Flexibility of ossicular joints reduces damaging impulse peaks

Abstract

The presence of three distinct middle-ear ossicles is a uniquely mammalian trait whose benefits are still debated. One hypothesis is that the flexibility afforded by the two synovial joints connecting the ossicles provides a protective advantage by dispersing potentially damaging impulsive stimuli before they reach sensitive cochlear structures. The 3D velocity of points along the ossicular chain in unaltered cadaveric human temporal bones (N = 9), stimulated with acoustic impulses, was measured in the time domain using a Polytec CLV-3D laser Doppler vibrometer. The measurements were then repeated after fusing one or both of the ossicular joints. Sound transmission was characterized by measuring the amplitude, width, and delay of the impulsive velocity profile as it traveled from the eardrum to the cochlea. In most cases, a delay was noted across either or both of the ossicular joints, and the velocity profile at the stapes was lower in amplitude and broader than at the umbo. Typically, fusing the incus-s...