Fibrovascularization of porous polyethylene (Medpor) orbital implant in a rabbit model.

OBJECTIVE

To evaluate the porous polyethylene (Medpor) orbital implant in a rabbit model and compare it with three other currently available porous implants: Bio-Eye coralline hydroxyapatite (HA), FCI(3) synthetic HA, and aluminum oxide (Bioceramic).

METHODS

The porous polyethylene implant was examined macroscopically and microscopically (with scanning electron microscopy). Implantation was performed in 10 adult male New Zealand albino rabbits. Each animal underwent enucleation of the right globe under general halothane gas anesthesia, followed by placement of a 12-mm porous polyethylene implant. In 5 animals, the implant was encased in polyglactin 910 (Vicryl mesh); in the other 5, it was left unwrapped. The implants were moistened in saline before placement. Implant vascularization was evaluated by histopathology at 4, 8, 12, 16, and 24 weeks.

RESULTS

The porous polyethylene implant was found to have a smoother exterior surface than the Bio-Eye, FCI(3) synthetic HA, and aluminum oxide implants. Rather than a uniform interconnected porous architecture, there was an extensive system of interconnected channels through the implant, ranging in size from 125 to 1000 microm. On high-power examination there was a more solid, woven appearance without any sign of the microcrystals seen in the other porous implants. One rabbit had a retrobulbar hemorrhage after surgery and was euthanized. All the other rabbits tolerated the implant well, and there were no complications. On histopathologic examination, fibrovascularization gradually increased over time. One implant was completely vascularized at 12 weeks, and both implants harvested at 16 weeks were completely vascularized. The implant harvested at 24 weeks showed only partial vascularization (14%).

CONCLUSIONS

The porous polyethylene orbital implant represents an alternative implant for use after enucleation or evisceration or for secondary implantation. In our rabbit model, the porous polyethylene implant was well tolerated without complication. Complete fibrovascularization was first seen at 12 weeks. Porous polyethylene orbital implants appear to vascularize more slowly than Bio-Eye coralline HA, FCI(3) synthetic HA, and aluminum oxide implants.