Mechanics and materials in middle ear reconstruction.

The normal anatomy and physiology of the middle ear is not reproduced in ossiculoplasty and an artificial mechanism for the transmission of sound results. This is true for all types of graft, be they of natural or man-made material. There are, therefore, 2 areas for consideration when looking at the problems encountered in such reconstructions: first, the materials' biocompatability and, secondly, the mechanical effects of the positioning of the graft in the reconstructed ossicular chain. The present work examines these mechanical effects using the finite element method to determine stress and displacement levels in the reconstructed ossicular chain. It is found that the stress levels at the implant-stapedial joint increases as the implant is gradually moved down the malleus. In contrast there is thought to be an increase in sound transmission as the implant is moved down the malleus. Changes in rigidity and hardness of the implant appear to make only modest stress attenuations at the implant-stapes interface.