Implantable Middle Ear Devices

History

• 1.

  History of present illness

  • a.

    Etiology, duration, and stability of hearing loss

  • b.

    Hearing aid experience: The patient’s reported experience with hearing aids provides good insight into their motivation for pursuing surgery and a starting point for discussing reasonable hearing expectations with the Esteem Implant.

  • c.

    Other symptoms suggestive of underlying ear disease, which may contraindicate Esteem surgery, such as dizziness, tinnitus, aural fullness, otalgia, or otorrhea should be identified.

  • d.

    Hearing status of the contralateral ear: The patient will not be able to hear in the operated ear for approximately 2 months postoperatively; therefore, it is important to optimize hearing in the nonoperative ear before surgery.

• 2.

  Past medical history

  • a.

    Prior otologic procedures: Prior myringotomy with or without tube placement, tympanoplasty, ossiculoplasty, or stapes surgery may be contraindications for this procedure.

  • b.

    Medical illness: Comorbidities that would impact wound healing, Eustachian tube function, or the need for future magnetic resonance imaging (MRI) scans. History of bleeding disorders is a relative contraindication since extensive soft tissue dissection is required for SP placement, and adherence of the mastoid cement may be challenging.

  • c.

    Other surgery: Prior soft tissue surgery in close proximity to the ear to be implanted, ventriculoperitoneal (VP) shunt, or craniotomy surgery may impact the design of the incision and the SP placement.

  • d.

    Medications: Anticoagulants, vitamins, and herbal products should be discontinued 1 week prior to surgery.

Physical Examination

• 1.

  Ears

  Look for a normal ear canal and tympanic membrane and the absence of any obvious tympanic membrane retractions or limited movement, middle ear lesions, or effusions. Inspect the postauricular scalp to ensure the absence of any skin pathology.

Audiogram

• 1.

  Pure tone audiogram: air and bone conduction thresholds

• 2.

  Speech audiogram: speech reception thresholds (SRTs), unaided word recognition scores

• 3.

  Sound field testing: aided thresholds, word recognition at 50 dB HL and at comfortable suprathreshold levels

• 4.

  Tympanograms

Imaging

• 1.

  Temporal bone computed tomography (CT) scan

  This is obtained preoperatively to ensure adequate space for the placement of transducers (minimum of 22 mm between sigmoid sinus and stapes capitulum and 2.5 mm between incudomalleal joint and tegmen tympani). If hearing is symmetric, the mastoid with larger dimensions is preferable for ease of implantation.

• 2.

  MRI brain with gadolinium ^∗

  ∗ The current Esteem Implant is not MRI compatible.

  Not routinely required. This is obtained preoperatively to screen for retrocochlear pathology ONLY if hearing loss is asymmetric.

Indications

• 1.

  Adults 18 years or older with stable bilateral moderate to severe sensorineural hearing loss (PTA 40 to 90 dB)

• 2.

  Unaided word recognition scores greater than or equal to 40%

• 3.

  Normal Eustachian tube function

• 4.

  Normal tympanic membrane

• 5.

  Normal middle ear anatomy

• 6.

  Adequate mastoid and middle ear space for implant placement determined on temporal bone CT scan

• 7.

  Minimum of 30 days’ experience with appropriately fitted hearing aids

• 8.

  Realistic hearing expectations

In general, experienced hearing aid users meeting indications 1 to 6 who desire the Esteem device for lifestyle, comfort, convenience, or cosmetic reasons and who have realistic expectations for comparable or more natural hearing relative to conventional hearing aids are ideal candidates.

Contraindications

• 1.

  History of significant Eustachian tube dysfunction, active chronic middle ear disease, or cholesteatoma

• 2.

  Prior ossiculoplasty or stapes surgery

• 3.

  Meniere disease or other inner ear diseases associated with fluctuating hearing loss

• 4.

  Retrocochlear pathology

• 5.

  Disabling tinnitus

• 6.

  Anticipated need for MRI in the future

Preoperative Preparation

• 1.

  Choice of ear to be implanted:

  • a.

    Poorer hearing ear

  • b.

    Larger mastoid dimensions

  • c.

    Poorer hearing aid fit

• 2.

  Discontinue any anticoagulants 10 to 14 days prior to surgery.

Anesthesia

General: Esteem surgery is always performed under general anesthesia.

Positioning

Supine: Patient is positioned supine with the body firmly secured to the operating table and the head turned away from the surgeon. The operating room table is turned 180 degrees.

Perioperative Antibiotic Prophylaxis

• First-generation cephalosporin for patients who are not allergic to penicillin or cephalosporin

• Clindamycin for penicillin-allergic patients

Monitoring

• Facial nerve monitoring

• Intraoperative system analyzer (ISA) testing is performed by field clinical engineer (FCE).

Instruments and Equipment to Have Available

• 1.

  Standard mastoid set

• 2.

  Additional middle ear instrumentation ^∗

  ∗ Indicates equipment/materials provided by the manufacturer at the time of surgery.

  : includes TABB double-edged flap knives, curved Rosen needle

• 3.

  SP and transducer templates ^∗

• 4.

  High-speed drill for mastoid surgery

• 5.

  Bipolar electrocautery: to be used for hemostasis after the implant is placed

• 6.

  Diode, ^∗ argon, CO ₂ , or KTP laser

• 7.

  Laser Doppler vibrometer and reflective tape ^∗

• 8.

  Sterile ear microphone ^∗

• 9.

  Esteem ISA ^∗ : used to test Esteem Implant function intraoperatively. Both equipment and engineer are provided by the manufacturer.

• 10.

  Second microscope fitted with laser Doppler vibrometer ^∗

• 11.

  Hydroxyapatite cement and glass ionomer cement ^∗

• 12.

  Deionized water

An FCE is provided by Envoy Medical for every initial and revision Esteem surgery to perform intraoperative functional and device testing.

Key Anatomic Landmarks

• 1.

  Incus: identified in the epitympanum anterolateral to the lateral semicircular canal. This provides an indicator for the approximate level of the facial recess along the posterior ear canal.

• 2.

  Facial nerve: The mastoid segment is the medial boundary of the facial recess.

• 3.

  Chorda tympani nerve: This is the lateral boundary of the facial recess and is often sacrificed in Esteem surgery for driver placement. The fibrous annulus of the tympanic membrane lies lateral to the chorda.

• 4.

  Tegmen tympani and mastoideum: the floor of the middle fossa and superior boundary of the mastoid and epitympanic dissection

Prerequisite Skills

• 1.

  Mastoidectomy and facial recess exposure

• 2.

  Ossiculoplasty surgery

• 3.

  Otologic laser certification

• 4.

  Otologic cement application

Operative Risks

Risks of mastoidectomy surgery, including injury to the sigmoid sinus, tegmen, dura, posterior ear canal, lateral semicircular canal, facial nerve, and ossicular chain are discussed elsewhere in this book. Those listed below highlight the additional risks incurred for placement of the Esteem Implant.

• 1.

  Injury to the facial nerve

  The facial nerve may be injured while opening the facial recess as a result of direct trauma or heat injury. The facial nerve also may be injured when using the diode laser to section the long process of the incus. The vertical segment of the nerve should be protected by placing a finger in the mastoid cavity while screwing the stabilizer bars to prevent inadvertent slipping of the screwdriver into the mastoid. The tympanic segment of the nerve should be well covered with moist Gelfoam while using the diode laser.

• 2.

  Trauma to the ossicles

  Drill trauma to the malleus and incus may occur as the epitympanum is being opened to expose the incudomalleal joint. The stapes is at risk for dislocation and fracture when separating the incudostapedial joint and removing mucosa from the capitulum. The incus is at risk for dislocation when creating a neojoint between the sensor and incus body. Trauma to the ossicles is best avoided with gentle manipulation of the mobile ossicular chain during surgery and gentle stabilization of the ossicle with a suction or other atraumatic micro-instrumentation.

• 3.

  Injury to or transection of the chorda tympani nerve

  Transection of the chorda tympani nerve is necessary in most cases to provide adequate surgical exposure for driver placement and cement application between the driver tip and stapes capitulum.

• 4.

  Tympanic membrane perforation

  This may occur when widening the facial recess after the chorda tympani nerve has been sacrificed. Once the fibrous annulus is identified, no further drilling should be performed on the lateral aspect of the facial recess. The tympanic membrane is also at risk with the use of the diode laser. Care should be taken to direct the laser away from the tympanic membrane and pause to allow heat dissipation between laser exposures.

Surgical Technique

• Mark position for SP placement ( Fig. 136.3 ) on a relatively flat part of the skull posterosuperior to the anticipated mastoid cavity. Mark a lazy S incision behind ear to accommodate placement of the SP at least 1.5 cm away from the anterior border of the SP. Perform small strip shave and inject incision site with local anesthetic containing 1:100,000 epinephrine solution.

  

• Place facial nerve monitoring electrodes in ipsilateral orbicularis oculi and orbicularis oris muscles and appropriate ground and stimulating electrodes. A separate ground electrode for the intraoperative implant testing is placed in the midline forehead.

• Prepare and drape the ear in usual sterile fashion.

• Insert the microphone into the sterile ear canal and secure the pinna forward with watertight adhesive dressing once the functionality of the microphone has been confirmed by the FCE.

• Make a postauricular incision down to the avascular plane superficial to the temporalis fascia layer and elevate the anterior and posterior skin flaps.

• Incise the temporalis fascial layer and periosteum in a vertical, stepped fashion anterior to the skin incision. Elevate the periosteum anteriorly and posteriorly. The spine of Henle and posterior-superior bony ear canal should be exposed anteriorly. Posterior exposure permits SP placement.

• Drill an SP bed in the previously identified SP location behind the anticipated mastoid cavity and a shallow electrode trough to accommodate the SP header and electrodes. Suture tying down of the holes on either side of the SP bed may be considered to secure the SP.

• Perform a cortical mastoidectomy with skeletonization of the mastoid tip, sigmoid sinus, posterior fossa plate, tegmen, and posterior ear canal. Open the epitympanic recess for clear exposure of the body of the incus and incudomalleal joint. This wide exposure is necessary for placement and visualization of the driver and the sensor, as well as the application of cement.

• Place a small saline-soaked Gelfoam pledget over the proximal body of the incus (sensor neojoint location) to keep the mucosa moistened through the remainder of the procedure until the placement of the sensor.

• Open the facial recess, keeping the incus buttress intact and skeletonizing the facial nerve. Unless the facial recess is unusually wide, the chorda tympani nerve is sacrificed, and the fibrous annulus of the tympanic membrane forms the lateral boundary of surgical exposure in these cases.

• Sharply remove any visible ossicular chain adhesions. Place small strips of reflective tape on the stapes and incus body (remove the Gelfoam for this purpose). Obtain intact chain measurements using the laser Doppler vibrometry (FCE). If the ossicular chain is hypomobile, do not proceed with Esteem implantation.

• If ossicular chain mobility is within the normal range, proceed to incise the mucosa of the incudostapedial joint with a #59 beaver blade, and elevate the stapes capitulum mucosa medially toward crura, then separate the incudostapedial joint.

• Place the saline-soaked Gelfoam medial and lateral to the incus in the middle ear to protect the tympanic facial nerve and tympanic membrane.

• Amputate the distal 3 to 4 mm of the long process of the incus long using a laser (for diode laser, use 5 to 8 watts, single pulse mode, pulse duration 100 to 200 ms). Then remove the Gelfoam from the middle ear.

• Paint the stapes capitulum with methylene blue-soaked Gelfoam.

• Remove any methylene blue-stained mucosa over the stapes capitulum and dry the capitulum with the laser (for diode laser use 2 watts, single pulse mode, 100 to 200 ms pulse duration). This is a critical step for reliable bonding of the ionomeric cement used to couple the Esteem driver tip to the stapes capitulum.

• Precoat the stapes capitulum with ionomeric cement and allow to cure for 10 minutes.

• Screw on the Glasscock stabilizer bars to the posterior cortical margin of the mastoid cavity, and attach the driver and the sensor.

• Test capacitance of the driver and sensor with the provided cables (FCE).

• Position the sensor in the mastoid with the tip over incus body adjacent to incudomalleal joint. Then place the driver in the mastoid with the tip over the cement-coated stapes capitulum, bellows parallel to the footplate, avoiding bony contact within the facial recess ( Fig. 136.4 ).

  

• Carefully place small saline-soaked Gelfoam pledgets in the mastoid cavity medial and adjacent to the sensor and driver transducer bellows, creating a physical barrier to prevent anterior migration of the hydroxyapatite cement.

• Rotate the patient toward the surgeon, and apply hydroxyapatite cement completely around transducer bodies proximal to their silicone shields. After 3 minutes, inspect the driver and sensor tips for migration as the cement cures. This can be controlled early in the cement curing process by applying gentle pressure on the stabilizer bars or bellows using micro-instrumentation. Allow the cement to cure for 15 to 20 minutes. Ensure there is no undo pressure on the transducer leads, which can displace the transducer tips.

• The Gelfoam is carefully removed from the mastoid 5 to 10 minutes after the application of cement.

• Apply ionomeric cement around the driver tip onto the stapes capitulum cement precoat, and allow it to cure for 10 minutes.

• Apply ionomeric cement to the sensor tip, and allow it to cure for 5 minutes. Then create a neojoint by incising the incus mucosa around cement-ossicle interface, separating the cement cap with the sensor tip from the incus. A sharp, gently curved pick and TABB knife are useful for this step.

• Irrigate the mastoid and middle ear with antibiotic solution.

• Test the sensor and driver placement and function using laser Doppler vibrometry (FCE). If either one is not functioning within the parameters defined by prior intact chain measurement, transducer placement must be revised and the testing repeated until acceptable measures are obtained.

• Clean the proximal sensor and driver leads with deionized water and dry.

• Insert the sensor and driver leads into the SP header, and secure the SP in the bony seat. Perform system testing (FCE).

• Remove stabilizer bars.

• Perform layered wound closure (2-0 Vicryl muscle/periosteum, 3-0 Vicryl subcutaneous, and 4-0 Vicryl subcuticular, and apply Steri-Strips).

• Remove the microphone, and inspect the ear canal and tympanic membrane.

• Place a pressure dressing over the ear for 24 hours.

Battery Change Technique

• Average battery life of the Esteem Implant is 5 years.

• Since the Esteem battery is integral to the SP unit, battery changes afford the patient any interval technology updates for the implant system.

• Battery change is usually performed under local anesthesia unless otherwise indicated by patient preference/tolerance.

• Only bipolar electrocautery should be used for battery change, and avoidance of any electrocautery is preferred.

• Prior to the procedure, the new SP is programmed using the patient’s existing SP parameters, and the Personal Programmer is linked to the new SP.

• Tape the surgical ear forward.

• After sterile preparation and draping, the original postauricular incision anterior to the SP component is infiltrated with local anesthetic with 1:100,000 epinephrine solution buffered with sodium bicarbonate solution.

• The initial skin incision is made with a scalpel. Thereafter, blunt and sharp dissection are used to isolate the proximal driver and sensor leads adjacent to the SP header and expose the fibrous capsule encasing the SP.

• Incise fibrous capsule, and remove SP from soft tissue pocket. Remove the driver and sensor leads from the SP header.

• Perform capacitance testing with the cable provided by the FCE.

• Inspect leads for surgical trauma. If the electrical component of either lead is violated during the procedure, the wound should be closed and the patient returned to the OR electively for a formal revision to replace the damaged transducer.

• Irrigate the SP pocket with bacitracin or other antibiotic solution.

• Clean the leads with sterile deionized water, and dry with instrument wipes.

• Insert the driver and sensor leads fully into appropriate header slots in the new SP.

• Confirm hearing restoration, and perform volume testing to confirm functionality of the new SP. The implant is active from the time of surgery.

• Close the wound in layers.

• Apply a pressure dressing over the ear for 24 hours.

Postoperative Management

• 1.

  Wound care: Expect mild soft tissue edema around the incision and implant. Keep a light pressure dressing over the ear for 24 hours.

• 2.

  Activate and program the SP 8 weeks after surgery. This allows adequate time for the resolution of retained blood within the middle ear, thus avoiding the possibility of mechanical feedback.

• 3.

  One or two additional programming visits may be helpful to optimize hearing outcomes within the first year.

Complications

• 1.

  Wound infection

  All wound infections should be treated aggressively with broad-spectrum skin flora coverage.

• 2.

  Wound dehiscence

  If primary wound closure without tension is not possible, a local soft tissue flap with or without skin grafting may be required to cover the SP. Prophylactic antibiotic coverage for skin flora should be prescribed.

• 3.

  Mastoid and/or middle ear scar tissue/adhesion formation

  Adhesions restricting mobility of the sensor or driver may limit gain and cause feedback. Functional testing with or without temporal bone CT imaging may help to localize involvement to the sensor or driver. A transmastoid approach for revision surgery is generally recommended unless functional testing localizes scar tissue formation between the driver tip and incus remnant or tympanic membrane.

• 4.

  Driver detachment

  This can be diagnosed on functional testing of the implant. A transcanal approach may be used to replace or augment ionomeric cement over the driver tip.

• 5.

  Poor functional gain with implant

  If hearing benefit with the Esteem Implant remains poor (significantly worse than the preoperative aided condition), revision surgery and transducer repositioning may improve function. Alternatively, the implant may be removed and hearing reconstructed with a partial ossicular replacement prosthesis, a Kraus K-Helix Crown prosthesis (Grace Medical), or ionomeric cement.

• 6.

  Facial paralysis

  Treat with 7- to 10-day oral steroid taper.

• 7.

  Dysgeusia

  Long-term dysgeusia is expected in 5% to 7% when the chorda tympani nerve is sacrificed.

Alternative Management Plan

For patients desiring the benefits afforded by the Esteem Implant System (24/7 function, limited water exposure, cosmesis, convenience) at a lesser cost or risk, deep insert extended-wear hearing aids (Lyric) may be considered. The average battery life on the Lyric hearing aid is 2 to 3 months.

Evidence-Based Medicine Question

Besides advantages in lifestyle with a totally implanted hearing system, are there any audiometric advantages with the Esteem Implant compared to conventional hearing aids?

A prospective, nonrandomized, multicenter, subject-as-own-control, FDA clinical trial demonstrated an improvement in SRT from 41.2 dB with the hearing aid to 29.4 dB with the Esteem Implant. Word recognition score at 50 dB HL (WRS50) improved from 46.3% with the subjects’ hearing aids to 68.9% with the Esteem. A pure tone average (PTA) improvement of 27 ± 1 dB was seen.