Hearing evaluation
In this study, pure-tone average (PTA), calculated using 0.5-, 1-, 2-, and 3-kHz air conduction thresholds, was used to evaluate the hearing level of the patients. The 3-kHz threshold used in this study was interpolated by averaging the thresholds at 2 and 4 kHz, because the 3-kHz threshold is not routinely tested in China. The postoperative evaluation included three time points, at 6 months,12 months and 18 months postoperatively. Hearing deterioration or improvement was assessed according to the A New Standardized Format for Reporting Hearing Outcome in Clinical Trials 9. Hearing deterioration was defined as a PTA elevating ≥10 dB when compared with the hearing level preoperatively. The definition of stages was based on the hearing levels of patients pre-operatively10. In brief, a stage I corresponded to a PTA < 25 dB HL, stage II corresponded to a PTA of 25 - 40 dB HL, stage III corresponded to a PTA of 41-70 dB HL and stage IV corresponded to a PTA >70 dB HL. The word recognition score cannot be reported in this study due to the variety of dialects. It is difficult to acquire reliable scores using a single standardization scale when evaluated patients speak different types of dialects.