Multicenter randomized controlled trial comparing surgical approaches to the cochlea for the Slim Modiolar Electrode: Assessing intracochlear trauma with intraoperative electrocochleography measurements, imaging, and residual hearing preservation.

In recent years, there has been a growing focus on the preservation of
preoperative residual hearing in cochlear implant (CI) surgery. As the criteria
for cochlear implantation have expanded, the significance of preserving
residual hearing (RHP) has become increasingly evident. Beyond serving as an
indicator of minimally traumatic implantation, RHP also enables natural sound
perception in some CI patients and facilitates electrical-acoustic stimulation
(EAS) in others. Studies have demonstrated that EAS can enhance sound
localization and improve both music appreciation and speech recognition in
noisy environments. Consequently, the preservation of residual hearing has
emerged as one of the main surgical goals in modern CI care. Nevertheless,
there is still an ongoing discussion about the long-term benefit of preserving
residual hearing in view of progressive hearing loss, either because of the
natural progression of hearing loss or the presence of the electrode within the
cochlea. A considerable amount of residual hearing should be present to be able
to make use of the abovementioned benefits. Furthermore, recent findings seem
to point out that preservation of acoustic input contributes to normal cortical
activity following sound stimuli processed electro-acoustically rather than in
the electric-only mode. In other words, maintaining peripheral acoustic hearing
has central effects.

Using the slim modiolar electrode (SME), several potential sites of damage that
may result in residual hearing loss can be envisioned. Firstly, concerning the
approach to the cochlear lumen. This involves drilling at the promontory with
potentially noise induced trauma to expose the round window (RW). Furthermore,
the optimal entry site into the cochlea (extended round window (eRW) or
cochleostomy (CO) which both imply drilling with bone dust or blood potentially
entering the cochlea. If one would wish to choose for the CO approach and leave
the RW anatomically intact, it is paramount to have an optimal position of the
CO, to avoid damage. Secondly, damage may occur proximal in the basal turn of
the cochlea on insertion of the sheath of the insertion tool hitting and
transecting the basilar membrane, the osseus spiral lamina or the modiolar
wall. Thirdly, further down the cochlea damage at the level of the basilar
membrane may be the result of an ill-positioned, rotating electrode or a tip
fold over.

Prospective cohort studies with this electrode involving postoperative
CT-imaging have shown very different results in residual hearing preservation
between the extended eRW and the CO approach. Recent observational data from
the Radboudumc look favorable for the CO, as long as the electrode does not
translocate to the scala vestibuli which in a prospective cohort study occurred
relatively often and proximal in the basal turn. Anecdotally, several
colleagues report the observation of immediate loss of residual hearing with
the CI632 using the eRW approach. Sofar, the only explanation for short-term
postoperative decline in threshold measured is the negative effect of
stiffening of the RW membrane creating a cochlear conductive hearing loss.

Although we now have electrocochleography (ECochG) measurements available to
suspect imminent damage occurring on insertion which could potentially prevent
distal damage and translocation of the electrode, it has not yet been used to
monitor what happens to the hearing during the insertion of the sheath. ECochG
refers to the recording of electrical potentials generated by hair cells and
auditory nerve in response to acoustic stimuli. ECochG can provide feedback
about the cochlear structures during electrode insertion, based on which the
surgeon can adapt the insertion to potentially reduce trauma. In addition,
ECochG can shed light on which aspects of cochlear implant surgery are
detrimental for hearing preservation.

The aim of this study is to investigate whether the type of surgical approach
to the cochlea; CO or eRW using the Nucleus 632 with the Slim Modiolar
electrode affects the final residual hearing and secondarily, intracochlear
trauma and electrode position.

Primary: To determine whether the surgical approach during implantation of the
CI632 electrode affects residual hearing at 3 months post-implantation.

Secondary:
• To determine whether the surgical approach affects residual hearing when
assessed at 1 week and 12 months post-implantation.
• To determine the stage of surgery at which the cochlear function is
compromised, as measured by electrocochleography.
• To determine whether the surgical approach affects the intracochlear
positioning of the electrode, as determined by pre- and postoperative
CT-imaging.

Exploratory: To determine whether the surgical approach affects impedances and
(e)CAPS at 6 weeks, 3 months, and 12 months post-implantation.

This is a prospective, randomized control trial, in adult patients recommended
cochlear implantation with Cochlear*s CI632 electrode. Participants will be
randomized to one of two surgical approaches: extended round window or
cochleostomy, with a 1:1 allocation in a parallel design.

Participants will be randomized to one of two surgical approaches: extended
round window or cochleostomy.

There are only minor additional risks to participation in this randomized
clinical trial.
The implantation of the CI is a standard hospital procedure and the CI will be
used within its licensed indication. Risks associated with the implant are
detailed in product information available on the manufacturer*s website (see
www.cochlear.com for company website).

In this study participants will be randomly assigned to undergo one of two
surgical approaches for cochlear implantation: the extended round window or
cochleostomy. We will use an equal 1:1 allocation rate. Both surgical
approaches represent standard care, ensuring that no additional risks will be
introduced to the participants. The trial will be performed in a multicenter
setting which may pose additional risk. However, as the sponsor we will ensure
to have sufficient oversight of execution at the three participating centers
which are internationally renowned implantation centers.

Moreover, one of the secondary objectives of this trial is to determine the
stage of surgery at which the cochlear function is compromised, by means of
electrocochleography. This ECochG measurement is CE marked. The surgeon will
conduct the surgical procedure as per standard clinical practice, however, the
ECochG measurement will take place intraoperatively. Intra-operative testing
may prolong the surgical time. It is anticipated that the additional time
required to conduct the intra-operative measurements will be no more than 30
minutes. This extension in the surgery duration may entail additional risks,
such as those related to prolonged anesthesia and an increased risk of
infection. These potential side effects are of moderate nature. The surgeon
will use his/her discretion as to the acceptable extension to the operating
time for each individual, and will terminate use of the ECochG tool as needed.
All supplied equipment belonging to the ECochG measurement is non-sterile.
There is potential for non-sterile equipment to enter the sterile surgical
field. In order to mitigate this potential risk, all investigational sites must
ensure the following non-sterile equipment is placed in a sterile bag(s):
Freedom processor, RF coil and programming cable. The following non-sterile
equipment must be isolated from the sterile field using the best surgical
practices of the hospital performing the surgery: insert earphone foam tip and
tubing.

Finally, the participant will encounter a small amount of burden due to the
additional time required for one extra follow-up visit and the supplementary
measurements conducted during this visit.

We are confident that this study represents negligible risks to subjects who
consent to participate in this study.

As has been rationalized in the above section, study related risks are
appropriately mitigated and reduced to acceptably low levels. Most of the
clinical trial procedures align with standard care practices. The use of
intraoperative ECochG measurements are CE-marked, and the additional surgical
time required presents a negligible risk. Consequently, it is concluded that
participation in this study and involvement in the intended study procedures
pose no additional risks to the study subjects, ensuring their safety
throughout the research.