6Power Beneath the Skin: Active Transcutaneous Bone Conduction

FMoving the engine inside

The two earlier designs sit at opposite ends of a compromise. Percutaneous systems drive bone directly but need an open abutment; passive transcutaneous systems keep the skin closed but lose output forcing vibration through it. Active transcutaneous implants resolve the tension by implanting the vibrating transducer itself beneath the intact skin, fixed to or within the skull. The external unit becomes a microphone-and-processor that simply captures sound and sends signal and power across the skin to the buried transducer; the actual mechanical drive happens inside.

Because the transducer now contacts bone directly, there is no skin in the vibration path at all. The skin still carries the signal and power link, but that transmission is electromagnetic, not mechanical, and is far more efficient than shaking tissue. The result combines the closed-skin advantage of the passive design with output closer to that of a percutaneous device, which is why active transcutaneous systems are the fastest-growing branch of implantable bone conduction.[2015][2020]

TTwo ways to drive bone: piezo and floating mass

Cochlear’s Osia uses a Piezo Power transducer: stacked piezoelectric layers that expand and contract under the digital drive signal, producing vibration with no air gap, no suspension spring, and crucially no magnet in the vibrating element. The OSI200 implant bolts onto an osseointegrated BI300 fixture, so the piezo actuator transmits straight into integrated bone. The absence of magnetic material gives it strong high-frequency output in a thin package and excellent MRI behaviour, with the system rated to a sensorineural fitting range up to about 55 dB HL.

MED-EL’s Bonebridge takes a different route with a bone-conduction floating-mass transducer (BC-FMT) seated in a drilled bony bed and held by screws. An electromagnetic coil drives a small internal mass whose reaction force shakes the skull. The first-generation BCI601 transducer was about 8.7 mm thick and demanded deep drilling; the second-generation BCI602 halves that to roughly 4.5 mm while keeping the same output, which dramatically widens the range of skulls and anatomies that can accept it. Both Osia and Bonebridge deliver more usable output than passive transcutaneous systems precisely because their drive force never passes through skin.[2025][2023]

CCandidacy and output in practice

Active transcutaneous implants serve the familiar bone-conduction indications: conductive and mixed losses, including congenital atresia and chronically draining ears, and single-sided deafness, where the device reroutes sound across the skull to the better cochlea. Their higher output extends candidacy slightly further into mixed losses than passive systems can manage, because they are not paying the skin tax, though like all bone-conduction devices they reach but cannot greatly exceed the bone-conduction curve and so do not treat severe sensorineural loss.

Reported outcomes are strong. Series with the Bonebridge BCI602 show large functional gains, with sound-field thresholds improving on the order of 25 dB and substantial speech-in-quiet benefit, and Osia series similarly report marked threshold and speech gains with high satisfaction. Surgery is short, the skin heals closed, and the candidacy conversation centres on anatomy (enough bone for the transducer bed or fixture, now easier with the thinner BCI602), the sensorineural component of the loss, and the patient’s MRI needs.[2023][2025]

CWhy active wins on skin and MRI

The closed-skin design removes the peri-abutment soft-tissue reactions that dominate percutaneous follow-up, and because retention can use a weaker magnet (or, for Osia, a thin profile) the skin pressure problems of strong passive magnets are reduced. Wound and skin complication rates in active transcutaneous series are correspondingly low, and there is no daily abutment hygiene to maintain.

MRI is where the two active systems diverge from passive ones most clearly. The Osia piezo transducer contains no magnet in its drive element, so it tolerates MRI with far less artifact and no risk of drive-element demagnetisation, an increasingly important advantage for patients likely to need repeated scans. The Bonebridge, which uses a magnet for external retention, has stricter MRI conditions, but both still outperform a fixed-magnet passive implant in terms of safe, useful imaging. Choosing among the bone-conduction families therefore weighs output, skin burden, anatomy, cosmesis, and lifelong imaging needs together rather than any single factor.[2025][2024]