Insertion Trauma Research Articles

MORPHOLOGIC AND ELECTROPHYSIOLOGIC EFFECTS OF COCHLEAR IMPLANTATION AND ELECTRICAL STIMULATION

The nondeafened guinea pig model was utilized in this study to assess the functional and morphologic effects of cochlear implantation and electrical stimulation. Auditory brainstem responses (ABRs) were recorded prior to and following intrascalar implantation of a 3M-House cochlear electrode (n = 41 ears), as well as after electrical stimulation (n = 23 ears). The experimental population was divided into the following groups according to implantation and stimulation parameters: 200 microA for 3 hours (group I); 200 microA for 24 hours (group II); 400 microA for 3 hours (group III); implanted, but not stimulated (group IV); and nonimplanted, not stimulated ears (group V). Of those cochleae that sustained the trauma of implantation, 32 percent had no detectable ABR to 110 dB SPL clicks, while only 7 percent additionally failed to respond to 130 dB SPL clicks. No significant difference (one-way ANOVA with repeated measures at the 95 percent confidence limit) could be detected when comparing those ears that retained ABRs according to experimental grouping. Morphologic analysis was performed on 29 cochleae. Spiral ganglion "packing densities" were not found to be significantly different among the groups (ANOVA). The status of the organ of Corti was significantly better in groups II and V in comparison to the other groups (Kruskal-Wallis test with pairwise comparisons, p less than 0.05); there was no discernible dose-response relationship. Morphologic and electrophysiologic changes correlated with insertion trauma and infection rather than with electrical stimulation at the levels tested in this study.(ABSTRACT TRUNCATED AT 250 WORDS)

Cochlear implant revision: effects of reimplantation on the cochlea.

The removal of an indwelling cochlear implant electrode followed by reinsertion of a new device has been a maneuver of uncertain consequences to the cochlea and its surviving neural population. The present study was conducted in an attempt to elucidate the factors that determine whether a reimplantation procedure will be successful. Cochlear implantation followed by explantation and subsequent reimplantation was performed in eight adult cats. Evaluation of cochlear histopathology suggested a significant increase in electrode insertion trauma when there was proliferation of granulation tissue in the round window area and scala tympani. In other cases, atraumatic reinsertion was achieved without apparent injury to the cochlea. The results of a survey of cochlear implant manufacturers and surgeons indicate that electrode replacement can usually be accomplished without adverse effects. Difficulties have been encountered, however, in removing implants with protuberant electrodes and when reimplantation was attempted on a delayed basis following explantation.

Loss of residual hearing after cochlear implantation.

Many cochlear implant recipients have some measurable hearing prior to implantation. Animal studies have demonstrated some loss of viable neural elements resulting from both mechanical insertion trauma and long-term electrical stimulation. The effect of implantation of a long intracochlear multichannel electrode array and subsequent electrical stimulation on residual hearing was evaluated. Forty consecutive cochlear implant recipients were assessed by audiometry at the Colorado Ear Clinic between July 1985 and June 1988. Twelve of these patients (30%) had some measurable residual hearing before implantation, although all had profound hearing loss, with no understanding of speech. All patients received a multichannel cochlear implant with all 22 electrodes inserted in each patient by an experienced cochlear implant surgeon. Audiometric testing was repeated between 2 and 24 months after implantation. Pure-tone threshold responses in the implanted ear were significantly reduced postimplant, while pure-tone threshold responses in the nonimplanted ear were stable.

Recurrent bone regeneration in titanium implants. Experimental model for determining the healing capacity of bone using quantitative microradiography

An experimental technique for quantitative assessment of bone repair was tested. The recurrent regeneration capacity of cortical bone was analysed in consecutive 3 wk periods, using an osseointegrated titanium implant, the Bone Harvest Chamber (BHC), in the proximal tibial metaphysis of the rabbit. The BHC is a divisible implant penetrated by a canal into which newly formed bone tissue will grow during a 3 wk healing period. The newly formed bone tissue may easily be collected (harvested) without the animal being killed. After 3 wk, bone tissue can again be harvested, in principle, indefinitely. Intact harvested specimens were quantified by microradiography-videodensitometry, yielding a total specimen mass in mg aluminium equivalent. This unit correlated very well to a specimen dry weight ( r = 0.996) and an average mineralized bone density ( r = 0.937). The specimens were also examined by correlative histology. Three weeks after implant insertion, the chambers had become integrated in the bone tissue but the average bone mass varied widely, influenced by the surgical insertion trauma. Six weeks after insertion, the greatest average bone mass was found, indicating an intense ongoing osseointegration. The amount of bone regenerated at later havests was fairly equal, indicating a stabilization of the implant bed to the repeat stimulus i.e. harvesting. Bone regeneration differed significantly between animals, but also intraindividual variations i.e. different amounts of bone formed in the same chamber, were observed.

Characterization of Mechanical Properties of Single Electrodes and Multielectrodes

Over recent years there has been increasing awareness of the potential damage to the fragile structures of the cochlea that could be caused by the insertion of intracochlear electrodes. Temporal bone histologic studies from chronically implanted human patients have shown that intracochlear electrodes can cause significant insertion trauma. This paper describes how the mechanical properties of the electrode array can influence insertion trauma, and compares the properties of solid wire electrodes with those of a tapered electrode array. The maximum force that can be applied by the tip of the solid wire electrode is 25 times what can be applied by the tapered electrode array, whereas the tapered array is ten times more flexible. These differences in mechanical properties suggest that evidence for insertion trauma should be assessed on an electrode-by-electrode basis.

Surgery for the Safe Insertion and Reinsertion of the Banded Electrode Array

Adhering to the surgical technique outlined in the protocol for the Nucleus implant has resulted in over 100 patients worldwide obtaining significant benefit from multichannel stimulation. A detailed analysis of the results in 40 patients shows that it improves their awareness of environmental sounds and their abilities in understanding running speech when combined with lipreading. In addition, one third to one half of the patients also understand significant amounts of running speech without lipreading and some can have interactive conversations over the telephone. It is clear that any insertion trauma is not significant, which is confirmed by the excellent clinical results.

Anatomy of the round Window with Respect to Cochlear Implant Surgery

Twenty-three human temporal bones were dissected to study the anatomy of the round window with respect to cochlear implantation. Information was also gathered concerning the passage of a 22-channel electrode array along the cochlear duct by using cochlear surface dissection preparations. The insertion length and any insertion trauma were noted both by observation at the time of insertion and by careful analysis of video recordings. The crista semilunaris did not interfere with smooth electrode insertion. The recommendation is made that enlarging the round window anteroinferiorly is unnecessary and potentially hazardous in most cases.

Pneumococcal Middle Ear Infection and Cochlear Implantation

A limited study for the experimental induction of pneumococcal otitis media is presented. It is a useful model to study the effects of otitis media in the implanted and nonimplanted cochlea of the cat. Pneumococcal otitis media caused minor pathological changes in two nonimplanted cochleas and more widespread changes together with significant loss of neural elements in two implanted cochleas. However, the small number of animals used in this study did not allow us to distinguish between the effects of electrode insertion trauma, infection, or the combination of both.

Brainstem auditory pathway degeneration associated with chronic cochlear implants in the monkey

The form and pattern of first-order and transsynaptic degeneration in the central auditory pathway was studied in monkeys following inner ear stimulation by a cochlear implant. Multielectrode, scala tympani, and modiolar systems were implanted; in some cases, neomycin was perfused into the cochlea to destroy the organ of Corti at the time of implantation. The monkeys were maintained chronically for 5 to 120 weeks, then the cochleas and brainstems were examined histologically. The extent of spiral ganglion cell loss across animals showed variability, reflecting the different procedures and devices used. The degree and distribution of spiral ganglion cell loss was related to the degree and distribution of neural degeneration seen in the cochlear nucleus in all cases. Peripheral damage progressed toward the cochlear apex as survival time increased, and this progression was reflected in the cochlear nucleus by a ventrolateral shift in the locus of degeneration over time. In addition, evidence for transneuronal degeneration was seen at the superior olive, the lateral lemniscus and the inferior colliculus. Our findings indicate that several factors inherent in the use of a cochlear prosthesis, i.e., insertion trauma, host reaction, and/or electrical stimulation, may be associated with a long-term, continuing process of central degeneration visible at several levels of the auditory system.