB-gap is present (gap between the air- and bone conduction hearing thresholds), a significant part of the BTE output (equal to the width of the air-bone gap) is lost before the amplified signal reaches the cochlea. Consequently, the remaining output, to ‘compensate’ for any cochlear hearing loss, might become too low or even absent. For example, consider a patient with mixed hearing loss with an AB-gap of 50 dB, who uses a standard rather powerful BTE. According to the documentation, the MPO of that BTE is 116 dB SPL and the maximum gain is 52 dB. Consequently, the MPO as perceived by the patient is 116-50 thus 66 dB SPL, and the maximum gain is (52-50) just 2 dB. Note that the 66 dB SPL equals the sound pressure level of normal speech. Louder sounds cannot be amplified properly. Therefore, when applying BTEs in mixed hearing loss, only the most powerful BTEs should be considered and, if the AB-gap is large, benefit might be limited.

The other amplification option is a hearing device that uses the bone-conduction route; Figure 2.2 shows such a bone-conduction device or ‘BCD’. From an efficiency perspective, by far, the bone-conduction route for sounds is not as effective as the air-conduction route. Amongst others, Skoda-Türk and Welleschik (1981) showed that the air-conduction route is approximately 50 dB more effective than the conventional bone-conduction route (when a bone-conduction hearing aid is pressed against the skin behind the ear; the so-called transcutaneous route). In other words, the first 50 dB produced by the amplifier of such a ‘BCD’s are ‘lost’, making this solution as (in)effective as the BTE for the patient with the 50 dB AB-gap.

Figure 2.2. A conventional transcutaneous ‘BCD’. A standard powerful BTE is connected to a bone-conduction transducer, worn contralaterally. The headband has to keep the transducer in place (behind the pinna) and to push the transducer against the skin with the required static pressure to enable the best transcutaneous transmission. Source: Internet

A new, more effective ’BCD’ has been developed in the mid 1980s (Hakansson et al., 1984). This so-called ‘Baha’ device comprises an externally worn processor with electronics and the actuator that is coupled to the skull by means of a skin-penetrating implant, anchored in the skull bone (see Figure 2.3). As shown by Hakansson et al. (1984) this ‘percutaneous’ bone-conduction route is approximately 15 dB more efficient than the transcutaneous route, owing to the absence of the attenuating skin and subcutaneous layers.

Combining Hakansson et al.’s finding with that of Skoda-Türk and Welleschik suggests that the percutaneous route is only 35 dB (50-15 dB) less effective than the air-conduction route. This implies that if a hearing-impaired subject has an AB-gap of 35 dB, a BTE and a ‘Baha’ might be equally effective. Furthermore, the ‘Baha’ will be the most effective device for patients with an AB-gap exceeding 35 dB while the BTE might be more effective than ‘Baha’ if the AB-gap is below 35 dB. Indeed, de Wolf et al. (2011) showed that this theoretical “cross-over” point is realistic.

Figure 2.3. The Bone-anchored hearing aid or Baha with its transducer (in the housing) connected to the skull via a titanium percutaneous implant. Source: Cochlear Company 

2.3 The maximum output-level of bone-conduction hearing implants and other implantable amplification options

BTEs cannot be used by hearing-impaired patients in case of atresia of the ear canal or stenosis or chronically infected ears (see Chapter 5). Then, ‘BCD’s are the next option. Carlsson and Hakansson (1997) studied the gain and MPO of the percutaneous Baha. The MPO, or the maximum power output, is the loudest sound that can be produced by a device. They studied the standard Baha (HC200 at that time) and showed that the MPO was 100, 112, 102, 95 dB FL (decibel-force-level) at 0.5, 1, 2 and 4 kHz, respectively, as measured on a so-called ‘skull simulator’. These data can be expressed in dB HL, using the so-called RETFLdbc (Reference Ear to Force Level for direct bone conduction; Carlsson and Hakansson, 1997), resulting in MPOs expressed in dB HL. In this case (HC200) the MPO was 53, 66, 78, 69 dB HL respectively, with a mean of 67 dB HL. As a reference, the mean MPO of a standard BTE might exceed 100-110 dB HL. Carlson and Hakansson also studied the noise-floor of that Baha, which was  inaudible. The MPO measurements have been reproduced and extended using other/newer types of Baha by Zwartenkot et al. (2014). They also studied the Ponto percutaneous ’BCD’ (Oticon Medical, Sweden), a competitor of Baha (see Table 2.1). 

Zwartenkot et al. developed an alternative technique to measure the MPO that can also be used for non-percutaneous ‘BCDs’. Knowing that the transcutaneous coupling is approximately 15 dB less effective than the percutaneous coupling (Hakansson et al., 1984), it is expected that the MPO of transcutaneous devices might be approximately 50-55 dB HL (the percutaneous MPO of 67 dB HL minus 15 dB). Indeed, measurements showed a mean MPO of 53 dB HL (Sophono transcutaneous ‘BCD’), see table. The Sophono ‘BCD’ comprises a conventional transcutaneous ‘BCD’ with magnetic coupling to the skull instead of an elastic softband or steel headband (Siegert & Kanderske, 2013; see Figure 2.4). The alternative is the Baha Attract (Cochlear BAS; Briggs et al., 2015), a standard Baha processor also with a transcutaneous magnetic coupling instead of a percutaneous one. Evidently, the Baha Attract is less powerful than the percutaneous Baha (see table).

In the late nineties, a more powerful (percutaneous) Baha was developed, the Baha Cordelle, which comprised a body-worn powerful amplifier that made this device the most powerful ’BCD’ on the market for many years. More recently, two updated super power percutaneous ‘BCDs’ became available, namely the Baha 5-super-power and the Ponto 5-super-power (head-worn devices). The Baha 5-super-power is the most powerful ‘BCD’ with a mean MPO of 88 dB HL.

Figure 2.4. The Sophono Alpha 1 device. The device is worn externally, coupled to the skull transcutaneously by coupling magnets; a (double) magnet is implanted under a closed skin. The footplate of the externally worn processor also contains such a magnet. Source: Internet  

Table 2.1. Objective measurement of the MPO of several hearing devices

Device	Mean MPO (0.5 – 4 kHz)	Reference	Manufacturer
Sophono Alpha 1	53 dB HL	Hol et al., 2013, van Barneveld et al, 2017	Sophono, Boulder, US
‘Bonebridge’	64 dB HL	Mertens et al. 2014; Ghoncheh et al., 2024	Med-El, Innsbruck, Austria
Standard Baha 5	70 dB HL	See note below this table	Cochlear BAS, Goteborg, Sweden
Standard Ponto 5	Idem	Idem	Oticon Medical, Askim, Sweden
Baha 6	77 dB HL	Idem	Cochlear BAS, Goteborg, Sweden
Baha 5-super-power=; Ponto-5-super-power	88 and 83 dB HL	Idem	Cochlear BAS, Goteborg, Sweden; Oticon Medical, Askim, Sweden
‘Vibrant Soundbridge’	81 dB HL	Zwartenkot et al. 2014, Maier, 2023	Med-El, Innsbruck, Austria
Codacs *	100 dB HL	Zwartenkot et al. 2014	Cochlear Mechelen, Belgium
‘Baha Attract’	64 dB HL	van Barneveld et al, 2017	Cochlear Mechelen, Belgium

Note. Following the procedure described by Carlsson and Hakansson (1997), the MPO can be derived from the product data sheets.
* no longer available since summer 2020

Figure 2.5. The ‘Bonebridge’ device; an active transcutaneous ‘BCD’ with its actuator implanted in the mastoid area. The actuator is driven by an externally worn audioprocessor. Source: Internet

In 2013, the first so-called active transcutaneous ‘BCD’ was released, the ‘Bonebridge’, see Figure 2.5 (e.g., Huber et al., 2013). The actuator (vibrator), which is implanted, is coupled with an externally worn speech processor (FM link). Mertens et al. (2014) measured the MPO of the ‘Bonebridge’ according to the protocol described by Zwartenkot et al. (2014) and reported a mean MPO value of 63 dB HL. Recently, Ghoncheh et al. (2024) reported a value of 65 dB HL, thus a rather similar outcome. The mean of the two studies is listed in the table.

In 2006, Colletti and co-workers published a paper on the coupling of the actuator of the ‘Vibrant Soundbridge’ middle ear implant (VSB; active middle ear implant) directly to one of the cochlear windows. This new option is meant for patients with conductive or mixed hearing loss (Colletti et al., 2006). Figure 2.6 shows the VSB in its classic application with its actuator (FMT; floating-mass-transducer) connected to the intact ossicular chain (to the incus) enabling the FMT to move in parallel to the stapes. The right-hand part of Figure 2.6 shows the FMT in its alternative position, coupled to the round window of the cochlea, according to Colletti et al. First report on the MPO of the adapted VSB for application in conductive and mixed hearing loss showed a MPO between 65 dB HL and 88 dB HL (Zwartenkot et al., 2014). This variability is probably owing to the variable effectiveness of the individual coupling of the actuator to the cochlea (Shimizu et al., 2011). As an estimate, ignoring Zwartenkot et al.’s two cases with, most probably, a poor coupling, a mean MPO of 82 dB HL was found. Recently, Maier (2023; their most recent cases) reported a mean MPO of 80 dB HL, thus rather similar as that reported by Zwartenkot et al. The mean of these two studies is presented in the table.

Regarding the Codacs device (e.g. Lenarz et al., 2013), developed for patients with otosclerosis, the MPO could not be determined as it exceeded the patients’ loudness-discomfort-levels (LDLs), exceeding 100 dB HL (Zwartenkot et al., 2014). Thus the Codacs is the only device that enabled full utilization of the patient’s dynamic range of hearing, from the cochlear thresholds up to the LDLs. Unfortunately, this device is no longer on the market.

   

Figure 2.6 The ‘Vibrant Soundbridge’ in classical application (for sensorineural hearing loss; left figure) with its actuator (FMT) coupled to the incus (shown enlarged) and the alternative application for conductive or mixed hearing loss with the FMT coupled to the round window membrane. Source: Internet

The VSB, developed for patients with sensorineural hearing loss, can be applied in conductive and mixed hearing loss. MPO might be equal to that of  ’BCDs’ , depending on the quality of the coupling between actuator and the cochlea

Note; nomenclature ‘BCD’s

Four ‘BCD’ subtypes are distinguished (Rheinfeldt et al, 2015);

1. the conventional transcutaneous ‘BCD’ with its actuator kept in place by a steel headband or a elastic soft band over the head (Figure 2.2),
2. the percutaneous ‘BCD’ like the Baha (Cochlear BAS, Goteborg, Sweden, see Figure 2.3) and Ponto (Oticon Medical, Askim, Sweden),
3. the passive transcutaneous ‘BCD’, e.g., Alpha 2 (Sophono Inc., Boulder, USA; Figure 2.4) and the Baha Attract (Iseri et al., 2015; Cochlear BAS, not shown)
4. the active transcutaneous ‘BCD’, a ‘BCD’ with its actuator implanted, e.g., the ‘Bonebridge’ (Med-El, Innsbruck, Austria, Figure 2.5), the Osia device (Cochlear BAS) and the Sentio device (Oticon Medical).

The first seven chapters of this website deal with amplification options for hearing impaired patients with conductive or mixed hearing loss. If reconstructive surgery is not an option, several amplification options (hearing devices) are available: besides the conventional behind-the-ear device (BTE), bone-conduction devices (‘BCDs’) and middle-ear-implants (MEIs). However, patients with conductive or mixed hearing loss cannot use a BTE if the hearing loss is caused by atresia of the ear canal or a chronic infected ear. Noteworthy, in contrast to BTEs, ‘BCDs’ and MEIs have limited capacity. Therefore, it is a challenge to find the best device for a given patient, especially as the brochures, provided by the manufacturers of these devices, are often quite optimistic. An objective comparison between the capacities and limitations of all the amplification options is needed, and that is one of the aims of this website. Second aim is to give an overview of basic knowledge in this field.

To choose a device, the output capacity and the amplification (gain) is of high importance, however, also other issues play a significant role like safety and stability, MRI compatibility, aesthetics, user’s satisfaction, costs, etc. Focus is on those parameters that can be assessed (rather) objectively and can be compared mutually, e.g., output/amplification of the devices, stability and MRI compatibility.

Chapters 2, 3 and 4 are the main chapters, addressing basal audiological/technical issues like device characteristics, categorisation of the available devices, device-fitting procedures with an overview of stability figures and complications. Special attention is paid to decreasing effectiveness of these devices in the elderly, owing to aging. Chapters 5 to 8 deal with clinical application in specific patient groups. Chapter 9 discusses borderline areas for the application of all the hearing devices, including cochlear implants (CIs).

This overview might not be fully accurate owing to on-going developments in this field, although it is updated regularly. Last partial update: early 2024. Information on relatively new active transcutaneous bone-conduction devices (the Osia device; Cochlear, Mechelen, Belgium and the de Sentio device; Oticon, Askim, Sweden) will be added later this year.

Scope of this website is to give a rather up-to-date overview of the effectiveness of
amplification options for hearing impaired subjects, written for professionals and
students. For further background information, see Appendix 1.

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Abbreviations

‘AB-gap’: gap between the air- and bone-conduction thresholds

AI: Audibility Index

‘BCD’: Bone-conduction device (general term)

‘iBCD’: implantable ‘BCD’

‘pBCD’: percutaneous ‘BCD’

‘tBCD’: transcutaneous ‘BCD’

BTE: Behind-The-Ear device (or air-conduction device)

CHL: conductive hearing loss

CI: Cochlear Implant

CSOM: Chronic Supprative Otitis Media 

DR: dynamic range of hearing

DSL rule: hearing-aid fitting-rule developed by Scollie et al (2005)

FMT: ‘Floating-Mass’ Transducer

ILD: Interaural Loudness Difference

ITD: Interaural Time Difference

LDL: Loudness-Discomfort-Level

MCL: Most Comfortable Listening level

MPO: Maximum (Power) Output

MRI: Magnetic Resonance Imaging

NAL rule: hearing-aid fitting-rule developed by Dillon and co-workers (Dillon 2012)

OME: Otitis Media with Effusion

PTA: Pure Tone Average

PTAbc Pure Tone Average for bone-conduction

s.d.: standard deviation

SII: speech intelligibility index

SNHLc: Sensorineural Hearing Loss component

SRT: speech reception threshold

VSB: VibrantSoundbridge

WDRC: wide-band dynamic-range compression

WRS: word recognition score

References of chapters 1 to 7

Chapters 8,9 have their references listed at the end

Aarnisalo AA, Vasama JP, Hopsu E, Ramsay H. Long-term hearing results after stapes surgery: a 20-year follow-up. Otol Neurotol. 2003;24:567-71.

Agterberg MJ, Hol MK, Cremers CW, Mylanus EA, van Opstal J, Snik AF. 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.

Agterberg MJ, Snik AF, Hol MK, Van Wanrooij MM, Van Opstal AJ. Contribution of monaural and binaural cues to sound localization in listeners with acquired unilateral conductive hearing loss: improved directional hearing with a bone-conduction device. Hear Res. 2012;286:9-18.

Ahn J, Ryu G, Kang M, Cho YS.  Long-term Hearing Outcome of Canaloplasty With Partial Ossicular Replacement in Congenital Aural Atresia. Otol Neurotol. 2018 Jun;39(5):602-608.

Alomari HM. Binaural hearing with bone conduction stimulation. Eprints.soton.ac.uk/370832/1/Hala%20Alomari%20thesis.pdf. Thesis, 2014, University of Southampton

Amlani AM, Punch JL, Ching TY. Methods and applications of the audibility index in hearing aid selection and fitting. Trends Amplif. 2002;6(3):81-129.

Baumgartner WD, Böheim K, Hagen R, Müller J, Lenarz T, Reiss S, Schlögel M, Mlynski R, Mojallal H, Colletti V, Opie J. The vibrant soundbridge for conductive and mixed hearing losses: European multicenter study results. Adv Otorhinolaryngol. 2010;69:38-50.

Baumgartner WD et al. A new transcutaneous bone conduction hearing implant: short term safety and efficacy in children. Otol Neurotol 2016;37:713-720.

Beck DL, Sockalingam R. Patient care and hearing instrument technology: tech topic. Hearing review 2010:17(4);44-47

Beleites T, Neudert M, Beutner D, Hüttenbrink KB, Zahnert T. Experience with vibroplasty couplers at the stapes head and footplate. Otol Neurotol. 2011;32:1468-72.

Beltrame AM, Martini A, Prosser S, Giarbini N, Streitberger C. Coupling the Vibrant Soundbridge to cochlea round window: auditory results in patients with mixed hearing loss. Otol Neurotol. 2009;30:194-201.

Bernardeschi D, Hoffman C, Benchaa T, Labassi S, Beliaeff M, Sterkers O, Grayeli AB.  Functional results of  Vibrant Soundbridge middle ear implants in conductive and mixed hearing losses. Audiol Neurootol. 2011;16:381-7.

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.

Bosman AJ, Snik AFM, Van der Pouw CTM, Mylanus EAM, Cremers CWRJ: Audiometric evaluation of bilaterally fitted bone-anchored hearing aids. Audiol 2001;40:158-167.

Bosman AJ, Kruyt IJ, Mylanus EAM, Hol MKS, Snik AFM. Evaluation of an abutment-level superpower sound processor for bone-anchored hearing. Clin Otolaryngol. 2018a Feb 16.

Bosman AJ, Kruyt IJ, Mylanus EAM, Hol MKS, Snik AFM. On the evaluation of a superpower sound processor for bone-anchored hearing. Clin Otolaryngol. 2018b Apr;43(2):450-455.

Bosman AJ, Snik AFM, Mylanus EAM, Cremers CWRJ. Fitting range of the BAHA Cordelle. Int J Audiol 2006;45:429-37.

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;24(6):505-13.

Bouhabel S, Arcand P, Saliba I. Congenital aural atresia: bone-anchored hearing aid vs. external auditory canal reconstruction. Int J Pediatr Otorhinolaryngol. 2012;76(2):272-7.

Boymans M, Goverts ST, Kramer SE, Festen JM, Dreschler WA. A prospective multi-centre study of the benefits of bilateral hearing aids. Ear Hear. 2008;29(6):930-41.

Bravo-Torres S, Der-Mussa C, Fuentes-López E. Active transcutaneous bone conduction implant: audiological results in paediatric patients with bilateral microtia associated with external auditory canal atresia. Int J Audiol. 2018 Jan;57(1):53-60.

Briggs R, Van Hasselt A, Luntz M, Goycoolea M, Wigren S, Weber P, Smeds H, Flynn M, Cowan R. Clinical Performance of a New Magnetic Bone Conduction Hearing  Implant System: Results from a Prospective, Multicenter, Clinical Investigation. Otol Neurotol. 2015 Jan 28

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.

Browning GG. Reporting the benefits from middle ear surgery using the Glasgow Benefit Plot. Am J Otol. 1993;14(2):135-40.

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;34(9):1711-8.

Busch S, Lenarz T, Maier H. Comparison of alternative coupling methods of the Vibrant Soundbridge floating mass transducer. Audiol Neurotol 2016; 21: 347-355

Burrell SP, Cooper HC, Proops DW. The bone anchored hearing aid–the third option for otosclerosis. J Laryngol Otol Suppl. 1996;21:31-7.

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

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(4):267-73.

Claros P, Pujol Mdel C. Active middle ear implants: Vibroplasty? in children and adolescents with acquired or congenital middle ear disorders. Acta Otolaryngol. 2013;133(6):612-9.

Colletti V, Soli SD, Carner M, Colletti L. Treatment of mixed hearing losses via implantation of a vibratory transducer on the round window. Int J Audiol. 2006;45:600-8

Colletti L, Carner M, Mandalà M, Veronese S, Colletti V. The floating mass transducer for external auditory canal and middle ear malformations. Otol Neurotol. 2011;32(1):108-15.

Colletti V, Mandalà M, Colletti L. Electrocochleography in round window Vibrant Soundbridge implantation. Otolaryngol Head Neck Surg. 2012;146(4):633-40.

Colletti L, Mandala M, Colletti V. Long-term outcome of round window Vibrant Soundbridge implantation in extensive ossicular chain defects. Otolaryngol Head Neck Surg. 2015; 149:134-141

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.

Danhauer JL, Johnson CE, Mixon M. Does the evidence support use of the Baha implant system (Baha) in patients with congenital unilateral aural atresia? J Am Acad Audiol. 2010;21:274-86.

Debeaupte M, Decullier E, Tringali S, Devèze A, Mom T, Darrouzet V, Truy E. Evolution of the reliability of the fully implantable middle ear transducer over successive generations. Otol Neurotol. 2015;36:625-30.

Declau F, Cremers C, Van de Heyning. Diagnosis and management strategies in congenital atresia of the external auditory canal. Br J Audiol 1999; 33:313-327

Desmet JB, Bosman AJ, Snik AF, Lambrechts P, Hol MK, Mylanus EA, De Bodt M, Van de Heyning P. Comparison of sound processing strategies for osseointegrated bone conduction implants in mixed hearing loss: multiple-channel nonlinear versus single-channel linear processing. Otol Neurotol. 2013;34:598-603.

den Besten CA,  Harterink E,  McDermott AL, Hol MK. Clinical results of Cochlear™ BIA300 in children: Experience in two tertiary referral centers.  “International journal of pediatric otorhinolaryngology.” Int J Pediatr Otorhinolaryngol. 2015;79:2050-2055

den Besten CA, Vogt K, Bosman AJ, Snik AFM, Hol MKS, Agterberg MJH. The Merits of Bilateral Application of Bone-Conduction Devices in Children With Bilateral Conductive Hearing Loss. Ear Hear. 2020;41(5):1327-1332.

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(3):382-7.

de Wolf MJ, Hendrix S, Cremers CW, Snik AF. Better performance with bone-anchored hearing aid than acoustic devices in patients with severe air-bone gap. Laryngoscope 2011;121:613-6.

de Wolf MJ, Hol MK, Huygen PL, Mylanus EA, Cremers CW. Nijmegen results with application of a bone-anchored hearing aid in children: simplified surgical technique. Ann Otol Rhinol Laryngol. 2008;117(11):805-14.

Dillon H, Storey L. The National Acoustic Laboratories’ procedure for selecting the saturation sound pressure level of hearing aids: theoretical derivation. Ear Hear 1998;19:255-66.

Dillon H. 2012. Prescribing hearing aid performance. Chapter 10 in ‘Hearing aids’, Dillon, 2012. Thieme Verlag, Stuttgart, Germany

Dimitriadis PA, Farr MR, Allam A, Ray J. Three year experience with the cochlear BAHA attract implant: a systematic review of the literature. BMC Ear Nose Throat Disord. 2016 Oct 1;16:12.

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.

Doshi J, Schneiders S, Foster K, Reid A, McDermott AL. Magnetic resonance imaging and bone anchored hearing implants: pediatric considerations. Int J Pediatr Otorhinolaryngol. 2014;78:277-9.

Dumon T, Gratacap B, Firmin F, Vincent R, Pialoux R, Casse B, Firmin B. Vibrant Soundbridge middle ear implant in mixed hearing loss. Indications, techniques, results. Rev Laryngol Otol Rhinol (Bord). 2009;130:75-81.

Dun CA, Agterberg MJ, Cremers CW, Hol MK, Snik AF. Bilateral bone conduction devices: improved hearing ability in children with bilateral conductive hearing loss. Ear Hear. 2013;34:806-8.

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;33:192-8.

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.

Ernst A, Todt I, Wagner J. Safety and effectiveness of the Vibrant Soundbridge in treating conductive and mixed hearing loss: A systematic review. Laryngoscope. 2016;126:1451-7.

Evans AK, Kazahaya K. Canal atresia: “surgery or implantable hearing devices? The expert’s question is revisited”. Int J Pediatr Otorhinolaryngol. 2007;71:367-74

Fan X, Yang T, Niu X, Wang Y, Fan Y, Chen X. Long-term Outcomes of Bone Conduction Hearing Implants in Patients with Bilateral Microtia-atresia. Otol Neurotol. 2019 Sep;40(8):998-1005.

Fan X, Yang T, Niu X, Wang Y, Fan Y, Chen X. Long-term Outcomes of Bone Conduction Hearing Implants in Patients With Bilateral Microtia-atresia. Otol Neurotol. 2019 Sep;40(8):998-1005.

Farnoosh S, Mitsinikos FT, Maceri D, Don DM. Bone-Anchored Hearing Aid vs. Reconstruction of the External Auditory Canal in Children and Adolescents with Congenital Aural Atresia: A Comparison Study of Outcomes.Front Pediatr. 2014,22;2:5.

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.

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;5 Suppl 1:S76-81.

Flynn MC, Sadeghi A, Halvarsson G. Baha solutions for patients with severe mixed hearing loss. Cochlear Implants Int. 2009;10 Suppl 1:43-7.

Frenzel H, Hanke F, Beltrame M, Wollenberg B. Application of the Vibrant Soundbridge in bilateral congenital atresia in toddlers. Acta Otolaryngol. 2010 ;130(8):966-70.

Frenzel H, Sprinzl G, Streitberger C, Stark T, Wollenberg B, Wolf-Magele A, Giarbini N, Strenger T, Muller J, Hempel JM. The Vibrant Soundbridge in Children and Adolescents: Preliminary European Multicenter Results.  Otol Neurotol. 2015;36(7):1216-1222.

Fuchsmann C, Tringali S, Disant F, Buiret G, Dubreuil C, Froehlich P, Truy E. Hearing rehabilitation in congenital aural atresia using the bone-anchored hearing aid: audiological and satisfaction results. Acta Otolaryngol. 2010;130(12):1343-51.

Gantner S, Epp A, Pollotzek M, Hempel JM. Long-term results and quality of life after vibrant soundbridge implantation (VSBs) in children and adults with aural atresia. Eur Arch Otorhinolaryngol. 2024;281(1):129-139.

Garin P, Schmerber S, Magnan J, Truy E, Uziel A, Triglia JM, Bebear JP, Labassi S, Lavieille JP. Bilateral vibrant soundbridge implantation: audiologic and subjective benefits in quiet and noisy environments. Acta Otolaryngol. 2010;130(12):1370-8.

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.

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;45(1):219-226.

Gordon K, Henkin Y, Kral A. Asymmetric Hearing During Development: The Aural Preference Syndrome and Treatment Options. Pediatrics. 2015;136(1):141-53.

Gunduz B, Atas A, Bayazıt YA, Goksu N, Gokdogan C, Tutar H. Functional outcomes of Vibrant Soundbridge applied on the middle ear windows in comparison with conventional hearing aids. Acta Otolaryngol. 2012;132:1306-10.

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

Hol MKS, Cremers CWRJ, Coppens-Schellekens W, Snik AFM. The BAHA Softband. A new treatment for young children with bilateral congenital aural atresia. Int J Ped Otorhinolaryngol 2005; 69:973-980

Hol MK, Spath MA, Krabbe PF, van der Pouw CT, Snik AF, Cremers CW, Mylanus EA.  The bone-anchored hearing aid: quality-of-life assessment. Arch Otolaryngol Head Neck Surg. 2004;130:394-9.

Hol MKS, Nelissen R, Agterberg M, et al. Comparison between a new implantable transcutaneous bone conductor and percutaneous bone-conduction hearing implant. Otol Neurotol 2013;34:1071-5.

Holland Brown T, Fitzgerald O’Connor I, Bewick J, Morley C. Bone conduction hearing kit for children with glue ear. BMJ Innovations. 2021:7:600-3. 

Holland Brown T, Salorio-Corbetto M, Gray R, James Best A, Marriage JE. Using a Bone-Conduction Headset to Improve Speech Discrimination in Children With Otitis Media With Effusion. Trends Hear. 2019 Jan-Dec;23:2331216519858303.

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

Hultcrantz M, Lanis A. A five-year follow-up on the osseointegration of bone-anchored hearing device implantation without tissue reduction. Otol Neurotol. 2014;35:1480-5.

Humes  LE. Dimensions of hearing aid outcomes. J Am Acad Audiol. 1999; 10:26-39

Hüttenbrink KB, Zahnert T, Bornitz M, Beutner D. TORP-vibroplasty: a new alternative for the chronically disabled middle ear. Otol Neurotol. 2008;29(7):965-71.

Ihler F, Blum J, Berger MU, Weiss BG, Welz C, Canis M. The Prediction of Speech Recognition in Noise With a Semi-Implantable Bone Conduction Hearing System by External Bone Conduction Stimulation With Headband: A Prospective Study. Trends Hear. 2016; 3;20. pii: 2331216516669330.

Iliadou V, Van Den Bogaert K, Eleftheriades N, Aperis G, Vanderstraeten K, Fransen E, Thys M, Grigoriadou M, Pampanos A, Economides J, Iliades T, Van Camp G, Petersen MB. Monogenic nonsyndromic otosclerosis: audiological and linkage analysis in a large Greek pedigree. Int J Pediatr Otorhinolaryngol. 2006;70(4):631-7.

Işeri M, Orhan KS, Kara A, Durgut M, Oztürk M, Topdağ M, Calışkan S. A new transcutaneous bone anchored hearing device – the Baha® Attract System: the first experience in Turkey. Kulak Burun Bogaz Ihtis Derg. 2014;24:59-64.

Iseri M, Orhan KS, Tuncer U, Kara A, Durgut M, Guldiken Y, Surmelioglu O. Transcutaneous Bone-Anchored Hearing Aids Versus Percutaneous Ones: Multicenter Comparative Clinical Study. Otol Neurotol. 2015 Feb 27. [Epub ahead of print]

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

Janssen RM, Hong P, Chadha NK. Bilateral bone-anchored hearing aids for bilateral permanent conductive hearing loss: a systematic review. Otolaryngol Head Neck Surg. 2012;147(3):412-22.

Killion MC, Christensen. The case of the missing dots: AI and SNR loss. Hear J 1998;41(5):1-6.

Killion MC, Mueller HG. Twenty years later, a new count-the-dots method. Hearing Journal 2010;63(1):11-17.

Koci V, Seebacher J, Weichbold V, Zorowka P, Wolf-Magele A, Sprinzl G, Stephan K. Improvement of sound source localization abilities in patients with bilaterally supplied active middle ear implants. Acta Otolaryngol 2016;136:692-698

Kontorinis G, Lenarz T, Mojallal H, Hinze AL, Schwab B. Power stapes: an alternative method for treating hearing loss in osteogenesis imperfecta? Otol Neurotol. 2011;32(4):589-95.

Kompis M, Kurz A, Pfiffner F, Senn P, Arnold A, Caversaccio M. Is complex signal processing for bone conduction hearing aids useful? Cochlear Implants Int. 2014;15 Suppl 1:S47-50.

Kompis M, Krebs M, Häusler R. Speech understanding in quiet and in noise with the bone-anchored hearing aids Baha Compact and Baha Divino. Acta Otolaryngol. 2007;127(8):829-35.

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;41(7):901-911.

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.

Kulasegarah J, Burgess H, Neeff M, Brown CRS. Comparing audiological outcomes between the Bonebridge and bone conduction hearing aid on a hard test band: Our experience in children with atresia and microtia. Int J Pediatr Otorhinolaryngol. 2018 Apr;107:176-182.

Kunst SJ, Leijendeckers JM, Mylanus EA, Hol MK, Snik AF, Cremers CW. Bone-anchored hearing aid system application for unilateral congenital conductive hearing impairment: audiometric results. Otol Neurotol. 2008;29(1):2-7.

Kuppler K, Lewis M, Evans AK. A review of unilateral hearing loss and academic performance: is it time to reassess traditional dogmata? Int J Pediatr Otorhinolaryngol. 2013;77(5):617-22.

Kürsten R, Schneider B, Zrunek M. Long-term results after stapedectomy versus stapedotomy. Am J Otol. 1994;15:804-6.

Kurz A, Caversaccio M, Kompis M. Hearing performance with 2 different high-power sound processors for osseointegrated auditory implants. Otol Neurotol. 2013;34(4):604-10.

Kurz A, Flynn M, Caversaccio M, Kompis M. Speech understanding with a new implant technology: a comparative study with a new non-skin penetrating Baha system. Biomed Res Int. 2014;2014:416205.

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.

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, 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 34:1215-25

Linder T, Schlegel C, DeMin N, van der Westhuizen S. Active middle ear implants in patients undergoing subtotal petrosectomy: new application for the Vibrant Soundbridge device and its implication for lateral cranium base surgery. Otol Neurotol. 2009;30(1):41-7.

Magliulo G, Turchetta R, Iannella G, Valpega di Massino R, de Vincentiis M. Sophono Alpha system and subtotal petrosectomy with external auditory canal blind sac closure. Eur Arch Otorhinolaryngol 2015;272:2183-2190

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

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;18;20:136-46.

Maier H. et al. Consensus Statement on Bone Conduction Devices and Active Middle Ear Implants in Conductive and Mixed Hearing Loss. Otol Neurotol. 2022;43(5):513-529

Mandala 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(8):1250-5.

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

Marsella P, Scorpecci A, Pacifico C, Tieri L. Bone-anchored hearing aid (Baha) in patients with Treacher Collins syndrome: tips and pitfalls. Int J Pediatr Otorhinolaryngol. 2011;75(10):1308-12.

Marino R, Linton N, Eikelboom RH, Statham E, Rajan GP. A comparative study of hearing aids and round window application of the vibrant sound bridge (VSB) for patients with mixed or conductive hearing loss. Int J Audiol. 2013;52:209-18.

McDermott AL, Williams J, Kuo M, Reid A, Proops D. The Birmingham pediatric bone-anchored hearing aid program: a 15-year experience. Otol Neurotol. 2009;30(2):178-83.

Merkus P, van Loon MC, Smit CF, Smits C, de Cock AF, Hensen EF. Decision making in advanced otosclerosis: an evidence-based strategy. Laryngoscope. 2011;121:1935-41.

Mertens G, Desmet J, Snik, AFM, Van den Heyning P. An objective method to determine maximum output and dynamic range of an active bone conduction implant: The BonebridgeTM. Otol Neurotol 2014;35:1126-30

Mlynski R. The Vibrant Soundbridge, past, present and the future. Presentation at Otology Jubilee, May 9th, 2014, Halle (Saale) Germany

Mondelli MF, Carvalho FR, Feniman MR, Lauris JR. Mild hearing loss: performance in the Sustained Auditory Attention Ability Test. Pro Fono. 2010;22(3):245-50.

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;34:1711-8.

Mueller, G. & Killion, M. (1990). An Easy Method for Calculating the Articulation Index. The Hearing Journal 1990;43(9):14-7.

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

Nassiri AM, Messina SA, Benson JC, Lane JI, McGee KP, Trzasko JD, Carlson ML. Magnetic Resonance Imaging Artifact Associated With Transcutaneous Bone Conduction Implants: Cholesteatoma and Vestibular Schwannoma Surveillance. Otolaryngol Head Neck Surg. 2024;170:187-194.

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. 1991; Baltimore: William and Wilkins

Orús Dotú C, Santa Cruz Ruíz S, De Juan Beltrán J, Batuecas Caletrio A, Venegas   Pizarro Mdel P, Muñoz Herrera A. Treatment of severe to profound mixed hearing loss with the BAHA Cordelle II. Acta Otorrinolaringol Esp. 2011;62:205-12.

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.

Pfiffner F, Caversaccio MD, Kompis M. Comparisons of sound processors based on osseointegrated implants in patients with conductive or mixed hearing loss. Otol Neurotol. 2011;32(5):728-35.

Powell HRF, Rolfe AM, Birman CS. A comparative study of audiologic outcomes for two transcutaneous bone-anchored hearing devices. Otol Neurotol 2015;36:1525-1531.

Priwin C, Jönsson R, Hultcrantz M, Granström G. BAHA in children and adolescents with unilateral or bilateral conductive hearing loss: a study of outcome. Int J Pediatr Otorhinolaryngol. 2007;71(1):135-45.

Ramakrishnan Y, Davison T, Johnson IJM. How we do it: Softband management of glue ears. Clin Otolaryngol 2006;31:224-227.

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

Ratuszniak A, Skarzynski PH, Gos E, Skarzynski H. The Bonebridge implant in older children and adolescents. Int J Pediatr Otorhinolaryngol. 2019 Mar;118:97-102.

Reinfeldt S, Hakansson B, Taghavi H, Eeg-Olofsson. New developments in bone-conduction hearing implants. Medical Devices: Evidence and Research 2015:8:79-93

Ren R, Zhao S, Wang D, Li Y, Ma X, Li Y, Fu X, Chen P, Dou J. Audiological effectiveness of Bonebridge implantation for bilateral congenital malformation of the external and middle ear. Eur Arch Otorhinolaryngol. 2019 Oct;276(10):2755-2762

Ricci G, Volpe AD, Faralli M, Longari F, Lancione C, Varricchio AM, Frenguelli A. Bone-anchored hearing aids (Baha) in congenital aural atresia: personal experience. Int J Otorhinolaryng Pediatr. 2011;75(3):342-6.

Roman S, Denoyelle F, Farinetti A, Garabedian EN, Triglia JM. Middle ear implant in conductive and mixed congenital hearing loss in children. Int J Pediatric Otorhinolaryngol 2012;76:1775-1778.

Roman S, Nicollas R, Triglia JM. Practice guidelines for bone-anchored hearing aids in children. Eur Ann Otorhinolaryngol Head Neck Dis. 2011;128(5):253-8.

Rotteveel LJ, Proops DW, Ramsden RT, Saeed SR, van Olphen AF, Mylanus EA. Cochlear implantation in 53 patients with otosclerosis: demographics, computed tomographic scanning, surgery, and complications. Otol Neurotol. 2004;25:943-52.

Schmerber S, Deguine O, Marx M, Van de Heyning P, Sterkers O, Mosnier I, Garin P, Godey B, Vincent C, Venail F, Mondain M, Deveze A, Lavieille JP, Karkas A. Safety and effectiveness of the Bonebridge transcutaneous active direct-drive bone-conduction hearing implant at 1-year device use. Eur Arch Otorhinolaryngol. 2016;30. [Epub ahead of print]

Schwab B, Kludt E, Maier H, Lenarz T. Subtotal petrpsectomy and Codacs: new possibilities in ears with chronic infection. Eur Arch Otorhinolaryngol 2016;273:1387-1391

Scollie S, Seewald R, Cornelisse L, Moodie S, Bagatto M, Laurnagaray D, Beaulac S, Pumford J. The Desired Sensation Level multistage input/output algorithm. Trends Amplif. 2005;9(4):159-97. 

Shannon CM, Gutierrez JA 3rd, Nguyen SA, Meyer TA, Lambert PR. Comparison of Outcomes of Surgery Versus Implantable Device for the Treatment of Hearing Loss Associated With Congenital Aural Atresia: A Systematic Review and Meta-Analysis. Otol Neurotol. 2023 Sep 1;44(8):758-766. 

Shimizu Y, Puria S, Goode RL. The floating mass transducer on the round window versus attachment to an ossicular replacement prosthesis. Otol Neurotol. 2011;32(1):98-103.

Shin JW, Kim SH, Choi JY, Park HJ, Lee SC, Choi JS, Park HQ, Lee HK. Surgical and Audiologic Comparison Between Sophono and Bone-Anchored Hearing Aids Implantation. Clin Exp Otorhinolaryngol. 2016;9:21-6.

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 2013;34:927-34.

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. Air conduction or bone conduction hearing aids? Comments on hearing aids for sound conduction deafness. Laryngol Rhinol Otol (Stuttg) 1981;60:478-83.

Souza MA, Vallejos Riart SL, Souza SR, de Brito R, Bento RF. Complications of Transcutaneous Protheses – A Systematic Review of Publications Over the Past 10 years. Int Arch Otorhinolaryngol. 2022 Feb 4;26(3):e505-e512.

Snik AFM, Cremers CWRJ. Vibrant semi implantable hearing device with digital sound processing. Effective gain and speech perception. Arch Otolaryngol Head Neck Surg 2001;127:1433-1437

Snik AF, Bosman AJ, Mylanus EA, Cremers CW. Candidacy for the bone-anchored hearing aid. Audiol Neurootol. 2004;9(4):190-6.

Snik A, Noten J, Cremers C. Gain and maximum output of two electromagnetic  middle ear implants: are real ear measurements helpful? J Am Acad Audiol. 2004;15(3):249-57.

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.

Snik A, Leijendeckers J, Hol M, Mylanus E, Cremers C. The bone-anchored hearing aid for children: recent developments. Int J Audiol. 2008;47(9):554-9.

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

Snik AFM. Are today’s implantable devices better than conventional solutions for patients with conductive and mixed hearing loss? ENT and Audiology news, 2014;23 (1):105-108

Snik AFM, Agterberg M, Bosman A. How to quantify binaural hearing in patients with unilateral hearin g using hearing implants. Audiol Neurootol. 2015;20 Suppl 1:44-47

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 Apr;40(4):430-435.

Sprinzl GM, Wolf-Magele A. The Bonebridge Bone Conduction Hearing Implant: indication criteria, surgery and a systematic review of the literature. Clin Otolaryngol. 2016;41:131-43.

Sprinzl G, Lenarz T, Ernst A, Hagen R, Wolf-Magele A, Mojallal H, Todt I, Mlynski R, Wolframm MD. First European multicenter results with a new transcutaneous bone conduction hearing implant system: short-term safety and efficacy. Otol Neurotol. 2013;34(6):1076-83.

Sprinzl GM, Schoerg P, Muck S, Jesenko M, Speiser S, Ploder M, Edlinger SH, Magele A. Long-Term Stability and Safety of the Soundbridge Coupled to the Round Window. Laryngoscope. 2021 May;131(5):E1434-E1442.

Stelmachowicz, Patricia G.; Hoover, Brenda; Lewis, Dawna E.; Brennan, Marc Is functional gain really functional? The Hearing Journal, 2002;55(11):38-42.

Stenfelt S, Håkansson B. Air versus bone conduction: an equal loudness investigation. Hear Res. 2002;167(1-2):1-12.

Stenfelt S. Bilateral fitting of BAHAs and BAHA fitted in unilateral deaf persons: acoustical aspects. Int J Audiol 2005;44:178-189

Stenfelt S. Transcranial attenuation of bone-conducted sound when stimulation is at the mastoid and at the bone conduction hearing aid position. Otol Neurotol. 2012;33:105-14.

Stenfelt S, Zeitooni M. Loudness functions with air and bone conduction stimulation in normal-hearing subjects using a categorical loudness scaling procedure. Hear Res. 2013;301:85-92.

Streitberger C, Perotti M, Beltrame MA, Giarbini N. Vibrant Soundbridge for hearing restoration after chronic ear surgery. Rev Laryngol Otol Rhinol (Bord). 2009;130:83-8.

Sylvester DC, Gardner R, Reilly PG, et al. Audiologic and surgical outcomes of a novel, non-percutaneous, bone conducting hearing implant. Otol Neurotol 2013;34:922-6

Sziklai I, Batta TJ, Karosi T. Otosclerosis: an organ-specific inflammatory disease with sensorineural hearing loss. Eur Arch Otorhinolaryngol. 2009;266:1711-8.

Thomeer HG, Kunst HP, Cremers CW. Isolated congenital stapes ankylosis: surgical results in a consecutive series of 39 ears. Ann Otol Rhinol Laryngol. 2010;119:761-6.

Thomeer HG, Kunst HP, Cremers CW. Congenital stapes ankylosis associated with another ossicular chain anomaly: surgical results in 30 ears. Arch Otolaryngol Head Neck Surg. 2011;137:935-41.

Thomeer HG, Kunst HP, Cremers CW. Congenital ossicular chain anomalies associated with a mobile stapes footplate: surgical results for 23 ears. Ann Otol Rhinol Laryngol. 2012;121:275-81.

Thomeer HGXM.  Congenital minor ear anomalies. Thesis, Radboud University, Nijmegen, The Netherlands. 2012.

Topsakal V(1), Fransen E, Schmerber S, Declau F, Yung M, Gordts F, Van Camp G, Van de Heyning P. Audiometric analyses confirm a cochlear component, disproportional to age, in stapedial otosclerosis. Otol Neurotol. 2006;27(6):781-7.

Tysome J. et al., The Auditory Rehabilitation Outcomes Network: an international initiative to develop core sets of patient-centered outcome measures to assess interventions for hearing loss. Clin Otolaryngol. 2015;40:512-515

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.

Van den Bogaert T, Klasen TJ, Moonen M, Van Deun L, Wouters J. Horizontal localization with bilateral hearing aids: without is better than with. J Acoust Soc Am 2006;119:515-26.

van Loon MC, Merkus P, Smit CF, Smits C, Witte BI, Hensen EF. Stapedotomy in cochlear implant candidates with far advanced otosclerosis: a systematic review. Otol Neurotol. 2014;35:1707-14.

Venail F, Lavieille JP, Meller R, Deveze A, Tardivet L, Magnan J. New perspectives for middle ear implants: first results in otosclerosis with mixed hearing loss. Laryngoscope. 2007r;117(3):552-5..

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;118(10):693-7.

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.

Verhaert N, Desloovere C, Wouters J. Acoustic hearing implants for mixed hearing loss: a systematic review. Otol Neurotol. 2013;34:1201-9.

Verhagen CV, Hol MK, Coppens-Schellekens W, Snik AF, Cremers CW. The Baha Soft Band. A new treatment for young children with bilateral congenital aural atresia. Int J Pediatr Otorhinolaryngol. 2008;72(10):1455-9.

Verheij E, Bezdjian A, Grolman W, Thomeer HG. A Systematic Review on Complications of Tissue Preservation Surgical Techniques in Percutaneous Bone Conduction Hearing Devices. Otol Neurotol. 2016;37:829-37

Vickers D, Briggs J, Lamping W, Andrew R, Bingham M, Toner J, Cooper S, Spielman P, Ghulam H, Nunn T, et al. Medical Safety and Device Reliability of Active Transcutaneous Middle Ear and Bone Conducting Implants: A Long-Term Multi-Centre Observational Study. Applied Sciences, 2023;13(14):8279. 

 

Vogt K, Wasmann JW, Van Opstal AJ, Snik AFM, Agterberg MJH. Contribution of spectral pinna cues for sound localization in children with congenital unilateral conductive hearing loss after hearing rehabilitation. Hear Res. 2020;385:107847.

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.

Vogt K, Desmet J, Janssen A, Agterberg M, Snik A. Unexplained variance in benefit of treatment of congenital unilateral aural atresia. Audiol Neurotol 2021; in press

Vyskocil E, Riss D, Honeder C, Arnoldner C, Hamzavi JS, Baumgartner WD, Flak S, Gstoettner W. Vibroplasty in mixed and conductive hearing loss: comparison of different coupling methods. Laryngoscope. 2014 Jun;124(6):1436-43.

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(3):125-132.

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

Wolf-Magele A, Koci V, Schnabl J, Zorowka P, Riechelmann H, Sprinzl G. Bilateral use of active middle ear implants: speech discrimination results in noise. Eur Arch Otorhinolaryngol. 2016;273:2067-207

Yu JK, Tsang WS, Wong TK, Tong MC. Outcome of vibrant soundbridge middle ear implant in cantonese-speaking mixed hearing loss adults. Clin Exp Otorhinolaryngol. 2012;5 Suppl 1:S82-8.

Zeitooni M, Mäki-Torkko E, Stenfelt S. Binaural Hearing Ability With Bilateral Bone Conduction Stimulation in Subjects With Normal Hearing: Implications for Bone Conduction Hearing Aids. Ear Hear. 2016;37(6):690-702.

Zernotti ME, Gregorio MF, Sarasty AC. Middle ear implants: functional gain in mixed hearing loss. Braz J Otorhinolaryngol. 2012;78:109-12.

Zernotti ME, Di Gregorio MF, Galeazzi P, Tabernero P. Comparative outcomes of active and passive hearing devices by transcutaneous bone conduction. Acta Otolaryngol. 2016;136(6):556-8.

Zernotti ME, Chiaraviglio MM, Mauricio SB, Tabernero PA, Zernotti M, Di Gregorio MF. Audiological outcomes in patients with congenital aural atresia implanted with transcutaneous active bone conduction hearing implant. Int J Pediatr Otorhinolaryngol. 2019 Apr;119:54-58.

Zhao S, Gong S, Han D, Zhang H, Ma X, Li Y, Chen X, Ren R, Li Y.  Round window application of an active middle ear implant (AMEI) system in congenital oval window atresia. Acta Otolaryngol. 2016;136(1):23-33.

Zwartenkot JS, Snik AFM, Mulder JJ, Mylanus EAM. Comparison of amplification options for mixed hearing loss. Otol Neurotol.  2014;35(2):221-6.

Appendix 1: History of the website and
acknowledgements

In September 2014, Franco Trabalzini organised the EAONO meeting in Siena and asked me, Ad Snik, to organize a panel on Consensus on Auditory Implants. Preparing that panel, I wrote a document what can be considered as the bleu print of the present website. Later that year, I sent an updated version of that document to my colleagues from Auronet (Auronet is a private initiative to develop a ’core-set’ of patient-centred outcome measures which enable the search for the best treatment options for a patient with conductive or mixed hearing loss; Tysome et al., 2015). Comments by my Auronet colleagues, especially Bill Hodgetts and Penny Hill, encouraged me to go on and to publish the document in the form of a website. 

As a start, on April 22, 2014, chapters 1 to 3 were published. Chapters 4 and 5 were added on May 6th and June 16th. During the Osseo meeting in Lake Louise, Alberta (May 21-23, 2015), the website was introduced to the audience for the first time.

On July 28th 2015, chapter 5.3 and 6 were uploaded. Martijn Agterberg critically read this part of the website before it was published. Chapter 7 was added in August. Owing to comments by Arjan Bosman, Martijn Toll, Tove Rosenbom and Marc Flynn, the text of chapters 1 to 4 was revised (September 7th and October 8th). During the latter update, the option for the readers to respond online, was skipped. From the start until early October, more then 90 responses were collected and all of them were spam. 

On March 29th 2016, chapters 5 and 6 were revised and Appendix 2 was added and on August 12th 2016, chapters 5 to 7 and Appendix 2 were updated. The remarks made by Hannes Maier are acknowledged. Chapter 8, on the use of auditory implants in patients with pure sensorineural hearing loss, was added on August 20th 2016.

January 20th 2017, data regarding relatively new devices was added (Chapter 3). This concerned the Sophono Alpha 2 processor, the Cochlear Baha Attract and the Med-El ‘Bonebridge’. On May 2nd 2017, chapter 1 was revised and chapters 2, 3 and 5 were updated. Amongst others, new data was added concerning new super-power percutaneous ‘BCDs’. Appendix 2 was rewritten. In the month of November 2017, this website was fully re-designed.

August 2018, Chapters 3, 4 were updated and in December 2018, Chapters 6 and 8. Blog 2018-4 added and in April 2019, Blog 2019-1 added. In October 2019, Tables 2.1, 4.1 were updated as well as Figure 4.2. In December 2019, Blog 2019-2 was added.

October 2020: Chapter 7 was updated. Blog 2019-2 was removed (concerned a power-point presentation at the Osseo conference). November 2020: Chapter 8 was updated and revised as two of the discussed auditory implants were taken off the market end 2019. On February 5th, 2021, Chapters 2, 4 and paragraph 5.3 were revised. Chapter 6 was updated and Chapter 8 was extended.

5 May 2024: Chapters 2.3, 4.1, 4.2 and 5.1.2 were updated and Chapter 9 was added. In July 2024, Martijn Agterberg took over the responsibility for the website as Ad Snik retired. An option was added to choose for the original English text or a translated Dutch version. For a proper automatic translation, several parts of the English texts have been reformulated.   

About the authors: 

Ad Snik studied physics at the Eindhoven University of Technology and got the master’s degree in 1976 and in 1982, he acquired the doctor’s degree from the same university. Afterwards he specialized in medical physics and was registered in 1987 as a medical physicist/ audiologist. In 1988 the author was employed as a clinical audiologist and researcher at the ENT department of the Radboud University Medical Centre Nijmegen and appointed as a professor in 2006 until his retirement in 2017. Since 2010, he worked one day a week as a researcher at the department of Biophysics, Radboud University Nijmegen until mid-2022. Ad Snik participated as an author in more than 250 peer-reviewed papers in the field of Audiology. His last paper concerning auditory implants was a consensus paper that he wrote together with Hannes Maier. The set-up was unique, based on a multi-stakeholder approach. Not only clinicians and audiologists participated in the consensus meetings but also representatives of all the major companies, and they were involved in the final report as (one of the 90) authors (Maier et al., Consensus Statement on Bone Conduction Devices and Active Middle Ear Implants in Conductive and Mixed Hearing Loss. Otol Neurotol. 2022;43(5):513-529).This paper covers most of the subjects addressed on this website. 

Martijn Agterberg studied Medicine and Psychology at the University of Utrecht and developed an interest in learning, memory and plasticity. In 2003 Martijn received a research grant to study plasticity of the auditory system in the laboratory of Prof. Merzenich at the University of California San Francisco (UCSF). In 2009 the PHD project ‘Neurotrophic treatment of the degenerating auditory nerve’ was finished  under supervision of Prof. Wiegant. In the same year he was appointed as Post-doc in the group of Prof. Van Opstal at the department Biophysics (Radboud University), and as researcher in the group of Prof. Snik at the department Otolaryngology (Radboudumc). In Nijmegen, he ‘bridged the gap’ between fundamental research and applied research and demonstrated that hearing impaired patients, adults and children, could be measured in advanced research facility. The work was presented on Dutch television (Pavlov, NTR NPO3). In 2010 a study demonstrating the advantage of having large ears was published. The Dutch newspaper NRC wrote about the interesting result that older adults with larger ears demonstrated improved sound localization abilities for stimuli with a limited bandwidth compared to children and young adults. So, not everything becomes worse when getting older! In 2014 Martijn received funding for the idea to build a sound localization setup in a mobile trailer (Wasmann et al., 2020). He started his own company and is now providing this sophisticated setup to other clinics in order to obtain international standardization on how to measure sound localization (Roosam B.V.). In 2018 Martijn was appointed associate professor and audiologist at the ENT department at the Radboudumc. In 2019 Martijn received the Dutch NWO Open Mind grant for the idea to study the dynamic ears of bees. The research was described in the Dutch daily newspaper ‘Trouw’, in the glossy ‘QUEST’ nr. 11, and presented on the Dutch radio (FOCUS, NPO1), and on the Dutch television (Atlas, NPO2).

• Article in the daily newspaper Trouw
• The glossy Quest published an article (Quest nr. 11)
• nl wrote an article about our work.
• Interview NPO1.

In 2021 Martijn received a NOW grant to perform a technical and commercial feasibility study for a new implant with a better noise reduction based on superior directional microphones. He founded the company BeephoniX in 2023.

In 2022 Martijn started an assistant professorship in Utrecht at the University Medical Centre Utrecht. The focus of his research is on the optimal treatment of conductive hearing loss.

‘Disclosure’:

The authors have and had no financial interests in any of the devices described in this webside. Martijn Agterberg is as founder of BeephoniX interested in the development of new superior hearing solutions. This webside is partly based on research carried out at the Radboud University, which was supported by Nobelpharma, Entific, Cochlear BAS, Symphonix, Med-El, Otologics, KNO fonds Nijmegen, Heinsius Houbolt fonds, the William Demant Foundation and European Union Grants.

Appendix 2: Quantifying the gain (amplification) of auditory implants

A2.1 Introduction

Outcome measures used to validate the fitting of a hearing device can be divided into subjective measures and objective measures. In general, subjective refers to the assessment of patients’ opinions while objective refers to data that are measured with equipment, like hearing thresholds and speech recognition (Humes, 1999).  To evaluate a hearing aid fitting, the most popular ‘objective’ outcome measure is the gain (amplification) provided by the device and the improvement in speech recognition (Gatehouse, 1998; Gurgel et al., 2012). Often, the ‘functional gain’ is reported which is the difference between the hearing thresholds without and with the fitted hearing device. However, although this approach is widely used, it has significant limitations.

Note: references are listed at the end of this Appendix 2

A2.2 Quantifying the amplification of a MEI in patients with sensorineural hearing loss

The use of the  ‘functional gain’ implicitly assumes linear amplification. Nowadays, most auditory implants don’t use linear amplification but non-linear amplification or compression amplification. The most frequently used type of compression amplification (wide dynamic range compression; WDRC) implies that for soft sounds the gain provided by the device is relatively high, while for louder sounds, the gain is gradually reduced to prevent uncomfortable loud sound levels (Dillon 2012). A direct consequence is that the hearing thresholds with the device are lower (better) than those when using linear amplification; therefore, the ‘functional gain’ is also higher. It should be noted that here, the ‘functional gain’ assesses just the amplification for soft sounds (e.g. Stelmachowicz et al., 2002).

Snik and Cremers (2001) discussed two options to estimate the amplification of an auditory implant (MEI, VSB) at more realistic listening levels (thus at supra-tone- threshold levels). They suggested determining the ‘gain at the patient’s most-comfortable-listening level (MCL)’. In short, the patient’s MCL is determined (at octave frequencies) twice, once without and once with the auditory implant switched on, and the results are subtracted. In this way, the ‘gain-at-MCL’ is determined, frequency specific. Snik and Cremers compared amplification measures in 14 VSB users with 304 processor using WDRC. Averaged at 0.5, 1, 2 and 4 kHz, the ‘gain-at-MCL’ was indeed approx. 10 dB lower than the ‘functional gain’. From the data published by Rameh et al. (2010) the ‘functional gain’ was calculated. They also provided the speech-recognition-thresholds (SRT) with and without the VSB (an alternative option for the ‘gain-at-MCL’ (Snik and Cremers, 2001), however, not frequency specific). They included 112 VSB users with sensorineural hearing loss. Using their data, a similar difference (10 dB) was found between ‘functional gain’ and the ‘gain-in-SRT’. So, the ‘functional gain’ should not be used or in combination with a supra-threshold measurement of amplification whenever compression amplification is used.

Furthermore, it should be noted that hearing thresholds with a hearing device might be further affected by advanced signal processing: viz. by expansion amplification used to prevent the patient from hearing the microphone noise of the device, or by noise reduction algorithms.

To evaluate MEI fittings in sensorineural hearing loss, the ‘functional gain’ is often used. However, when evaluating devices with non-linear amplification ‘functional gain’ doesn’t have the usual significance. Additionally, the supra-threshold  ‘gain-at-MCL’ or ‘gain-at-SRT’ should be reported.

A2.3 Qualifying amplification in patients with conductive or mixed hearing loss using MEIs or ‘BCDs’

To assess benefit of auditory implants for patients with mixed or conductive hearing loss, the ‘functional-gain’ is not an appropriate measure at all, for a second reason. It should be realized that MEIs with their actuator coupled to one of the cochlear windows as well as ‘BCDs’ directly stimulate the cochlea; consequently, the mal-functioning outer/middle ear plays no role. However, the status of the outer/middle ear, as quantified by the width of the AB-gap (the difference between the air- and bone-conduction thresholds) significantly affects the  ‘functional gain’. To illustrate this, let us assume a patient with pure conductive hearing loss of 65 dB HL (full bony atresia of the ear canal) using a powerful ‘pBCD’ that stimulates the cochlea rather perfectly (thresholds with the ‘pBCD’ at 15 dB HL). Then, following the definition, the ‘functional-gain’ is 65-15=50 dB. However, if the AB gap is 30 dB instead of 65 dB (partial atresia of the ear canal) while using the same device, then the ‘functional-gain’ is (only) 30-15=15 dB. This example shows that owing to its definition, the ‘functional gain’ depends strongly on the width of the AB-gap, and, therefore, it is an inadequate amplification measure.

How to proceed? If a patient with pure conductive hearing loss is fitted with a powerful ‘pBCD’ and if some every-day sound of 40 dB is indeed perceived as 40 dB by the patient, evidently, the gain is 0. In other words, the ‘pBCD’ has effectively compensated the conductive hearing loss. In the audiogram, this shows up as device-aided thresholds coinciding with the cochlear (thus bone-conduction) thresholds. This gain, the difference between the ‘BCD’-aided thresholds and the bone-conduction thresholds is referred to as the ‘bone-conduction gain’ (Carlsson and Hakansson, 1997) or the ‘effective gain’ (e.g., Bush et al., 2017). Note that by definition, the ‘functional gain’ equals the ‘effective gain’ plus the AB-gap. Once more; the bigger the AB-gap, the higher the ‘functional gain’. Therefore, in contrast to the ‘effective gain’, the ‘functional gain’ is not a measure of the capacity of the particular device used.

The ‘effective-gain’ might be negative, indicating that the device-aided thresholds are worse than the bone-conduction thresholds; see Chapter 3 and 4. That means that every-day sounds are (still) perceived attenuated and, in the audiogram, a persistent, although reduced AB-gap is seen. When the patient has mixed hearing loss with an obvious sensorineural hearing loss component (SNHLc) of e.g., 50 dB HL, obviously an‘effective gain’ of 0 is not enough; part of the SNHLc should be ‘compensated’ as well, to make speech sufficiently audible. The ‘effective gain’ should be positive, e.g., 22 dB (calculated target gain using the adapted NAL-rule; see Chapter 4); then, a 28 dBHL sound is just audible for his patient, using that amplification.

As said before, device-aided thresholds are affected by the kind of amplification that is used; linear versus expansion- and/or compression-amplification. Compression amplification, to deal with a relatively low maximum output of MEIs and ‘BDCs’ (Chapter 3) results in low (thus favourable) device-aided thresholds and expansion (to deal with device noise) results in higher (worse) device-aided thresholds. Consequently, the ‘effective gain’ respectively over- and under-estimates the amplification of sounds at e.g., normal conversational levels. 

In the previous section (A2.2) we discussed the use of alternative, supra-threshold amplification measures (viz. ‘gain-in-SRT’ and ‘gain-at-MCL-level’). However, these measures cannot be applied easily in conductive or mixed hearing loss. This is caused by limitations of the bone-conduction transducer (part of the audiometer) used to determine the bone-conduction stimulation. The standard B71 bone-conduction transducer has a relatively low maximum output (might be at or below the patient’s MCL levels) affecting the MCL measurements, especially in high and low frequencies (Alomari, 2014). Additionally, perception of speech produced by the B71 might be affected by distortions, especially of low-frequency sounds and the poor frequency response of the B71 (limited bandwidth). 

Evidently, to avoid or minimalize problems with quantifying the gain caused by non-linear amplification, always use auditory implants with a high MPO so that compression amplification is not needed or with reduced compression settings.

If MEI/’BCD’ are used in patients with conductive or mixed hearing loss, the ‘functional gain’ doesn’t provide any useful information on the quality MEI/’BCD’-fitting. Instead, the ‘effective gain’ should be used, as it is a fitting-quality measure. The ‘effective gain’ is by definition the difference between bone-conduction thresholds and device-aided thresholds and, therefore, might be negative (what is acceptable according to the new practise-based device-fitting procedure introduced in Chapter 4).