Biomaterials for ossicular chain reconstruction. A review

This review gives a survey of biomaterials used for ossicular chain reconstruction. The survey is focussed on application, biophysical requirements, properties and goals for future developments. The implantation site middle ear differs from others due to aeration and potential bacterial colonization. As a consequence, implant materials must exhibit excellent biocompatibility, biostabilty and sound conducting properties. In vitro and in vivo biocompatibility investigations and clinical observations determine the choice of material. Additionally the implants must provide the possibilty of intraoperative shaping or should be available in different variations in order to allow reconstruction appropriate to the individual conditions. Ceramics, metals and plastics are materials in current use. Based on thorough experimental and long term clinical experiences, the bioinert aluminum oxide is favorable amoung the ceramics. Bioactive ceramics may have minor biostability and the risk of fixation to surrounding bone which impairs sound conduction. This is also true for hydroxyapatite although biodegradation occurs only rarely. Today, titanium is the metal best established in middle ear implantation, reflected by excellent biocompatibility in vitro and in vivo, and good clinical results. Titanium is preferred by many surgeons, considering that sound transmission properties are mainly dependent on the implant weight. In stapes surgery, when the implant has direct contact to inner fluids, gold was accused to cause granuloma formation with subsequent inner ear damage in selected cases. In frequent past and present use, plastics (porous polyethylene and teflon) have proven to be of limited value in ossicular chain replacement because of high extrusion rates and the observation of material desintegration and bacterial colonization. In order to individually manage the pathological conditions in the middle ear, the implant design is of crucial importance. It is dependent on the ossicle to be replaced and the implant material. Future investigations have to minimize implant extrusions possibly by modifying and improving implant surfaces.