Hearing preservation in cochlear implantation: a comprehensive review with emphasis on atraumatic and robot-assisted electrode insertion

Abstract

Background:

Preservation of residual hearing has become a central objective in modern cochlear implantation (CI), enabling electro-acoustic stimulation and improved speech, music, and noise perception. Achieving this goal depends critically on minimizing intracochlear trauma during electrode insertion. Despite atraumatic surgical techniques, a substantial proportion of recipients lose part or all of their residual hearing over time, and manual insertion remains constrained by human motor variability.

Purpose:

This review synthesizes current evidence on the mechanisms of insertion-related cochlear trauma and evaluates surgical, pharmacological and technological strategies for hearing preservation, with particular attention to the role of robot-assisted cochlear implantation surgery (RACIS).

Methods:

A narrative synthesis of experimental, histopathological, and clinical literature addressing atraumatic electrode insertion principles, electrode design, insertion kinematics, perioperative corticosteroids, and robotic insertion systems (including RobOtol, OTODRIVE, and iotaSOFT). PubMed/MEDLINE, Embase and Web of Science were searched from January 1980 to May 2026, with Google Scholar and the reference lists of key articles as supplementary sources. Preclinical data are reported separately from clinical data.

Results:

Insertion-related trauma, including scalar translocation, electrode tip fold-over, and basilar membrane rupture, triggers inflammation, fibrosis, and neo-osteogenesis, compromising both residual hearing and long-term neural survival. Insertion speed and trajectory stability are identified as key modulators of intracochlear force and pressure generation. In cadaveric and in vitro models, robotic systems achieve significantly lower and more reproducible insertion angular errors and force profiles than manual insertion, with higher rates of full scala tympani placement and lower trauma scores. Clinical studies suggest improved hearing preservation (up to 85% vs. 71% following manual insertion in a non-randomized comparative study). Meta-analytic data report an overall RACIS procedural success rate of 97.2% and a complication profile comparable to conventional surgery. Postoperative impedance trends are also more stable, suggesting attenuated fibro-inflammatory remodeling. Pooled hearing preservation estimates, however, show very high statistical heterogeneity (I2 = 98.41%).

Conclusions:

RACIS represents a maturing, reproducible approach to atraumatic cochlear implantation that reduces inter-operator variability and improves the consistency of electrode placement. Integration with real-time intraoperative monitoring, such as electrocochleography, offers further potential for adaptive, personalized insertion strategies. At present, the technical superiority of robotic insertion is better established than its long-term functional benefit. Future randomized controlled studies incorporating long-term functional outcomes, cost-effectiveness and anatomical imaging are required to establish the true clinical benefit of RACIS.

1 Introduction: atraumatic cochlear implant surgery

Since their clinical introduction in the 1980s by William House, cochlear implants (CIs) have revolutionized the treatment of severe-to-profound sensorineural hearing loss. Initially designed for bilaterally deaf children, indications have steadily expanded over recent decades to include adults and patients with significant residual hearing, particularly in low frequencies. This shift has been catalyzed by improved candidacy criteria, technological advancements, and a growing emphasis on preserving native cochlear function.

With current flexible lateral-wall arrays and refined surgical technique, functional low-frequency hearing can be preserved in a majority of adults. A systematic review of medium- and longer-length lateral wall arrays reported high preservation rates across electrode lengths (Van de Heyning P. H. et al., 2022). A prognostic-factor systematic review confirmed wide between-study variability in outcome (Sladen et al., 2025), and a meta-analysis of pediatric implantation found hearing preservation in 78% of ears (Madgar et al., 2025). These figures nevertheless deteriorate with time (Snels et al., 2019), which is precisely why the mechanisms of insertion-related injury deserve detailed examination. The principal clinical studies and syntheses on which this review draws are summarized in Table 1.

Comparisons across studies remain difficult because hearing preservation has been defined inconsistently. Two reporting frameworks are now widely used and should be applied systematically. The HEARRING classification expresses preservation as the proportion of the preoperative dynamic range that is retained, independently of the initial threshold (Skarzynski et al., 2013). The American Academy of Otolaryngology-Head and Neck Surgery minimum reporting standards define residual hearing on the low-frequency pure-tone average at 125–500 Hz and prescribe fixed reporting intervals (Adunka et al., 2018). Throughout this review, reported rates are interpreted in the light of the definition used by each source study.

Throughout this review, atraumatic (or structure-preserving) cochlear implantation is defined operationally. The objective is complete placement of the array within the scala tympani, without disruption of the basilar membrane, the osseous spiral lamina, the spiral ligament or the stria vascularis, and without breach of the endolymphatic compartment. It combines: (i) round window or minimally extended round window access with preservation of the endosteum; (ii) avoidance of bone dust, blood and perilymph suction; (iii) a thin, flexible lateral-wall array; (iv) a slow, continuous insertion along the axis of the basal turn; and (v) perioperative anti-inflammatory therapy. This definition is functional rather than merely descriptive: each component targets one identified mechanism of cochlear injury.

Modern cochlear implantation aims not only to restore auditory input but also to maximize speech perception, enhance musical appreciation, and enable effective electro-acoustic stimulation (EAS) by maintaining residual low-frequency hearing. These goals have stimulated critical changes in both surgical technique and electrode design, with an overarching emphasis on minimizing intracochlear trauma.

The rationale for this emphasis is biological. Electrode insertion can injure the cochlea through four partly independent routes. First, direct mechanical laceration of the basilar membrane, osseous spiral lamina or lateral wall destroys hair cells and disrupts scalar compartmentalization. Second, contact between the array and the lateral wall generates frictional forces whose peaks correlate with histological trauma (De Seta et al., 2017). Third, displacement of perilymph by the advancing array produces intracochlear pressure transients whose peak amplitudes are equivalent to acoustic exposures above 170 dB SPL, a level sufficient to damage sensory cells (Greene et al., 2016; Banakis Hartl et al., 2019). Fourth, injury to the spiral ligament and stria vascularis compromises the endocochlear potential and thus the driving force of transduction.

Each of these events initiates a shared secondary cascade of cytokine release, macrophage recruitment, fibrosis and neo-osteogenesis that unfolds over months and underlies delayed hearing loss (Rahman et al., 2022; Bas et al., 2012; Quesnel et al., 2016). Insertion trauma is therefore not only an immediate mechanical event but the trigger of a chronic biological process (Figure 1).

Figure 1

The clinical relevance of this cascade is well documented. Scalar translocation is associated with poorer speech perception and with loss of low-frequency acoustic hearing (Aschendorff et al., 2007; Skinner et al., 2007; Jwair et al., 2021; O'Connell et al., 2016b). In implanted human temporal bones, the volume of intracochlear new bone correlates negatively with consonant-nucleus-consonant word scores, and neo-osteogenesis in the scala media and scala vestibuli is strongly associated with the severity of insertion trauma (Kamakura and Nadol, 2016). Minimizing trauma is thus a direct determinant of auditory outcome, not a purely anatomical objective.

Current best practices involve slow, controlled insertions using thin, flexible arrays designed to conform to cochlear anatomy. These “soft surgery” techniques aim to avoid injury to delicate structures such as the stria vascularis, the basilar membrane (BM), and surrounding neural tissues (Lehnhardt, 1993). Innovations in electrode design now allow for full insertions, limiting mechanical and inflammatory injury risks (Lenarz et al., 2006).

Despite these refinements, suboptimal insertions remain a challenge. Historically, straight electrodes were inserted through the round window (RW); however, limited visibility, unfavorable anatomy, and early resistance at the modiolus often hindered full insertion. Meta-analytic data from Hoskison et al. reveal a 17.6% overall cochlear trauma rate, with BM elevation and rupture observed in 5.2% of cases. Notably, 84.4% of trauma involved translocation from the scala tympani (ST) to the scala vestibuli (SV), and 5.2% reached grade 4 severity with both SV entry and osseous spiral lamina (OSL) fracture (Hoskison et al., 2017).

Although standardized insertion protocols and robotic assistance may mitigate such risks, key limitations persist. Most studies lack audiometric correlation, rely on cadaveric specimens, and exhibit considerable heterogeneity in electrode design. Moreover, trauma detection is more reliable histologically (28.9%) than radiologically (13.3%), underscoring the limitations of current imaging modalities (Hoskison et al., 2017).

As surgical candidates become increasingly diverse, with varying cochlear anatomies and residual hearing profiles, minimally traumatic, anatomically guided electrode insertion becomes essential. Achieving this requires a synergistic approach combining advanced imaging, intraoperative monitoring, electrode innovation, and individualized surgical planning. The determinants of hearing preservation span patient, device, surgical and pharmacological domains, and are summarised in Figure 2.

Figure 2

The present review is organized accordingly. After describing its methodology, it examines the benefits of preserved residual hearing, the biomechanical principles of atraumatic insertion, pharmacological protection, and the contribution of robot-assisted cochlear implantation surgery (RACIS). It then addresses adjacent questions—vestibular preservation, pediatric implantation, revision surgery, imaging and cost—before outlining future directions.

2 Methods

This article is a narrative review structured with reference to the domains of the Scale for the Assessment of Narrative Review Articles (SANRA) (Baethge et al., 2019). It was not registered as a systematic review and does not claim the exhaustiveness of one; the search strategy is reported so that readers can judge its coverage.

2.1 Information sources and search strategy

PubMed/MEDLINE, Embase and Web of Science were searched from 1 January 1980 to 31 May 2026. The search period was extended back to 1980 to ensure identification of seminal publications that established the principles of hearing preservation and atraumatic cochlear implant surgery.

Google Scholar was used as a supplementary source, to identify records not retrieved by the primary databases. The reference lists of relevant reviews and key articles were examined for the same purpose.

The search combined the following terms, adapted to the syntax of each database, using Boolean operators and MeSH terms where available: (“cochlear implantation” OR “cochlear implant”) AND (“hearing preservation” OR “residual hearing” OR “electric-acoustic stimulation” OR “partial deafness”) AND (“insertion trauma” OR “scalar translocation” OR “insertion force” OR “insertion speed” OR “intracochlear pressure” OR “electrode array” OR “round window” OR “cochleostomy” OR “robot-assisted” OR “robotic” OR “electrocochleography” OR “impedance” OR “fibrosis” OR “corticosteroid” OR “dexamethasone”).

Given the broad scope of the review, complementary topic-specific searches were also performed. Cochlear implantation terms were combined in turn with terms relating to electrode design and insertion depth; surgical approach; insertion mechanics and intracochlear pressure; robot-assisted insertion; intraoperative electrophysiological monitoring; intracochlear tissue response; and pharmacological strategies for hearing preservation.

2.2 Eligibility criteria

Records were eligible if they were published in English or French and reported original data or a synthesis relevant to hearing preservation, intracochlear trauma, electrode design, insertion kinematics, robotic insertion, intraoperative monitoring or intracochlear pharmacotherapy in cochlear implantation. Human clinical studies, human temporal bone and cadaveric studies, animal models, in vitro and computational models, systematic reviews and meta-analyses were all eligible, and are reported separately.

Records were excluded if they were conference abstracts without a full text, case reports of fewer than two subjects (except where they described a first-in-human use of a device), editorials and commentaries without original data, or non-peer-reviewed manufacturer material. Papers published before 1990 were retained only when they established a concept of continuing relevance, such as the original description of soft surgery (Lehnhardt, 1993).

Because of the narrative nature and historical scope of the review, seminal publications were retained when necessary to document the development of concepts that remain relevant to contemporary hearing-preservation cochlear implant surgery.

2.3 Screening and appraisal

Records identified through the database and supplementary searches were assessed for relevance to the predefined topics of the review. Potentially relevant publications were evaluated in full text, with particular attention to their methodological quality, clinical or experimental context, and contribution to the understanding of hearing preservation and intracochlear trauma. Given the narrative design of the review, study selection was not intended to constitute an exhaustive systematic screening process.

Given the broad scope of the review and the substantial heterogeneity in study designs, experimental models, interventions, outcome definitions and follow-up periods, quantitative pooling was not considered appropriate; therefore, no formal meta-analysis or pooled estimates were performed.

Two conventions are used throughout. First, preclinical findings (animal, cadaveric, in vitro, computational) are explicitly identified as such and are never presented as clinical evidence. Second, statements are graded verbally: “demonstrated” is reserved for findings replicated in controlled clinical studies or meta-analyses, “suggested” for consistent but uncontrolled clinical observations, and “hypothesized” for mechanistic inferences derived from preclinical data.

Where a level of evidence is cited in the text or in the tables, it follows the hierarchy defined in the footnote to Table 1. Every summary table additionally labels each entry as preclinical or clinical, and Table 2 separates the two columns explicitly, so that the origin of each claim can be read directly from the table.

3 Preservation of residual hearing and benefits of electro-acoustic stimulation

This section concerns adults. Electro-acoustic stimulation has been most extensively studied in postlingually deafened adults with high-frequency sensorineural hearing loss, and the evidence base summarized below derives almost entirely from that population. Hearing preservation in children is addressed separately in Section 12.2.

In adults, high-frequency sensorineural hearing loss is the most frequently encountered form. It is generally associated with a combination of etiologies, including age-related degeneration, genetic predisposition, metabolic and inflammatory processes, as well as environmental factors such as noise exposure and ototoxic treatments, and primarily affects the basal region of the cochlea.

In this context, apical hair cells may remain functional, allowing for some perception of low-frequency sounds. However, the perception of consonants, rich in high frequencies crucial for speech intelligibility, remains significantly impaired. This spectral dissociation often results in very poor word recognition scores, especially since acoustic amplification becomes ineffective when thresholds exceed 65 dB HL in high frequencies (Ching et al., 1998; Hogan and Turner, 1998).

To address this limitation, cochlear implantation surgery has progressively evolved toward atraumatic techniques aimed at preserving residual hearing. This shift has led to the development of technical strategies such as partial insertion of long electrodes and the use of shorter or more flexible electrode models (Lenarz et al., 2006; Gantz et al., 2005; Rizer et al., 1988; Kiefer et al., 2004; Von lberg et al., 1999; James et al., 2005; Skarzynski et al., 2006; Büchner et al., 2009). These advances have expanded the indications for cochlear implantation to a new population of patients with partial deafness, particularly those presenting with high-frequency hearing loss and preserved apical hearing.

This paradigm shift has favored the emergence of electro-acoustic stimulation (EAS), which combines electrical stimulation of high frequencies via the implant with acoustic stimulation of low frequencies via a hearing aid. This hybrid approach optimizes overall perception, particularly in noisy environments.

What matters is therefore not the mere presence of residual hearing, but its functional quality. Preserved low-frequency hearing conveys complementary spectral, temporal and harmonic information, in particular the fundamental frequency, temporal envelope cues and distortion products. Its integration into hybrid strategies such as bimodal or electro-acoustic stimulation appears to be the principal determinant of improved outcomes.

4 Principles of atraumatic electrode insertion

The preservation of residual hearing, whether partial or complete, has become a cornerstone objective in contemporary cochlear implant (CI) surgery. Achieving this goal critically depends on minimizing intracochlear trauma during electrode insertion, as both hearing preservation and long-term implant performance are significantly influenced by the quality of insertion.

4.1 Target: complete scala tympani placement

Atraumatic electrode insertion, particularly one that ensures full placement of the electrode array within the scala tympani (ST), is essential. This is especially true along the initial segment of the basal turn, where anatomical vulnerability is greatest. Translocation of the array into the scala vestibuli (SV) is strongly associated with poorer auditory outcomes and should be systematically avoided (Aschendorff et al., 2007; Skinner et al., 2007).

To mitigate insertion trauma, the trajectory must align closely with the longitudinal axis of the ST, avoiding contact with delicate structures such as the osseous spiral lamina (OSL) and the basilar membrane (BM). Insertion angle, cochlear curvature along the lateral wall and insertion force are mechanically coupled. Maintaining a linear, controlled path at a low and constant speed is therefore the central requirement, and it is this requirement that motorized or robotic assistance is designed to meet.

Despite these precautions, scalar translocation remains a common and largely unpredictable complication. This phenomenon, wherein the electrode unintentionally migrates from the ST to the SV, is associated with significantly reduced speech comprehension and diminished preservation of residual acoustic hearing (Aschendorff et al., 2007; Finley et al., 2008; Wanna et al., 2015). Recent evidence emphasizes the importance of optimizing the insertion vector, particularly in the basal turn, to minimize structural disruption and reduce the likelihood of translocation (Torres et al., 2018b; Rau et al., 2015).

Outcomes are consistently superior when the electrode remains confined within the ST (Aschendorff et al., 2007; Skinner et al., 2007). Therefore, surgical strategies should prioritize atraumatic techniques not only to support hair cell preservation (Carlson et al., 2011) but also to maintain the viability of future regenerative therapies and electro-acoustic stimulation (EAS) applications (Ibrahim et al., 2011).

4.2 Biomechanics of insertion: forces, pressures and their thresholds

The rationale for slow, axially aligned insertion rests on three measurable physical quantities: contact force, intracochlear pressure, and the temporal variability of both.

Contact force arises when the array meets the lateral wall of the basal turn. In human temporal bones, traumatic insertions are defined by scalar translocation or basilar membrane rupture. They show an early force peak of approximately 30 ± 18.2 mN at first contact with the lateral wall. At identical insertion depths, forces differ significantly between traumatic and atraumatic insertions (p < 0.001) (De Seta et al., 2017).

Higher global thresholds in the order of 0.1 N have been proposed as the level above which structural damage becomes likely (De Seta et al., 2017). These values should be regarded as indicative rather than prescriptive. They are model-dependent, they cannot be measured intraoperatively with current instrumentation, and they have never been validated prospectively against audiometric outcome in patients.

Intracochlear pressure is the second mechanism. Advancing an array displaces perilymph and generates pressure transients that, in cadaveric preparations, reach peak equivalent sound pressure levels above 170 dB SPL—comparable to the acoustic exposures known to produce permanent threshold shift (Greene et al., 2016). These transients scale with insertion speed (Todt et al., 2014) and with abrupt changes in velocity, and can be substantially attenuated by micro-mechanical control of the insertion (Banakis Hartl et al., 2019). This provides a direct physical explanation for the protective effect attributed to slow, uninterrupted insertion.

Temporal variability is the third and probably the most important. In vitro work analyzing the insertion profile has identified discrete vulnerable phases in which force and pressure rise sharply, in particular around first contact with the lateral wall and during the ascent of the basal turn (Aebischer et al., 2024). It is the abrupt, high-amplitude excursions rather than the mean force that correlate with microstructural damage. Human hand tremor and re-grasping maneuvers generate precisely such excursions, which is the biomechanical argument for robotic assistance (Kashani et al., 2024a).

4.3 Limits of intraoperative feedback

Robotic-assisted insertion techniques have shown promise in achieving precise electrode placement with stable force profiles and consistent insertion velocities. These attributes are essential in minimizing intracochlear damage. Nevertheless, scalar deviations continue to occur in both manual and robot-assisted procedures, reflecting the inherent complexity of intracochlear navigation (Daoudi et al., 2021).

According to Starovoyt et al. (2019), most insertion-related trauma occurs during the first 180 degrees of the cochlea. Maintaining strict alignment with the natural curvature of the ST is essential to avoid iatrogenic injury. A primary obstacle to achieving this is the absence of real-time visual feedback. Surgeons rely solely on external landmarks, such as the round window (RW) or cochleostomy site, without intraoperative visualization of the electrode path. Conventional imaging techniques lack the resolution to delineate fine cochlear anatomy intraoperatively, particularly in the hook region.

Although improved electrode flexibility and soft-surgical techniques have reduced overall trauma rates, studies still report trauma in up to 40% of insertions. This underscores the need for integrated intraoperative technologies such as optical coherence tomography (OCT) and electrocochleography (ECochG), which, when combined with robotic-assisted systems, further enhance surgical precision and reproducibility (Starovoyt et al., 2019).

Taken together, these data provide a coherent mechanistic rationale for slow, axially aligned insertion guided by preoperative imaging and, where available, intraoperative monitoring. It should be emphasized that this rationale is derived predominantly from cadaveric and in vitro models. The extent to which the measured reductions in force and pressure translate into preserved audiometric thresholds in patients remains to be established prospectively.

5 Pharmacological strategies for hearing preservation

Surgical atraumaticity addresses the mechanical component of cochlear injury. It does not address the inflammatory and fibrotic cascade that follows even an uneventful insertion, and pharmacological protection is therefore a complementary rather than an alternative strategy. Corticosteroids are the most extensively studied agents in this setting and are used in most high-volume programs, although protocols remain highly variable.

5.1 Routes of administration

Three routes are in clinical use. Systemic administration uses intravenous or oral methylprednisolone or dexamethasone, given before, during or after surgery. It is simple, but limited by the blood-labyrinth barrier and by first-pass metabolism. Adequate perilymph concentrations therefore require high doses, with the corresponding systemic risk (Parys et al., 2022).

Topical (intratympanic) administration is given as an injection before surgery, or as direct application of a steroid-soaked material to the round window niche. It produces higher intracochlear concentrations with negligible systemic exposure. Diffusion across the round window membrane is nevertheless slow and uneven, with a basal-to-apical gradient that limits delivery to precisely the apical regions supporting residual low-frequency hearing (Parys et al., 2022).

Intracochlear administration, by direct injection or by drug-eluting carriers, overcomes the round window barrier but introduces an additional intracochlear maneuver and is generally discouraged when hearing preservation is the primary goal, except when integrated into the array itself.

5.2 Clinical evidence

A systematic review of 15 human studies (n = 659) found a tendency toward better hearing and vestibular preservation with perioperative steroids in 12 of them. Dose, route, timing and follow-up were nonetheless highly heterogeneous, and audiometric endpoints inconsistent. Topical administration showed the most favorable risk-benefit profile (Pimentel de Morais et al., 2024).

A separate systematic review of inner-ear pharmacotherapy reached a similar conclusion. In animal models, corticosteroids consistently improve auditory brainstem response thresholds, impedance and histology, though durably only with sustained delivery. Evidence of an anti-inflammatory benefit in humans remains scarce (Parys et al., 2022).

The honest summary is therefore that perioperative corticosteroids are biologically plausible, widely used, apparently safe when given topically, and supported by a consistent but low-level body of clinical evidence. No adequately powered randomized trial has yet defined the optimal agent, dose, route or duration, and this remains one of the clearest unmet needs in hearing preservation research. Sustained intracochlear delivery from dexamethasone-eluting arrays, discussed in Section 15, is the most promising means of resolving the pharmacokinetic limitations of the current routes (Parys et al., 2022; Wilk et al., 2016).

6 Robot-assisted cochlear implant surgery

Even in the absence of usable acoustic hearing, the occurrence of insertion-related trauma has been identified as a predictive factor for reduced neuronal survival and poorer long-term outcomes (Rahman et al., 2022; Carlson et al., 2011). Despite modern hearing-preservation techniques, complete anatomical integrity of the cochlea remains difficult to guarantee.

6.1 Limitations of manual insertion and the emergence of robotic assistance

In the majority of cases, electrode array insertion is still performed manually. This approach presents major limitations related to human motor variability and the surgeon's limited ability to perceive the forces applied within the cochlea.

Immediate postoperative hearing loss often reflects acute intracochlear trauma. However, a significant proportion of patients experience delayed hearing loss, occurring several months to several years after initial hearing preservation (Scheperle et al., 2017; Tejani et al., 2022). This observation suggests that even minimal trauma may trigger an inflammatory and fibro-osseous cascade responsible for the progressive deterioration of residual hearing.

Atraumatic techniques aim to minimize this acute trauma (Tarabichi et al., 2021). Nevertheless, the inherent limitations of manual electrode insertion are well documented.

These limitations are consistent with the observation that approximately 50% of patients with immediate hearing preservation experience a significant loss (>10–20 dB) over time. Furthermore, complete loss of residual hearing occurs in approximately 20%−25% of patients with initially preserved hearing at long-term follow-up, although this rate varies considerably between studies (range 10%−50%), depending on electrode design, surgical technique, and follow-up duration (Gantz et al., 2005; James et al., 2005; Dhanasingh and Jolly, 2017; Li et al., 2007; Locher et al., 2014; Rask-Andersen et al., 2011; Kawano et al., 1996).

A meta-analysis by Snels et al. (2019) confirmed a declining trend in hearing preservation outcomes over time, regardless of the surgical approach or electrode type used. It should be noted that these figures are descriptive: no study has causally attributed delayed hearing loss to manual insertion specifically, and comparable declines are reported in cohorts implanted with every available technique (Sladen et al., 2025).

In this context, otologic robotics has emerged to provide more precise, more stable, and less invasive access to the cochlea (Gawecki et al., 2022). Robotic assistance for electrode array insertion represents one of the most promising advances, aiming to overcome the intrinsic limitations of human motor control.

6.2 General philosophy of RACIS

All of these systems share a common objective: to provide controlled, regular, and stable electrode insertion, surpassing the limitations of human motor control.

The shared conceptual principles include: reduction of insertion forces; reduction of intracochlear pressure peaks; prevention of scalar trauma; and potential improvement in hearing preservation.

The central principle of robot-assisted cochlear implantation surgery (RACIS) is based on the use of a reduced and constant insertion speed, combined with lower insertion forces and a more reproducible trajectory than during manual insertion (Kontorinis et al., 2011).

Three architectures should be distinguished, because they are supported by different levels of evidence and carry different risks. Fully robotic procedures automate both the keyhole access to the middle ear and the insertion. Robotic access systems automate the drilling of a direct cochlear access while insertion is performed by hand. Robotic insertion systems, the most widely adopted category, automate only the insertion phase following conventional mastoidectomy and posterior tympanotomy. Throughout this review, results are attributed to the relevant architecture rather than to “robotic surgery” as a single entity (Sili et al., 2026). The sequence of operative steps common to these systems, and the point at which each may be automated or monitored, is shown in Figure 3. The principal systems, the step they automate and the evidence supporting each are summarized in Table 2.

Figure 3

6.3 Safety and precision of the insertion axis

Alignment of the electrode insertion axis is a critical determinant of intracochlear trauma: improper alignment increases the risk of scalar injury and translocation (Torres et al., 2018a).

The RobOtol system can be used safely and in a controlled manner as a support for micro-instruments or an endoscope; no complications directly related to the robot were reported in a clinical series of 32 cases, including 10 cochlear implantations. In this series, seven of the 10 electrode insertions were located entirely within the scala tympani (Vittoria et al., 2021).

Semi-automated robotic techniques significantly improve this alignment. In one study the angular error between the insertion tool and the optimal reference axis was 3.4 ± 1.56 degrees with robotic assistance. The corresponding values were 8.3 ± 2.82 degrees for the manual procedure and 8.6 ± 2.83 degrees for navigation-assisted manual insertion (Torres et al., 2017).

One optimized approach combined robotic alignment along the ideal axis with a motorized insertion tool at a constant speed of 0.25 mm/s. It significantly increased the number of electrodes fully positioned within the scala tympani, compared with manual insertion (P = 0.03) (Torres et al., 2018b).

The clinical implication of improved alignment is a higher probability of complete scala tympani placement, which is itself a validated predictor of speech perception and of low-frequency hearing preservation (Aschendorff et al., 2007; Skinner et al., 2007; Jwair et al., 2021; O'Connell et al., 2016b). Improved alignment is therefore a surrogate endpoint with a credible mechanistic link to outcome. It remains a surrogate nonetheless. No trial has yet shown that a reduction in angular error produces a measurable audiometric gain at a defined time point.

6.4 Experimental data on robotic systems: OTODRIVE and others

The studies summarized in this subsection are cadaveric or in vitro, and therefore correspond to level 5 evidence (mechanism-based reasoning; see footnote to Table 1). They establish mechanical and anatomical superiority; they do not establish clinical benefit.

The study by Chen et al. (2025) evaluated the safety and efficacy of the OTODRIVE system for cochlear implant electrode array insertion. Fifteen human cadaveric temporal bones were implanted with different electrode arrays (FLEX26, FLEX28, FLEXSOFT, FLEX34) and an inner ear catheter. The OTODRIVE system maintained a constant insertion speed of 0.1 mm/s. Specimens were subsequently analyzed using synchrotron radiation phase-contrast imaging (SR-PCI) to quantify intracochlear trauma.

Mean linear insertion depth was 24.8 ± 3.5 mm and mean angular insertion depth 527 ± 81 degrees, with cochlear coverage of 74 ± 7%. Only one partial scala media translocation and two basilar membrane elevations were observed, with no tip fold-over, scala vestibuli translocation or osseous spiral lamina fracture (Chen et al., 2025). The study included no manual comparison arm, so the absolute trauma rate cannot be interpreted as a between-technique difference.

The conclusions of Chen et al. are consistent with those of Kaufmann et al. (2020), who compared manual and robot-assisted insertions. In that study, manual insertions exhibited a mean trauma score of 3.1, compared with 0.9 for robot-assisted insertions.

Manual insertions showed a high proportion of severe events. These were 25% scala vestibuli translocations, 17% fractures of the osseous spiral lamina, and 33% combined fracture and translocation injuries. The corresponding figures in the robotic group were 8%, 0%, and 0% (Kaufmann et al., 2020). Robot-assisted insertions exhibited only minor trauma, mainly basilar membrane elevation (33%) and scala media translocations (17%) (Kaufmann et al., 2020).

Independent in vitro work has used a force- and pressure-instrumented cochlear model. It confirmed that a robot-assisted insertion system reduces peak forces and force variability relative to manual insertion, and localized the reduction to the vulnerable phases of the trajectory (Aebischer et al., 2024, 2025).

These experimental data consistently demonstrate that robotic systems reduce intracochlear trauma and better preserve structural integrity in temporal bone and in vitro models. Three caveats apply. First, cadaveric specimens lack perilymph turnover, an intact inflammatory response and any audiometric endpoint, so the extrapolation from trauma score to preserved hearing is inferential. Second, sample sizes are small (typically 10–20 specimens) and specimens are rarely randomized between techniques. Third, the manual comparator is usually a single experienced surgeon, which may either overestimate or underestimate the average manual performance. Adequately powered clinical trials with audiometric endpoints remain necessary before superiority in routine practice can be claimed.

6.5 Current limitations of robotic systems

A balanced appraisal requires that the limitations of RACIS be stated explicitly.

6.5.1 Technical limitations

Current insertion robots control speed and, in some configurations, trajectory; none provides validated real-time force or pressure feedback to the surgeon, so the very parameters shown experimentally to determine trauma are not yet monitored intraoperatively. Robotic assistance does not modify the mechanical properties of the array, and cannot compensate for the stiffness of a precurved electrode or for an unfavorable basal turn geometry. Scalar deviation continues to occur under robotic assistance, particularly with precurved arrays (Daoudi et al., 2021; Torres et al., 2021).

6.5.2 Procedural limitations

Robotic insertion adds operative time—approximately 18 ± 7 min in one consecutive clinical series using RobOtol (Mom et al., 2022)—and requires device-specific training and set-up. Anatomical obstacles such as basal turn fibrosis or ossification may preclude robotic insertion altogether and require conversion to a manual technique (Mom et al., 2022).

6.5.3 Evidential limitations

To date there is no published randomized controlled trial of robotic vs. manual electrode insertion with an audiometric primary endpoint. The available clinical evidence consists of small single-center cohorts, frequently retrospective, with non-contemporaneous control groups and heterogeneous electrode arrays. Publication bias in favor of positive early experience with a new technology cannot be excluded, and several key studies were conducted by groups with a developmental or advisory relationship to the manufacturers concerned.

7 Reduction of intracochlear trauma

7.1 Biological mechanisms of cochlear injury

The synthesis by Bas et al. (2012) identifies several major mechanisms that may lead to deterioration of auditory function. Five mechanisms are described. The first three are direct injury to hair cells along the basilar membrane, an inflammatory response evolving toward fibrosis, and damage to the spiral ligament and stria vascularis, which disrupts the endocochlear potential. The last two are rupture of the basilar membrane with scalar translocation, and high pressure peaks damaging sensory cells, analogous to acoustic trauma.

These traumatic events induce the expression of mediators such as TNF-alpha and IL-1beta, triggering hair cell apoptosis (Ichimiya et al., 2000; Dinh et al., 2015; Yamane et al., 1995). Intracochlear pressure peaks reproduce the effects of intense acoustic exposure, with accumulation of free radicals, oxidative stress, and tissue alterations (De Seta et al., 2017). Disruption of cochlear compartmentalization, mixing of perilymph and endolymph, or loss of the endocochlear potential secondary to strial injury further aggravate the functional deficit. The resulting trauma and inflammation promote intracochlear fibrosis, which is closely associated with reduced residual hearing and diminished cochlear implant performance (Rahman et al., 2022; Quesnel et al., 2016; Tejani et al., 2022). These mechanisms are summarized schematically in Figure 4.

Figure 4

7.2 Insertion force: experimental findings

The correlation between insertion force and intracochlear trauma has been demonstrated in human temporal bone specimens (De Seta et al., 2017). In the same experimental setting, a motorized insertion tool produced a more controlled and predictable force profile than manual insertion. It showed fewer abrupt force peaks and reduced variability, despite a similar overall force momentum (Nguyen et al., 2014).

This effect is primarily attributed to the ability of motorized systems to maintain a constant insertion velocity and a stable insertion axis, thereby limiting sudden mechanical interactions with intracochlear structures.

7.3 Insertion speed: a non-linear relationship

Available data also highlight that insertion speed is a critical determinant of intracochlear force generation and its temporal profile. Surgeons generally aim to maintain a slow and stable insertion speed; however, human capabilities do not allow reliable achievement of the very low speeds considered optimal. The average speed achievable during continuous manual insertion is approximately 0.87 mm/s, whereas a speed of 0.25 mm/s is virtually unattainable for a human operator, as demonstrated by Kesler et al. (2017).

Robotic assistance directly addresses this limitation by enabling highly controlled, constant, and very low insertion speeds, thereby reducing intracochlear forces (Majdani et al., 2010) and certain forms of trauma such as tip fold-over (Claussen et al., 2022). This technological advantage complements its ability to stabilize the insertion axis, contributing to a more reproducible and atraumatic insertion process.

Optimized robotic insertion has also been associated with less intracochlear trauma than manual insertion (P = 0.04) (Torres et al., 2018b). Force variability and the number of high-amplitude peaks were both reduced, and these peaks are strongly associated with microstructural damage and scalar translocation. Quantitative force values are nonetheless not reported systematically in these studies.

However, the relationship between insertion speed and intracochlear trauma is not strictly linear. Avci et al. (2017) observed no significant difference in forces for speeds from 0.05 to 2 mm/s. Dhanasingh et al. (2021) described a non-linear relationship, in which certain moderately low speeds paradoxically generated higher forces; the overall trend nonetheless favored the lowest speeds. Similarly, Kaufmann et al. (2020) showed that ultra-slow speeds (0.01 mm/s) increased maximal forces in synthetic models, without reproducing this effect in cadaveric temporal bones.

These findings suggest that excessively low speeds may increase prolonged mechanical contact, reduce the lubricating effect of perilymph, and exacerbate friction or transient pressure peaks. Such discrepancies are partly explained by differences between experimental models. Synthetic models have variable friction coefficients. Cadaveric temporal bones reproduce cochlear mechanics more faithfully, largely because of the elasticity of the basilar membrane, but at the cost of anatomical variability (Mirsalehi et al., 2017; Hrncirik et al., 2023).

Additional factors, including measurement methods, electrode design, insertion technique, and the physicochemical properties of the lubricating environment, further contribute to variability in reported results (Hrncirik et al., 2023).

Thus, while a slow and stable insertion speed remains a major objective, selection of the optimal speed profile must take into account these experimental limitations and the complex mechanical interactions within the cochlea.

7.4 Force thresholds and the limits of their interpretation

Traumatic insertions, meaning scalar translocation or rupture of the basilar membrane, exhibit more irregular force profiles. An early peak of approximately 30 ± 18.2 mN corresponds to the initial contact of the electrode with the lateral wall (De Seta et al., 2017). This value should be interpreted as an early localized peak occurring during electrode-wall interaction, whereas higher thresholds around 0.1 N correspond to more global critical force levels associated with an increased risk of structural damage. At identical insertion depths, forces differ significantly between traumatic and atraumatic insertions (p < 0.001) (De Seta et al., 2017).

The region between 150 and 180 degrees of insertion angle represents a particularly high-risk zone for scalar translocation with certain straight electrode arrays (Torres et al., 2018a).

Several caveats must be attached to any numerical force threshold. Measured values depend on the sensor position, on whether the force is recorded at the array tip or at the insertion tool, and on the sampling rate, so absolute values are not comparable across laboratories. Friction coefficients differ markedly between synthetic models, fresh-frozen and formalin-fixed temporal bones, and the lubricating properties of the medium used in place of perilymph are rarely reported.

Cochlear duct length and basal turn geometry vary substantially between specimens, and few studies normalize for this. Above all, insertion forces cannot currently be measured in patients, so no threshold has been validated against a clinical endpoint. For these reasons the values reported above should be regarded as ordinal indicators of relative risk rather than as absolute safety limits.

Taken together, these findings suggest that the temporal profile and variability of insertion forces matter as much as their absolute magnitude. Insertion speed emerges as a key modulator of these dynamics, and therefore as a major lever for optimization through robotic assistance. This conclusion rests on preclinical evidence and should be read as a mechanistic hypothesis awaiting clinical confirmation.

8 Preservation of residual hearing and the importance of atraumatic insertion

Up to 80% of current cochlear implant candidates retain residual acoustic hearing, a proportion that is expected to increase further (Sheffield et al., 2015). The literature robustly demonstrates that patients in whom this residual hearing is preserved achieve superior postoperative outcomes. The combination of acoustic stimulation (hearing aid) and electric stimulation (CI) improves pitch perception (Talbot and Hartley, 2008), speech understanding (Gantz and Turner, 2004; Gstoettner et al., 2008; Incerti et al., 2013), listening in noise (Dunn et al., 2010; Dorman and Gifford, 2017), and music appreciation (Gfeller et al., 2006, 2012). However, residual hearing is lost in nearly half of patients, either early after surgery or progressively over several years (Gifford et al., 2013).

Several studies, as previously discussed, suggest that reducing insertion speed may promote better clinical outcomes. Rajan et al. compared two insertion speeds, 0.25 mm/s and 1 mm/s, using the same electrode array. Slow insertion was associated with better hearing preservation, more complete insertion, and fewer vestibular symptoms during the first 24 postoperative hours (Rajan et al., 2012).

This study remains one of the few prospective clinical comparisons of insertion speed, but it was small and unblinded, and its audiometric follow-up was short. Confirmation of these benefits in terms of long-term auditory performance and quality of life, however, requires further studies.

Even in patients without usable residual hearing, atraumatic insertion remains essential. Intracochlear lesions may affect spiral ganglion neurons, which are the target structures of electrical stimulation (Nadol, 1997; Roland and Wright, 2006). Insertion trauma also triggers an inflammatory response leading to peri-electrode fibrosis, which increases electrical impedance, displaces the electrode away from the modiolus, and reduces stimulation efficiency (Kawano et al., 1998). This fibrosis has been associated with poorer scores on consonant–vowel–consonant word tests, a key indicator of auditory performance (Kamakura and Nadol, 2016).

9 Choice of electrode array and surgical approach for RACIS

The systematic review by Van de Heyning P. et al. (2022) aimed to determine the electrode array type best suited to reducing complications during cochlear implant surgery, whether robot-assisted (RACIS) or conventional. The complications analyzed included electrode tip fold-over (ETFO), electrode scalar deviation (ESD), and electrode migration (EM). It is important to note that this review analyzed adverse events reported after manual insertion; its conclusions are extrapolated, not directly measured, in the robotic setting.

9.1 Electrode tip fold-over (ETFO)

ETFO refers to a situation in which the tip of the electrode array (EA) becomes trapped and folds back on itself within the scala tympani. The consequences are of three kinds. Electrically, apical contacts may short-circuit and pitch percepts become confused. Perceptually, speech understanding may fall by up to 20% on the Bamford–Kowal–Bench Speech Test (BKB) or the Hearing In Noise Test (HINT), although some cases still reach 80% in quiet (Sabban et al., 2018; Gomez Serrano et al., 2019; Zuniga et al., 2017). Anatomically, facial nerve co-stimulation and vertigo may occur, and damage to the basilar membrane may lead to fibrosis, hydrops and ossification.

Surgical revision or deactivation of the involved contacts generally improves speech perception and resolves symptoms of facial nerve co-stimulation and vertigo (Sabban et al., 2018; Zuniga et al., 2017; Gabrielpillai et al., 2018). Intraoperative imaging has been proposed as a means of detecting ETFO during surgery, allowing immediate correction (Sabban et al., 2018; Durakovic et al., 2020; Garaycochea et al., 2020).

ETFO is significantly more frequent with precurved electrode arrays (5.3%) than with straight electrodes (0.5%) (Van de Heyning P. et al., 2022). This difference may be related to premature withdrawal of the stylet or polymer sheath, orientation of the contacts away from the modiolar wall during insertion, or cochlear anatomical variations. Experimental studies on cadaveric temporal bones have shown that robotic insertion, by applying a constant speed along an optimized axis, can reduce intracochlear trauma (Torres et al., 2018b). It can therefore be expected that RACIS may reduce the frequency of traumatic insertions, although no evidence has yet demonstrated a reduction in ETFO rates for precurved electrodes. The future integration of haptic pressure feedback could help detect an electrode tip becoming trapped.

9.2 Electrode scalar deviation (ESD)

ESD corresponds to perforation of the basilar membrane, resulting in the presence of part of the apical contacts within the scala vestibuli. It occurs primarily between 90 and 180 degrees of insertion angle and is associated with intracochlear fibrosis, neo-osteogenesis, and irreversible neuronal degeneration (Kamakura and Nadol, 2016). The resulting mixing of perilymph and endolymph may lead to complete loss of residual hearing.

ESD represents the most frequent severe intracochlear complication and is clearly associated with poorer auditory outcomes (Jwair et al., 2021; O'Connell et al., 2016a,b). A meta-analysis showed that ESD reduced speech perception scores in patients implanted after post-lingual deafness and significantly decreased the likelihood of complete scala tympani placement (Jwair et al., 2021). O'Connell et al. (2016b) concluded that insertions strictly confined to the scala tympani provided better auditory outcomes and that ESD negatively affected low-frequency residual hearing.

In the review by Van de Heyning P. et al. (2022), ESD was more frequent with precurved electrodes (28.7%) than with straight electrodes (11%) .

Robotic systems have demonstrated superiority in terms of directionality and precision. Daoudi et al. (2021) compared 40 manually operated patients with 20 patients implanted with robotic assistance and observed a lower rate of ESD for straight electrodes in the robotic group. Barriat et al. (2021) reported a mean hearing preservation of 13.60 ± 7.70 dB, correlated with a lower insertion speed (0.88 ± 0.12 mm/s) achieved using RobOtol. Animal studies show that more flexible electrodes result in less ESD, reduced intracochlear fibrosis, and better hearing preservation (Drouillard et al., 2017).

9.3 Surgical approach

The cochlear approach also influences the incidence of ESD. Early cochleostomy series reported higher rates of scalar deviation (Bourn et al., 2020), whereas more recent studies did not confirm a significant difference between cochleostomy and round window (RW) approaches (Helbig et al., 2016). However, several meta-analyses demonstrate that the RW approach is associated with a lower incidence of ESD compared with cochleostomy (Wanna et al., 2014; Fischer et al., 2015). A consensus statement has recommended the RW approach, supported by histopathological observations suggesting less trauma (Rajan et al., 2018) and by a clinical study showing greater hydrops and fibrosis in the scala tympani and scala vestibuli after cochleostomy than after RW insertion (Ishiyama et al., 2016). In living subjects, no ESD was observed following RW insertion, in contrast to cochleostomy (Ishiyama et al., 2016).

Thus, robotic surgery centered on round window access (RACIS) aims to ensure minimally traumatic access consistent with normal anatomy (Mueller et al., 2021). Cadaveric studies show that slow, coaxial motorized insertions reduce the incidence of ESD (Torres et al., 2017). Nevertheless, ESD may still occur with precurved electrodes even under robotic assistance (Torres et al., 2021). For straight electrodes, robotics improves accuracy of scala tympani placement, limits injury to scalar walls, and provides optimal orientation, thereby reducing human error and inter-surgeon variability (Torres et al., 2017, 2016).

A meta-analysis estimated the overall rate of electrode scalar deviation, meaning passage from the scala tympani to another cochlear compartment, at 12.66% (95% CI: 4.82%−20.51%). It was less frequent with robotic middle ear access (6.4%) and more common with robotic electrode insertion (17.1%) (Sili et al., 2026). This apparently paradoxical finding most probably reflects confounding by indication rather than a genuine disadvantage of robotic insertion. Series using robotic access alone are dominated by centers implanting straight lateral-wall arrays through a planned direct cochlear access. Robotic insertion series include a higher proportion of precurved arrays. The subgroups are not otherwise comparable, and the comparison should not be read as a head-to-head result (Sili et al., 2026).

Navigation systems can be used to assess and improve surgeons' mental representation of the scala tympani axis, particularly in cochlear implant surgery (Torres et al., 2016).

9.4 Electrode migration (EM)

EM corresponds to displacement of the electrode out of the cochlea, which may occur at the end of surgery, in the immediate postoperative period, or at a later stage. It is associated with increased impedances and decreased speech recognition (Dietz et al., 2016). EM is more frequent with straight electrodes (3.2%) than with precurved electrodes (0.53%) (Van de Heyning P. et al., 2022).

9.5 Electrode rigidity and patient-specific factors

More flexible electrodes generate lower insertion forces and favor hearing preservation. Therefore, to preserve residual hearing, electrode design and insertion strategy should aim to minimize mechanical trauma by favoring thin and flexible arrays that facilitate atraumatic placement within the scala tympani and reduce the risk of fibrosis (Drouillard et al., 2017).

Electrode selection cannot, however, be reduced to a single dimension. Precurved perimodiolar arrays place the contacts closer to the modiolus, which lowers stimulation thresholds, widens the electrical dynamic range and may reduce channel interaction—advantages that matter particularly in recipients without usable residual hearing. Straight lateral-wall arrays offer lower stiffness and a lower rate of insertion trauma, and permit deeper apical coverage, which matters when the objective is preservation of low-frequency hearing and electro-acoustic stimulation. The choice is therefore a trade-off between stimulation efficiency and structural preservation, and it should be made according to the therapeutic goal for the individual patient.

Anatomical variability further individualizes this decision. Cochlear duct length varies by more than 25% between individuals, and cochlear size predicts both scala tympani volume and insertion force (Dhanasingh et al., 2021). Preoperative segmentation and planning software allow the array length to be matched to the measured duct length, so that adequate cochlear coverage is achieved without excessive apical force.

Basal turn geometry, the angle of the round window relative to the scala tympani axis, and the presence of malformation, fibrosis or ossification are all relevant to both electrode choice and the feasibility of robotic insertion (Mom et al., 2022). An individualized approach combining preoperative cochlear morphometry, an explicit therapeutic goal and the selection of an appropriately compliant array is more defensible than any general recommendation of one array type over another.

9.6 Conclusion on electrode type for RACIS

The literature reviewed in this section suggests that electrode choice plays an important role in insertion-related complications during RACIS. Available data tend to favor the use of straight electrodes, which are associated with lower rates of insertion trauma, particularly ETFO and ESD, compared with precurved electrodes, as reported in systematic reviews including Van de Heyning P. et al. (2022). However, this conclusion should be interpreted in light of the underlying mechanical factors discussed in this section, including insertion forces, stiffness, and trajectory control, which are key determinants of intracochlear injury.

It should also be interpreted in the light of the level of evidence available: the comparative data derive from pooled observational series rather than from randomized comparisons, and adverse event ascertainment differed between the included studies. Table 3 summarizes the reported event rates and the resulting trade-off between array designs.

Among these lesions, ESD is considered an irreversible intracochlear injury and its prevention should be an absolute priority, whereas ETFO and electrode migration (EM) are most often correctable. RACIS systems offer additional potential for trauma reduction through slow, regular, and controlled insertion, a prerequisite for residual hearing preservation. Robotic assistance nevertheless acts on the kinematics of insertion, not on the mechanical properties of the array. It cannot compensate for the stiffness of a precurved electrode, and scalar deviation continues to be reported with such arrays under robotic control (Torres et al., 2021). Nevertheless, the use of straight electrodes requires anticipation of secondary migration risk and implementation of appropriate fixation strategies.

Overall, RACIS is a promising technique whose capacity to reduce insertion-related complications is supported by consistent preclinical data and by early clinical series. Whether this translates into improved long-term auditory outcomes remains to be demonstrated.

10 Clinical and functional outcomes of RACIS

This section provides an integrated overview of the clinical and functional outcomes of robot-assisted cochlear implantation, encompassing surgical feasibility and safety, audiological performance, intracochlear tissue responses, and the influence of key surgical parameters such as insertion depth and frequency-place matching.

10.1 Feasibility and safety

Several clinical feasibility studies have demonstrated that robot-assisted cochlear implantation is feasible in both adult and pediatric populations (Torres et al., 2018b; Jia et al., 2021).

The iotaSOFT system (iotaMotion Inc., USA) was one of the first single-use robotic insertion devices to be evaluated in a clinical setting. Its safety and utility were demonstrated in the first-in-human trial of a single-use robotic surgical device (Gantz et al., 2023), and subsequently confirmed in the study by Khan et al. (2025), which reported 1-year audiological outcomes in a comparative cohort.

A recent meta-analysis estimated the overall rate of postoperative complications following RACIS at 11.85% (95% CI: 0.00%−23.86%), which appears comparable to the 12.8% overall complication rate reported for conventional manual cochlear implantation in large pooled series (Carlson, 2020). Complications ranged from minor events such as bruising, edema, or mild wound dehiscence to rare major complications, including cerebrospinal fluid leakage or extracochlear electrode placement compromising implant function.

However, direct comparison remains limited by the wide confidence interval reflecting heterogeneity across RACIS studies, the relatively small number of cases, and the absence of stratification by electrode type, which introduces a significant and uncontrolled source of bias (Sili et al., 2026). A confidence interval whose lower bound is zero indicates that the pooled estimate is compatible with a complication rate close to zero and with one exceeding 20%; it should not be interpreted as evidence of equivalence with conventional surgery.

10.2 Audiological performance and quality of electrode placement

Insertion speed has been identified as a major determinant of auditory and vestibular preservation following cochlear implantation, as discussed previously (Kontorinis et al., 2011; Rajan et al., 2012; Van de Heyning P. et al., 2022; Nguyen et al., 2016).

In parallel with technological advances in robotics, electrode array designs have evolved to more closely conform to cochlear anatomy. A meta-analysis examining surgical and technical factors did not demonstrate clear superiority of one electrode array model over others in terms of hearing preservation based on electrode length alone (Santa Maria et al., 2014). However, more recent studies, including comparisons across different manufacturers, suggest that shorter, flexible lateral wall arrays such as the MED-EL FLEX24 may be associated with improved low-frequency hearing preservation (Hallin et al., 2024). These observations, together with systematic reviews reporting lower rates of insertion-related adverse events with straight electrodes, support their preferential use in the context of RACIS (Van de Heyning P. et al., 2022; Causon et al., 2015).

A more recent systematic literature review nevertheless found high hearing preservation rates with both medium-length and longer lateral wall arrays, and concluded that array length alone does not determine outcome (Van de Heyning P. H. et al., 2022). Electrode length should therefore be selected on the basis of measured cochlear duct length rather than on a general preference for shorter arrays.

The study by Khan et al. (2025) compared manual and robot-assisted insertions under intraoperative electrocochleographic (ECochG) monitoring. Insertion assisted by the iotaSOFT system was associated with a clinically meaningful trend toward better hearing preservation and more stable thresholds at 1 year. The preservation rate was 85% (23/27) in the robotic group and 71% (17/24) in the manual group, functional acoustic hearing being defined as a low-frequency pure-tone average below 80 dB HL. Although this 14% difference did not reach statistical significance, likely due to the limited sample size and the already high preservation rate in the manual group, it remains clinically relevant.

The study compared two non-contemporaneous cohorts without randomization, manual from 2015 to 2022 and robotic from 2021 to 2024. A period effect therefore cannot be separated from the effect of the robot itself; this includes the progressive introduction of preoperative planning software in the robotic group. It corresponds to level 3 evidence, a non-randomized comparative cohort study.

This 85% preservation rate is noteworthy against previously published figures for the FLEX20 and FLEX24 electrodes. Those rates were 48.8% and 50%, respectively, defined as a pure-tone average threshold change of 15 dB or less at 1 year (Suhling et al., 2016). This comparison should be made with caution. The two studies used different definitions of preservation: a categorical threshold of functional hearing in the first, a fixed threshold shift in the second. Cross-study comparison of preservation rates is precisely what standardized reporting frameworks are intended to prevent (Skarzynski et al., 2013; Adunka et al., 2018).

Comparable results were also reported with RobOtol, in which the robotic group demonstrated an approximately 12% improvement in hearing preservation compared with the manual group (Gersdorff et al., 2024).

In the study by Khan et al. (2025), five patients in the robotic group received a longer electrode array (FLEX26), whereas no patient in the manual group did, which could theoretically bias the results against robotics. Conversely, no patient in the robotic group implanted with a FLEX20, the shortest model, experienced hearing loss, whereas three of the seven subjects who lost hearing in the manual group were implanted with a FLEX20. The absence of functional hearing loss after initial activation in the robotic group is consistent with the hypothesis that assisted insertion may attenuate the acute trauma responsible for the inflammatory cascade and tissue remodeling involved in delayed hearing loss.

Robotic assistance also facilitates integration of intraoperative ECochG, providing the surgeon with real-time functional feedback on the impact of each insertion step (Kashani et al., 2024b). The main limitations of the available clinical studies nevertheless lie in their retrospective design, despite prospective data collection, as well as in the small sample size included (Khan et al., 2025). An independent matched-cohort analysis of motorized insertion has since reported comparable trends, again without randomization (Oetiker et al., 2025).

Balance requires that the negative findings also be reported. A prospective series of robot-assisted implantation found audiological outcomes comparable to, but not better than, those of conventional surgery (Heuninck et al., 2023). No study to date has demonstrated superior speech perception with robotic insertion.

10.3 Meta-analysis of robotic strategies and hearing preservation

In the meta-analysis dedicated to RACIS, procedures were classified by the degree of robotic involvement (Sili et al., 2026). Three categories were used: fully robotic procedures, in which all key steps are performed by the robot; robotic access to the middle ear with manual array insertion; and robotic insertion following manual drilling.

The overall success rate, defined as the proportion of procedures completed without conversion to a manual technique, was 97.2% (95% CI: 94.03%−100.00%). The rate differed by subgroup, without reaching statistical significance (p = 0.08) (Sili et al., 2026). It reached 98.70% (95% CI: 95.28%−100.00%) for robotic electrode insertion, where only the insertion phase is automated. It was 88.44% for robotic access to the middle ear, where the approach is automated but insertion remains manual, and 86.95% for fully robotic procedures covering both steps.

This success rate is a measure of technical feasibility, not of clinical benefit. It quantifies the proportion of procedures completed without conversion to a manual technique and says nothing about whether the robotic procedure produced a better anatomical or audiological result than a manual one would have. A procedural completion rate of 97.2% establishes that RACIS is reliably performable in experienced hands; it does not establish superiority over conventional implantation, and it should not be cited as if it did.

Preservation of residual hearing was reported in 60.69% of patients (95% CI: 23.21%−98.18%), albeit with very high heterogeneity (I2 = 98.41%), reflecting the wide diversity of indications, electrode types, and surgical and audiological protocols.

An I2 of 98.41% indicates that almost all of the observed variability between studies reflects genuine between-study differences rather than sampling error, and the corresponding confidence interval spans from 23% to 98%. A pooled point estimate of 60.69% is therefore of very limited interpretative value and should not be used as a benchmark. Five sources of heterogeneity can be identified. The first is the definition of preserved hearing, which may be a functional threshold, a percentage of preserved dynamic range or a fixed threshold shift. The others are preoperative residual hearing, which differs across cohorts; electrode type and length; follow-up duration, critical given the documented decline of preservation over time (Sladen et al., 2025; Snels et al., 2019); and the degree of robotic involvement.

Until these are standardized, meta-analysis of hearing preservation after RACIS will remain descriptive rather than inferential.

Finally, RobOtol was evaluated in a pilot study involving two patients with residual hearing, under intraoperative ECochG monitoring (Gawecki et al., 2022). A usable ECochG response was recorded after complete electrode insertion in both subjects, and residual hearing at the tested frequencies was preserved 1 month after surgery (Gawecki et al., 2022). Integration of ECochG into robotic cochlear implantation is conceptually attractive because it allows insertion to be adapted dynamically to the cochlear response. The supporting evidence is nevertheless preliminary: it consists of feasibility studies in very small samples, with 1-month follow-up in the study cited above.

Present evidence supports intraoperative ECochG as a monitoring tool capable of detecting acute intracochlear events; it does not yet establish that ECochG-guided modification of the insertion improves long-term hearing preservation. Randomized comparison of ECochG-guided vs. non-guided robotic insertion has not been reported. Table 4 sets out what is and is not established for each application of intraoperative ECochG.

11 Impedance outcomes and intracochlear tissue remodeling in the context of atraumatic (robotic-assisted) cochlear implantation

In the context of robotic-assisted cochlear implantation (RACIS), which aims to minimize intracochlear trauma through controlled, slow, and highly reproducible electrode insertion, understanding impedance evolution and intracochlear tissue remodeling is essential to interpret postoperative functional outcomes and long-term cochlear preservation.

11.1 The fibro-inflammatory response: established findings

Even with optimized electrode arrays and atraumatic insertion techniques, cochlear alterations may still occur, and residual hearing may deteriorate over time. Intracochlear neural injury may manifest either immediately following mechanical trauma or secondarily as a result of chronic processes. This delayed deterioration has been attributed to persistent inflammatory responses, fibrosis, or neo-osteogenesis triggered by trauma or by an immunological foreign-body reaction (Nguyen et al., 2016; Foggia et al., 2019). These phenomena may disrupt cochlear physiology, compromise residual hearing, and limit postoperative performance (Choi and Oghalai, 2005).

Intracochlear fibrosis is frequently observed after implantation, presenting as a fibrotic sheath surrounding the electrode array. It may result from traumatic events (such as scalar deviation) or from a foreign-body reaction even in the absence of major trauma (Foggia et al., 2019). This process plays a major role in outcome degradation by disturbing the physiological environment of the inner ear and reducing residual hearing (Choi and Oghalai, 2005). Cochlear fibrosis has also been associated with increased electrical impedances, which may compromise implant function (Jia et al., 2011). In addition, larger volumes of intracochlear new bone formation correlate with poorer word recognition scores (Kamakura and Nadol, 2016).

Histopathological analyses of implanted human temporal bones show that cochlear implantation, despite the biocompatibility of current electrode arrays, induces immediate insertion trauma followed by a delayed inflammatory response with fibrosis and neo-osteogenesis (Kamakura and Nadol, 2016). In these specimens, fibrous tissue and newly formed bone were found in all cases. CNC word scores correlated positively with the number of spiral ganglion cells. They correlated negatively with the percentage of new bone volume in the scala tympani, the scala media and vestibuli, and the cochlea as a whole, but not with the volume of fibrous tissue (Kamakura and Nadol, 2016). Neo-osteogenesis in the scala media/vestibuli was strongly associated with the severity of insertion trauma, particularly basilar membrane injury.

These observations underscore that residual neuronal survival and the degree of neo-osteogenesis are major determinants of postoperative auditory performance, reinforcing the importance of minimizing insertion trauma and further improving electrode biocompatibility (Kamakura and Nadol, 2016).

11.2 Impedance: a multifactorial signal

Impedance values vary depending on whether electrodes are stimulated or not; in adults, higher impedances are generally associated with higher thresholds and lower comfort levels, although this relationship is less clear in children (Busby et al., 2002).

The typical temporal profile of postoperative impedances includes low intraoperative baseline values, an early increase during the wound-healing phase, and a secondary decrease after device activation, without complete return to baseline values (Neuburger et al., 2009).

This evolution reflects the formation of deposits on the electrode surface (partially removed by stimulation) and the development of a connective tissue sheath that prevents full normalization. Long attributed solely to inflammation, impedance increases are now considered the result of both inflammatory processes and stimulation-related mechanisms. In the absence of pre-existing inflammation, increasing the stimulation pulse width has been shown to normalize elevated impedances (Neuburger et al., 2009).

Electrical stimulation itself induces rapid and dynamic impedance changes: after implantation, impedance increases and then decreases within minutes following stimulation onset, remaining low as long as stimulation continues (Newbold et al., 2014). This decrease is mainly related to the polarization component, indicating that stimulation primarily affects electrode surface properties rather than the global tissue environment. This phenomenon persists for several years after implantation in chronic in vivo models, supporting the concept that stimulation modifies the electrode-tissue interface rather than the surrounding tissue or fluid (Newbold et al., 2014).

At the microscopic level, electrical stimulation causes immediate loss of cells covering the electrode surface, reflecting localized changes in cell adhesion at commonly used stimulation levels (Newbold et al., 2011). The similarities between in vivo and in vitro impedance variations support the validity of experimental models, although the underlying mechanisms may differ. Under in vitro conditions, changes in the porosity of the cellular layer have been proposed to explain these variations, providing further insight into the dynamic processes at the electrode-tissue interface (Newbold et al., 2011).

Longitudinal impedance monitoring is recommended, as impedance variations may reflect device malfunction, periods of non-use, hormonal influences, or perceived changes in sound quality (Spitzer et al., 2013). Data beyond three years remain limited but suggest progressive stabilization of impedances after initial fluctuations, with a downward trend in apical electrodes (Spitzer et al., 2013). Larger-scale studies are required to determine the functional significance of these changes.

Finally, the relationship between impedance and functional performance is complex: a recent clinical study found no direct correlation between impedance variations and speech perception scores, suggesting that impedance alone cannot predict cochlear implant failure or poor performance (Pisa et al., 2023).

Impedance is therefore determined by at least five partly independent factors. The first two are the volume and composition of peri-electrode connective tissue, and the position of the array relative to the modiolus and the scalar walls. The remaining three are the surface state of the platinum contacts, including protein and cellular deposits; the stimulation parameters, in particular pulse width and duty cycle; and periods of device non-use.

Attributing a difference in impedance between two surgical techniques to a difference in insertion trauma alone is therefore not justified unless electrode type, array position, stimulation strategy and device usage are controlled for. Impedance is best regarded as a sensitive but non-specific marker of the electrode-tissue interface.

11.3 Modulating the tissue response: emerging evidence

Growth of connective tissue around the electrode array is a major determinant of cochlear implant efficiency and a primary contributor to chronic impedance elevation (Wilk et al., 2016). Experimental data demonstrate a correlation between the volume of newly formed tissue surrounding the electrode array and the magnitude of impedance changes. Dexamethasone-eluting (DEX) electrode arrays significantly reduce fibrotic tissue growth and impedance increases during the first 3 months. Although the volume of fibrous tissue at 91 days is not correlated with hearing loss, it is strongly associated with impedance elevation, suggesting that impedance could serve as an in vivo marker of intracochlear fibrosis (Wilk et al., 2016).

Incorporation of DEX into the electrode silicone allows delivery of a biologically active intracochlear dose, making DEX-eluting cochlear implants a promising strategy to reduce fibrosis and impedance increases (Wilk et al., 2016). These findings derive from a controlled animal model; first-in-human data are discussed in Section 15.

Within this framework, it has been hypothesized that subtle differences in insertion mechanics, such as those attenuated by robotic assistance, might influence the magnitude of the subsequent inflammatory and fibrotic response. This hypothesis is mechanistically coherent but has not been tested directly: no study has compared histologically quantified intracochlear fibrosis after robotic and after manual insertion in humans.

Gersdorff et al. compared robotic-assisted and manual cochlear implantation using MED-EL Flex24 electrode arrays. Robotic insertion was associated with a higher rate of residual hearing preservation, with more stable and consistently lower apical impedances over time, and with sustained improvement in speech perception during the first postoperative year. In contrast, manually implanted patients showed greater impedance variability and a plateau in speech recognition after 6 months, particularly in those with significant residual hearing loss.

These findings suggest that slow, controlled robotic insertion may reduce intracochlear tissue response, thereby promoting a more favorable electrode-neural interface and improved long-term functional outcomes (Gersdorff et al., 2024). This was a single-center retrospective comparative study without randomization, and the inference from impedance stability to reduced fibrosis is indirect.

Altogether, the association between insertion trauma, fibro-inflammatory remodeling and auditory outcome is well established, and the capacity of robotic insertion to reduce mechanical trauma is supported by preclinical data. The intervening step—that robotic insertion durably reduces intracochlear fibrosis in patients—remains a plausible hypothesis supported only by indirect impedance evidence, and constitutes a priority for future histopathological and imaging studies.

12 Additional considerations in hearing and structure preservation

12.1 Vestibular preservation

The scala tympani is continuous with the vestibule, and the same insertion that threatens the cochlear partition also threatens the vestibular end-organs. Vestibular loss after implantation is clinically relevant because it may cause disequilibrium, oscillopsia and, in bilateral cases, substantial functional disability.

The determinants of vestibular preservation largely mirror those of hearing preservation. In a series of 66 recipients implanted through a round window approach with flexible arrays, function was preserved in 93.9% on caloric testing, 82.4% on cervical vestibular evoked myogenic potentials (VEMP) and 92.5% on ocular VEMP. Abnormal cervical VEMP responses were significantly more frequent after cochleostomy than after round window insertion (Tsukada and Usami, 2021). Rajan et al. (2012) also observed fewer vestibular symptoms in the first 24 postoperative hours with slow insertion.

In children, vestibular function can likewise be largely preserved with structure-preserving technique (Licameli et al., 2024), which matters given the role of vestibular input in motor development. Perioperative steroids have been associated with better vestibular as well as auditory preservation (Pimentel de Morais et al., 2024).

These favorable figures should nevertheless be read against the pooled evidence. A meta-analysis of adult recipients confirms measurable postoperative deterioration on cervical VEMP and caloric testing, with a less consistent signal on video head impulse testing and posturography (de Castro Vaz et al., 2022). A recent scoping review emphasizes that no single test is sufficient, that a pre- and postoperative battery is required, and that protocols, retest intervals and abnormality thresholds remain highly heterogeneous between centers, which limits fine comparison between surgical techniques (Massa and Honaker, 2026).

Two clinical studies have specifically compared vestibular outcome after robotic and after manual insertion, and their results temper the expectation that the mechanical advantages of robotic insertion translate automatically into vestibular benefit. Derieppe et al. conducted a monocentric comparison using caloric testing, VEMP and video head impulse testing. They found no statistically significant difference between robotic (RobOtol) and manual insertion on any objective measure. The only difference favoring the robotic group was a lower rate of patient-reported postoperative vertigo (Derieppe et al., 2024).

Koutna et al. used static posturography and subjective visual vertical, preoperatively, on the first postoperative day and at 3 weeks. Both groups showed the same pattern, a transient postoperative deviation followed by spontaneous compenzation, with no difference between robotic and conventional surgery (Koutna et al., 2024).

The current position is therefore that robotic insertion has not been shown to improve objective vestibular outcome, and that the only signal in its favor concerns subjective vertigo. Three qualifications apply: both comparative studies are small and non-randomized; objective vestibular tests and patient-reported symptoms are known to correlate poorly (Massa and Honaker, 2026); and no systematic review dedicated to vestibular outcome after robot-assisted implantation has yet been published. Vestibular function should nonetheless be regarded as a second structural endpoint of atraumatic surgery, and the systematic inclusion of a standardized pre- and postoperative vestibular battery in future robotic trials would settle a question that two small studies cannot.

12.2 Hearing preservation in children

Hearing preservation is achievable in children. A systematic review and meta-analysis of pediatric implantation found preserved hearing in 78% of ears. No patient characteristic or surgical technique was significantly associated with the outcome, most probably because the contributing series were small and heterogeneous (Madgar et al., 2025). Pediatric preservation raises specific considerations. These include the growing temporal bone, and the difficulty of obtaining reliable behavioral thresholds in very young children. Long-term rather than 1-year outcome data are also required, and preserved acoustic hearing has a role in the development of pitch perception and music appreciation.

Robotic insertion has been reported in children (Jia et al., 2021; Sykopetrites et al., 2025), and a robotic insertion device has recently received regulatory clearance for pediatric use, but published pediatric robotic series remain very small.

12.3 Revision cochlear implantation

Revision surgery is directly relevant to structure preservation because reinsertion into a cochlea that already contains a fibrotic sheath is mechanically different from primary insertion. In a large single-center cohort, the revision rate was 11.7%, most often for device failure, and speech perception was unchanged or improved in 85% of cases but declined in 15% (Sagiv et al., 2021). The risk of losing residual hearing at revision is higher than at primary surgery, and the choice of array at first implantation should anticipate this possibility. Basal turn fibrosis may also preclude robotic insertion and require conversion to a manual technique (Mom et al., 2022).

12.4 Imaging, image-guided insertion and machine learning

Preoperative segmentation of the cochlea allows measurement of cochlear duct length and individualized selection of array length, and defines the optimal insertion vector into the basal turn (Torres et al., 2018a,b; Mueller et al., 2021). Intraoperative imaging can detect tip fold-over in time for immediate correction (Sabban et al., 2018; Durakovic et al., 2020; Garaycochea et al., 2020), and fluoroscopic feedback has been combined with robotic insertion to visualize the array in real time (Mom et al., 2022). Optical coherence tomography offers sufficient resolution to image the cochlear microstructures at risk through the round window (Starovoyt et al., 2019, 2023), although it is not yet integrated into a routine surgical workflow.

Machine learning is beginning to be applied to the same problem from the opposite direction, by predicting rather than observing outcome. A systematic review of machine-learning prediction of implant outcome found useful discrimination from models using imaging, neural response and clinical predictors. Few of these models have been externally validated, and almost none has been integrated into clinical decision-making (Mo et al., 2025). Applied specifically to hearing preservation, such models could eventually support individualized choice of array and insertion strategy; at present they should be regarded as research tools.

12.5 Genetic hearing loss and MRI considerations

Etiology influences both the prognosis of residual hearing and the rationale for preserving it. Patients with defined genetic etiologies may have predictable patterns of progression, and the identification of a genetic cause is increasingly relevant to candidacy: for otoferlin-related deafness, gene therapy is now an alternative or complement to implantation (Lv et al., 2024). Preserving cochlear structure and the surviving neural population maintains eligibility for such biological therapies, which is an additional argument for atraumatic technique independent of immediate audiometric benefit.

Compatibility with magnetic resonance imaging has improved substantially with self-aligning and diametric magnet designs, and most current devices are conditionally compatible at 1.5 T and 3 T. This matters for recipients who require repeated neuroimaging. Magnet-related considerations concern the receiver-stimulator rather than the intracochlear array, and therefore do not bear directly on hearing preservation; a detailed treatment is beyond the scope of this review.

13 Cost, accessibility, and implementation

Cochlear implantation itself is a well-established cost-effective intervention: a health technology assessment combining a systematic review with an economic model concluded that unilateral implantation is cost-effective for severe-to-profound deafness in both adults and children (Bond et al., 2009). Robotic assistance is an additional cost layered on top of this, and its economic case has not been made.

No dedicated economic evaluation of robot-assisted cochlear implantation has been published. None of the comparative clinical or experimental studies of robotic vs. manual insertion cited in this review reports a cost per case, an incremental cost-effectiveness ratio, quality-adjusted life years or a budget-impact analysis. Contemporary reviews of robotic cochlear implantation identify cost and cost-efficiency not as demonstrated advantages but as unresolved obstacles to wide adoption (Panara et al., 2021; De Seta et al., 2021).

The costs are of three kinds. Capital cost applies to reusable platforms and to the navigation and imaging infrastructure required for robotic direct cochlear access. Per-procedure consumable cost applies to single-use insertion devices. Operating-room time is the third, and it depends critically on the architecture used. Robotic insertion following conventional access automates only the insertion phase and does not necessarily prolong the whole procedure, since set-up is short (Kashani et al., 2024a); one consecutive series reported an additional 18 ± 7 min (Mom et al., 2022).

Fully robotic procedures using a keyhole direct cochlear access are considerably longer. One feasibility series reported a mean operative time of 247 min (Fourez et al., 2025), and a small pediatric comparison reported 161 min for robotic against 123 min for manual insertion (Sykopetrites et al., 2025). Operative time is therefore determined by the robotic architecture chosen rather than by robotic assistance as such.

Evidence from robot-assisted surgery in other specialties is instructive and largely cautionary. Economic evaluations in this field are methodologically heterogeneous and frequently omit acquisition, maintenance and organizational costs, so that reported savings are difficult to interpret (Lai et al., 2025; Bosscha et al., 2025). Cost-effectiveness depends strongly on annual caseload and on sharing the platform between specialties, and a minimum caseload is generally required before a favorable economic profile is reached (Garavini et al., 2026). This is directly relevant to otology, where per-center volumes are far below those of urological or colorectal surgery, so that this threshold may not be reached in many cochlear implant programs.

Three potential offsets may be set against these costs. The first is a reduction in scalar translocation and tip fold-over, the latter occasionally requiring revision surgery. The second is preservation of residual hearing, with the associated quality-of-life gain. The third is reduced inter-surgeon variability, which may be of particular value in lower-volume centers and during surgical training. Each of these is plausible; none has been quantified in monetary terms.

Moreover, several clinical comparisons have shown no superiority in speech perception or overall audiological outcome with robotic surgery (Heuninck et al., 2023). Without a clear and durable clinical gain, a favorable cost-effectiveness ratio cannot be demonstrated, however real the technical advantages may be (Bosscha et al., 2025).

The honest conclusion is therefore that the economic value of robot-assisted cochlear implantation is currently undemonstrated rather than established. A cost-utility analysis using quality-adjusted life years, conducted alongside a randomized trial, incorporating device, disposable, training and theater-time costs, and stratified by center caseload, should be considered a priority before wide adoption is recommended.

13.1 Access to cochlear implantation

Cost is only one determinant of who is implanted, and in global terms not the dominant one. Hearing loss affects more than 1.5 billion people, of whom some 430 million currently require rehabilitation, and the World Health Organization projects 2.5 billion people with some degree of hearing loss by 2050. Unaddressed hearing loss carries an annual global cost approaching one trillion US dollars, and the report identifies a gap of roughly 83% in access to ear and hearing care services worldwide (World Health Organization, 2021).

Against this background, cochlear implantation is markedly underused. A recent synthesis of a decade of reported data found that uptake remains at or below 20% of those with profound to complete hearing loss in most high-income countries, and approximately 2.5% when the global population is considered (D'Haese et al., 2026). The contrast between pediatric and adult uptake is striking: pediatric rates approach or exceed 90% in several European countries, whereas adult uptake in most settings remains below 10%.

The barriers are not principally surgical. A scoping review of 68 studies grouped them into an ecological framework. It spans policy and structural factors, including reimbursement and documented racial and ethnic disparities; organizational factors such as referral pathways, catchment area and travel distance; and individual factors such as awareness, stigma and fear of surgery (Neukam et al., 2024). Limited professional awareness of current candidacy criteria is a recurring theme, as is the shortage of clinicians trained in implant care.

These are determinants of who reaches an operating theater at all, and they operate upstream of any question of insertion technique.

13.2 Implications of robotic assistance for access

Robotic assistance could act on access in two opposite directions, and the balance is not yet known. It may improve it: by standardizing the most variable step of the operation, robotic insertion could reduce the dependence of outcome on individual surgical experience, which would matter most in lower-volume centers and during training. If that effect is real, it would extend consistent-quality implantation beyond high-volume referral centers.

It may equally worsen it. Capital equipment, disposables and the imaging infrastructure required for robotic direct cochlear access are affordable mainly to well-resourced programs, and the caseload dependence of robotic cost-effectiveness favors concentration in high-volume centers. In a field where the principal problem is that too few eligible adults are implanted anywhere, a technology that raises the cost per procedure without a demonstrated outcome gain could divert resources from the expansion of capacity. Economic evaluation of RACIS should therefore include a distributional analysis, and not confine itself to cost per quality-adjusted life year in a single high-income setting.

A related point deserves emphasis, because it follows from the body of this review rather than from any economic argument. Most of what is known to protect residual hearing costs very little. It amounts to a round window approach, a thin flexible lateral-wall array matched to measured cochlear duct length, avoidance of suction and bone dust, a slow uninterrupted insertion, and perioperative corticosteroids. These measures are deployable in any setting equipped for cochlear implantation.

Robotic assistance refines one component of that strategy; it does not replace it, and it should not be presented as a prerequisite for hearing preservation.

14 Limitations of this review

This is a narrative rather than a systematic review. Although the search strategy is reported in Section 2, study selection was not duplicated independently at the title and abstract stage, no formal risk-of-bias instrument was applied to individual studies, and no protocol was registered. Some selection bias in favor of frequently cited work and of studies published in English or French cannot be excluded.

The evidence base itself imposes further limits. There is no randomized controlled trial of robotic vs. manual electrode insertion, and the clinical comparative literature consists of small single-center cohorts, several of which originate from centers involved in device development. Preclinical studies are heterogeneous in model, instrumentation and outcome definition, which precludes quantitative synthesis. Hearing preservation is defined differently across the studies cited, and follow-up rarely exceeds one to 2 years, whereas the decline in preserved hearing continues well beyond that horizon (Sladen et al., 2025; Snels et al., 2019). Figure 5 summarises which of the claims made for robot-assisted implantation are supported at which level of evidence, and which remain untested. Finally, one of the present authors has published clinical work on robotic implantation that is cited here (Gersdorff et al., 2024); readers should weigh the corresponding sections accordingly.

Figure 5

15 Future directions

Several lines of development are likely to shape hearing preservation over the coming decade. They differ widely in maturity, from strategies already in clinical use to those still confined to animal models; Figure 6 places each on that scale, and the subsections below follow the same order.

Figure 6

15.1 Robotics and closed-loop insertion

The most immediate priority is the closed-loop insertion, in which real-time electrocochleography and, eventually, force or pressure sensing modulate the advance of a robotically controlled array. Feasibility of ECochG-guided robotic insertion has been shown (Gawecki et al., 2022; Kashani et al., 2024b), but the step from monitoring to automated response has not been taken clinically. Randomized comparison of guided vs. unguided robotic insertion, with audiometric primary endpoints, is the trial the field most needs.

Two obstacles must be solved first. The physiological latency of an ECochG response is of the order of milliseconds whereas the mechanical response of an insertion tool is slower, so the control loop must anticipate rather than react. And no agreed criterion yet defines what magnitude of amplitude drop should trigger a change in insertion, which is why current systems alert the surgeon rather than act.

15.2 Drug-eluting, sensing and steerable arrays

Dexamethasone-eluting arrays reduce fibrous tissue growth and impedance elevation in animal models (Wilk et al., 2016), and first-in-human use has been reported. Sustained local delivery addresses the pharmacokinetic limitations of systemic and intratympanic steroids (Parys et al., 2022), and future carriers may deliver neurotrophins or anti-apoptotic agents.

Smart arrays address the instrumentation gap identified in Section 4, namely that the parameters governing trauma are not measurable during surgery. Three lines are being pursued. Sensing arrays and insertion tools integrating force transducers resolve forces of the order of 0.005 N, far below the threshold of human tactile perception, and can flag an abnormal force profile during insertion.

Steerable arrays, actuated mechanically or magnetically, allow the tip to be pulled away from the lateral wall. Magnetic steering of a robotically inserted lateral-wall array reduced force on a phantom basilar membrane by at least 62% beyond 14.4 mm of insertion, provided the steering was strong enough to lift the tip off the wall (Hendricks et al., 2021). Arrays combining drug elution with sensing would in principle allow the tissue response to be both measured and modulated.

Two reservations apply. Steering mechanisms add stiffness, which is precisely the property that atraumatic design seeks to minimize, so the net effect on trauma cannot be assumed. And all of this work is preclinical: no sensing or steerable array is in clinical use, and none has been evaluated against an audiometric endpoint.

15.3 Artificial intelligence

Artificial intelligence operates on three distinct fronts, which should not be conflated. The first is signal processing. Deep neural networks tested in thirteen implant recipients improved speech intelligibility in multi-talker interference, where conventional single-microphone algorithms fail, without degrading perceived sound quality (Borjigin et al., 2024). The constraint is computational rather than conceptual. A transformer-based separator required approximately five times real time on a general-purpose processor, whereas a lightweight recurrent network needed about 3%. A sound processor must stay below roughly 10–20 ms of delay to avoid disturbing audio-visual integration (Borjigin et al., 2024).

Low-complexity causal architectures are therefore the realistic near-term route.

The second front is prediction. A systematic review of machine-learning models of implant outcome found useful discrimination from imaging, neural-response and clinical predictors, but few externally validated models and almost none integrated into clinical decisions (Mo et al., 2025).

The third front is planning: automated cochlear segmentation, duct-length measurement and individualized frequency-to-place mapping. These bear directly on hearing preservation because they determine array selection and insertion depth. Of the three fronts, only the first has been tested on hearing outcomes in implant users; the value of the others for hearing preservation remains to be demonstrated in independent cohorts.

15.4 Gene therapy

Adeno-associated viral delivery of OTOF has restored useful auditory function in children with autosomal recessive deafness 9 (Lv et al., 2024), establishing proof of principle for biological correction of a genetic hearing loss. Several trials of OTOF gene therapy have now been registered internationally, most using dual-AAV constructs, with a safety profile so far dominated by low-grade adverse events (Zeng et al., 2025). The scope nonetheless remains narrow: otoferlin-related deafness accounts for a small fraction of congenital hearing loss, and the intervention requires an intact hair cell population, which is not the situation of most implant candidates. The considered view is that implantation will remain the standard intervention for severe-to-profound hearing loss in the near term, with gene therapy an alternative in selected monogenic forms (Zeng et al., 2025).

This reframes the objective of atraumatic implantation: preserving cochlear architecture and the spiral ganglion population preserves the substrate on which such therapies act.

15.5 Regenerative and neuroprotective strategies

Two distinct objectives must be separated here: restoring sensory cells, and preserving the neural population that an implant stimulates. Regeneration of mammalian hair cells remains unachieved in humans despite consistent results in non-mammalian models. A phase I/IIa trial of an intratympanic gamma-secretase inhibitor was safe and well tolerated but did not meet its primary efficacy endpoint (Schilder et al., 2024), a result that usefully calibrates expectations in this field.

Neuroprotection is the nearer prospect. Loss of endogenous neurotrophic support drives spiral ganglion degeneration after hair cell loss, and sustained delivery of brain-derived neurotrophic factor from nanoporous carriers improves neuronal survival in vitro (Schmidt et al., 2018). Because the array is already in contact with the scala tympani, it is a natural vehicle for such delivery, and this is the point at which regenerative strategies converge with the drug-eluting arrays discussed above. All of this evidence is preclinical; no neurotrophin has entered a hearing-preservation trial in implant recipients.

15.6 Optical cochlear implants

Optogenetic stimulation of spiral ganglion neurons promises far greater spectral selectivity than electrical stimulation, and multichannel optical implants have been demonstrated in animal models (Huet et al., 2024). Clinical translation will require an optogene therapy in addition to a new implant, and remains distant: it combines the regulatory burden of a gene therapy with that of an active implantable device, and no first-in-human study has been announced. Two further problems are unresolved, namely the light power required for reliable spiking without thermal injury, and the long-term stability of opsin expression. The concept nonetheless bears directly on the subject of this review, because optogenetic stimulation depends absolutely on the survival of spiral ganglion neurons, and therefore on atraumatic surgery.

16 Conclusion and perspectives

Taken together, current data indicate that robot-assisted cochlear implantation surgery (RACIS), when combined with atraumatic electrode arrays, represents a meaningful evolution toward implantation strategies that are more respectful of cochlear anatomy and function. Beyond mere technical feasibility, RACIS is part of a broader effort to standardize the surgical gesture, aiming to reduce inter-operator variability and to secure critical insertion parameters.

A clear distinction should be drawn between what is demonstrated and what remains hypothetical. Experimental studies in temporal bones and in vitro models demonstrate that robotic insertion lowers insertion forces, reduces force variability and intracochlear pressure transients, and produces lower trauma scores and more frequent complete scala tympani placement than manual insertion. Clinical series demonstrate that RACIS is feasible and safe, with a procedural success rate of 97.2% and a complication profile comparable to conventional surgery.

Four propositions, by contrast, remain unproven. That RACIS durably improves hearing preservation rests on small non-randomized cohorts, reporting differences of the order of 12%−14% that did not reach statistical significance. That it limits intracochlear fibrosis rests on indirect impedance evidence alone. No vestibular benefit has been demonstrated on objective testing, and no economic advantage has been established. The technical advantages of RACIS are therefore established; its long-term functional and economic benefit is suggested but not proven.

By facilitating more reliable insertions of long lateral-wall electrodes, robotic assistance also opens perspectives in terms of cochlear coverage and frequency matching. Improved correspondence between electrical stimulation and the individual tonotopic organization of the cochlea appears to be a central lever for reducing frequency-place mismatch and optimizing speech perception, particularly in cochlear implant-only users. This approach is consistent with a more structural and personalized coding strategy, taking into account interindividual cochlear anatomical variability.

Finally, the integration of intraoperative functional feedback, such as electrocochleography, in synergy with robotic systems represents a further step toward adaptive cochlear implantation, guided in real time by cochlear responses. The combination of robotic insertion with intraoperative electrocochleography may enhance the reliability and interpretability of electrophysiological signals, potentially enabling more precise incident detection, improved predictive value for trauma or insertion-related events, and more refined intraoperative electrode position corrections. While the available results are encouraging, prospective randomized clinical trials, including long-term functional outcomes, standardized hearing preservation definitions, systematic vestibular assessment and health-economic evaluation and direct comparisons between robotic platforms, remain essential to establish the definitive clinical benefit of RACIS.

Robot-assisted cochlear implantation is thus best characterized at present as a reliable and maturing technique that standardizes one critical step of the operation. Whether this standardization translates into sustained improvement in auditory outcomes is the question that the next generation of trials must answer. In the meantime, hearing preservation should be pursued as a multimodal objective, in which surgical atraumaticity, individualized electrode selection, pharmacological protection and intraoperative monitoring each contribute, and in which no single technology should be presented as sufficient on its own.

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