Bone-Anchored Hearing Devices

Radiation, severe osteoporosis, and Paget disease can affect the quality of the bone.

• Torque applied when the fixture is tightened may have to be adjusted accordingly

Previous surgical history (mastoidectomy, craniotomy), presence of a ventriculoperitoneal (VP) shunt, or history of a temporal bone fracture will influence device type/location/incision.

If the patient has ipsilateral intracranial/extracranial pathology that will require magnetic resonance imaging (MRI) for surveillance, the patient and corresponding treatment team should be adequately informed before implantation.

• MRI performed with an implant magnet in place results in significant artifact that can adversely affect visualization of nearby pathology.

  • Artifact may extend over 11 cm.

• Baha Attract—internal magnet approved for 1.5 Tesla

• Alpha 2 (Sophono)—internal magnet approved for 3 Tesla

Patients who form keloids are particularly prone to develop adverse soft tissue reactions.

Check for the presence of scars and/or VP shunt tubing that may impact the placement of the incision or the device.

In patients with microtia/atresia, if auricular reconstruction is planned, a decision regarding the placement of the device should be made with the planned reconstruction flaps in mind.

• The device may have to be placed more posteriorly to avoid contacting the anticipated rim of the reconstructed auricle.

  • This prevents disruption of the vascular supply to the temporoparietal skin flap used for its coverage.

Generally not indicated for preoperative planning

• It should be confirmed that patients undergoing a procedure for the indication of single-sided deafness have been appropriately evaluated for internal auditory canal (IAC)/cerebellar pontine angle (CPA) pathology prior to surgery

In certain patients where there is concern about the thickness of the bone, CT can be useful.

• Children with craniofacial anomalies, such as Treacher Collins syndrome or microcephaly, are more likely to have thin cortical bone or a low-hanging middle fossa tegmen.

There are two indications for bone-anchored devices:

• Unilateral profound hearing loss

  • Patient must have excellent hearing in the contralateral ear (air conduction pure tone average [PTA]) ≤ 20 dB).

• Mixed or conductive hearing loss and patients who are not candidates for conventional amplification/ossiculoplasty (i.e., because of atresia with unfavorable middle ear anatomy, chronic otorrhea after a canal wall down mastoidectomy, history of canal closure as part of lateral temporal bone resection, and/or allergy to ear mold material)

  • Patients with a mixed loss must have a bone line PTA equal to or less than 45 dB to be fitted with the Baha 5 processor, equal to or less than 55 dB for the larger Baha 5 Power processor, and equal to or less than 65 dB sensorineural hearing loss (SNHL) with the SuperPower, which has a behind the ear (BTE) component.

  • Patients with a mixed loss must have a bone line PTA equal to or less than 45 dB to be fitted with the Ponto, Ponto Plus, or Ponto Pro processors and equal to or less than 55 dB for the Ponto Power Plus and Ponto Pro Power processors.

Patients should experience a benefit with the demonstration device in the office.

• If the patient is a candidate for a transcutaneous (magnet-based) coupling, the demonstration device should be attached to a soft band during the trial.

  • A soft band more closely approximates the benefit of a transcutaneous device.

• If the patient is a candidate for a percutaneous (direct-coupling) device, the demonstration device should be attached to a more rigid over-the-head metallic tension band.

  • A tighter metallic headband more closely approximates the benefit of a percutaneous device.

  • Advantages of the percutaneous devices include

    • No dampening of signal at the skin

      • Better sound transmission

    • Less artifact on MRI

      • The large magnets of the transcutaneous devices cause significant scatter and are not well suited for patients who need serial imaging for pathology located near the device.

    • Better retention of the processor

    • Preferable in patients with very thin/frail skin

      • A transcutaneous device may risk skin dehiscence and/or erosion.

  • Advantages of the transcutaneous devices include

    • Good cosmesis

    • No requirements for abutment care

    • Significantly lower rates of skin complications compared with the percutaneous device (infections, skin overgrowth)

    • Easier handling for patients with manual dexterity issues

    • Ability to be converted to a percutaneous device if hearing deteriorates

      • If implantation is started with the a percutaneous device, the skin overlying the device would be compromised and it would be difficult to convert to a transcutaneous system.

Patients who have lived with unilateral profound SNHL may not report much of a benefit compared with those who have recently become deafened.

Bone-anchored hearing devices are US Food and Drug Administration (FDA)–approved for children 5 years of age or older.

• Children less than 5 years of age can be fitted with a processor attached to a soft band.

Caution is advised in patients with reduced hearing and a bone line greater than 55 dB in considering a bone-anchored hearing device.

• Although the higher-power devices can allow patients with bone lines up to 55 to 65 dB to get benefit, it is helpful to get a sense of the rate of deterioration in hearing.

• If the hearing is deteriorating rapidly, the patient may quickly lose benefit from the bone-anchored hearing device and a cochlear implant may be more advisable.

Relative contraindications

• Radiation, severe osteoporosis, Paget disease, presence of a VP shunt, and patients prone to keloid formation.

• If the patient has pathology close to the ear that requires monitoring with MRI, a percutaneous device is preferable to a transcutaneous device.

• Some patients with developmental delay, psychiatric issues, and/or autism spectrum disorders may not be able to perform the hygiene necessary to keep an abutment site healthy.

  • If possible, consider a transcutaneous device.

Until approximately age 9, it is recommended that a two-stage approach be used.

• At the first stage, the implant (fixture) is placed but the abutment or magnet is not attached. Instead, a cover screw is used to maintain patency of the inner threads of the implant.

  • In children, consideration should also be given to insertion of a “sleeper” implant.

    • This is maintained under the skin with a cover screw and serves as a backup in case of failure of osseointegration or secondary trauma with loss of the initial fixture.

• After allowing for a 3- to 6-month time period for osseointegration, at the second stage the cover screw is removed and the abutment and/or magnet is attached.

Two-stage surgery should also be considered for adults in the setting of abnormal (irradiated) bone or when insertion of a bone-anchored hearing device is being performed in conjunction with another surgery such as excision of an acoustic neuroma.

Although in most adults the skull is thick enough to accommodate a 4-mm implant, it is good practice to have a 3-mm countersink and a 3-mm implant available for every case.

An appointment with an audiologist is typically scheduled prior to surgery so that information regarding the use of the processor and warrantees can be reviewed.

• The color of the sound processor should also be selected ahead of surgery, since the internal and external components are typically ordered simultaneously