The Role Of Mechanical Factors In Steroid-associated Osteonecrosis

[Obejetive]Divide the rats into the controls of normal rats,the model of the femoral head necrosis by long term glucocorticoid treatment,the model of hyper-weight with GONFH and the model of weightlessness with GONFH.To observe and compare the differences of MRI and Micro-CT among the four groups.To explore the changes of the expression levels of lnc RNA H19,lnc RNA XIST,OPG,Run X2,and ALP among the four groups,and study its biomechanics and the relationship with mechanical factor.[Method]30 healthy 8-week SD rat were divided into four groups randomly,5 of control,5 of models of GONFH,10 of models of hyper-weight(runing on treadmill)with GONFH,and 10 of models of weightlessness(overhung)with GONFH.After the precise measurement,the model group were given the Intramuscular injection with methylprednisolone 20mg/kg?d,7 day a weak for 8 weeks.After the injection,the group of models of hyper-weight were made to run on the running machine at a speed of 25m/min for 30 minutes,5 times a week,forming the hyper-weight model.It was averagely divided into two subgroups,one run 2 weeks and another 4 weeks.At the same time,the group of models of weightlessness with GONFH were put into a particular box and overhung where their back legs could not reach the ground.This group was also divided into two subgroups,one overhung 3 weeks,and another 6weeks.From the 6th week of intramuscular injection of glucocorticoid,each group was subjected to MRI scanning every two weeks under the condition of living anesthesia.The signal changes of T1-weighted images and T2-weighted images of femoral heads were observed.Each group was killed after the interventions were completed,bilateral femoral heads were taken.The left femoral head was used for Micro-CT scan.The right femoral head was used to detect changes in the expression levels of lnc RNA H19,lnc RNA XIST,OPG,Run X2,and ALP.Statistical analysis was performed using SPSS 20.0 software.[Result]Glucocorticoid-induced femoral head necrosis model was successfully established.There was abnormally high signal in the GONFH group on T2-weighted images.With the prolonged use of GC,the area of?high signal gradually increased.The high signal area in the treadmill group was higher than that in the GONFH group,and the crescent sign was found in the 4-week treadmill group.The high signal in the tail-suspension group was reduced compared to the GONFH group,and the high signal area gradually decreased with the prolong of the suspension time.Micro-CT:The trabecular volume,trabecular thickness,and trabecular number were decreased in the GONFH group compared with the control group,and the trabecular surface area/bone volume and trabecular space were increased compared to the normal group.As for the 2-week treadmill group,the trabecular volume,trabecular thickness,and trabecular number were all increased compared with the GONFH group,and the trabecular bone surface area/bone volume and trabecular space were decreased.As for the 4-week treadmill group,the volume of trabecular bone and the thickness of trabecular bone increased,the surface area of bone trabecular/bone volume and trabecular space decreased,but the number of trabecular bone did not increase.The tail-suspension group showed a significant increase in trabecular bone surface area/bone volume and trabecular space compared to the GONFH group,and they increased when the suspension time increased.The trabecular thickness decreased significantly;however,the volume of trabecular bone and the number of trabecular bone did not change significantly between 3-week suspension group and the GONFH group,whereas there was a significant decrease in the 6-week suspension group.We also calculated the relative area of voids.There was no void in the normal group,and the void area of the treadmill group was significantly larger than that in the hormone group(P<0.05).After 3 weeks of suspension,the void area decreased compare with hormone group(P<0.05).By 6 weeks,the voids have already disappear.The expression of lnc RNA H19 in the GONFH group was significantly lower than that in the control group.The expression level of lnc RNA H19 in treadmill group was significantly higher than that in other groups.With the increase of treadmill time,the expression level of lnc RNA H19 continued to increase.The expression level of lnc RNA H19 in the suspension group has no significant difference with GONFH group.The expression of lnc RNA XIST in GONFH group was lower than that in the normal control group.The expression level of lnc RNA XIST was increased,compared treadmill group with GONFH group,but it was not statistically significant(P>0.05);Comparing suspension group with GONFH group,the expression level of lnc RNA XIST was decreased,but there is no statistical difference between the two groups(P>0.05).The m RNA expression levels of OPG,Runx2,and ALP in the hormone-injection group were lower than those in the normal group(P<0.05).The expression levels in the 2-week treadmill group were higher than those in the hormone-injection group,and with the extension of the treadmill time,The level of expression has also increased.[Conclusion]1.The rat model of femoral head necrosis can be successfully established by intramuscular injection of methylprednisolone.2.Weight-bearing can promote the progress of steroid-induced femoral head necrosis,which may be caused by increasing trabecular bone fractures and micro-fractures of trabecular bone.3.Stress-less stimulation can delay the progression of steroid-induced femoral head necrosis.4.Lnc RNA H19 may participate in the pathogenesis of steroid-induced femoral head necrosis by regulating the expression of osteogenic genes.Under load conditions,the expression of lnc RNA H19 and osteogenic genes was elevated.The expression of lnc RNA H19 and osteogenic genes decreased with stress.5.lnc RNA XIST is involved in the onset of steroid-induced femoral head necrosis,but may not play an important role in the influence of mechanical factors on steroid-induced femoral head necrosis.