Role of the Carhart Effect and Outcomes from Surgery: A Retrospective Study of 532 Patients with Conductive Hearing Loss Due to Otosclerosis, Otitis Media with Effusion, and Chronic Otitis Media.

BACKGROUND The Carhart effect consists of a reduction in bone conduction thresholds associated with conductive hearing loss. The aim of this study was to evaluate the role of the Carhart effect in predicting outcomes from surgery in 3 age groups. MATERIAL AND METHODS This study included 532 patients with conductive hearing loss due to otosclerosis, otitis media with effusion, and chronic otitis media who underwent surgery between 2010 and 2020. RESULTS The depth of the Carhart effect is a favorable prognostic factor for changes in BC (bone conduction) thresholds after ear surgery in younger patients. A deep Carhart effect in older people is an unfavorable prognostic factor for improving BC thresholds. The restoration of physiological amplification of the sound that was transmitted through the ossicular chain led to a statistically significant change in the Carhart effect and a strong positive correlation between the change in the Carhart effect and the change in average BC thresholds. The influence of the Carhart effect on the postoperative change in the ABG (air-bone gap) is most noticeable when the physiological strengthening of the middle ear is maintained. CONCLUSIONS This findings from this study have shown that the depth of the Carhart effect is one of many factors that should be considered when predicting the results of ear surgery. The depth of the Carhart effect is a favorable prognostic factor for the postoperative changes in BC threshold and for change in the ABG when the physiological strengthening of the middle ear is maintained.