EXPERIMENTAL INVESTIGATIONS ON THE FUNCTIONAL EFFECT OF OSSICULAR JOINT FIXATION

In the normal middle ear, stapes displacement during atmospheric pressure changes is physiologically reduced by the gliding ossicular joints. In fixed ossicular joints, static pressure is assumingly transfered directly towards the inner ear. Therefore unphysiological movements could eventually initiate exceeding displacements and consecutively lead to a risk for inner ear function. Experimental investigations were performed in order to evaluate the dynamic and quasi-static effect of ossicular joint fixation on the middle ear. Acoustic transfer characteristics and stapes displacement were determined in 12 fresh temporal bone specimens. Stapes vibration amplitude was measured using Laser-Doppler-Vibrometry (LDV) before and after stepwise artificial fixation of the ossicular joints; the same applied to measurements of stapes displacement during standardized pressure changes in the external ear canal. In comparison to a regular middle ear, fixed ossicular joints demonstrated a minimal decrease of footplate vibration amplitude in the low frequency range whereas an improvement of the transfer characteristics of less than 10 dB was demonstrable in the middle and high frequency region. It furthermore shows that atmospheric pressure changes in the external ear canal lead to an unphysiological footplate displacement.