Influence of a totally open oval window on bone conduction in otosclerosis.

OBJECTIVE The aim of this study was to evaluate changes in bone conduction thresholds before, during and after total stapedectomy. STUDY DESIGN Prospective clinical study. METHODS In 27 ears of 26 patients undergoing stapedectomy under local anesthesia, bone conduction was measured before surgery, during surgery under open oval window conditions, and after the insertion of a steel wire connective tissue prosthesis. Statistical data analysis was performed on the audiometric results. RESULTS Under open oval window conditions, bone conduction hearing was found to be improved between 500 and 2000 Hz, but not at 4000 Hz. After insertion of the prosthesis, an additional improvement was evident at 500 and 1000 Hz, but a loss was seen at 2000 and 4000 Hz. CONCLUSION This is the first investigation reported in which audiometry was performed under open oval window conditions during stapes surgery. Our results demonstrate that at least part of the preoperative bone conduction hearing loss in otosclerosis must be of mechanical, but not of sensorineural origin, as already suspected by Carhart. The fixed footplate suppresses cochlear micromechanics mainly at frequencies between 500 to 2000 Hz. Furthermore, the loss in bone conduction hearing at 2000 and 4000 Hz after insertion of the prosthesis indicates that rather than the surgical procedure of total removal of the footplate, other factors such as the handling of the prosthesis or its mechanical properties after insertion cause high-frequency hearing loss after stapes surgery.