ABSTRACT
Objective(s)
Robotic‐assisted electrode array (EA) insertion is a promising technique that may enhance hearing preservation in cochlear implant (CI) surgery. The purpose of our study is to understand the extent to which robotic‐assisted EA insertion improves hearing preservation.
Methods
Twenty‐four adult patients underwent CI surgery with manual EA insertion and 27 adult patients underwent CI surgery with robotic‐assisted EA insertion using the iotaSOFT system. The EAs used included the Flex 20/24/26. The primary outcome variable was low frequency pure‐tone average (LFPTA), defined as mean audiometric threshold at 125, 250, and 500 Hz. This was measured preoperatively, at initial activation (within 4 weeks of surgery), and subsequently at 2 weeks, 3 months, 6 months, and 1 year. Functional acoustic hearing was defined as LFPTA < 80 dB HL.
Results
Seventeen out of 24 patients (71%) in the manual insertion group and 23 out of 27 patients (85%) in the robotic‐assisted EA insertion group had preserved functional acoustic hearing (< 80 dB HL) up till 1 year (Fisher's exact test (two‐tailed) is not statistically significant, p = 0.31). The number needed to treat with robotic‐assisted EA insertion to prevent one additional negative outcome of loss of functional acoustic hearing would be 7 (1/0.14).
Conclusion
Robotic‐assisted EA insertion is associated with improved hearing preservation over 1 year compared with manual insertion. Hearing preservation leads to improved outcomes and therefore every effort should be made to preserve the delicate structure and function of the cochlea during EA insertion. Robotic‐assisted EA insertion advances that objective.
Level of Evidence: III (cohort study).
Keywords: cochlear implant, hearing preservation, robotic‐assisted insertion
The purpose of our study is to understand the extent to which robotic‐assisted electrode array (EA) insertion improves hearing preservation. Our results show that robotic‐assisted EA insertion is associated with improved hearing preservation over 1 year compared with manual insertion. Hearing preservation leads to improved outcomes and therefore every effort should be made to preserve the delicate structure and function of the cochlea during EA insertion—robotic‐assisted EA insertion advances that objective.
1. Introduction
Cochlear implants (CI) are the predominant intervention for treating patients with severe to profound sensory hearing loss. Despite improvements in CI technology and sound processing strategies, hearing performance has largely plateaued [1, 2, 3, 4]. Successful hearing preservation surgery, whereby surgeons aim to limit surgical trauma and preserve the delicate intracochlear tissues during insertion of the electrode array (EA), has emerged to be a significant factor leading to improved outcomes in cochlear implant recipients. The maintenance of acoustic hearing post CI surgery dramatically improves outcomes, especially with complex listening tasks such as hearing in noise, music appreciation, sound quality, quality of life, and sound localization [5, 6, 7, 8, 9, 10]. Given the dramatic benefit that preservation of residual acoustic hearing provides for CI recipients, every effort should be made to preserve the delicate structure and function of the cochlea.
Hearing loss immediately after CI is often attributed to acute insertion trauma. However, following successful initial hearing preservation, some patients suffer a delayed (e.g., months to years later) loss of residual hearing [11, 12], which is associated with increased electrode impedances. It has been postulated that acute insertional trauma that is not severe enough to cause peri‐operative hearing loss may still be one contributing factor that initiates a cascade of tissue remodeling and cochlear inflammation, leading to delayed hearing loss. A critical component of hearing preservation surgery is therefore to minimize the acute insertion trauma to the delicate intracochlear tissues associated with the insertion of an electrode array (EA). An important strategy to minimize acute insertion trauma, and consequently preserve residual acoustic hearing, is optimizing “soft” surgical techniques to insert the EA [13]. Other patient and procedural factors that likely impact hearing preservation outcomes include cochlear volume, cochlear coverage, optimizing the design of the EA that is being inserted, opening of the round window, and the direction in which the array is inserted.
Despite careful manual insertion “soft surgery” techniques, there are inherent limitations in human kinetics that prevent reliable and consistent reduction of acute insertion trauma during EA insertion [14, 15, 16]. The minimum force required to damage cochlear tissue lies below the threshold of human perception, thus manual insertion cannot be sustained at a speed that minimizes cochlear damage. Following this human‐factor limitations, 50% of hearing preservation CI recipients experience loss of greater than 10 dB, and 10%–> 50% lose functional residual function [7, 17, 18, 19, 20, 21, 22, 23].
Robotic‐assisted EA insertion is a promising technique that may enhance hearing preservation CI surgery [24, 25]. Robotic‐assisted EA insertion allows for a controlled, slow, and steady insertion. It is associated with decreased insertion force, decreased intracochlear pressure spikes, and decreased cochlear trauma [16]. Following the hypothesis that decreased insertion trauma may mitigate cochlear inflammation, decreased electrode impedances (a biomarker of cochlear fibrosis) are seen after robotics‐associated EA insertion [26, 27].
The purpose of our study is to understand the extent to which robotic‐assisted EA insertion is associated with preservation of functional acoustic hearing after CI compared with manual insertion. Functional acoustic hearing is defined as low frequency pure‐tone average (LFPTA) (125, 250, 500 Hz) < 80 dB HL [28]. We will specifically be evaluating the iotaSOFT (iotaMotion Inc., USA) robotic‐assisted EA insertion system, whose clinical utility and safety have been previously demonstrated as part of the first human trial of a single‐use robotic‐assisted surgical device for CI EA insertion [18]. We hypothesize that the group of patients who undergo robotic‐assisted EA insertion will have a higher rate of functional hearing preservation.
2. Materials and Methods
2.1. Study Population
The study was conducted according to the guidelines for the protection of human subjects as set forth by the Institutional Review Board (IRB) at the University of Iowa. Fifty‐one adult patients, including 24 with manual EA insertions (control group) and 27 with robotic‐assisted EA (experimental group), meeting Food and Drug Administration criteria for CI were included in this study. All patients had intact low‐frequency acoustic hearing, defined as thresholds of 60 dB HL or less averaged across 125, 250, and 500 Hz. All patients underwent CI surgeries at a single institution. Three faculty neurotologists performed the CI surgeries.
Twenty‐four adult patients underwent CI surgery with manual EA insertion over the course of June 2015 to February 2022. Twenty‐seven adult patients underwent CI surgery with robotic‐assisted EA insertion typically coupled with intraoperative ECochG monitoring over the course of January 2021 to March 2024. The EAs used in this study included the Flex 20/24/26 (MED‐EL Corp., Durham, NC). Electrode selection was done by individual surgeons on a case‐by‐case basis. For 20 out of the 27 subjects in the robotic‐assisted cohort, OTOPLAN (MED‐EL Corp., Durham, NC) image analysis software was used in pre‐operative planning. All surgeons completed manufacturer‐recommended presurgical device training with the iotaSOFT system.
Table 1 displays baseline characteristics for each group. In the manual EA insertion group, mean age was 70.71 years (±2.57), 63% were male, and the most common etiology of hearing loss was idiopathic (54%) followed by noise exposure (17%) and genetic/familial (17%). In the robotic‐assisted EA insertion group, mean age was 61.08 years (±3.36), 59% were male, and the most common etiology of hearing loss was idiopathic (49%) followed by noise exposure (22%). Table 2 displays procedural characteristics. Out of the 24 patients in the manual EA insertion group, nine received a Flex 20 CI (37.5%) and 15 received a Flex 24 CI (62.5%). Out of the 27 patients in the robotic‐assisted EA insertion group, six received a Flex 20 CI (22%), 16 received a Flex 24 CI (59%), and five received a Flex 26 CI (19%).
TABLE 1.
Baseline characteristics of study population.
| Baseline variable | Control (N = 24) (%) | Robotic (N = 27) (%) |
|---|---|---|
| Age at surgery (mean ± SE) | 70.71 (Std error: 2.57) | 61.08 (Std error: 3.36) |
| Sex | ||
| Male | 63% | 59% |
| Female | 37% | 41% |
| Etiology of hearing loss | ||
| Idiopathic | 54% | 49% |
| Noise exposure | 17% | 22% |
| Genetic/Familial | 17% | 26% |
| Viral | 4% | |
| Trauma | 4% | 3% |
| Syndrome | 4% | |
TABLE 2.
Procedural characteristics of study population.
| Baseline variable | Control (N = 24), n (%) | Robotic (N = 27), n (%) |
|---|---|---|
| CI arrays | ||
| Flex 20 | 9 (37.5%) | 6 (22%) |
| Flex 24 | 15 (62.5%) | 16 (59%) |
| Flex 26 | 0 (0) | 5 (19%) |
2.2. Robotic‐Assisted Insertion
The combination of robotic‐assisted EA insertion and intraoperative electrocochleography protocol has been previously described by our institution [22]. Briefly, the robotic‐assisted EA insertion procedure begins with a conventional postauricular approach with mastoidectomy and posterior tympanotomy to gain access to the round window. The iotaSOFT Insertion System (iotaMotion Inc., Iowa City, IA), a single‐use robotic‐assisted insertion system, is used to advance the electrode array (EA) near the round window membrane. After the opening of the round window membrane, the EA can be advanced/retracted at a speed set between 0.1 and 1 mm/s at 0.1 mm/s intervals, stopped, or reversed. The EA is advanced, typically at 0.2 mm/s, while monitoring with electrocochleography (ECochG).
2.3. Audiometric Data and Follow‐Up
The primary outcome variable was low frequency pure‐tone average (LFPTA), defined as mean audiometric threshold at 125, 250, and 500 Hz. This was measured preoperatively, at initial activation (within 4 weeks of surgery), and at subsequent programming visits (after initial activation at 2 weeks, 3 months, 6 months, and 1 year). Functional acoustic hearing was defined as LFPTA < 80 dB HL. While some individuals with hearing loss thresholds poorer than 80 dB HL may be aidable, the amplification characteristics used in current combined acoustic and electric speech processors to meet real‐ear prescriptive targets are more limited with hearing losses with LFPTAs poorer than 80 dB HL.
2.4. Speech Perception Testing
The primary speech perception measures were two subtests from the minimum speech test battery: consonant‐nucleus‐consonant (CNC) words and Arizona Biomedical (AzBio) sentences [29]. Participants were tested in their everyday listening condition (e.g., use of both ears with the assistive technology used in everyday life). CNC words were tested in quiet while AzBio were tested with a +5 dB signal‐to‐noise ratio (SNR). These tests were administered preoperatively and at 3 months, 6 months, and 1 year. Due to COVID‐19 restrictions during the study time period and due to time restrictions during clinical visits, some participants are missing data at intervening time points. As a result, we have shown preoperative scores and the most recent postoperative score.
3. Results
3.1. Audiometric Data
Audiometric data were collected preoperatively, at initial activation (within 4 weeks of surgery), and at subsequent programming visits (after initial activation at 2 weeks, 3 months, 6 months, and 1 year). All 24 patients in the manual insertion group and all 27 patients in the robotic‐assisted insertion group have data up to and including the 1‐year time point.
Figure 1a,b, display the LFPTA of all the patients in the manual‐insertion and robotic‐assisted insertion groups, respectively. As shown in Figure 1a, seven out of 24 patients in the manual‐insertion group lost functional acoustic hearing (i.e., ≥ 80 dB HL) over the postoperative course up till 1 year. As shown in Figure 1b, four out of 27 patients in the robotic‐assisted EA insertion lost functional acoustic hearing (i.e., ≥ 80 dB HL) over the postoperative course up till 1 year. This results in hearing preservation rates of 71% and 85% in the manual and robotic‐assisted EA insertion CI surgeries, respectively. Despite a 14% difference in hearing preservation rates across groups, Fisher's exact test (two‐tailed) is not statistically significant (p = 0.31). Of the seven subjects who lost functional hearing in the manual‐insertion group, four lost functional hearing at initial activation and one each at 3 months, 6 months, and 12 months (mean: 3 months, 95% confidence interval: 0–7.2 months). In comparison, all four subjects who lost functional hearing in the robotic‐assisted group lost it at initial activation (mean: 0 months). Of the seven subjects who lost hearing in the manual‐insertion group, three had Flex 20 and four had Flex 24 EAs. Of the four subjects in the robotic‐assisted group who lost hearing, three had Flex 24 and one had Flex 26.
FIGURE 1.
Hearing preservation in (A) 24 patients with manual insertion and (B) 27 patients with robotic‐assisted insertion. 0a—initial activation. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]
The number needed to treat (NNT) is a mathematical measure that reflects how many subjects need to be treated with a particular intervention for one person to benefit from it compared to a control group. It is calculated by dividing 1 by the absolute risk difference. The absolute risk difference of hearing loss between the two techniques is 0.14 (0.29–0.15). Accordingly, the NNT with robotic‐assisted EA insertion to prevent one additional negative outcome of loss of functional acoustic hearing would be 7 (1/0.14).
Figure 2 displays the changes in LFPTA between (1) preoperative and initial activation and (2) preoperative and 1 year time points for 24 patients with manual insertion (Figure 2a) and in 27 patients with robotic‐assisted insertion (Figure 2b). At initial activation, the mean change in LFPTA is 24 dB (95% CI: 17–30 dB) for the manual group and 25 dB (95% CI: 20–31 dB) for the robotics group, which do not significantly differ (Welch's t‐test, p = 0.77). At 1 year, the group mean LFPTA changes relative to pre‐operative values are 25 (95% CI: 16–35 dB) and 21 dB (95% CI: 15–27 dB), respectively (Welch's t‐test, p = 0.46).
FIGURE 2.
Changes in LFPTA between (1) preoperative and initial activation and (2) preoperative and 1 year time points in (A) 24 patients with manual insertion and (B) 27 patients with robotic‐assisted insertion. 0a—initial activation. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]
In a multivariable logistic regression model, study cohort (odds ratio (OR): 0.52, 95% confidence interval (CI): 0.10–2.37, p‐value: 0.40), age (OR: 1.07, 95% CI: 1.01–1.17, p‐value: 0.07), and preoperative hearing thresholds (OR: 0.99, 95% CI: 0.92–1.05, p‐value: 0.66) were not found to be significant predictors of functional residual hearing.
3.2. Speech Perception Scores
Speech perception scores are presented for the manual and robotic‐assisted EA insertion groups in Figure 3 (CNC) and Figure 4 (AzBio +5 dB SNR). Speech perception scores were tested at variable time points postoperatively as determined by clinical needs. Patients with single‐sided deafness (SSD) were not included in this comparison due to ceiling effects pre‐ and postoperatively in their everyday listening condition that included a normal or near‐normal contralateral ear.
FIGURE 3.
CNC speech perception scores in (A) 17 patients with manual insertion and (B) 20 patients with robotic‐assisted insertion. Black solid (preserved acoustic hearing, increased CNC). Black dashed (preserved acoustic hearing, decreased CNC). Red solid (loss of acoustic hearing, increased CNC). Red dashed (loss of acoustic hearing, decreased CNC). [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]
FIGURE 4.
AzBio speech perception scores in (A) 11 patients with manual insertion and (B) 18 patients with robotic‐assisted insertion. The legend is the same as in Figure 3. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]
As shown in Figure 3a, of the 24 patients in the manual insertion group, CNC scores were considered for a subset of 17. Of the 17, three had loss of residual hearing while 14 had preserved hearing. Of the three who had loss of residual hearing, none had a decrease in CNC scores between preoperative testing and most recent testing up to 1 year. Of the 14 with preserved hearing, two had a decrease in CNC (5% and 9%). As shown in Figure 4a, of the 24 patients in the manual insertion group, AzBio scores were considered for a subset of 11. Of the 11, two had loss of residual hearing while nine had preserved hearing. Of the two who had loss of residual hearing, both had a decrease in AzBio scores between preoperative testing and most recent testing up to 1 year (1% and 16%). Of the nine with preserved hearing, one had a decrease in AzBio scores (11%).
As shown in Figure 3b, of the 27 total patients with robotic‐assisted insertion, CNC scores were considered for a subset of 20. Five of those not shown are SSD. Of the 20, three had loss of residual hearing while 17 had preserved hearing. Of the three who had loss of residual hearing, one had a decrease in CNC between preoperative testing and most recent testing up till 1 year (12%). Of the 17 with preserved hearing, one had a decrease in CNC (8%). As shown in Figure 4b, of the 27 total patients in the robotic‐assisted EA insertion group, AzBio scores were considered for a subset of 18. Of the 18, two had loss of residual acoustic hearing and 16 had preserved hearing. Of the two with loss of hearing, one had a decrease in AzBio scores between preoperative testing and most recent testing up till 1 year (18%). Of the 16 with preserved hearing, one had a decrease in AzBio scores (2%).
Neither raw post‐operative speech perception scores nor changes compared to pre‐operative scores differed across groups (Table 3; Welch's t‐test, p > 0.05).
TABLE 3.
Comparison of post‐operative speech perception outcomes across groups.
| Control | Robotic | |
|---|---|---|
| Post‐op CNC (N = 17 vs. 20) | 65% (SD: 26%) | 69% (SD: 19%) |
| Changes in CNC (post‐vs. pre‐op) | 23% (SD: 21%) | 20% (SD: 15%) |
| Post‐op AzBio +5SNR (N = 11 vs. 18) | 49% (SD: 28%) | 60% (SD: 27%) |
| Changes in AzBio +5SNR (post‐ vs. pre‐op) | 12% (SD: 22%) | 25% (SD: 23%) |
Note: None of the group differences were statistically significant (Welch's t‐test, p > 0.05).
Lastly, of the 17 subjects with preserved hearing in the manual insertion group, 16 (94%) were using an electric‐acoustic sound processor at the one‐year time point. Of the 23 subjects with preserved hearing in the robotic‐assisted insertion group, 21 (91%) were using an electric‐acoustic sound processor at the one‐year time point.
4. Discussion
Robotic‐assisted insertion was associated with a clinically meaningful, but not statistically significant, trend towards improved hearing preservation with more stable thresholds over 1 year compared with manual insertion in surgeries done by the same surgeons using similar electrode arrays. Five of the robotics‐assisted EA patients received the longer Flex 26 EAs compared with none in the manual group, so it is possible that these results are slightly biased against robotic assistance. Furthermore, when outcomes are stratified by EA type, it is noteworthy that three of the seven control subjects who lost hearing had the shorter Flex 20 EA, while none of the patients in the robotic‐assisted group with the shorter Flex 20 EA lost hearing. Nevertheless, our study shows the rate of functional hearing preservation to be 85% with robotic‐assisted EA insertion and 71% with manual insertion, a difference of 14%. While this difference does not reach statistical significance, this is likely due to the overall low numbers of patients and the relatively high hearing preservation rate in the manually inserted EAs. In comparison, previously published rates of hearing preservation (defined as PTA shifts ≤ 15) at 1 year postoperatively for Flex 20 and Flex 24 EAs were 48.8% and 50%, respectively [30]. These results are similar to those obtained using the RobOtol robotic‐assisted insertion system, which showed a better hearing preservation rate in the robotics‐assisted group by 12% [26]. The timing of hearing loss in each group is noteworthy. For the manual insertion group, three patients lost functional acoustic hearing between 3 months and 1 year, while the robotic‐assisted group did not have any patients lose functional acoustic hearing after initial activation. The data reported here also highlight the importance of hearing preservation for difficult listening tasks. Those patients in both groups who retained functional acoustic hearing tended to perform better in AzBio scores in +5 dB SNR background noise compared with those that lost functional acoustic hearing. Correlated with this observation and the higher hearing preservation rate for robotic assistance, there was a trend for patients with robotic‐assisted EA insertion to perform better on the AzBio +5SNR speech task compared with manual insertion (60% vs. 49%, respectively).
The increased rate of hearing preservation in robotic‐assisted EA insertion can be attributed to reduced acute insertion trauma associated with robotic‐assisted EA insertion. The reduced acute insertion trauma is likely due to the advantages of robotic‐assisted EA insertion, which include steadier and slower insertions, decreased insertion forces, and reduced spikes in intracochlear pressure [16]. Additionally, robotic‐assisted insertion facilitates use of intraoperative ECochG monitoring, allowing real‐time feedback to the surgeon based on intraoperative measurement of cochlear electrophysiological activity [22]. When considering clinical application, it is important to note that surgeon and surgical technique matter to optimize the advantages of robotic‐assisted EA insertion. The surgeon must understand how to use the robotic‐assisted technology correctly and appropriately incorporate ECochG feedback. Critical steps of the surgical technique include release of the CI from the robotic drive head and securing the CI device after release from the robotic drive head to help prevent migration out of the cochlea.
Limitations of this study include retrospective design, although the data were collected prospectively. Additionally, patients have different times of follow‐up. However, the comparisons we have shown are all done at a similar time. Further research could involve a randomized controlled trial and, therefore, prospective collection of data. Additionally, analysis of other types of CIs from different manufacturers should also be done in the future. And finally, we have only evaluated the iotaSOFT Insertion System in this study. There are other robotic‐assisted insertion systems under development and testing, for example RobOtol and OTODRIVE, as well as a system (HEARO) that provides robotic cochlear access but requires manual implantation of the electrode array [31, 32, 33]. Although the benefits of robotic‐assisted insertion should theoretically apply to those systems designed to provide a slow and steady EA insertion, the actual effectiveness of these individual systems in improving cochlear implant outcomes should be evaluated separately.
Despite improvements in CI technology and sound processing strategies, hearing performance has largely plateaued. Hearing preservation is the most significant factor leading to improved outcomes. Robotic‐assisted EA insertion enhances structure and functional preservation—our results show the rate of hearing preservation to be 85% with robotic‐assisted insertion and 71% with manual insertion. Additionally, based on this relatively small dataset, the number needed to treat with robotic‐assisted EA insertion to prevent one additional negative outcome of loss of functional acoustic hearing would be 7. Our results show improved hearing preservation and support further development of robotic‐assistance technologies, particularly efforts to integrate the control mechanisms afforded by robotics with complementary technologies such as preoperative imaging and intraoperative ECochG. Given the dramatic impact of preservation of both the structural and functional elements of the cochlea on CI outcomes, every effort should be made to preserve the delicate structure and function of the cochlea both for ears with functional acoustic hearing and for ears with more severe hearing loss. Robotic‐assisted EA insertion is an advance in this objective. Once surgeons are properly trained, robotic‐assisted EA insertion also democratizes the most critical step in CI surgery—it enables similar insertion profiles across centers and surgeon experience. It can therefore help lead to the goal where most patients across all centers are able to preserve functional acoustic hearing.
5. Conclusion
Robotic‐assisted EA insertion is associated with improved hearing preservation over 1 year compared with manual insertion. Hearing preservation leads to improved outcomes, and therefore every effort should be made to preserve the delicate structure and function of the cochlea during EA insertion. Robotic‐assisted EA insertion represents a new technology that can enhance these imperatives.
Conflicts of Interest
C.C.D. serves as a consultant for Cochlear Corporation and iotaMotion Inc. R.A.S. serves as a consultant for iotaMotion Inc. B.J.G. serves as a consultant for Cochlear Corporation and iotaMotion Inc. M.R.H. is the co‐founder and chief medical officer of iotaMotion Inc. with an equity interest. The other authors declare no conflicts of interest.
Acknowledgments
This work was supported by NIH NIDCD P50‐DC000242, NIH NIDCD T32‐DC000040‐29 grants.
Khan U. A., Dunn C. C., Scheperle R. A., et al., “Robotic‐Assisted Electrode Array Insertion Improves Rates of Hearing Preservation,” The Laryngoscope 135, no. 11 (2025): 4364–4371, 10.1002/lary.32318.
Funding: This work was supported by NIH NIDCD P50‐DC000242, NIH NIDCD T32‐DC000040‐29 grants.
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.