Baha® System (Bone-Anchored Hearing Aid) (Osseointegrated Implant) - Modified Operative Note

last modified on: Mon, 09/11/2023 - 09:48

Modified Operative Note 9-11-2023

Prep and drape the patient in sterile fashion.
Mark postauricular skin incision site 50-60 mm posterior superior to the external auditory canal along the along the temporal line.
Utilize a sterile needle to determine scalp thickness. Appropriate abutment length is 2-3 mm longer than the measured thickness.
Inject site with 1% lidocaine with 1:100,000 epinephrine, then use 4 mm punch to remove skin.
Incise through the skin and dermis to the periosteum, maintaining hemostasis as needed with bipolar cautery.
Expose the bone with a periosteum elevator.
Drill at 2000 rpm into the skull perpendicularly using the drill guide bit to form a 4mm hole. Ensure that dura is not exposed before removing spacer.
Place 4 mm implant attached to the abutment using drill set to 32 Newtons. Do not allow the titanium to touch anything but the hole.
Close skin with 3-0 nylon. Place healing cap with Allevyn gauze and bacitracin.

Note (August 2023): Below offers perspective of historical interest with upgraded revision above.

GENERAL CONSIDERATIONS

Patient Selection
1. Conductive Hearing Loss
  1. The Baha System is available for patients who have a conductive or mixed hearing loss and can still benefit from amplification.
  2. Patients who wear a conventional BC hearing aid have been generally most suitable for this procedure.
2. Single Sided Deafness (SSD)
  1. The Baha System has been supported for patients with a unilateral sensorineural deafness or SSD.
  2. The Baha device picks up sound on the deaf side and the sound is transmitted via bone conduction to the contralateral ear/cochlea.
  3. This offers reduction of the head shadow effect and improved speech intelligibility.
Reported indications
1. Patients with chronically draining ears, where use of a conventional hearing aid aggravates the infection, causes feedback problems, poor wearing comfort or poor sound quality
2. Patients presenting with congenital malformations
3. Patients with a conductive hearing loss due to ossicular disease who are not appropriate for surgical correction and are unable to be aided by conventional hearing aids.
4. Patients with cochlear insufficiency in one ear, and a conductive hearing loss in the other ear where there is a potential risk of making the only functioning cochlea unusable by ear surgery.
5. Patients with SSD due to acoustic neuroma surgery, sudden deafness, etc., who for some reason cannot or do not want to use a CROS hearing aid.
Audiological indications
1. For Baha Divino and Baha Compact
  1. PTA BC thresholds of the indicated ear should be better than or equal to 45dB HL (@500, 1000, 2000, &3000Hz).
  2. A maximum speech intelligibility score better than 60% when using a phonetic balanced (PB) word list is recommended.
  3. The audiologist may determine whether the candidate has sufficiently good speech intelligibility based on that particular patient’s need.
  4. For severe mixed hearing losses, the Baha Cordelle II or Intenso is an alternative.
2. For SSD, the Baha System may be considered when the PTA AC threshold of the normal ear is better then or equal to 20dB HL.
3. For bilateral fitting, the recommendation is that BC thresholds should be symmetric, where the definition of symmetric is less than a 10dB difference, on average (500, 1000, 2000, 3000Hz) or less than 15dB at individual frequencies.
Additional indications
1. Sufficient bone volume and bone quality must be present for successful implant placement.
2. Capacity for patients to maintain and clean the skin around the abutment. Consideration to the patient’s psychological, physical, emotional and developmental capabilities to maintain hygiene.
3. Age 5 years or older.
Contraindications
1. General medical condition of the patient
  1. Inability to tolerate the procedure
2. Relative reported contraindications
  1. Prior radiation
  2. Inability to follow up
  3. Inability to clean the device

PREOPERATIVE PREPARATION

Evaluation
1. History to include:
  1. General suggestions have included that patients present with de-novo hearing loss, established hearing loss and don’t like their hearing aids, or iatrogenic loss after surgical treatment.
    1. Unilateral or Bilateral CHL or mixed hearing loss
    2. Unilateral sensorineural hearing loss with good bone curve in the opposite ear
  2. PMHx regarding prior skin conditions, soft tissue and bone diseases, and prior radiation to the proposed implant site is important to note.
  3. Pediatric patients and those with syndromes and/or developmental issues can be implanted, but there social networks as far as follow-up and care of the device need to be explored preoperatively.
2. Physical Exam
  1. General Skin and soft tissue exam of the ear to be implanted
  2. Otomicroscopy- other causes of possible conductive loss should be evaluated
  3. Tuning forks
    1. Weber and Rinne exams tested bilaterally with 256, 512 and 1024 Hz tuning forks. (supplemented with audiogram)
3. Audiology
  1. Complete audiometric testing
    1. Pure tone averages are measured to determine air conduction, bone conduction.
    2. Speech thresholds and discrimination.
  2. Acoustic Reflex:
    1. The acoustic reflex may be absent.
4. Temporal Bone CT Scan
5. MRI if considering for SSD and concerned about retrocochlear pathology
Consent
1. Purpose of procedure
  1. Improve hearing
2. Alternatives
  1. Amplify hearing with a hearing aid for CHL
  2. Observation
  3. Surgical correction of conductive HL, if possible.
  4. CROS or BiCROS for SSD
3. Expected outcomes
  1. Improved hearing, especially directional and with background noise
  2. Better sound localization for mixed or CHL ONLY
  3. Reduced external otitis from hearing aid use
4. Possible Risks:
  1. Failure of implant to osseointegrate
  2. Skin overgrowth of the implant and need for revision surgery
  3. CSF leak if bone is too thin (very rare as the placement of the fixture would usually seal any leak)
  4. Subdural hematoma
  5. Local wound issues: minimal permanent hair loss, may rub on hats or other headwear, hematoma

NURSING CONSIDERATIONS (see equipment and instrument list)

ANESTHETIC CONSIDERATIONS

Our preferred approach is MAC anesthesia or local anesthesia without sedation
1. Goal: No pain, low blood pressure, but the patient alert enough to follow instructions, answer questions
2. Consider general:
  1. Claustrophobic
  2. Previous bad/paroxysmal reactions to MAC
  3. Pediatric
  4. Consider in patient in non-English speaking patients (difficulty communicating during surgery)
3. May do under local anesthesia to titrate Versed/Demerol/Phenergan/other
Preoperative Systemic Medications:
1. see [otology antibiotic administration protocol]
Positioning: see [general considerations for otologic surgery]

OPERATIVE PROCEDURE

There are several different ways to perform BAHA surgery. These differ by the degree of soft tissue removal and include
1. Dermatome
  1. allows for maximal exposure and tissue removal
  2. may be necessary for morbidly obese
  3. slower healing
  4. greatest area of hair loss
2. Linear incision
  1. Hair loss limited to area 1 cm around abutment
  2. faster healing and fewer complications in literature
  3. More operator-dependent to avoid skin overgrowth
3. Minimal invasive
  1. good for thin scalps, not as good for obese patients
  2. no hair shaving
  3. minimal hair loss---may be good for patients with thinning hair
  4. fairly new technique; literature still pending on outcomes
Mark the skin site: generally 50-60 mm from the EAC posterior to the ear on a line adjacent to the top of the helix (in the temporal line where bone is thick)
1. Approximately 45 degrees from EAC
Use the template for the BAHA to trace out the dimensions of the external processor. You must remove soft tissue in at least this area in order to eliminate feedback by the processor touching the scalp.
Shave hair in area around incision
1. Alternately, prep in hair, and then slick back from incision line with copious bacitracin ointment
Soft tissue technique
1. Linear incision
  1. Mark a vertical line approx 4-5 cm incision with the proposed implant site at its mid point
  2. inject local (may be the only time you need anesthesia to give any extra sedation)
  3. Use a 4 mm punch at the implant site to remove skin and subcutaneous tissue
  4. Incise the line down to subcutaneous tissue. Leave periosteum intact
  5. Using pickups and a 10 blade, create very thin skin flaps anterior and posterior to the implant.
    1. Make sure to remove hair follicles. May fine-tune with sharp scissors
    2. Undermine in 2-3 cm in all directions removing soft tissue down to periosteum
2. Dermatome
  1. Mark your implant site as above
  2. You will be using a dermatome to create an inferiorly pedicled split-thickness skin graft
  3. Inject an area approx 3x5 cm around your implant site
  4. Use the dermatome at 2000 rpm on BAHA drill setup
  5. Cut all soft tissue out down to periosteum out within the confines of the skin graft site.
  6. Bevel the soft tissue at the skin edges so that the skin graft gently slopes from periosteum up to the surrounding skin when replaced
3. Minimally-invasive
  1. First use 18 gauge needle and hemostat to probe to the periosteum in order to determine scalp thickness: for odd number add 3 mm to determine length of abutment and for even number add 2 mm (ie. place needle and clamp with hemostat flush with scalp, withdraw and measure - for 6 mm scalp thickness, use 8 mm abutment)
  2. Use the 4 mm skin punch at the designated BAHA site
  3. Extend the incision approx 1 cm in either direction from the skin punch
  4. Elevate planes down to periosteum
Drilling fixture guide hole
1. Make a cruciate incision in periosteum at site of incision and elevate periosteum off bone only in area to be drilled
2. Attach the 4 mm drill guide bit to the drill with the 3mm spacer attached
3. Drill fixture hole to 3mm depth at 2000 rpm, irrigate simultaneously
4. To assure drilling perpendicular to the bone, attach drill guide to back side of drill and make sure this is perpendicular to the bone surface at all times during drilling
5. Use lacrimal probe to ensure to dura is exposed
6. If no dura exposed, take spacer off and drill depth to 4mm at same rpm
Countersink
1. Attach appropriate depth (4 mm or 3 mm) countersink attachment to drill.
2. At 2000 rpm drill countersink to depth of 0.5mm- Important not to rock but to apply firm steady perpendicular pressure so that countersink is uniform in depth circumferentially
3. Irrigate area during and after drilling to clear of bone chips.
Fixture/abutment placement
1. One stage system: the fixture and abutment come as one piece
  1. Double check the abutment for length (5.5 mm or 8.5 mm) and fixture length (3mm or 4mm)
    1. Chose the 8.5 mm abutment for the minimally invasive technique or whenever scalp thickness presents a problem
  2. Do not allow the TITANIUM fixture to touch anything but the clean drill hole on the skull !!
  3. Place fixture on drill with special attachment.
  4. Change drill to 20-40 NCm torque
  5. Do not irrigate while placing fixture until after the first thread has caught the bone
  6. Allow drill to torque out, turn off drill and lift off gently, do not rock the fixture
2. Two-stage system: The fixture is placed in the skull alone, and then the abutment is screwed onto the fixture separately.
  1. May occur at the time of surgery, or may occur as a secondary surgery after osseointegration
  2. Consider in young children or osteopenic patients
Wound closure
1. Linear incision and minimally invasive technique
  1. Consider tacking thinned skin to periosteum
  2. Close incision with 5-0 nylon
2. Dermatome technique
  1.Replace skin graft over wound and mark on graft site of implant
  2. Use 4mm punch biopsy on a tongue blade to make hole at implant site in the skin graft. May be widened with a 15 blade as necessary
  3. Replace skin graft over area and put implant through hole in graft
  4. tack graft to periosteum and close skin edges with fast gut suture
Healing Cap
1. Fashion thin layer of Xeroform gauze around implant
2. Snap healing cap onto abutment
Mastoid dressing
More info on the two stage system
1. Done the same way as above except only the fixture is placed at the first visit
2. Fixture placement
  1. Only difference is that the fixture is place only with a square screw cap instead of the abutment
  2. Healing cap placed and removed after one week
3. Abutment placement
4. The abutment is placed after 6 months of osseointegration
  1. This must be done in the OR
  2. Remove screw cap with square screwdriver
  3. Place abutment and secure to fixture with screwdriver
Intraoperative Complications/Issues
1. CSF leak
  1. As long as sterility as been maintained, place the fixture and the CSF leak should be sealed
2. Thin Bone
  1. Drill 3mm guide hole only
  2. Convert to two stage system
3. Implant not well-seated in skull
  1. Carefully back out fixture by reversing drill
  2. Evaluate hole, try to identify issue
  3. If cannot find issue, fill with bone wax and drill new implant site

POST-OPERATIVE CARE

Disposition
1. Discharge home
Wound care
1. Mastoid dressing off on POD 1
2. Keep healing cap on
3. Keep incision line clean, if visible around Xeroform gauze, otherwise no special care needed until cap comes off
Activity restrictions
1. None
Follow-up
1. 1 week to remove cap.
  1. leave cap on one more week if not healed well
  2. Otherwise, remove cap and Xeroform
  3. remove sutures as necessary
2. Wound care
  1. Clean site daily with q-tip to remove debris
  2. Copious use of ointment
3. Hook-up
  1. One stage system: 3-4 months
  2. SIX MONTHS MINIMAL FOR CHILDREN
  3. Two-stage system: six months

References

Bosman AJ. Snik AF. Van der Pouw CT. Mylanus EA. Cremers CW. Audiometric evaluation of bilaterally fitted bone-anchored hearing aids. Audiology. 40(3):158-67, 2001

Abramson M. Fay TH. Kelly JP. Wazen JJ. Liden G. Tjellstrom A. Clinical results with a percutaneous bone-anchored hearing aid. Laryngoscope. 99(7 Pt 1):707-10.

Spitzer JB. Ghossaini SN. Wazen JJ. Evolving applications in the use of bone-anchored hearing aids. American Journal of Audiology. 11(2):96-103, 2002

Wazen JJ. Caruso M. Tjellstrom A. Long-term results with the titanium bone-anchored hearing aid: the U.S. experience. American Journal of Otology. 19(6):737-41, 1998.

Wazen JJ. Spitzer J. Ghossaini SN. Kacker A. Zschommler A. Results of the bone-anchored hearing aid in unilateral hearing loss. Laryngoscope. 111(6):955-8, 2001.

Wazen JJ. Spitzer JB. Ghossaini SN. Fayad JN. Niparko JK. Cox K. Brackmann DE. Soli SD. Transcranial contralateral cochlear stimulation in unilateral deafness. Otolaryngology - Head & Neck Surgery. 129(3):248-54, 2003

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