*3.1. Patients*

Patients who underwent implantation with a MED-EL cochlear implant and who used the IES CMD prior to the insertion of the electrode array were included in the IESgroup. Patients with different types of electrodes were included: FLEX 16 CMD (*n* = 1), FLEX 20 (*n* = 3), FLEX 24 (*n* = 3), FLEX 28 (*n* = 21), and STANDARD (*n* = 5).

Of these patients, twenty-seven were treated unilaterally and three were implanted bilaterally. In the following, each implanted ear is considered individually, yielding a dataset of 33 ears with nearly equal sex distribution (17 male and 16 female). Of the implantations, 20 (60.6%) were performed on the right side and 13 (39.4%) on the left side. At the time of implantation, the mean age was 37.6 years (range: 10 months–80 years).

The SPLIT group consisted of eight patients (five male and three female; mean age at the time of implantation 38.5 years; range: 1–74 years) who were implanted with a Split-Array CMD. In this group, the IES CMD was not used or its application was unsuccessful in the previous intervention (*n* = 3).

Both groups, the IES group and the SPLIT group, consisted of diverse and partly multimorbid patients. Table 1 provides an overview of the relevant comorbidities of the subjects as listed in their medical records.


**Table 1.** A summary of the occurrence of relevant concomitant diseases in subjects of the IES, SPLIT, and REGULAR groups.

For better comparability with various CI patients, for whom no IES CMD application was necessary or indicated, the REGULAR group was included. The REGULAR group consisted of patients who were age- (±5 years) and gender-matched (17 male and 15 female) to the subjects of the IES group. For the implanted patients of this group, the distribution of electrode variants was identical to the IES group. Only the implantation with a Flex 16 electrode array was excluded from the REGULAR group as no suitable comparison case was identified. This resulted in a dataset of 32 subjects for the REGULAR group. Table 1 shows the concomitant diseases of the REGULAR group to provide a complete survey.

#### *3.2. Aetiology of Deafness*

Regarding the aetiology of deafness in the IES group, seven patients (21.2%) suffered from meningitis, eight (24.2%) suffered from anatomical malformations in the inner ear, five (15.2%) suffered from other congenital hearing impairment, two (6.1%) suffered from sudden hearing loss, one (3.0%) suffered from trauma of the temporal bone, one (3.0%) suffered from otosclerosis, and the aetiology was unknown or not documented in nine other patients (27.3%).

In the SPLIT group, four patients (50%) suffered from meningitis, two (25%) suffered from trauma of the temporal bone, one (12.5%) suffered from sepsis due to pneumonia, and the cause was unknown or not documented for one other patient (12.5%).
