500 Section - Bone formation around terminally gamma‑ray‑sterilized screws coated with fibroblast growth factor 2‑calcium phosphate composite layers in non‑human primates

Objectives : A clinical problem of spinal instrumentation surgery is loosening. We developed screws coated with fibroblast growth factor-2-calcium phosphate (FGF-CP) composite layers to improve bone formation around screws. Moreover, we developed terminally gamma‑ray‑sterilized screws coated with the FGF-CP composite layers. The mitogenic activity of the FGF-2 within the composite layers remains unchanged after gamma-ray sterilization, which can improve the bone formation around screws. Therefore, we designed a long-term implantation study that estimated the bone-forming efficacy of gamma‑ray‑sterilized screws coated with the FGF-CP composite layer in cynomolgus monkeys.

Design: Three types of screws were implanted in the lumbar vertebrae of three female adult cynomolgus monkeys: high-dose FGF group, low-dose FGF group, and non-coated group. The bone formation around screws was evaluated histologically 12 weeks after surgery. The measured values were analyzed using Weibull plots, a method for analyzing the probability of failure.

Results: The bone formation rate was 32.8±11.6% in the high-dose FGF group, 31.1±13.0% in the low-dose FGF group, and 33.0±12.6% in the non-coated group. Weibull analysis confirmed that the high-dose FGF group had a reduced risk of impaired bone formation compared to the non-coated group.

Conclusion: The study suggests that terminally gamma‑ray‑sterilized screws coated with the high-dose FGF-CP composite layers can promote osteointegration, reduce the probability of screw loosening. Developing implants that achieve stable surgical results can reduce re-operation, lower medical costs, and maintain the physical status of older patients.