PAEDIATRIC BONE CONDUCTION HEARING SOLUTIONS PAST, PRESENT AND THE FUTURE IN A TERTIARY PAEDIATRIC SETTING MAX SALLIS OSBORNE
PAEDIATRIC BONE CONDUCTION HEARING SOLUTIONS PAST, PRESENT AND THE FUTURE IN A TERTIARY PAEDIATRIC SETTING MAX SALLIS OSBORNE
Paediatric Bone Conduction Hearing Solutions Past, Present and the future in a Tertiary Paediatric setting Max Sallis Osborne Thesis RijksUniversiteit Groningen Cover image: The cover image was generated with the use of an AI image generator (WOMBO Dream, Wombo Studios, Inc.) which incorporated prompt images of Bone conduction hearing devices along with the thesis main title text. Layout inside and cover: Bregje Jaspers | ProefschriftOntwerp Print: Ridderprint |www.ridderprint.nl Financial support for the publication of this thesis was provided by Oticon Medical, Dudley Group of Hospital NHS Foundation Trust, Med El and University Medical Center Groningen. Copyright© 2024 M.S. Osborne All rights reserved. No part of this thesis may be reproduced, stored, or transmitted in any form or by any means without prior permission of the author.
Paediatric Bone Conduction Hearing Solutions Past, Present and the future in a Tertiary Paediatric setting Proefschrift ter verkrijging van de graad van doctor aan de Rijksuniversiteit Groningen op gezag van de rector magnificus prof. dr. ir. J.M.A. Scherpen en volgens besluit van het College voor Promoties. De openbare verdediging zal plaatsvinden op woensdag 5 juni 2024 om 16.15 uur door Max Sallis Osborne geboren op 11 juli 1983 te Worcester Verenigd Koninkrijk
Promotores Prof. Dr. M.K.S. Hol Prof. Em. dr. C.W.R.J. Cremers Copromotor Dr. Ms. A.-L. McDermott Beoordelingscommissie Prof. dr. G. Raghoebar Prof. dr. E. Mylanus Prof. dr. C. Smits
For Rufus and Alexander - Dream Big
Contents Chapter 1 General Introduction 9 Chapter 2 Osborne MS, Hoskison E, Child-Hymas A, McDermott AL Five year clinical outcomes and evaluation following implantation of the Oticon TM wide bone anchored hearing system in 47 children. Int J Pediatr Otorhinolaryngol. 2020 Oct;137:110244 PMID: 32896356 37 Chapter 3 Clinical evaluation of a novel laser ablated titanium bone-anchored hearing implant 53 Chapter 3.1 Osborne MS, Child-Hymas A, Holmberg M, Thomsen P, Johansson ML, McDermott AL. Clinical Evaluation of a Novel Laser-Ablated Titanium Implant System for Bone Anchored Hearing Systems in a Pediatric Population and the Relationship of Resonance Frequency Analysis with Implant Survival. Otol Neurotol. 2022 Feb 1;43(2):219-226 PMID: 34816808 55 Chapter 3.2 Osborne MS, Child-Hymas A, McDermott AL. Clinical evaluation and resonance frequency analysis of laserablated titanium bone-anchored hearing implant system in children with Down Syndrome. Int J Pediatr Otorhinolaryngol. 2021 Dec;151:110981 PMID: 34781113 75 Chapter 4 Paediatric experience with a novel adhesive adapter retained bone conduction system 95 Chapter 4.1 Osborne MS, Child-Hymas A, Gill J, Lloyd MS, McDermott AL. First Pediatric Experience With a Novel, Adhesive Adapter Retained, Bone Conduction Hearing Aid System. Otol Neurotol. 2019 Oct;40(9):1199-1207 PMID: 31469800 97
Chapter 4.2 Osborne MS, Child-Hymas A, McDermott AL. Longitudinal study of use of the pressure free, adhesive bone conducting hearing system in children at a tertiary centre. Int J Pediatr Otorhinolaryngol. 2020 Nov;138:110307 PMID: 32810685 117 Chapter 5 General Discussion 129 Chapter 6 Summary 149 Samenvatting 155 Chapter 7 List of publications 163 Acknowledgements - Dankwoord 169 About the author/Curriculum Vitae 173 PhD portfolio 177 Data management plan 183 Abbreviations 187
Chapter 1 Introduction
Chapter 1 10
Introduction 11 1 Introduction History The concept of augmenting hearing via bone conduction was first introduced over 300 years ago [1], and as technologies and understanding have developed so too has the application of bone conduction hearing devices (BCHD). The fundamental concepts have remained the same, whereby sound is transmitted to the inner ear by the vibration of a processor in contact with the skull, bypassing the normal auditory canal in those individuals with congenital or acquired absence of the ear canal or those with pathology preventing effective sound conduction. Physiology of Hearing Air conduction hearing relies on the mechanism of effective vibration of the tympanic membrane caused by changes in air pressure generated by sound. This enters the external auditory canal and is converted to mechanical movement of the ossicular chain and ultimately the stapes footplate. This mechanical movement is then transduced into the movement of fluid within the cochlea causing deflection of the basilar membrane and stimulation in the Organ of Corti with generation of action potentials which in turn are transmitted to the auditory processing centre leading to the perception of sound. The maximal point of deflection is determined by the frequency of the tone as the sound wave travels towards the apex of the basilar membrane [2]. Bone conduction hearing relies on the same stimulation of the basilar membrane by generating a pressure gradient around a specific point along it. As with air conduction, the maximal point of deflection and its subsequent propagation is determined by the frequency of the tone and there is no physiological difference between these points in either air or bone conduction [3,4]. The stimulation occurs due to multiple alternative mechanisms which generate the pressure gradient across the basement membrane [5]. The physiological principal of the generation of the pressure gradients is grounded by the asymmetry in the movement of inner ear fluid within the scala vestibuli (SV) and scala tympani (ST) due to both volume and impedance, which are both higher in the SV [6]. Physiological Principles In 2005 Stenfelt and Goode proposed five contributing physiological factors influencing bone conduction hearing [7]. 1. Cochlear fluid inertia – proposed as the most influential factor in bone conduction hearing. The pressure gradient is created by the vibration of the cochlea and resulting movement of the round window and oval window in a compensatory fashion. This movement is larger toward the round window due to lower impedance [8].
Chapter 1 12 2. Compression, deformation, and distortion of the cochlear wall via direct vibration effect [9] 3. Sound energy vibration of soft tissues of external ear and middle ear ossicles. This is transmitted to the cochlear via the stapes footplate [10]. As the ossicular chain is suspended between the annular ligament and the tympanic membrane the movement is dependent on the frequency and is reduced above the ossicular chain’s resonant frequency. 4. Pressure transmission from the cerebrospinal fluid 5. Sound transmission through the external ear canal These fundamental physiological principles are capitalised on in the application of BCHD in modern audiological rehabilitation and over time significant technological developments have enabled rapid progression in design and application. [Figure 1] Figure 1: Vibration pathway from processor to inner ear. Application of hearing physiology in BCHD BCHD are comprised of two parts, a processor that converts sound to a digital signal and a mount or attachment connecting this device to the overlying skin or directly to the temporal bone.
Introduction 13 1 The processor is comprised of a microphone, amplifier, digital processor, and a transducer. Here, sound is converted into a digital signal which drives a floating mass transducer. This vibration energy is then transmitted to the skull by the proximity of the vibrating processor to bone. Over time the footprint of the processor has reduced (34mm to 26mm), as has the technological application and connectivity to other electronic devices such as smart phones and computers. The processor can be held in place on the mastoid bone by either non-surgical or surgical options and can be provided either unilaterally or bilaterally in the treatment of conductive hearing loss, mixed hearing loss or a single sided sensorineural deafness. Non-Surgical Hearing Systems Non-surgical mounts have been widely applied due to their simplicity, flexibility, and low cost. They are easily removable and replaceable based on the social or acoustic needs of the patient. The simplest solution uses a soft headband made from stretch fabric which is washable. An alternative to this is a hard headband mount which provides a greater contact pressure than the softband. It has been demonstrated that although a pressure of 2N is required to ensure an effective transmission of bone conducted sound [11] increasing the contact force provided limited (< 3dB) gain and that it is volume rather than contact force which is of greater importance [12]. Therefore, a softband is preferrable because of improved patient comfort and wearing time. Softband options are provided by Oticon TM supporting the Ponto processor, Cochlear TM Baha® Start, Alpha MPO ePlusTM and the contact mini-TM (BHM Austria). In the 1960’s technological improvements reducing the size and weight of the electronic component allowed the sound processor to be mounted to spectacles. This type of mount still exists today and can provide both unilateral and bilateral mounting options and is particularly useful if eye glasses interfere with standard behind the ear hearing aids. More recently the Sound Arc (Baha® Cochlear) was released, designed to be worn above the ears and behind the head. A semi rigid light-weight frame holds a connection disk in place to which the processor is mounted, and this again can be bilateral if required. This style of device has gained popularity in recreational sports where the application of bone conduction headphones (Shokz [13]) allow for an open ear canal. This is particularly useful where the user wishes to remain aware of their surroundings while undertaking a sporting activity such as running or cycling. Although audiologically effective, subjective feedback from patients demonstrates poor compliance with headbands due to concerns about the aesthetics. This can be a particular deterrent to many older children with self-perception issues and concerns about integrating
Chapter 1 14 with their peers. Eye glass mounted options have specific limitation due to the weight of the processor. This is even more pronounced in patients with microtia, many of whom may not have sufficient external pinna to hold their eyeglasses level with the additional weight. Furthermore, microtia is often asymmetrical and pinna position may be lower making the use of eye glasses very unsightly and impractical [14,15]. With the headband options, migration of the sound processor away from an optimal position over the mastoid bone reduces its efficacy [16]. It can also increase artifact production by movement over the patient’s own hair, clothing, head dresses or hats. This often leads to the position of the processor being far from the mastoid process and therefore the cochlea. This becomes more pronounced for those children requiring eye glasses or those with variations in skull shape and contour. When compared to the unaided condition, both soundfield thresholds and speech reception thresholds are improved with the application of a softband and sound arc, with no significant difference being demonstrated between the two [17,18]. An adhesive bone conduction system was designed as an alternative to these. It is comprised of two components - a novel sound processor and an adhesive adaptor. The sound processor attaches to the adhesive adaptor via a preformed snap coupler in the centre of the adhesive pad. The adhesive pad is placed onto the hairless post auricular skin, directly over the mastoid bone and is replaced every 3-5 days to maintain adequate adhesion to the skin. This adhesive adaptor is designed to prevent sound processor migration and removes the requirement for an unsightly and tight-fitting headband. To date, reports of outcomes with the adhesive hearing system in adults and children demonstrated high levels of user satisfaction with improvement in pure tone threshold (functional gain of 23 dbHL and speech recognition of 23 dB SPL [1922]. However, there is significant variation in the longevity of the adhesive pad and a narrow fitting range of <25dB BC PTA. Historically novel devices such as ‘Sound bite hearing system,’ have been trialed but with limited success. The soundbite processor is mounted on a dental splint where sound is conducted through the maxilla and indirectly to the mastoid bone. At this time these bone conduction solutions are not widely offered for hearing rehabilitation, although have been repurposed and applied in the military setting in the United States of American.
Introduction 15 1 Limitation of non-surgical options Whatever the mounting option applied, transmission relies on the vibration signals from each processor through intact skin and soft tissues that overlie the skull, resulting in two limitations which decrease the effective amplification: 1. Signal attenuation – especially at high frequency 2. Limited wearing time due to the external pressure effect of the mounting option Although taking into account the acoustic limitations of non-surgical mounts, their use in early rehabilitation for conductive hearing losses has distinct advantages. As a temporary solution, they can be used on an extended trial basis to introduce patients into the concept of bone conducting hearing aids, as often patients have limited knowledge or experience of this technology and may be skeptical of its application. With the advent of a trial period, patients are encouraged to gain experience with a bone conducting processor and their various mounting options. In the adult population, trials of non-surgical mounts have the advantage of preoperatively demonstrating the hearing benefit a patient may expect and thus improve engagement with the overall process in a step toward an ultimate surgically mounted option. In children there is the further advantage of being an ongoing rehabilitation option for those who may be too young to undergo surgery and those who are non-compliant with standard hearing aid options. For many children, especially those with additional care needs or cognitive impairment, the trial of a non-surgical mount provides excellent predictions of audiological results rather than conventional pure tone and speech audiology. Additionally in those children with microtia or anotia, it preserves the post auricular skin envelope until the child can engage autonomously with decisions regarding future pinna reconstruction options. Surgically Implanted Hearing Systems Surgically implanted Bone anchored hearing implants (BAHI), utilise the same transduction processors whereby sound is converted to a digital signal and ultimately mechanical vibration which is transmitted directly to the skull. Classically these are divided into Percutaneous (skin penetrating) and Transcutaneous (skin preserving). Percutaneous Processors Percutaneous devices were introduced in 1977 by Tjellström [23] and became commercially available in 1987. A skin penetrating abutment is attached to an anchoring fixture screw in the skull to which a sound processor is attached, bypassing the attenuation caused by skin and overlying soft tissue [Figure 2]. Originally described surgical techniques involved complete
Chapter 1 16 split thickness skin grafts both with and without a dermatome use [24,25] to reduce soft tissue depth overlying the implanting area. Over time the approach now focuses on tissue preservation avoiding the possible complications caused by skin flap necrosis [26,27] and thus reducing skin complications [28]. Linear incision techniques have been shown to have a faster healing time and to inflict less pain than dermatome techniques [29,30]. Currently the use of tissue preservation techniques is reported to have the best soft tissue outcomes [31]. Oticon introduced minimally invasive Ponto Surgery (MIPS) which has been shown to have comparable soft tissue outcomes to linear incision techniques [32,33,34] and reduced tissue reaction in some centres to 4.5%, [35] however others have reported fixture failure rate of up to 35% [36]. Figure 2. Components of a percutaneous bone conduction hearing device: comprise of implantable titanium screw, skin penetrating abutment and sound processor. Direct contact with the temporal bone creates two immediate benefits: firstly, better audiological results in both sound field thresholds and speech recognition. Secondly the power of the processor can be increased without complications of migration or significant skin irritation. Limitations of BAHI include peri-abutment soft tissue reactions and fixture loss through either trauma or failed osseointegration, both of which are demonstrated to be higher in paediatric populations [37,38]. Soft tissue reaction is classically monitored and described by the application of the Holgers score (0-4) [39] which shows a wide variation in incidence depending on the surgical technique utilised, the abutment used for mounting the processor and finally subjective reporting by clinicians.
Introduction 17 1 Skin reactions require special consideration in the paediatric population. Pubertal hormonal changes result in sebaceous hypertrophy and an associated skin overgrowth which may require a longer abutment [40]. There is also an acceptance that the lifestyle and behaviour of children can result in an anticipated proportion of abutment loss secondary to trauma [41]. This underlies the philosophy of sleeper fixture insertion at the time of the primary procedure. Any fixture loss can be replaced quickly without any delay associated with waiting for osseointegration of a new implant. Physiological factors and Osseointegration Successful implantation is dependent upon osseointegration of the implanted fixture with the surrounding bone which occurs during wound healing, and is defined by three factors; (i) the formation of a stable support and absence of relative motion between the implant and surrounding tissues, (ii) the apposition of bone to the implant without intervening soft tissue, and (iii) the tissues closest to the implant surface are identified as normal bone and marrow constituents (at light and electron microscopic levels [42]. These factors are in turn influenced by implant geometry (macro, micro and nano scale), drilling protocol, osteotomy configuration, surface, and material properties, surrounding bone quality as well as systemic and local characteristics of the host [43]. Patient-related conditions such as high BMI, diabetes, osteogenesis imperfecta, previous radiotherapy of the temporal bone, various co-morbidities and smoking have been implicated in higher rates of implant loss [44,45,46]. For this reason, despite the overall low incidence of implant failure, there is a need to further enhance the implant stability and osseointegration, and thereby survival rates. Furthermore, some centres advocate early or even immediate loading of processors in adults [47,48,49,50] and at 6 weeks in children [51]. This too, leads to increased demands on implant stability and accelerated osseointegration. The common strategy for addressing these challenges, both for dental, orthopaedic and BAHI applications, have been two-fold, (i) increased implant diameter and primary implantto-bone contact and (ii) application of surface modification to the implant. The use of wider diameter implants was shown to improve outcomes in dental implantation with lower implant failure rates [52,53]. Application of wide diameter BAHI (4.5 mm diameter) has been found to have comparable adverse skin reaction rates to the previous generation implants (3.75mm diameter) and associated with increased survival [54,55,56,57]. The wider diameter increases the surface area contact between the implant and temporal bone thereby providing a greater primary stability with the aim to promote a reduction in
Chapter 1 18 spontaneous fixture loss. Implant surface modification has been the main strategy to promote biological reactions to accelerate and promote its integration with bone. In dental applications, most surface modifications employ techniques that increase the roughness of the surface [58] with benefits in terms of a stronger bone response and better clinical results compared with non-modified implants [59]. A recent review reported a survival rate of 1166 BAHI implants of various designs, of 97.7% over an average follow-up time of 17 months across a predominantly adult population [60]. For adult populations, the failure rates for wide diameter implant systems are reported between 2.6-4.2%. [61,62,63,64]. Recent meta-analysis supports these findings in children demonstrating a 17.1% loss in small-diameter implants compared with a 5.9% for wide-diameter implants [65]. Currently Available Percutaneous BAHI [66] CochlearTM Baha® Connect System (Cochlear Bone-Anchored Solutions AB, Mölnlycke, Sweden) [67] 4.5mm wide BI300 titanium fixation screw (3-4mm length) + BA400 hydroxyapatite – coated abutment (6-14mm length) Processors available - Baha® 5 (45 dB HL), Baha® 5 Power (55 dB HL), and the Baha® 5 SuperPower (65 dB HL). Baha® 6 (55 dB HL) Oticon Ponto System (Oticon Medical AB, Askim, Sweden) [68] 4.5mm wide BHX titanium screw (3-6mm length) + abutments (6, 9, 12 and 14 mm length) Processors available - Ponto 3 (45 dB HL), Ponto 3 Power (55 dB HL) and Ponto 3 Superpower (65 dB HL), Ponto 4 (45 dB HL), Ponto 5 Mini (45 dB HL) and Ponto 5 Superpower (65 dB HL). Processor development Substantial developments in connectivity and streaming have been made in all processors, seamlessly integrating with apps and accessories to improve patient satisfaction. This also aids streamlining the fitting process where wireless and remote fitting can be undertaken. Oticon Ponto (Oticon Medical AB, Askim, Sweden) Ponto, the latest version of the Ponto (Oticon processor) the 5 mini, focuses on reducing size and weight rather than increasing power and maximal output. The processor has decreased in size over time from a footprint of 34x21x11mm (Ponto 3) to 26x19x11mm (Ponto 5 mini) with a weight reduction from 14g to 13.2g respectably.
Introduction 19 1 Cochlear Baha® (Cochlear Bone Anchored Solutions AG, Mölnlycke, Sweden) processor have decreased in size while simultaneously maintaining maximal power output and increasing the fitting range from 45db SNHL to 55 dB SNHL. The footprint of this processor decreased from 30x21x12mm 11.6g in the Baha® 4 to 26x19x12mm 11.5g in the Baha®6. Audiological benefit Audiological gain is not an ideal parameter when comparing different BCHDs. Some authors prefer to use aided hearing thresholds as a better parameter for comparison. A literature review shows there is little consensus on this topic. In 2019, Snik et al undertook meta-analysis of published data and found that the gain was 10dB higher in the Baha®5 sound processor when compared to the Ponto 3 sound processor [69]. Snik et al concluded that this difference in gain was due to the maximal power output being 9 dB higher in the Baha® 5. Interestingly there was no significant difference between these two processors' word recognition scores presented at 65 dB SPL [70]. Transcutaneous Processors Transcutaneous devices provide sound transmission through intact skin to remove the skin complication created by a skin penetrating abutment. First developed in 1986 by Hough et al [71] these systems are comprised of two components. An implanted fixture which is implanted into the temporal bone to which a magnet is attached. The overlying skin is closed. An external processor with an external magnet is then connected to allow for transmission of either vibration stimuli or digital information. Although Hough’s initial system the Xomed Audiant was eventually withdrawn from the market due to high retention pressures combined with insufficient amplification, the concept remained viable and new systems were brought to market in 2013. In the modern setting, transcutaneous systems are available in two categories; • The vibrating mass transducer is implanted under the skin and signals sent via electromagnetic induction from the external processor to it (active device) • The transducer is placed externally, and the vibration is transmitted through the intact skin and soft tissue (passive device). These options minimise skin complications caused by a skin penetrating abutment. However, the retention forces of the magnets required to stabilise them on the skin surface can cause pain and irritation. Up to 38% of the adult population reported skin numbness, pain or discomfort in the first 6 months after implantation [72] and there are reported cases of skin necrosis from this type of device [73]. A similar rate of skin irritation has been reported in paediatric populations (16%) [74].
Chapter 1 20 A slow increase in magnet strength from the point of fitting is advised to improve wearing time and acclimatise the skin to the processor. This irritation can be compounded by the vibration caused by passive devices, which also need to overcome the attenuation of the soft tissue and skin: As with non-surgical BCHDs, this can result in paraesthesia or numbness [75]. Magnets are available in a variety of strengths which can be tailored to the patients’ needs. Over the initial 12 months of use, it has been observed that the overlying soft tissue becomes thinner due to the compression forces effect of the magnets, and this has the additional benefit of thus reducing the required magnet retention strength [76]. Surgical approaches to these devices are more invasive than with percutaneous systems, requiring either a larger subcutaneous pocket to be created or a bony well to be drilled into the temporal bone to secure the transducer. The position of these devices can be limited by anatomy, and this needs special consideration in children who have a small skull and small mastoid, those individuals who had previous mastoid surgery and also in children with microtia. Another consideration is the compatibility for MRI. Although most systems are compatible up to 1.5 Tesla as with cochlear implants, the presence of the magnet can also interfere with Magnetic Resonant Imaging creating large imaging shadows and this may necessitate removal of the internal magnets if an MRI of the head is be undertaken. Currently Available Transcutaneous BAHI Subcutaneous transducer (active system) [77] • Osia® System Cochlear Bone-Anchored Solutions AB, Mölnlycke, [78] Implant OSI200 system fixed to BI300 Osseointegrated screw Surgical consideration Bone polishing may be required. MRI compatible: OSI200 1.5 Tesla, OSI300 3 Tesla Processor Osia® 2 (55 dB HL) • BONEBRIDGE TM MED-EL, Innsbruck, Austria [79] Implant BCI602 floating mass transducer. Surgical consideration Drilling of a Pre sigmoid bone bed required. Cortical fixation screws. (No osseointegration) MRI compatible: 1.5 Tesla Processor SAMBA 2 (45 dB HL)
Introduction 21 1 Currently under development • Sentio System Oticon Medical, Askim, Sweden Implant Sentio Ti Surgical consideration Bone bed required MRI compatible: 1.5 Tesla Processor Sentio 1 External Transducer (passive system) • Baha® Attract Cochlear Bone-Anchored Solutions AB, Mölnlycke, [80] Implant BIM400 magnet fixed to BI300 osseointegrated screw Surgical consideration O verlying soft tissue >6mm, no contact of magnet to bone MRI compatible: 1.5 Tesla (11 cm shadow) Processor B aha® 5 (45 dB HL), Baha® 5 Power (55 dB HL), and the Baha® 5 SuperPower (65 dB HL). Baha® 6 (55 dB HL) • Sophono/Alpha 2 MPO ePlus™ Medtronic, Minneapolis, USA [81] Implant Two internal magnets with five screws fixation Surgical Consideration Shallow bony bed MRI compatible: 3 Tesla (5cm shadow) Processor Alpha 2 MPO ePlus™ (45 dB HL) Audiological Comparisons of BCHD Selection of processor and mounting options is specific to each patient’s audiological, and rehabilitation needs and with the increasing options brought to market it can be challenging to make conclusions on which is ultimately the best choice for the patient. To overcome these challenges, significant audiological research has been published comparing these products. However, comparison between these studies has its own limitations due to the vast variability in mounting and processor options being studied. In fact, patient preference is often the main factor in decision making. The fundamental principles of a BCHD hierarchy remain unchanged: The best audiological outcomes are gained through direct contact of a vibrating processor with the skull and, the fitting range is determined by the maximum output. Percutaneous and active transcutaneous BCHDs therefore have significant audiological benefit over softband mounting, ADHEAR and passive devices as they do not need to overcome the
Chapter 1 22 attenuation caused by the overlying skin and soft tissues. A significant difference of 5-20db is observed between 1-4 kHZ when comparing softband mounting to percutaneous mounted devices, associated with a SRT improvement of 4- 7 dB which translates into a 20-40% difference in speech understanding [82,83]. However, as these studies utilised different processors for this analysis direct comparison is challenging. A study comparing the same Baha® 5 processor in a matched patient group with single sided deafness concluded that word understanding and phoneme recognition scores at both 62 and 47 dB SPL were significantly worse for the softband group as compared to the percutaneous group by 16%. Furthermore, the greatest deviations were in the high frequencies above 2000 Hz [84]. In mixed hearing losses [85] and in conductive hearing losses [86] less of an improvement was demonstrated. For a conductive loss of <25db, both the passive Baha® Attract and ADHEAR have comparable audiological performance to a softband system without the requirement of pressure. Aided sound field thresholds of 33+/- 6 in Baha® Attract, 32+/-9 ADHEAR and 27+/-6 in softband were reported and, no significant difference in speech understanding in both the quiet (20dB) and in noise (54dB) found [87]. With regards to the superiority of percutaneous verses active transcutaneous, there is ongoing debate of which provides the best rehabilitation option. When comparing the percutaneous Oticon Ponto system to the active transcutaneous Med-EL bone bridge it was found that the Bonebridge® performed slightly better in the mid-frequencies, while the Ponto had superior results for the lowest and the highest frequencies. The PTA4 improvement was 31.0 ± 8.0 dB for Bonebridge®, and 31.5 ± 2.8 dB for the Ponto system. However, there was no statistically significant difference between the two devices. [88] Passive systems provide excellent audiological rehabilitation however limited by the maximal output as compared to percutaneous option. Hol et al 2013 demonstrated that although either option provides audiological benefits, percutaneous options provided better sound field thresholds, speech recognition and speech comprehension combined with a 10 dB higher output [89]. In 2015, M Iseri et al demonstrated poorer transcutaneous audiological outcomes when compared to the percutaneous BAHI due to the indirect connectivity between the processor and implant [90]. These conclusions were again supported in 2019 by Kohan et al who compared average audiological results in (dB) between two different passive transcutaneous devices and the percutaneous Baha® system. Again, this showed the percutaneous Baha® to be better at low and mid frequencies. Interestingly it also compared different versions of the
Introduction 23 1 Baha® processor on these mounting options providing a direct comparison in audiological outcomes between the mounting systems and the processor used. It concluded that The Baha® 5 processor had better audiological results than its predecessor Baha® 4 when mounted on either the Baha® connect (31 vs 49) or Baha® Attract (22 vs 35) [91]. Overall, the best audiological results were seen in the percutaneous system with the processor with the highest maximal output [92]. With the recent release of the Osia® system by Cochlear, further comparison can be made between this active device and its passive Baha® Attract system. Both speech audiometry and free field were greater in the subcutaneous implanted device (42.8 dB SPL) compared to the Baha® Attract (38.8 dB SPL). In addition, superior quality of hearing was reported with the use of the Osia® system [93]. The potential benefits of this system combine the ease of implantation without the requirement of a bone well. A 4.5mm wide fixation screw with a good survival rate is likely to make this the preferred option for patients in the future. Audiological outcomes are comparable to available data for percutaneous options. To the author’s knowledge there is currently no available published data directly comparing this device to percutaneous options, and further research to establish this would be illuminating. The additional benefit of this system is the low skin complication rates which can often accompany skin penetrating abutments and ease of maintenance. Overall selecting the appropriate device for an individual patient is complex and is influenced by a combination of audiological, subjective and objective factors including patients choice [94] Application of BCHI in the paediatric population The positive impact of overcoming a conductive hearing loss on a child’s language acquisition and social development with the use of BAHI is well documented [95-102]. As hearing technology develops, breakthroughs have been made in both active and passive transcutaneous bone conduction systems with improving audiological outcomes [103-110]. In addition, there are many reports of improvement in quality of life as well as better speech and language acquisition [111,112,113]. The benefits of bilateral implant insertion, in particular with sound localisation and speech recognition, are now well appreciated [114,115,116]. However, complications associated with paediatric BAHIs continue: Lack of engagement from the child to accept such a hearing solution, peri-abutment soft tissue reactions and fixture
Chapter 1 24 (implant) loss through both trauma and failed osseointegration, have been demonstrated to be higher in paediatric populations [117,118]. Skin reactions require special consideration in the paediatric population. Pubertal hormonal changes result in sebaceous hypertrophy and an associated skin overgrowth which may require a longer abutment and attention to the soft tissues [119]. As the population of implanted paediatric patients is heterogeneous and often accompanied by systemic co-morbidities as well as additional childcare needs from a medical, learning, and social aspect, the burden of care for percutaneous implants may be a limiting factor. Unlike in the adult population where hearing rehabilitation options are offered based on audiological test results, undertaking these tests in children poses additional challenges. The validity of subjective hearing tests such as play audiometry, VRA or PTA in young children requires conditioning of a child to provide a response to indicate hearing thresholds. Speech assessments and hearing in noise tests require patient to repeat sentences or words and is dependent on the child’s age and ability to understand and repeat a complex sequence of instruction in an unfamiliar and noisy environment. Many children who require audiological rehabilitation are too young, restricted by co-morbidities or have additional learning needs to gain any meaningful results from many of these tests and so their application is limited. Auditory Brainstem response test (ABR) thresholds can be utilised to guide implantation. However, in the paediatric population parental/carer and patient reported outcome measures bare far more weight in assessing the effectiveness of a BCHD. If an observed improvement is reported during the trial period, this can provide sufficient evidence to offer formal implantation for the patient. In many cases, such a device trial may take months or even years before the decision to move to implantation is taken. To aid clinical decision-making, validated health benefit questionnaires are applied to provide objective evidence of any observed improvement. The Glasgow Children’s Benefit Inventory (GCBI) [120] and an additional visual analogue scale (VAS) are often applied, and many other scoring systems have been proposed [121]. The responses from these can be subdivided to provide assessment relating to emotion, physical health, learning and vitality. This information is easier for parents/careers to relate to in terms of benefits to their child rather than just hearing thresholds and this helps guide them in making the decision to undertake implantation. Transcutaneous implant systems reduce potential for skin complications traditionally associated with percutaneous implants. Such implant systems produce excellent audiological outcomes but still require the surgical implantation of either an osseointegrated fixture and/or
Introduction 25 1 magnet or a bone conduction floating mass transducer [122-126]. Magnetic retention is also a consideration in children whose activities and lifestyles may result in displacement or loss of a processor held in place by magnetic force alone. A comparative study comparing Baha® connect to Baha® Attract in paediatric patients found that 58% of patients with Baha® connect had complications in the first 12 months compared to no major complication (removing magnet strength issues) in the Baha® Attract group. These complications included high rates of skin overgrowth, infection, nursing phone calls and ENT visits with the Baha® connect group [127]. The latest studies into the application of the Osia® system in the paediatric population have demonstrated mean audiological benefit of 43.1 dB (+/- 10.2 dB), with a preference of this system over their previous percutaneous implants [128] and although morphometric studies show paediatric patients to have different anatomical skull dimensions to adults, this option is feasible and requires only a small alteration in positioning [129]. For those children with isolated microtia and canal atresia, the cosmetic considerations are extremely important. Care must be taken in choosing the placement of any implant system in such children to ensure that a sufficient post auricular skin envelope is maintained for potential future autologous reconstruction. Scaring in this region may compromise the option of reconstruction in later life as coverage of the neoauricle with local tissue might be insufficient [130,131,132]. Therefore, surgical options may be delayed until the child is older and non-surgical systems preferred and applied until this point. Non-surgical transcutaneous hearing systems provide a simple and effective solution in both unilateral and bilateral conductive hearing loss. Although audiologically effective, subjective patient feedback highlights poorer compliance with headbands due to concerns about the aesthetics. This can be a deterrent for many older children with self-perception issues and concerns about integrating with their peers. Additionally, the retention pressure by headbands may produce some complications and limitations in daily usage [133]. The transcutaneous adhesive bone conducting ADHEAR system demonstrated high levels of user satisfaction and no skin irritations [134], as well as comparable results to conventional softband devices with regards to speech understanding and sound localization [135] however is limited to conductive hearing losses of >25dB.
Chapter 1 26 Thesis Prelude The paediatric BCHD was introduced to Birmingham Children’s Hospital in 1988 and over the last 36 years has produced one of the largest cohorts of implanted paediatric patients in the United Kingdom. Previous research from this Institution has resulted in 6 preceding PhD theses in association with Radboud University, Nijmegen. This thesis focuses on the clinical impact of the introduction of the Oticon wide diameter fixation screws and the clinical outcome in the paediatric population. This is compared to previously utilised narrow implants at the same centre. It then examines the impact of laser ablation on the surface of the implanted fixture with regards to clinical outcome and examines the relationship between survival rates and Resonance Frequency Analysis (RFA) in both the general paediatric population and patients with trisomy 21. Due to the availability of comparable data sets published previously from the same centre this thesis provides compelling evidence of how developments in implant design have directly impacted clinical outcomes in the paediatric population. In addition, it cross examines the usefulness of RFA in predicting fixture failures in the paediatric population and its feasibility in real-world application. Finally, this thesis investigates the audiological outcomes and impact on quality of life of the novel adhesive retained bone conduction hearing system (ADHEAR) at its introduction in 2015 and again in 2019. This longitudinal review allows for analysis of paediatric patient compliance, conversion rates to alternative systems, skin complications and limitations with regards to its application in the paediatric setting.
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