Age Effect To The Clinical Prognosis Of Infection After Fracture Fixation And Related Experiment Research

Background:Infection after fracture fixation(IAFF)can increase the risk of bone nonunion,osteomyelitis and internal fixation failure.The correlation between age and infection has become a hotspot in recent years.Studies reported that children showed lower infection rate and better prognosis when underwent serious injury,serious illness or open tibia fracture,which associated to the effect of the different innate immune cells,inflammatory cytokines and bone marrow mesenchyme stem cells(BMSCs).Few large-scale studies have addressed the difference in infection rate between children and adults following fixation of closed fractures in limbs,as well as the effect of age in anti-infection mechanism in animal model research.Purpose:combined with the clinical findings,we established a mouse femur closed micro fracture intramedtullary nail and Staphylococcus aureus acute infection animal model which was comparability between young and adult,and further detcect the effect of age in anti-infection mechanism.Methods:The medical records were reviewed of the children(2405 cases)and adults(1422 cases)who had been treated from 2012 to 2016 for closed fracture in Fuzhou Second Hospital Affiliated to Xiamen University and Nanfang Hospital of Southern Medical University Hospital.The C57BL/6 mice were chosen,divide into Young group(5 Week)and Adult group(8 Mon),Micro fractures of distal femur medullare,intramedullary nail(IN)and staphylococcus aureus(S.aureus)during acute infection period,Young and Adult mice both were split into Control,IN,IN+S.aureus groups.Intramedullary tissue and heart blood gradient bacteria culture,bone tissue HE staining improved Smeltzer score and Micro-CT scans technique were used to evaluate the results of infection,qPCR and ELISA detect tissue and serum levels of cytokines,flow cytometry detect the change of proportions of innate immune cells and BMSCs in the medullary cavity after infection,immunohistochemical staining detecting osteoblast marker osteocalcin(OCN),CFU dyeing test the proliferation ability of BMSCs in group Control and IN.Bacteria removal ability and the level of cytokine were testing in Adult-IN+S.aureus group after injection BMSCs from young mice.Results:The overall infection rate was 0.62%(15/2,405)in the children and 6.82%(97/1,422)in the adults,P<0.05.Bacterial cultures demonstrated that Staphylococcus aureus was the most common pathogen in both the adults and the children.Heart blood and marrow cavity content gradient bacteria training in youth group was significantly less than in adult group,and improved Smeltzer scores was also significantly lower.Micro-CT scans showed the bone mineral density(BMD)slightly elevated in group Adult-IN,but decreased significantly in group Adult-IN+S.aures(P<0.05),however there was no significant difference in the youth groups;Bone volume fraction(BV/TV),OCN dyeing also significantly dropped after infection in group Adult-IN+S.aureus,but no obvious changes in youth groups.In summary,better bacteria removal ability and prognosis showed in young group.IL-12 and IL-17a detected through qPCR showed significantly increased in group Adult-IN and group Adult-IN+S.aureus compared with the previous group(P<0.05),ELISA results showed that although the IL-12 and IL-17a changed not obviously in group Adult-IN but also increased significantly after infection,but also not obvious in youth groups.Flow's cells showed macrophages were slightly higher after infection in both young and adult groups,furtherly,the expression of M2 macrophage subtype marker Arg1 increased significantly in the youth infection group(Adult-IN+S.aureus)than adult infection group(Adult-IN+S.aureus);BMSCs proportion was significantly decline after infection.After injection of BMSCs,bacteria colonies decreased significantly in group Adult-IN+S.aureus,qPCR detection showed IL-10 significantly increased but IL-17a significantly reduced,changes happened in other cytokine but had no statistical difference.Conclusions:There is significant lower rate of IAFF in children compare with adults in clinical studies.A mouse femur closed micro fracture intramedullary nail and Staphylococcus aureus acute infection animal model which was comparability between young and adult,was successfully established.Stronger bacteria removal ability in Young group may associate with the increased macrophages transformation to M2 phenotype.Proinflammatory factor of IL-12 and IL-17a levels may be linked to the increased inflammation reaction and tissue necrosis in Adult group.After injection of BMSCs from young mice,bacteria removal ability enhanced in Adult-IN+S.aureus group,which might be associated to the increasesing of the anti-inflammatory factor IL-10 and the reducing of the proinflammatory factor IL-17a.