PONE-D-22-13880Accessing the stapedius muscle via novel surgical retrofacial approach during cochlear implantation surgery: intraoperative results on feasibility and safetyPLOS ONE

Dear Dr. Guntinas-Lichius,

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Additional Editor Comments:

Reviewers all presented with different opinions from rejection to minor revision. This paper is interesting ans presents an innovating and interesting surgical approach that could be beneficial for cochlear implant fittings. We suggest to accept with Major Revisions after authors properly adress the reviewers comments.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: N/A

Reviewer #3: No

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors investigated and compared the feasibility, reproducibility, and safety of two surgical approaches in cochlear implant surgery. The main aim of the study is to evaluate the stapedius muscle (SM) more objectively, via direct measurement from the muscle itself. With this hypothesis pre and retrofacial routes have been studied. Additionally, an image processing-based surgical planning tool in pre-surgical assessment was also investigated.

Virtual 3D reconstruction of the temporal bone has been used lately especially in the robotic cochlear implantation and also for resident training programmes.

The article, in general, is well written with very few grammatical errors.

In the methodology, the authors should specify the inclusion and exclusion criteria of the participants.

The main point of the discussion should focus on the benefit of SRT measurements directly form SM. The authors did not clarify this issue. Are there any investigations comparing the outcomes of traditional SRT mesurements with the direct SM SRT measurements on the CI fittings and tuning?

Although retrofacial approach can be used in selected CI cases, the rationale on choosing this approach should be more clarified. Maybe a preliminary evaluation on the benefits of SRT measurements directly from SM will make this study more understandle and clear.

Reviewer #2: This study report the safety of a new indication of the retrofacial approach to expose the stapedius muscle body. The goal of the study is to allow the stapedius reflex electrically evoqued in the context of cochlear implantation and fittings.

Even though the retrofacial approach can be used for other indication, the goal of the approach in this study is original.

I would like to discuss a few points with the authors in order to rise the interest of the paper:

- Introduction: ok

- Material and methods

1) How long did the segmentation and the surgical planning take to perform?

2) You describe an optimal head orientation, how could reach the correct orientation in the operating room?

3) Wich facial nerve monitoring did you use?

4) What was the additional duration added to the surgery once the learning curve of stapedius muscle exposure was achieved?

- Results

1) You extracted many interesting metrics from the surgical planning tool (table 2 and 3)? Could you compare these simulated metrics with real intra operative measurements or measurements on postoperative ct scans?

2) Did you test the eSRT in late postoperative and was it preserved? (Did exposure of the body muscle induced fibrosis that could impair the reflex long term preservation?)

- Discussion :

1) The main point of the article that is not discussed is why the electrical measurement of eSRT would be better than a visual assessment such as describe by Weiss et al (Weiss BG, Söchting F, Bertlich M, Busch M, Blum J, Ihler F, Canis M. An Objective Method to Determine the Electrically Evoked Stapedius Reflex Threshold During Cochlea Implantation. Otol Neurotol. 2018 Jan;39(1):e5-e11.)

Considering the risk for the facial nerve in non expert surgeons, would a video assessment yield to the same information? Was is the added value of an electrical measurement? The authors need to justify this comment to understand the goal of their study.

2) You tested this new approach in adults only in this study. Do you expect more difficulties to perform such an approach in pediatric cases?

3) Would you consider the use of a 30° endoscope to better expose the stapedius muscle body through an anterior approach?

-Conclusion :ok

-Figures : ok

Reviewer #3: This article presents a possible new approach to assessing the likely maximal stimulation levels that will be possible for people who will receive a cochlear implant. Cochlear implants enable otherwise profoundly deaf people to hear, they are typically very successful. Unlike many implants they are used across the lifespan with infants (18mo or less) through to older adults (90+ years) being eligible and gaining good hearing benefit. As more people, globally, receive implants there is a need to improve and enhance aspects of the assessment of the implants. Loudness of sounds delivered by an implant can be increased by changing the current release at the electrodes which are deep within the temporal bone in the cochlea. A limit to what can be achieved regarding loudness is affected by the point at which the amount of current being released in the cochlea starts to stimulate other major nerves including the facial nerve, due to unwanted current spread. The current assessment of the maximum stimulation is done by subjective reporting by the patient - in response to programming changes of the implant in the clinic. This is therefore hard to reliably evaluate in young children, people of all ages with complex needs and adults who may have cognitive decline. An alternative objective measurement would be valuable in improving patient outcomes. A single intraoperative test may also reduce follow up clinic time enabling greater capacity in clinics and lower burden on follow-ups for patients.

This paper builds on findings of previous work from the authors where surgical imaging and access to the stapedial muscle in a study of temporal bones enabled the identification of anatomical landmarks to support the choice of surgical access route to expose the belly of the stapedial muscle. This paper reports on reliable access to the belly of the muscle in a small cohort of people undergoing cochlear implantation. The value of this is that once accessed it may be possible to reliably measure the stimulation thresholds of this muscle, in-situ, during the surgical work-up for implantation. This would give objective data that could be used to predict the maximal likely tolerable stimulation levels that can be programmed into the cochlear implant, reducing the likelihood of discomfort and possible device under-use by patients. The paper also highlights the potential value of of using 3D reconstructive imaging during surgery, using a protocol that has not yet been fully validated - but that could improve outcomes if an algorithm can be developed from the landmark information recorded from the imaging.

The study is small - and the group sizes for the surgical approaches are therefore very small, this makes the statistical analysis indicative rather than absolute (hence the no for statistical reliability question). Based on the pilot data include a power calculation to determine the minimum group sizes likely to be needed for reliable analysis and data.

The approach reports reliable exposure of the belly of the stapedial muscle - however there is no report of the electrical stimulation or measurement of the stapedial responses. At a minimum the authors should consider describing the approach that will be used to make the measurement and to compare them with the current measures.

The patient cohort is not well described, basic audiological and outcome with the cochlear implant data for the cohort should be reported and compared with an appropriate control group that did not include exposure of the SM in the surgical protocol to ensure that outcomes are with the expected range despite the additional/alternative surgical approach.

Finally children are one of the likely groups where this may be of large benefit, while the direct lack of inclusion of children in the study is appropriate from an ethical point of view - comment on the imaging methods needed for the 3D reconstruction (X-ray doses) and the likelihood of being able to apply the landmark algorithm (once developed) in this population.

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

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Accessing the stapedius muscle via novel surgical retrofacial approach during cochlear implantation surgery: intraoperative results on feasibility and safety

PONE-D-22-13880R1

Dear Dr. Guntinas-Lichius,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Adrien A. Eshraghi, M.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: All comments have been addressed

Reviewer #3: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: Yes

Reviewer #3: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

Reviewer #3: N/A

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: Yes

Reviewer #3: Yes

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #2: Yes

Reviewer #3: Yes

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #2: all comments have been adresssed.

Reviewer #3: The authors have addressed the issues raised and the manuscript has been improved with key points clarified.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #2: No

Reviewer #3: Yes: Tracey A Newman

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