Different types of surgical implant
You may hear people refer to BCHIs as ‘bone anchored hearing aids’, ‘direct drive bone conduction devices’ or ‘skin drive bone conduction devices’.
Direct drive device – there is direct stimulation of the bone; the sound is picked up and converted into vibrations which are transmitted via an abutment to the implant in the bone.
Skin drive device – the skin remains intact and the vibrations are transmitted through the skin to the implant.
The Cochlear Baha and Oticon Ponto both require an operation to implant a titanium fixture (small screw) into the bone of the skull behind the ear. The bone naturally grows into the fixture, holding it securely in place (osseointegration). An abutment is connected to the fixture through the skin. The sound processor is attached to the abutment and is easy to take off, for example, when your child is going to bed.
BCHIs tend to be more comfortable and give a better sound quality than BCHDs on headbands. Children are generally considered for this type of BCHI when there is sufficient bone thickness to allow for the implant to be inserted. This can vary from child to child, but it is usually around four or five-years-old.
The MED-EL Bonebridge requires an operation to attach a vibratory device (known as a floating mass transducer or FMT) to part of the middle ear and an internal implant in the bone behind the ear. Sounds are picked up by the microphone of the audio processor and converted into electrical signals which are transmitted through the skin to the implant. The implant then converts the signal to vibrations which are transmitted through the bones of the skull to the cochlea of the inner ear where they are converted into sound in the usual way.
This type of device includes a Cochlear Baha Attract and the Medtronic Sophono.
The Cochlear Baha Attract requires an operation to insert a small titanium screw in to the bone behind the ear. An internal magnet is attached to the screw. The sound processor attaches to an external magnet which connects magnetically to the implant under the skin. The sound processor transmits the vibrations through the magnet to the bone where they are transferred to the inner ear.
With the Medtronic Sophono an operation is needed to insert a magnetic implant within the bone behind the ear. The implant is secured with five tiny screws to the bone and it consists of two magnets which are completely sealed in the titanium case. The external sound processor is connected to a magnetic plate (spacer) which holds it in place against the magnetic implant. The processor transmits the signal through the skin to the implant. The implant then converts the signal to vibrations which are transmitted through the bones of the skull to the cochlea of the inner ear where they are converted into sound in the usual way.