Internally coupled ears in living mammals.

It is generally held that the right and left middle ears of mammals are acoustically isolated from each other, such that mammals must rely on neural computation to derive sound localisation cues. There are, however, some unusual species in which the middle ear cavities intercommunicate, in which case each ear might be able to act as a pressure-difference receiver. This could improve sound localisation at lower frequencies. The platypus Ornithorhynchus is apparently unique among mammals in that its tympanic cavities are widely open to the pharynx, a morphology resembling that of some non-mammalian tetrapods. The right and left middle ear cavities of certain talpid and golden moles are connected through air passages within the basicranium; one experimental study on Talpa has shown that the middle ears are indeed acoustically coupled by these means. Having a basisphenoid component to the middle ear cavity walls could be an important prerequisite for the development of this form of interaural communication. Little is known about the hearing abilities of platypus, talpid and golden moles, but their audition may well be limited to relatively low frequencies. If so, these mammals could, in principle, benefit from the sound localisation cues available to them through internally coupled ears. Whether or not they actually do remains to be established experimentally.This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s00422-015-0675-

Osseointegration of Prostheses on the Stapes Footplate: Evaluation of the Biomechanical Feasibility by Using a Finite Element Model

Restoration of hearing is one of the main issues of tympanoplasty. Depending on the extent of destruction, the ossicular chain is partially or totally replaced by prostheses. In the unfavorable event of complete ossicular chain destruction with only the stapes footplate remaining in the oval niche, implanting of a columella prosthesis represents the gold standard. Besides ventilation problems, the main causes of unsatisfactory hearing results are dislocation of the prosthesis and poor coupling to the footplate. Therefore, stable fixation of prostheses is desirable but has not been realized to date. In line with our experimental intention to realize a bony prosthesis fixation on the footplate, we designed a finite element model for the simulation of the interacting forces once an osseointegration was achieved. These preliminary results predict the mechanical feasibility of this endeavor and the necessary general preconditions, which have to be carefully considered. A specially designed titanium prosthesis anchor needs a minimal bony fixation of 104 μm accretion height on the footplate to withstand all emerging forces. Therefore, providing a sort of artificial stapedial suprastructure in the form of a firm, preferably bony, integration of a prosthesis anchor on the footplate seems to be realistic and worthwhile from a mechanical and medical point of view