Angular Insertion Depth Research Articles

Deep insertion – round window approach by using SRA electrode

Hearing preservation surgery requires specially a traumatic technique. Having some preoperative anatomical data of the size of patient's cochlea surgeon can design his or her insertion depth. In the study we have evaluated a relation between hearing preservation rate and angular insertion depth estimated intraoperatively and postoperatively having measured insertion angle from radiological assessment and calculations given by Escude. There has not been no statistically significant difference between insertion depth angle, either estimated intraoperatively and measured and calculated post-operatively, and hearing preservation rate in the group. This analysis confirms a traumaticy of insertion in hearing preservation surgery.

Atraumaticity Study of 2 Cochlear Implant Electrode Arrays

Evaluate, based on morphologic and histologic parameters, the atraumaticity of 2 electrode arrays implanted in 10 human temporal bones. Atraumatic surgery and electrode arrays are current topics in otologic surgery. The preservation of cochlear anatomy and its functions is a priority and morphologic evaluation of the surgical trauma is essential to continue improving in this field. Ten preserved human temporal bones (TB) without anatomic alterations were used in this study. They were divided into 2 groups of 5, and atraumatic surgery was performed to insert HiFocus 1J (group A) and HiFocus Helix (group B) electrode arrays. Anatomic comparisons were performed using computed tomography and histologic analysis. Group A: the mean length for the cochlear longitudinal axis was 10.30 mm, and the cochlear transversal axis was 7.2 mm. Scala tympani insertion was achieved in 4/5 TB studied, with a mean depth and angle of insertion of 19.2 mm and 325.5°, respectively. Lateral location of the electrode array was achieved in all specimens. No significant correlation was observed between these dimensions and depth of insertion. Group B: the mean length for the cochlear longitudinal axis was 9.52 mm, and cochlear transversal axis was 6.38 mm. Scala tympani insertion was achieved in 4/5 TB studied, with a mean depth and angle of insertion of 17.5 mm and 352°, respectively. Modiolar location of the electrode array was achieved in all specimens. A positive correlation was established between the linear and angular insertion depths (p = 0.044). In summary, it is safe to state that neither electrode array shows significant insertion trauma.

High-Resolution Secondary Reconstructions with the Use of Flat Panel CT in the Clinical Assessment of Patients with Cochlear Implants

Radiologic assessment of cochlear implants can be limited because of metallic streak artifacts and the high attenuation of the temporal bones. We report on 14 patients with 18 cochlear implants (17 Med-El standard 31.5-mm arrays, 1 Med-El medium 24-mm array) who underwent flat panel CT with the use of high-resolution secondary reconstruction techniques. Flat panel CT depicted the insertion site, cochlear implant course, and all 216 individual electrode contacts. The calculated mean angular insertion depth for standard arrays was 591.9° (SD = 70.9; range, 280°). High-resolution secondary reconstructions of the initial flat panel CT dataset, by use of a manually generated field of view, Hounsfield unit kernel type, and sharp image characteristics, provided high-quality images with improved spatial resolution. Flat panel CT is a promising imaging tool for the postoperative evaluation of cochlear implant placement.

Electric-acoustic pitch comparisons in single-sided-deaf cochlear implant users: Frequency-place functions and rate pitch

Eight cochlear implant users with near-normal hearing in their non-implanted ear compared pitch percepts for pulsatile electric and acoustic pure-tone stimuli presented to the two ears. Six subjects were implanted with a 31-mm MED-EL FLEXSOFT electrode, and two with a 24-mm medium (M) electrode, with insertion angles of the most apical contacts ranging from 565° to 758°. In the first experiment, frequency-place functions were derived from pure-tone matches to 1500-pps unmodulated pulse trains presented to individual electrodes and compared to Greenwood's frequency position map along the organ of Corti. While the overall median downward shift of the obtained frequency-place functions (−0.16 octaves re. Greenwood) and the mean shifts in the basal (<240°; −0.33 octaves) and middle (−0.35 octaves) regions were statistically significant, the shift in the apical region (>480°; 0.26 octaves) was not. Standard deviations of frequency-place functions were approximately half an octave at electrode insertion angles below 480°, increasing to an octave at higher angular locations while individual functions were gradually leveling off.In a second experiment, subjects matched the rates of unmodulated pulse trains presented to individual electrodes in the apical half of the array to low-frequency pure tones between 100 Hz and 450 Hz. The aim was to investigate the influence of electrode place on the salience of temporal pitch cues, for coding strategies that present temporal fine structure information via rate modulations on select apical channels. Most subjects achieved reliable matches to tone frequencies from 100 Hz to 300 Hz only on electrodes at angular insertion depths beyond 360°, while rate-matches to 450-Hz tones were primarily achieved on electrodes at shallower insertion angles. Only for electrodes in the second turn the average slopes of rate-pitch functions did not differ significantly from the pure-tone references, suggesting their use for the encoding of within-channel fine frequency information via rate modulations in temporal fine structure stimulation strategies.

Assessment of intracochlear trauma caused by the insertion of a new straight research array

ObjectiveTo assess the degree of intracochlear trauma using the Cochlear™ Straight Research Array (SRA). This electrode has recently been released by Cochlear™ on the CI422 implant.BackgroundElectroacoustic stimulation (EAS) enables recipients to benefit from cochlear implantation while retaining their natural low-frequency hearing. A disadvantage of short EAS electrodes is that short electrodes provide limited low-frequency stimulation. Thus, loss of the residual hearing may require reimplantation with a longer electrode. In order to overcome this problem, the slim diameter SRA with increased length (20–25 mm) has been designed to provide a deeper, yet non-traumatic insertion.MethodsTwo insertion studies into temporal bones were undertaken. The first involved dissection of the cochlea to gain a view into the scala vestibuli and insertion of the SRA and control electrodes with a microactuator for a surgeon-independent yet controlled insertion. High-speed photography was used to record data. The second study involved a high-resolution X-ray microcomputed tomography (microCT) study to assess electrode placement and tissue preservation in surgeon-implanted bones.ResultsThe SRA had a smooth insertion trajectory. The average angular insertion depth was 383° when inserted until resistance was encountered, and 355° if inserted to a predetermined mark for EAS use. In addition, microCT data showed that this caused no significant trauma or distortion of the basilar membrane up to 20 mms depth.ConclusionTemporal bone studies show that the SRA appears to cause no intracochlear trauma if used as an EAS electrode up to 20 mm depth of insertion.

Development and evaluation of the modiolar research array – multi-centre collaborative study in human temporal bones

ObjectiveMulti-centre collaborative study to develop and refine the design of a prototype thin perimodiolar cochlear implant electrode array and to assess feasibility for use in human subjects.Study DesignMulti-centre temporal bone insertion studies.Materials and MethodsThe modiolar research array (MRA) is a thin pre-curved electrode that is held straight for initial insertion with an external sheath rather than an internal stylet. Between November 2006 and February 2009, six iterations of electrode design were studied in 21 separate insertion studies in which 140 electrode insertions were performed in 85 human temporal bones by 12 surgeons. These studies aimed at addressing four fundamental questions related to the electrode concept, being: (1) Could a sheath result in additional intra-cochlear trauma? (2) Could a sheath accommodate variations in cochlea size and anatomies? (3) Could a sheath be inserted via the round window? and (4) Could a sheath be safely removed once the electrode had been inserted? These questions were investigated within these studies using a number of evaluation techniques, including X-ray and microfluoroscopy, acrylic fixation and temporal bone histologic sectioning, temporal bone microdissection of cochlear structures with electrode visualization, rotational tomography, and insertion force analysis.ResultsFrequent examples of electrode rotation and tip fold-over were demonstrated with the initial designs. This was typically caused by excessive curvature of the electrode tip, and also difficulty in handling of the electrode and sheath. The degree of tip curvature was progressively relaxed in subsequent versions with a corresponding reduction in the frequency of tip fold-over. Modifications to the sheath facilitated electrode insertion and sheath removal. Insertion studies with the final MRA design demonstrated minimal trauma, excellent perimodiolar placement, and very small electrode dimensions within scala tympani. Force measurements in temporal bones demonstrated negligible force on cochlear structures with angular insertion depths of between 390 and 450°.ConclusionThe MRA is a novel, very thin perimodiolar prototype electrode array that has been developed using a systematic collaborative approach. The different evaluation techniques employed by the investigators contributed to the early identification of issues and generation of solutions. Regarding the four fundamental questions related to the electrode concept, the studies demonstrated that (1) the sheath did not result in additional intra-cochlear trauma; (2) the sheath could accommodate variations in cochlea size and anatomies; (3) the sheath was more successfully inserted via a cochleostomy than via the round window; and (4) the sheath could be safely removed once the electrode had been inserted.

Evaluation of the hybrid‐L24® electrode using microcomputed tomography

To compare electrode array position, and depth of insertion of the Cochlear Hybrid-L24 electrode array following traditional cochleostomy and round window (RW) insertion. Prospective cadaveric temporal bone study. Ten cadaveric temporal bones were implanted with the Hybrid-L24 electrode array; half were introduced through a RW approach, whereas the other half were inserted through a traditional scala tympani cochleostomy. A micro-CT scanner was then used to evaluate electrode position, intracochlear trauma, and depth of insertion. All electrodes were inserted into the scala tympani without significant resistance. No electrodes demonstrated tip fold-over or through-fracturing of the osseous spiral lamina, basilar membrane, or spiral ligament. The average angular depth of insertion for all 10 electrodes was 252.4°. Compared to cochleostomy insertions, electrodes inserted through the RW more commonly acquired a proximal perimodiolar orientation, followed a more predictable course, and less commonly contacted critical soft tissue structures. The results of this study demonstrate that the Hybrid-L24 electrode can be successfully inserted using a RW or traditional cochleostomy technique with minimal intracochlear trauma. Our data also suggests that with this model, RW insertions may provide particular advantages with respect to hearing preservation over the traditional cochleostomy approach.

Cochlear Implantation Using Thin‐Film Array Electrodes

Current limitations in language perception may stem from an inability to provide high-resolution sound input. Thin-film array technology allows for a greater density of stimulating sites within the limited diameter of the scala tympani. This study examines the use of a flexible carrier to achieve adequate depth of insertion. A prospective human cadaveric temporal bone insertion analysis. Academic otolaryngology department and school of electrical and computer engineering collaboration. A prototype thin-film array electrode coupled with an insertion test device (ITD) was manufactured and inserted into 10 human cadaveric temporal bones. As controls, 2 additional temporal bones were implanted with the ITD only and 2 were unimplanted. Radiologic and histologic data were collected. Ten thin-film array electrodes were successfully implanted into 10 individual temporal bones via round window (5) and cochleostomy (5) approaches. Seventeen millimeters of insertion was noted for each device, with an average angular insertion depth of 292° by radiographic measurements and 392° by histologic sectioning. Electrode distance to the modiolus averaged 0.88 mm by computed tomography and 0.67 mm by histologic measurements. Average percentage trauma was 26% for the ITD-backed arrays compared with 15% and 29% for ITD only and unimplanted temporal bones, respectively. Thin-film array electrodes coupled with an ITD were successfully inserted into the human cochlea with limited trauma. With continued development and testing of this electrode design, the thin-film array may improve the language perception achieved through cochlear implantation.

Variance of Angular Insertion Depths in Free-Fitting and Perimodiolar Cochlear Implant Electrodes

To assess the variance in cochlear implant electrode insertion depth in degrees around the modiolus (angular insertion depth) in free-fitting and perimodiolar electrode arrays. Twenty-eight fresh human temporal bones were implanted with free-fitting cochlear implant electrodes, and 18 bones were implanted using perimodiolar electrode arrays. Specimens were embedded, and 2-dimensional radiographs were obtained to assess angular insertion depths. Histologic serial sections of undecalcified bones were then evaluated to analyze intracochlear electrode positions. Finally, linear surgical insertion depths (in millimeters) were correlated with angular insertion depth (degrees around the modiolus). A moderate variance of angular insertion depth was documented for both free-fitting and perimodiolar electrode arrays. Full insertions into the scala tympani ranged from 540 to 630 degrees with free-fitting arrays and from 270 to 375 degrees with perimodiolar electrodes. In free-fitting devices, a linear relationship between linear (in millimeters) and angular (degrees) insertion depths was observed. Insertions into scala vestibuli were observed in 9 of 28 and 5 of 18 of the specimens for free-fitting and perimodiolar electrodes, respectively. Additionally, scala vestibuli insertions showed greater angular insertion depths when compared with scala tympani implantations. Variances in angular insertion depths seem to be moderate and similar in free-fitting and perimodiolar electrode arrays. Scala vestibuli insertions showed greater angular insertion depths than comparable insertions into the scala tympani. In perimodiolar electrodes, angular insertion depths equal or greater than 390 degrees suggested scala vestibuli placement.

A temporal bone study of insertion trauma and intracochlear position of cochlear implant electrodes. II: Comparison of Spiral Clarion™ and HiFocus II™ electrodes

In recent years, several new designs of cochlear implant electrodes have been introduced clinically with the goal of optimizing perimodiolar placement of stimulation sites. Previous studies suggest that perimodiolar electrodes may increase both the efficiency and performance of a cochlear implant. This is the second of two studies designed to examine the positioning of electrodes and the occurrence of insertion-related injury with these newer designs and to directly compare two perimodiolar electrodes to their predecessors. In our previous report we compared the Nucleus™ banded electrode with the Nucleus Contour™ perimodiolar electrode. In the present study, using the same protocol, we examine the Spiral Clarion™ electrode and its successor, the HiFocus II™ electrode with attached positioner. Eight Spiral Clarion™ arrays and 20 HiFocus II™ electrodes with positioners were inserted into human cadaver temporal bones. Following insertion, the specimens were embedded in acrylic resin, cut in quarters with a diamond saw and polished. Insertion depth, proximity to the modiolus and trauma were evaluated in X-ray images and light microscopy. The newer electrode was consistently positioned closer to the modiolus than the previous device whereas the angular depth of insertion measured for the two electrodes was similar. The incidence of trauma was minimal when either electrode was inserted to a depth of less than 400°. However, severe trauma was observed in every case in which the HiFocus II™ with positioner was inserted beyond 400° and in some cases in which the Spiral Clarion ™ was inserted beyond 400°. To evaluate the possible role of electrode size in the trauma observed we modeled both devices relative to the dimensions of the scala tympani. We found that the fully inserted HiFocus II™ electrode with positioner was larger than the scala tympani in approximately 70% of temporal bones measured. The results suggest that both the Clarion™ spiral and HiFocus II™ with positioner can be inserted with minimal trauma, but in many cases not to the maximum depth allowed by the design.