Patient selection for incus body coupling of a totally implantable middle ear implant

To evaluate audiologic selection criteria for incus body coupling (IBC) of a totally implantable middle ear implant (TI-MEI) for the treatment of sensorineural hearing loss (SNHL).

The protocol is specified in the Investigational Device Exemption of a Food and Drug Administration-approved multicenter clinical trial. The prospective study compared pre- and postoperative hearing levels using each patient as their own control. In addition, an implant on/off comparison was made. All patients had a follow-up interval of at least 6 months. Audiologic assessment tests included speech discrimination in quiet as the primary efficacy variable and pure-tone audiometry (aided thresholds), gain, speech recognition in noise and subject satisfaction using standardized questionnaires and visual analog scales (VASs) as secondary efficacy variables. The study group of patients (n = 13) was divided into 3 subgroups based on their pure-tone and speech discrimination scores: Group A consisted of 6 patients, Group B 9 patients and Group C of all 13 patients. All patients suffered from long-standing bilateral moderate to severe SNHL. Five patients were dissatisfied hearing aid (HA) users and eight subjects could not wear HAs. All patients were implanted with a TI-MEI which was coupled to the incus body. The amplification level of the device was set postoperatively using inductive digital fitting based on "most comfortable loudness" specifications.

The implant produced median improvements from 30% (optimally fit bilateral HAs; n = 5) and 50% (HA non-users; n = 8) to 70% word recognition at 60 dB SPL. Average word recognition scores at 60, 80 and 90 dB SPL in Groups A and B showed increases from 42% (interquartile range +27%, -12%) to 93.5% (+3%, -5%) and 92.5% (+3%, -7%), respectively. In the presence of background noise, the sentence recognition threshold ranged from -2 to 1 dB signal-to-noise ratio. Maximum amplification was 50 dB at 3 kHz and 55 dB at 4 kHz. In Groups A and B, VASs revealed improvements in both natural sound impression and clarity from 62-70% of a natural sound impression to maximum scores of 100%. Using the standardized Gothenburg profile, subjective evaluations of hearing, orientation, social behavior and self-confidence reached 96-98%, 92-96% and 84-92% of the maximum score for Groups A-C, respectively.

In selected cases, IBC of the TI-MEI investigated herein may be indicated for the treatment of SNHL, provided the following four conditions are met. First, the patient does not derive sufficient benefit from conventional HAs. Second, the specific indication for IBC is restricted to situations that do not allow the coupling of the MEI to the long incus process (e.g. due to an anatomical variation of facial nerve location). Third, IBC is restricted to patients with a steeply sloped moderate to severe high frequency SNHL, amounting to 90 dB HL from 3 to 8 kHz. Patients with low frequency SNHL should not be operated on with the IBC technique, as maximum low frequency hearing loss at 0.5 kHz must not exceed 30 dB. Fourth, Schueller's X-ray should reveal normal mastoid pneumatization. Being restricted to a 6-month follow-up period, this paper provides early clinical results and no clinical evidence of long-term efficiency of the implant.