10.14639/0392-100X-N2752
Objective. To determine the benefits of binaural hearing rehabilitation in patients with monaural conductive or mixed hearing loss treated with a unilateral bone conduction implant (BCI). Methods. This monocentric study includes 7 patients with monaural conductive or mixed hearing loss who underwent surgical implantation of a unilateral BCI (Bonebridge, Med- El). An ITA Matrix test was performed by each patient included in the study - without and with the BCI and in three different settings – to determine the summation effect, squelch effect and head shadow effect. Subjective hearing benefits were assessed using the Abbreviated Profile of Hearing Aid Benefit (APHAB) questionnaire. Results. The difference in signal to noise ratio of patients without and with BCI was 0.79 dB in the summation setting (p &lt; 0.05), 4.62 dB in the head shadow setting (p &lt; 0.05) and 1.53 dB (p = 0.063) in the squelch setting. The APHAB questionnaire revealed a subjective discomfort in the presence of unexpected sounds in patients using a unilateral BCI (aversiveness score) compared to the same environmental situations without BCI, with a mean discomfort score of 69.00% (SD ± 21.24%) with monaural BCI versus 25.67% (SD ± 16.70%) without BCI (difference: -43.33%, p &lt; 0.05). In terms of global score, patients wearing a unilateral Bonebridge implant did not show any significant differences compared to those without hearing aid (difference: -4.00%, p = 0.310).Conclusions. Our study shows that the use of a unilateral BCI in patients affected by monaural conductive or mixed hearing loss can improve speech perception under noise conditions due to the summation effect and to the decrease of the head shadow effect. However, since monaural BCIs might lead to discomfort under noise conditions in some subjects, a pre-operative assessment of the possible individual benefit of a monaural BCI should be carried out in patients affected by unilateral conductive or mixed hearing loss in order to investigate the possible additional effect of the fitting of hearing aids.
text/xml
1827-675X
2752
en
Andrea Albera
http://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
binaural hearing
Binaural hearing in monaural conductive or mixed hearing loss fitted with unilateral Bonebridge
Text.Serial.Journal
https://www.actaitalica.it/
44
Audiology
2024-04-22
2023-09-12
2024-04-23
2024-04-23
113-119
1
Andrea Albera
2024/04/22
10.14639/0392-100X-N2752
113
ENT Unit, Department of Surgical Sciences, University of Turin, Turin, Italy
1827-675X
binaural hearing
en
119
Binaural hearing in monaural conductive or mixed hearing loss fitted with unilateral Bonebridge
https://www.actaitalica.it/article/download/2752/1087
44
ACTA OTORHINOLARYNGOLOGICA ITALICA 2024;44:113-119; doi: 10.14639/0392-100X-N2752




Audiology


Binaural hearing in monaural conductive or mixed
hearing loss fitted with unilateral Bonebridge
Andrea Canale1, Anastasia Urbanelli1, Roberto Albera1, Maria Gragnano2, Valerio Bordino1, Giuseppe Riva1,
Eugenio Sportoletti Baduel1, Andrea Albera1
1
 ENT Unit, Department of Surgical Sciences, University of Turin, Turin, Italy; 2 Department of Public Health Sciences and Paediatrics,
University of Turin, Turin, Italy


SUMMARY
Objective. To determine the benefits of binaural hearing rehabilitation in patients with mon-
aural conductive or mixed hearing loss treated with a unilateral bone conduction implant
(BCI).
Methods. This monocentric study includes 7 patients with monaural conductive or mixed
hearing loss who underwent surgical implantation of a unilateral BCI (Bonebridge, Med-
El). An ITA Matrix test was performed by each patient included in the study - without and
with the BCI and in three different settings – to determine the summation effect, squelch
effect and head shadow effect. Subjective hearing benefits were assessed using the Abbrevi-
ated Profile of Hearing Aid Benefit (APHAB) questionnaire.
Results. The difference in signal to noise ratio of patients without and with BCI was 0.79
dB in the summation setting (p < 0.05), 4.62 dB in the head shadow setting (p < 0.05) and
1.53 dB (p = 0.063) in the squelch setting. The APHAB questionnaire revealed a subjec-
tive discomfort in the presence of unexpected sounds in patients using a unilateral BCI
(aversiveness score) compared to the same environmental situations without BCI, with
a mean discomfort score of 69.00% (SD ± 21.24%) with monaural BCI versus 25.67%
(SD ± 16.70%) without BCI (difference: -43.33%, p < 0.05). In terms of global score,
patients wearing a unilateral Bonebridge implant did not show any significant differences
compared to those without hearing aid (difference: -4.00%, p = 0.310).
Conclusions. Our study shows that the use of a unilateral BCI in patients affected by mon-
aural conductive or mixed hearing loss can improve speech perception under noise condi-
tions due to the summation effect and to the decrease of the head shadow effect. However,
since monaural BCIs might lead to discomfort under noise conditions in some subjects, a
                                                                                                Received: September 12, 2023
pre-operative assessment of the possible individual benefit of a monaural BCI should be
                                                                                                Accepted: November 13, 2023
carried out in patients affected by unilateral conductive or mixed hearing loss in order to
investigate the possible additional effect of the fitting of hearing aids.
                                                                                                Correspondence
KEY WORDS: monaural hearing loss, conductive hearing loss, unilateral bone conduction           Andrea Canale
implant, binaural hearing                                                                       E-mail: andrea.canale@unito.it


                                                                                                  How to cite this article: Canale A, Urbanelli
                                                                                                  A, Albera R, et al. Binaural hearing in mon-
Introduction                                                                                      aural conductive or mixed hearing loss fit-
                                                                                                  ted with unilateral Bonebridge. Acta Otorhi-
The benefits of binaural over monaural hearing in terms of sound localisa-                        nolaryngol Ital 2024;44:113-119. https://doi.
tion and speech understanding have been known for several years 1,2. Some                         org/10.14639/0392-100X-N2752
previous works showed how both air conduction (AC) and bone conduction
                                                                                                © Società Italiana di Otorinolaringoiatria
(BC) hearing pathways activate the cochlear basilar membrane in a compara-                      e Chirurgia Cervico-Facciale
ble way 3. On the other hand, Stenfelt showed that, since there is more cross-
hearing with BC than with AC, the binaural processing of sound delivered by                                    OPEN ACCESS

BC is expected to be less than that achieved with AC transmission 4. For this                   This is an open access article distributed in accordance with
                                                                                                the CC-BY-NC-ND (Creative Commons Attribution-Non-
reason, AC hearing aids are generally the first choice for hearing stimulation,                 Commercial-NoDerivatives 4.0 International) license. The
including in patients with conductive hearing loss. However, rehabilitation                     article can be used by giving appropriate credit and mentio-
                                                                                                ning the license, but only for non-commercial purposes and
with bone conduction implant (BCI) hearing aids (e.g., bone-anchored hearing                    only in the original version. For further information: https://
aids, BAHA implant systems, Bonebridge) represents the first choice for pa-                     creativecommons.org/licenses/by-nc-nd/4.0/deed.en




                                                                                                                                                        113
A. Canale et al.




tients suffering from conductive or mixed hearing loss who           plantation of a monolateral bone conduction hearing
cannot wear conventional AC hearing aids (e.g., patients             aid (BonebridgetM, Med-El, Innsbruck, Austria) at the
with atresia auris, recurrent external otitis, chronic otitis        Otolaryngology Division of Molinette Hospital, Turin,
media, cavities after radical mastoidectomy) 5.                      between 2015 and 2021. The mean age at implantation
Recent studies reported speech perception advantages in              was 48 years (SD ± 15.09). Participation in the study was
the binaural fitting of BC devices in bilateral conductive           voluntary. The following inclusion criteria were applied:
hearing loss 6,7. In particular, some previous works in chil-        patients older than 18 years affected by monaural con-
dren showed that, due to the binaural unmasking, the bilat-          ductive/mixed hearing loss and normal hearing capacity,
eral application of a percutaneous BC implant in symmetric           or mild hearing loss in the contralateral ear. The Interna-
bilateral conductive hearing loss results in better sound lo-        tional Organization for Standardization (ISO) 7029:2017
calisation and speech perception under noise conditions 8,9.         standard was adopted to assess the hearing threshold de-
The question remains whether unilateral BC devices can               viation for audiometric tones of subjects included in the
ensure an adequate hearing rehabilitation in patients af-            study and prove that any observed hearing loss in the AC
fected by monaural conductive hearing loss who cannot be             thresholds was associated with age and not with any coch-
fitted with AC hearing aids 10.                                      lear injury. Exclusion criteria were: age under 18 years,
The importance of hearing rehabilitation in patients af-             bilateral hearing loss, learning disability and attention
fected by monaural conductive hearing loss was stressed              disorders. Information for each subject, including age at
by some authors who demonstrated how unilateral conduc-              implantation, gender, aetiology of deafness (congenital or
tive hearing loss leads to deficits in the auditory skills that      acquired, aural atresia or tympanoplasty), type of hear-
rely on binaural input, and results in damages of the neu-           ing loss (pure conductive or mixed), side of implantation
ral coding of spatial information in the inferior colliculus         and pre-implantation audiometric scores are summarised
neurons, which persists after the conductive hearing loss is         in Table I. In accordance with the indications provided
resolved 11. In addition, previous authors demonstrated that         by the manufacturer (Med-El), the retrosigmoid approach
children with unilateral congenital conductive hearing loss          was used for all subjects in the study. All patients under-
might run into poor school performances and academic dif-            went pre-operative CT and MRI before surgery to evalu-
ficulties due to their hearing disability 10,12. In the past, only   ate the individual anatomy of the skull and to exclude any
a few authors have tried to demonstrate the binaural hear-           bone deformity that could interfere with the implantation
ing restoration after fitting BCIs in such patients, and their       of the aid.
results turned out to be conflicting 13,14.                          Participants underwent pure tone audiometry (250-8000
Meanwhile, recent studies are evaluating and researching             Hz) to measure their bilateral hearing threshold in daily life
the benefits of treating unilateral conductive hearing loss          1 month before implantation, and speech intelligibility in
(UCHL) in unilateral aural atresia. Brotto et al. reinforce          noise without and with the BCI using the ITA Matrix test 17.
the idea that using BCIs in UCHL might improve speech                Results are expressed in decibels and represent the signal
perception in noise thanks to the summation effect, but the          to noise ratio (SNR) at which a subject understands 50% of
setting of the study prevented the investigation of real bin-        the words given during the test. Audiological evaluations
aural hearing 15. Vogt et al., in a 2021 review, suggest in-         after implantation of all patients were conducted in October
stead that the benefits of BCIs might be related to bilateral        2022, after at least one week of continuous use of the BCI.
hearing (2 “separate” inputs) rather than “binaural hearing”         We thus obtained an average post-operative ITA-Matrix
(a fused concept) 16.                                                Test time interval of 55 months (minimum of 12 months
For this reason, the use of unilateral BCIs in patients with         for P3 and maximum of 84 months for P6).
monaural conductive hearing loss remains controversial.              For this study, the ITA Matrix test was performed using two
The aim of this study is to determine whether the use of a           loudspeakers in three different settings to determine speech
unilateral Bonebridge device in patients affected by mon-            intelligibility in three noise situations, and to evaluate the
aural conductive or mixed hearing loss improves hearing              benefits of binaural hearing with a monolateral bone con-
and speech perception under noise conditions thanks to the           duction aid. The scores of all three settings were registered
advantages of binaural hearing.                                      without and with the aid:
                                                                     • summation setting: speech and noise were both present-
                                                                        ed from the front of the patient (S0N0);
Materials and methods                                                • head shadow effect: speech was presented on the side
The cohort included 7 adult Italian mother tongue speak-                affected by conductive or mixed hearing loss and noise
ers (3 females and 4 males) who underwent surgery im-                   on the better ear (S90N-90);



114
                                                                       Binaural hearing in monaural conductive or mixed hearing loss fitted with unilateral Bonebridge




Table I. Anamnestic and baseline audiometric data of the sample.
 Patient    Age      Sex      Congenital/     Type of hearing                     Year of surgery          Side      Ear      AC (BC) thresholds (dBHL) at frequency
            (yrs)              acquired          impairment                     (months between                                0.5         1         2       4 kHz
                                                                                 surgery and ITA-
                                                                                 Matrix-Test after
                                                                                     surgery)
 P1              68         M         Acquired               Mixed                   2018 (46)             Left     Normal      25        30        30         35
                                                         (tympanoplasty)                                           Impaired   70 (30)   70 (35)   85 (45)    85 (55)
 P2              24         M        Congenital             Conductive               2017 (58)             Left     Normal      10        15        10         10
                                                          (aural atresia)                                          Impaired   80 (15)   70 (15)   65 (20)    60 (25)
 P3              61         M        Congenital               Mixed                  2021 (12)             Right    Normal      15        15        20         40
                                                          (aural atresia)                                          Impaired   85 (15)   60 (15)   75 (15)    65 (25)
 P4              54          F        Acquired               Mixed                   2015 (82)             Right    Normal      10        10        15         10
                                                         (tympanoplasty)                                           Impaired   65 (30)   60 (20)   50 (35)    75 (35)
 P5              43          F       Congenital               Mixed                  2018 (51)             Right    Normal      10        10        10         10
                                                          (aural atresia)                                          Impaired   80 (15)   75 (20)   60 (30)    55 (20)
 P6              30         M         Acquired              Conductive               2015 (84)             Left     Normal      10        10        10         10
                                                         (tympanoplasty)                                           Impaired   50 (15)   45 (10)   40 (15)    60 (15)
 P7              56         F         Acquired              Conductive               2018 (54)             Left     Normal      25        30        20         40
                                                         (tympanoplasty)                                           Impaired   55 (15)   65 (20)   70 (35)    50 (30)
AC: air conduction; BC: bone conduction; dBHL: decibel hearing loss; kHz: kilohertz; M: male; F: female.



• squelch setting: speech was presented from the front and                                   parameters for the two listening modes (without and with
   noise on the side affected by conductive or mixed hear-                                   BCI) was calculated for each patient. The difference be-
   ing loss (S0N90);                                                                         tween the GS obtained without BCI and the GS obtained
• tests were conducted in a sound-attenuated room with                                       with BCI resulted in the global benefit obtained by each
   the speakers placed one meter away from the patient.                                      patient from the implantation of the BCI. All scores of the
   Subjects were asked not to move their head during the                                     APHAB questionnaire were expressed as percentages. All
   test. We performed a calibration of the perceived signals                                 surveys on the APHAB questionnaire were carried out 2
   using a sound level meter (Volcraft, Schallpegelmess-                                     months after BCI implantation for every subject of the
   gerät 332 Datalogger).                                                                    study; all subjects used the implant correctly throughout
In addition, each patient was administered a 24-ques-                                        the day until our evaluation.
tion self-assessment questionnaire (Abbreviated Profile
of Hearing Aid Benefit questionnaire, APHAB) to assess                                       Statistical analysis
the perceived satisfaction of the subject with the BCI. The                                  Categorical variables are reported as frequency and per-
scores obtained provided the surgeon and audioprothesist                                     centage; continuous variables are reported as mean ±
with information on:                                                                         standard deviation (SD). Due to the small sample size of
• ease of communication (EC), defined as communication                                       the study, the statistical analysis was performed using the
   under quiet conditions;                                                                   Wilcoxon Signed Ranks test, a non-parametric test used to
• reverberation (RV), defined as communication under re-                                     compare the means between two groups. The test allowed
   verb conditions;                                                                          us to evaluate the significance of the difference between
• background noise (BN), defined as communication in                                         test results at t2 (Matrix test performed with BCI) and t1
   places with different noise levels;                                                       (Matrix test performed without BCI). The statistical signifi-
• aversiveness (AV), defined as the discomfort deriving                                      cance was set at p < 0.05.
   from ambient sounds.                                                                      As for the APHAB questionnaire, results were analysed
The subjects involved in the study were asked not to wear                                    using the Wilcoxon Signed Ranks non-parametric test to
the BCI for one week and to fill in the questionnaire. Sub-                                  highlight differences in subjective hearing and quality of
sequently, they filled in the same questionnaire after at least                              life without and with BCI for all four categories (EC, RV,
one week of continuous use of the hearing aid. A global                                      BN, AV). Statistical analysis was performed using the IBM
score (GS) calculated from the average scores of the four                                    SPSS Statistics for Macintosh software, Version 28.0.



                                                                                                                                                                 115
A. Canale et al.




Results                                                                                     ence: -4.01%, p = 0.310). However, looking at the individ-
                                                                                            ual items of the APHAB questionnaire, AV score averages
The hearing profile of each subject was obtained by testing                                 revealed a significant difference (-43.33%) between the
pure tone thresholds, showing a mean air conduction pure                                    two patterns (without and with BCI), resulting in a subjec-
tone average (PTA) of 63.31 dB (SD ± 13.05) without BCI                                     tive discomfort of 69.00% (SD ± 21.24%) in the presence
for frequencies between 250 to 8000 Hz. Table II shows the                                  of unexpected sounds in patients with BCI versus 25.67%
results of the Italian Matrix test in all settings.                                         (SD ± 16.70%) of discomfort without BCI (p < 0.05).
In the summation setting, the mean SNR without BCI is                                       Table III shows the individual results of the APHAB ques-
-2.11 dB (SD ± 1.90 dB), compared to an average SNR                                         tionnaire.
of -2.90 dB (SD ± 1.56 dB) with unilateral BCI. The dif-
ference between the scores obtained in these settings
(0.79 dB) was statistically significant (p < 0.05). In the head                             Discussion
shadow configuration, we obtained a mean SNR of 0.63 dB                                     Binaural hearing in the rehabilitation of patients affected
(SD ± 2.58) without unilateral BCI and a mean SNR of                                        by monaural conductive hearing loss using a unilateral
-3.99 dB (SD ± 3.76 dB) with unilateral BCI, resulting in                                   hearing device has been investigated over the years, but the
a statistically significant decrease between the two scores                                 question whether monaural conductive hearing loss should
(4.62 dB, p < 0.05). The squelch setting showed an average                                  be amplified with a unilateral BCI remains unclear 13,14.
SNR of -3.06 dB (SD ± 3.53 dB) without unilateral BCI,                                      Some previous studies reported improved speech percep-
compared to an average SNR of -4.59 (SD ± 3.89) with a                                      tion in patients with monaural hearing loss after fitting a
monaural Bonebridge. The difference was not statistically                                   BCI, but they did not investigate speech intelligibility in
significant (1.53 dB, p = 0.063).                                                           different settings under noise conditions. For example,
As for the APHAB questionnaire, in terms of GS, patients                                    Danhauer et al. showed that patients affected by congenital
with a unilateral Bonebridge implant did not show signifi-                                  monolateral aural atresia perceived benefits with the im-
cant differences compared to those without BCI (differ-                                     plantation of unilateral BAHA devices and reported a re-


Table II. Results of Matrix Test in the three settings.
                      Summation effect (dB)                                       Squelch effect (dB)                                Head shadow effect (dB)
                   Without BCHA          With unilateral BCHA          Without BCHA            With unilateral BCHA           Without BCHA       With unilateral BCHA
                        (t1)                      (t2)                      (t1)                        (t2)                       (t1)                   (t2)
 P1                    -1.3                          -3                      -2.5                       -1.9                        3.4                      -9
 P2                    -3.7                         -4.7                     -2.4                       -6.2                        -0.9                    -5.9
 P3                    -0.6                         -1.4                     -4.6                       -6.1                         4.7                     3.2
 P4                    -2.6                         -2.8                     -0.8                       -3.1                        -1.6                    -3.1
 P5                    -1.8                         -2.1                     -3.3                       -2.1                         1.4                    -5.6
 P6                    -5.2                         -5.2                     -9.6                       -12                         -1.7                    -3.1
 P7                     0.4                         -1.1                      1.8                       -0.7                        -0.9                    -4.4
dB: decibel; BCHA: bone conduction hearing aid.



Table III. Individual results of the Abbreviated Profile of Hearing Aid Benefit (APHAB) questionnaire.
                                         Without BCHA (%)                                                                     With BCHA (%)
              EC scale        BN scale            RV scale       AV scale            GS           EC scale         BN scale          RV scale    AV scale           GS
 P1            41.67           45.83               49.83           24.50            40.46           6.5              47.67            43.33        83              45.13
 P2            6.83            45.67               14.50             31             24.50          8.33              58.33            20.83       72.50             40
 P3            82.83           51.67               56.17           60.17            62.71           83               49.67            58.17       64.17            63.75
 P4            31.17           84.67               55.83             21             48.17          14.50             71.83             54          48              47.08
 P5             6.50            29                 15.75           18.50            17.44          37.50             29.00             22          87              43.88
 P6            37.67           49.67               56.17            9.17            38.17           29               20.83            37.17        93               45
 P7            23.33           70.50               82.67           15.33            47.96            1               28.83            25.17       35.33            22.58
BCHA: bone conduction hearing aid; EC: ease of communication; RV: reverberation; BN: background noise; AV: aversiveness; GS: global score.




116
                                                      Binaural hearing in monaural conductive or mixed hearing loss fitted with unilateral Bonebridge




duction in activity limitations when using it. In their work,           (Tab. II). This divergence could be explained by the different
both speech and noise were presented at the frontal speaker             TA of the patients in the study, which might lead to vari-
(S0N0), and no further settings were analysed 18. Priwin et             ous outcomes in the squelch setting regardless of the type
al. investigated the benefits of using both bilateral BAHAs             of hearing impairment (congenital or acquired). The role of
in children with bilateral conductive hearing impairment                TA in determining different results in patients affected by
and unilateral BAHAs in children affected by unilateral                 congenital or acquired hearing loss fitted with unilateral
conductive hearing loss, and concluded that – contrary to               BCIs was also stressed by Snik et al. who noticed, partially
those implanted with bilateral BAHA, who experimented                   in contrast to our results, that patients with congenital unilat-
benefits in terms of better sound localisation and speech               eral conductive hearing loss did not benefit from a monaural
recognition in noise – children affected by monaural con-               BCI in terms of sound localisation, while patients affected
ductive hearing loss benefited from the fitting of a unilat-            by acquired conductive hearing loss showed an improved
eral BAHA in terms of better speech recognition. However,               sound localisation ability under noise conditions 13, calling
no advantages were noticed regarding sound localisation                 into question the impact that altered neural processing might
under noise conditions 14. These results were observed with             have in individuals with congenital UCHL.
adhesive bone conduction hearing aids (Adhear); these de-               Our audiometric results find some correspondence in the
vices provide a similar hearing gain compared to BCIs in                APHAB questionnaire, which revealed a subjective dis-
conductive hearing loss in the summation context 19 and                 comfort in the presence of unexpected sounds (e. g., smoke
may have a role in assessing the individual hearing out-                detectors and alarms) and evidenced annoying hearing sen-
come with BCI. However – in line with the above results                 sations in noisy environments such as busy streets and con-
– they were shown to be unable to obtain real binaural hear-            struction sites while using the hearing device. The global
ing in monaural conductive hearing loss 20.                             dissatisfaction of patients using a BCI for unilateral BC
We now know that one must consider two further aspects                  is also confirmed in previous studies, which showed that
that can affect the benefits of treatment. On one hand, the             patients with monaural hearing impairment seemed not to
impaired-deprived neural processing in subjects with con-               use the BAHA all day and that they were not overly im-
genital UCHL who did not experience binaural hearing                    pressed by BC sound quality 24. Furthermore, Priwin et al.
and, therefore, might not have a normally developed neural              found that some children with unilateral hearing loss used
auditory system, and the possibility that patients with con-            the BCI only in the classroom, thus revealing that unilateral
genital UCHL might be “forced” to develop a unilateral                  BC hearing might show benefits in the school environment
hemispheric dominance if an atretic ear is not stimulated in            due to the better speech perception with the device, but did
the first years of life 21. On the other, a different transcranial      not seem to represent a subjective fundamental tool for pa-
attenuation (TA) was measured in human subjects by No-                  tients in their everyday hearing life 14.
lan and Lyon in 1981 (mean TA: close to 10 dB, SD ± 5-10                The APHAB questionnaire was also used by Ratuszniak et
dB) 22 and by Stenfelt in 2012 (range from 3 to 10 dB, with             al. to assess the benefits of the Bonebridge system in pa-
intersubject variability around 40 dB) 23.                              tients affected by unilateral or bilateral conductive hearing
Despite the limitation of the small sample size of the study,           loss: they noticed a significant improvement in the satisfac-
our data suggest that unilateral BCIs in patients affected by           tion of subjects with the hearing aid, resulting in a mean re-
monaural conductive hearing loss improve loudness by stim-              duction of problems with hearing from 45% before implan-
ulating both ears (summation effect) and improve speech in-             tation to 22% after implantation 25. However, they did not
telligibility by eliminating the physical reduction of speech           differentiate patients affected by bilateral conductive hear-
due to the head shadow effect, but do not show advantages in            ing loss from those who suffered from unilateral hearing
terms of improving SNR when the existing conditions cause               loss, both fitted with unilateral BCIs. It follows that, due
a squelch effect (the difference appeared not to be statisti-           to the huge improvement of speech intelligibility through
cally significant (p = 0.063)). By analysing the individual re-         the use of a BCI in patients with bilateral conductive hear-
sults of the subjects included in the study, we noticed that pa-        ing impairment, the mean level of satisfaction may result
tient P2 – who was fitted with unilateral Bonebridge because            in an overestimation of the subjective benefits of patients
of a left monaural atresia and had never used AC hearing                affected by unilateral conductive hearing loss fitted with
aids – showed the highest reduction of SNR in the squelch               monaural Bonebridge. According to a recent work by Irmer
setting, while the worst result in this setting was achieved by         et al. who highlighted the benefits of BC implantation in
patient P5, also suffering from congenital unilateral conduc-           terms of subjective hearing 26, our results account for the
tive hearing loss due to right monaural atresia, and for whom           better speech perception of patients implanted with mon-
the cause of a congenital neural deprivation was excluded               aural Bonebridge.



                                                                                                                                               117
A. Canale et al.




To the best of our knowledge, this is the first study on        ESB: substantial contribution to the design and writing of
speech recognition in three different setting under noise       the work; AA: substantial contribution to the design of the
conditions after fitting a unilateral Bonebridge aid system     work, final approval of the version to be published.
in monaural conductive or mixed hearing loss, and the first
on a new model of BC rehabilitation which aims to inves-        Ethical consideration
tigate the benefits of binaural hearing in unilateral conduc-   This retrospective study has been performed in accordance
tive hearing impairment. The limitations of our work are        with the ethics standards laid down in the 1964 Declaration
represented by the small sample size and the heterogeneity      of Helsinki. Committee approval was obtained from “Città
of subjects affected by both congenital and acquired hear-      della Salute e della Scienza” University Hospital Ethics
ing loss. In particular, subjects with congenital hearing im-   Committee (March 13, 2018, Protocol Number: 0026286;
pairment who have never been fitted with a BCI before are       CS2/622). Informed consent was obtained from all subjects
expected not to have developed neuronal binaural process-       involved in the study.
ing. The outcomes of some (e. g., patient P2 and patient P3,
Table II) – which turned out to be better than those obtained
by subjects with acquired hearing loss – may be explained       References
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to investigate the possible supplementary effect of the fit-         ps://doi.org/10.1080/14992020500031561
ting of hearing aids, a pre-operative trial with Softband or    5
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adhesive devices may be of value in patients affected by             fants with normal hearing. J Am Acad Audiol 2011;22:81-92. https://
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unilateral conductive or mixed hearing loss. Further stud-
                                                                6
                                                                     Canale A, Ndrev D, Sapino S, et al. Speech in noise with bilateral
ies are required to investigate the neural mechanism of the
                                                                     active bone conduction implant for conductive and mixed hearing
squelch effect in determining various outcomes of patients           loss. Otol Neurotol 2022;1;43:1000-1004. https://doi.org/10.1097/
with different TA.                                                   MAO.0000000000003671
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Conflict of interest statement                                       aids for bilateral permanent conductive hearing loss: a systematic
                                                                     review. Otolaryngol Head Neck Surg 2012;147:412-222. https://doi.
The authors declare no conflict of interest.                         org/10.1177/0194599812451569
                                                                8
                                                                     Zeitooni M, Mäki-Torkko E, Stenfelt S. Binaural hearing ability with
Funding                                                              bilateral bone conduction stimulation in subjects with normal hearing:
This research received no specific grant from any funding            implications for bone conduction hearing aids. Ear Hear 2016;37:690-
agency in the public, commercial or not-for-profit sectors.          702. https://doi.org/10.1097/AUD.0000000000000336
                                                                9
                                                                     den Besten CA, Vogt K, Bosman AJ, et al. The merits of bilateral
                                                                     application of bone-conduction devices in children with bilateral
Author contributions
                                                                     conductive hearing loss. Ear Hear 2020;41:1327-1332. https://doi.
AC: substantial contribution to the conception and design            org/10.1097/AUD.0000000000000853
of the work, final approval of the version to be published;     10
                                                                     Kesser BW, Krook K, Gray LC. Impact of unilateral conductive hear-
AU: substantial contribution to the design and writing of            ing loss due to aural atresia on academic performance in children. La-
the work, final approval of the version to be published;             ryngoscope 2013;123:2270-2275. https://doi.org/10.1002/lary.24055
RA: substantial contribution to the selection of patients       11
                                                                     Thornton JL, Anbuhl KL, Tollin DJ. Temporary unilateral hearing
                                                                     loss impairs spatial auditory information processing in neurons in the
eligible for the study; MG: execution of audiometric test;           central auditory system. Front Neurosci 2021;1;15:721922. https://
VB: substantial contribution to the statistical analysis and         doi.org/10.3389/fnins.2021.721922
interpretation of the data; GR: substantial contribution to     12
                                                                     Lieu JE. Unilateral hearing loss in children: speech-language and
the assessment and evaluation of APHAB questionnaires;               school performance. B-ENT 2013;21:107-115.




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