COMPARISON OF FIBROVASCULAR INGROWTH INTO HYDROXYAPATITE AND POROUS POLYETHYLENE ORBITAL IMPLANTS

Two porous orbital implants available for clinical use in the anophtha lmic socket are hydroxyapatite (HA) and porous polyethylene (PP). We e xamined the rate and the extent of fibrovascular ingrowth into these i mplants using histopathologic criteria in a rabbit model. Thirty-two N ew Zealand white rabbits underwent a unilateral enucleation with place ment of a 14-mm spherical orbital implant. Twelve rabbits received HA, 12 small-pore PP, and 8 large-pore PP. The implants inserted were wra pped either in autologous sclera with and without anterior fenestratio ns or as unwrapped spheres. The implants were harvested at 6 and 12 we eks. The extent of fibrovascular ingrowth was assessed by determining the percentage of the cross-sectional area penetrated by fibrovascular tissue. On gross inspection, 12 implants (37.5%) were found to be exp osed at harvesting; however, only two were grossly infected. The highe st- rate of exposure was found among the unwrapped implants. Wrapped v ersus unwrapped and fenestrated versus unfenestrated implants did not result in significant differences in the extent of vascularization. Hy droxyapatite implants were vascularized most rapidly. The small-pore P P implants did not become fully vascularized during the study, and yet complete vascularization was found in the large-pore PP at 12 weeks. The most intense areas of microscopic fibrovascular ingrowth were in t he region where the extraocular muscles were in direct contact with th e implant and at the posterior opening. Exposure of the implant was ac companied by chronic and acute inflammation. Both HA and large-pore PP spherical implants are capable of complete vascularization in this an imal model. Increasing the interstitial pore size resulted in more com plete vascularization of the PP. Vascularization of the implants is li mited by exposure, secondary inflammation, and infection.