Result: The mean follow-up period was 50.4 months; the mean pre-operative air conduction threshold improved significantly (P < 0.001) from 33.3 dBHL (SD 7.8) to 19.5 dBHL (SD 6.7); at the frequency of 1000 Hz, the post-op hearing level was 18.4dBHL; closure of Air-Bone gap was 12.5dB (from 25.9dB pre-op to 13.4dB post-op); the time of improvement was 3 - 6months after surgery.