CLINICAL AND HISTOLOGIC RESPONSE OF SUBCUTANEOUS EXPANDED POLYTETRAFLUOROETHYLENE (GORE-TEX) AND POROUS HIGH-DENSITY POLYETHYLENE (MEDPOR) IMPLANTS TO ACUTE AND EARLY INFECTION

Objective: To examine the responses of subcutaneously implanted expand ed polytetrafluoroethylene (e-PTFE, Gore-Tex) and porous high-density polyethylene (PHDPE, Medpor) to experimentally induced infection. Desi gn: Sprague-Dawley rats were implanted subcutaneously with either e-PT FE or PHDPE implants. Inocula of Staphylococcus aureus were injected d irectly over the implants and the wounds were observed for clinical si gns of infection. After the animals were killed, the implants were har vested and underwent histologic examination. Subjects: Twenty-eight ad ult male Sprague-Dawley rats weighing 200 to 250 g. Intervention: A 8- mm diameter, 1-mm-thick implant of either e-PTFE or PHDPE was placed i n a subcutaneous pocket over each animal's dorsum. Either at the time of implantation or 14 days afterward, an inoculum of 10(9) colony-form ing units of S aureus was injected transcutaneously directly over each implant. The animals were observed for 7 days before being killed. Th e implants were harvested and examined by both conventional light and scanning electron microscopy, and the degree of capsule reaction, infe ction, inflammation, and implant degradation was evaluated. Results: I mplants inoculated at the time of implantation were more likely to bec ome clinically infected. Results for e-PTFE and PHDPE implants were si milar in this group (5 of 5 e-PTFE and 5 of 5 PHDPE implants infected) ;. The PHDPE implants inoculated 14 days after implantation were less likely to become infected (1 of 4 infected) than e-PTFE implants (3 of 4 infected), and were statistically less likely to become infected th an PHDPE implants inoculated immediately after implantation (25% vs 10 0%; P<.O2). Histologically, this resistance to infection correlated wi th increasing fibrovascular ingrowth into the PHDPE implants. The infe cted PHDPE implant had little to no ingrowth compared with PHDPE contr ol implants. The uninfected e-PTFE implant had evidence of early fibro vascular ingrowth into the peripheral pores of the implant. Conclusion s: Because of differences in pore size, PHDPE promotes faster fibrovas cular ingrowth. The presence of vascularized host tissue in and around the implant lends stability and resistance to experimentally induced infection. Conservative management of clinical implant infections shou ld be considered if bacterial seeding occurs after substantial fibrova scular ingrowth is present. Future alloplast designs should include po re sizes that will encourage invasion of the implant by host tissue.