Objective:To investigate the value of fibroblast growth factor 2 (FGF-2) and microRNA-206 (miR-206) in predicting postoperative delayed union of closed tibial shaft fractures.Methods:The clinical data of 136 patients who underwent closed tibial shaft fracture surgery in Hospital of the 80 th Group Army of Chinese People's Liberation Army Ground Forces from May 2018 to May 2021 were retrospectively analyzed. Eighty-six patients who had delayed union of closed tibial shaft fractures were included in the observation group, and fifty patients who had normal union of closed tibial shaft fractures were included in the control group. Serum FGF-2 level was measured using the enzyme-linked immunosorbent assay, and serum miR-206 expression was detected using the real-time fluorescence polymerase chain reaction. The relationship between FGF-2 expression and miR-206 expression and closed tibial shaft fractures was analyzed. Results:At 1 day, 1, and 4 weeks after surgery, serum FGF-2 level was significantly lower in the observation group than the control group [(14.24 ± 2.15) ng/L vs. (20.36 ± 3.42) ng/L, (21.38 ± 3.27) ng/L vs. (30.45 ± 4.29) ng/L, (23.59 ± 4.36) ng/L vs. (36.67 ± 4.51) ng/L, t = 7.42, 8.42, 16.66, all P < 0.001]. Serum FGF-2 level gradually increased with time in each group. At 1 day after surgery, serum miR-206 expression was significantly lower in the observation group than the control group ( t = 7.50, P < 0.001). At 4 weeks after surgery, serum miR-206 expression was significantly higher in the observation group than the control group ( t = 17.24, P < 0.001). At 1 week after surgery, there was no significant difference in serum miR-206 expression between the two groups ( P > 0.05). Univariate analysis results showed that postoperative infection, FGF-2, and miR-206 were closely related to the delayed union of closed tibial shaft fractures after surgery (all P < 0.05). Multivariate logistic regression analysis results showed that postoperative infection ( OR = 1.93, 95% CI: 1.20-3.07), FGF-2 ( OR = 2.10, 95% CI: 1.31-3.36), miR-206 ( OR = 2.30, 95% CI: 1.35-3.89) were independent risk factors for delayed union of closed tibial shaft fractures after surgery (all P < 0.05). The receiver operating characteristic (ROC) curves plotting serum FGF-2 level and serum miR-206 expression after closed tibial shaft fractures showed that at 4 weeks after surgery, the optimal cut-off value of FGF-2 for predicting delayed union of closed tibial shaft fractures was 29.83 ng/L, with the area under the curve, sensitivity, and specificity of 0.76 (95% CI: 1.23-3.25), 79.34%, and 68.82%, respectively; at 4 weeks after surgery, the optimal cut-off value of miR-206 for predicting delayed union of closed tibial shaft fractures was 0.63, with the area under the curve, sensitivity and specificity of 0.72 (95% CI: 1.10-2.45), 75.33%, and 67.25%, respectively. The area under the curve, the sensitivity, and specificity of combined use of FGF-2 and miR-206 in predicting delayed union of closed tibial shaft fractures were 0.81 (95% CI: 1.35-3.26), sensitivity and specificity were 83.45% and 67.36% respectively. Conclusion:The decrease in serum FGF-2 level and the increase in serum miR-206 expression at 4 weeks after surgery are independent risk factors for delayed union of closed tibial shaft fractures. Combined use of FGF-2 and miR-206 can better predict the delayed union of closed tibial shaft fractures.