Equivalent noise level generated by drilling onto the ossicular chain as measured by laser Doppler vibrometry: a temporal bone study.
BACKGROUND
Inadvertent drilling on the ossicular chain is one of the causes of sensorineural hearing loss (HL) that may follow tympanomastoid surgery. A high-frequency HL is most frequently observed. It is speculated that the HL is a result of vibration of the ossicular chain resembling acoustic noise trauma. It is generally considered that using a large cutting burr is more likely to cause damage than a small diamond burr.


OBJECTIVE
The aim was to investigate the equivalent noise level and its frequency characteristics generated by drilling onto the short process of the incus in fresh human temporal bones.


METHODS
Five fresh cadaveric temporal bones were used. Stapes displacement was measured using laser Doppler vibrometry during short drilling episodes. Diamond and cutting burrs of different diameters were used. The effect of the drilling on stapes footplate displacement was compared with that generated by an acoustic signal. The equivalent noise level (dB sound pressure level equivalent [SPL eq]) was thus calculated.


RESULTS
The equivalent noise levels generated ranged from 93 to 125 dB SPL eq. For a 1-mm cutting burr, the highest equivalent noise level was 108 dB SPL eq, whereas a 2.3-mm cutting burr produced a maximal level of 125 dB SPL eq. Diamond burrs generated less noise than their cutting counterparts, with a 2.3-mm diamond burr producing a highest equivalent noise level of 102 dB SPL eq. The energy of the noise increased at the higher end of the frequency spectrum, with a 2.3-mm cutting burr producing a noise level of 105 dB SPL eq at 1 kHz and 125 dB SPL eq at 8 kHz. In contrast, the same sized diamond burr produced 96 dB SPL eq at 1 kHz and 99 dB at 8 kHz.


CONCLUSIONS
This study suggests that drilling on the ossicular chain can produce vibratory force that is analogous with noise levels known to produce acoustic trauma. For the same type of burr, the larger the diameter, the greater the vibratory force, and for the same size of burr, the cutting burr creates more vibratory force than the diamond burr. The cutting burr produces greater high-frequency than lower-frequency vibratory energy.
Jiang
Dan
D
Department of Otolaryngology, Head and Neck Surgery, Auditory Implantation Centre, Guy's and St. Thomas Hospitals, London, United Kingdom.
Bibas
Athanasios
A
Santuli
Carlo
C
Donnelly
Neil
N
Jeronimidis
George
G
O'Connor
Alec Fitzgerald
AF
D004429:Ear Ossicles / Q000601:surgery*; D006317:Hearing Loss, Noise-Induced / Q000209:etiology; D006319:Hearing Loss, Sensorineural / Q000209:etiology; D006801:Humans; D053685:Laser Therapy / Q000295:instrumentation*; D009622:Noise; D010036:Otolaryngology / Q000295:instrumentation*; D012399:Rotation / Q000009:adverse effects*; D013525:Surgical Instruments / Q000009:adverse effects*; D013701:Temporal Bone / Q000601:surgery*; D014465:Ultrasonics; D014732:Vibration