[Mechanics and function of the middle ear. 2: Hearing physiologic comments on middle ear surgery].

The reconstruction of the destroyed ossicular chain has the purpose to re-establish an unhindered sound reception and transmission. With respect to the hydraulic factor, the reconstructed chain should be attached to a large effective area of the drum membrane, ideally to the malleus handle. The sensitivity is furthermore diminished in a linear relationship with increasing mass and stiffness. Therefore, cartilage cannot represent an acoustically ideal material for a drum membrane replacement. The reconstructed chain must vibrate without restraint for an unhindered transmission. Furthermore, the interposed prosthesis must be secured firmly to the remnants of the ossicular chain; the reconstructed chain must vibrate like one solid body. A loose contact attenuates the transmission and might result in a dislocation of the prosthesis with excessive ambient air pressure induced displacements of the drum membrane. A solid anchoring might be created by glueing, bony adhesion, special design of the prosthesis or with a wire connection. With unfavorable middle-ear conditions, the piston-like vibrational mode of the footplate has to be met with a direct driving of the stapes by a T-like prosthesis in the extension of the stapedial's vertical (high) axis. Ineffective rocking movements of the footplate are thus reduced. The almost perfect hearing result of the stapesplasty demonstrates that the impedance-matching middle-ear function is determined by the area ratio between the drum membrane and the width of the cochlear scala. Both components are not altered by the operation.(ABSTRACT TRUNCATED AT 250 WORDS)