Cochlear implant revisions: a 10-year review of the victorian cochlear implant program

Introduction

Cochlear implantation is an established and effective intervention for individuals with severe to profound sensorineural hearing loss, restoring auditory perception and improving communication outcomes and quality of life (1,2). Following the development of the first cochlear implants (CIs) in the early 1960s and the introduction of multichannel systems in the late 1970s, continuous advances in device technology and surgical technique have enhanced patient outcomes (1).

CI candidacy has since broadened to include populations previously considered ineligible, such as individuals with unilateral sensorineural hearing loss, prelingual deafness and those receiving sequential or bilateral implantation (3,4). Amongst unilateral CI recipients, bimodal hearing, the combined use of a CI with a contralateral hearing aid, has become an increasingly common configuration (5). As implant candidacy criteria broaden and hearing preservation techniques improve, the number of individuals with aidable residual hearing in the non-implanted ear, and therefore potential bimodal users, is expected to continue to rise (6). Bimodal listeners typically achieve superior speech perception and overall communication outcomes compared with unilateral CI users (6,7).

Recent Australian data indicate that the total number of CI procedures has increased substantially over the past two decades, with annual implantations rising from approximately 200 in the early 2000s to over 1,400 from 2017–2018 (8). Despite this growth, the estimated adult CI uptake rate remains modest at approximately 10.5% of Australian adults with severe to profound hearing loss, highlighting a persistent disparity between clinical eligibility and device utilisation (8). Although contemporary implants demonstrate excellent long-term reliability, device failure and medical issues may necessitate revision surgery. Revision procedures carry important implications for patient morbidity and cost alongside overall healthcare expenditure. Reported revision rates range from 5–8%, reflecting heterogeneity in patient demographics, follow-up durations and implant technology (9-11).

With an expanding cohort of CI recipients and substantial unrealised potential for increased utilisation, the absolute number of revision procedures is expected to rise correspondingly in the coming years (12-14). Institution-specific evaluations provide valuable insights into local factors influencing revision risk and offer benchmarking data for quality improvement initiatives, surgical auditing and patient counselling. In this study, we evaluate the incidence and causes of cochlear implant revision (CIR) surgeries performed at the Royal Victorian Eye and Ear Hospital over a recent 10-year period. By characterising revision patterns within a single tertiary institution with an experience of more than 6,000 cochlear implantations, this study aims to contribute to the broader understanding of implant reliability and surgical outcomes.

Methods

This was a single-centre, retrospective cohort study undertaken at the Royal Victorian Eye and Ear Hospital in Victoria, Australia. The study was reported according to the STROBE reporting guidelines (available at https://www.theajo.com/article/view/10.21037/ajo-2025-1-95/rc). The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. Ethics approval was sought and approved by the Royal Victorian Eye and Ear Hospital Human Research and Ethics Committee (Project 04/564H/24) and all patients consented to the use of their clinical data for research purposes. For patients under 18 years old, informed consents were obtained from their parents. All cases of CIR between 2015 and 2025 were identified. Revision surgeries were assumed to have been performed at the original CI centre, as transfer of care to alternative centres could not be reliably verified for all patients within the available institutional records. This assumption may result in an underestimation of the true revision rate if revisions were performed at external centres and not captured within our dataset. CIR procedures included cases involving device explantation alone, as well as explantation followed by immediate or staged re-implantation. Procedures limited to device repositioning, without device removal or replacement, were also classified as CIR.

Chart review was performed to extract individual patient data, including demographics, primary CI device, duration to CIR, CIR procedure and indication for CIR. Patients were excluded from the study if they had previously undergone a CIR or had research implants. Age at primary cochlear implantation was used to stratify patients into adult and paediatric cohorts (≥18 or <18 years of age). The indications for CIR were classified according to the 2005 European Consensus Statement for Cochlear Implant Failure and Explantations, alongside the 2005 Soft Failures Consensus Development Statement (15,16). Broadly, CIR patients were divided into those with soft failure, hard failure or medical failure. Hard failure patients had abnormal findings on integrity testing and explanted device analysis. Soft failure patients had signs and symptoms of device failure despite normal integrity testing and explanted device analysis, with improved performance following reimplantation. Patients were considered to have a performance decrement if they had reduced clinical benefit but integrity testing that remained within normal limits. In patients with performance decrement who underwent reimplantation, the explanted device analysis and presence or absence of clinical benefit after reimplantation were used to classify these patients as soft failure or medical failure. Medical failure encompassed several indications not related to device failure, including infection, cholesteatoma, head trauma, tip malposition, magnet migration, magnetic resonance imaging (MRI) requirement or patient decision.

Statistical analysis

All statistical analyses were performed using R (version 4.5.1; R Foundation for Statistical Computing, Vienna, Austria). Data was imported, cleaned, and summarised using standard R packages for data manipulation and table generation. Continuous variables were reported as means with standard deviations (SDs) and categorical variables as frequencies with percentages. Summary tables were produced to describe demographic, device, and procedural characteristics. Missing data were handled using available-case analysis. Variables with incomplete documentation were reported as unknown where applicable and no imputation was performed, given the retrospective design and small proportion of missing values. The extent of missing data for key variables is reflected in the summary tables.

Results

Between June 2015 and June 2025, a total of 1,820 primary and revision CI procedures were performed on 1,668 patients at the Royal Victorian Eye and Ear Hospital, of which 444 were for paediatric patients. This cohort included 78 patients (4.7%) who underwent bilateral cochlear implantation. All implants were Cochlear^TM Nucleus^® devices. The overall CIR rate was 3.8% (63/1668 patients), corresponding to 63 revision procedures among 1,820 CI procedures (3.5% per procedure). Of these, 10 (15.9%) occurred in paediatric patients and 53 (84.1%) in adults. The paediatric and adult revision rates were 2.6% (10/389) and 4.1% (53/1,279), respectively.

Demographics and device characteristics

Table 1 summarises the demographic and implant characteristics of the CIR cohort. The mean age at primary implantation was 1.2 years (SD 1.2) for paediatric and 47.7 years (SD 21.8) for adult recipients. The mean time interval from the primary CI to revision surgery was 5.2 years (SD 3.9) in paediatric patients and 9.3 years (SD 9.4) in adults, corresponding to an overall mean interval of 8.6 years (SD 8.8). A slight majority of revision surgeries involved the left ear (32/63, 51%), with 49% (31/63) performed on the right. The cohort was 62% (39/63) female and 38% (24/63) male. The CI512 accounted for 22% (14/63) of revisions; however, as outlined in Table 2, it represented 17.8% (314/1,762) of all implanted devices during the study period. Other common models amongst CIR cases included the CI24RE (6/63, 9.5%) and the CI622 (6/63, 9.5%), with the remainder distributed among older and newer generation devices, such as the CI22M, CI24M and the CI422. Table 2 summarises the distribution of CI device models inserted during the study period. Over the 10-year cohort, the most commonly implanted devices were the CI632 (477/1,762, 27.1%), CI512 (314/1,762, 17.8%), CI532 (283/1,762, 16.1%) and CI622 (234/1,762, 13.3%). Device models were included only where clearly documented in the medical records and did not include revision procedures where a new device was not implanted.

Indications for revision surgery

As outlined in Table 3, the predominant indication for CIR was medical failure, accounting for approximately 74.6% (47/63) of all cases, followed by hard failure in 23.8% (15/63) and soft failure in 1.6% (1/63). Among those with hard failures, the most common problems were insulation failure (8/15, 53.3%), hermeticity failure (2/15, 13.3%), and electrode array failure (2/15, 13.3%). Medical failures were more heterogeneous, most frequently attributed to infection (13/47, 27.7%), electrode tip malposition (8/47, 17%), head trauma (6/47, 12.8%) and patient decision (6/47, 12.8%). When indications were stratified by the type of revision procedure, as highlighted in Table 4, medical failures comprised the entirety of cases in explant, adjustment and staged reimplantation groups. Device failure was the major indication in the immediate reimplantation group, representing 59.7% (16/27) of cases, the majority (15/16, 93.8%) of which were hard failures.

In our cohort, 8 adults were identified with electrode tip malposition, with no cases occurring in paediatric recipients. Of these, 5 patients (62.5%) had tip fold-over, 2 (25%) had poor pitch matching on second side CI that was revised with deeper electrode insertion, 1 (12.5%) had a shallow insertion depth with extracochlear electrodes requiring deeper insertion. When categorised by array design, perimodiolar electrodes accounted for all five cases of tip fold-over. Amongst tip fold-overs, four cases were in slim modiolar arrays (CI532/CI632) and one case involved the Contour Advance (CI512) array. All lateral-wall tip malpositions occurred in slim straight CI622 arrays, with no malpositions seen in older straight electrode arrays (CI22, CI24, CI422).

In this cohort, patient decision referred to cases where recipients (or parents/guardians) requested explantation due to a combination of lack of perceived benefit and a patient-perceived need, such as persistent pain at the implant site. Importantly, these indications did not involve revision of electrode position at patient request but rather elective explantation driven by patient-reported symptoms or limitations.

Revision surgery characteristics

Explantation followed by immediate reimplantation was the most common revision procedure, representing 42.9% (27/63) of CIR procedures overall. Delayed reimplantation and adjustments without explantation occurred less frequently in 19% (12/63) and 12.7% (8/63) of overall cases, respectively. As shown in Table 5, paediatric patients underwent explant followed by staged reimplantation in 50% (5/10) of cases, of which 80% (4/5) of cases were due to infection, precluding immediate reimplantation.

Discussion

In this 10-year, single-centre cohort, we observed an overall CIR rate of 3.8% (63 of 1,668 patients) among both adult and paediatric recipients. This revision rate is broadly consistent with published contemporary series, which have reported rates ranging between 4–9% (9,10,17,18). Notably, several large retrospective series with follow-up durations extending up to three decades have reported higher crude revision proportions (10,17,18). However, such comparisons should be interpreted cautiously, as longer observation periods inherently capture a greater cumulative risk of revision and include earlier implant technology. In contrast, the present study was designed to reflect contemporary surgical practice and modern device utilisation.

The relatively younger mean age among adults of 47.7 years (SD 21.8) in this revision cohort reflects a predominance of younger adult recipients requiring revision, compared with the broader adult CI population at our centre, where the mean age at implantation is 61 years. The mean interval from primary implantation to revision was 8.6 years (SD 8.8), indicating longer device survival among revised cases than has been reported previously (10,17,18). Paediatric recipients demonstrated a shorter mean interval to revision (5.2 years, SD 3.9) compared with adults (9.3 years, SD 9.4). The paediatric revision rate in our cohort of 2.6% (10/389) was lower than that reported in prior studies, which have typically shown higher revision rates in children (19). Head trauma accounted for only one paediatric revision in our series, contrasting with previously published findings where trauma has been a more common contributing factor (19).

The predominance of the CI512 device among revision cases (22%, 14/63) in our cohort aligns with reported patterns following its global recall in 2011 (13,20,21). Notably, the CI512 was a frequently inserted CI model during the study period, representing 17.8% (314/1,762) of cochlear implantations over the 10-year follow-up duration. The CI512 recall was initiated after an increased incidence of hermetic seal failures within specific manufacturing batches, which resulted in loss of device function (22). Although the overall reliability of modern implants remains high, this difference underscores the importance of robust post-market monitoring and transparency in reporting device-specific outcomes. Importantly, the increase in annual cochlear implantations in recent years compared with 20 to 30 years ago has resulted in a greater number of modern devices, such as the CI512, in circulation (8).

Device failure was the predominant indication for revision among reimplantation cases in our cohort, aligning with international reports where 55–75% of CIRs are attributed to device failure (9,10,17). Within our primary reimplantation group, device failure accounted for 59.7% (16/27) of revisions. In contrast, when all CIR procedures were considered collectively, device failure represented a significantly smaller proportion at 25.4% (16/63). This lower overall proportion of device failures compared with published series is likely explained by differences in the distribution of CIR procedure types across cohorts, with studies reporting higher proportions of device failures typically including a greater proportion of reimplantation cases. For instance, Wang et al. reported 57.8% device failures in a CIR cohort comprising 88% reimplantations, compared with 61.9% (39/63) reimplantations in our series (17).

The lower proportion of device failures may also reflect differences in patient demographics across study cohorts. Studies such as Wang et al.’s study had a greater proportion of paediatric CIRs, among whom device failures represented a significant majority (17). An earlier retrospective series of CIRs performed at the Victorian Cochlear Implant Program between 1986–2006 demonstrated this same trend, where adult CIRs were primarily caused by medical failures, while paediatric CIRs were most commonly due to device failures (23). Other contemporary cohorts have also identified this predominance of medical failures amongst CIR indications in adult recipients (24). Consistent with previous literature, soft failures represented a relatively uncommon cause for CIR in our study, accounting for 6.25% (1/16) of device failures (10,11).

Among CIR cases performed for hard failure, post-explant device analysis identified insulation failure (53.3%, 8/15), hermeticity failure (13.3%, 2/15) and electrode array failure (13.3%, 2/15) as the most frequent underlying causes. Prior studies incorporating post-explantation analyses have reported hermeticity failure, electrode array failure, and electronics failure as the predominant mechanisms of hard failure, although such analyses have been inconsistently included in historical CIR cohorts (25,26). The predominance of medical failures in our series, accounting for nearly three-quarters of all revision procedures, marks a notable shift from earlier reports in which device failure constituted the primary indication for revision. Several factors likely contribute to this trend. First, advances in device design and manufacturing have improved reliability, thereby reducing the incidence of device-related failures and increasing the relative proportion of revisions prompted by patient-related or external factors. Second, the expansion of cochlear implantation candidacy criteria now includes patients with more complex temporal bone anatomy, pathologies and clinical profiles, such as cochlear ossification, which inherently carry greater surgical and postoperative risk (27). Third, the increasing reliance on MRI for non-otologic indications has introduced new challenges, with magnet migration and demagnetisation during MRI emerging as recognised causes of revision despite ongoing refinements in magnet design (28,29). Finally, a growing subset of patient-initiated explantations driven by lack of hearing benefit, discomfort or personal preference may further account for the rising proportion of medical failures observed in this cohort.

The pattern observed in our cohort aligns closely with published data on electrode tip fold-over across implant designs. The literature consistently reports higher fold-over rates among perimodiolar compared to lateral wall electrodes, with a recently published review estimating an incidence of approximately 5.3% and 1% for perimodiolar and lateral wall arrays, respectively (30). Our results reflect this tendency with perimodiolar arrays accounting for all of this cohort’s tip fold-overs. The absence of paediatric cases also mirrors findings from earlier retrospective reviews, including one conducted at this institution, where Chaul et al. found eight adult and no paediatric tip fold-overs in a cohort of 125 adult and 69 paediatric CI532 insertions (31). Slim modiolar devices (CI532/CI632) have been highlighted as more susceptible to tip fold-over due to their thin profile and stylet-free design, which is consistent with the predominance of slim modiolar tip fold-overs in our dataset. Three tip malpositions occurred among straight lateral-wall arrays in our 10-year series, all of which were CI622. Although CI532/CI632 arrays demonstrate a greater propensity for tip fold-over, this should not be construed as a reason to discontinue their use, given their recognised advantages achieved through close modiolar proximity (32,33). Rather, these findings underscore the need for heightened intraoperative vigilance during slim modiolar insertions, including consideration of real-time verification techniques such as fluoroscopy or neural response telemetry to facilitate early detection of malposition.

At our institution, intraoperative X-ray was performed routinely following slim modiolar (32) or Contour Advance (12) electrode array insertion but not for straight lateral wall arrays. This study did not investigate cases of tip fold-over that were corrected within the primary procedure however, for revision cases due to tip fold-over, intraoperative X-ray did not clearly demonstrate tip malposition. In these instances, the diagnosis became evident on subsequent post-operative cone-beam computed tomography (CBCT), which provided superior spatial resolution of intracochlear electrode configuration. The Nucleus^® SmartNav system was released in the late phase of the study period and therefore had minimal impact on the operative practice within this cohort. However, emerging evidence supports its utility in facilitating intraoperative detection of electrode malposition, potentially identifying subtle tip malposition missed on intraoperative X-ray (34). Overall, our findings support the broader evidence base indicating that electrode design and insertion mechanics influence fold-over risk, with perimodiolar arrays exhibiting a higher propensity than straight lateral-wall electrodes.

Taken together, these observations suggest a changing profile of revision surgery from one dominated by hardware faults to one increasingly defined by medical and patient-centred factors. Addressing these issues will require not only ongoing technical refinement but also meticulous perioperative infection prevention, patient education, and long-term multidisciplinary follow-up.

Limitations

This study is subject to limitations inherent to retrospective, single-centre analyses. Revision rates may be underestimated due to variable durations of follow-up and the possibility that some patients underwent revision surgery at external institutions not captured within our database. As transfer of care between CI centres could not be systematically verified, revision procedures performed elsewhere may not have been identified, potentially biasing revision rate estimates toward lower values. The 10-year study period was selected to capture contemporary patterns of CIR; however, changes in implant technology, surgical technique, and reporting practices over this time may have influenced case distribution and outcomes. Additionally, the classification of revision indications relied on clinical documentation and operative records, introducing the potential for misclassification bias. Missing or incomplete documentation may have influenced categorisation in a small number of cases. As a single-institution study, findings may not be generalisable to centres with different patient demographics, implant manufacturers or surgical protocols.

Conclusions

This institutional series demonstrates that CIR remains an uncommon but clinically significant occurrence, with an overall revision rate of 3.8% (63/1,668) over the past decade. Device failure was the leading indication among reimplantation procedures, whereas medical failures were the most common overall cause for revision. Paediatric recipients demonstrated a lower revision rate than adults but a shorter interval to revision among those affected.

These findings indicate a shift in the underlying causes of CIR from hardware-related issues toward medical and patient-related factors. Improvements in implant reliability, expansion of candidacy criteria and greater exposure to external influences such as MRI-related complications likely contribute to this trend. As the population of CI recipients continues to expand, sustained surveillance, structured outcome auditing, and integrated multidisciplinary follow-up are critical to maintaining device reliability and optimising long-term patient outcomes.

Importantly, the predominance of medical failures reinforces the need for robust post-operative infection prevention, careful longitudinal monitoring and increased intraoperative vigilance, particularly regarding electrode position and malposition risk.

Future multicentre studies incorporating device-specific reliability data, surgical variables and long-term functional outcomes would further enhance understanding of revision risk and inform preventive strategies within Australian CI programs.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://www.theajo.com/article/view/10.21037/ajo-2025-1-95/rc

Data Sharing Statement: Available at https://www.theajo.com/article/view/10.21037/ajo-2025-1-95/dss

Peer Review File: Available at https://www.theajo.com/article/view/10.21037/ajo-2025-1-95/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://www.theajo.com/article/view/10.21037/ajo-2025-1-95/coif). R.B. and J.M.G. received consulting fees from Cochlear LTD. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the Royal Victorian Eye and Ear Hospital Human Research and Ethics Committee (Project 04/564H/24). All patients consented to the use of their clinical data for research purposes. For patients under 18 years old, informed consents were obtained from their parents.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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