The atretic plate--a conduit for drill vibration to the inner ear?

Inner ear energy exposure while drilling a cochleostomy

CONCLUSION

Drilling a cochleostomy exposes the cochlea to acoustic and mechanical trauma, particularly during the final stage when the running burr is in contact with an intact membranous labyrinth that is then breached. To minimize cochlear damage we recommend avoidance of prolonged contact of the running burr with the membranous labyrinth. The promontory should be drilled until a thin eggshell of bone remains that can be removed with microinstruments, thus allowing the atraumatic opening of the membranous labyrinth with a sharp instrument.

OBJECTIVES

To determine the energy transmitted to the inner ear while drilling a cochleostomy.

METHODS

Eight human cadaveric temporal bones were used. Stapes velocity as measured with the laser Doppler vibrometer was used as a reflection of energy input to the cochlea. Measurements were taken during the different stages of cochleostomy formation using a 1 mm diamond burr: drill on promontory, edge of the fenestration, blue-lined fenestration, membranous labyrinth and through the membranous labyrinth.

RESULTS

Drilling the promontory in preparation for the cochleostomy causes minimal energy transmission into the cochlea. There is significant and marked cochlea energy transfer when the running burr touches the membranous labyrinth and enters the scala tympani of a magnitude similar to touching the incus.