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1 IMPLANTABLE BONE ANCHORED HEARING AID SOLUTIONS ASPECTS OF INDIVIDUALIZED INDICATION JÁNOS ANDRÁS JARABIN MD Ph.D. Thesis University of Szeged, Faculty of Medicine Department of Otorhinolaryngology and Head -Neck Surgery Szeged 2016 2 IMPLANTABLE BONE ANCHORED HEARING AID SOLUTIONS ASPECTS OF INDIVIDUALIZED INDICATION János András Jarabin MD Ph.D. Thesis Supervisor: Dr. habil. József Géza Kiss PhD CSc Co-supervisor: Ferenc Tóth PhD Doctoral School of Clinical Medicine Chair: Prof. Lajos Kemény MD, DSc University of Szeged, Faculty of Medicine Department of Otorhinolaryngology and Head -Neck Surgery Szeged 2016 1 PUBLICATIONS RELATED TO THE THESIS I. Jarabin J, Bere Z, Hartmann P, Toth F, Kiss JG, Rovo L Laser-Doppler microvascular measurements in the peri-implant areas of different osseointegrated bone conductor implant systems. EUROPEAN ARCHIVES OF OTO-RHINO-LARYNGOLOGY 272:(12) pp (2015) IF: II. Jarabin János, Bere Zsófia, Tóth Ferenc, Perényi Ádám, Jóri József, Kiss József Géza, Rovó László Első tapasztalataink a Baha DermaLock implantátum rendszerrel OTORHINOLARYNGOLOGIA HUNGARICA 61:(3) pp (2015) III. Jarabin János, Bere Zsófia, Tóth Ferenc, Perényi Ádám, Jóri József, Kiss József Géza, Rovó László A Baha DermaLock implantátum rendszerrel elért audiológiai eredményeink OTORHINOLARYNGOLOGIA HUNGARICA 61:(4) pp (2015) IV. Jarabin János, Kiss József Géza, Tóth Ferenc, Jóri József, Rovó László Alternatív lehetőség a tympanoplasticai módszerekkel nehezen megoldható, dominálóan vezetéses jellegű, szerzett halláscsökkenések kezelésére felnőtt korban - a BAHA Magyarországi indikációjának kibővítése. OTORHINOLARYNGOLOGIA HUNGARICA 58:(4) pp (2012) V. Jarabin János, Matievics Vera, Tóth Ferenc, Rovó László, Kiss József Géza A BAHA implantációt megelőző audiometriai és betegelégedettségi tesztek értékelése, és összehasonlítása a hagyományos csontvezetéses hallókészülékekkel elérhető eredményekkel FÜL-ORR-GÉGEGYÓGYÁSZAT 58:(2) pp (2012) VI. Torkos A, Czigner J, Jarabin J, Toth F, Szamoskoezi A, Kiss JG, Jori J Recurrent bacterial meningitis after cochlear implantation in a patient with a newly described labyrinthine malformation INTERNATIONAL JOURNAL OF PEDIATRIC OTORHINOLARYNGOLOGY 73:(1) pp (2009) IF: 1.148 2 I. INTRODUCTION I. 1. Hearing through bone conduction and its application in assistive hearing devices historical review During the Renaissance an Italian physician, philosopher and mathematician, Girolama Cardano ( ) mentioned his peculiar phenomenon how sound may be perceived by means of a rod or the shaft of a spear held between one s teeth through bone conduction. He noted his observation in De Subtilitate (1551). Other authors (Ingrassia, Fabricius, and Plater) mentioned the bone-conduction phenomenon only with theoretical interest. Hieronymus Capivaccius (died 1589) an Italian physician interpreted the diagnostic value of Cardano s observations, and employed it in the differential diagnosis of the disorders of the tympanic membrane. In the coming century an English physician, John Bulwer ( ), who is known for developing a method for communicating with the deaf and dumb, also illustrated in his impressive work, Philocophus a remarkable case of a man who is listening to music through bone conduction by his teeth. Falling into oblivion for a time perceiving sounds through the vibration of the skull bones mediated by the teeth was re-unfolded by Joannes Jorrison in 1757, and subsequently by Jean Marie Gaspard Itard ( ) a French military surgeon, who invented a teeth-to-teeth bone conduction stimulator. His book, the Traite des Maladies de l oreille et de L audition presented several illustrations of different hearing devices. In 1920 Joseph Prenn patented a mechanical bone conductor. The first electric bone vibrator was invented by Augustus G. Pohlmann and Frederick W. Kranz in the 1920 s, for use in some audiometers and a few table model hearing aids. In 1929, the Sonotone Company was established by Hugo Lieber (born in 1868 in Germany, died 1936), as an outgrowth of Siemens hearing aids. He invented the revolutionary bone conduction receiver in In 1934 it was advertised as the Leiber Oscillator. An improved bone vibrator was patented by E. H. Greibach and Sonotone became the licensor for this in Hearing aids mounted into eyeglasses were commercialized first in 1954 and until the last decades were the first rehabilitative option in those conductive hearing losses that could not be managed with reconstructive ear surgeries. Nevertheless the frequent problems with this concept (loss of vibration energy in the soft tissues, feed-back phenomenon, uncomfortable wearing, frequent problems with the adaptation to the individual shape of the head, etc) promoted the idea to put the vibrator directly into the temporal bone. The first system pioneering of this new therapeutic concept, based on the histological observation of direct titanium-to-bone integration (i.e. osseointegration) was introduced in 1977, called Bone Anchored Hearing Aid (BAHA). 3 I.2. The physiology of bone conduction I.2.1. Fundamental observations on bone conducted sound perception Perceiving a sound through bone conduction is when the vibration energy propagates through the skull bones, cartilages, skin and soft tissues, acting on the basilar membrane of the organ of Corti, generating travelling waves, resulting in the excitation of the sensory hair cells in the cochleae. Although many studies have been carried out since the beginning of the 20 th century, the mechanisms of bone conduction are still not fully clarified. The first question was whether bone conduction stimulates the same cochlear sensory apparatus or acts on a different sensory end organ. Békésy was the first to study the function of the auditory organ experimentally, replacing theoretical considerations by empirical evidence. In his famous cancellation experiment, that air conduction pure tone can be cancelled by bone conduction tone concluded that being the stimulated sensory apparatus identical one. He succeeded in subjective cancellation of an air conducted tone with a bone conducted tone at 400 Hz. Observations gained on the analysis of finite element models of the human middle ear and cochlea confirmed that basilar membrane vibration characteristics are essentially invariant regardless of whether the excitation is via bone conduction, independent of excitation direction, or via air conduction, as the basilar membrane is effectively driven by the anti-symmetric component of the oval and round window volume velocities resulting in differential slow wave component (i.e. anti-symmetric) of the fluid pressure. The best frequency map indicates the frequency corresponding to the peak basilar membrane vibration as a function of location along the basilar membrane. The best frequency map doesn t change significantly due to differences in the method of cochlear excitation. Distortion product otoacoustic emission (DPOAE) could be elicited by air and one bone conduction tones either. Properties unique to bone conduction, such as simultaneous bilateral stimulation and reduction of stimulus magnitude in the ear canal, may make bone conduction attractive for clinical measurement of DPOAEs. Emissions of similar magnitude are obtained with stimuli that are of similar magnitude at the place of generation, the bone conduction IOgram may be aligned with the one obtained using air conduction. I.2.2. Bone conduction pathways Experimental researches aimed to identify different ways of vibration energy transmission in the skull bones that inherently involve multiple pathways with different importance. The terminal stimulation of the basilar membrane of the organ of Corti is contributed by the summation of these hardly distinguishable vectors of sound vibrations, travelling through different media (i.e. air, soft-tissue, and bone or fluid). Narrowing the possible pathways for propagation of bone conduction summarized by Tonndorf in 1966, Stenfelt and Goode in 2005 described five components declared to be the most significant ones contributing to sound perception through bone conduction in human: 1) Sound pressure in the ear-canal and the occlusion effect osseo-tympanic stimulation. 2) Inertia of the middle-ear ossicles. 3) Inertia of cochlear fluids and fluid pressure transmission. 4) Alteration (compression and expansion) of the cochlear space. 5) Pressure transmission from the cerebrospinal fluid. 4 The inertia of cochlear fluids and fluid pressure transmission might be the most significant component of bone conduction in normal and pathological ear as well. Fluid itself regarded as incompressible since the wavelength of the fluid acoustic wave is much larger than the size of the cochlea. The cochlear fluid vibrates in response to the translational vibratory movement of the surrounding bone. When the temporal bone vibrates the secondary fluid displacement is possible due to the existence of the membranes of the oval and round window and the pressure gradient between them that promotes fluid flow between the scala vestibuli and scala tympani, resulting in the travelling waves of the organ of Corti. The oval and round windows are comparatively large in area and short in length, thereby minimizing the impedance of bulk fluid motion between these windows and promoting sound transmission. There are other relatively thin and long normal windows between the inner ear fluids and the cranial cavity, contributing to compliant pathways on both sides of the basilar membrane. The complex compliant structure of third window, collectively referred to as a normal third-window, includes the: - cochlear aqueduct (openings: 1. the posterior cranial fossa; 2. the scala tympani of the cochlea adjacent to the round window membrane) - vestibular aqueduct (openings: 1. the posterior cranial fossa; 2. the medial wall of the bony vestibule) - as well as micro channels parallel to blood vessels and nerves while entering or leaving the cochlea. These smaller diameter and longer channels are functionally closed to sound flow due to their high impedance, therefore considered to have negligible auditory impact in physiological hearing. On the contrary pathologic third-windows may direct the air-conducted sound energy away from the cochlea, while improving thresholds for bone-conducted sounds of leaving them unchanged, appearing in a picture of conductive hearing loss on the audiogram. Anatomical discrete lesions may be classified by their location, possessing variable inertial effects on cochlear fluids: - semicircular canals (superior, lateral or posterior canal dehiscence), - bony vestibule (large vestibular aqueduct syndrome, or other inner ear malformations), - cochlea (carotid-cochlear dehiscence, DNF-3 or X-linked deafness with stapes gusher, Apert-syndrome, etc.). Developmental disorders of the inner ear according to Jackler et al can be considered as a result of prematurely arrested embryogenesis: - With an absent or malformed cochlea: Complete labyrinthine aplasia (Michel deformity) Common cavity Cochlear aplasia Cochlear hypoplasia Incomplete partition (Mondini deformity) - With a normal cochlea: Vestibule-lateral semicircular canal dysplasia Enlarged vestibular aqueduct 5 Those malformations that are not able to be explained by this system are potentially being the result of an aberrant embryogenesis or the combination of the two possibilities. Such a malformation has been observed and published as a newly described one in the International Journal of Pediatric Otorhinolaryngology co-authored by the author of this present thesis. In Paget disease of the temporal bone the excessive breakdown and formation of bone, followed by disorganized bone remodeling may lead to a diffuse anatomical lesion of the bony labyrinth, resulting in diffuse third window effect. Third window lesions should be considered in the differential diagnosis of patients with conductive hearing loss. Consideration should always be given that conductive hearing loss, defined as an airbone gap (ABG) on the audiogram may due to disorders of the inner ear as well, with pathologic third windows in the background. Clues to suspect such a lesion include a lowfrequency ABG with supranormal thresholds for bone conduction, the presence of acoustic reflexes, vestibular myogenic responses or otoacoustic emissions. Imaging techniques are also essential for detailed differential diagnostics. I.2.3. Physical aspects of bone conduction The frequency-to-place conversion occurs within the cochlea, responding similarly when is fed via air or bone conduction either, although central mechanisms believed to be involved in pitch perception. The overall shapes of the basilar membrane velocity magnitude distributions are similar among different excitation cases. Different vectors of bone conduction excite the inner ear through the above mentioned pathways, characterized by several modes of skull vibrations. Longitudinal/compressional, transversal/shear waves and their combination, as well as bending/flexural waves all can propagate within the skull bones linearly, at least for frequencies between khz and up to 77 dbhl. At low frequencies the skull vibrates as a rigid body. Increasing the forced vibration frequency up to around 800 Hz a bi-nodal line pattern appears in opposite phases. At around 1600 Hz the skull starts to vibrate in quadrants. Newer techniques showed complex vibrations, made up of rotational and translational components, without any dominating one. Transcranial attenuation of a bone-conducted sound is defined as the difference in sensitivity between an ipsilaterally transmitted and a contralaterally transmitted sound positioned at identical points at the two sides of the head. In the frequency range of 0.25 to 4 khz transcranial attenuation is approximately 0 to 15 db, highly depending on the stimulation position and the frequency. Stenfelt reported 2 to 3 db lower median transcranial attenuation at the position of an implanted bone conduction hearing aid, compared to that gained from the stimulation in the mastoid region, with large intersubject variability (up to 40dB). I.3 Epidemiology of hearing impairment Hearing loss is the leading cause of disability worldwide. Approximately 15 % of the world s population has hearing loss to some degree, and 5.3 % out of them, around 360 million people, has hearing loss greater than 40 db in the better hearing ear in adults, and 30 db in children. The current production of hearing aids covers the 10 % of the global need. 6 I.4. Implantable bone conduction solutions Based on the route of the vibration energy transmission, implantable bone-conduction hearing solutions can be divided into three groups, direct drive, skin drive and in the mouth systems. Those that directly vibrate the bone are referred to as direct drive implant systems (i.e. without a skin barrier), whereas those systems that transmit vibration energy to the bone through intact skin are referred as skin drive devices (this includes devices held to the head via soft band devices or eyeglasses and magnet connection implants). Finally, in the mouth systems generate vibrations of the skull bone through placement at the upper back teeth. The scope of this thesis focuses on the clinical and experimental based assessment of the Baha Connect and Baha Attract systems. Since the introduction in 1977, osseointegrated, direct-drive systems have used different kinds of modified percutaneous abutment connections through snap coupling to maintain the connection between the implanted component and the sound processor (SP). These systems have provided hearing rehabilitation with good clinical outcome for over patients in the last forty years with conductive or mixed hearing loss and singlesided sensorineural deafness. The classic, well-established surgical techniques of implantation, which rely on different skin flap creation and soft tissue reduction (STR), have been successfully used in the last decades. The primary aim of the STR was to achieve a stable epidermal covered bone surface around the implant. Later experiences, gained on large series of patients in independent studies have shown a range of incidence from rare to more frequent for variably severe peri-implant skin complications. Short-term complications arise in % of the cases. Long-term follow-up reveals an incidence of 3.3 % of skin reactions classified as Holgers grade 2 or higher, which may often require revision surgeries. Long-term follow-up identified an increasing risk of complications over time. The risk of adverse skin reactions has been addressed by new developments that incorporated microsurface technology for the implant component (e.g., titanium-dioxide surface), aimed at reducing the loading time, coupled with advanced redesign of the physical attributes of the abutment (new concave shape), which lowered the tendency for peri-implant pocket formation and adverse skin reactions. Other studies showed that patients receiving the 8.5 mm abutment during initial implantation are significantly less likely to require in-office procedural intervention or revision surgery postoperatively as compared to those receiving the shorter, 6 mm implant at initial surgery, furthermore applying linear incision with no or minimal soft tissue removal, with the longer (8.5 mm) abutment provided comparable or better complication rates than the previously accepted surgical techniques. The percutaneous osseointegrated implantation technique without skin thinning proved to be also beneficial for children. However while titanium is ideal for integrating with bone, it does not bond with soft tissues (skin and the underlying layers). With the application of hydroxyapatite coating on the abutment the overall soft tissue tolerance has improved through the reduced tendency for epidermal down-growth and pocket formation. Animal experiments have proven the excellent soft tissue adherence to the implant surface and faster wound healing around the abutment, which are key factors in the effectiveness of this therapeutic concept. Due to these characteristics of the abutment during the FAST surgical method of implantation the reduction of any soft tissues became unnecessary). According to the individual s soft tissue thickness (preoperatively measured) the abutment s length can vary form 6-12 mm. However, this method might have other substantial advantages compared to 7 the classic surgical procedures. Further explanation may be derived through observations of surgical outcomes for treatment of other diseases, where deteriorated peripheral blood circulation leads to similar skin reactions, such as complications of diabetes mellitus, including ulcerations and infections in the most severe cases. In view of these similarities, it was hypothesized that a major causative factor for the peri-implant skin reactions is diminished vascular capacity, which could be reduced by soft tissue preservation (STP) methods. As such the skin s macro-, and microcirculatory reservoirs are maintained through minimal traumatization of the soft tissues. Microvascular assessments with Laser-Doppler Flowmetry (LDF) have recently grown in importance in the diagnosis and treatment of hypoxia and ischemia-related tissue disorders, providing valuable information about the management of peripheral vascular disease, or diabetes treatment, or in plastic surgery, the evaluation of flaps, etc. These studies conclude that the better blood supply, the better skin conditions. LDF of the peri-implant areas, by assessing the preservation of macro-, and microvascular capacity patterns, thus might give important information about the expectable improvement in soft tissue complications compared to the earlier methods. Nevertheless, irrespectively the surgical approach or t
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