THE USE OF CORALLINE HYDROXYAPATITE IN A BIOCOMPOSITE FREE FLAP

An animal model was developed to determine the feasibility of vascularizing a porous biomaterial and transferring it as part of a free flap to a recipient site with enhanced resistance to infection due to the maintenance of a blood supply. To that end, the experiment was divided into three stages. Stage 1 compared the soft-tissue response of Interpore-200 to Interpore-500, both continuously porous hydroxyapatite materials implanted beneath the panniculus carnosus of the male Sprague-Dawley rat. Pore size was an important factor as it influenced vascular ingrowth, with Interpore-200 vascularizing earlier (complete at 1 week) and more intensely. Interpore-200 was therefore used for the remainder of the experiment. After 1 week of tissue ingrowth, the implants were moved from the abdomen to the skull on a vascular pedicle as a "biocomposite" free flap. Stage 2 was the histologic evaluation of 15 "biocomposite" free flaps over various time intervals up to 8 months. The free flaps formed a fibrous union to the skull, while a simple nonvascularized Interpore-200 onlay graft (stage 2 control) demonstrated a bony union in three of four implants placed up to 2 months. Stage 3 confirmed the free flap's resistance to bacterial infection. A highly significant difference (p < 0.005) in infection rates was demonstrated between the "biocomposite" and nonvascularized stage 3 controls with no Pseudomonas growth from 9 of 10 cultures of the free flaps 5 days after exposure to 10(4) Pseudomonas aeruginosa, while stage 3 controls demonstrated Pseudomonas growth in all cultures (heavy growth in 8 of 10). The "biocomposite" free flap has excellent potential to provide form and structure to wounds requiring reconstruction where bacterial contamination is a significant risk factor.