Xenogeneic ossicular implants: an experimental study of heterotopic, demineralized, lyophilized, porcine implants in the guinea-pig

This study was done to compare the outcome of porcine ossicular implants in the middle ear and the subcutaneous dorsal region of the guinea-pig to tho se of allo-implants implanted in parallel in the dorsal region. The implant s were heteropic, xenogeneic, demineralized (HCl), lyophilized and steriliz ed. The evaluation was histological (light microscopy and scanning electron microscopy) and immunological (immunofluorescence staining). Fifty-four gu inea-pigs were implanted in the middle ear and 14 of them were also implant ed subcutaneously in the dorsal region with xeno-implants and alloimplants. The middle ear implants were found to be constantly reossified and coated with normal mucose with only a minimal immune reaction. In contrast, the do rsal xeno-implants were found to be the target of mononucleic infiltration, fibrous encapsulation and an influx of immunoglobulins resulting in segreg ation. The corresponding allo-implants were found to be partially reoccupie d and reossified. These findings highlight the value of HCl demineralizatio n in the induction of non-species-specific Bone Morphogenetic Protein and t he failure of attempts at immuno-despecification. It appears that the fate of the implant depends less on its antigenic load than on the site of impla ntation. In this regard the middle ear is apparently very advantageous. The very good short-term tolerance and recovery observed in the middle car xen o-implant suggest that these implants offer sufficiently good results to wa rrant clinical testing.