Ten years of experience with the Ponto bone‐anchored hearing system—A systematic literature review

Abstract Background Bone‐anchored hearing systems (BAHSs) are widely used for hearing rehabilitation and are indicated in cases of conductive and mixed hearing loss and in single‐sided deafness. The Ponto system, that is one available option, has been on the market since 2009. Objective of review The aim of this study is to systematically review the literature reporting on the Ponto system, with regard to audiological and surgical outcomes and patient's quality‐of‐life scores. Type of review A systematic literature search was performed in the PubMed database 2009‐July 2019. Search strategy Search term: ((osseointegrated hearing aid) OR (bone conduction implant) OR (bone anchored hearing) OR BAHA OR BAHS OR BAHI). Pre‐defined inclusion and exclusion criteria were applied. Evaluation method English‐language articles reporting original clinical data (audiological, surgical or quality‐of‐life outcomes) on the Ponto system were included. Articles reporting on Ponto and another BAHS system where the results on Ponto constituted less than 50% of the patient population or including only results on testband or softband devices were excluded. Results Audiological outcomes were discussed in 20 publications. Improvement against the unaided thresholds was demonstrated. The functional improvement was on average 33.9 dB. The effective gain or remaining air‐bone gap was on average 6.7 dB. All evaluated data showed aided speech reception thresholds significantly below normal speech level. Twenty‐seven publications reported surgical and follow‐up data for the Ponto system. Implant survival was 97.7%, adverse skin reactions (Holgers ≥ 2) were 5% across visits and 15% across patients. No complications were life‐threatening, causing permanent disability/damage or requiring a hospitalisation. Five studies reported quality of life using the Glasgow benefit inventory, 98% reported an improvement when analysing the score on an individual level. Conclusions The outcomes of this systematic review confirm that percutaneous systems provide consistent audiological benefits and improved quality of life for patients. Further, the review demonstrates that the percutaneous systems are safe, with relatively low complication rates. Skin‐related complications are the most common complication type and are experienced by approximately one patient out of seven, or in less than one of 20 follow‐up visits.


| INTRODUC TI ON
Bone-anchored hearing systems (BAHSs) are widely used for hearing rehabilitation and are indicated in cases of conductive and mixed hearing loss and in cases of single-sided deafness (SSD).
Bone-anchored hearing systems are based on bone conduction (BC) of sound, in which vibrations of the skull are transferred to the inner ear and transformed to a hearing sensation. 1 The discovery that bone can firmly attach to titanium, a process termed osseointegration, 2

| ME THODS
A systematic literature search was performed in the PubMed database from 2009 (the year Ponto was released) to July 2019. The following search terms were used: "osseointegrated hearing aid" OR "BC implant" OR "bone anchored hearing" OR "BAHA" OR "BAHS" OR "BAHI." All identified abstracts were reviewed for relevance, and full-text articles were further reviewed and were included or excluded after applying the following criteria: 1. Inclusion criteria: Any English-language article reporting original clinical data on the Ponto system and included at least one of the following data points: surgical, audiological or quality-of-life outcomes.
2. Exclusion criteria: Preclinical, cadaveric or laboratory studies and review articles; articles reporting on Ponto and another BAHS system where the results on Ponto constituted less than 50% of the patient population and studies including only results on testband or softband devices.
The included publications were divided into two groups: 1. Publications exclusively reporting on the Ponto system (and in the case of sound processor studies, data reported separately on all patients using the Ponto sound processor).

Publications with mixed brands of implants/sound processors
where the number of Ponto implants/sound processors was specified and accounted for more than 50% of the total.
Double reporting was avoided as far as possible, and articles reporting on preliminary results for which later publications described patients. Further, the review demonstrates that the percutaneous systems are safe, with relatively low complication rates. Skin-related complications are the most common complication type and are experienced by approximately one patient out of seven, or in less than one of 20 follow-up visits.

Key points
• The functional improvement, the improved hearing experience by the patient, was significant and on average 33.9 dB.
• All evaluated data showed aided speech reception thresholds significantly below normal speech level.
• Approximately one of seven patients experienced adverse skin reactions among the studies included in this review.
• The survival rate of Ponto implants was 98%, including traumatic losses, over an accumulated follow-up time of 1623 years.
• A total of 98% of the patients reported an improvement in quality of life using the Ponto system.  The same study (but other outcomes) reported in Bosman,15 patients therefore not included in total.
c Average of all measured frequencies instead of PTA4 (average of 0.5, 1, 2 and 4 kHz).

TA B L E 1 (Continued)
the same cohort of patients were included in the groups (Tables 1 and 2) but not included in the meta-analyses.

| Audiological outcome measures
All audiological outcomes reported in the publications were categorised into four groups: threshold-based, speech in quiet, speech in noise and other.
For the threshold-based measures, meta-analyses were performed for functional gain (the difference between unaided and aided sound-field thresholds) and effective gain. 9,10 The effective gain/BC gain (or remaining air-bone gap) is calculated as the difference between the aided sound-field threshold and the BC threshold. Random effect models using the restricted maximum-likelihood method were fitted using JASP (University of Amsterdam, Amsterdam, The Netherlands, version 0.11.0.1). A heterogeneity test was performed, and Q and I 2 statistics were reported.
The results from the speech intelligibility test, both in quiet and in background noise, are summarised in the tables.

| Surgical/medical outcome measures
Implant survival and adverse skin reactions according to Holgers classification 11 (Holgers ≥ 2) were investigated, and a meta-analysis was performed. In addition, the intra-operative events and postsurgical complications reported in the publications were summarised.

| Patient satisfaction measures
Quality-of-life data, but no other self-reported outcomes, were included in the review.

| Level of evidence
As part of the review, the study designs were collected, no limitation on the level of evidence was applied.

| Ethical considerations
No ethical considerations were made as this is a review of existing literature.

| RE SULTS
The search strategy yielded 1041 publications ( Figure 1). After reviewing the abstracts, 408 publications were selected for further full-text review. After the full-text review, 68 publications mentioned the use of Ponto. Forty-three publications (41 studies) that fulfilled the inclusion criteria were used for the analyses.
The results of the literature search are summarised in two tables; Table 1 lists all included publications with audiological or quality-of-life outcomes, including the main findings. Table 2   Several different models of the Ponto sound processors were used in the reviewed studies and are listed in Table 1 Within-subject comparisons of different generations of Ponto sound processors were performed in three studies. [12][13][14][15] Comparisons to other brands of sound processors were performed with a within-subject crossover design in four studies [16][17][18][19] and between groups in two studies. 20,21 Comparison to other treatment options was performed for SSD patients and contralateral routing of signals devices with a within-subject design. 22 A single study reported the difference between patients with softband and a subset of patients with implanted devices. 23 Studies with only softband results were excluded. For this review, we were interested in the outcomes across Ponto sound processors.

| Audiological outcomes with the Ponto system
Functional gain was reported in seven studies. 13,16,17,[23][24][25][26] No study reported effective gain; however, the (average) effective gain for Ponto devices could be derived from seven studies. 13,16,17,20,[23][24][25] Six studies also reported standard deviations or individual data for respective outcome, allowing these data to be included in the meta-analysis models ( Figure 2). Speech recognition results in quiet were reported in nine studies (speech reception threshold [SRT] and/or percentage correct at a fixed level), and 11 studies reported speech in noise results (speech recognition scores in fixed background noise or adaptive signal-to-noise ratio thresholds). The overall weighted functional gain from the meta-analysis displayed in Figure    The calculated average effective gain, or remaining air-bone gap, was 6.7 dB and varied between 0 and 17 dB across studies ( Table 3).
Aided thresholds were reported for predominantly conductive and mixed groups, with two SSD patients included in the data. The average BC threshold of the conductive/mixed population in the review was 24.6 dB HL, with individual studies reporting averages between 10 and 37 dB HL (

| Quality-of-life outcome
Five studies with a total of 176 patients reported quality of life (

| Summary of the main results
The literature reporting on the Ponto BAHSs was reviewed. In total, data from 1352 patients were included in the review.
It can be concluded that the Ponto system provides an improvement in hearing ability compared to unaided hearing, in terms of both audibility and speech recognition. Based on the review, the average Ponto patient experienced an improvement in hearing of 35 dB. This is the average functional gain or functional benefit reported across studies, with all studies reporting an improvement.
From an audiological perspective, the effective gain is more relevant to evaluate and compare system performance since it is not affected by the patients' air-bone gap. 9,10 The average effective gain was 6.7 dB across seven studies (98 patients). The effective gain can also be interpreted as the remaining air-bone gap (compared below).
The data on

| Overall completeness and applicability of evidence
All patient indications were covered in the reviewed data. The proportion of SSD patients in the data set reporting audiological outcomes was 15.4% (59/383). The proportion of SSD patients in the data is representative of European clinical practice but is significantly lower than that in North America. The incidence of severe mixed hearing loss (with BC thresholds larger than 45 dB HL) is underrepresented in the data sets. This might be a reflection of that

| Comparison with other reviews
This review had a different angle than previous reviews of percutaneous BAHS in that it covers both surgical and implant-related outcomes, as well as audiological outcomes, and further explores a single system only.
The surgical and implant-related results of this study can be compared to the more general reviews of BAHS [37][38][39] and with the conclusions of large retrospective studies. 5,40 In agreement with the literature, 39 the rate of serious complications was very low (in fact, no cases were found in the data reviewed). Unfortunately, effective gain was not reported as part of any of the reviews. The effective gain is not affected by the air-bone gap and is therefore a better measure for comparing device performance. By analysing a subset of publications from last 3 years (Tables S9 and   S10), we calculated an average effective gain of 10.

| Implications for clinical practice
Bone-anchored hearing systems and the Ponto system reviewed in this paper consistently improved hearing and quality of life.
Complications are rare and typically minor in nature.
When counselling future patients considering their options, the main results of this study indicate that all prospective patients can expect better hearing after surgery and that the improvement is relatively predictable. The risk for any major complication requiring surgery is very low (<5%). One in seven patients can expect a skin complication requiring treatment. Furthermore, 98% of patients reported an improvement in quality of life following the intervention.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data sharing is not applicable to this article as no new data were created or analysed in this study.