Siu, Jennifer1; Negandhi, Jaina2; Harrison, Robert2,3; Wolter Nikolaus1,3; James Adrian1,2,3
1 Department of Otolaryngology – Head and Neck Surgery, University of Toronto, Toronto ON, Canada;
2 Auditory Science Laboratory and Program in Neuroscience and Mental Health- Hospital for Sick Children, University of Toronto, Toronto, ON, Canada;
3 Department of Otolaryngology, Hospital for Sick Children, Toronto, ON, Canada.
Ultrasonic bone removal tools (UBRT) are capable of cutting through bony tissue without injury to adjacent soft tissue. The feasibility and safety of using this technology for removal of bone from an intact ossicular chain (eg for otosclerosis or congenital fixation) was investigated in an animal model.
Study Design: Prospective animal study
Setting: Auditory Science Laboratory
Subjects: Seven anesthetized adult chinchilla
Intervention: Removal of bone from the malleus head in situ using UBRT
Main outcome measures: Pre and post-operative auditory brainstem responses (ABR) thresholds and distortion product otoacoustic emissions (DPOAE) levels. Cochlear haircell integrity assessed with scanning electron microscopy (SEM).
Results: Application of up to 30 seconds of UBRT precisely removed a small quantity of bone from the malleus head with without disruption of the ossicular chain or tympanic membrane. Following intervention, DPOAE levels were reduced from pre-operative levels by an average of 12dB (p<0.05) at 1kHz, 22dB (p<0.05) at 2kHz, 29 (p<0.05) at 4kHz, and 42 dB (p<0.05) at 8kHz. Average ABR threshold increased following intervention for all subjects: by 67dB to 85dB HL at 2kHz (p<0.05), by 71dB to 8dB HL7 at 4kHz (p<0.05), and by 77dB to 83db HL at 8kHz (p<0.05). SEM showed extensive disruption of inner and outer hair cells.
Although UBRT can be used to reshape an ossicle without middle ear injury, prolonged contact with the ossicular chain can cause structural and functional injury to the cochlea. In the authors’ opinion, further study should be undertaken before consideration is given to use of the device for release of ossicular fixation.