Assessment of Temporal Bone Thickness for Implantation of a New Active Bone-Conduction Transducer

Early Results With the New Active Bone-Conduction Hearing Implant: A Systematic Review and Meta-Analysis

OBJECTIVE

The bone conduction implant (BCI) 602 is a new transcutaneous BCI with smaller dimensions. However, limited patient numbers restrict the statistical power and generalizability of the current studies. The present systematic review and meta-analysis summarize early audiological and medical outcomes of adult and pediatric patients implanted with the BCI 602 due to mixed or conductive hearing loss.

DATA SOURCE

Following the Preferred Reporting items for Systematic Reviews and Meta-analyses guidelines, 108 studies were reviewed, and 6 (5.6%) were included in the meta-analysis.

REVIEW METHOD

The data on study and patient characteristics, surgical outcomes, and audiological test results were extracted from each article. Meta-analysis employed the fixed-effect and random-effects models to analyze the mean differences (MDs) between pre- and postoperative performances.

RESULTS

In total, 116 patients were evaluated, including 64 (55%) adult and 52 (45%) pediatric patients. No intraoperative adverse events were reported, while postoperative complications were reported in 2 (3.1%) adult and 2 (3.8%) pediatric patients. Studies consistently showed significant improvements in audiological outcomes, quality of life, and sound localization in the aided condition. In the meta-analysis, we observed a significant difference in the unaided compared to the aided condition in sound field thresholds (n = 112; MD, -27.05 dB; P < 0.01), signal-to-noise ratio (n = 96; MD, -6.35 dB; P < 0.01), and word recognition scores (n = 96; MD, 68.89%; P < 0.01).

CONCLUSION

The implantation of the BCI 602 was associated with minimal surgical complications and excellent audiological outcomes for both the pediatric and the adult cohort. Therefore, our analysis indicates a high level of safety and reliability. Further research should focus on direct comparisons with other BCIs and long-term functional outcomes.

Focused ultrasound heating in brain tissue/skull phantoms with 1 MHz single-element transducer

PURPOSE

The study aims to provide insights on the practicality of using single-element transducers for transcranial Focused Ultrasound (tFUS) thermal applications.

METHODS

FUS sonications were performed through skull phantoms embedding agar-based tissue mimicking gels using a 1 MHz single-element spherically focused transducer. The skull phantoms were 3D printed with Acrylonitrile Butadiene Styrene (ABS) and Resin thermoplastics having the exact skull bone geometry of a healthy volunteer. The temperature field distribution during and after heating was monitored in a 3 T Magnetic Resonance Imaging (MRI) scanner using MR thermometry. The effect of the skull's thickness on intracranial heating was investigated.

RESULTS

A single FUS sonication at focal acoustic intensities close to 1580 W/cm2 for 60 s in free field heated up the agar phantom to ablative temperatures reaching about 90 °C (baseline of 37 °C). The ABS skull strongly blocked the ultrasonic waves, resulting in zero temperature increase within the phantom. Considerable heating was achieved through the Resin skull, but it remained at hyperthermia levels. Conversely, tFUS through a 1 mm Resin skull showed enhanced ultrasonic penetration and heating, with the focal temperature reaching 70 °C.

CONCLUSIONS

The ABS skull demonstrated poorer performance in terms of tFUS compared to the Resin skull owing to its higher ultrasonic attenuation and porosity. The thin Resin phantom of 1 mm thickness provided an efficient acoustic window for delivering tFUS and heating up deep phantom areas. The results of such studies could be particularly useful for accelerating the establishment of a wider range of tFUS applications.

Cochlear implant positioning: development and validation of an automatic method using computed tomography image analysis

The aim of this study was to preoperatively asses the feasibility of drilling a bony recess for the fixation of a cochlear implant in the temporal bone. Even though complications are rare with cochlear implantations, drilling at the site of implantation have resulted in hematoma or cerebrospinal fluid leakage. Mainly in cases with a reduced temporal bone thickness, the risk for complications has increased, such as in paediatric patients.

Methods

An in-house designed semi-automatic algorithm was developed to analyse a 3D model of the skull. The feasibility of drilling the recess was determined by a gradient descent method to search for the thickest part of the temporal bone. Feasibility was determined by the residual bone thickness which was calculated after a simulated drilling of the recess at the thickest position. An initial validation of the algorithm was performed by measuring the accuracy of the algorithm on five 3D models with known thickest locations for the recess. The accuracy was determined by a part comparison between the known position and algorithm provided position.

Results

In four of the five validation models a standard deviation for accuracy below the predetermined cut-off value of 4.2 mm was achieved between the actual thickest position and the position determined by the algorithm. Furthermore, the residual thickness calculated by the algorithm showed a high agreement (max. 0.02 mm difference) with the actual thickness.

Conclusion

With the developed algorithm, a semi-automatic method was created to analyse the temporal bone thickness within a specified region of interest on the skull. Thereby, providing indications for surgical feasibility, potential risks for anatomical structures and impact on procedure time of cochlear implantation. This method could be a valuable research tool to objectively assess feasibility of drilling a recess in patients with thin temporal bones preoperatively.

Results of a Novel, Nonsurgical Bone-Conduction Hearing Aid for the Treatment of Conductive Hearing Loss in Australian Children

OBJECTIVE

To determine and compare the benefits a novel adhesive bone-conduction system and a conventional bone-conduction hearing aid (BCHA) on a softband for children with conductive hearing loss.

STUDY DESIGN

Prospective, single-subject randomized, crossover trial.

SETTING

Tertiary referral center in Australia.

PARTICIPANTS

Eight children aged from 4 to 17 years with conductive hearing loss.

INTERVENTION

Rehabilitative with participants using the novel adhesive bone-conduction aid and a BCHA.

MAIN OUTCOME MEASURES

Aided thresholds, as well as speech perception in quiet, unaided and aided with the novel adhesive bone-conduction aid and BCHA on a softband. For the six older children, speech in noise testing was also conducted.

RESULTS

The mean unaided four frequency average hearing levels was 48 dB HL for air conduction, 10.5 dB HL for bone conduction, with a mean air-bone gap in the aided ear of 37.5 dB HL.Four-frequency average hearing level aided thresholds were 20.2 dB for the novel device and 19.8 dB for the BCHA, with no significant difference between the devices. Aided monosyllabic word scores improved from an average of 45% in the unaided condition to 81.6 and 85% for the novel adhesive and BCHA devices, respectively. Aided speech in noise performance improved, on average, by 1.6 dB SNR when wearing the BCHA and the novel adhesive device, with no significant difference in performance between the two devices.

CONCLUSIONS

The novel device provided equivalent performance to the BCHA on all measures and can be considered as an alternative device for pediatric patients with conductive hearing loss.

Average thickness of the bones of the human neurocranium: development of reference measurements to assist with blunt force trauma interpretations

The accurate interpretation of a blunt force head injury relies on an understanding of the case circumstances (extrinsic variables) and anatomical details of the individual (intrinsic variables). Whilst it is often possible to account for many of these variables, the intrinsic variable of neurocranial thickness is difficult to account for as data for what constitutes 'normal' thickness is limited. The aim of this study was to investigate the effects of age, sex and ancestry on neurocranial thickness, and develop reference ranges for average neurocranial thickness in the context of those biological variables. Thickness (mm) was measured at 20 points across the frontal, left and right parietals, left and right temporals and occipital bones. Measurements were taken from post-mortem computed tomography scans of 604 individuals. Inferential statistics assessed how age, sex and ancestry affected thickness and descriptive statistics established thickness means. Mean thickness ranged from 2.11 mm (temporal squama) to 19.19 mm (petrous portion). Significant differences were noted in thickness of the frontal and temporal bones when age was considered, all bones when sex was considered and the, right parietal, left and right temporal and occipital bones when ancestry was considered. Furthermore, significant interactions in thickness were seen between age and sex in the frontal bone, ancestry and age in the temporal bone, ancestry and sex in the temporal bone, and age, sex and ancestry in the occipital bone. Given the assorted influence of the biological variables, reference measurement ranges for average thickness incorporated these variables. Such reference measurements allow forensic practitioners to identify when a neurocranial bone is of normal, or abnormal, thickness.

Surgery Training System Supported by Organic Materials

The aim of the study was the qualitative assessment of new materials based on a polycarbonate matrix in terms of its use in 3D printing and its processing and geometric modification (cutting). Filaments made of the new material doped with talc in five different proportions were visually inspected with a microscope. The calibration and test models were made using the FFF (fused filament fabrication) technique. In addition, its susceptibility to the drill and the behavior of the shavings were assessed and the temperature changing during drilling was measured. The implant was inserted to measure its resonance stability in each of the holes made and translated into the value of the implant stability quotient (ISQ) ranging from 1 to 100. The results were compared to those obtained for the training model of the skull bone. The amount of filler has been shown to affect the composite. Moreover, due to the properties of talc, a compatibilizer (polyol) was used. Differences were observed between the model made of the commercial material, the model made of the dried, tested material, and the model made of the undried material. It was confirmed that the presence of water in the material during its processing is important.

Pediatric morphometric study to guide the optimized implantation of the Osia® 2 implant system

PURPOSE

Continuous technological advances result in the availability of new bone conduction hearing implants, of which their suitability for pediatric patients is of major concern. The Cochlear^TMOsia^® 2 is a new active osseointegrated steady-state implant system that uses digital piezoelectric stimulation to treat hearing loss. The implant in the United States was approved for patients aged 12 years and above, whereas the CE mark is independent of age, the only requirement is body weight of at least 7 kg. Therefore, further clinical studies are required to assess device characteristics in younger patients. The aim of our study was to perform a morphometric study among 5-12-year-old children, and to develop a surgical protocol for Osia 2 system implantation based on these findings.

METHODS

We examined retrospectively cranial CT scans of 5-12-year-old patients from our clinical database. We measured the bone and soft-tissue thickness in the region of interest, and the position of the sigmoid sinus. 3D printed temporal bones were also used for planning.

RESULTS

Soft-tissue thickness varied between 3.2 ± 0.5 mm and 3.6 ± 0.6 mm and bone thickness varied between 3.5 ± 1.1 mm and 4.7 ± 0.3 mm. The sigmoid sinus was located 1.3 ± 0.2 cm posterior to the ear canal, and the anterior distance was 4.8 ± 0.9 to 7.1 ± 1.1 mm.

CONCLUSIONS

Our morphometric studies showed that patients aged 5-12 have different anatomical dimensions compared to adults, but that implantation of the Osia 2 system is feasible in these patients using an altered implant positioning recommended by our data. The Cochlear™ Osia^® 2 is, therefore, an option for hearing rehabilitation in younger pediatrics.

In Silico Assessment of Safety and Efficacy of Screw Placement for Pediatric Image-Guided Otologic Surgery

Introduction: Current high-accuracy image-guided systems for otologic surgery use fiducial screws for patient-to-image registration. Thus far, these systems have only been used in adults, and the safety and efficacy of the fiducial screw placement has not yet been investigated in the pediatric population.

Materials and Methods: In a retrospective study, CT image data of the temporal region from 11 subjects meeting inclusion criteria (8–48 months at the time of surgery) were selected, resulting in n = 20 sides. These datasets were investigated with respect to screw stability efficacy in terms of the cortical layer thickness, and safety in terms of the distance of potential fiducial screws to the dura mater or venous sinuses. All of these results are presented as distributions, thickness color maps, and with descriptive statistics. Seven regions within the temporal bone were analyzed individually. In addition, four fiducial screws per case with 4 mm thread-length were placed in an additively manufactured model according to the guidelines for robotic cochlear implantation surgery. For all these screws, the minimal distance to the dura mater or venous sinuses was measured, or if applicable how much they penetrated these structures.

Results: The cortical layer has been found to be mostly between 0.7–3.3 mm thick (from the 5^th to the 95^th percentile), while even thinner areas exist. The distance from the surface of the temporal bone to the dura mater or the venous sinuses varied considerably between the subjects and ranged mostly from 1.1–9.3 mm (from the 5^th to the 95^th percentile). From all 80 placed fiducial screws of 4 mm thread length in the pediatric subject younger than two years old, 22 touched or penetrated either the dura or the sigmoid sinus. The best regions for fiducial placement would be the mastoid area and along the petrous pyramid in terms of safety. In terms of efficacy, the parietal followed by the petrous pyramid, and retrosigmoid regions are most suited.

Conclusion: The current fiducial screws and the screw placement guidelines for adults are insufficiently safe or effective for pediatric patients.

Quantitative Analysis of Temporal Bone Density and Thickness for Robotic Ear Surgery

Background and Objective: Quantitative assessment of bone density and thickness in computed-tomography images offers great potential for preoperative planning procedures in robotic ear surgery. Methods: We retrospectively analyzed computed-tomography scans of subjects undergoing cochlear implantation (N = 39). In addition, scans of Thiel-fixated ex-vivo specimens were analyzed (N = 15). To estimate bone mineral density, quantitative computed-tomography data were obtained using a calibration phantom. The temporal bone thickness and cortical bone density were systematically assessed at retroauricular positions using an automated algorithm referenced by an anatomy-based coordinate system. Two indices are proposed to include information of bone density and thickness for the preoperative assessment of safe screw positions (Screw Implantation Safety Index, SISI) and mass distribution (Column Density Index, CODI). Linear mixed-effects models were used to assess the effects of age, gender, ear side and position on bone thickness, cortical bone density and the distribution of the indices. Results: Age, gender, and ear side only had negligible effects on temporal bone thickness and cortical bone density. The average radiodensity of cortical bone was 1,511 Hounsfield units, corresponding to a bone mineral density of 1,145 mg HA/cm³. Temporal bone thickness and cortical bone density depend on the distance from Henle's spine in posterior direction. Moreover, safe screw placement locations can be identified by computation of the SISI distribution. A local maximum in mass distribution was observed posteriorly to the supramastoid crest. Conclusions: We provide quantitative information about temporal bone density and thickness for applications in robotic and computer-assisted ear surgery. The proposed preoperative indices (SISI and CODI) can be applied to patient-specific cases to identify optimal regions with respect to bone density and thickness for safe screw placement and effective implant positioning.

Clinical and functional results after implantation of the bonebridge, a semi-implantable, active transcutaneous bone conduction device, in children and adults

Purpose

Aim of the study was to evaluate the surgical, clinical and audiological outcome of 32 implantations of the Bonebridge, a semi-implantable transcutaneous active bone conduction implant.

Methods

In a retrospective cohort study, we analyzed data for 32 implantations in 31 patients (one bilateral case; seven age < 16 years) with conductive or mixed hearing loss, malformations, after multiple ear surgery, or with single-sided deafness as contralateral routing of signal (CROS).

Results

Four implantations were done as CROS. Five cases were simultaneously planned with ear prosthesis anchors, and 23 implantations (72%) were planned through three-dimensional (3D) “virtual surgery.” In all 3D-planned cases, the implant could be placed as expected. For implant-related complications, rates were 12.5% for minor and 3.1% for major complications. Implantation significantly improved mean sound field thresholds from a preoperative 60 dB HL (SD 12) to 33 dB HL (SD 6) at 3 postoperative months and 34 dB HL (SD 6) at > 11 postoperative months (p < 0.0001). Word recognition score in quiet at 65 dB SPL improved from 11% (SD 20) preoperatively to 74% (SD 19) at 3 months and 83% (SD 15) at > 11 months (p < 0.0001). The speech reception threshold in noise improved from − 1.01 dB unaided to − 2.69 dB best-aided (p = 0.0018).

Conclusion

We found a clinically relevant audiological benefit with Bonebridge. To overcome anatomical challenges, we recommend preoperative 3D planning in small and hypoplastic mastoids, children, ear malformation, and simultaneous implantation of ear prosthesis anchors and after multiple ear surgery.