Vibrant Soundbridge - 10 Mark Answer (MS ENT)

Definition / Introduction

Components

1. External Component - Audio Processor (AP)

• Microphone
• Audio processing electronics
• Magnet (for transcutaneous coupling)
• Telemetry transmission equipment
• Standard 675 zinc battery

2. Internal Component - Vibrating Ossicular Reconstruction Prosthesis (VORP)

Fig: MED-EL Vibrant Soundbridge - (A,B) External AP couples via inductive link to VORP clipped to incus long process. (C) Implanted VORP. (D) FMT actuator. (E) Programming unit. (F,G,H) Surgical placement - internal receiver in retromastoid bone, VORP via facial recess approach.

Working Principle / Mechanism

1. Sound is picked up by the microphone in the external audio processor.
2. The AP processes the signal and transmits it via an inductive transcutaneous telemetry link to the internal receiver - similar to a cochlear implant.
3. The signal passes to the demodulator, which generates a current encoding the sound.
4. This current travels to the FMT, where electromagnetic induction between the coil and the magnet causes the FMT to vibrate.
5. Since the FMT is firmly clipped to the long process of the incus, these vibrations are transmitted directly to the ossicular chain and then to the cochlea.
6. This bypasses the outer ear and tympanic membrane entirely, eliminating occlusion and feedback problems seen with conventional hearing aids.

Indications (Audiologic Selection Criteria)

• Moderate to severe sensorineural hearing loss (SNHL) - pure tone average (PTA) up to 70 dB HL
• Normal middle ear anatomy
• Word recognition score ≥ 50% using recorded material
• Absence of retrocochlear or central auditory involvement
• Patient age ≥ 18 years
• Medical contraindication or intolerance to conventional hearing aids (e.g., recurrent otitis externa, canal atresia, chronic skin reactions)

• Mixed hearing loss (otosclerosis, ossicular erosion/agenesis) - via VORP placement on stapes superstructure, oval window, or round window
• Conductive hearing loss

Contraindications

• Age < 18 years (pediatric use not FDA-approved at initial approval)
• Retrocochlear pathology (acoustic neuroma, central auditory processing disorder)
• Active middle ear disease
• Word recognition < 50%
• Hearing loss beyond 70 dB PTA (may require cochlear implant instead)

Surgical Technique

• Standard transmastoid, facial recess approach to the middle ear
• The internal receiver is placed in a bony trough drilled in the retromastoid/retrosigmoid bone behind the ear (similar to cochlear implant placement)
• The VORP is crimped onto the long process of the incus (crimping force must balance maximal vibration coupling against risk of incus ischemia and necrosis - same principle as stapedectomy)
• For mixed hearing loss: VORP may be placed on the stapes superstructure, oval window, or round window

Advantages Over Conventional Hearing Aids

Clinical Results

• Phase III trial (53 patients): Statistically significant improvement in functional gain at all frequencies (250-8000 Hz), PHAP, and HDSS scores vs. conventional hearing aids
• Improvement >10 dB noted at 2, 4, and 6 kHz
• Implantation caused <10 dB residual hearing change in 96% of subjects
• Long-term multicenter data (97 patients, 5-8 year follow-up): 72% would repeat the procedure; ~40% interested in binaural implantation
• Device failure rate: 0.3% (post-1999 design); revision surgery needed in 5% due to fibrosis, malpositioning, or inadequate fixation
• Common side effects: persistent aural fullness (27%), taste alteration/dysgeusia (8%)

MRI Compatibility

Summary Points for Exam

1. Semi-implantable, active middle ear device (not fully implantable)
2. Key component = FMT (Floating Mass Transducer) - distinguishes it from passive prostheses
3. Indication: moderate-severe SNHL, PTA up to 70 dB
4. Approach: transmastoid, facial recess
5. VORP clipped to long process of incus (standard); alternatives - stapes, RW, OW
6. No occlusion, no feedback - key advantages
7. First FDA-approved middle ear implant (2000)
8. MRI: 1.5T allowed (VORP 503), not 3T