Why can otosclerosis cause conductive hearing loss?

Otosclerosis causes conductive hearing loss by interfering with the mechanical transmission of sound through the middle ear.12

In a healthy ear, the stapes (stirrup) acts as a piston, vibrating against the oval window to conduct sound energy into the fluids of the inner ear. In individuals with otosclerosis, a nodule of abnormal, spongy bone grows around the stapes. As this nodule expands, it eventually welds or fixes the stapes against the surrounding bone.134

This fixation immobilizes the stapes, preventing it from vibrating in response to sound waves striking the eardrum. Because the ossicular chain can no longer effectively transform and transmit these vibrations to the cochlear fluids, sound conduction is significantly impeded, resulting in conductive hearing loss. This condition is often treated through stapedectomy, a surgical procedure where the fixed stapes is removed and replaced with an artificial substitute to restore the ear's mechanical function.1432