A synthetic hydroxyapatite implant: the so-called counterfeit implant

This article evaluates three generations of synthetic hydroxyapatite implants in a rabbit model. Fourteen New Zealand white rabbits received synthetic hydroxyapatite orbital implants (first, second, and third generation). The rabbits underwent enucleation of one eye and then received a 12-mm synthetic hydroxyapatite implant wrapped in Vicryl (polygalactin 910; Ethicon, Inc.) mesh or sclera. Magnetic resonance imaging was conducted to assess host fibrovascularization of the implant 4 and 12 weeks after implantation. Animals were killed at each of these times and the implant was removed for histopathologic examination. Enhancement on magnetic resonance imaging and extent of fibrovascularization by histopathologic examination were assessed. The first-generation synthetic hydroxyapatite (FCI, Issy-Les-Moulineaux, France) was not 100% hydroxyapatite as is the Bio Eye (Integrated Orbital Implants, Inc., San Diego, CA, U.S.A.). It contained 3.2% calcium oxide. The implant was heavier and much less porous than the original Bio Eye implant. Central vascularization eventually occurred but was not extensive. The second-generation implant was more porous than the first, with rapid central vascularization to the center of the implant by 4 weeks. However, the second-generation implant was very fragile and crumbled easily. The second-generation synthetic implant was chemically identical to the original Bio Eye implant with no calcium oxide. The third-generation implant was more porous than its predecessors. When compared side by side with the Bio Eye, a difference in pore uniformity and interconnectivity seems apparent. However, an early extensive vascularization pattern to the center of the implant is seen histopathologically, similar to that with the Bio Eye. Magnetic resonance imaging also shows extensive enhancement as is the case with the Bio Eye. The third-generation synthetic implant is not fragile as was the second-generation implant, and chemically it is identical to the Bio Eye with no calcium oxide present. The third-generation implant is approximately half the price of the original Bio Eye implant.