OBJECTIVETo compare the influences of stapedectomy and small fenestra stapedotomy on the hearing of guinea pigs.

METHODSTwenty-four (48 ears) guinea pigs were randomized equally into two groups, and the left ears were subjected to stapedectomy and total stapes replacement with a prosthesis, or sham operation (12 ears) to expose the footplate of the stapes and the round window. Each guinea pig was tested by ABR perioperatively. Four guinea pigs were chosen randomly from each group and decapitated for morphological examination by light microscopy and scanning electron microscopy after ABR test.

RESULTSIn the sham operation group, the post-operative latencies of each wave, the intervals and the hearing threshold exhibited no significant changes other than prolonged latency of wave I. In stapedectomy group, the hearing threshold increased to 23.75-/+3.77 dBSPL 1 h after operation with significantly prolonged post-operative latencies of all the waves and intervals but for III-IV interval, which was shortened. The latencies of each wave (especially waves I and III) in the stapedectomy group were increased by a greater magnitude than those in the sham operation group, but the intervals were comparable between the two groups. No significant difference was noted in the parameters of ABR either 1 h or 1 day after the operation between the two groups, in which the architecture of cochleas remained intact with similar number of spiral ganglion cells. The stereocilia of the outer hearing cells (OHC) were normal in the sham operation group while in stapedectomy group, slight stereocilia disorder occurred but became normal 1 day after operation. No obvious changes were found in the stereocilia of the inner hearing cell (IHC) in either groups.

CONCLUSIONStapedectomy can induce mild hearing loss without seriously damaging the function of the cochlea in guinea pigs.