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

Abstract

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 mm 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.

Osseointegration of Titanium Prostheses on the Stapes Footplate

“…Focusing on the two specimens that were histologically proven to be integrated in newly formed bone, the radiographically detected bone implant contact area accounts for 32% (0.134 mm 2 ) in the coll-II-coated footplate anchor and for 44% (0.187 mm 2 ) in the coll-I/BMP-4-coated footplate anchor (related to the whole coated implant surface). We have shown previously that a minimal bony fixation of one bump up to 60% of its height was calculated to be necessary to endure all arising forces in the accretion zone (Neudert et al 2007). Since a single bump accounts for 5% (0.02 mm 2 ) of the implant surface, the here achieved osseointegrated area exceeds the required percentage of osseointegration by 578% and 807, respectively.…”

Tympanoplastik – Neues und neu Beleuchtetes

“…Das Restrisiko einer Dislokation ließe sich nur durch eine knochenstabile Verankerung im Sinne einer Osseointegration von Prothesenmaterial auf der Steigbügelfußplatte vollends verhindern [114]. Dies wäre biomechanischen Berechnungen nach möglich [115]. Auch experimentell konnte im Säugetierorganismus eine wachstumsfaktorvermittelte Osseointegration auf der Fußplatte realisieren, für die klinische Anwendung steht dieses Konzept, auch aus finanzieller Sicht, derzeit noch nicht zur Verfügung [116].…”

“…Dieses wird jedoch durch die fehlende feste Verankerung in diesem Bereich nicht auf die Fußplatte übertragen. Auch die Verwendung von Zentrierungshilfen ändert dies nicht, so dass Verkippungen der Fußplatte mit daraus resultierender Ringbandvorspannung nicht auftreten [115].…”

Tympanoplasty – news and new perspectives

“…The remaining risk of dislocation might only be completely avoided by a bone-stable anchoring in the sense of osseo-integration of prosthetic material on the stapes footplate [ 114 ]. According to biomechanical calculations, this could be possible [ 115 ]. Even experimentally, a growth-factor mediated osseo-integration on the footplate could be realized in mammalian organisms, for the clinical application, however, this concept is currently not available, also because of economic reasons [ 116 ].…”