How does otosclerosis prevent the stapes from transmitting sound?

In otosclerosis, the stapes—the smallest bone in the middle ear—is prevented from transmitting sound due to the abnormal growth of spongy bony tissue around it.12

Normally, the stapes footplate rests in the oval window and acts as a piston, vibrating to conduct sound energy from the eardrum into the fluids of the inner ear. In the presence of otosclerosis, this new bone growth effectively "welds" the stapes to the surrounding wall of the inner ear. This fixation immobilizes the bone, breaking the link in the ossicular chain and preventing the vibrations necessary for sound transmission. Because the middle ear can no longer function as an impedance-matching transformer to deliver sound to the cochlea, the result is conductive hearing loss.132