The Ponto Bone-Anchored Hearing System – Benefits Following Radical Mastoidectomy

Introduction

According to the World Health Organization (WHO), chronic otitis media (COM) is a persistent inflammation of the middle ear and/or mastoid cavity characterized by hearing loss and chronic (≥2 weeks) or intermittent otorrhea, tympanic membrane perforation, otalgia, or ear discomfort [1]. It is usually a preventable and treatable cause of hearing loss. COM is categorized as either chronic suppurative otitis media (CSOM) or COM with cholesteatoma development [2].

Cholesteatoma, a destructive lesion of the temporal bone, can result in osteitis and bony erosion of the surrounding structures (including the ossicular chain) and can cause hearing loss, vestibular dysfunction, and potentially dangerous intracranial complications [3]. For infection and inflammation, a conservative treatment with local or systemic drugs is first used. In the case of cholesteatoma, the primary treatment to prevent further bone destruction and intracranial complications is surgery.

There are 2 common surgical approaches in managing COM. In canal wall up (CWU)/intact canal wall (ICW) mastoidectomy, the posterior canal wall is preserved. It is preferred when the cholesteatoma is limited and the posterior wall is intact; it is not recommended when better ventilation is needed [4]. On the other hand, CWD mastoidectomy (which is further divided into modified radical mastoidectomy and radical mastoidectomy) is usually easier to perform than CWU and gives good access to the middle ear, particularly with extensive cholesteatomas [5]. Post-CWD patients have less need for frequent follow-up visits or second operations, and recurrence of ear disease is less likely [6]. The choice of procedure depends on patient factors as well as surgical expertise. After the CWD procedure, there is the option of reconstructing the posterior wall [7,8], which provides better quality of life (such as fewer vestibular disorders after contact with water and less need for regular cleaning of the radical cavity). Reconstruction is carried out with bioactive glass or bone pate, and can be done when a passive middle ear implant is being inserted.

One common consequence of chronic cholesteatoma and surgery is hearing loss [9]. In the case of hearing loss after surgery, it is necessary to use hearing prostheses. Depending on the degree and type of hearing loss and local and anatomical conditions, these may be hearing aids, bone-anchored hearing aids, active bone implants, or cochlear implants. In some cases, when there is a need to offer the patient a solution other than an air conduction hearing aid, the next option is a semi-implantable bone conductor [10].

Implantable bone conduction devices are either percutaneous and transcutaneous [11–14]. In the case of transcutaneous devices, implantation options are determined by the size of the internal part and the anatomical conditions, whether natural or changed through surgery [15]. After some mastoid surgeries, a bone conduction implant is not possible. In percutaneous devices, the implantable part is an osseo-integrated screw placed in the temporal bone with a skin-penetrating abutment; since it is small, the anatomical requirements are less.

The principle of a bone-anchored device is that sound vibrations are led directly to the inner ear via the mastoid bone, bypassing the middle ear [16]. The Ponto system is one such device available in clinical practice.

The Ponto system was introduced to the market in 2009 by Oticon Medical (Askim, Sweden) [17]. Since then, its effectiveness has been widely reported in terms of audiologic and self-report outcomes, intra- and postoperative adverse events, and different surgical techniques [18–20]. The Ponto system is suitable for patients with conductive and mixed hearing loss (with bone conduction thresholds not exceeding 65 dB HL for the Superpower processor) and those with single-sided deafness (SSD). Due to the small size of the implant and low bone penetration in the retroauricular area, the system can be used in patients after mastoid surgery.

The literature indicates that mechanical changes caused by surgical intervention in the course of COM affect the characteristics of sound transmission [21]; therefore, patients after mastoidectomy can be treated as having mixed hearing loss. It is important to specify this and assess the audiological benefits of using bone conduction hearing aids in this context.

Chronic otitis media (COM) is not only a cause of hearing loss, but it also significantly impacts quality of life [22]. Effective treatment of COM and its complications is essential to prevent long-term health consequences, reduce healthcare burdens, and improve patients’ functional outcomes.

This study aimed to evaluate the audiological and subjective benefits of Ponto implantation in patients who have undergone radical modified mastoidectomy. The aim was to fill the knowledge gap regarding the efficacy and limitations of the system in this unique patient population.

Material and Methods

STUDY GROUP:

In this retrospective assessment, we analyzed results from 27 adult patients diagnosed with chronic inflammation of the middle ear who, after radical modified mastoidectomy, were implanted with the Oticon Ponto bone-anchored device in 2022. There were 13 men and 14 women, with an average age at implantation of 59 years (36–75 years, SD=11). There were no significant differences (t(25)=0.2; P=0.84) in age distribution between men (M=59.0; SD=11.0) and women (M=58.9; SD=12.7). The left ear was implanted in 15 cases and the right ear in 12. Bilateral hearing loss was diagnosed in 23 patients and unilateral in 4. In terms of severity, 5 patients had moderate, conductive hearing loss in the implanted ear; in 22 cases the hearing loss was mixed, from moderate to very severe according to BIAP classification [23]. Details of the patients are presented in Table 1.

SURGICAL TECHNIQUES:

All Ponto implantations were performed under general anesthesia. The MIPS technique (Minimally Invasive Ponto Surgery) was used in 12 patients and MONO (in which a MONO drill is used) in 15 patients. In all cases, a Ponto BHX implant (4.5 mm wide, 4 mm long) and abutments of various lengths (9, 12, 14 mm, see Table 1) were placed in a one-step surgical procedure. Abutment length was determined based on skin thickness.

MIPS TECHNIQUE:

An incision was made using a 5-mm biopsy punch and a cannula was then inserted. Drilling was performed through the cannula (filled with saline solution), using it as a guide. An appropriate drill bit was then used to widen the hole. Remaining bone fragments were removed by generous flushing, and the implant prepared for installation. The cannula was then removed and the implant installed in the circular incision (preset torque of 40–50 N·cm for normal adult bone quality). Finally, a soft healing cap was attached to the abutment and a suitable dressing was applied [24].

MONO TECHNIQUE:

Based on the MIPS, the MONO procedure has been developed to further streamline installation of a Ponto implant. With the MONO procedure, complete osteotomy for the implant is done in a single drilling step. The MONO drill allows bone to be removed in a single step without overheating. In the MONO procedure, drilling is performed through a cannula, in the same way as in the MIPS procedure. In addition to protecting soft tissue, the cannula also acts as a depth stop and is filled with irrigation fluid to help keep the bone cool. Drilling is performed perpendicular to the skin surface, and an insertion indicator is used during installation of the implant. The indicator displays the number of turns that the implant has been engaged into the bone, ensuring that it is fully inserted at the chosen torque setting (5 turns indicate full insertion) [25]. If the bone is spongy, or if the mastoid has not been consistently obliterated, additional MIPS is recommended.

In all our patients, dressings were removed 10 days after surgery. All patients were then fitted with an external audio processor – a Ponto 3 Superpower. It was activated 1–2 months after implantation based on BC-Direct, Genie Medical software, in which hearing thresholds are measured in situ.

AUDIOLOGICAL ASSESSMENT:

We assessed the benefits of Ponto implantation based on the following tests:

PATIENT-REPORTED OUTCOME MEASURES:

Subjective benefits were assessed using 2 PROMs (Patient-Reported Outcome Measures): the APHAB questionnaire (Abbreviated Profile of Hearing Aid Benefit) and the SSQ12 questionnaire (Speech, Spatial and Qualities of Hearing Scale).

The APHAB focuses on assessing the difficulty of hearing speech and other sounds in different conditions, whereas the SSQ provides a broader assessment of hearing function, including the ability to localize sounds.

STATISTICAL ANALYSES:

A Student’s t-test was used to make pair-wise comparisons of patient outcomes between pre- and post-surgery in terms of pure-tone audiometry (unaided and aided) and free-field thresholds, as well as for PROMs. To evaluate the effect of test condition on speech outcomes, a repeated measures ANOVA was implemented. The WRSs in quiet were tested using 3 within-subject factors: unaided, with a bone conduction hearing aid on a soft band before surgery, and with the Ponto system. Additionally, sex was assessed as a potential confounding factor. Normal distribution of the data was evaluated using a Shapiro-Wilk test. Sphericity was tested using Mauchly’s test. To check which combination of variables differed significantly from the others, a post hoc pair-wise multiple comparison procedure using the Tukey test was applied. The test compares the difference between each pair of means with appropriate adjustment for the multiple testing. The level of significance was set at α=0.05.

The local bioethics committee gave consent for retrospective analysis of data obtained during routine clinical practice (KB.IFPS: 3/2022), which was in accordance with the Helsinki Declaration.

Results

Audiological Assessment

PURE-TONE AUDIOMETRY:

Pure-tone audiometry was analyzed in all 27 patients. Pure-tone audiometry was performed to assess the safety of the surgical procedure immediately before surgery and at the first postoperative visit. Preoperatively, PTA4 for AC thresholds in the implanted ear was 50–110 dB HL (mean=76.7 dB, SD=16.0); at 1–2 months after implantation, PTA4 for AC was 51.25–108.75 dB (mean=76.4 dB, SD=16.2). Thresholds remained stable in all subjects (preoperative vs 1–2 months, t(26)=0.23; P=0.82).

Likewise, PTA4 for BC thresholds in the implanted ear was 15–62.5 dB HL (mean=35.3 dB, SD=11.7) and remained stable in all subjects in the same time interval as before; PTA4 for BC was 7.5–61.25 dB (mean=34.7 dB, SD=12.9; pre vs 1–2 months, t(26)=0.65; P=0.52).

Average hearing thresholds for AC and BC before and after implantation are presented in Figure 1.

PATIENT-REPORTED OUTCOME MEASURES:

The mean results for the APHAB and SSQ questionnaires, and the results of pair-wise comparisons, are provided in Table 2.

THE BC-DIRECT THRESHOLDS:

BC-Direct thresholds were measured through the sound processor during activation of the Ponto system for 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, and 8 kHz. During this measurement, signals are generated in the processor and sent directly to the cochlea via the implant. These results show the true bone conduction thresholds. Measurements were done using the same audiometric techniques as in pure-tone audiometry but with the sound processor microphone turned off. The BC pure-tone thresholds after implantation, BC-Direct thresholds (for frequencies corresponding to audiometric frequencies), and the differences between them are presented in Figure 4.

POST-SURGICAL COMPLICATIONS:

Skin reaction around the implant was assessed using the Holgers scale in all test subjects [28]. At the 12-month postoperative follow-up, redness with slight swelling (Holgers 1) was noted in 3 patients; there were no skin reactions (Holgers 0) in the others.

USAGE TIME:

All patients used the Ponto system regularly (data collected from the interview). The average daily usage time (read from the data logger in 25 patients) after 12 months of using the processor was 7 hours (SD=3 h).

Discussion

Before wide implantation based on bone conduction, our preferred solution was the Vibrant Soundbridge with floating mass transducer (FMT) located directly on the round window [29,30]. Now, in the area of implantable bone conduction devices, the first choice in our clinic has become active transcutaneous solutions.

Nevertheless, it should be noted that if the ear canal wall has been removed, the options of using a transcutaneous implantable devices become limited. After obliteration and reconstruction of the ear canal wall, the Bonebridge (BB) active bone conduction implant (MedEl, Innsbruck, Austria) can still be used in the most common location (at the sino-dural angle) [31], but two-stage surgery is then needed – obliteration of the postoperative cavity, followed by implantation.

In percutaneous solutions, the size, design, and location of the implant screw do not require prior obliteration of the mastoid cavity. Naturally, the presence of a postoperative cavity lead to several restrictions [32,33]. Closing the cavity is generally recommended, although this is not necessary for placing the percutaneous implant in an appropriate space (as needed for a BB implant).

Ponto implantation calls for the relatively simple procedure of making a small skin incision and embedding the implant in the bone of the skull, although this means the abutment is exposed on the skin surface. In contrast, active bone conduction implants or middle ear implants require a higher degree of surgical precision; however, unlike Ponto, no part of the implant is exposed on the skin. Given the distinctive differences between each device, selecting the appropriate one is important, noting that the likelihood of infection in the middle ear cavity is a significant factor. In cases where surgery is performed on the infected ear, a bone conduction device could be suitable [34]. Choosing the Ponto system can improve hearing in people for whom further surgical treatment is currently contraindicated (or not required), although it remains possible in the future. Ponto does not rule out the possibility of extensive surgical treatment in the future and creates good conditions for further radiological evaluation if necessary.

Surgical techniques for installing percutaneous bone-anchored hearing systems are continuously developing and have become less invasive. Oticon Medical developed the MIPS procedure for installation of the Ponto system in 2015 [24] and the MONO procedure in 2021 [25]. The Ponto procedure is now one of the least invasive hearing-related procedures available, and there are multiple papers describing the surgical techniques involved [19,25,35,36].

There is also a wide literature describing audiological outcomes after use of the Ponto system in patients with hearing loss. In postoperative patients with refractory otitis media, the structure of the middle ear is often altered by mastoidectomy or posterior wall removal, so it is unclear whether the hearing device is truly effective. Few reports have evaluated auditory outcomes based on the etiology of hearing loss, particularly in cases of refractory otitis media and required surgical treatment. Kurihara et al [34] have demonstrated the positive impact of bone-anchored hearing aids in patients who have undergone implantation after surgery for refractory otitis media. They reported an average aided threshold of 37.3 dB HL (based on 23 users), a figure that was close to the BC threshold of the better-hearing ear side. In our study, the average aided thresholds were very similar (35.4 dB HL). The paper describes similar results to ours in selected aspects, although Kurihara et al used the BAHA system (Cochlear, Sydney, Australia) in their study.

In a study by Skarżyński et al on the effects of using the Ponto implant in a group of 16 adults with severe-to-profound and mixed hearing loss, 7 underwent radical mastoidectomy in the ear that was later implanted with the Ponto system [20]. Similarly, in a study by Bosman et al in a group of 19 Ponto patients, 8 operations were performed after radical mastoidectomy [37], but the results were only analyzed in terms of the entire group, so it is impossible to separate out the effect of mastoidectomy.

Based on a systematic literature review [18], the WRS scores in several works show figures of 78% to 96.5% in Ponto patients who had conductive and mixed hearing loss. In our study, the average WRS at 65 dB SRT was 93%, a result consistent with those findings.

The safety of the surgical procedure is reflected by the lack of significant changes in PTA thresholds before and after surgery.

Several works have used questionnaires to assess subjective benefits, not only in terms of aided versus unaided, but also for comparing alternative bone conduction solutions, including for SSD patients [38,39]. Among PROMs, the APHAB and SSQ have been widely used to assess Ponto. In a study by Cuda et al of 19 adult patients with conductive and mixed hearing loss, the perceived performance with a Ponto connected to the abutment was, according to the SSQ questionnaire, significantly better compared to unaided across all subscales [40]. Skarżyński et al used the APHAB questionnaire to assess the outcomes of Ponto implantation in a group of 15 adults with severe-to-profound mixed hearing loss. The average APHAB scores before and 12 months after implantation reflected a decrease in the frequency of difficulties with everyday functioning on all 3 subscales (EC, BN, RV). Global scores after 12 months decreased significantly from 70.2% before surgery to 34.5%. In our study, global scores decreased significantly from 66.9% before surgery to 23.0% after 6 months, reflecting reductions in all 3 subscales.

Direct bone conduction involves generating test signals in the sound processor and transmitting them directly to the cochlea via the osseo-integrated implant [41]. In this way, better thresholds can be obtained than in traditional audiometric, a result which we also observed. Flynn et al [42] gave several reasons for this observation, including asymmetrical hearing loss, in which the bone conduction device is placed on the side with worse sensorineural hearing thresholds; loudness summation, in which both cochleas hear the sound at the same time; and implant placement or other anatomical variables. All these reasons may apply in our study. The differences ranged from 3.8 dB (at 0.25 kHz) to 8.7 dB (at 2 and 4 kHz) and were larger at higher frequencies. This may be due to damping of vibrations by the skin and soft tissues when testing bone conduction hearing thresholds by pure-tone audiometry.

Finally, it is true that the use of percutaneous solutions is associated with a risk of dermatological complications due to permanent skin penetration by the abutment [28]. The most commonly used scale for assessing dermatological complications is the scale proposed by Holgers [28]. It is a 5-point scale, where 0 indicates no skin reaction and 4 indicates severe reaction, sometimes requiring removal of the abutment (0 – normal skin, 1 – reddish, 2 – red and moist, 3 – granulation tissues, 4 – skin complication leading to removal of the abatement). Based on a systematic literature review on Ponto implantation, skin-related complications were the most common event (Holgers ≥2) and were experienced by approximately 1 in 7 patients [18]. In our study, dermatological complications were very slight. One year after implantation, minor skin complications (Holgers=1) were observed in 3 patients (1 in 9 patients). Holgers scores showed no major complications.

Conclusions

The Ponto system is safe and effective in compensating for conductive or mixed hearing loss in patients who have had radical modified mastoidectomy. The system can support auditory functioning in people who are at risk of recurrent otitis media with cholesteatoma and who may therefore require later revision or further surgical intervention.