Reducing the risk of impaired bone apposition to titanium screws with the use of fibroblast growth factor-2−apatite composite layer coating

BACKGROUND Loosening of screws is a common problem in orthopedic and maxillofacial surgery. Modifying the implant surface to improve the mechanical strength of screws has been tried and reported. We developed screws coated with fibroblast growth factor-2 (FGF-2)-apatite composite layers. We then showed, in a percutaneous external fixation model, that this composite layer had the ability to hold and release FGF-2 slowly, thereby reducing the risk of pin tract infection of the percutaneous external fixation. The objective of the current study was to clarify the effect of FGF-2-apatite composite layers on titanium screws on bone formation around the screw. METHODS We analyzed samples of previously performed animal experiments. The screws were coated with FGF-2-apatite composite layers by immersing them in supersaturated calcium phosphate solutions containing FGF-2. Then, the uncoated, apatite-coated, and FGF-2-apatite composite layer-coated screws were implanted percutaneously in rabbits. Finally, using inflammation-free histological sections, we histomorphometrically assessed them for the presence of bone formation. Weibull plot analysis was then applied to the data. RESULTS On average, screws coated with FGF-2-apatite composite layers showed a significantly higher bone apposition rate than the uncoated or apatite-coated screws. Although the difference in the average bone apposition rate was small, the FGF-2-apatite composite layers produced a significant, marked reduction in the incidence of impaired bone formation around the screw compared with the incidence in the absence of FGF-2 (uncoated and apatite-coated screws). The probability of resulting in a bone apposition rate equal to or less than 63.75%, for example, is 3.5 × 10-4 for screws coated with the FGF-2-apatite composite layers versus 0.05 for screws in the absence of FGF-2. CONCLUSIONS FGF-2-apatite composite layer coating significantly reduced the risk of impaired bone apposition to the screw. Thus, it is feasible to use titanium screws coated with FGF-2-apatite composite layers as internal fixation screws to decrease the risk of loosening.