EXPERIMENTAL SENSORINEURAL HEARING-LOSS FOLLOWING DRILL-INDUCED OSSICULAR CHAIN INJURY

In a guinea pig model, a standardized drill-induced injury to the body of the incus was applied, and the effects on hearing were characteriz ed by electrocochleography. Drilling resulted in a threshold shift wit hin seconds, and after 15 min it averaged 35.7 dB for clicks, 35 dB nH L for 4 kHz bursts, 36.7 dB nHL for 6 kHz bursts and 39 dB nHL for 8 k Hz bursts. The deterioration of the threshold shift remained stable th roughout the 5-week post-operative observation period. In five animals a disarticulation of the incudostapedial joint was performed prior to drilling, but this did not reduce the threshold shift. Caution is man datory during drilling around an intact ossicular chain to avoid a per manent sensorineural hearing loss, and disarticulation of the incudost apedial joint prior to drilling has no protective value.