The Effect of Ossicular Joint Fusion on the Human Middle Ear Frequency Response

Introduction: There are different clinical scenarios in which the middle ear ossicular chain is either disrupted, partially absent or fused, which necessitates ossicular chain reconstruction (OCR) with partial or total prosthesis (PORP or TORP). This reconstruction bypasses the middle ear joints. The literature is divided regarding the relative effectiveness of these two methods1,2 . We present a frequency response comparison of the effects of fusing the incusstapes joint (ISJ), incus-malleus joint (IMJ) and both and relate this to the above mentioned clinical scenarios.

Material and Methods: The 3D velocity of the stapes was first measured in unaltered cadaveric human cadaver temporal bones (N=9), stimulated with pure tones (100Hz-20kHz), using a Polytec CLV-3D laser Doppler vibrometer. The measurements were then repeated after fusing one or both of the ossicular joints.The sound source was used to play a wide range of frequencies, and the pressure at the TM was measured using the TM microphone.

Results: Fusing the incudo-malleolar joint cuased a gain in the high frequencies. Fusing the incudo-stapedial joint caused a mild loss at the very low frequencies and a mild gain along the rest of the frequencies. Fusing both joints caused low frequency loss along side with mid and high frequencies gain.

Disscution: By fusing the incus-malleus joint we simulate a PORP. Fusing both joints mimics a TORP, and by fusing only the incus-stapes joint we mimic the piston stapedotomy prosthesis. When comparing the 3 fusion cases it’s clear that the IMJ fusion created the most prominent effects, with not a big difference from both joint fused state, which implies that when compering the PORP to the TORP reconstruction the difference in the clinical outcomes is not derived solely by the anatomical change. Fusing the ISJ did not have a major impact on the response which corresponds to the excellent clinical outcomes that are reported following stapedotomy surgery.