Measurement, visualization and quantitative analysis of complete three-dimensional kinematical data sets of human and cat middle ear

Using interferometry and micro-tomography in combination, we obtained a gold mine of data, embedding a complete description of the middle ear and its spatial motion, all for the same ear Studies are performed on fresh temporal bones (5 cat, 4 human) due to the limited in-vivo accessibility. Vibrations of the 3 middle ear ossicles are first measured from different viewing angles. Coordinates of points on the chain are recorded to define the spatial position of the ossicles. Assuming rigid body behavior, 3-D motion parameters for translation and rotation are calculated for each ossicle separately. In a second step the experimental middle ear is scanned using x-ray tomography and a dedicated 3-D anatomical model for the ossicular chain is constructed. The data are used to study middle ear vibration in a direct, visual way by animating the 3-D models of the 3 ossicles. For cat the classical "rotation about a fixed axis" mode is only approximately present at low frequencies (below 1.5 kHz). Around 10 kHz, the umbo, and the stapes footplate vibrate in phase opposition The animation clearly shows how this is possible. In human, large slippage in the malleus-incus joint, even at low frequencies, is most remarkable. Slippage has also been mentioned in studies by other investigators, but we are aware that part may be due to the fact that only bones of persons over 80 could be measured. The data can be also be used in innumerable quantitative ways. As the motion of every point of the ossicular chain can be calculated we compared umbo motion to footplate motion as a measure of the middle ear transfer, compared motion of the lenticular process and stapes head to study joint slippage. We also calculated the kinetic energy of the ossicles which makes it possible to evaluate transmission losses in the middle ear.