Noise exposure when drilling at the round window niche – A temporal bone study

Introduction Enlarging the round window niche by drilling is a routine surgical procedure of cochlear implantation (CI). Bone vibrations induced by drilling, especially near the cochlea, are regarded a great risk for hearing impairment of the patients. In this study we measured drilling induced noise exposure with an acceleration sensor at the patients head. Since it is not possible to place the sensor near the cochlear, a correction strategy has been developed to evaluate the noise exposure when drilling at the round window niche.

Methods The calculation of correction coefficient is based on the assumption that the bone conductive hearing level is proportional to the vibration of the promontory, which can be measured by Laser Doppler Vibrometer (LDV). Two pairs of acceleration values were recorded by drilling near the sensor a_s, a_LDV and at the round window niche a_s, a_LDV’ in 9 temporal bone specimens. The correction coefficient is (a_s, a_LDV)/(a_s’/a_LDV’). The equivalent induced sound pressure level (SPL) can be calculated from the measured and corrected accelerations and an individual calibration curve, determined by defined bone conduction stimulation. A noise damage model can be used to calculate a daily noise dose, which should not exceed 100%.

Results The maximal SPL when drilling at the round window niche was 111 dB(A). The induced daily noise dose did not exceed 6%. Both values were considerably lower than those obtained when drilling at e.g. the implant bed.

Conclusion The SPLs induced by drilling at the round window niche exceeded the safety limit of 85dB but were always below 120 dB. There is no risk to reach or exceed the daily noise dose. These statements apply only to drilling on the bone.

Publication History

Article published online:
12 May 2023