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Bone conduction

Bone conduction is the transmission of sound vibrations through the bones of the skull to the cochlea, enabling auditory perception via the sensorineural structures of the inner ear, in contrast to air conduction which relies on the outer ear canal and middle ear ossicles.^[1] This process involves mechanical vibrations that stimulate the cochlear fluids and basilar membrane, activating the auditory nerve and bypassing potential pathologies in the external or middle ear.^[1] The discovery of bone conduction dates back to the 16th century, when anatomist Giovanni Filippo Ingrassia described related auditory phenomena in 1546, followed by mathematician Geralamo Cardano's 1550 proposal that sound could travel through skull bones to the inner ear.^[2] By 1589, physician Hieronymus Capivacci demonstrated its practical use by transmitting vibrations from a zither rod held between the teeth to distinguish hearing disorders, and in 1603, the effect was posthumously named "Ingrassia's phenomenon" after Ingrassia's observations of vibrations via a table fork.^[2] In the 19th century, French otologist Jean Marie Gaspard Itard (1774–1838) developed early bone conduction devices, such as a rod held to the teeth, advancing clinical applications for the deaf.^[3] Physiologically, bone conduction arises from multiple pathways, including inertial forces on the cochlear fluids and ossicles, pressure changes in the ear canal, and, in some cases, a third cochlear window created by inner ear pathologies.^[1] These vibrations typically occur at frequencies between 250 and 8000 Hz, with optimal sensitivity around 512 Hz as tested by tuning forks.^[1] Clinically, bone conduction testing—via methods like the Weber and Rinne tuning fork tests or pure-tone audiometry—helps differentiate conductive hearing loss (affecting outer/middle ear) from sensorineural loss (inner ear or nerve), guiding diagnoses for conditions such as otosclerosis or presbycusis.^[1] Bone conduction has significant applications in hearing rehabilitation, particularly through bone-conduction devices (BCDs) for patients with conductive, mixed, or single-sided deafness where traditional aids fail.^[4] Early 20th-century BCDs used headbands or spectacles, but the 1970s breakthrough in titanium osseointegration by Per-Ingvar Brånemark enabled percutaneous implants like the Bone-Anchored Hearing Aid (BAHA), first implanted in 1977 and, as of 2014, used in over 150,000 patients worldwide.^[4] Modern advancements include transcutaneous options such as the Bonebridge (active implant) and Baha Attract (passive magnet), reducing skin penetration risks while improving sound transmission for chronic ear diseases or congenital malformations.^[4] Beyond medicine, bone conduction supports military communications, newborn hearing screenings, and consumer audio devices like headphones that vibrate the skull for immersive listening without ear canal blockage.^[5]

Principles

Mechanism of Action

Bone conduction refers to the process by which sound is transmitted as mechanical vibrations through the bones of the skull directly to the inner ear, bypassing the outer and middle ear structures.^[6] This vibration-based mechanism allows auditory perception when conventional air conduction pathways are impaired, such as in cases of conductive hearing loss.^[7] The physiological process begins when a sound source, such as a transducer applied to the skull (often at the mastoid process of the temporal bone), generates vibrations that propagate through the cranial bones. These vibrations travel via the petrous portion of the temporal bone to the otic capsule surrounding the cochlea, where they induce relative motion between the cochlear walls and the perilymphatic fluids. This fluid displacement creates a pressure differential across the basilar membrane, stimulating the hair cells in the organ of Corti within the cochlea; the activated hair cells then generate neural signals transmitted via the auditory nerve to the brain for sound perception.^[6]^[8] Two primary theories explain the inner ear stimulation in bone conduction: the inertial theory and the bone displacement (or compressional) theory, as elucidated by Georg von Békésy through cadaveric and model experiments. In the inertial theory, predominant at lower frequencies, the vibrating skull causes relative motion of the lighter ossicles and cochlear fluids due to their inertia, leading to fluid flow between the oval and round windows that drives the basilar membrane. The bone displacement theory, more relevant at higher frequencies, posits that compressive forces from skull vibrations directly deform the cochlear walls, generating pressure gradients in the cochlear fluids without significant ossicular involvement; von Békésy observed vibration paths showing the skull acting as a unified vibrator below 800 Hz but fragmenting into independent parts above this frequency, with resonances around 800–1000 Hz and 1500–1600 Hz influencing transmission efficiency.^[6]^[9] Bone conduction is most effective in the frequency range of approximately 250 Hz to 4000 Hz, where auditory thresholds are lowest due to optimal coupling of vibrations to the cochlea; above 4000 Hz, transmission attenuates because of increased skull damping and viscous losses in the bone and fluids, reducing the amplitude of vibrations reaching the inner ear.^[6] Key anatomical structures include the temporal bone, which encases the cochlea and serves as the primary conduit for vibrations from peripheral skull sites to the inner ear; the cochlea, where fluid and hair cell responses convert vibrations to neural activity; and the vestibular system, which shares perilymphatic connections with the cochlea and may interact through the saccule to perceive higher-frequency or ultrasonic vibrations (up to 40–100 kHz) not optimally processed by the cochlea alone.^[6]^[8]

Comparison to Air Conduction

In air conduction, the primary pathway for sound perception, acoustic waves travel through the external ear canal to vibrate the tympanic membrane, which transmits these vibrations via the ossicular chain (malleus, incus, and stapes) to the oval window of the cochlea, initiating fluid motion in the inner ear.^[10] This process benefits from the impedance-matching function of the outer and middle ear, which amplifies sound pressure by approximately 20-23 dB, particularly at low to mid frequencies below 1 kHz.^[11] Bone conduction differs fundamentally by bypassing the outer and middle ear, transmitting vibrations directly through the skull bones to the cochlea, resulting in higher absolute sound pressure level (SPL) thresholds of about 50-60 dB SPL compared to 0-20 dB SPL for air conduction in normal hearing.^[12] Additionally, bone conduction exhibits poorer high-frequency response due to greater attenuation by skull bone and soft tissues, limiting sensitivity above 4 kHz, whereas air conduction maintains better transmission across a broader frequency range thanks to the middle ear's amplification.^[13] Without the outer and middle ear's natural gain, bone conduction is inherently less efficient, requiring stronger stimuli to achieve equivalent cochlear activation.^[14] Clinically, these differences are quantified through audiometry, where the air-bone gap—the difference between air and bone conduction thresholds—exceeds 10 dB at any frequency to indicate conductive hearing loss involving the outer or middle ear, while bone conduction thresholds alone reflect inner ear (cochlear) function and help differentiate it from sensorineural loss.^[15] For instance, in conductive loss, air conduction thresholds are elevated relative to normal bone conduction, but bone thresholds remain unaffected, confirming the site of pathology.^[16] Bone conduction also alters sound quality, producing an occlusion effect where ear canal blockage (e.g., by plugs or devices) boosts low-frequency perception by 10-20 dB below 2 kHz due to trapped resonances in the canal, creating a hollow or boomy sensation absent in open-ear air conduction.^[17] Furthermore, it provides fewer directional cues because vibrations spread bilaterally across the skull, reducing interaural time and level differences critical for sound localization in air conduction.^[18] Despite these limitations, bone conduction offers advantages in scenarios involving ear canal obstructions, such as cerumen impaction, chronic infections, or congenital atresia, as it circumvents the external auditory pathway entirely, enabling sound transmission to the inner ear without interference.^[1]

History

Early Discoveries

The phenomenon of bone conduction, where sound vibrations are transmitted directly through the bones of the skull to the inner ear, was first systematically described in the 16th century. Observations date back to 1546 when anatomist Giovanni Filippo Ingrassia described related auditory phenomena, followed by Italian polymath Girolamo Cardano. In his 1550 work De Subtilitate, Cardano detailed experiments using a rod held between the teeth to convey vibrations from a musical instrument, enabling the perception of sound despite impaired air conduction pathways.^[19] This observation marked the initial recognition of bone conduction as a viable alternative route for auditory stimulation, predating formal scientific inquiry by centuries. By 1589, physician Hieronymus Capivacci demonstrated its practical use by transmitting vibrations from a zither rod held between the teeth to distinguish hearing disorders.^[2] In the early 19th century, scientific experimentation advanced with Ernst Chladni's studies on vibrations in solid bodies. Chladni, in works published around 1802–1809, visualized nodal patterns on vibrating rods and plates, demonstrating how longitudinal vibrations in solids like bone could propagate sound effectively, providing early empirical evidence for transmission through skeletal structures.^[20] The mid-19th century saw key breakthroughs in controlled experiments for diagnosing hearing loss; by the 1850s, physicians employed bone-vibrating instruments like tuning forks to assess auditory function. Notably, Friedrich Rinne's 1855 test compared bone conduction duration to air conduction, establishing a clinical method to identify conductive versus sensorineural impairments.^[21] Milestones in animal studies underscored bone conduction's universality. In 1812, French otologist Jean Marie Gaspard Itard conducted experiments demonstrating sound transmission via bone in human subjects, using devices to vibrate the skull and observe preserved hearing after external ear disruption. In the 1930s and 1940s, Georg von Békésy developed mechanical cochlear models to trace bone conduction pathways, confirming how skull vibrations generated fluid waves in the cochlea akin to air conduction. Békésy's seminal contributions, detailed in his 1948 publication on middle ear structure and voice perception via bone, earned him the 1961 Nobel Prize in Physiology or Medicine for elucidating inner ear stimulation mechanisms.^[22]

Technological Advancements

In the 1920s and 1930s, the development of electronic audiometers incorporated bone oscillators to enable precise bone conduction testing, building on the Rinne test's principles for differentiating conductive and sensorineural hearing loss.^[23] These devices, such as the Western Electric model 2-A introduced in 1923 and enhanced with bone conduction capabilities by 1928, allowed for standardized measurement of hearing thresholds via skull vibrations, marking a shift from tuning forks to electromechanical transducers.^[23] By the 1940s, wartime demands accelerated refinements, including portable audiometers with improved bone oscillators that facilitated clinical audiometry in military settings, enhancing diagnostic accuracy for hearing impairments.^[23] The concept of osseointegration, pioneered by Per-Ingvar Brånemark in the 1950s through his 1952 observation of titanium's direct bonding with bone during rabbit studies, laid the foundation for implantable bone conduction devices.^[24] This breakthrough enabled the first bone-anchored hearing aid prototypes in 1977, when surgeons Anders Tjellström and Brånemark implanted a titanium fixture in patient Mona Andersson at Sahlgrenska University Hospital in Gothenburg, Sweden, coupling it to an external vibrator for effective sound transmission.^[25] Commercialization followed in the 1980s and 1990s, with the Bone Anchored Hearing Aid (BAHA) system receiving FDA approval in 1996 and market release by Entific Medical Systems (later acquired by Cochlear Ltd.), which utilized percutaneous abutments for stable attachment and improved sound quality over conventional aids.^[26] From the 2000s, bone conduction technology shifted toward non-surgical options and advanced signal processing, with headband-mounted transducers like the BAHA Softband enabling temporary use in infants and those unsuitable for surgery, while digital signal processors (DSP) in devices such as the BAHA Cordelle II (2002) introduced noise reduction and programmable amplification.^[25] The 2010s saw the rise of active transcutaneous systems, avoiding skin penetration; notable examples include MED-EL's BONEBRIDGE (2012), which embeds a piezoelectric transducer under the skin for direct bone vibration, and Oticon Medical's Bone Conduction Implant (BCI, first trials 2013), both demonstrating superior output and reduced feedback compared to passive magnetic systems.^[27] By the 2020s, integrations of Bluetooth connectivity in processors like Cochlear's Baha 6 Max (2021) allowed direct streaming from smartphones and TVs, enhancing accessibility for users with single-sided deafness or conductive loss.^[25] Adaptive AI features emerged in newer models, such as real-time environmental analysis for amplification adjustments in the Osia 2 (2022), improving speech clarity in noise. Advancements in piezoelectric materials have boosted transducer efficiency in prototypes for bone-anchored designs.

Medical Applications

Hearing Aids and Implants

Bone conduction hearing aids and implants are primarily indicated for individuals with conductive hearing loss, mixed hearing loss, or single-sided deafness (SSD), where traditional air conduction devices are ineffective due to issues in the outer or middle ear, such as chronic otitis media or congenital malformations like microtia/atresia.^[28]^[29] These devices bypass the impaired pathway by transmitting sound vibrations directly through the skull to the cochlea, making them suitable for cases where air conduction thresholds show significant impairment but bone conduction remains viable.^[30] Candidacy for bone conduction systems is determined through comprehensive audiological assessments, including pure-tone audiometry to measure air-bone gaps (ABG) and bone conduction thresholds. Patients typically qualify if they exhibit a conductive or mixed hearing loss with an ABG greater than 30 dB pure-tone average (PTA) across 500, 1000, 2000, and 3000 Hz, and bone conduction thresholds of 55 dB HL or better, ensuring sufficient residual cochlear function.^[28]^[31] For SSD, candidacy includes profound sensorineural loss in one ear (bone conduction thresholds >65 dB HL) and normal hearing in the contralateral ear (air conduction PTA ≤20 dB HL). Surgical implantation is generally approved for patients aged 5 years or older, with non-surgical options available for younger children; psychological evaluations may be recommended to assess motivation and expectations, particularly for pediatric or complex cases.^[28]^[32] Bone conduction aids are categorized into conventional (non-surgical) devices, which use external headbands or softbands to position a vibrator against the skull, and implanted systems, such as bone-anchored hearing aids (BAHA) or active transcutaneous implants like the Osia or Bonebridge, which involve surgical placement of a titanium fixture or internal transducer.^[29] Implanted systems offer superior comfort and consistent transmission compared to conventional aids, particularly for long-term use. A key benefit of both types is enhanced speech discrimination in noisy environments, where users often achieve 10-20% better word recognition scores than with air conduction aids alone, due to direct bone stimulation reducing the impact of outer ear obstructions.^[33]^[34] In cases of profound hearing loss, bone conduction implants can integrate with cochlear implants to provide bilateral stimulation, especially in SSD or asymmetric hearing loss, where a bone conduction device on the poorer ear complements the cochlear implant on the other side for improved sound localization and spatial awareness.^[35] Hybrid systems preserve any residual hearing by combining bone conduction with cochlear implantation, minimizing further auditory deprivation.^[36] Clinical outcomes demonstrate high efficacy, with user satisfaction rates ranging from 70% to 90% across studies, reflecting improvements in daily communication, quality of life, and sound localization when bilateral stimulation is achieved.^[37]^[38] For instance, patients with conductive hearing loss report mean satisfaction scores of approximately 78% on standardized questionnaires like the Glasgow Hearing Aid Benefit Profile, alongside significant gains in speech reception thresholds in noise.^[37]^[39]

Surgical Techniques

Pre-operative evaluation for bone conduction implant surgery includes imaging such as computed tomography (CT) scans or magnetic resonance imaging (MRI) to assess skull bone thickness and plan implant placement, ensuring adequate cortical bone support typically at least 3-4 mm thick.^[40] Anesthesia options range from local with sedation to general anesthesia, selected based on patient age, anatomy, and surgical complexity, with general anesthesia commonly used in pediatric or extensive cases.^[40] Implantation begins with a linear or C-shaped incision behind the ear over the mastoid process, followed by subperiosteal dissection to expose the bone. A titanium fixture is then drilled and screwed into the skull to promote osseointegration, a process where the implant fuses with living bone over 3-6 months, though accelerated protocols can reduce this to 6 weeks in adults with sufficient bone quality.^[41] For percutaneous systems like bone-anchored hearing aids (BAHA), an abutment is attached to the fixture to protrude through the skin, connecting to the external processor; alternatively, transcutaneous systems employ magnetic coupling between an internal implant and external component, avoiding skin penetration.^[42] Surgical variations include one-stage procedures, where the fixture and abutment or magnet are placed simultaneously for patients with thicker bone (over 4 mm), minimizing anesthesia exposures, versus two-stage approaches that implant the fixture first, allow healing, and add the external connector later, often preferred in children or thin-boned adults to reduce failure risk.^[43] Minimally invasive techniques, such as small-incision or endoscopic approaches, are increasingly used in pediatric cases to limit tissue disruption, with surgery durations as short as 20 minutes compared to 44 minutes for traditional linear incisions.^[44] Post-operatively, the surgical site is monitored for healing, with the external sound processor activated 1-4 weeks after implantation once swelling subsides, typically around 2-4 weeks for most systems.^[42] Rehabilitation involves audiology sessions for device mapping and fitting, along with auditory training protocols to optimize sound perception and adaptation over several weeks.^[40] Complications are managed proactively, with infection rates reported at 5-10% post-surgery, often treated with antibiotics or debridement; persistent cases may require implant removal in about 1-2% of patients.^[45] Skin overgrowth or reactions around percutaneous abutments occur in up to 21% of cases and may necessitate revisions, such as soft tissue reduction or flap adjustments, to maintain device stability.^[46]

Device Technologies

Non-Surgical Devices

Non-surgical bone conduction devices are externally worn hearing aids that transmit sound vibrations through the skull to the inner ear without requiring any implantation, making them suitable for individuals with conductive hearing loss, mixed hearing loss, or single-sided deafness who prefer non-invasive options. These devices typically consist of a sound processor and a transducer that couples to the skull via mechanical pressure or adhesion, bypassing the outer and middle ear. They are particularly valuable for temporary use or as an alternative for those unsuitable for surgery.^[29] In terms of design, these devices often employ headbands, softbands, or adhesive attachments to position the transducer against the mastoid process behind the ear or the zygomatic bone in front of the ear, generating vibrations through electromechanical drivers that conduct sound directly to the cochlea. Some models integrate the transducer into eyeglass frames or rigid arches for discreet wear, such as the SoundArc system, which mounts conventional bone conduction processors on an arch resembling headphones to improve bone coupling without skin penetration. The vibration is produced by pressing the transducer firmly against the skin-covered bone, ensuring efficient sound transmission while allowing for easy removal and adjustment. A recent advancement is the Baha Soundband, introduced in 2025, offering improved comfort and connectivity for softband applications.^[29]^[47]^[48] Key technologies in these devices include piezoelectric or electromagnetic converters to generate precise vibrations from electrical signals, paired with digital signal processing (DSP) for frequency equalization, noise reduction, and amplification tailored to the user's hearing profile. For instance, processors like those in the Baha 7 series incorporate DSP to optimize sound quality across frequencies, compensating for the natural attenuation in bone conduction pathways. These components enable clear speech perception, though high-frequency response may be limited compared to air conduction.^[29] Prominent examples include the Oticon Medical Ponto system with its softband attachment, which uses electromagnetic transducers for reliable bone vibration in pediatric and trial applications; the Cochlear Baha softband devices, suitable for patients with bone conduction thresholds up to 45 dB HL, providing functional gains of approximately 40 dB; and the MED-EL ADHEAR, an adhesive-based system employing piezoelectric technology for pressure-free wear. Consumer-grade vibration-based headphones, such as Shokz (formerly AfterShokz) models, demonstrate similar transducer principles but are adapted for non-medical audio rather than clinical amplification.^[29]^[49]^[50] These devices offer significant advantages, including the absence of surgical risks, high portability for daily use, and reversibility, allowing users to trial bone conduction efficacy before considering implants. However, limitations include potential skin pressure discomfort from headband tension, especially during prolonged wear, and comparatively lower maximum output—typically up to 50 dB gain—resulting in reduced performance for severe losses or in noisy environments. Adhesive options like ADHEAR mitigate pressure issues but may cause mild skin irritation in sensitive users.^[29]^[47] Common usage scenarios encompass temporary aids for young children under five years old, whose developing skulls may not tolerate implants, or as preoperative trials to assess benefit for adults with conductive hearing impairments. They are also prescribed for patients contraindicated for surgery due to medical conditions, providing functional gains in speech understanding while supporting language development in pediatrics. Clinical studies show improved quality-of-life scores with consistent use, though long-term adherence can vary based on comfort.^[29]^[47]

Surgical Devices

Surgical bone conduction devices are implantable systems designed to transmit sound vibrations directly to the skull bone, bypassing the outer and middle ear, for patients with conductive or mixed hearing loss. These devices are categorized primarily into percutaneous and transcutaneous variants, with further distinctions between active and passive mechanisms within transcutaneous designs. Percutaneous systems involve skin-penetrating components for direct mechanical coupling, while transcutaneous systems use non-invasive magnetic or electromagnetic links across intact skin to minimize tissue trauma.^[29] Percutaneous devices feature a titanium fixture surgically implanted into the temporal bone, connected via a skin-penetrating abutment to an external audio processor that vibrates the skull directly. The Bone-Anchored Hearing Aid (BAHA), developed by Cochlear Ltd., exemplifies this approach, with the Baha Connect model utilizing an osseointegrated titanium screw for stable anchorage. This direct vibration transfer provides efficient sound conduction with minimal attenuation, offering superior thresholds compared to non-implanted options. However, the skin-penetrating abutment increases risks of soft tissue complications, including infections and adverse skin reactions; in a retrospective study of 88 patients over 4 years, 55.7% experienced at least one inflammatory or infectious episode, primarily mild and responsive to topical treatment but often recurring within the first three years.^[29]^[29]^[51] Transcutaneous devices employ magnetic coupling to transmit vibrations from an external processor to an internal implant without skin penetration, thereby reducing infection risks associated with open wounds. Examples include the Sophono Alpha 2 MPO, a passive system where the external unit magnetically drives an internal titanium implant, and the BONEBRIDGE by MED-EL, an active transcutaneous implant that embeds the transducer internally. These designs lower the incidence of skin complications compared to percutaneous systems, with studies reporting fewer adverse reactions due to the absence of abutments. Nonetheless, passive transcutaneous variants suffer from signal attenuation through soft tissue, potentially up to 20 dB, which can compromise high-frequency transmission and overall audibility.^[29]^[29]^[29]^[52] Within transcutaneous systems, active and passive subtypes differ in vibration generation. Active implants, such as the Bone Conduction Implant (BCI) by Oticon Medical and the BONEBRIDGE, house the electromagnetic transducer and processor internally, directly vibrating the bone via percutaneous or embedded fixtures after receiving wireless signals from an external unit. Passive systems, like the Baha Attract, rely on the external processor's magnet to drive the internal component through the skin, simplifying implantation but introducing variability from skin thickness and coupling strength. Active transcutaneous devices generally outperform passive ones, achieving 10-15 dB better pure-tone thresholds by eliminating skin-dampening effects and providing consistent force output. Newer models, such as the Osia 2 System by Cochlear, extend applications to pediatrics (ages 5-11), with studies as of 2025 showing significant audiological improvements and safety.^[29]^[29]^[29]^[52]^[53] Material innovations underpin the reliability of these implants, particularly titanium's capacity for osseointegration, where the metal fuses with bone to create a stable anchor without fibrous encapsulation. This principle, pioneered by Per-Ingvar Brånemark and first applied to bone conduction in 1977 by Anders Tjellström's team in Sweden for the initial BAHA prototype, enables long-term functionality and load-bearing. Post-2010 developments have focused on MRI-compatible designs to accommodate imaging needs; for instance, the BONEBRIDGE (introduced in 2012) is conditional for 1.5 Tesla scans with the processor removed, while newer models like the Osia System by Cochlear support up to 3 Tesla without surgical intervention, using non-ferromagnetic materials and optimized magnet strengths.^[29]^[29]^[54]

Broader Applications

Consumer Audio Devices

Consumer audio devices utilizing bone conduction technology primarily consist of open-ear headphones designed to transmit sound vibrations through the cheekbones, allowing users to listen to music, podcasts, and calls while maintaining awareness of ambient surroundings. These devices, such as the Shokz OpenRun introduced in 2021 by Shokz (formerly AfterShokz), which debuted their bone conduction headphones in 2011, feature lightweight frames that rest on the temporal bones near the ears, bypassing the eardrum to deliver audio directly to the inner ear. This design is particularly popular among runners and cyclists for its ability to keep ears open to environmental sounds like traffic or footsteps, enhancing safety during outdoor activities.^[55]^[56]^[57] The core technology in these consumer headphones involves miniaturized bone conduction transducers, typically weighing around 26 grams for models like the OpenRun, integrated with Bluetooth connectivity for wireless streaming. Many variants include dual noise-canceling microphones for clearer calls, though they lack active noise cancellation for music playback due to the open-ear structure. The global bone conduction headphones market, driven by demand for situational awareness in fitness and commuting, exceeded $1 billion in value by 2023 and reached approximately $1.3 billion as of 2025 (with estimates up to $1.5 billion), growing at a compound annual rate of 22%.^[58]^[59]^[60] Despite their advantages, bone conduction consumer devices face limitations including weaker bass response compared to traditional in-ear headphones, as vibrations are less effective at reproducing low frequencies, and noticeable sound leakage at higher volumes, where audio can be heard by nearby individuals. Innovations addressing these challenges include waterproof models with IP67 ratings, such as the original OpenRun, enabling use in sweat-heavy workouts or light rain without damage. Additionally, bone conduction has been integrated into augmented reality wearables, exemplified by Google Glass in 2013, which used the technology for private audio delivery through bone vibrations.^[58]^[61]^[62]^[63]

Military and Specialized Uses

Bone conduction technology has been integrated into military communication systems to enable clear voice transmission in high-noise environments, such as under gunfire or while wearing helmets, without compromising situational awareness. In the early 2000s, the U.S. Army evaluated bone conduction headsets during field exercises, including the 2007 Patriot Joint Field Training Exercise, where prototypes demonstrated effective squad coordination by allowing soldiers to hear radio communications through skull vibrations while keeping ears open to ambient sounds. These systems reduce ear fatigue by bypassing traditional ear canal insertion, which can cause discomfort during prolonged wear in tactical gear. For instance, BAE Systems developed a prototype in 2015 that leverages bone conduction to transmit audio directly to the inner ear, enhancing soldier safety and mission effectiveness in combat scenarios.^[64]^[65] In industrial settings, bone conduction headsets provide noise-canceling capabilities for workers in extreme acoustic environments, such as aviation and mining operations. Pilots benefit from bone conduction headsets that deliver cockpit communications while maintaining awareness of engine noise and alerts without over-ear coverage. Similarly, for miners exposed to continuous machinery roar, systems like the 3M Peltor ComTac series, introduced in the 2010s, incorporate bone conduction microphones and transducers to facilitate team coordination under protective helmets and in dust-filled conditions exceeding 100 dB. These applications allow users to wear double hearing protection—such as earplugs beneath the headset—while still receiving intelligible audio, minimizing the risk of noise-induced hearing loss.^[66] Beyond terrestrial uses, bone conduction extends to specialized environments like underwater and space exploration. In scuba diving, transducers integrated into masks or clipped devices enable voice communication by converting speech into vibrations that travel through the diver's facial bones, bypassing water's sound distortion; the Casio Logosease, announced in 2012, exemplifies this with ultrasonic transmission up to 15 meters and bone conduction playback for depths to 35 meters. For space applications, NASA has tested bone conduction headphones in the 2020s for the xEMU spacesuit, addressing audio challenges in zero-gravity extravehicular activities where traditional headphones fail due to helmet pressure and fluid shifts; evaluations show improved voice intelligibility during simulated lunar and microgravity EVAs.^[67]^[68] Key advantages of these military and specialized implementations include the ability to bypass ear protection for direct inner-ear delivery and secure transmission via bone-conducted microphones, which capture voice vibrations without external elements that could be detected or compromised in hostile settings. During U.S. operations in Iraq and Afghanistan from 2003 to 2021, such technologies supported squad coordination in urban combat, as evidenced by field trials that informed broader adoption for maintaining operational tempo amid explosive noise and protective gear.^[64]

Safety and Efficacy

Risks and Side Effects

Surgical risks associated with bone conduction implants, such as bone-anchored hearing aids, include postoperative infections occurring at rates of approximately 2-5% in adults, often requiring antibiotic treatment.^[69] Fixture failure, due to poor osseointegration or trauma, affects 1-3% of cases, potentially leading to implant loss and necessitating revision surgery.^[70] Skin necrosis and soft tissue complications, including overgrowth or breakdown at the implant site, can also arise, particularly in percutaneous devices where the skin penetrates the abutment. Long-term bone resorption around the fixture may contribute to instability, with reported rates of delayed implant extrusion ranging from 1-5% over several years of follow-up.^[46] Non-surgical bone conduction devices, which rely on headbands or adhesives, commonly cause skin irritation from prolonged pressure on the temporal bone or mastoid area, affecting up to 20% of users and manifesting as redness, soreness, or allergic reactions. Headaches from extended vibration exposure are another frequent complaint, resulting from the mechanical transmission of sound waves through the skull, which can induce tension or pressure-related discomfort in sensitive individuals. Auditory side effects from bone conduction devices are generally minimal but include temporary threshold shifts (TTS) following high-volume use, where hearing sensitivity recovers within hours to days after exposure ceases. Additional risks encompass balance disturbances from unintended vestibular stimulation, as bone-conducted vibrations can activate inner ear balance organs, leading to transient dizziness or vertigo in susceptible users.^[71] Electromagnetic interference poses concerns for patients with other implants, such as pacemakers or during MRI scans, where magnetic fields may cause device malfunction, heating, or dislodgement of components. Mitigation strategies for these risks include perioperative antibiotic protocols to reduce infection rates, with topical or oral administration showing efficacy in resolving over 90% of minor cases without removal. Adjustable fittings for non-surgical devices, such as customizable headbands, help minimize pressure-related irritation by allowing personalized tension control. The U.S. Food and Drug Administration (FDA) continues to monitor bone conduction devices through post-market surveillance and 510(k) clearances as of 2025, ensuring ongoing safety assessments and updates to labeling for adverse event reporting.

Clinical Outcomes and Research

Bone conduction devices have demonstrated substantial efficacy in improving speech recognition, particularly for patients with conductive, mixed, or unilateral sensorineural hearing loss. A study on unilateral deaf adults using bone-conduction devices reported speech recognition rates rising from 0% to over 80% for monosyllabic and spondee words post-implantation.^[72] Meta-analyses of active bone-conduction implants, including percutaneous and transcutaneous systems, show significant functional gain in sound field thresholds (mean difference of approximately 25-28 dB) and improved word recognition scores in quiet and noise, outperforming conventional air-conduction aids for unilateral loss by providing better sound localization and signal routing.^[73] These benefits are especially pronounced in single-sided deafness, where devices enhance contralateral routing of signals, leading to 40-55 percentage point improvements in speech reception thresholds at low sound levels.^[33] User satisfaction and quality of life metrics further support these outcomes, with studies indicating reduced tinnitus severity in approximately 25-30% of affected patients following implantation.^[74] For pediatric populations, long-term use shows no adverse impacts on skull bone growth or temporal bone integrity, allowing safe application from age 5 onward without compromising craniofacial development.^[75] Overall, bone conduction interventions yield high satisfaction rates, with meta-analyses reporting consistent gains in hearing-specific quality of life domains such as communication ease and social participation.^[76] Ongoing research in the 2020s emphasizes advancements in fully implantable active transcutaneous devices, such as the Bonebridge system, with multicenter trials demonstrating stable audiological performance and low revision rates over 2-5 years in adults and children.^[77] European studies from 2024 explore optimized fitting protocols, including automated verification tools to enhance audibility and personalization, potentially integrating computational models for better outcomes in mixed hearing loss.^[78] However, cost-effectiveness remains debated, as implants typically exceed $10,000 per procedure, limiting accessibility in developing regions where infrastructure and funding gaps exacerbate inequities in hearing care provision.^[79]^[80] Looking ahead, synergies with emerging gene therapies for congenital hearing losses could complement bone conduction by addressing underlying genetic defects, while ongoing longitudinal cohorts project sustained efficacy through 2030, with projections indicating broader adoption via refined implantation techniques and reduced costs.^[81]^[82]

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Soft tissue conduction (STC) is a recently explored mode of auditory stimulation, complementing air (AC) and bone (BC) conduction stimulation.
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Audiogram Interpretation - StatPearls - NCBI Bookshelf - NIH
An air-bone gap is noted on the audiogram, which is present when the difference between air conduction and bone conduction thresholds at a specific frequency ...
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Audiology Pure-Tone Testing: Overview, Indications, Contraindications
Sep 28, 2023 · Conductive hearing loss has normal bone-conduction thresholds, but air-conduction thresholds are poorer than normal by at least 10 dB.Overview · Types Of Hearing Loss · Technique<|separator|>
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A model of the occlusion effect with bone-conducted stimulation
Jul 7, 2009 · The occlusion effect is often defined as the perceived increase in low frequency sound subsequent to an occlusion of the ear-canal opening ...<|separator|>
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Sound Localization of Listeners With Normal Hearing, Impaired ...
Bone conduction will stimulate both cochleae near-simultaneously, causing reduced binaural cues. However, bilateral bone stimulation may improve ...
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Historical background of bone conduction hearing devices and bone ...
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Early Bone Conduction Hearing Aid Devices - JAMA Network
6. Chladni EFF: On the longitudinal vibrations of strings and rods, with observations on the conveyance of sound through solid bodies . The Philosophical ...
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Rinne Test - StatPearls - NCBI Bookshelf - NIH
The Rinne test differentiates sound transmission via air conduction from sound transmission via bone conduction. It can serve as a quick screen for conductive ...
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Georg von Békésy clarified how processes in the cochlea in the inner ear proceed, in part by studying vibrations in membranes with the help of a microscope.
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In the 1920s, Western Electric developed a commercially successful electronic audiometer ... bone-conduction testing capability by 1928. In the 1940s and ...
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Per-Ingvar Brånemark: father of osseointegration
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The Evolution of the Baha system 1977 – 2021
Apr 20, 2021 · In 1977 Mona Andersson became the world's first recipient of a bone conduction implant. Since that momentous time, over more than four ...
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In such patients the introduction of the bone-anchored hearing aid (BAHA) has proved to be an invaluable alternative rehabilitation resource. Hearing aids can ...
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The bone conduction implant: Clinical results of the first six patients
The BCI is a new direct drive active transcutaneous bone conduction device that does not need a percutaneous abutment, like the BAHA. This paper reports the ...Abbreviations · Audiometric Outcomes · Audiometric Results
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[PDF] Efficient Bone Conduction Hearing Device with a Novel ...
Nov 24, 2022 · Conclusion: We developed a novel type of bone conduction device that efficiently transmits sound to the cochlea by skipping the external ...
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Bone Conduction System Candidacy Criteria | Cochlear
Patients with an air-bone gap (ABG) of > 30 dB PTA will experience significant advantages from a bone conduction system as compared to using an air conduction ...
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May 18, 2021 · ... air conduction hearing [5]. ... (D) represents a 25 dB BC PTA, the recommended bone conduction hearing threshold for the ADHEAR processor [31].
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Bone Conduction Hearing Aids | Johns Hopkins Medicine
Bone conduction hearing aids amplify sound via bone conduction, or vibrations through the bones of the skull which directly stimulate a functioning cochlea.
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Candidacy Guide for Bone Conduction Systems
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Implantation Criteria · Patients five years or older (if younger than age 5, a soft band may be implemented in place of surgery). · Mixed or conductive hearing ...
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Effects of SoundBite Bone Conduction Hearing Aids on Speech ...
Sep 8, 2020 · SoundBite bone conduction hearing aids are a good choice for patients with SSD, as it could improve the speech recognition ability of patients ...
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Single-sided deafness: Bone conduction devices or cochlear ...
Bone conduction devices are better regarding speech discrimination in noise and background noise quality of life assessment.
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Cochlear and Bone Conduction Implants in Asymmetric Hearing ...
Apr 27, 2025 · Cochlear implants (CIs) and bone conduction implants (BCIs) are rehabilitation options used in SSD and AHL to improve auditory perception and ...
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A Novel Hybrid Solution for Hearing Impairments
Feb 8, 2025 · The Hybrid system, combining conventional air-conduction HAs with bone-conduction devices, offers promising improvements in sound quality ...
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Evaluating the effectiveness of bone conduction hearing implants in ...
Feb 23, 2023 · The postoperative assessment using GHABP showed a benefit score mean of 70.95 ± 18.79, patient satisfaction score mean of 78.15 ± 18.39. The ...
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Active Bone Conduction Implant and Adhesive Bone ... - NIH
Keywords: aural atresia, bone conduction hearing aids, conductive hearing loss ... Using the BCI, the users reported a mean satisfaction rate of 79 ± 15%, and ...
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The role of bone conduction hearing aids in congenital unilateral ...
There was a consistent gain in speech reception thresholds and speech discrimination, especially in noisy environments.<|control11|><|separator|>
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Implantation of a new active bone conduction hearing device ... - NIH
Jul 28, 2020 · Here, we describe the surgical technique for implanting a new, active, transcutaneous bone conduction hearing aid.
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Osseointegration timing for Baha system loading - PubMed
The reduction of the waiting period from 3 months to 6 weeks did not result in any failure of osseointegration of the titanium implants.
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Bonebridge Bone Conduction Implant - PMC - NIH
Bone conduction implants ... Furthermore, the authors analyze the functioning of this bone conduction implant, as well as three possible surgical techniques.
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One-stage vs. two-stage BAHA implantation in a pediatric population
Conclusions: One-stage BAHA insertion surgery in the pediatric population is a reliable, safe and efficient therapeutic option that allows a good result in a ...Missing: anchored | Show results with:anchored
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Minimally invasive surgery as a new clinical standard for bone ...
Jul 3, 2023 · The minimally invasive technique is associated with shorter surgery duration, 20 vs. 44 min as compared to a linear incision technique.
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A Systematic Review of Surgical Characteristics and Adverse Events ...
Sep 22, 2024 · Across all studies, the postoperative infection rate was 5%. About 2% of patients reported magnet retention issues. About 1.65% of cases were ...
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Long-term complications of bone-anchored hearing aids - PubMed
Results: Twenty-one per cent of patients (3.4 per cent of those observed) suffered from skin reactions; this rate did not increase over time. Seventeen per cent ...
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A Non-Surgical Wearable Option for Bone Conduction Hearing ...
Oct 11, 2024 · A non-surgical wearable option for bone conduction hearing implants: a comparative study with conventional bone conduction hearing aids mounted on eyeglasses.Missing: glasses | Show results with:glasses
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Long term cutaneous complications related to bone conduction ...
The aim of this study was to establish the frequency of cutaneous complications due to surgically implanted bone conduction hearing aids.Missing: risks | Show results with:risks
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Review of Bone Conduction Hearing Devices - MDPI
Active transcutaneous devices contain an external microphone and processor which send electronic signals to an implanted, vibrating device in direct contact ...<|control11|><|separator|>
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About Shokz
Shokz launches the flagship bone conduction headphone, OpenRun Pro 2 ... The brand, formerly known as AfterShokz, makes its debut in the headphone industry in ...
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https://www.mdpi.com/2039-4349/11/2/19
[53]
Sound Starts With Shokz
Dec 28, 2021 · Shokz introduced bone conduction technology, a new way of transmitting sound to consumers with their debut product line in 2011. For the first ...
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Shokz OpenRun review: Listen to it all - SoundGuys
Rating 7/10 · Review by Lil KatzAug 27, 2024 · The Shokz OpenRun are great pair of bone conduction headphones that work well for athletes and city dwellers alike. Are they worth a buy?
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Bone Conduction Headphones Market Size | CAGR of 22.0%
The Global Bone Conduction Headphones Market size is expected to be worth around USD 7,428.1 Million by 2033 from USD 1,016.9 Million in 2023, growing at a CAGR ...Missing: limitations | Show results with:limitations<|control11|><|separator|>
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Bone Conduction Headphones: What are the Technical Difficulties ...
Sep 19, 2024 · Common issues with bone conduction headphones include poor bass, vibrational discomfort, short battery life, and sound leakage.
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Buy Shokz OpenRun Running Headphones - Perfect for Sports ...
In stock Rating 4.5 (35,435) "...NOTE: these are not noise canceling so you can hear things around you... If you are in a loud environment, these are not the best choice, I go to my ...Missing: transducers | Show results with:transducers
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Google Glass to use bone vibration instead of traditional headphones
Feb 4, 2013 · Google Glass will make use of bone conduction to generate sound rather than relying on a traditional earphone/speaker setup.
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[PDF] User Evaluation of a Bone Conduction Communication Headset ...
An Evaluation of Selected Communications Assemblies and. Hearing Protection Systems: A field Study Conducted for the Future Force Warrior. Integrated Headgear ...
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The science of sound: BAE Systems adapts bone conduction ...
Sep 8, 2015 · The prototype system is designed to improve soldier safety and drive mission success by harnessing the body's natural ability to transmit sound through bone ...
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Pilot headset, Pilot aviation headset - Page 2 - AeroExpo
It utilizes bone conduction technology which vibrates the user's jawbone to produce internal ...
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[PDF] 3m-peltor-military-catalogue-2017.pdf
A microphone with bone conduction picks up the sound of your voice through the vibration of the bones of your face (jaw bones and cheek bones). In other words ...
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Casio device lets scuba divers converse underwater - New Atlas
Nov 13, 2012 · Casio's Logosease device allows scuba divers to talk to one another while underwater.
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Bone Conduction Headphone Research and Testing for xEMU ...
Jul 21, 2024 · The new space suit being developed for exploration EVAs on the surface of the Moon and in microgravity environments is referred to as xEMU.
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Effect analysis of unilateral deaf adults wearing bone-conduction ...
The discovery that bone-anchored hearing devices can significantly enhance hearing thresholds in patients with unilateral conductive hearing loss represents a ...
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Early Results With the New Active Bone‐Conduction Hearing ...
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Influence of Bone Conduction Hearing Device Implantation ... - MDPI
Aug 1, 2023 · Furthermore, tinnitus symptoms were improved in over a quarter of tinnitus patients 1 year post-device implantation.
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Surgical and Audiological Considerations in Pediatric Bone ...
Oct 28, 2013 · The highest fixture failure rate (40%) occurred in the group who were less than three years, followed by the group who were three to five years ...
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Association of Bone Conduction Devices for Single-Sided ...
Oct 14, 2021 · These findings suggest that adult patients who receive BCDs may experience improvements in hearing-specific QOL measures but not in generic QOL measures.
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https://karger.com/books/book/2740/chapter/15625190/Complications-of-Bone-Anchored-Hearing-Devices
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Objective verification of audibility in bone conduction devices
Apr 11, 2024 · To objectively measure audibility in patients wearing bone conduction devices (BCDs) with a new approach using a skin microphone at the patient's forehead.Missing: optimized EU
[72]
Bone-Anchored Hearing Aid (BAHA) Cost and Procedure Guide
Jul 25, 2025 · The average cost* for a transcutaneous BAHA implant (completely under the skin) is $13,854, but it can range from $10,670 to $24,674. In ...
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Advancing Equitable Hearing Care: Innovations in Technology and ...
Apr 14, 2023 · Global access to hearing care is severely limited with management options, like hearing aids, inaccessible to most. The cost and centralised ...
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Nanotechnology-enhanced gene therapy for hearing loss
Aug 11, 2025 · In cases where medical intervention is insufficient, hearing aids or bone-conduction implants can help improve sound transmission. While CHL ...
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Equity Concerns and Trade Offs for Bone Conduction Implants
This study will present on two main objectives: first, a systematic review aimed to identify barriers and social determinants contributing to any ...Missing: aids | Show results with:aids