Investigations on Directional Hearing With One-Sided Fitting of an Active Middle Ear Implant or Bone Conduction Hearing Implant.

Objective: In patients with conductive or combined unilateral hearing loss, implantable hearing systems can be a treatment option. Due to the overlapping indications of hearing implants, a systematic evaluation of audiologic differences in terms of speech intelligibility and binaural hearing abilities is necessary. Because of the unilateral cochlear stimulation in patients implanted with an active middle ear implant, we expect superior binaural hearing performance compared with patients implanted with a bone-conducting implant that causes bilateral cochlear stimulation. This study focuses especially on comparing directional hearing abilities between the aforementioned groups of implantable hearing aid users.

Methods: In 13 patients unilaterally fitted with Vibrant Soundbridge (VSB) and 8 patients fitted with Bonebridge (BB) (both implants manufactured by MED-EL, Austria) (implantation at least 6 months ago, contralateral ear with at most mild hearing loss [pure tone average across 4 frequencies <30 dB]), sound localization ability, speech intelligibility (Freiburger monosyllabic word test and Oldenburgsentencetest), audiometric threshold-based measurements and patient-reported outcome measures (International Outcome Inventory for Hearing Aids and Speech, Spatial and Qualities of Hearing Scale 12) have been examined.

Results: The groups did not differ significantly (p > 0.05) in terms of patient age (VSB: 44.6 ± 14.4 years [SD]; BB: 44.5 ± 17.3 years), pure tone average across 4 frequencies of bone conduction (VSB: 26.4 ± 6.9 dB; BB: 23.3 ± 6.7 dB), speech intelligibility (VSB: 80.0% ± 16.7%; BB: 69.4% ± 13.2% [Freiburger]) and Oldenburgsentencetest (VSB -8.9 ± 2.6 dB; BB: -7.2 ± 4.4 dB). Implantation was 4.2 ± 2.7 years (VSB) and 7.5 ± 3.5 years (BB) (p < 0.05). Sound tended to be localized more frequently (56% ± 16%) within the reference range in the VSB group than in the BB group (49% ± 12.9%) (p > 0.05). The VSB group tended to show a smaller lateral deviation of sound detection from the actual sound presentation direction, especially with frontal sound presentation, compared with the BB group. Lateral sound presentations above 60° were increasingly perceived in the direction contralateral to the sound source in both groups (p > 0.05). Subjective hearing disabilities were scored significantly lower in the VSB group compared with the BB group.

Conclusion: When comparing the sound localization ability between BB and VSB users, the study displayed a trend toward better results with the VSB. Further measurement data of patient cohorts with larger group sizes have to be collected for a final judgment on the clinical significance of these differences.