Introduction
Bone conduction hearing devices are used for hearing rehabilitation in patients with hearing losses where a conventional air conduction hearing aid cannot be used. This can be because of recurrent ear infections caused by the air conduction hearing aid, unfavourable anatomy, or single-sided deafness.Reference Dimitriadis, Farr, Allam and Ray1,Reference Dimitriadis, Carrick and Ray2 There are two main categories of bone conduction hearing devices: the percutaneous (skin-penetrating) and the transcutaneous (non-skin-penetrating) types.
The original surgical technique was to raise a split-thickness skin flap in the post-aural region using a dermatome. The advent of newer types of implant abutments has encouraged teams to experiment with different surgical approaches. We developed the Sheffield ‘S’ incisionReference Carr, Moraleda, Baldwin and Ray3 based on the linear incision developed by the Nijmegen group.Reference de Wolf, Hol, Huygen, Mylanus and Cremers4 This involves a small S-shaped incision in the post-aural region with circumferential partial thinning of subcutaneous tissue. Subsequently, a hydroxyapatite-coated abutment was introduced,5 which encouraged adherence of surrounding skin to the abutment, eliminating any local pockets.
Currently, there are numerous transcutaneous bone conduction hearing devices in the market.Reference Edmiston, Aggarwal and Green6 Some are passive, where the implanted magnet merely anchors the active external processor, magnetically. Others are active, with the transducer being implanted in the mastoid bone and the external processor linking through a magnet across intact skin. The usual approach is through a single skin incision in the post-aural region, with the elevation of a full-thickness skin flap.Reference Dimitriadis, Hind, Wright, Proctor, Greenwood and Carrick7
The issues that prompted the evolution of newer surgical techniques were related to the incision and the handling of soft tissues, as well as the device itself and the response of skin to the device-related interface. The most relevant problems were: soft-tissue reactions (skin overgrowth and granulations) and infections, aftercare with daily cleaning requirements, fixture loss, lateral projection, and aesthetic issues.Reference Clamp and Briggs8,Reference Dimitriadis, Vlastarakos, Nikolopoulos and Dupont9
This study aimed to assess the surgical outcomes of the different soft-tissue techniques in order to compare the soft tissue related complications associated with each.
Materials and methods
Ethical approval
Approval from an ethics committee was not required for this study, as the data described were routinely collected and assessed for service evaluation.
Study design
This is a convenience study, where the data were collected prospectively for all patients, apart from those undergoing skin thinning with use of a dermatome, in light of the timing of surgery. The study period was January 2008 to December 2016.
Outcome measures
The outcome measures were soft-tissue complications, including: flap breakdown, granulations, fixture loss, inflammation and infection. Any association with patient-related risk factors, such as diabetes, was determined.
Patients
The study comprised 120 adults (aged over 18 years) who underwent the implantation of different types of bone conduction hearing device, performed or directly supervised by the first author. Consecutive patients were included from each group. The mean follow-up duration was 12 months.
Groups
A pictorial overview of the different incisions used in the five groups (described below) is presented in Figure 1.
Overview of the different incisions utilised in each of the five groups.
Group 1
In the dermatome with skin thinning group, a split-thickness skin flap of 3 × 3 cm was raised in the post-aural region using a dermatome. All soft tissue down to periosteum and hair follicles were removed. The abutment was delivered to the outside through a hole in the flap.
Group 2
In the Sheffield ‘S’ incision with skin thinning group, a short ‘lazy S’-shaped incision with circumferential skin thinning was undertaken, but without hair follicle removal. The abutment was usually delivered outside through a separate hole punched anterior to the incision line.Reference Carr, Moraleda, Baldwin and Ray3
Group 3
The linear incision without skin thinning group utilised a percutaneous bone conduction hearing device: the DermaLock abutment with hydroxyapatite coating (Cochlear, Sydney, Australia). A small vertical incision was made in the post-aural region without any thinning of the subcutaneous tissue, as described by the Nijmegen group.Reference de Wolf, Hol, Huygen, Mylanus and Cremers4 The abutment was delivered outside through a separate hole punched anterior to the incision line.
Group 4
This group underwent a ‘C’-shaped full-thickness incision for the passive transcutaneous BAHA Attract bone conduction hearing device (Cochlear). We used the modified procedure with an inferiorly facing C-shaped incision.Reference Dimitriadis, Hind, Wright, Proctor, Greenwood and Carrick7 The skin and subcutaneous tissue were not thinned unless the overall thickness exceeded 6 mm.
Group 5
In this group, a post-aural incision was made for the active transcutaneous Bonebridge bone conduction hearing device (Med-El, Innsbruck, Austria). We used a standard post-aural incision placed behind the post-aural sulcus. A superiorly based temporalis flap was raised to allow access for the implant to be housed, and for the well that accommodated the transducer to be fitted.
Results
Skin outcomes per group
Group 1 comprised 20 patients. The soft-tissue outcomes included a bald patch of postage stamp size and a large divot formation. All patients experienced wide numbness around the wound. Soft tissue related problems were encountered in 55 per cent of the patients: four patients (20 per cent) had flap breakdown, five (25 per cent) had granulation and two (10 per cent) had fixture loss.
Group 2 included 35 patients. The participants found the scar to be acceptable and they did not complain of a bald patch. There was, however, a divot formation with significant numbness. Wound haematoma and dehiscence were observed in one patient (3 per cent), requiring surgical closure. Skin granulation was observed in four patients (12 per cent), skin redness in three (9 per cent) (Holgers grade 2 soft-tissue reactionReference Holgers, Tjellström, Bjursten and Erlandsson10), and small wound dehiscence in one (not requiring surgical closure) (3 per cent). All of these issues settled with conservative management. We did not observe major complications, such as flap necrosis.
Group 3 consisted of 35 patients. The outcome was aesthetically pleasing, without the presence of a bald patch or divot. No granulations were observed in this group, but most patients developed a small area of numbness. Wound breakdown was noted in one patient (3 per cent), in whom the abutment was placed in the incision line; this required surgical closure.
Group 4 included 20 patients. Skin flap thinning was required in three cases. Post-operative pain and oedema developed in two patients and one patient, respectively. These issues settled with conservative management. The aesthetic outcome was well accepted by all patients. When asked, 80 per cent of patients admitted developing an area of numbness around the incision. However, this shrunk over time. None of these patients developed granulations or wound breakdown, and none of the patients required skin aftercare.
Group 5 comprised 10 patients. The incision faded with time, and there was no bald patch, divot or granulation formation. There was only a small, post-auricular area of numbness. Exceptionally, for this group, the need for pre-planning and liaison with the radiology department is important. The dura was exposed in three cases (30 per cent) and the sigmoid sinus needed compressing in three cases (30 per cent).
Skin outcomes related to patients’ risk factors
Amongst all patients with a complication, two had diabetes (non-insulin-dependent and well controlled), both of whom were in the dermatome group: one developed flap breakdown and the other granulation tissue. None of the smokers (n = 19) experienced any soft-tissue complications. Five patients had eczema but it was not localised to the implant site in any of the cases; none of the patients experienced any soft-tissue problems.
Discussion
The concept of bone conduction hearing devices as hearing devices coupled to an osseointegrated fixture and abutment assembly started with the invention of osseointegration techniques, introduced by Branemark and Harders in 1963.Reference Branemark and Harders11 The original surgical technique, as described by Tjellström and colleagues in 1977, involved raising a split-thickness skin graft in the post-aural region using a dermatome.Reference Tjellström, Lindström, Hallén, Albrektsson and Brånemark12 Ongoing issues with aftercare, granulations, flap breakdown, fixture loss and cosmesis led to modifications in fixtures, abutments and the soft-tissue approach used.Reference Devèze, Rossetto, Meller and Sanjuan Puchol13
Less handling and the reduction of soft tissue appeared to improve the soft tissue related complications. The percutaneous DermaLock bone conduction hearing device abutment with hydroxyapatite coating allows the skin to be closed without thinning, and encourages some degree of bonding between the abutment coating and the skin margin. The difference in soft-tissue complications between the first three groups demonstrates this and is in line with other published literature.Reference Kruyt, Kok, Bosman, Nelissen, Mylanus and Hol14
The most significant improvements in soft tissue related problems were apparent with the advent of passive transcutaneous devices. Initial experiences with the transcutaneous bone conduction hearing device, which used two magnets and a large contact area, were slightly disappointing because of inadequate amplification associated with skin attenuation and reports of skin breakdown.Reference Edmiston, Aggarwal and Green6,Reference O'Niel, Runge, Friedland and Kerschner15 The passive transcutaneous bone conduction hearing device technology that we present here uses a single point of contact to maximise sound transmission, and incorporates a soft pad to distribute the pressure uniformly across the magnet–skin interface. Our results demonstrate favourable skin outcomes when comparing group 4 against groups 1–3.
The active transcutaneous bone conduction hearing device retains the advantages of the soft tissue related benefits seen in the passive transcutaneous devices. Our results demonstrate comparable benefits between passive and active transcutaneous bone conduction hearing devices, and considerable improvement over the other soft-tissue techniques, consistent with other studies.Reference Schmerber, Deguine, Marx, Van de Heyning, Sterkers and Mosnier16 The sheer size of the active transcutaneous bone conduction hearing device makes the surgery a bit more complicated in cases of unfavourable anatomy.
Study limitations
Data from group 1 were collected retrospectively. In addition, the number of included patients in each group is low, preventing power analysis.
• The two main types of bone conductive hearing devices are percutaneous (skin-penetrating) and transcutaneous (non-skin-penetrating)
• There are several surgical techniques with different incisions and soft-tissue handling methods
• This study compared soft-tissue complications following implantation of different bone conduction hearing devices
• It showed a reduction in soft tissue related complications with reduced soft-tissue handling
• It also revealed a shift from a skin-penetrating (percutaneous) to a non-skin-penetrating (transcutaneous) approach
Conclusion
There has been a steady reduction in soft tissue related complications with the shift from the initial skin-penetrating (percutaneous) approach towards a non-skin-penetrating (transcutaneous) approach. The latter is much more discreet and low maintenance, requiring little or no aftercare. Further evaluation of the longer-term soft-tissue outcomes of the newer devices is important.
Competing interests
None declared
