Objective To explore the effect of traumatic brain injury on the fracture healing and its related mechanism by observing the expression of platelet-derived growth factors (PDGF) in serum and bone callus in rats with bone fracture and cerebral trauma.Methods One hundred and forty-four SD rats were randomized into 4 equal groups (n =36) which were subjected respectively to:no treatment (group N),traumatic brain injury (group TBI),bone fracture (group F) and bone fracture and cerebral trauma (group TBI + F).The animals were sacrificed at 3 days,1,2,3 and 4 weeks after modeling.In all the 4 groups,ELISA was used to detect the expression of PDGF in serum.In groups F and TBI + F,the callus growth was observed at the right tibial fracture site by X-ray,the callus growth and morphology were also observed by HE staining,the expression of PDGF in the callus tissue was measured by immunohistochemieal analysis,and the expression of PDGF mRNA in the callus tissue was measured by RT-PCR.Results X-ray showed that fracture healing was accelerated in group TBI + F compared with group F.The serum expression of PDGF in group TBI + F was significantly higher and the peak time was significantly earlier than in the other 3 groups (P ＜ 0.05).H-E staining showed that osteoblastic activity at the fracture ends in group TBI + F was stronger than in group F.Inmunohistochemica[staining showed that the expression of PDGF in the local callus was significantly higher at 3 days and 1 week in group TBI + F and the peak time was significantly earlier than in group F (P ＜ 0.05).RT-PCR showed that the expression of PDGF mRNA in the local callus was significantly higher at 3 days and 1 week in group TBI + F than in group F (P ＜0.05).Conclusions Traumatic brain injury can promote fracture healing in rats,which is probably related to increased expression of PDGF after cerebral trauma.