Graeme Clark Collection
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ItemPaediatric cochlear implantation: radiologic observations of skull growth( 1993)We investigated the effects of long-term implantation of auditory prostheses on skull growth in young animals. Four monkeys were implanted with dummy cochlear implants at 6 months of age. To simulate implantation in children, the bed for the receiver-stimulator or interconnecting plug was drilled across a calvarial suture down to the underlying dura. Plain skull oentgenograms were periodically taken to monitor head growth for up to 3 years after implantation. These longitudinal measurements revealed no significant asymmetric skull growth. Postmortem measurements using computed tomographic scans confirmed these results and showed no significant difference in the intracranial volumes between the implanted and control sides of each animal or between experimental and nonimplanted control monkeys. These results suggest that long-term cochlear implantation in very young children will not cause any significant deformity of the skull.
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ItemThe postnatal growth of the temporal bone and its implications for cochlear implantation in children( 1993)The postnatal growth of the human temporal bone was examined by direct anatomical measurements on 60 cadaver specimens of all ages. The bones were dissected as one would perform cochlear implant surgery using a posterior tympanotomy approach. Nineteen anatomical /surgical landmarks with implications for cochlear implant surgery were identified on each bone and the distance between these points measured. The temporal hone was found to be a complex structure, phylogenetically, anatomically and functionally consisting of four different parts with independent postnatal development. The inner and middle cars were adult size at birth. The external auditory canal and most parts of the temporal hone were subject to significant lateral growth. The size of the pneumatised mastoid increased in all directions. In the facial recess, however, no postnatal growth was observed. Between birth and adulthood an average of 12 mm (SD 5 mm) of growth was seen directly between the sino-dural angle and the round window, the landmarks approximating the Implantation site for the receiver-stimulator and the electrode entry point into the inner car. However, if an electrode leadwire is fixed at a cortical fixation site such as the posterosuperior point of Macewen's triangle, the leadwire would be subject to approximately 20 mm of growth. These results indicate that a paediatric cochlear implant design incorporating an expandable leadwire to accommodate this growth should allow up to 25 mm of leadwire lengthening. The fossa incudis showed no growth relative to the round window and was found to be a convenient fixation site for the electrode array close to the cochlea. From an anatomical and surgical point of view, cochlear implantation in very young children is feasible, provided the electrode array is secured and the design accommodates for controlled leadwire lengthening.
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ItemThe postnatal growth of the temporal bone and its implications for cochlear implantation in children( 1993)The growth of the human temporal bone is of practical concern if young children are implanted. It is feared that the normal development of the temporal bone after implantation may displace the electrode array and jeopardize the success of the device. To evaluate the extent of growth 60 cadaver specimens of all ages were examined by direct anatomical measurements. The bones were dissected by imitating the cochlear implantation surgical procedure in the temporal bone laboratory. 19 anatomical/surgical landmarks with implications for cochlear implant surgery were identified and the distance between them measured. The inner ear and middle ear are adult size at birth. The external auditory canal and most parts of the temporal bone are subject to significant lateral growth. The size of the pneumatised mastoid was found to increase in all directions. In the facial recess however, no postnatal growth could be noted. Between birth and adulthood a considerable amount of growth is to be expected between the sino-dural angle and the round window, the landmarks representing the implantation site for the receiver/stimulator and the electrode entry site respectively. From an anatomical and surgical point of view, cochlear implantation in very young children proved to be feasible, provided the electrode array is secured close to the cochlea and the design accommodates for controlled leadwire lengthening.
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ItemThe postnatal growth of the temporal bone and its implications for cochlear implants in children( 1993)An understanding of the postnatal growth of the temporal bone is an important prerequisite for the development of cochlear implantation in very young children. Such information will have an important bearing on both the design of the implant and the surgical procedure. We have measured the postnatal growth of the temporal bone by direct anatomical measurements on 60 cadaver specimens with ages ranging from 2 months to 84 years. Nineteen anatomical landmarks with implications for cochlear implant surgery were identified on each bone and the distance between these points measured. The inner and middle ears were adult size at birth. The external auditory canal and most parts of the temporal bone were subject to significant lateral growth. The size of the pneumatized mastoid increased with age in all directions. Significantly, no postnatal growth was observed in the facial recess. The fossa incudis showed no growth relative to the round window and was found to be a convenient fixation site for the electrode array close to the cochlea. However, with the electrode leadwire fixed at a cortical site such as the osterosuperior point of McEwan's triangle, the leadwire would be subject to approximately 20 mm of growth between this point and the cochlea. These anatomical results indicate that a paediatric cochlear implant would require an expandable leadwire to accommodate these growth changes.
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ItemMultichannel cochlear implants in children: an overview of experimental and clinical results at the University of Melbourne [Opening Lecture]( 1992)During the last decade there has been great progress in the clinical management of profound, postlinguistically deafened adults through the use of multichannel cochlear implants. The device developed by The University of Melbourne in association with Cochlear Pty Ltd, electrically stimulates selective regions of the auditory nerve using an array of 22 platinum (Pt) electrodes located in the scala tympani. Its development followed basic experimental studies and the development and evaluation of a prototype device in the 1970's. Following safety studies and a successful clinical trial, the Melbourne/Cochlear multichannel implant was approved for use in adults by the United States Food and Drug Administration (FDA) in 1985. More than 3000 patients throughout the world have since been implanted with this device, many being able to understand a significant amount of unfamiliar, connected speech without lipreading Following miniaturization of the implant, it became suitable for use with children. In 1990, after additional biological safety and clinical investigations, the FDA approved the use of the Melbourne/Cochlear multichannel implant for profoundly deaf children above the age of two years. And in 1991, the device received the medical device implantation approval certificate from the Japanese Government. The present paper presents an overview of our recent biological safety studies and clinical experience in children, and discusses the likely future development of these devices.
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ItemAn antibacterial seal and fixation device for cochlear implants in young children [Abstract]( 1992)Concerns associated with cochlear implantation in young children include intracochlear spread of infection along the electrode array during otitis media, and electrode extraction caused by skull growth post-implantation. New biomaterials were used to seal and secure the electrode at its entry point into the cochlea. Hydroxyapatite was deposited around the outside of an electrode cuff and it bonded well to the surrounding bone of the otic capsule. The electrode cuff accommodated variable insertion depths with the help of a new, silicone based hydroscopic polymer. Preliminary results, including experimental testing of the device in an animal model of pneumococcal otitis media, indicate protection of the implanted cochlea against the spread of infection. Electrode leadwire displacement is prevented by fixation of the array at its entry point This concept may play an important role in the development of a safe cochlear implant design for children under two years of age, who are expected to benefit most from early auditory rehabilitation.
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ItemCochlear implantation in young children: studies on head growth, leadwire design and electrode fixation in the monkey model [Abstract]( 1992)For the safety of cochlear implantation in children under two, the implant assembly must not adversely effect the tissue of compromise head growth. Furthermore, growth changes and tissue responses should not impair functioning of the device. Dummy receiver-stimulators, interconnect plugs and leadwire-lengthening systems have been implanted for periods of 40 months in the young monkey to most effectively model the implantation of the young human child. The results show that implanting a receiver-stimulator package has no effect on skull growth or brain tissue under the package. The system for fixing the electrode at the fossa includes proved effective. There was marked osteoneogenesis in the mastoid cavity and this also resulted in fixation of the leadwire outside the cochlea. This study provides evidence for the safety of cochlear implantation in young children.
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ItemCochlear implantation in young children: long-term effects of implantation on the skull and underlying central nervous system tissues in a primate model [Abstract]( 1992)Recent independent studies reporting results obtained by profoundly deaf children implanted with the Melbourne 22-channel cochlear implant have provided further impetus for assessing the feasibility of implanting children under two. Studies in appropriate animal models must first establish the safety of this procedure.
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ItemCochlear implantation in young children: long-term effects of implantation on normal hair cells and spiral ganglion cells in the monkey model [Abstract]( 1992)Recent independent results obtained by profoundly deaf children implanted with the Melbourne 22-channel cochlear implant (1) have provided further impetus. for examining thefeasibility of implanting children under two and children with profound deafness. Safety st1,ldies, in appropriate animal models, must first establish the safety of this procedure.