Primary placement of a titanium motility post in a porous polyethylene orbital implant: animal model with quantitative assessment of fibrovascular ingrowth and vascular density

Abstract

Purpose: To determine whether a Medpor porous polyethylene orbital implant, at the time of initial orbital implant surgery, will tolerate the insertion of a titanium screw on the anterior surface of the implant.

Methods: Twelve New Zealand white rabbits were enucleated and implanted with a porous polyethylene orbital implant. At the time of enucleation, the porous polyethylene orbital implants were drilled, and titanium motility coupling posts were inserted. The motility coupling posts were inserted at two projection heights (2 or 4 mm) and either covered within Tenon capsule/conjunctiva (eight implants) or left exposed (four implants). Rabbits were killed at 6 or 12 weeks. Clinical tissue tolerance, histologic response to the motility coupling post, and vascular density of the porous polyethylene orbital implant were evaluated.

Results: The motility coupling posts were well tolerated, and extrusion or migration of the motility coupling post did not occur. The average percentage cross-sectional area of the implant occupied by fibrovascular tissue at 6 and 12 weeks was 76.3% and 97.5%, respectively. In comparing the vascular density (number of vessels per square millimeter) in the porous polyethylene orbital implant within a 1-mm zone immediately surrounding the motility coupling post, no significant difference between this zone and the vascular density found within its entire corresponding annulus was found at either 6 or 12 weeks.

Conclusions: During the 6- and 12-week observation periods, all implanted motility coupling posts demonstrated favorable tissue tolerance and stable interfaces with surrounding tissues. The extent of fibrovascular tissue ingrowth and vascular density verify that initial screw insertion does not adversely affect the healing process after porous polyethylene orbital implant implantation. Thus, primary placement of the motility coupling post may obviate the need for a secondary surgical procedure.