Does bilateral otosclerosis make pre-operative bone conduction more inaccurate?

OBJECTIVES: To assess whether bilateral otosclerosis renders pre-operative bone conduction more inaccurate by increasing the Carhart effect. METHODS: Retrospective review of a database of pre and post-operative audiograms of 745 ears with otosclerosis treated with stapedectomy from 2013 to 2020 in a tertiary centre. MAIN OUTCOME MEASURES: Change in bone conduction after stapedectomy for otosclerosis in: unilateral otosclerosis (U1); bilateral otosclerosis undergoing first side surgery (B1); bilateral otosclerosis undergoing second side surgery (B2). The magnitude of change in bone conduction post-operatively within and between each group. RESULTS: The average difference in pre and post-operative bone conduction was significant within in all groups (T-stat > 2 and P-value <0.05) with the greatest change observed in the U1 group. Analysis of average change in bone conduction between groups did not reach statistical significance (P-value = 0.37). Analysis of change per frequency demonstrated the greatest change in bone conduction post-operatively at 2000 Hz in all groups. The magnitude of change at 2000 Hz was the greatest in the bilateral groups; however, it did not reach statistical significance when compared to the unilateral group (P-value = 0.36). CONCLUSIONS: This is the first study in the literature to assess the accuracy of pre-operative bone conduction in bilateral versus unilateral otosclerosis. There is no evidence that pre-operative bone conduction in bilateral otosclerosis is more inaccurate than in unilateral disease. In order to assess accuracy of pre-operative bone conduction in otosclerosis a reliable method of assessing post-operative bone conduction is required, without assumption of its equivalence to cochlear reserve.