The Mechanical Impedance of the Human Skull via Direct Bone Conduction Implants

Purpose: The mechanical skull impedance is used in the design of direct bone drive hearing systems. This impedance is also important for the design of skull simulators used in manufacturing, service, and fitting procedures of such devices. Patients and Methods: The skull impedance was measured in 45 patients (25 female and 20 male) who were using percutaneous bone conduction implants (Ponto system or Baha system). Patients were recruited as a consecutive prospective case series and having an average age of 55.4 years (range 18-80 years). Seven patients were treated in Gothenburg, Sweden, and 38 patients in Edmonton, Canada. An impedance head (B&K 8001), driven by an excitation transducer with emphasized low-frequency response, was used to measure the mechanical point impedance with a swept sine from 100 to 10k Hz. Results and Discussion: The skull impedance was found to have an anti-resonance of approximately 150 Hz, with a median maximum magnitude of 4500 mechanical ohms. Below this anti-resonance, the mechanical impedance was mainly mass-controlled corresponding to an effective skull mass of 2.5 kg at 100 Hz with substantial damping from neck and shoulder. Above the anti-resonance and up to 4 kHz, the impedance was stiffness-controlled, with a total compliance of approximately 450n m/N with a small amount of damping. At frequencies above 4 kHz, the skull impedance becomes gradually mass-controlled originating from the mass of the osseointegrated implant and adjacent bone. No significant differences related to gender or skull abnormalities were seen, just a slight dependence on age and major ear surgeries. The variability of the mechanical impedance among patients was not found to have any clinical importance. Conclusion: The mechanical skull impedance of percutaneous implants was found to confirm previous studies and can be used for optimizing the design and test procedures of direct bone drive hearing implants

Ankle Audiometry: A Clinical Test for the Enhanced Hearing Sensitivity for Body Sounds in Superior Canal Dehiscence Syndrome

Introduction: The aim of this study was to develop a clinical test for body sounds\u27 hypersensitivity in superior canal dehiscence syndrome (SCDS). Method: Case-control study, 20 patients affected by SCDS and body sounds\u27 hypersensitivity and 20 control matched subjects tested with a new test called ankle audiometry (AA). The AA consisted of a psychoacoustic hearing test in which the stimulus was substituted by a controlled bone vibration at 125, 250, 500, and 750 Hz, delivered at the medial malleolus by a steel spring-attached bone transducer prototype B250. For each subject, it was defined an index side (the other being non-index), the one with major symptoms in cases or best threshold for each tested frequency in controls. In 3 patients, the AA was measured before and after SCDS surgery. Results: The AA thresholds for index side were significantly lower in SCDS patients (115.6 \ub1 10.5 dB force level [FL]) than in control subjects (126.4 \ub1 8.56 dB FL). In particular, the largest difference was observed at 250 Hz (-16.5 dB). AA thresholds in patients were significantly lower at index side in comparison with non-index side (124.2 \ub1 11.4 dB FL). The response obtained with 250 Hz stimuli outperformed the other frequencies, in terms of diagnostic accuracy for SCDS. At specific thresholds\u27 levels (120 dB FL), AA showed relevant sensitivity (90%) and specificity (80%) for SCDS. AA did not significantly correlate to other clinical markers of SCDS such as the bone and air conducted hearing thresholds and the vestibular evoked myogenic potentials. The AA thresholds were significantly modified by surgical intervention, passing from 119.2 \ub1 9.7 to 130.4 \ub1 9.4 dB FL in 3 patients, following their relief in body sounds\u27 hypersensitivity. Conclusion: AA showed interesting diagnostic features in SCDS with significantly lower hearing thresholds in SCDS patients when compared to healthy matched subjects. Moreover, AA could identify the affected or more affected side in SCDS patients, with a significant threshold elevation after SCDS surgery, corresponding in body sounds\u27 hypersensitivity relief. Clinically, AA may represent a first objective measure of body sounds\u27 hypersensitivity in SCDS and, accordingly, be an accessible screening test for SCDS in not tertiary audiological centers

Bone Conduction Stimulated VEMP Using the B250 Transducer

Objective: Bone conduction (BC) stimulation is rarely used for clinical testing of vestibular evoked myogenic potentials (VEMPs) due to the limitations of conventional stimulation alternatives. The aim of this study is to compare VEMP using the new B250 transducer with the Minishaker and air conduction (AC) stimulation.Methods: Thirty normal subjects between 20 and 37 years old and equal gender distribution were recruited, 15 for ocular VEMP and 15 for cervical VEMP. Four stimulation conditions were compared: B250 on the mastoid (FM); Minishaker and B250 on the forehead (FZ); and AC stimulation using an insert earphone.Results: It was found that B250 at FM required a statistically significant lower hearing level than with AC stimulation, in average 41 dB and 35 dB lower for ocular VEMP and cervical VEMP, respectively, but gave longer n10 (1.1 ms) and n23 (1.6 ms). No statistical difference was found between B250 at FM and Minishaker at FZ.Conclusion: VEMP stimulated with B250 at FM gave similar response as the Minishaker at FZ and for a much lower hearing level than AC stimulation using insert earphones

Long-term follow-up and review of the Bone Conduction Implant

Active transcutaneous bone conduction devices are a type of bone conduction device developed to keep the skin intact and provide direct bone conduction stimulation. The Bone Conduction Implant (BCI) is such a device and has been implanted in 16 patients. The objective of this paper is to give a broad overview of the BCI development to the final results of 13 patients at 5-year follow-up. Follow-up of these patients included audiological performance investigations, questionnaires, as well as safety evaluation and objective functionality testing of the device. Among those audiological measure-ments were sound field warble tone thresholds, speech recognition threshold (SRT), speech recognition score (SRS) and signal to noise ratio threshold (SNR-threshold).The accumulated implant time for all 16 patients was 113 years in February 2022. During this time, no serious adverse events have occurred. The functional improvement for the 13 patients reported in this paper was on average 29.5 dB (average over 0.5, 1, 2 and 4 kHz), while the corresponding effective gain was-12.4 dB. The SRT improvement was 24.5 dB and the SRS improvement was 38.1%, while the aided SNR-threshold was on average -6.4 dB.It was found that the BCI can give effective and safe hearing rehabilitation for patients with conduc-tive and mild-to-moderate mixed hearing loss

Effect of transducer attachment on vibration transmission and transcranial attenuation for direct drive bone conduction stimulation

Direct drive bone conduction devices (BCDs) are used to rehabilitate patients with conductive or mixed hearing loss by stimulating the skull bone directly, either with an implanted transducer (active transcutaneous BCDs), or through a skin penetrating abutment rigidly coupled to an external vibrating transducer (percutaneous BCDs). Active transcutaneous BCDs have been under development to overcome limitations of the percutaneous bone anchored hearing aid (BAHA), mainly related to the skin penetration. The attachment of a direct drive BCD to the skull bone can differ significantly between devices, and possibly influence the vibrations\u27 transmission to the cochleae. In this study, four different attachments are considered: (A) small-sized flat surface, (B) extended flat surface, (C) bar with a screw at both ends, and (D) standard bone anchored hearing aid screw. A, B, and C represent three active transcutaneous options, while D is for percutaneous applications. The primary aim of this study was to investigate how the different transcutaneous attachments (A, B, and C) affect the transmission of vibrations to the cochleae to the ipsilateral and the contralateral side. A secondary aim was to evaluate and compare transcranial attenuation (TA, ipsilateral minus contralateral signal level) between transcutaneous (A, B, and C) and percutaneous attachments (D). Measurements were performed on four human heads, measuring cochlear promontory velocity with a LDV (laser Doppler vibrometer) and sound pressure in the ear canal (ECSP) with an inserted microphone. The stimulation signal was a swept sine between 0.1 and 10 kHz. The comparison of ipsilateral transmission between transcutaneous adaptors A, B, and C was in agreement with previous findings, confirming that: (1) Adaptor C seems to give the most effective transmission for frequencies around 6 kHz but somewhat lower in the mid frequency range, and (2) keeping a smaller contact area seems to provide advantages compared to a more extended one. The same trends were seen ipsilaterally and contralaterally. The observed TA was similar for adaptors A, B, and C at the mastoid position, ranging -10-0 dB below 500 Hz, and 10-20 dB above. A lower TA was seen above 500 Hz when using adaptor D at the parietal position

Biomechanical Characterisation of Bone-anchored Implant Systems for Amputation Limb Prostheses: A Systematic Review

Bone-anchored limb prostheses allow for the direct transfer of external loads from the prosthesis to the skeleton, eliminating the need for a socket and the associated problems of poor fit, discomfort, and limited range of movement. A percutaneous implant system for direct skeletal attachment of an external limb must provide a long-term, mechanically stable interface to the bone, along with an infection barrier to the external environment. In addition, the mechanical integrity of the implant system and bone must be preserved despite constant stresses induced by the limb prosthesis. Three different percutaneous implant systems for direct skeletal attachment of external limb prostheses are currently clinically available and a few others are under investigation in human subjects. These systems employ different strategies and have undergone design changes with a view to fulfilling the aforementioned requirements. This review summarises such strategies and design changes, providing an overview of the biomechanical characteristics of current percutaneous implant systems for direct skeletal attachment of amputation limb prostheses

The bone conduction implant - a review and 1-year follow-up

Objective: The objective of this study is to evaluate its safety and effectiveness of the bone conduction implant (BCI) having an implanted transducer and to review similar bone conduction devices. Design: This is a consecutive prospective case series study where the patients were evaluated after 1, 3, 6 and 12 months. Outcome measures were focussed on intraoperative and postoperative safety, the effectiveness of the device in terms of audiological performance and patient\u27s experience. Study sample: Sixteen patients with average age of 40.2 (range 18-74) years have been included. Thirteen patients were operated in Gothenburg and three in Stockholm. Results: It was found that the procedure for installing the BCI is safe and the transmission condition was stable over the follow-up time. No serious adverse events or severe adverse device effects occurred. The hearing sensitivity, speech in noise and the self-assessment as compared with the unaided condition improved significantly with the BCI. These patients also performed similar or better than with a conventional bone conduction reference device on a softband. Conclusions: In summary, it was found that the BCI can provide a safe and effective hearing rehabilitation alternative for patients with mild-to-moderate conductive or mixed hearing impairments

Three-Year Follow-Up with the Bone Conduction Implant

Background: The bone conduction implant (BCI) is an active transcutaneous bone conduction device where the transducer has direct contact to the bone, and the skin is intact. Sixteen patients have been implanted with the BCI with a planned follow-up of 5 years. This study reports on hearing, quality of life, and objective measures up to 36 months of follow-up in 10 patients. Method: Repeated measures were performed at fitting and after 1, 3, 6, 12, and 36 months including sound field warble tone thresholds, speech recognition thresholds in quiet, speech recognition score in noise, and speech-to-noise thresholds for 50% correct words with adaptive noise. Three quality of life questionnaires were used to capture the benefit from the intervention, appreciation from different listening situations, and the ability to interact with other people when using the BCI. The results were compared to the unaided situation and a Ponto Pro Power on a soft band. The implant functionality was measured by nasal sound pressure, and the retention force from the audio processor against the skin was measured using a specially designed audio processor and a force gauge. Results: Audiometry and quality of life questionnaires using the BCI or the Ponto Pro Power on a soft band were significantly improved compared to the unaided situation and the results were statistically supported. There was generally no significant difference between the two devices. The nasal sound pressure remained stable over the study period and the force on the skin from the audio processor was 0.71 \ub1 0.22 N (mean \ub1 1 SD). Conclusion: The BCI improves the hearing ability for tones and speech perception in quiet and in noise for the indicated patients. The results are stable over a 3-year period, and the patients subjectively report a beneficial experience from using the BCI. The transducer performance and contact to the bone is unchanged over time, and the skin area under the audio processor remains without complications during the 3-year follow-up

Analysis of the mechanical impedance of bone-anchored hearing aids

Some patients who need hearing aids are unable to use an apparatus which transmits the sound via the external ear canal and have to use a bone conduction hearing aid. The bone vibration transducer of this aid is applied to the skin over the mastoid process and the sound is transmitted via the soft tissue and bone to the cochlea. The pressure needed to apply the transducer often gives the patient discomfort and the damping effect of the soft tissue gives poor quality of the sound transmitted. Advances in the ability to permanently implant foreign material in the body and perform permanent skin penetration has made it possible to develop a bone-anchored hearing aid. Fourteen patients have been equipped with such hearing aids. To be able to give these patients the best hearing aid, a new transducer has to be constructed to match the new situation. The impedance of the bone-anchored titaniumscrew/skull has been studied and the resistance and reactance of the mechanical impedance have been measured. The influence of a damping soft tissue layer over the bone has been analyzed. The difference between the impedance of the skull and the impedance of the soft tissue + skull was in the order of 10 to 25 dB depending on the frequency