Comparison of Early Fibrovascular Proliferation According to Orbital Implant in Orbital Floor Fracture Reconstruction

Backgrounds: Although reports of successful treatment results of orbital fractures are numerous, histopathologic changes associated with favorable outcomes have not yet been established. The purpose of this study was to observe fibrovascular ingrowth into implants, fibrovascularization, and inflammatory reactions in surface tissues of implants in an animal model of orbital floor fractures. Methods: Twenty-four New Zealand white rabbits were used in the study. A standardized 6-mm-diameter defect was made bilaterally in the maxillary sinuses to include bone and mucosa, and an 8 x 8-mm alloplastic implant was inserted. In the control group, a bone defect was made, but no implant was inserted. Two different implant materials 1 mm in width were used: porous high-density polyethylene (Medpor, group A) and absorbable copolymer (Macropore, group B). The implants were harvested at 1, 2, and 6 weeks after implantation. Hematoxylin-eosin stains and immunohistochemical studies of basic fibroblast growth factor (bFGF) and CD31 (platelet/endothelial cell adhesion molecule) were conducted. Results: Full-thickness fibrovascular ingrowth into the implants was observed in group A after 2 weeks, but there was no fibrovascular ingrowth into the implant in group B. The inflammatory reactions between the implant and the connective tissue were grade 2 at 1 week and grade 1 at 2 and 6 weeks in both groups. The bFGF indexes in fibrovascular tissue growing into the nonabsorbable porous polyethylene implants (group A-1) were 0.3 at 1 week, 2.3 at 2 weeks, and 3.0 at 6 weeks. The bFGF indexes at the surface tissues of the implant in the nonabsorbable porous polyethylene implants (Medpor, group A-2) and group B were 1.0 and 1.8 at 1 week, 2.5 and 2.8 at 2 weeks, and 3.0 and 3.0 at 6 weeks. Expressions of CD31 in group A-1 were 3.8 at 1 week, 6.0 at 2 weeks, and 20.3 at 6 weeks. Expressions of CD31 in group A-2 and group B were 19.8 and 23.3 at 1 week, 38.0 and 49.3 at 2 weeks, and 64.3 and 72.0 at 6 weeks. Conclusions: Because there was no fibrovascular ingrowth into the absorbable copolymer implant, such implants may be advantageous in orbital wall fractures with exposures of extraocular muscle. However, the possibility of migration and extrusion of the implant cannot be excluded because there was no fibrovascular ingrowth into the absorbable copolymer implants. Therefore, nonabsorbable porous polyethylene implants are better suited for use in orbital wall fractures when there is concern about implant migration and extrusion during the early postoperative period and large orbital wall fractures.