Three dimensional vibration of the ossicular chain in the cat

To investigate the relationship of the motion of the malleus, incus and stapes in the middle ear of cat the 3-D vibrations of the three ossicles were measured in the same ear utilizing a confocal heterodyne interferometer. Each ossicle was treated as a separate rigid body and its motion was calculated individually. A micro CT scanner was used to obtain serial sections of the experimental temporal bone. A 3-D reconstruction of the three ossicles was made using these sections. The parameters derived from the rigid body motion calculation were combined to animate a 3-D model of the complete middle ear. While the malleus vibration changed from simple, nearly hinged motion at low frequencies to very complex at higher frequencies, the stapes moved in a predominantly piston-like way. The incus transforms the complex malleus motion into the simple motion of the stapes. The incudo-stapedial joint plays a major role in this complex transmission mechanism. It is accepted that the ossicles rotate around a fixed axis and function as mechanical levers. Our precise vibration measurements on malleus do not confirm this theory.