Anatomy of the distal incus in humans.

The anatomy of the distal incus, including the lenticular process, was examined in histological sections from 270 normal cadaveric human temporal bones aged between less than 1 month and 100 years. All but nine of these sectioned specimens showed signs of a bony connection between the long process of the incus and the flattened plate of the lenticular process, and in 108 specimens a complete bony attachment was observed in a single 20 microm section. In these 108 ears, the bony lenticular process consisted of a proximal narrow "pedicle" connected to a distal flattened "plate" that forms the incudal component of the incudo-stapedial joint.

Non-ossicular signal transmission in human middle ears: Experimental assessment of the "acoustic route" with perforated tympanic membranes.

Direct acoustic stimulation of the cochlea by the sound-pressure difference between the oval and round windows (called the "acoustic route") has been thought to contribute to hearing in some pathological conditions, along with the normally dominant "ossicular route." To determine the efficacy of this acoustic route and its constituent mechanisms in human ears, sound pressures were measured at three locations in cadaveric temporal bones [with intact and perforated tympanic membranes (TMs)]: (1) in the external ear canal lateral to the TM, P(TM); (2) in the tympanic cavity lateral to the oval window, P(OW); and (3) near the round window, P(RW). Sound transmission via the acoustic route is described by two concatenated processes: (1) coupling of sound pressure from ear canal to middle-ear cavity, H(P(CAV) ) identical withP(CAV)P(TM), where P(CAV) represents the middle-ear cavity pressure, and (2) sound-pressure difference between the windows, H(WPD) identical with(P(OW)-P(RW))P(CAV).

Experimental ossicular fixations and the middle ear's response to sound: evidence for a flexible ossicular chain.

A human temporal-bone preparation was used to determine the effects of various degrees of artificial ossicular fixation on the sound-induced velocity at the input-side (the umbo of the malleus) and the output-side (the stapes) of the ossicular chain. Construction of various degrees of attachment between an ossicle and the surrounding temporal bone provided a range of reduction in ossicular mobility or "fixations". The results demonstrate different effects of the fixations on the umbo and stapes velocity: fixations of the stapes or incus produce larger reductions in sound-induced stapes velocity (as much as 40-50 dB with extensive stapes fixation), than reductions in umbo velocity (typically less than 10 dB).

Experimental and clinical studies of malleus fixation.

Objectives/hypothesis: Preoperative clinical diagnosis of malleus fixation can be difficult. "Fixation" of the malleus can be caused by various disorders or diseases: fibrous tissue, bony spurs, and neo-osteogenesis around the malleus head or stiffening of the anterior malleal ligament. The conductive hearing loss produced by these disorders or diseases has not been well characterized.