Do Stainless-Steel Pins Coated with Fibroblast Growth Factor–Calcium Phosphatase Composite Layers Have Anti-Infective Effects?

<i>Background:</i> The most problematic complication of external fixation is infection at the pin insertion site. Technology that improves the adhesion of the external fixation pin to the skin, subcutaneous tissue, and bone may prevent infection at the pin site. The purpose of this study is to formulate a calcium phosphate-fibroblast growth factor (Cp-FGF) coating on a stainless-steel external fixation pin and to verify its effectiveness in reducing infection at the pin site and its possible influence on bone fixation in animal experiments. <i>Methods:</i> We compared stainless-steel screws without coating (SS group; <i>n</i> = 32), those with a calcium phosphate coating (Cp group; <i>n</i> = 30), those with a Cp-FGF coating (FGF group; <i>n</i> = 32), and those with a Cp-FGF coating having enhanced biological activity (FGF+ group; <i>n</i> = 32) in male Japanese white domesticated rabbits. Screws were inserted percutaneously into the bilateral proximal tibial diaphysis of the rabbits and implanted for 4 weeks. Screws and periscrew tissue were observed postoperatively for qualitatively assessing infection. <i>Results:</i> Infection assessment by gross findings after 4 weeks (at screw removal) showed no significant differences between the groups. Histopathological evaluation of soft tissue infection and bone tissue infection showed no significant differences between the groups for either soft tissue or bone tissue. Since neither the FGF+ group nor the FGF group showed anti-infective effects, the biological activity of FGF is not the only determining factor. We compared SEM, XRD, coating detaching test, sustained release test, and bioassay to examine physicochemical properties among the coatings but found no sufficient differences. <i>Conclusions:</i> It is suggested that improving the tissue adhesion to and/or biocompatibility of pins is also important to improve the in vivo performance of Cp-FGF-coated external fixation pins.